NBSIR 88-3716

Proceedings of the Symposium on

Gaseous and Vaporous Removal

Equipment Test Methods

Held at the National Bureau of Standards

September 2, 1986

Preston E. McNall, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

Sponsored by:

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

r\T op

February 1988

Stimulating America's Progress

1913-1988

BCE

NBSIR 88-3716

PROCEEDINGS OF THE SYMPOSIUM ON

GASEOUS AND VAPOROUS REMOVAL

EQUIPMENT TEST METHODS

Held at the National Bureau of Standards

September 2, 1986

Preston E. McNall, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Environment Division

Gaithersburg, MD 20899

February 1988

Sponsored by:

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

This symposium proceedings summarizes the current state-of-the-art on

gaseous and vaporous removal test methods for equipment designed for use in

the general ventilation of buildings. Papers by the ten (10) invited

authors are included. A discussion section outlines the conclusions

reached concerning the future direction for test method development.

Key Words: absorption, adsorption, air cleaning, catalysis, chemisorption,

gaseous, validation and vapors.

i
TABLE OF CONTENTS

Page

Introduction by Preston E. McNail 1

Acknowledgement 2

Partial Glossary of Terms 3

Activated Charcoal Performance in Removing Toxic Waste by

Victor R. Deitz © © o « c • * • © o « © • 4

Optimizing Carbon for Removal of Certain Contaminants by Amos Turk .. 12

Reduction in Gaseous Contaminant Concentration with the Use of

In-Duct Complex Electrical Fields by Allan H. Frey ................ 15

The Control of Indoor Air Quality - The Use of Impregnated Alumina

Substrates by Steve L. Zeis 26

Monitoring Mass Transfer Zones in Adsorbers by Basil G. Louros ...... 28

Characterization of the LTC Catalyst: Performance Against Common

Air Pollutants by Marcia F. Collins 31

Effects of Relative Humidity on Adsorption of Contaminants on

Activated Carbon by Dwight W. Underhill, Gina Micarelli and

Maria Javorsky 42

Practical Test Requirements for Gaseous Contaminant Removal Equipment

by Richard D . Rivers 54

Comparative Performance for Gas Removal by Cyrus M. Bosworth ........ 65

Comparison of Chromotropic Acid, Pararosaniline , and Gravimetric

Formaldehyde Determinations by Samuel Silberstein 73

Discussion and Conclusions by Preston E. McNail ...................... 83

i i
INTRODUCTION

Preston E. McNall

National Bureau of Standards

For many years , gaseous and vaporous removal equipment has been used in

general ventilation systems in buildings. The American Society of

Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) , the

American Society for Testing Materials (ASTM) , and others have considered

test standards for such apparatus without notable success. As a result,

we have used standard methods to evaluate particulate filtering systems,

but no standard methods exist for gaseous and vaporous removal equipment

for use in general ventilation systems. Over the last decade, the energy

crisis has focused attention on the energy cost of building ventilation,

and increased research has also brought attention to many gaseous and

vaporous pollutants which can be present in inside air.

These factors have intensified the need for standard evaluation methods

for such equipment, as their application is increasing, and many new

devices are being introduced into the marketplace.

This symposium was organized to bring together a number of experts in the

field to examine the state of the art and summarize, insofar as possible,

the conclusions concerning the future of test methods and provide a frameowrk for their development and/or future necessary research.

The problem seems complex. There is a wide variety of materials with

differing physical and chemical characteristics of interest. A wide

range of concentration levels of various pollutants are found in indoor

air. Several known removal or mitigation methods have been employed,

such as adsorption, absorption, chemisorption, catalysis, and complex

electrical fields.

The symposium proceedings are presented as an aid to those who may

contribute to the growing need for standardized test methods which will

be useful for orderly commerce among the suppliers and users of such

devices

.

1
'
Glossary of Terms

Some definitions are listed to assist readers who are not thoroughly

familiar with this field.

Absorption - A substance dissolved in another, such as oxygen dissolved

in water.

Adsorption - A substance retained on the surface of another, such as

carbon tetrachloride adsorbed on activated carbon.

Breakthrough - A condition which exists with a sorption device, when a specified penetration of a challenge contaminant is reached. (The massloading at which breakthrough occurs is dependent on many parameters,

such as bed depth, velocity, temperature, humidity, challenge

concentration, etc.).

Capacity - The ability of a sorption device to retain a material before

breakthrough.

Catalyst - A material which accelerates a chemical reaction, whose

concentration is unchanged.

Challenge - The concentration of a known material fed to an air treatment

device

.

Chemisorption - A substance taken up and held during the sorption

process, usually irreversibly, in another material, by chemical reaction.

Efficiency - The ratio of concentration of a fed material less the outlet

concentration divided by the fed concentration expressed as a percent.

Cf - CO

eff = x 100

Cf

Loading - The amount of a challenge material held by an air treatment

device, at a specified condition.

Penetration - The ratio of the outlet concentration to the fed

concentration of a material, expressed as a percent.

CO

P = -- x 100 = 100 eff

Cf

3
ACTIVATED CHARCOAL PERFORMANCE IN REMOVING TOXIC WASTE

Victor R. Deitz

Naval Research Laboratory

Code 6170

Washington, DC 20375-5000

1 • Abstrac

t

The applications of granular activated carbons for the removal of

undesirable gases and vapors have been extended by their use as catalyst

and impregnation supports. For long service times in ventilating systems,

the atmospheric contaminants become important factors and can limit service

efficiency. The moisture content of the air also is an important

parameter. Carbons used with physically adsorbed gases can frequently be

regenerated by extended air flows, but chemically adsorbed gases require

special treatment and generally cannot be economically regenerated in situ.

A test procedure for used carbon should reveal the residual life as well as the existing penetration of the test gas. Test procedures for new

adsorbents are of value for procurement requirements, but need to be

modified when used materials are examined. The relative humidity and the

dew point of the air stream are both factors in a test procedure and the

applications

.

2 . B ac kg.ro und_Cons id gra t ions

The large volume of air processed in the ventilating systems of buildings

contains significant amounts of atmospheric contaminants. Those that

degrade an activated charcoal adsorbent (Table 1) include ozone, sulfur

dioxide, nitrogen oxides and the volatile hydrocarbons (non-methane).

Although the concentrations are in the ppm range, the summation over

extended service times degrades the efficiency of the charcoal. The

example in Table 1 is a 30,000 CFM filter operating for 90 days in the air

purification facility of a nuclear power plant. The reactive gases are

ozone, sulfur dioxide and the nitrogen oxides.

Table 1: Atmospheric Contaminants Entering an Activated Charcoal

Adsorber in 90 Days

ppm (V/V x 10 6)* Weight ( lbs)

wt - % of

Charcoal

ozone 0.019 10 0.27

so

2 0.023 16 0.43

Nox 0.043 21 0.56

Hydrocarbons 0.23 210 5.0

* 3-year average at NRL

The second factor that influences the efficiency of a charcoal adsorbent is

the concentration of water vapor in the air flow. There are seasonal

variations (Figure 1) in the monthly averages, which were calculated from

observations over a 4-year period recorded at the National Airport. These

results demonstrate that wet air is prevalent for June, July and August in

the Washington area. The influence of the wet air on the adsorptive

4
F igure 1

Seasonal variation of the monthly average dew point at

the National Airport Weather Station, Washington, D.C.

properties of a whetle-rite charcoal (Figure 2) shows a corresponding

behavior for the adsorptive properties of samples exposed during one-month

periods. In general, a high concentration of water vapor degrades the

adsorption efficiency for a toxic vapor which in some cases can be

recovered on exposure to a flow of dry air.

The breakthrough concentrations for a charcoal bed for toxic and obnoxious

vapors occur at low surface coverage. The breakthrough will occur in

shorter intervals as the time in service of the charcoal bed is extended.

Both physical adsorption and chemisorption processes can take place

simultaneously at different parts of an adsorbent surface.

3 . Removal via Physical Adsorption

Many organic vapors in air flows may be removed by charcoal adsorbents by a physical adsorption process. The extent to which this is accomplished

depends on the carbon. An example (Figure 3) is the adsorption of benzene

vapor at 30°C by each of four commercial activated carbons which differ in

adsorptive surface area. When the amount adsorbed is divided by the

monolayer coverage for each type of activated carbon, the four isotherms

coincide, see Figure 4.

The water content of the air flow has a strong influence on the adsorption

of benzene vapor. Adsorption is also dependent on the initial water

content of the carbon. The results of J.K. Thompson (Figure 5) were

obtained for air flows of different relative humidities and for carbons

prehumidified at specified relative humidity. The points on the line of

5
80

Figure 2: Seasonal influence on the removal of cyanogen chloride after

weathering whetlerite in one-month intervals at NRL„

Figure 3: Adsorption isotherms (30°C) of benzene vapor on four

coal-base charcoals.

6
Figure 4: Benzene isotherms (30°C) of Figure 3 plotted as fractional surface coverage.

Figure 5: Influence of relative humidity on the adsorption of benzene

vapor in air flows - measurements by J .K . Thompson, NRL

7
Figure 5 were obtained when the prehumidified carbon (16 hours) was exposed

to the same relative humidity as the air flow*

An important characteristic property of physical adsorption in a flowsystem is the continued penetration of the vapor after the challenge

pollutant has been turned off. An example is the benzene-air system shown

in Figure 6. The dose was 500 ppm benzene in air and this was continued

for 120 minutes; thereafter* only the air purge was continued at the same

flow for 240 minutes. The effluent benzene gradually leveled-off and

eventually decreased to the baseline (not shown). The behavior resembles

the effluent from a chromatographic column under inefficient separation

conditions

.

Figure 6: Penetration behavior of benzene-air flows through a new and a weathered ASC whetlerite

Another example of the above desorption behavior is the adsorption of

methyl iodide on a nuclear grade carbon as shown in Figure 7. The dose

into the air flow of 30% RH lasted 120 minutes, but the peak concentration

was observed at 1800 minutes and the effluent methyl iodide concentration

(0.001 mg/M^) was detected after 5 days.

4. Remova l , via , C hemigorp tipp

Many toxic gases combine chemically with activated carbon and with

impregnated carbons. For example, ozone and hydrazine vapors react

directly with the carbon; hydrogen cyanide, however, is held by a cooperchromium impregnation on a coal-base activated carbon. When the products

of a chemisorption process are retained by the carbon bed, a slow

8
Figure 7: 127 ICH3

in Effluent (mg/M^) for the prolonged (5

days) purge at 30% RH with NRL 5144.

degradation of the removal efficiency takes place and the carbon bed must

be replaced. Frequently, the chemisorption process may lead to a volatile

product often toxic in itself. An example is the chemisorption of HCN by

whetlerite charcoal (Figure 8) in which cyanogen (CN^ is formed and is

present in the effluent air flow. Protection against HCN was realized for

more than 80 minutes, but the cyanogen broke through in one-tenth of the

time. This example stresses the importance of the test gas that is

selected to evaluate the efficiency of the ventilating system.

5 . Depth Profile within a Charcoal Bed

A test procedure for activated carbons in service (used carbons) should

reveal the residual life as well as the observed penetration of the test

gas. Test procedures for new adsorbents are of value for procurement

decisions, but the procedure must be modified for used materials.

The depth profile has been determined for a number of test beds containing

nuclear-grade activated carbons. The count profile in the penetration of

radioactive methyl iodide-131 at equal increments of depth was determined

and was found to be exponential along the line of flow. A large numerical

magnitude of the slope (Figure 9) is characteristic of new and good

carbons; a low value signifies poor retention by the test column.

As the time in service increases, the sequential count from inlet to outlet

sections at the sample may not decrease exponentially. In fact, fewer

counts have sometimes been observed in the inlet sections than in the

remaining sections. The presence of adsorbed contaminants is held

9
Figure 8: Effluent concentrations for HCN on Type A.

Figure 9: Progressive decrease of the count profile as the penetration

of radioactive methyl iodide-131 increases.

10
responsible for the migration of the radioactive methyl iodide-131 and such

behavior can occur in other applications where charcoal is used in

ventilating systems.

6 . Concluding Remarks

It is evident that the application of an activated carbon adsorber for

gaseous and vapor removal in ventilating systems can involve many chemical

problems. The moisture content of the air and the atmospheric contaminants

are background considerations. The analysis of the building air can reveal

the presence of those constituents easily removed and those removed with

more difficulty. The design of the carbon bed depends on the desired level

of removal. More than one type of test gas should be used to evaluate the

carbon efficiency and its possible regeneration capacity. A carbon bed may

be considered as a holding unit which only gradually released the

undesirable gases and vapors at a lower concentration below an undesirable

level. There are, as usual, many compromises to be made in the ultimate

design of the system.

11
OPTIMIZING CARBON FOR REMOVAL OF CERTAIN CONTAMINANTS

Amos Turk

Department of Chemistry

The City College of the City University of New York

New York , NY 10031

Evaluation of activated carbons or other granular media used for air

cleaning requires testing both for efficiency and capacity®

Efficiency - Practically all granular media utilize one or a combination of

three processes: (a) physical adsorption; (b) acid-base neutralization;

(c) oxidation. The potential efficiencies of these actions in granular

beds depend on their rates as well as on the bed characteristics. Physical

adsorption requires contact between the molecules of gas or vapor and the

adsorbent surface. The adsorbents commonly used for indoor air cleaning

are granules of mixed sizes ranging in diameter from about 1 to 5 mm,

packed into beds of uniform thickness. Under such conditions, the halflife of a molecule in the gas phase before it reaches the surface of a granule is about 0.01 s [1]. Then, if the air stream containing

contaminant molecules enters such a bed, the contact efficiency, E, the

fraction of molecules that have contacted a solid surface after n seconds

is

:

E = 1 - 2“ 100n

From this equation, typical contact efficiencies are 75% for a residence

time of 0.02 s, 93.75% for 0.04 s, and 98.44% for 0.06 s. However, such

efficiencies are realized only with a fresh bed. .As soon as some

adsorption occurs, the mass transfer zone begins to move downstream.

Acid-base neutralization, which involves the transfer of a proton, is

practically an instantaneous reaction, so it is not rat e- 1 imi t ing in

granule beds. Furthermore, the neutralization of a base by a strong acid,

or of an acid by a strong base, goes practically to completion. Thus,

activated carbon impregnated with NaOH or KOH can remove weakly acidic

gases such as SO-? or H 2

S (2), and carbon impregnated with phosphoric acid

can remove ammonia or amines.

Oxidation reactions, on the other hand, vary widely in rates, are generally

slower than the actions afforded by physical adsorption or by acid-base

neutralization, and are therefore usually rate controlling when they are

used for air cleaning in granular beds.

Capac itv of an air cleaning device using granular media can be determined

by monitoring the medium for exhaustion or the effluent for breakthrough,

or by using some other analytical system to predict breakthrough and thus

estimate probable capacity. Monitoring could conceivably be carried out by

observing color change, recording the change of mass of the medium with

time, analyzing the effluent, removing test samples of the medium for

analysis, or extracting parts of the air stream from within the bed for

analysis. Carbon does not change color. Potassium permanganate (purple)

is reduced to manganese dioxide (brown), but the surface color obscures

that of the interior. Changes in mass due to saturation with organic

vapors are obscured by gains and losses of moisture. Analysis of air

12
streams after or within the bed, or testing of the medium itself, requires

instrumentation that is usually impractical in domestic or commercial

settings, but is appropriate in a testing facility.

It is sometimes helpful to carry out simultaneous competitive tests on the

same air stream to evaluate different media, or to compare different

impregnations for the same substrate. One suitable device [3] utilizes an

air sampler comprising 16 respirator cartridges mounted on a manifold

plate. The cartridges can be loaded with different media and removed and

tested from time to time for air cleaning efficiency or for degree of

saturation. Alternatively, an air stream can be split between two larger

units for direct one-on-one competitive testing. For devices that have low

air cleaning efficiencies, either because of the inherent inefficiencies of

their media or because of their bed characteristics, and which therefore

are designed to handle air in recirculation with multiple passes, tests

with recirculation in closed systems are appropriate. The test protocol

makes use of the first order decay relationship (4),

C . c oe-^Q‘/V

where C = vapor concentration at time t

C 0 - initial concentration

Q

= air flow rate

m = mixing factor in the space

E = efficiency of the unit

V = volume of the space

To evaluate E, a combination of air cleaner and test gas that is known to

be 100% efficient, such as activated carbon and CCl^ vapor, is used in a space of known volume for a specified time and flow rate, and the initial

and final concentrations are measured. Then E = 1 and the mixing factor in

the space, m, can be calculated. Now the air cleaner to be tested is

substituted under the same conditions and, knowing m, the efficiency of the

unit can be determined.

New approaches for specific gases and vapors - The capacity of activated

carbon for adsorption of vapors depends in part on their boiling points.

In general, the lower the boiling point of a liquid, the lower is the

capacity of activated carbon to retain its vapor by physical adsorption.

When the boiling point is below about 50° or 60°C, activated carbon is

usually impractical as a physical adsorbent. The common alternative is the

use of a chemically reactive impregnant on activated carbon or other

substrate. Examples are the use of permanganated-impregnated alumina for

removal of formaldehyde by oxidation, or caut ic-impregnated carbon for

removal of hydrogen sulfide by neutralization. Such impregnations,

however, occupy pore volume and surface area and thus limit the capacity of

the substrate for physical adsorption of other vapors. One other

possibility is the use of a gaseous reactant that is innocuous in itself

and that does not remain on the adsorbent. A useful reactant for the

removal of hydrogen sulfide and methyl mercaptan is ammonia gas (5), which

acts as a catalyst for the oxidation of H 2

S to sulfur by atmospheric

oxygen. The ammonia can be used in concentrations below its odor

threshold. A suggested mechanism for the reaction is:

2 NH

2 + H2

S = (NH^^S (1, fast equilibrium)

13
(NH4 ) 2 $ + 1.5 02 —> ( NH4) 2 S03 (2, rate controlling)

( NH^) 2 SO3 = 2 NH3 + SO2 + H2 O (3, fast equilibrium)

2(NH4) 2S + S02 —> 3S + 4NH3 + 2H2 0 (4, fast redox)

Sum: 3H

2

S +1.5 02 —> 3S + 3H2 0 ( NH3 catalyst)

References

(1) A. Turk, H. Mark, and S. Mehlman, "Tracer gas nondestructive testing

of activated carbon cells," Materials Res. & Stds. SL* No. 11, 24

(1969)

.

(2) R. K. Sinha, M. J. Wagner, and R. J. Joyce, "Impregnated activated

carbon for improved removal of malodorous compounds." U.S. Patent

4,072,479 (1978)

.

(3) A. Turk, L. K. Oti, A. E. Steinberg, and T. E. Wolf, "Assessing the

performance of activated carbon in the indoor environment," Am. Ind.

Hyg. Assoc. J. 714 (1984).

(4) A. Turk, "Measurements of odorous vapors in test chambers:

theoretical," ASHRAE J. I, 10 (Oct. 1953).

(5) A. Turk, E. Sakalis, and J. Lessuck, "The use of ammonia and

activated carbon for removing sulfur gases from air," Proc. Third

Inti. Conf. of Israel Soc. for Env. Quality, Jerusalem, June 11, 1986.

14
REDUCTION IN GASEOUS CONTAMINANT CONCENTRATION WITH THE

USE OF IN-DUCT COMPLEX ELECTRICAL FIELDS

Allan H. Frey, Ph.D.

Randomline, Inc.

County Line and Mann Roads

Huntingdon Valley, PA 19006

ABSTRACT

The complex electrical fields that exist in all spaces interact with

airborne charges, particulates, water droplets, and adsorbed gases. These

interactions in large part determine the deposition of contaminants in and

on people, objects, and walls in a room, as I described in a recent paper

(Frey 1986a). Thus, such fields have substantial implications for the

development of test procedures for the measurement of gaseous contaminants.

Recently published research has shown that in-duct electrical fields can be

created which reduce the concentration of gaseous and particulate

contaminants in a room. This also bears on the development of methodology

for the valid measurement of gaseous contaminants. Reported here are data

on the effect of in-duct electrical fields.

The objective of the first experiment reported here was to determine the

mechanism by which in-duct electrical fields reduce the concentration of

particulates in a room. The statistical analyses of the data indicate that

the operation of these specific electrical fields in the duct significantly

reduced the particle count in the room and suggest a mechanism for the

effect. There was a shift in particle size spectrum that can be

interpreted as the in-duct electrical field accelerating the normal

coagulation of small particles into larger particles which are more readily

trapped in the filter.

Since gaseous contaminants to a large extent adsorb on particulates, the

second experiment was undertaken to gather information on the influence of

these in-duct complex electrical fields on gaseous contaminants. The

results with gases are consistent with the mechanism suggested by the

particulate data. The concentrations of formaldehyde, ammonia, sulfur

dioxide, and carbon dioxide were substantially decreased and the decrements

were statistically significant. Thus, it appears that some gaseous

contaminants can be controlled in the process of controlling particulates

with this technique.

The third experiment was a practical application of the information

gathered. We tested for and found that animal room odor concentration was

decreased by passing the room air supply through in-duct complex electrical

fields. The odor panel reported a substantial decrease that was

statistically significant. Taken together, the results of these three

experiments provide information which bear on methods of measurement of

gaseous contaminants.

INTRODUCTION

The complex electrical fields that exist in all spaces interact with

airborne charges, particulates, water droplets, and adsorbed gases. These

15
interactions, in large part, determine the deposition of contaminants in

and on people, objects, and walls in a room, as I described in detail in a recent paper (Frey 1986a). Thus, such fields have substantial implications

for the development of test procedures for the measurement of gaseous

contaminants. Complex electrical fields can be created in ducts, and they

can modify the concentration of both gaseous and particulate contaminants

in a room, as has been shown in recently published research (Frey 1983 , 1984, 1985, 1986b). It was established that such effects were not due to

ionization or ozone. This also bears on the development of methodology for

the valid measurement of gaseous contaminants. The three experiments

reported here were directed toward obtaining data to begin to define the

nature of the effect of in-duct complex electrical fields on gaseous and

particulate contaminants and to test a practical application.

EXPERIMENT 1

The objective of this experiment was to determine the mechanism by which

in-duct electrical fields reduce the concentration of particulates in a room.

MgthQd

The testing was carried out in a room 4 x 11 x 2.5 meters high (13 x 36 x 8

ft.). The room had its own closed circuit air handling system. Air

entered the room through a pair of slot supply diffusers near the ceiling

centerline, passed down through the room, and exited into a duct through a pair of slot return grilles at the bottom of the walls that were parallel

to the diffuser slots. In the duct, the air passed sequentially through a smoking .device , a 55 percent filter, a blower, three electrical field

screens, and then re-entered the room through the supply diffusers. The

room air change rate was 10 per hour with fifty percent recirculation. The

air supply was filtered through activated alumina to remove moisture. The

temperature was about 70°F with a relative humidity less than 3%. Tests

have also been run with a humidity of 50% and 85% with similar results.

The air in the room was purged to the outside between test runs and said

runs were separated by at least two days.

The electrical field screens installed in the duct were 60 x 60 cm (2x2

ft.), except the center one which was 5 cm (2 in.) larger. They were

spaced 7.6 cm (3 in.) apart and were perpendicular to the air flow. The

screens were made of braided wire configured as shown in Figure 1.

Electric field generators supplied a 700 V peak to peak 177 kHz signal that

was applied to the center screen and also a 25 kV DC signal that was

applied to the other two screens. The current was less than 3 mA. The

smoke was generated by burning cigarettes in a smoking device in the duct.

For a 75-minute period in each run a mean rate of 1044 mg/min of airborne

burned cigarette products was produced.

Two particle measuring instruments were used concurrently in the

experiment. One was a Royco, Inc., Model 218 Particle Monitor, which

measured particle concentration and size by light scattering. The other

instrument used was a California Measurements, Inc., Model PC-2 Aerosol

Particle Analyzer, which measures particle concentration and size by mass.

It is a 10-stage cascade impactor with quartz crystal microbalance mass

monitors in each state. This instrument provided a printout of the mass

16
4

"

’ , /

i-r" — 4 ?

Figure 1. Electrical field screens

17
for each stage at the end of each 180 second sampling period throughout

each test run.

During each 90-minute test run, there was no smoke introduced into the air

for the first 15 minutes. During the next 20 minutes, the smoking of the

cigarettes began and the smoke distribution in the room was allowed to

stabilize. During the remaining 55 minutes, the smoking was held at an

essentially constant rate. Thus, the primary data for the analyses were

the last 55 minutes of each experimental run.

A counterbalanced experimental design was used with the electrical fields

off for days 1 and 4 and on for days 2 and 3.

Results

In accordance with the experimental design, the days 1 and 4 data (field

off) gathered after smoke levels stabilized were combined and the days 2

and 3 data (field on) were combined.

The first objective in analyzing data was to see if the results from the

two instruments were consistent. Since one instrument operates by light

scattering and the other operates by mass measurement, one would expect

substantial, though not complete, correlation in the results. The

statistical analyses showed that both instruments indicated the electrical

field in the duct was decreasing the particulate concentration in the room

compared to the control situation.

A statistical analysis using the data from all ten stages of the impactor

was carried out. The results showed there was a difference between the

field on and off conditions, and it was significant (t = 5.02, p< 0.005).

Statistical analyses were also done stage by stage. These showed that the

operation of the in-duct electrical field substantially reduced the mass of

small particulates in the air and slightly increased the mass of large

particulates. This relationship is shown in Figure 2 as percent decrease

or increase in mass from the mass determined in the electrical field off

condition. The difference between field on vs. off data on each stage was

statistically significant except for the 1.6 micron stage data.

Since the 1.6 micron size seemed to be the transition point, it was used as

a break point in further analyses. The mean mass for the small particles

(0.05 to 0.8 micron) was calculated. For the electrical field on

condition, it was 0.232 mg/m^; and for off condition, it was 0.378 mg/m^.

Thus, the operation of the electrical field reduced the mass of small

particles in the room air to 61 percent of what it was in the field off

condition

.

The mean mass for the large particles (3.2 to 25.0 microns) was calculated.

For the electrical field on condition, it was 0.033 mg/m^; and' for the off

condition it was 0.009 mg/m^. Thus, the operation of the electrical field

increased the mass of the large particles in the air to 367% if what it was

in the off condition.

Note that the loss of small particle mass is not balanced by the gain in

large particle mass. The gain of 367% in large particle mass in the field

18
oo

X

z

O

Q_i

UJ

LL

(I)

cn

<

LJJ g

£

£

PARTICLE SIZE IN MICRONS

Figure 2. Percent decrement or increment of particle mass with the

electrical field on when compared against the electrical

field off data as the baseline. The field off data would

all be 100%. The difference in mass between on and off

conditions at each particle size are statistically

significant, except at the 1.6 micron size.

19
on condition accounts for only 6% of the mass lost in small particles* The

other 94% of the decrement in small particle mass is going elsewhere. In

view of the fact that there is a significant increase in large particles,

these data could be interpreted as indicating that the 94% of small

particle mass that is unaccounted for is being deposited in the filter.

P i geugg iQP

The statistical analysis of the Royco data indicated that the operation of

these specific electrical fields in the duct significantly reduced the

particle count in the room. The statistical analyses of the cascade

impactor data support that conclusion and add further information that

suggests a mechanism for the effect. The shift in particle size can be

interpreted as the operation of the electrical field to accelerate the

normal coagulation of small particles into larger particles which are more

readily trapped in the filter.

EXPERIMENT 2

In view of the findings on particulates, a complementary set of experiments

were undertaken to gather information on the influence of these in-duct

complex electrical fields on gaseous contaminants. Gaseous contaminants to

a large extent adsorb on particulates.

Method

The gases used were formaldehyde, ammonia, sulfur dioxide, and carbon

dioxide. The testing was carried out in a room 2.74 x 5.79 x 2.44 meters

(9 x 19 x 8 ft. high) with a floor of vinyl tile and walls and ceiling

paneled. The paneling was coated with polyurethane varnish and the joints

were sealed with duct tape. The room had its own closed circuit air

handling system. Air entered the room through supply diffusers at one side

passed across the room, and exited into a duct through return grills at an

air change rate of 21 per hour. In the duct, the air passed sequentially

through a 55% filter, three electrical field screens, the blower, and then

re-entered the room through the supply diffusers. The temperature was

about 70°F with a relative humidity bout 65%.

There were two series of experiments using these gases. In the first

series, the initial gas concentrations were set at levels at which the

effects on people are just noticeable. In the second series, the initial

gas concentrations were set at approximately hazardous levels for short

exposure. A Gastec gas detector tube system was used as the measuring

instrument. In the first series, two evaluators independently read each

tube; one evaluator had no knowledge of the test conditions, so the

experiment was double-blind for him. Because of the reliability of the

evaluators, as noted in the results, there was only one in the second

series

.

The procedure was that the air handling system was turned on and the air in

the test room purged to the outside for 30 minutes. This reduced the

concentration of the gas of interest to normal ambient as verified by a Gastec tube measurement at the end of each purge. A gas, such as sulfur

dioxide, was then injected into the test room. Sufficient gas was released

to bring the concentration up to approximately the predetermined standard

20
concentration used in the test. At this point, the gas was turned off and

a 60-minute run was started. The gas concentration was measured with the

Gas tec tubes five minutes after injection stopped, 30 minutes into the run,

and at the end of the 60 minute run. At the end of each run, the room was

purged to baseline concentration and the next test in the series was then

begun. There were twelve runs in each series of experiments for each gas,

six with the fields on and six with them off. The runs were done in an

ordered, counterbalanced sequence.

The sulfur dioxide and carbon dioxide were injected into the center of the

room via a hose connected to a cylinder of gas located outside the room.

The ammonia and formaldehyde were injected into the room with a Paasche

model H airbrush spraying a 10 percent formaldehyde solution or an ammonium

hydroxide solution.

Results

The first question addressed was the reliability of the readings of the

Gastec tubes. Pearson product -moment correlations were computed between

the data provided by evaluators 1 and 2. There was near perfect

correlation in each set of their readings (r > 0.95). This indicates that

they were reliably reading the Gastec tubes and were doing so without bias.

There was natural decay in gas concentrations over time without the

electrical field on. Thus, for clarity of presentation, the data are

presented as the percent reduction in the field-on condition compared to

the control (field-off) condition. For testing the significance of the

differences between conditions, an analysis of variance was done on the

data. The results of the statistical analyses for each of the gases are

shown in Tables 1 and 2.

TABLE 1

Reduction of gas concentration by use of in-duct complex electric fields

when compared to controls. The initial concentrations were set at levels

that would produce the first noticeable effects in people. The

significance levels were determined by analysis of variance.

Gas End of 30 Minutes End of 60 Minutes

Mean Percent

Reduc tion Signif

.

Mean Percent

Reduc tion Signi

ce2 o 26 0.001 39 .01

nh

3 27 0.01 29 .001

so

2 0 ns 22 .05

c °2 0 ns 11 .01

The mean concentration at the 5, 30, and 60 minute points were formaldehyde

(CH2 O): 2.8, 2.5, 1.5 ppm; ammonia (NHg): 24.7, 14.4, 7.5 ppm; sulphur

dioxide (SO

2 ): 25.3, 18.7, 14.3 pm; carbon dioxide (CO

2 ): 2.4, 1.9, 1.5%.

21
TABLE 2

Reduction of gas concentration by use of in-duct complex electrical fields

when compared to controls. The initial concentrations were set at levels

that would be hazardous to people when exposed for a short period. The

significance levels were determined with use of the analysis of variance.

Gas End of 30 Minutes End of 60 Minutes

Mean Percent

Reduction Signif

.

Mean Percent

Reduction Signif

ch2 o 39 .001 49 .01

NH

3 0 ns 25 .001

S°2 13 .01 14 .001

co

2 10 .01 13 .001

The mean concentration at the 5, 30, and 60 minute points were formaldehyde

(GI^O): 4.3, 2.0, 1.3 ppm; ammonia (NH^)? 39.6, 24.6, 14.1 ppm; sulphur

dioxide (SO 2

): 49.8, 40.5, 32.9 ppm; carbon dioxide ( 002)2 4.8, 4.0,

3.4%.

Discussion

The data on gases extend the finding that passing room air through in-duct

complex electrical fields has a statistically significant effect on

contaminants. The extent and rate of the effect on the concentration of

gaseous contaminants varies as a function of which gas is used. The extent

of the effect, with at least some gases, is so substantial that it should

be of practical significance.

EXPERIMENT 3

The objective of this experiment was to determine if the perception of

animal room odors, which have a substantial ammonia component, would be

influenced by passing the room supply air through an in-duct complex

electrical field.

Methods

The exposure room was approximately 7 x 5.5 x 3 meters high (23 x 19 ft. by

10 ft.). Within this room was a 3.5 x 3.5 meter (12 x 12 ft.) clean room

enclosure made of vinyl nylon fabric. Approximately 48 rabbits and six

cats lived within the clean room enclosure at the time of each subexperiment and provided the odor. The air within the enclosure was changed

170 times per hour. This was accomplished by blowing ambient room air

through a prefilter, the electrical field screens, a HEPA filter, and then

through a vinyl nylon fabric duct into the enclosure. The air blown into

the enc losure was then exhausted into the exposure room through an opening

between the enclosure skirt and floor. The exposure room had an air

circulation system which normally involved 17 air changes per hour. Air

from the common building ventilation system was blown into the room. This

22
mixed with the air exhausted from the clean room enclosure and the mixture

in part exhausted from the room and in part recirculated through the

screens and into the clean room enclosure. During this experimentation,

the room air change rate was reduced to seven changes per hour (according

to the building engineer) by partially blocking the exhaust ducts in the

room. This was done to increase the odorant level. Except for the last

sub-experiment, the temperature in the exposure room was 70°F and the

relative humidity was 50%. At the last sub -experiment, the temperature was

75°F and the relative humidity was 52%. The electric field generator

supplied a 700 V peak-to-peak 0.177 MHz signal that was applied to the

center screen, and a 25 kV DC signal applied to the two outside screens

that were in the duct.

An odor panel consisting primarily of male college students was formed.

The panel was trained in odor intensity discrimination using several

odorants, e.g», amyl acetate, butyl alcohol. They were trained to make

odor intensity discriminations using as a scale a graduated series of

odorant concentrations in a series of ten identical amber 250 cc bottles.

Each bottle held 10 cc of liquid, consisting of the odorant and sufficient

solvent to bring the volume up to standard. These ten bottles were held in

a rack in order of concentration and thus odor intensity.

After initial intensity discrimination training which involved scaling

bottles of unknown odor intensities, the subjects were moved to the second

state of intensity discrimination training. In this stage, the unknown

odorant intensity was presented as an airborne odorant in the exposure room

and the scale bottles were located outside of the room. The subject now

walked into the exposure room in order to smell the odorant that was in the

room. He then walked out of the room and smelled the odor in any of the

scale bottles he wished in order to select which was most similar in

intensity to the intensity of the one in the room. The order of unknown

intensities presented in the room was determined by using a table of random

numbers. After this second stage was completed, the hypothesis under

consideration was tested.

The trained subjects were their own controls within the experimental

design, and they did not know the conditions of the experiment. The

experimentation consisted of four sub-experiments. The 20 minute cycles

called for in the design allowed the use of four subjects in each subexperiment. The electrical field alternated between off and on for a total

of five periods, each consisting of two cycles.

Animal room odor is complex, so we prepared an aqueous extract of pan

sweepings to make up our scale. A twenty-step scale was used. The odorant

prepared consisted of distilled water extract of rabbit pan sweepings which

included the wood chips used as bedding, urine, feces, and also some of the

alfalfa food which was always available in the cages. Because of

deterioration of the scale odorants after several days, a new odorant scale

was prepared from extracts of fresh pan sweepings before each subexperiment .

The subjects were briefed prior to each experiment. It was made clear to

the subjects that they were the measuring instruments in this situation.

It was emphasized that on the basis of their judgments, important decisions

would be made concerning the nature of odor perception. In this way, their

23
responsibilities were emphasized and their interest and motivation were

peaked. They were asked not to discuss the experiment with other subjects.

Each subject* individually with the experimenter, walked into a small room

(bottle room) off the subject waiting room where he smelled from various

bottles of the scale for reference. He then walked with the experimenter

approximately 12 meters (40 ft.) and through two doors to the exposure

room. The experimenter would open the door to the exposure room and the

subject would step in five feet to a standard position two feet from the

clean room enclosure. the experimenter closed the door, the subject

smelled the air, and they then returned to the bottle room. There the

subject would sniff several scale bottles and pick one whose odor intensity

matched that of the room. Then the experimenter and the subject would

repeat the procedure. This was done with each subject in turn and a cycle

with all subjects was completed within 20 minutes. At the end of 20

minutes, a new cycle began.

It was explained to the subjects that we would not make any deliberate

changes in exposure room odor level between each pair of judgments which

were normally separated by a minute or so in each cycle. They were told

that changes in odor intensity might be made, however, on a pre-determined

schedule after certain of the cycles.

At the end of each day^s experimental session, the subjects were separately

debriefed by the experimenter to gather additional information.

Results

Using the combined data from pre-determined test points, i.e., cycles prior

to period change, the independent sub-experiments 1., 2, and 4 data were

evaluated and the null hypothesis was rejected at the .001 significance

level using the Wilcoxon matched-pairs signed ranks test. This indicated

that the in-duct electrical field did have an effect on perceived odor

intensity. The effect amounted to a reduction by half in perceived odor

intensity

.

Sub-experiment 3 data is not included in the analysis. Two-thirds of the

way through the data collection in sub-experiment 3, the experimenter

noticed that the data indicated there was little odor in the room in the

control as well as in the test condition. This suggested that the exhaust

ducts in the room were not blocked as they should have been. It was found,

on investigation, that the building engineer had not blocked the ducts due

to a scheduling error. Thus, sub-experiment 3 was discontinued, and the

data discarded as not being valid within the context of the experimental

des ign.

Some rather useful incidental information, however, was obtained from subexperiment 3. This amounted to a double blind experiment and it showed

that the experimenter was not inadvertently biasing the subjects. The fact

that the fault in the air handling system could be identified from the data

indicates that the subjects were fulfilling their role quite well.

Discussion

It is clear that the complex electrical field significantly reduced the

24
perceived odor in the test room. The reduction in this particular set of

circumstances is equivalent to reducing the perceived concentration of

odorant by about 50%. According to the subjects at the final debriefing,

this reduction was enough to change an unpleasant room to an acceptable

one

.

It appears that it takes approximately 45 minutes of air recirculation

through the field to make such a reduction in perceived odor. The effect

continues for approximately 20 to 30 minutes after the electrical field is

turned off. It should be kept in mind that these numbers are specific to

this test situation.

CONCLUSIONS

In-duct complex electrical fields can significantly influence the

concentration of contaminants in a room. Both particulates and gases are

affected. The data from these experiments suggest that the fields

accelerate the 1 normal coagulation of small particles into large particles.

This would result in the particulates and the adsorbed gases being able to

escape the normal electrostatic forces that exist in all rooms. The air

currents could then carry them to the filter to be trapped.

Disc laimer - NBS does not endorse commercial products. Responsibility for

the information included here rests solely with the manufacturer. The

information is included here because it is deemed useful to the objectives

of the symposium.

REFERENCES

Frey, A. H. 1983. Modification of animal room odor by passing the room

supply air through a complex electrical field. Bull etin of

Environmental Contamination and Toxicology . 31(6) , 699-704.

Frey, A. H. 1984. Change in room aerosol concentration by in-duct complex

electrical fields. The Journal of Environmental Sciences . Jan. /Feb.

34-36.

Frey, A. H. 1985. Modification of aerosol size distribution by complex

electric fields. Bull etin of En v ironmental C ontamination a nd

Toxicology . 34, 850-857 .

Frey, A. H. 1986a. The influence of electrostatics on aerosol deposition.

ASHRAE Transactions 1986 . 92 (Part IB) , 55-64.

Frey, A. H. 1986b. Reduction of formaldehyde, ammonia, SO

2 and CO2

concentrations in air. Journal of Environmental Sciences . July/Aug.,

57-59.

25
THE CONTROL OF INDOOR AIR QUALITY

THE USE OF IMPREGNATED ALUMINA SUBSTRATES

Steve L. Zeis

Purafil, Inc.

Box 8043

Atlanta, GA 30366

There are two principal types of gas-phase air purification media in

general use for indoor air quality (IAQ) control today.

Activated carbons are high surface area (1000 to 1300 m^/g) coconut shell

or bituminous coal based adsorbents. These materials are generally not

impregnated with chemical reagents and, within certain limits, are

considered to be reversible adsorbents.

Impregnated aluminas are moderate surface area (250 to 350 m^/g) alumina

pellets, impregnated with one or more chemical reagents. The most commonly

used impregnant is potassium permanganate (KMnO^). These media are

considered to be irreversible adsorbents, or chemisorbents.

To discuss these materials, three terms must be clarified:

Adsorption - the adherence of the atoms, molecules, or ions of a gas or

liquid to the surface of (usually) a solid. Adsorption depends on the

surface area of the adsorbent, temperature, pressure, the molecular weight

and partial pressure of the adsorbate.

Absorption - the penetration of one substance (usually a gas or vapor) into

the inner structure of another (usually a liquid) as CC>2 is absorbed in

water . . . forming "Soda Water".

Desorption - the reverse of either adsorption or absorption, the process of

removing an adsorbed material from the surface on which it is held, or an

absorbed material from its absorbent. Desorption is accomplished by

heating, reduction of pressure, by the presence of a more strongly adsorbed

substance, or by a combination of these methods.

The reversible carbons operate purely by adsorption and, either factors

being equal, the higher the internal or pore surface area, the higher the

capacity. Reversible media tend to favor high molecular weight compounds

(complex organics and heavy hydrocarbons), and have higher capacities at

higher concentrations. Carbons are generally preferred for IAQ control

when most contaminants are about 100 molecular weight, above about 5 ppm

v/ v , or both.

In irreversible media, given sufficient residence time, chemical

contaminants that react with the impregnant will be modified. and bound in

the pellet, preventing desorption. For example, in KMn 04 impregnated

aluminas, formaldehyde (HCHO) is first adsorbed onto the surface of the

pores in the pellet, then adsorbed into solution with the KMn 04 where a chemical reaction takes places, yielding water, carbon dioxide, potassium

hydroxide and manganese dioxide.

26
TEST METHODS

For reversible adsorbents, there is no chemical technique for determining

when or whether a sample from an adsorbent device is saturated with one or

more air contaminants under normally varying conditions of temperature,

relative humidity, and contaminant character and concentration.

Research performed under ASHRAE sponsorship, on test method development,

confirmed the variance of reversible media performance and capacity as

these operating conditions change.

At the present time, to determine when to replace a reversible media bed

that is being used to control one or more specific contaminants, the air in

the building must be sampled and analyzed for those contaminants.

This can be done chemically, for a finite number of contaminants, but

normally building operators wait until occupant complaints become numerous

(or loud) enough before taking action.

Since irreversible media depend on chemical reagents to react with, and

bind contaminants, sample or partially used media may be analyzed for the

remaining reagent and the remaining life, predicted by comparing the amount

remaining with the reagent present in a new sample.

Manufacturers publish curves developed empirically from a combination of

lab and field experience to project a replacement date for impregnated

aluminas

.

Systems designers, specifiers and building operators need test methods

and/or standards of performance that will allow them to know how a given

system will perform and when the media must be replaced.

Presently, for reversible media systems, either air sampling and analysis

must be performed periodically, or the building operator must depend on his

nose, or on the noses of the building occupants.

Irreversible systems are a little more sophisticated, since a competent

chemical laboratory can analyze a sample of media for the concentration of

the active chemical reagent, but how does the building operator know if the

system really removes the contaminants with which he is concerned?

How does the system designer or specifier know what to use and how much to

use?

Standard test methods, comparable to the ASHRAE test method for particulate

filters, would remove much doubt as to possible bias on the part of the

manufacturer and would allow a designer or building owner to meet a '’Standard" level (or one of several levels) of air quality, without

resorting to complex, expensive air sampling and analysis.

Disc laimer - NBS does not endorse commercial products. Responsibility for

the information included here rests solely with the manufacturer. The

information is included here because it is deemed useful to the objectives

of the symposium.

27
MONITORING MASS TRANSFER ZONES IN ADSORBERS

Basil G. Louros

Sales Manager

Unisorb Corporation

South Houston, TX 77587

I. INTRODUCTION

Granular activiated carbon or alumina impregnated with potassium

permanganate have been used to remove corrosive gases from commercial and

industrial plant atmospheres. The corrosive gases interfere with the

operation of sensitive computer and other instruments by corroding

terminals resulting in costly downtime. These media are also used to

remove noxious gases from work environments for personnel safety and

protection*

II. PROBLEM

Once a corrosion or odor removing system has been installed the problem has

been to change the media frequently enough so that the instruments will

continue to be protected with time* What is needed is a quick and easy

determination of the breakthrough front which will project media

consumption and also determine any effects of any corrosive gas spills in

the plant environment. It is important that breakthrough of the media be

avoided to protect equipment and personnel.

III. Concept

The mass transfer zone is defined as the depth of the media bed where the

media goes from complete exhaustion to 100% activity. For most vapor phase

applications we believe this mass transfer zone to be anywhere from 1 to 3

inches. The mass transfer zone (MTZ) is determined by activity or chemical

remaining tests. These tests are currently done in the laboratory and are

time consuming and expensive. A quick reliable field test method is needed

to assist the plant operator.

Samples are obtained from the last inch of a given packed bed in the

direction of air flow since that is the only critical area in filtration.

As long as the last inch has 100% activity remaining, this system is still

efficient at 100%. The Unisorb sampling technique is to use a sample thief

to remove a representative sample and then analyze the sample depending on

the given media. For activiated alumina impregnated with permanganate the

sample was reacted with ferrous ammonium sulfate and back filtrated with

potassium permanganate solution. The test is carried out with a Unisorb

Test Kit and a colormetric method is used. The color intensity of the

filtrate from a Mark 2 (permanganate impregnated alumina) sample is

measured in a colorimeter, the reading is then compared to a known standard

to determine the remaining chemical activity. Figure 1 shows the K-20

meter reading as compared with the percent by weight on a dry basis of

chemical activity remaining on the alumina.

This colormetric method offers fast, reproducible results in a portable

equipment which is not affected by moisture in the sample and minimum error

in the test procedure. Results from analytical and colormetric methods

28
agree in the high range within experimental errors, that is, a range from

1% to 4%. If the sample is less than 1% KMNO^ analytical method will give

a higher reading than the colormetric method. We believe this discrepancy

in the lower range is probably due to interference between test solutions

of the analytical method and chemicals adsorbed onto the sample surface.

Therefore, we believe the colormetric method to be more indicative of the

remaining activity.

IV. TEST METHODS FOR ACTIVATED CARBON

For activated carbon the standard for activity has been carbon

tetrachloride adsorption as measured in a complicated laboratory procedure.

The colormetric test developed by Unisorb is again carried with the Unisorb

Test Kit and involves treating a ground sample of activated carbon with a fixed amount of Methylene Blue Solution. The color intensity of the

filtrate is then measured in a colorimeter and co-related with an

equivalent carbon tetrachloride number for interpretation of the remaining

capacity. Figure 2 shows a correlation curve between Methylene Blue number

and carbon tetrachloride activity.

In comparison the colormetric method offers a quick convenient field

testing method and is repeatable and accurate within a 10 to 15% range. No

elaborate setup is required and all interferences by humidity have been

taken into account in the correlation curve.

V. CONCLUSION

Both colorimetric methods offer quick reproducible results in the field for

accurate determination and prediction of media bed breakthrough. For more

information on the Unisorb model K-20 Field Test Kit, please contact

Unisorb Corporation, 1310 Genoa, South Houston.

29
2 3 k PERCENT BY WEIGHT (DRY BASIS) KMnO^

Figure 1

PERCENT CCL 4 Figure 2

^'inf^a’tfof inc" uTed TerTleTrTl^ pr°duCts * R«ponsibi lity for

information is included here because it

^ manufac turer. The

of the symposium.

because it is deemed useful to the objectives

30
CHARACTERIZATION OF THE LTC CATALYST:

Performance Against Common Air Pollutants

Marcia F. Collins

Research & Development, Teledyne Water Pik

1730 East Prospect St., Fort Collins, Colorado 80525

INTRODUCTION

The Environmental Protection Agency has been conducting various studies of

indoor air contaminants and their exposure [1, 2, 3]. These results and

others indicate that personal exposure to specific pollutants is often to

significantly greater concentrations than outdoor exposure limits.

Tightening up of residences for reasons of energy conservation, greater use

of synthetic materials in building and furnishing interiors, tobacco

smoking, and increased use of solvents all are major contributors to the

deterioration of indoor air quality.

Most individuals spend up to 90 percent of their time indoors; about 70

percent is in residential and office environments. The various types of

pollutants — as particulate, or harmful gases — have been linked to ill

health effects. Currently, the most controversial issue is the effect of

sidestream tobacco smoke on non-smokers in the same environment.

As reported in an earlier paper [4], Teledyne Water Pik has developed a novel room temperature catalyst (LTC) for removal of various gaseous

contaminants. In particular, this catalyst oxidizes carbon monoxide to

carbon dioxide at very efficient rates. It also has shown good rates of

removal for ozone, nitrogen and sulfur oxides, hydrogen sulfide, ammonia,

and certain toxic components of cigarette smoke.

LTC CATALYST MATERIAL

In general, the LTC catalyst consists of a solution of copper and palladium

salts deposited on a porous alumina substrate. It appears that this

substrate material provides a certain enhancement of catalytic activity due

to its specific surface chemistry, as well as large surface area for

dispersion of the LTC composition. Also a minimum of post-deposition water

content, tightly held by the alumina, is necessary to achieve reasonable

rates of catalytic efficiency.

Reaction Mechanism

The reaction of LTC with carbon monoxide is analogous to the Wacker

commercial process for producing acetaldehyde [5]. The oxidation-reduction

cycle requires exchange of electrons between the copper and palladium

metals of the complex; water is both consumed and returned to the catalytic

cycle.

A simplified diagram of this reaction is shown in Figure 1. The

depositions of metal salts contain activated complexes which create sites

for selective chemisorption of oxygen and carbon monoxide. Present theory

holds that "islands” of atomic oxygen are adsorbed, surrounded by carbon

monoxide molecules and that the oxidation reaction occurs at their

31
rface [6]. The rate of reaction is determined by the catalyst's

iC iency

.

DESORBED CO:

Figure 1. Diagram of Catalytic CO Oxidation Mechanism

LTC ACTIVATED COMPLEX

Several simple tests imply the formation of a palladium-cooper complex,

probably stabilized by surrounding anions. This complex is the active

species which is responsible for catalytic rates of CO oxidation to CO

2

.

A "catalyst” made with only the palladium salt —all else equal —was able to

achieve 50 percent CO removal under standard tube test conditions.

Likewise, a "catalyst" containing the two copper salts gave only 15 to 4

percent CO removal. The LTC combination of these three salts consistently

removes greater than 85 percent CO.

A series of tests using stepwise additions of the metal salts constituents

in various sequence (same final composition) clearly shows the best CO

removals occur with the simultaneous deposit of the LTC composition.

SPECIFICATIONS FOR PERFORMANCE TESTS

Tube Test for Catalytic Activity

A one gram sample of LTC catalyst is packed in a glass tube to minimize bypass and exposed to feed gas flow of known concentration in a single

contaminant. Relative humidity in the feed stream may be varied from 10 to

32
90 percent, while temperature is unregulated ambient. Typical test

conditions are 50 parts per million of carbon monoxide and 60 percent

relative humidity at a flow rate of 500 cc/minute. The difference in CO

concentration between feed gas passed over untreated substrate alumina

beads versus over the LTC catalyst measures activity, which can be

monitored over time. Equilibrium removal rates are the percentage of

pollutant concentration lost after 6 hours. The standard deviation of 8

repetitive test results was a satisfying 2.1.

The actual amount of contaminant removed, of course, depends on physical

parameters—-the amount of LTC, the size and thickness of the catalyst bed,

gas flow rate, length of testing, and initial concentration of contaminant

CO. Time of contact with LTC reflects the former variables and is

calculated from:

In (CQ /C t

) = K * t c (1)

Assuming a first-order reaction rate (oxidation of CO to CO2 ), C

t is the

contaminant concentration at some time t, C

Q is the initial concentration,

K is the reaction rate constant, and t

c is contact time. In reality, the

reaction rate also varies with the amount of surface coverage of oxygen and

carbon monoxide, therefore a first order reaction scheme is a considerable

simplification. The reaction constant is characteristic of catalyst

material, independent of test procedures. For example, an LTC catalyst

with an equilibrium CO removal rate of 93 percent, has a calculated K of

about 12 seconds”^.

Room Test of Air Filtration Appliance

The second type of performance test measures contaminant removal in a sealed room, using the LTC catalyst filter in our air filtration appliance.

Filters were designed to hold about 230 grams of LTC catalyst in a thin bed

with minimal air flow by-pass. This test is conducted in a 1008 cubic foot

stainless steel room with an initially known amount of gaseous contaminant.

The rate of decay is subtracted from the performance of the appliance. Air

flow through the appliance was 300 c fm for the test duration of 2 hours.

The standard deviation of 7 repetitive test results wa an excellent 1.4.

TUBE TEST PERFORMANCE

Temperature Dependence

The temperature dependence of LTC performance has been reported

previously [4], but a brief description is included for completeness.

Figure 2 maps results of a series of tests for CO removal of LTC at various

temperatures. Between room temperature and about 400°C, CO oxidation

ranges between 90 and 100 percent. Below about 65°F, the reaction rate

drops off sharply, probably as a result of increased dissipation of the

heat of reaction.

In contrast, the physical adsorption of NO

2 decreases as the temperature

increases. Near 100 percent adsorption occurs between -50° and 25°C,

gradually decreasing to 50 percent at 175°C.

33
TEMPERATURE (°C)

Figure 2. LTC Removal of CO and NO2 as a Function of Temperature

Relative Humidity Dependence

The dependence of LTC activity on relative humidity was also reported

previously [4i, and is illustrated in Figure 3. CO oxidation is optimum

between about 25 and 70 percent relative humidity. Inadequate water

present inhibits the reaction at interfaces of adsorbed "island oxygen" and

surrounding CO molecules. Too much moisture fills the micropores of the

alumina, effectively "drowning" these active metal deposits.

The physical adsorption of NO

2 is unaffected by humidity, presumably

because most of the chemisorption is on the surface of the LTC/alumina bead

and in the micropores. A common commercial material, Hopcalite, is

severely poisoned by water vapor; it is ineffective about 10 percent

relative humidity.

Contact Time

One of the physical parameters which strongly affects the LTC rate of CO

oxidation is the time that the contaminant is in contact with the catalyst.

Table I shows data for contact time of 0.4 to 0.01 second, achieved by

varying the gas flow rate (5 to 0.5 /min) and/or the bed depth of LTC

packed in the tube. All tests were conducted at room temperature and 60

percent relative humidity with 50 parts per million CO.

34
LTC: NO2

Figure 3. Catalyst Removals as a Function of Relative Humidity

TABLE' I Effect of Contact Time on CO Oxidation

Contact Time

(S ec fl

Bed Depth

( Inches)

% Average

CO Removal

0.4

0.2

0.1

0 .08

0.05

0.025

0.01

1 .0 84

0.5 52

0.5 30

0.4 28

0.25 14

0.25 7 0.25 2

Although Equation 1 postulates a log-linear plot, the data fits a log-log

curve—confirmed by regression analysis. The amount of surface coverage of

the active LTC sites with CO and oxygen molecules accounts in large part

for the discrepancy, as well as the fact that the oxygen-palladium bonds

are weakened by the co-adsorption of CO molecules [6]. Thus, the reaction

conforms more closely to the Langmuir-Hinshe lwood mechanism rather than a simple first order dependency [7].

ROOM TEST PERFORMANCE RESULTS

One present application of LTC catalyst is a portable air filtration

appliance for home and office environments. The LTC beads are tightly

packed into a thin filter to minimize pressure drop; in the product filters

35
LTC and activated carbon are mixed 50:50. The Instapure Air Filtration

System units used in this series of tests had LTC only (about 230 grams)

and an air flow rate of 300 cfm. The contact time is thus approximately

0.02 second, or an order of magnitude less than that in the tube test. All

of the following tests were conducted in a 1008 cubic foot sealed room at

40 percent relative humidity and ambient temperature. Initial contaminant

concentrations are noted in each test, each of 2 hour duration. Figure 4

summarizes all of the results as adjusted for each species^ rate of decay.

The Threshold Limit 7alue— Short Term Exposure Limit (STEL) are

recommendations issued by the American Conference of Governmental

Industrial Hygienists (1983). The STEL values cited are for a 15 minute

time-weighted average which should not be exceeded during a work day.

Carbon Monoxide

A filter using 50:50 LTC to activated carbon was tested, using 30 parts per

million CO to begin. The STEL limit is 400 parts per million, but 30 parts

per million corresponds to the lower limit of the "dangerous" category

established by the EPA. After 2 hours running, 55 percent of the CO was

removed. Given the brief contact time, a per-pass f i 1 ter ef f ic iency of

14.6 percent may be calculated. An LTC filter removed 78 percent CO in 2

hours .

Ozone

An LTC -on ly filter in the appliance was run in the sealed room containing

164 parts per billion ozone (STEL limit is 300 parts per billion). After

36
38 minutes, 99+ percent was removed. Other tests indicate that the very

reactive ozone molecules are decomposed to oxygen by chemisorption and

subsequent interaction on the alumina surface, as well as the LTC active

sites .

Nitric Oxide

An LTC filter was exposed to 20 parts per million NO at 300 cfm (STEL is 35

parts per million). After 80 minutes, the LTC had remove 20 percent,

whereas the LTC/carbon filter was able to remove 40 percent of the initial

concentration

.

Nitrogen Dioxide

The LTC filter was exposed to 4 parts per million NO2 (STEL is 5 parts per

million). Removal was 40 percent after 100 minutes versus 100 percent

removal for the LTC/carbon filter. The NO

2 molecules seem to be more

tightly adsorbed to active carbon surfaces than to the LTC/alumina

surfaces. As shown in Figure 2, increasing temperatures increase the rate

of desorption (tube tests).

Sulfur Dioxide

An LTC filter in our appliance was run in the sealed room containing 5

parts per million SO 2 (STEL is 5 parts per million). Removal of 100

percent was achieved after 90 minutes. Other tube tests [4] have shown

that SO2 is chemisorbed by LTC active Cu(II) sites until saturation.

Hydrogen Sulfide

The LTC filter was subjected to 4 parts per million H

2 S (STEL is 15 parts

per million). After 60 minutes, about 100 percent of the ^S was removed.

Earlier tube tests indicate an irreversible reaction of ^S with LTC which

results in a gradual poisoning of the active sites. Apparently, cooper

sulfide is the reaction product [4].

Ammonia

An LTC filter in the air filtration appliance was run in an atmosphere

containing 140 parts per million of ammonia. An STEL recommended limit of

35 parts per million is published. After 60 minutes, 58 percent was

removed; 76 percent at the end of the 2 hour test. Subsequent, continuing

test runs show that the catalyst is gradually saturated, with NH

2 removal

dropping to 6 percent after 6 hours.

Benzene

The LTC filter was exposed to 17 parts per million of vapor in the test

room (STEL limit is 25 parts per million). Only 8 percent was removed

after 2 hours, whereas the LTC/carbon filter was able to remove greater

than 90 percent of the benzene concentration, even after each of five

successive test runs. The benzene molecule is non-polar and readily

adsorbed by the porous activated carbon. LTC is relatively unreactive to

the benzene structure.

37
Components of Tobacco Smoke

Chemical components of both mainstream and sidestream tobacco smoke are

present in air as particulate or aerosol and a gaseous phase. The major

portion of particulate is tar, nicotine, and water; the majority of the gas

phase is carbon dioxide, carbon monoxide and methane. Particulate can be

removed mechanically from mainstream smoke by a paper filter (cigarettes).

Table II lists some of the higher concentration constituents of tobacco

smoke along with their biological effects®

TABLE II

Some Cigarette Smoke Gaseous Constituents

Mainstream Smoke: Unfiltered Cigarettea

Gas Phase Components Biological Activity Wt/ Cigaret

Carbon Dioxide 10-60 mg

Carbon Monoxide Toxic 10-20 mg

Methane 1.3 mg

Acetaldehyde Toxic 770 mg

Acetone 100-600 mg

Nitrogen Oxides Toxic 60-600 mg

Isoprene * 582 mg

Hydrogen Cyanide Toxic 430 mg

2 - Butanone 80-250 mg

Acetonitrile 120 mg

Toluene 180 mg

Ammonia Toxic 80 mg

Benzene Co -Care inogen 67 mg

Acetylene 27 mg

D ime thy Initrosamine Care inogen 10-65 mg

Nitrosopyrrolidine Care inogen 10-35 mg

U.S. Dept, of Health, Education and Welfare, ''The Health Consequences

of Smoking'', 1981.

The most acute biological effect of tobacco smoke is suffered first from

nicotine, and secondly from carbon monoxide. The latter markedly decreases

the oxygen-carrying capacity of the blood and may impair the nervous system

functions. Its effects range from inducing headaches and dizziness to

implication in heart attacks and strokes [8].

Room Test for CO From Cigarette Smoke

The test results for CO removal from sidestream cigarette smoke using the

Ins tapure^ Air Filter (AF-1) are shown in Figure 5. Two cigarettes were

smoked every half-hour in a 1152 cubic foot sealed room to generate the

upper curve ending at 48 parts per million CO in 8 hours. The same

procedure was followed while running the AF-1 appliance, which gave the

center curve (32 parts per million CO in 8 hours). The lower curve is for

a repeat of the second test with cigarette smoking terminated after 6

hours. The air filter removes 34 percent of the cumulative CO

concentration

.

38
Figure 5. Room Tests of Product Filter for CO (Smoke) Removal Rate

Mainstream Smoking Test

A small filter containing 6 grams of LTC was attached to unfiltered

cigarettes to test for removal of mainstream tobacco smoke components. The

tests were conducted by an independent laboratory and are summarized in

Figure 6. Oxidation of CO is dramatic —from 17,000 to 430 parts per

million with the LTC filter. Referring to Table II, several other

hazardous compounds are significantly reduced by use of LTC. Acetaldehyde

and ammonia are diminished from 1 ,600 to 18 and 160 parts per million or

less respectively, Likewise, methyl alcohol is mechanically removed;

several constituents are below the detection level and therefore show no

change

.

POLLUTANT CIGARETTE (dm) LTC /Cl GARETTE (onm)

Carbon monoxide 17 ,000 430

Hydrocarbons 2,700 600

Ammonia 1 ,600 160

Acetaldehyde 1 ,600 < 18

Methyl chloride 550 84

Acetone 480 < 7 Methyl alcohol 350 < 60

Methyl ethyl ketone 100 < 6

Hydrogen sulfide 41 < 1

Figure 6. LTC Removal of Contaminants in Cigarette Smoke

39
SUMMARY

One of the important qualities of the LTC catalyst is the rapid oxidation

of carbon monoxide to carbon dioxide under a wide variety of conditions.

The catalytic material is a palladium-copper activated complex which reacts

with various contaminant molecules through a continuous oxidation/reduc tion

cycle. The alumina substrate enhances LTC activity with its favorable

surface chemistry and very high surface area. About 10 percent surface

water is necessary to facilitate the oxidation of CO. This reaction shows

a log-log dependence on contact time, suggesting a Langmuir-Hinshe Iwood

mechanism.

In the tube tests, LTC removed 90 to 100 percent of contaminating carbon

monoxide in the temperature region of 20° to 400°C, and at ambient over a range of 25 to 65 percent relative humidity. In contrast, NO2 is

chemisorbed by the LTC/alumina materia 1-the amount strongly dependent on

temperature increases but independent of humidity.

Performance tests in the Instapure^ Air Filtration appliance were done in a sealed room using 300 cfm air flow rate. CO was 78 percent removed, Og 100

percent removed, SOg and H2S 100 percent, NHg 58 percent, N©2 40 percent,

and benzene 8 percent removed. CO from sidestream tobacco smoke was 34

percent removed by the appliance. Hazardous components of mainstream

tobacco smoke were effectively reduced using a small ancillary filter

containing LTC.

The LTC catalyst has demonstrated excellent capability to remove an

important variety of hazardous pollutant gases which are common factors to

poor indoor air quality. The Instapure^ Air Filtration System incorporates

the LTC catalyst in a 50:50 mixture with activated carbon to effectively

remove particulate, odors, and hazardous gages at room temperature and

humidities. The ability to remove hazardous gases is unique for the

category of portable air filtration equipment. The wide variety of

pollutant gases that LTC removes suggests the catalytic technology is

adaptable to a considerable range of commercial and industrial

applications

.

D isc laimer : NBS does not endorse commercial products. Responsibility for

the information included here rests solely with the manufacturer. The

information is included here because it is deemed useful to the objectives

of the symposium.

REFERENCES

1. Wallace, L. A., "Results From the First Three Seasons of the Team

Study: Personal Exposures, Indoor-Outdoor Relationships, and Breath

Levels of Toxic Air Pollutants Measured for 355 Persons in New Jersey."

U.S. EPA Research Triangle Park, N.C., 78th Annual APCA meeting, June

16-21, 1985.

2. Ibid, Et Al. "Personal Exposure to Volatile Organic Compounds: Direct

Measurement in Breathing-Zone Air, Drinking Water, Food, and Exhaled

Breath," Environmental Research , volume 35, 1984.

40
3. Ibid, Et Al. "Assessing Sources of Volatile Organic Compounds, in

Homes, Building Materials, and Consumer Products," Conference on

Characterization of Sources of Indoor Air Contaminants, Releigh, N.C.,

May 13-15, 1985.

4. Collins, M. F. "Room Temperature Catalyst for Improved Indoor Air

Quality," Transactions of the Air Pollution Control Association,

International Specialty Conference-Indoor Air Quality in Cold Climates:

Pollutant Abatement Research, Ottawa, April 29 to May 1, 1985.

5. C. Thomas, Catalytic Process and Proven Catalyst . Academic Press, 1970.

6. Gasser, R. P. H., An Introduction to Chemisorption and Catalysis bv

Materials . Oxford University Press: 1985, pp . 220-224.

7. Ibid, pp. 249-252.

8. "Smoking and Health: A report of the Surgeon General," U.S. Dept, of

Health, Education, and Welfare, Part 15, Biological Influences on

Cigarette Smoking, 1981.

41
EFFECTS OF RELATIVE HUMIDITY ON ADSORPTION OF

CONTAMINANTS ON ACTIVATED CARBON

Dwight W. Underhill, Corresponding Author

Graduate School of Public Health

University of Pittsburgh

130 DeSoto Street

Pittsburgh, PA 15261

Gina Micarelli and Maria Javorsky

Industrial Health Foundation, Inc.

34 Penn Circle West

Pittsburgh, PA 15206

SUMMARY

The Dub inin-Radushkevich potential theory was extended to include a term

giving the effects of relative humidity on the adsorption coefficient.

This extended equation permits the adsorptive capacity of the activated

charcoal in a respirator cartridge to be estimated for any combination of

temperature, relative humidity, and concentration of contaminant.

Application of this theory to previously published data of Werner showed a good correlation between theory and experiment. This equation is

consistent with the experimental observations that 1) below a certain

value, the relative humidity has little effect on the adsorption

coefficient and 2) the effect of relative humidity, if observed, is more

severe for lower than for higher concentrations of contaminant.

Because the uptake of water by activated charcoal increases rapidly as the

relative humidity increases above 40%, the performance of a respirator

cartridge in humid atmospheres may be quite unsatisfactory. A worker may

be at risk if he or she uses, in a highly humid environment, a respirator

cartridge tested only 1) under dry conditions, or 2) only for a short

period of time at a high relative humidity, or 3) for some other compound

at a high relative humidity. The importance of this problem is compounded

by the fact that the interfering compound, water vapor, is colorless,

odorless, and usually present at very high concentrations.

In this paper we will develop from ideas of Polanyi, Dubinin, and Manes, a simple mathematical model for the effect of relative humidity on water

insoluble compounds. We will then examine the predictions of this

theoretical model and its accuracy when applied to previously published

data. We also give data on the adsorption of water-immiscible solvents by

a simulated respirator cartridge operating in an atmosphere of 100%

relative humidity.

The Polanvi Potential Theory

In this study the uptake of mixtures of water vapor plus the vapors of an

organic vapor, will be approached starting with the broad viewpoint of the

Polanyi potential theory [1]. This theory is already known to be useful in

predicting the adsorption of binary vapor mixtures [2, 3], including the

uptake of binary mixtures of water vapor and organic vapors [4].

42
The basic concept of the Polanyi potential theory is that an adsorbent can

be characterized by a series of force fields over the microporous surfaces

of the adsorbent (Fig. 1, from Smisek and Cerny [5]). These attractive

forces, which compress the molecules of a gas, act from the surface to a finite distance in the surrounding space. Polanyi has described these

forces of attraction by the adsorption potential, which is defined for a point near the surface of the adsorbent, as the work done by the attractive

forces in bringing a molecule of a gas to that given point. The adsorption

potential has its maximum value at the surface of the adsorbent and it

decreases to zero at some limiting distance. The broken lines shown in

Fig. 1 represent planes of equal adsorption potential.

£,-0

Fig. 1 Schematic representation of the force field at the surface of

solid adsorbents according to the potential theory a) Idealized

case of a plane homogeneous surface, b) Real surface from Smisek

and Cerny [ 5 ] .

Because the adsorption potential increases as the distance from the surface

decreases, the density of the compressed adsorbate is not constant

throughout the adsorption space. The adsorption potential may be defined

in terms of , the isothermal work of compression per unit volume of

adsorbed absorbate:

= RT/V 1 n(

P

Q /P

)

( 1 ) where

T = absolute temperature, °K

R = ideal gas constant (8.3143 Joule/Mole/ °K)

V = molar volume, cc/mole

P = partial pressure of adsorbate, atm

43
p Q = partial pressure of compressed absorbate on the given

equipotential surface, atm

In the adsorption of vapors, if the isothermal work of compression causes

P

D , the partial pressure of adsorbate on a given equipotential surface, to

be greater than P s» the vapor pressure of the pure adsorbate at the

temperature of adsorption, then the adsorbate will be compressed to form a liquid phase held within this equipotential plane.

For the adsorption of vapors, it is usually a sufficiently accurate

assumption to associate all of the adsorption that is observed with this

liquefaction. This volume is calculated with the assumption that the

adsorbate has the density of the saturated liquid phase. The relationship

between the volume of adsorbate enclosed in the adsorption space and the

adsorption potential is described by a characteristic curve. On a characteristic curve (so named because it should be the same for a given

vapor and adsorbent at all temperatures below the critical temperature) the

volume (V

t

) of an adsorbed film is expressed as a function of RT/

V

ln(P /P). This characteristic curve takes the place of the more familiar O plot of the adsorption isotherm, which gives the amount adsorbed as a function of pressure at a constant temperature.

Potential adsorption theories can be extended to given one characteristic

curve for a wide number of compounds if provisions are made for the

differences in the polarizability of the compounds under study. See for

example Sansone and Jonas [6].

One of the limitations of the Polanyi potential theory is that it does not

provide an analytical expression for the adsorption isotherm. Such

equations must be found experimentally. Grant et al. [43 in their study of

adsorption of organic compounds on activated charcoal used the following

expressions to characterize the Polanyi potential curve. For one activated

carbon (30/100 mesh BPL activated carbon Audit Sample 104), they derive a fifth order polynomial to determine the adsorption space from the

adsorption potential. And to calculate the inverse, i.e., the adsorption

potential from the adsorbate volume, they use an eighth order polynomial.

The Dub in in -Rad us hkevie h Model

Dubinin and Radushkevich [7] noted that in many cases it is not necessary

to use high order polynomials to describe the adsorption potential. Very

often the relationship between the adsorption potential and the adsorbed

adsorbate is Gaussian:

W

t

=• W

Q exp [ -k 2

3 (2)

where: W

t = weight of adsorbed adsorbate/gm adsorbent

W

Q = total (limiting) volume of the adsorption space

= density of liquid adsorbate at temperature of adsorption

k = constant

Golovoy and Bras law [8], working at Ford Motor Company, have demonstrated

the high accuracy possible with the Dub in in-Radus hke v ic h equation. In

their work, a mean error of 1.9% was found when the Dub inin-Radushke vich

equation was used to predict the adsorption coefficients of 14 solvents.

44
Given the high accuracy possible with the use of the Dubinin-Radushkevich

isotherm, the task that we have set for ourselves is to modify this

equation so that it can be applied to the adsorption of water-immiscible

solvents. Before this is done, we will examine how Manes has developed a graphical procedure using the Polanyi potential theory to describe the

effect of adsorbed water on water- immisc ib le solvents.

Manes Treatment of the Polanvi Potential Theory

Manes [3] and Manes and Greenbank [9] have shown how, by simple geometric

constructions, the Polanyi adsorption potential theory can be extended to

the adsorption of water-immiscible adsorbates in the presence of water

vapor. The basic concepts are shown graphically in Fig. 2, which describes

the effect of relative humidity on the adsorption of butane from air. In

Fig. 2, the curve on the far right represents the Polanyi potential curve

for butane alone, and the curve marked represents the Polanyi potential

curve for water vapor. In the presence of water vapor at 100% relative

humidity, the Polanyi potential curve for butane is shifted to the left by

an amount that is equal to the potential energy for the adsorption of the

water vapor. The lower set of horizontal arrows shows how this shift is

made in order to determine the adsorption of butane from air saturated with

water vapor.

Fig. 2 Illustrative graphic calculation for adsorption of butane and

water and 50% and 100% relative humidity. From Manes [3]

If the air is only partially saturated with water vapor, the Polanyi

potential for adsorption in the presence of water vapor is shifted to the

left by an amount determined by the free energy lost by the water vapor

45
because of its partial saturation. This shift is proportional to

RT°1 n( RH/ 1 00) , where R and T have their usual values, and RH is the

relative humidity. In Fig. 2, the upper set of horizontal arrows shows the

determination of the adsorption of butane from air which was 60% saturated

with water vapor. The result of this shift is an increase in the quantity

of adsorbate over what would be seen in the presence of air completely

saturated with water vapor.

From Fig. 2, other effects of the combined concentrations of water vapor

and organic adsorbate on the adsorption of the organic adsorbate may be

determined. At the higher adsorption potentials (i.e. at low

concentrations of the organic adsorbate), the filled pore volume changes

very rapidly with small changes in the adsorption potential, and thus it

would be expected that at low concentrations of organic adsorbate, the

relative humidity would have its strongest effect.

A second prediction from Manes' correlation is that at relative humidities

less than 100% and at a sufficiently high concentration of an organic

vapor, the relative humidity causes a negligible reduction in the

adsorption coefficient of the organic component. The physical explanation

for this effect is that at less than 100% relative humidity, the pores are

only partially filled with water. At a certain vapor pressure of the

organic adsorbate, the organic adsorbate will fill the pores beyond the

level occupied by the water, displacing all the water, and at this

concentration (as well at higher concentrations) of organic adsorbate, the

presence of water vapor has no effect on the adsorption of the organic

vapor. This effect is seen in Fig. 2, in which at pressures of butane over

10“^ atm, and at a relative humidity of 60%, the quantity of adsorbed

butane is the same as from dry air.

Calculation of the Adsorption Coefficient

Rather than depend on the graphical analysis, we develop here an equation

which permits a rapid calculation of the effect of water vapor on the

adsorption of water immiscible organic compounds. We use three assumptions

implicit in the geometrical analysis that Manes developed from the Polanyi

diagram, for estimating the effect of moisture on the adsorption of water

immiscible compounds. The first is that if, from dry air the potential

free energy required to fill a micropore with organic vapor is , then the

potential energy required in the presence of completely saturated air is

some multiple of the free energy required in the absence of water vapor,

i .e .

100% RH " (1 + k l> dry air

The second assumption is that the free energy required to fill a micropore

with condensed organic vapor decreases linearly with a decrease in the free

energy of the water vapor. Thus, to calculate the adsorption of organic

vapors from air which is partially saturated with water vapor, .a correction

factor of proportional to RT/ Vj

1 °ln(RH/100) , where is the molar volume

for water and RH is the percent relative humidity, should be used. Thus

the potential free energy required for pore filling by a water immiscible

organic compound is:

' = (1 + k^RT/VlnCPg/P) + k2 RT/Vh *ln(RH/100) (4)

46
where: kj = factor defined in Eq. 2 to describe the change in the

adsorption potential of a water immiscible compound brought

about by replacing the air with water in the micropores

= factor giving the change in the adsorption potential of a water immiscible compound as a function of the relative

humidity* O V

h

= molar volume of water, (55.5 cmJ /gm)

R, T, V, P, and P

g are as defined previously.

However if k

2 RT/ V^’ln(RH) > k^RT/ V*ln(Ps /P) , then the organic adsorbate can

displace all the water from the micropores and the adsorption potential for

the organic solvent is given by Eq. 1, which does not contain any factors

for the effect of coadsorbed water, as it is presumed that under this

condition any competing coadsorbed water has been completely displaced from

the adsorbent.

After the adsorption potential for the organic solvent has been determined,

using either Eq. 1 or 4, whichever is appropriate, the uptake of organic

adsorbate is calculated from Eq . 2.

Experimental Studies

Realistic tests on the effect of relative humidity on the adsorption of a water immiscible organic compound were reported recently by Werner [ 1 0 ] , who challenged small beds (containing 37.5 gms) of activated charcoal to

input concentrations of 300 to 1300 mg/m^ of trichloroethylene (TCE) at

relative humidities ranging from 5 to 85%. Werner found that the lower the

concentration of adsorbate (trichloroethylene), the stronger the effect of

relative humidity. In Werner's paper this effect was shown in a series of

empirical curves in which the uptake was plotted against the square of the

logarithm of the concentration. Our object in reanalyzing these data is to

find a quantitative expression of these results. To do this we reexamined

Werner's data in terms of the procedure we developed above.

Table I gives Werner's measurements of the uptake of trichloroethylene on

activated carbon, as a function of the temperature and relative humidity.

The first step in this analysis, to determine the appropriate values for k

and W qj was based on Werner's measurements of the adsorption of

trichloroethylene at 5% relative humidity. It was assumed that at this

relative humidity, the experimental data were equivalent to the adsorption

on dry charcoal. These two parameters, the usual parameters in the

Dub inin-Radushke vich equation, were then used in conjunction with trial and

error tests to find the best values for kj and k 2 t0 fit Eq. 4 to the

measurements of adsorption of trichloroethylene at higher relative

humidities. Thus the effect of relative humidity was determined with only

two adjustable parameters, one of which, k^ , gives the maximum effect of

adsorbed water on the adsorption of the immiscible compound, and the other

parameters, k

2 , describes the increase in the adsorption of the immiscible

compound as the partial pressure of the water vapor is reduced. For k^ and

k

2 the values found by a trail and error procedure were 0.87 and 4.75,

respectively. When these values were used with Eqs. 4 and 2, the mean

error between our calculated values and Werner's experimental values is

10.5%, which is in the same range as the experimental error in Werner's

measurements. These two equations give a quantitative way of representing

47
the basic findings of Werner, i.e. 1) below a certain value, the relative

humidity has little effect on the adsorption coefficient and 2) the effect

of relative humidity, if observed, is more severe for lower than for higher

concentrations of contaminant.

Table I

Predicted vs. Theoretical Uptake of Trichloroethylene

in the Presence of Water Vapor

Uptake at Uptake at Uptake at Uptake at

1300 mg/

m

3 1000 mg/m3 600 mg/m3 300 mg/m3

R.H. Calc

.

Meas

.

Calc . Meas . Calc

.

Meas

.

Ca lc . Meas .

5% 0.429 0.434 0.397 0.399 0.346 0.334 0.281 0.286

25% 0.434 0.431 0.434 0.370 0.250 0.262 0.114 0.121

50% 0.399 0.403 0 .3 87 0 .342 0 .209 0.218 0.091 0 .098

65% 0.334 0.320 0.297 0.284 0.147 0.160 0.059 0.054

85% 0.286 0.257 0.190 0.180 0.084 0.114 0.030 0.027

In using Eqs. 2 and 4 to make the calculations given in Table I, the

following parameters were used:

= 1.455 gm/cm3

P

s = 500 ,500, mg/M3

Wq = 0.62 cm3

/ gm

k = 2.89X10 -3 cm^/ Joule3

k^ = 0.87 (dimensionless)

k£ = 4.76 (dimensionless)

Experimental data from Werner [ 1 0

]

We were fortunate in having an extensive set of data, such as Werner's,

through which our equation for the effect of relative humidity on the

adsorption coefficient can be tested. But Werner's data extends to

relative humidities no higher than 85%, and it is important to know the

adsorption coefficient and mass transfer efficiency of respirator

cartridges at relative humidities as high as 100%. Performance of

simulated respirator cartridges at higher relative humidities will be

examined next.

Table II shows the results from a different study [11 ] in which xylene was

adsorbed from air saturated with water vapor. The purpose of this work was

to examine the performance of simulated respirator cartridges in air

totally saturated with water vapor, and therefore the experimental

parameters, i.e., the mass of charcoal (40 gms) , the flow of air (20 1pm),

and the concentration of contaminant (ranging from 250 to 1000 ppm)

represented realistic parameters for estimating the in-use performance of a respirator cartridge at a high relative humidity. The adsorbent, 8/16 mesh

Barnebey-Cheney Grade #177, activated carbon having an activity of 60%, was

dried overnight at 145-155°C before being tested. The adsorption

48
coefficient, in liters/gm, was calculated from the breakthrough curves

using a d imens iona 1 ized version of Eq. 16-47 of the Chemical Engineers'

Handbook [12]. The "Use Time" in Table II represents the time before the

effluent concentration of xylene from the adsorption bed reached 5% of the

input concentration. It is seen from the "Use Times" in Table II that the

simulated respirator offered protection against xylene fro an appreciable

time, even though the carrier gas, air, had been saturated with water

vapor. For xylene concentrations of 500 ppm and lower, effective

protection (based on the criterion of less than 5% breakthrough) would be

expected to be longer than a standard workday of 8 hours (480 minutes).

Table II

Effect of Concentration on Adsorption of Xylene by

Predried Charcoal from Air Saturated with Water Vapor

(from Micarelli [11])

Input

Concentrat ion

Run

#

Adsorption

Coef f ic ien

t

( liter/ gm)

Theoretical

Plates

Use

Time

(Mins)

Percent

Saturation

1000 ppm 34 202.5 37 .0 204.4 50

500 ppm 29 460.0 46 .6 527 .0 57

250 ppm 30 755 .7 79.7 1023 .0 68

In the above table:

Use Time = Time (in minutes) for which breakthrough remained less than 5%

of inflowing adsorbate.

% Saturation = Percent saturation of adsorbent at time of 5% breakthrough.

The salient point from these measurements is not the protection offered

against xylene, per se, but rather that it is reasonable to expect that

there may be a large number of compounds which like xylene are water

immiscible and will show similar retention times. We next present data on

the adsorption of chlorinated hydrocarbons, which are water immiscible, and

further, because of the high polarizability of the chlorinated

hydrocarbons, which are water immiscible, and further, because of the high

polarizability of the chloride atom, these compounds would be expected to

be strongly attracted by the van der Waals force to the micropores of the

charcoal and therefore to strongly resist displacement by adsorbed water.

Table III gives results of Javorsky [13], from experiments in which she

measured the performance of simulated respirator cartridges when challenged

with vapors of chlorinated hydrocarbons in air at both high and low

relative humidities. The test compounds were chlorobenzene,

te t r ac h

1

or oe thy 1 ene , methyl chloroform, carbon tetrachloride, and

chloroform. Other than the adsorbates (chlorinated hydrocarbons) and their

concentration, the experimental conditions were unchanged from those

selected by Micarelli. For each compound, two breakthrough curves were

determined using air at 100% R.H. and a comparison breakthrough curve was

made using air at a relative humidity of 25%. From each breakthrough curve

the adsorption coefficient, the "Use Time" (time of 5% breakthrough), and

49
percent saturation, which is the percent of the adsorption capacity of the

bed that was utilized at the time when the effluent concentration reached

5% of the input concentration. To an industrial hygienist, this work has

special importance because chlorinated hydrocarbons are often used in

processes, such as degreasing, where steam is also used and thus where

exceptionally high relative humidities may be expected.

Table III

The Performance of Respirator Cartridges with the Input

Concentration of Chlorinated Hydrocarbon Maintained at 750 ppm

(from Javorsky [133)

Ratio of

CMPD

Run

# RH

Use

Time

( Min)

Adsorption

Coef f ic ient

,

k , ( 1 / sm)

Percent

Saturat ion

k at 100%

RH to k at

25% RH

CB 1 100% 375 298.1 62

CB 2 100% 370 290.4 63 0.93

CB 19 25% 508 315.2 80

TC 36 100% 315 247.2 75

TC 37 100% 290 243.1 60 0.70

TC 41 25% 542 349.1 77

MC 43 100% 290 216.5 66

MC 44 100% 273 214.7 63 0.78

MC 45 25% 407 276.7 73

CT 25 100% 183 124.3 74

CT 26 100% 176 119.4 73 0.81

CT 29 25% 243 150.0 81

CF 5 100% 123 86 .3 71

CF 6 100% 120 85.7 70 0 .71

CF 20 25% 182 119.8 76

where

:

CB = Chlorobenzene

,

TC = Te trachloroethy lene

MC = Methyl Chloroform,

CT --- Carbon Tetrachloride, and

CF = Chrloroform.

From Table III, it can be seen that the change from 25% R.H. to 100% R.H.

reduced the adsorption coefficient, on the average by 21% and the percent

saturation, on the average by 12%. Both these factors affect the "Use

Time", which, on the average, was reduced by 32%. The important point to

be learned from Table III is that both the adsorption coefficient and the

mass transfer efficiency are reduced by high relative humidities, and that

both factors must be considered in determining the performance of

respirator cartridges at a high relative humidity.

Why does the relative humidity affect the mass transfer efficiency (as

described here by the percent saturation at 5% breakthrough)? The answer

50
lies in the pore structure of the adsorbent. In most carbonaceous

adsorbents [14] there are usually two isolated pore varieties, adsorbing

pores and transport pores, which vary in their properties. Adsorbing pores

consist of micropores (r < 6-7A) and supermicropores (6-7 A < r < 15-16 A)

whereas transport pores consist of mesopores (15-16 < r < 1000-2000 A) and

macropores (r > 1000-2000 A)^^). The overall controlling rate of

adsorption is usually the rate of transport of the adsorbate through the

transport pores to the adsorbing pores, where it becomes bound by the van

der Waals force. The probable explanation for the reduced mass transfer

efficiency at a relative humidity of 100%, is that the transport pores had

become partially, but not fully clogged by water under the test conditions.

Had the transport pores become fully clogged with water, then much poorer

performance would have been expected because the diffusion of organic

compounds through water is about a thousand times slower than through air.

It is important to understand the exact cause of the loss of respirator

performance. If it were the reduction in the adsorption coefficient that

caused the major loss of efficiency at a high relative humidity, then the

only way to design a respirator cartridge that will be effective for a longer time under the same conditions is to use a respirator cartridge with

more adsorbent. But if, instead, it is the mass transfer efficiency that

is primarily affected, than an alternative to the use of more charcoal

would be a redesign of the respirator to give a geometry conducive to a higher mass transfer efficiency. This study has shown that for the

adsorption of chlorinated hydrocarbons at a high relative humidity, both

factors appear to be important.

Topics for Additional Study

The calculations reported here apply only to the adsorption of waterimmiscible compounds. The extension of the Dubinin-Radushkevich theory to

the adsorption of water-miscible solvents are solved theoretically by

Bering and coworkers [16, 17], who rewrote the Dubinin-Radushkevich equation

in terms of partial molar quantities of the competing solvents and then

experimentally proved the validity of their extension. There is no reason

as to why the equations developed by Bering et al. would not apply to the

coadsorption of water and water-miscible solvents.

Recently there has been an increased interest in the performance of

respirator cartridges at high relative humidities. For example at the 1986

American Industrial Hygiene Conference there were six papers giving

additional data in this area [References 18, 19, 20 , 21 , 22 , 23 ]. We hope

that the general procedures described here will be of value in correlating

data in this very active field.

Acknowledgment

This work was supported by NIOSH Grant 1 R01 OHO1644-01.

References

1. Polanyi, M.: Adsorption of Gases (Vapors) by a Solid Nonvolatile

Adsorbent. Verh. deut. phys. Ges. 18:55 (1916).

51
2. Jonas, L. A., Sansone, E. B., Farris, T. S.: Prediction of Activated

Carbon Performance for Removal of Binary Vapors,* Am. Ind. Hyg. Assoc.

J. 44:716-719 (1983.

3. Manes, M.: Estimation of the Effects of Humidity on the Adsorption

onto Activated Carbon of the Vapors of Water-Immiscible Organic

Liquids. Fundam. Adsorpt. Proc. Eng. Found. Conf. P335-44 (1984).

4. Grant, R. J.* Joyce, R. S„, and Urbanic, J. E.: The Effect of

Relative Humidity on the Adsorption of Water Immiscible Organic Vapors

on Activated Carbon, Fundam. Adsorpt. Proc. Eng. Found. Conf. P219-

227. (1984).

5. Smisek, M., and Cerny, S.: Active Carbon, Manufacture, Properties and

Applications, P104, Elsevier Publishing Co., Amsterdam (1970).

6. Sansone, E. B., and Jonas, L. A.: Prediction of Activated Carbon

Performance for Carcinogenic Vapors, Amer. Ind. Hyg. Assn. J. 42:688-

691 (1981)

.

7. Dubinin, M. M., and Rad us hke v i c h , L. V.: Equation of the

Characteristic Curve and Activated Charcoal, Doklady Akad. Nauk.

S.S.S.R. 55:327-9 (1947) .

'

8. Golovoy, A., and Bras law, J.: Adsorption of Automotive Paint Solvents

on Activated Carbon, J. Air Pollut. Control Assn. 31:861-5 (1981).

9. Manes, M. , and Greenbank, M.: Adsorption of Multicomponent Liquids

from Water onto Activated Carbon: Convenient Estimation of Methods;

Advances in Chemistry Series, No. 202, Treatment of Water by Granular

Activated Carbon, eds, M. J. McGuire and I. H. Suffet, Published by

the American Chemical Society, Washington, D.C.

10. Werner, M. D.: The Effects of Relative Humidity on the Vapor Phase

Adsorption of Trichloroethylene by Activated Charcoal, Am. Ind. Hyg.

Assoc. J. 46:585-90 (1985).

11. Micarelli, Gina M.: The Performance of Respirator Cartridges at High

Relative Humidities, Masters Essay, Graduate School of Public Health,

University of Pittsburgh (1986).

12. Perry, R. H., and Green, D.: Perry's Chemical Engineers' Handbook,

Sixth Ed., Section 16, Page 17, McGraw-Hill (1984).

13. Javorsky, M.: The Performance of a Prototype Respirator Cartridge at

High Relative Humidity, Masters Essay, Graduate School of Public

Health, University of Pittsburgh (1986).

14. Dubinin, M., Erashko, I. T. s Kadlec, 0., U 1 in , V. I., Voloshchuk, and

Zolotarev, P.: Kinetics of Physical Adsorption by Carbonaceous

Adsorbents of Biporous Structure, Carbon 13:193-200 (1975).

15. Dubinin, M.: New Experimental and Theoretical Investigations into

Kinetics of Physical Adsorption by Microporous Adsorbents, Pure Appl.

Chem. 48:407-14 (1976) .

52
16. Bering, B. P., and Serpinsky, V. V.: Thermodynamic Tests for the

Applicability of the Potential Theory of Adsorption, Dokl. Akad. nuak,

S.S.S.R. 153 :129 (1963) .

17. Bering, B. P., Serpinsky, V. V., and Surinova, S. I.: Joint

Adsorption of Binary Mixtures of Vapors and Activated Carbon, Izv.

Akad. nauk. S.S.S.R. 1965:769-76.

18. Swearengen, P. M., and Weaver, S. C.: The Effects of Organic Vapor

Mixtures on Respirator Service Life - II, Paper 324, The American

Industrial Hygiene Convention, Dallas, TX (1986).

19. Moyer, E. S.: Methyl Isocyanate Studies, Part 1: Air-Purifying

Respirator Cartridge Evaluations, Paper 325, The American Industrial

Hygiene Convention, Dallas, TX (1986).

20. Yoon, Y. H.: The Effect of Humidity on Respiratory Cartridge Service

Life, Paper 326, The American Industrial Hygiene Convention, Dallas,

TX (1986)

.

21. Wood, G.O.: Effects of Humidity on Air-Purifying Beds, Paper 328, The

American Industrial Hygiene Convention, Dallas, TX (1986).

22. King, W. P., Roberts, C. C., and McKee, E. S.: Effects of

Environmental Conditions on the Removal of Methyl Iodide by Air

Purifying Respirators, Paper 329, The American Industrial Hygiene

Convention, Dallas, TX (1986).

23. Ackley, M. W.: Chemical Cartridge Respirator Performance: 1,3

Butadrene, Paper 331, The American Industrial Hygiene Convention,

Dallas, TX (1986).

53
PRACTICAL TEST REQUIREMENTS FOR

GASEOUS CONTAMINANT REMOVAL EQUIPMENT

Richard D. Rivers, Vice President

Environmental Quality Sciences

P.O. Box 2147, Louisville, KY 40204

Intelligent design of gaseous contaminant removal equipment for general

ventilation systems is surely one of the more difficult aspects of building

technology. The designer is merely guessing if he does not have data for

the following factors for the space in question,,

Chemical and physical properties of gaseous contaminants

Contaminant concentrations or internal generation rates

Allowable contaminant concentrations within the protected space

Air flow requirements and level of mixing

In addition, the designer must know the following things about the

contaminant-removal equipment;

Removal efficiency at operating levels

Life or maintenance requirements at operating levels

Sensitivity to humidity, temperature and contaminants

Nature of effluent products, if any, created by the equipment

Energy Consumption

Capital and maintenance costs

The difficulty of the problem becomes apparent with the first two listed

factors. In most cases, the gaseous contaminants present are not entirely

identifiable, nor are their concentrations known, even as averages.

Information on the contaminant levels which can be tolerated is scarce, and

argued over by experts. Yet the designer must seek to control these

unknowns to innocuous levels, using manufacturers' data for the remaining

factors in the table. Much of this 'data' is in the form of 'excellentgood-fair-poor'. Where numerical information is available, it reports the

results of tests by the methods listed in Table 1.

The first listed test method, the complete isotherm, does allow approximate

calculation of field performance for a set of assumed contaminants and

operating conditions. The translation of the isotherm into filter

penetration and life is, however, a major undertaking in chemical

engineering, and far beyond the interest of HVAG system designers. Test

methods 2 through 5 provide only order-of-magnitude performance data, and

are essentially quality-control procedures. Test method 6 offers the best

hope for the HVAC system designer. It provides data on at least one

contaminant, with the major effects of mass transfer and sorbtion evaluated

54
at the operating conditions of the test. If these conditions are met by

the installed system, there is reason to believe it will deliver

performance equivalent to that obtained in the test. This discussion seeks

to determine parameters for a useful and practical gaseous-contaminant

penetrat ion-vs-load test.

1. Al lowab l e concentrations . The concentrations allowable for a given

contaminant can be dictated by considerations of safety, health, annoyance,

or material damage. Table 2 lists a few contaminants, with levels for

human safety (IDLH, the level immediately dangerous to life and health);

health (TWA8, 8-hour time-weighted averages acceptable for 40-hour work

weeks); and annoyance (OTH, odor threshold for 50% of the population). No

values are listed for material damage, since these depend on the materials

present. It is possible, however, for material damage to be the critical

factors. The values listed for IDLH and TWA8 are taken from OSHA and ACGIH

tables [10,11], with the exception of the values for sarin, a chemicalwarfare nerve agent. The contaminants were selected to illustrate the wide

range of values for any one allowable concentration index - and also that

no one index governs the allowable level. In most cases odor threshold is

the lowest level, and this determines the maximum concentration allowable

for the chosen contaminant. In the case of CO and C0£, which are odorless

(infinite OTH), odor has no influence, and TWA8 sets the allowable

concentration.

Much adsorption data are available for gas-mask canisters. Such canisters

reduce a relatively high concentration (often IDLH) outside the mask,

upstream of the filter, to an acceptable TWA8 level inside the mask,

downstream of the filter. In a general-ventilation situation, however, the

air from the conditioned space appears ups tream of the filter. The

concentration entering the filter will be at far lower levels than in the

gas-mask case. A test for genera 1 -vent i 1 at ion filters needs to reflect

this difference.

TABLE 1 . EXISTING TEST METHODS FOR GASEOUS CONTAMINANT ADSORBERS

Test Type*

1. Complete Isotherm S

2. One-Point Isotherm S

3 . Breakthrough D

4. Integrated Penetration D

5 . Odor Breakthrough D

6. Penetration-vs-Load D

* S = static equilibrium (no air flow)

D = dynamic (air flow through test bed) ** Volume of adsorbate in bed = function of (adsorbate concentration in gas)

Description/ Ex amp le

See ** below; [ 1

]

ASTM D3467 (CC14) [2]

Time to set penetration;

BuMines "23B' [3], MIL STDs.

[4], 15]

Penetration at set load;

ASTM D3803 [6]

Perceived Breakthrough [7]

Nelson [8], Ostajic [9]

55
TABLE 2. SELECTED GASEOUS AIR POLLUTANTS?

TOXICITY, ODOR AND BOILING POINT

Concentration

,

mg/ m3 BP

Compound IDLH TWA8 OTH deg C

Acrolein 13 0.25 0.35 52

Ammonia 350 35 33 -33

Carbon dioxide 90000 9000 00 -7 8

Carbon monoxide 1650 55 00 -192

Carbon disulfide 1500 60 0 .6 46

Carbon tetrachloride 1800 60 130 77

Forma Idehyde 124 4 1 .2 97

Hydrogen sulfide 420 30 0.007 -60

Ozone 20 2 CS O ft -112

Sarin (GB) 0.40? 0.000003? ? 158

IDLH = Immediately dangerous to life and health

TWA8 - 8-hour time weighted average, allowed for 40-hour work week

OTH = Odor threshold

BP - Boiling point at 760mmHg

2. Efficiency (or Penetration -^ ) and Sorber Life. These two filter parameters are inextricably related. The instantaneous value of sorber

penetration is dependent on many factors, including?

a. Whether the filter material is a physical adsorber, an adsorber,

chemisorber, or a catalyst.

b. The surface properties of the sorption material.

c. Sorber granule size and packing density.

d. The physical and chemical properties of the contaminant.

e. The temperature and humidity of the carrier gas.

f. Carrier gas bed velocity.

g. Bed depth.

h. Contaminant concentration.

i. The previous history of the sorption material, especially its

sorbed load of contaminant and water vapor.

j. Competition from other contaminants.

k. Generation of contaminants by the sorption device.

This large list of factors means that test conditions need to be fully

specified if the results are to be interpreted intelligently. Factors a through d are fixed in evaluating a given adsorber/adsorbate combination.

If we are only interested in one set of operating conditions, factors e through h can be at the values of that set; if we seek to determine the

effect of variations in the factors, testing will have to be done at

several values of each, unless the function relating each factor to

penetration and life is known.

(1) When efficiency is near 100%, as is often the case for fresh sorption

devices, it is better to use the term pene trat ion (= 100 - efficiency, in

percent), the measure of what passes the filter, rather than what is

caught

.

56
A common view of adsorbtion devices is that they have 0% penetration until

a sudden 'breakthrough' to 100% penetration. This is not true. Actual

performance is as in Figure 1, which shows penetration for a physical

adsorber or chemisorber as a function of the amount of captured adsorbate,

for two different inlet concentrations. When the adsorbent bed is new,

penetration is low, but not zero; it rises slowly as adsorption sites are

filled, then very rapidly when almost all sites are filled. The absolute

level of downstream concentration will be lower when the inlet

concentration is low, but the percent penetration will generally be higher

at low inlet concentrations. Note that the two load scales are different,

and that breakthrough occurs at a lower adsorbate load for the low inlet

concentrations than for high inlet concentrations. Replenished adsorbers,

such as spray towers, maintain a steady penetration level, and true

catalysts show a slowly increasing penetration as they become 'poisoned'.

Both of these, however, have some penetration, and its value is a function

of the inlet contaminant concentration among other things.

Total load for 1000 mg/m3 inlet concentration

(arbitrary units)

0 500 1000 1500 2000

Total load for 0.01 mg/m3 inlet concentration

(Same units as upper scale)

Figure 1. Pene trat ion-vs-Load for Typical Adsorber

Evaluating every adsorber for ranges of all the listed factors is

impractical. It is important to narrow down the number and ranges of

parameters as much as possible. To do this, a simplified mass-balance

model of the contaminant-control system (Figure 2) will be helpful. The

model has an internal contaminant source (G), make-up air (ventilation air,

V) from outdoors, recirculation ( R) , and a filter with penetration P. We

neglect infiltration and exfiltration, and removal mechanisms like

adsorption on which we would like to reduce to zero; it is scarcely proper

to take advantage of them in designing a system.

57
Rc i (P)+G = (V+R)c

i

whence = G/(V+R(1-P))

( 1 )

( 2 )

Figure 2. Mass-Balance Filtration Model

Table 3 lists some factors which allow us to estimate the concentrations

met in typical protected spaces, hence which might make reasonable test

concentrations

.

TABLE 3. INLET CONCENTRATION CALCULATIONS

Indoor Contaminant Generation Factors

Space Type; Arena Office Units Reference

Population: 1 .5 0 .2 occupants/m2 [12]

Area: 7500 100 m2 [12]

Smoking

:

2.0 0.7 c igarettes/hr/ occ [14]

Ventilation: 8.5 25.5 m3/hr/ occ [12]

Human Emissions

Hydrogen sulfide: 0.02 0 .015 mg/ hr/ occ [13]

Ammonia

:

35 20 mg/ hr/ occ [13 ]

Smoking.

Volatile organics: 15 15 mg/c igare tte [14]

These factors applied to the mass-balance model give concentrations which

are listed in Table 4. The minimum steady-state concentration exists when

the filter has zero penetration, the maximum when it has 100% penetration.

There are some striking things about the results. The steady-state

concentrations due to internal sources are below or near the odor

thresholds; they are far below the levels at which the usual tests are run. This may explain a lot of testimonials from users to the effectiveness of

odor-control devices when they in fact have near-zero performance. The

systems simply have enough infiltration or make-up air to push the average

contaminant concentrations below odor thresholds. With the space, there

may be smoking or other local odor sources which are easily detectable; yet

the return air from the zero-efficiency filter system will smell 'fresh' - hence the filter is perceived to be doing a fine job. From the standpoint

of toxicity or material damage, of course, a zero-efficiency devices does

nothing

.
TABLE 4. INLET CONCENTRATION CALCULATIONS

Contaminant Concentrations and Loads

Calculated from Factors in Table 3a Using Eq. 2

Space Type: Arena Office Units

Total Ventilation: 95600 510 m3/hr

Recirculation: 1816400 2040 m3 /hr

% Recirculation: 95 90 %

Human Emissions

Hydrogen sulfide: 225 0.3 mg/hr

Min, ma cone: 10"4 , 0.002 10"4 , 0.0006 mg/m3

Odor threshold: 0.007 0.007 mg/ m3

Ammonia: 3 94000 400 mg /hr

Min, max cone: 0 .2 ,4.12 0.16,0.78 mg/m

3

Odor threshold: 35 35 mg/m3

Smoking Emissions

Volatile organics: 169000 300 mg /hr

Min, max cone: 0.09,1 .77 0.12,0.59 mg/m3

Odor threshold: ? ? mg/m3

This type of calculation shows that a useful test procedure for gaseous

contaminant control devices must somehow evaluate the devices at odorthreshold levels. This is not easy. Both feeding and detection at low

levels are difficult, and loading a filter at low concentration is timeconsuming. The time involved with available sorption materials may not be

as long as one would expect from equilibrium capacity (activity) data,

however. Nelson et al [8] ran data on the adsorption capacity of gas-mask

carbon canisters fro several solvent vapors in the range 100-1000 ppm.

They found that filter life (time to 10% penetration) was related to

concentration by eq. 3:

t = k C

b (3)

where t is breakthrough time, C concentration, and k and b constants. For

one tested compound, hexane, b was -1, which one would expect if there were

no concentration effect. In general, however, b was about -0.67. If this

value is generally true, then the life of a carbon adsorber at 1 ppm inlet

concentration would be about 102 times the life measured at 1000 ppm.

Measured breakthrough times at 1000 ppms were typically 2 hours, hence one

would expect lives of 200 hours at 1 ppm. This seems to agree with other

reported low-concentration data; Hanna and Kuehner [15], for example, show

lives of 150 hours for activated carbon and Purafil (activated alumina

impregnated with potassium permanganate) on acrolein at 0.25 and 0.5 ppm

respectively, with stay-times of 0.075 s. Jonas and Svirbely [16] showed a life at 10% penetration of 1 7 .5 • minutes, using 14.4 ppm of carbon

tetrachloride, 0.5 s stay-time, and Pittsburgh BPL carbon. While lowconcentration testing may be tedious for adsorbate-sorber combinations

which work well, in many cases the test will be completed very quickly.

Ostajic [9] reports on attempts to speed up testing by loading at high

concentration and switching occasionally to a low concentration for

59
penetration tests. This is not feasible in general, for molecules that

would eventually migrate to secure capture sites if they were deposited

slowly may be very poorly retained if deposited rapidly. When the feed at

high concentration was switched to low concentration, the loosely bound

adsorbate molecules eluted out of the bed, actually at higher concentration

than the then existing feed. Ostajic suggested that automated test

equipment would make low-concentration test possible over periods of

several hundred hours. This seems reasonable, since we are not seeking

quality-control data, but data to characterize a specific sorber

formulation for design purposes.

Life data is obtained simultaneously with penetration data. It is,

however, necessary to define some breakthrough penetration which defines

the ‘''life' of the sorber, if that is to be published. Nelson's 10% of

upstream concentration is probably satisfactory for general ventilation

purposes, since upstream concentration has already been set at an

acceptable level for the space. It is unlikely that a sorber with greater

than 10% penetration will be economically competitive with simple,

ventilation. It is a reasonable assumption that the make-up air will

contain significant amounts of the EPA ''Criteria Pollutants' - sulfur

dioxide, carbon monoxide, nitrogen dioxide, ozone, and nonmethane

hydrocarbons. In addition, methane is present at about the 1 mg/m3 level,

and water vapor. Designers need to know the influence of these

contaminants on the penetration and life of the sorbtion devices they

evaluate. They should therefore be present in the air flow used to test

sorbers. If the concentration of test contaminants is multiplied by some

factor to speed up the test, then these criteria pollutants should be

present in their usual concentration multiplied by that factor. We might

take the usual concentrations to be the EPA primary air-quality standards

[17], as listed in Table 5, exerpted here.

TABLE 5. EPA PRIMARY STANDARD FOR CRITERIA AIR POLLUTANTS

Pollutant Primary Standard, mg/m3

Sulfur Dioxide 0.08

Nitrogen Dioxide 0 .10

Ozone 0.24

Carbon Monoxide 10.0

Nonmethane Hydrocarbons 0.16

Since filters will generally be located in the recirculation loop, design

humidity conditions will generally be the indoor design condition, perhaps

50% RH at 23C (73F). Chemisorbers cannot operate at bone-dry conditions,

while physical adsorbers suffer from high humidities. If the loading is

carried out at actual allowable concentration levels, there is no problem;

use 50% RH at 23C. If the contaminant concentrations are multiplied by a factor as large as 2, however, the most prevalent contaminant of all, water

vapor, will be at saturation. There seems to be little choice but to run

the test at the 50% RH, 23C condition. The air entering the test rig

should be converted to 'zero air' by filtering through particulate filters

followed by deep beds of sorption media able to remove acid gases as well

as ambient organics and ozone to well below test conditions. Controlled

amounts of test contaminants, including water vapor, would then be added to

the test air flow.

60
3. Nature of Effluents . The test procedure must verify that any reaction

products from the filter are innocuous (including being below odor

thresholds). This is rarely a problem with physical adsorbers, unless some

catalytic effects are present. However, physical adsorbers may give up

adsorbate when unpolluted air passes through the bed; hence a period of

elution using unpolluted air at test temperature and humidity must be a part of the test.

4. Air Flow. This will normally be determined by factors not related to

contaminant filtration, such as thermal control and satisfactory air

distribution. Obviously, test conditions should match manufacturer design

flow range for the device or material tested. The test canister described

in ASTM D3803 (Figure 3) is of practical size for small-scale tests of

granular adsorbers, chemisorbers and catalysts. This canister, which is

intended for a face velocity of about 0.2 m/ s (40 ft/min), is small enough

to allow convenient control of all test conditions, yet large enough to

average out filter media variations and avoid significant edge effects.

Scrubbers and other devices may require larger test prototypes, but test

costs encourage use of the smallest representative test prototypes.

Energy Consumption . For granular beds, energy consumption is a matter

of bed pressure drop. In a practical filter device this is not the drop

through the granular bed alone, but includes the drop through the retaining

screens, and the inlet and outlet passages to the beds. Pressure drop must

be measured on full-size, typical unit configurations, and be presented as

a function of gas flow or face velocity. Wet scrubbers require energy for

pumping spray water, and there may be other energy inputs.

61
6. Capital and Operating Costs. These must be fully identified so that

system designers can do meaningful life-cycle costing. This means that

reasonable estimates must be made of things like waste of media and manhours for reloading cells. If maintenance costs are based on reactivation

of the sorber material, then performance data must be given on reactivated

material

.

7. Design of Test Facility . The design of the test facility is not

simple. ASTM D3803 gives a schematic (see Figure 4) for a system intended

to test activated carbon at both room humidity conditions and near

saturation. This may be a little ornate for testing adsorbers for general

ventilation, and indeed, many of the problems identified in ASTM D3803

originate in its 95% RH test. Nevertheless, the schematic shows the

essential piping, thermal controls, contaminant feed systems, and

measurement of flow, temperature and pressure. Any facility proposed for

industry-wide use should be adaptable to a wide range of contaminants,

including those that condense out at room temperature. There is a large

body of literature on generating and detecting specific contaminants.

Figure 4. ASTM D3803 Gaseous Contaminant Test System Schematic

8. Su ggested Contaminant Lis t. A standard test for general-ventilation

service might include contaminants from major chemical groups, (Table 6).

Feeding and detecting such a list simultaneously would pose severe

problems, and would not simulate any real situation. The contaminants

would therefore be fed in separate tests, along with the criteria air

contaminants at the concentrations listed in Table 5. .."Nonmethane

hydrocarbons" could be simulated by 2 ,2 ,4-Tr ime thy 1 pen t ane , and methane

itself would be added at 1 mg/m3. Where a test is run to evaluate

penetration and life on sulfur dioxide, ozone, or 2 ,2 ,4-Trimethy Ipentane

,

these would be left out of the 'background' feed. Even this pattern would

require up to seven simultaneous feeds of contaminant gases, though some

would be at rather low levels. It might be possible to determine which of

these have little or no influence on the aging of different categories of

62
sorbers, and to eliminate them from the required feed if they have no

effect. The sorber performance on these contaminants would have to be

measured and reported if this alternate feed was chosen.

TABLE 6. SUGGESTED TEST CONTAMINANTS

Suggested BP

Contaminant Group mg/m3 MW °C

Sulfur dioxide Acid Gas 1 .2 64 -10

Formaldehyde Aldehyde 1 .2 30 97

Methanol Alcohol 260 32 65

2 ,2 ,4-Trimethylpentane* Alkane 1450 114 98

2-Butanone (MEK) Ketone 30 72 80

Ozone Oxidant 0.2 48 -112

1 ,1 ,1 Trichloroethane Halocarbon 1 .1 133 75

* = iso-octane

where special capabilities exist in the sorber device, such as the ability

to remove carbon monoxide, that contaminant would be added to the list.

Some saving of test time is perhaps possible by simultaneous measurement of

penetrations at several bed depths. A sampling valve could be switched

from one sequential bed sampling point to the next, using the same

detector. Both experimental and theoretical work is needed to validate a test procedure and provide ways in which designers can estimate performance

at conditions different from the standard test, and on other contaminants.

REFERENCES

[1] Many texts, for example Chemisorption . D. 0. Hayward and B. M. W.

Trapnell, Butterworths , Washington, 1964.

[2] ASTM D3467, Carbon Tetrachloride Activity of Activated Carbon, Annua 1 Book of ASTM Standards . Part 30. ASTM, Philadelphia, PA 19103.

[3] Department of Interior, Bureau of Mines: Respiratory Protective

Devices: Tests for Permissibility. 30 CFR 11, subparts I and L.

[4] MI1-C-13724: Charcoal, Activated, Impregnated, ASC. Naval

Publications and Forms Center, Philadelphia, PA 19120.

[5] MIL-STD-282: Filter Units, Protective Clothing, Gas-Mask Components

and Related Products: Performance Test Methods (1956) (address: see

Ref. 6) .

[6] ASTM D3803, Radioiodine Testing of Nuclear-Grade Gas-Phase Adsorbents,

Annua l Book of ASTM Standards . Part 30. ASTM, Philadelphia, PA

19103.

[7] ASTM E544, Referencing Suprathresho Id Odor Intensity. Annual Book of

ASTM Standards . Part . ASTM, Philadelphia, PA 19103.

63
[8] G. 0. Nelson and A. N. Correia, Respirator cartridge efficiency

studies; VIII, Summary and Conclusions. Am. Indus. Hyg. Assn. J.

37 :514-525 (1976).

[9l N. Ostajic, Test method for gaseous contaminant removal devices.

ASHRAE Transactions, 1985, Vol. 91, Pt. 2.

[10] Code of Federal Regulations Title 29 (Labor) 1900.1000ff (annual).

[11] Threshold Limit Values for Chemical Substances in the Work

Environment. ACGIH, Cincinnati, OH 45211 (annual).

[12] ASHRAE Standard 62-1981, Ventilation for Acceptable Indoor Air

Quality. ASHRAE, Atlanta, GA 30329 (1981).

[13] Bioastronautics Data Book (p. Webb ,ed) NASA SP-3006 (1964) (NTIS).

[14] D. M. Burns, Involuntary Smoking. In Smoking and Health: A Report of

the Surgeon General PHEW PHS 79-50066 (1979).

[15] G. F. Hanna and R. L. Kuehner, Critical factors in odorant measurement

and control. ASHRAE Symposium "Odors and Odorants; The Engineering

View’8 , ASHRAE, Atlanta, GA 30329 (1969).

[16] L. A. Jones and W. J. Svirbely, The kinetics of adsorption of carbon

tetrachloride and chloroform from air mixtures by activated carbon.

[17] ASHRAE Handbook - 1985 Fundamentals, Ch. 11.6., ASHRAE, Atlanta, GA

30329.

64
COMPARATIVE PERFORMANCE FOR GAS REMOVAL

Cyrus M. Bosworth

Cyrus M. Bosworth and Assoc

.

Waldoboro, Maine

INTRODUCTION

The ASHRAE Technical Committee 2.3 (and 5.4) have been looking for a standardized test procedure for more than 25 years. ASHRAE has

standardized procedures for particulate removal filters but not for gas

removal. So, the suppliers of gas removal equipment have developed their

own procedures (using procedures published by Dr. Amos Turk and others). I would like to relate some of these which I used when I was a "supplier" and

experiences when I was a "user" of gas removal equipment.

BASES FOR COMPARISON:

There are three important parameters to be evaluated:

1. How much is left in the air,

2. How long will it last and do its job, and

3. How much power is required?

Other parameters can be important, such as the thickness required, crosssectional area, maximum velocity, and especially the price.

^ THEORETICAL EVALUATIONS:

The designer of the gas removal equipment may need to evaluate the

theoretical surface required. He may calculate the mass transfer

coefficient needed, if he knows (a) what the gas is, (b) the concentration

of the gas in the air, and (c) how much it must be reduced; see equation 1.

N

1 = k

g

At (P 1 " v (1)

where: Nj = Quantity removed

kg = Mass transfer coefficient

At = Transfer area

Pj = Partial pressure of gas in air

P e - Partial pressure of gas on adsorbent

The designer would like to know the porosity of dry adsorbent, what packing

density, in order to have low power loss. Any of a number of equations can

be used to correlate pressure drop with velocity and the momentum loss

through the specific media. This is also true for the developer of liquid

adsorption systems, in pressure loss through the media and prevention of

liquid carry-over.

The ratio of the quantity of gas removed divided by the power required to

move the air through the media, has been used to evaluate both the dry

adsorbent systems and the wet air scrubber systems, and to make

comparisons. I developed a ratio I called the MERIT FACTOR and presented

it as part of a paper over 20 years ago. We used it to compare gas removal

65
equipment, but I never heard of anybody else using this "B”1 number (see

equation 2).

( 2 )

Merit factor

Mass transfer coefficient

Surface area (transfer)

Pressure drop

Air flow rate

PRACTICAL EVALUATIONS:

Figure 1 shows a typical air conditioning equipment sequence. The return

air is drawn into the system along with the outside air and mixed in the

mixing section. The outside air may be prefiltered and pre-heated, and is

controlled by the dampers at the inlet. The filter section usually

contains only a roughing filter to protect the coils from dirt. Shown here

is a better grade particulate filter to protect the gas removal filter.

Next is the coil section with cooling coil first and the.re-heat coil

second. Finally the fan in the fan section pulls the air through the

equipment and fills the ducts to distribute the conditioned air to the

space. The cooling coil on humid summer days removes water vapor from the

air and at the same time removes many gaseous contaminants. However, on

the off cycle, the coil warms, evaporates the water and puts the gaseous

pollutants back into the air, sometimes causing complaints from the

occupants

.

kgAt

where

:

Pf'

S

tPf

Figure 1

66
TESTS TO COMPARE GAS REMOVAL EQUIPMENT:

A. Figure 2 shows a "once through" test. There are no end of variations,

but the essentials are a source of fairly clean air, a means to add a pollutant gas, obtaining a sample upstream that is well-mixed, a test

section for the gas removal device in which pressure drop can be measured

and a well-mixed downstream sample can be taken, and finally the fan or

other means for moving the air. Reference 4 present one procedure.

0/JC£-Th RU

The results could be reported as concentration vs time, but we usually

measure pollutant removal per pass and pressure drop at several velocities,

some higher and lower than whose we expect to use the device. We usually

express the removal as efficiency per pass, or Eff. = 1 00 ( Cu-Cd) / Cu

.

We used this procedure in situ in the chemical plant for evaluating and

comparing air scrubbers in the exhausts, (Figure 3) also a variation of the

test when we evaluated air washers used to air condition textile plants for

removing formaldehyde in the air. Figure 4 shows a high velocity air

washer which has sprays of chilled water that removes particulates as well

as pollutant gases.

CLEGTROLYT1CALLY REGENERABLE SCRUBBER

67
Figure 4

B. Figure 5 shows a "re-cycle loop" test. With the air flowing through

the fan and back through the gas remover, a pollutant is injected, and

immediately the pollutant concentration is measured, (without removing a large sample) at very frequent intervals. The results can be plotted as a decay curve (Figure 6), efficiency may be calculated from equation 3.

Re- Cycle

Figure 6

68
c = C e

~( Qi+nQr) T/ V + EiSilS [i-e -(Qi+nQrT/V)

j (3)

0 Qe+nQr

C i Qi +G

C = Qe+nQr

C = Concentration

Q

= Air flow

n = Efficiency

T = Time

V = Volume of Space

G = Rate of generation

Reference 5 gives the procedure.

Pressure drop could also be meas

downstream of the filter.

Cu“Cd

n = —

Cu

0 = At zero time

1 = Infiltration

r - Recirculation

e = Exfiltration

u = Upstream

d = downstream

red by putting taps upstream and

C. The most practical test is an actual use test. We could use the "oncethrough" test on the scrubbers because the gas concentrations were high and

easy to measure, but it could not be used in the parts per billion range.

Neither could we use the completely closed recycle test, due to instrument

inaccuracy

.

The chemical plant produced cellulose products by the Viscose Process.

Some of the by-products of the process are sulfide gases. The gas

collecting hoods over the tanks of the process are designed to collect the

gases and exhaust them through scrubbers. I mention this because the order

of magnitude of the concentration is so important: The range of

concentration:

(a) The concentration range in the exhaust ducts going to the scrubbers is

in the order of 60 to 200 ppm.

(b) The concentration leaving the scrubber might be 2 to 10 ppm. (The gas

removal efficiency is 95% to 98%.

)

(c) Concentration in the plant might be 0 to 10 ppm, because few exhaust

hoods collect 100%. The OSHA 8-hour is 20 ppm.

(d) The instrument rooms are located within the plant (see Figure 7). we

hold the concentration of sulfides below 0.5 ppm in about 12 areas to

prevent corrosion of the sensitive instruments in these rooms (see

Figure 8).

(e) Finally, there have been occasions when there was an upset in the

process building, and the wind was in the right direction, and the

sulfides were carried to the inlet of the air conditioners of the

office building. Even though the concentration might only be in the

range of 10 to 20 parts per billion, we had the "sick building

syndrome" and I receive the complaints.

69
Figure 7

lrtSTRUMEA/T Ko©M

Figure 8

AN ACTUAL USE TEST:

Figure 7 shows a diagram of the equipment designed to maintain the

temperature and the air quality in one instrument room, and also designed

to compare gas removal filters. Outside air is brought in through a packed

bed of carbon. The dampers are set after balancing the system. The

outside air is mixed with some return air, and both flow through a good

particulate filter and the cooling coil. (Actually thee is no heating coil

here because this is a room within the heated plant, but there is a preheat coil after the carbon in the outside air duct.) The fan forces the

air through the past filter, which is a replaceable bed of adsorbent.

Note that the bed is the last piece of equipment in line, in order to

prevent infiltration of pollutant.

The room is slightly pressurized and the excess air flows out near the

bottom through weighted dampers. When the door is opened, the dampers

close, and the excess air flows out through the open door.

70
The post filter was loaded first with alumina that had been impregnated

with potassium permanganate (PURAFIL) and then after three months the

PURAFIL was replaced with carbon that had been impregnated with caustic.

The carbon was replaced with PURAFIL after another three months, and both

tests were repeated.

The low concentration of the sulfides (which is required in the instrument

rooms to prevent corrosion) is difficult to measure. For these tests a lead acetate tape instrument was used. Time for recording the integrated

sample was two hours, or exactly twelve continuous samples per 24 hours.

When three months of tests are plotted, the results looked something like

Figure 8. The considerable scatter of the concentration was probably

caused changed in concentration outside the room and the number of times

the door was opened. While the temperature in the room was held at 21 + or

-2 degrees C, the humidity was not held constant and may have modified the

effectiveness of the adsorbents.

Both the impregnated carbon and the impregnated alumina prevented the

sulfide concentration from exceeding 1/2 ppm in the period of three months

before changing. We learned from this test that either material can be

used when operating at this temperature, these humidities, and at these

very variable concentrations of many pollutant gases. However, the scatter

in the results was too great to prove one product superior.

CONCLUSIONS:

1. Gases and vapors can be removed from air effectively with

a. Many types of solid adsorbents with specific impregnants, and

b. Many types of liquid surfaces, with specific adsorbents and

liquids .

2. The gas removal system must be designed to remove more of the specific

pollutant gas than the other gases in the air.

3. The gas removal system must be evaluated at conditions similar to

those expected in the application of the equipment; i.e., at the same

temperature and humidity, and at the expected concentration of the

pollutant and of the other components in the air.

71
REFERENCES?

1. Trebal, Robert E. 1985, Mass Transfer Operations, McGraw Hill Book

Co., New York, NY.

2. ASHRAE Handbook, Chapter 2, Fundamentals 1985, American Society of

Heating, Refrigerating and Air Conditioning Engineers, Atlanta, GA

„

3. Bosworth, C„ M. and Barduhn, A. J., Recent Advances in Odor Control by

Air Washing, Annals of the New York Academy of Sciences, Vol® 116, Art

2, p. 638.

4. Csermely, T. J. and Bosworth, C.M., New Techniques for Evaluating Odor

Control Methods, ASHRAE Transactions, Vol. 70, 1964, p. 354.

72
COMPARISON OF CHROMOTROPIC ACID, PARAROSANILINE

,

AND GRAVIMETRIC FORMALDEHYDE DETERMINATIONS

Samuel Silberstein, Biologist

Indoor Air Quality and Ventilation Group

Building Environment Division

Center for Building Technology

National Bureau of Standards

Abstract

An automated formaldehyde emission rate monitor was developed at the

National Bureau of Standards to measure emission rates of pressed wood

products. A concentration monitor measured the airborne formaldehyde

concentration by means of the pararosaniline method, within a medium-size

dynamic measuring chamber containing a single pressed wood board. A gas

chromatograph-electron capture detector measured the air exchange rate by

means of the sulfur hexafluoride tracer decay method. To calibrate the

formaldehyde concentration monitor, "span gas" containing a fixed

formaldehyde concentration was generated by heating polyoxymethylene

permeation tubes. The concentration was determined from the rate of mass

loss of the tubes. Concentrations determined by the pararosaniline and

gravimetric methods were compared to concentrations determined by the

chromotropic acid method because the chromotropic acid method is widely used

by the pressed wood industry to measure formaldehyde emission rates of their

products

.

It was found that formaldehyde concentrations of span gas agreed with those

determined by the chromotropic acid method, validating the calibration

method. Formaldehyde concentrations due to emissions from three lots of

particleboard underlayment from two different manufacturers, determined by

the chromotropic acid method agreed with those determined by the

pararosaniline method.

Key words: Formaldehyde; indoor air quality; pressed-wood products;

pararosaniline; permeation tubes; chromotropic acid.

1. Introduction

The pararosaniline and chromotropic acid methods, among other techniques,

are widely used to measure airborne formaldehyde concentrations. For

example, the pressed wood industry commonly uses the chromotropic acid

method for testing the formaldehyde emissions of its products [1]

.

Formaldehyde emission rates are measured by placing pressed wood products

into measuring chambers whose air exchange rates can be adjusted to obtain

varying airborne formaldehyde concentrations. Emission rates can then be

calculated from concentration and air exchange rate. Oak Ridge National

Laboratory, Lawrence Berkeley Laboratory, and the National Bureau of

Standards (NBS) , on the other hand, commonly use the pararosaniline method

[2-4] in surveys of formaldehyde concentrations and tests of emission rates

of pressed wood products. The main advantage of the pararosaniline over the

chromotropic acid method is that it can be automated. It would be difficult

to automate the chromotropic acid method because of its requirement for

concentrated sulfuric acid as a reagent, and for boiling water baths [5]

.

73
As part of a project for the Consumer Product Safety Commission described

previously [2], NBS designed an automated pararosaniline-based system to

measure formaldehyde emissions from pressed wood products. The measurements

are done in medium-sized dynamic measuring chambers located in a temperature- and RB-controlled environmental chamber. The measuring

chambers are teflon-lined to minimize formaldehyde absorption, and can

accomodate intact 1.2-m x 2.4-m (4-ft. x 8-ft.) boards as used in

buildings

.

NBS compared formaldehyde concentrations resulting from particleboard

underlayment determined by the pararosaniline and chromotropic acid methods.

Preliminary results indicate that the two methods yielded similar

concentrations for the emissions of four different specimens of

particleboard. The boards were from three different lots from two different

manufacturers. The two methods were also shown to agree with each other on

"pure" formaldehyde, by tests on standard formaldehyde atmospheres formed by

emissions from polyoxymethylene permeation tubes. The concentrations of the

standard atmospheres were determined by measuring the rate of mass loss of

the permeation tubes.

2 . Methods

2. a. Automated Pararosaniline and Gravimetric Analyses

A HCHO surface emission-rate measurement system was constructed by linking

an airborne HCHO concentration monitor (a TGM-555 air monitor fitted with

with a HCHO analytical module) to a microcomputer-based automated tracer-gas

decay system used to measure air exchange rate, as described elsewhere [2]

.

The HCHO concentration monitor measures HCHO concentration by a modified

pararosaniline method [4, 6-8] . The concentrations determined by the

pararosaniline method are denoted "pa-concentrations."

Pa-concentrations were measured automatically using the HCHO concentration

monitor as follows. An air sample stream was continuously pumped into the

monitor at a fixed air flow rate between about 0.5 and 1.0 L/min and

scrubbed with 0.02% pararosaniline solution in 100 mN HC1. Sodium sulfite

solution was then added, resulting in a pararosaniline concentration of

0.013% in 67 mN HC1, and a Na2S03 concentration of 0.17 g/1 (1.3 mM) . The

mixture reacted for about eight to ten minutes as it was pumped through a coil to a photometer, where its absorbance at a wave length of 570 run relative to a pararosaniline-HCl blank was measured.

In order to calibrate the HCHO concentration monitor, HCHO-free "zero air"

and "span gas" containing a known concentration of HCHO were used [2]

.

Zero

air was prepared by filtering room air through a Mine Safety Appliances

chemical cartridge against formaldehyde vapor. Span gas was prepared by

heating a permeation tube containing polyoxymethylene, a HCHO polymer, at

80°C in the oven of a gas standards generator and passing a' HCHO-free

airstream over it. Polyoxymethylene decomposes into HCHO when heated. The

polymer is sealed in teflon, which is slightly permeable to HCHO [9]. The

span gas concentration was calculated by the following equation:

C

s - <VmwHCHO>

' e/F (1)

74
where

C

s = span gas HCHO concentration, ppb

MWrcho = molecular weight of HCHO, 30.03

V = volume occupied by 1 kg-mole of HCHO at 25°C, 24.45 nr

e = emission rate of HCHO from permeation tube, ng/min

F = air flow rate through gas standards generator, L/min

Formaldehyde concentrations resulting from permeation tubes are denoted "grconcentrations .

Two automated monitors located in two different environmental chambers were

used. In both environmental chambers, the temperature was kept at 23°C and

the RH at 50%. In the first system, the air flow rate, F, was determined by

both a wet test meter and a gas flow meter to be 2.37 L/s. Two permeation

tubes were used to obtain a high enough formaldehyde concentration. The

tubes were weighed approximately monthly for over one year to determine the

formaldehyde permeation rate. The rate of mass loss is shown in figure 1.

The emission rate was 201 ng/min with r^ = 0.997 and a relative error of 2%,

corresponding to a span gas concentration of 69 ppb. The relative error of

the concentration is the difference between the relative error of the

emission rate and the relative error of the flow rate. Because the relative

error of the flow rate was observe to be at most as great as that of the

emission rate, the maximum relative error of the concentration is

approximately twice that of the emission rate.

In the second system, F was determined by a gas flow meter to be 2.43 L/s.

The permeation tubes were weighed approximately monthly for over one year.

The rate of mass loss is shown in figure 2. The formaldehyde emission rate

was 285 ng/min with r

z = 0.998 with a relative error of 1.1%, corresponding

to a span gas concentration of 95 ppb.

2. b. Chromotropic acid analysis

The chromotropic acid analysis was performed as follows. For one hour or

more, air was drawn through teflon tubing into a midget impinger or two in

series ("double impinger test") containing 20 ml of 1% Na

2 HSO^, a canister

containing desiccant, and a flowmeter, which was carefully calibrated with a bubble meter, and a pump at 1 L/min. The solution was then analyzed by the

chromotropic acid method, using formalin standardized by titration as a calibration standard [5]

.

All sampling was done in duplicate, and two

analyses were done for each sample. Formaldehyde concentrations determined

by the chromotropic acid method are denoted "ca-concentrations .

2. c. Medium-size dynamic measuring chambers

The medium-size dynamic measuring chambers for determining HCHO surface

emission rates of individual pressed-wood products are shown schematically

in figure 3. The interior dimensions are 1.2 mx2.4mx0.6m(4ft. x 8

ft. x 2 ft.), for a volume of 1.8 nr (64 ft. ) . All inner exposed surfaces

were lined with teflon sheets to minimize HCHO adsorption. Two small DC

fans with a rated capacity of 7 L/s (15 ft. /min) were installed at both

75
weight.

q

ng

weight,

Permeation Tubes 6473 and 6482

igure 1 . Mass loss calibration for permeation tubes used for calibrating

HCHO monitor #1.

Permeation Tubes 6893 and 6897

Figure 2. Mass loss calibration for permeation tubes used for making

calibrating HCHO monitor #2,

76
ends of the chambers to supply and exhaust the air. Three valves in the

system controlled the amount of air brought in, exhausted, and recirculated.

The fans were run at constant speed and the air exchange rate was controlled

by the three valves in order to maintain a constant air velocity over the

sample. The outlet valve was usually adjusted to slightly pressurize the

chamber, thus assuring that air entered only through the inlet. Further

details of the dynamic measuring chambers are given elsewhere [2]

.

Figure 3. Schematic of medium-size chamber for measuring HCHO emission

rates

.

Air exchange rates were measured using a tracer-gas decay method [2, 10]

.

Sulfur hexafluoride was injected into the inlet of the chamber and sampled

at the outlet. The HCHO concentration was also sampled at the outlet. Good

air mixing within the chambers was demonstrated through smoke visualization

of the air-flow patterns within the chamber. After releasing smoke into the

chamber inlet, the smoke density quickly became uniform in the chamber and

there were no dead spots.

It was reported elsewhere [11] that only background levels of formaldehyde

could be detected in empty measuring chambers . It was further reported that

when formaldehyde from permeation tubes was injected into an empty measuring

chamber, the pa-concentration agreed with the concentration predicted from

the emission rate of the permeation tube and the air exchange rate.

2. d. Pressed wood products

Four different particleboard underlayment specimens were measured in mediumsize chambers located in the two different environmental chambers. The four

boards are listed in table 1. Boards B2, B3, and B8, all from one

77
manufacturer, were measured in the first system, and board Gil, from another

manufacturer, was measured in the second system. Board B2 was from one lot;

boards B3 and B8 from another. Boards B3 and B8 were each measured at two

different air exchange rates in order to obtain additional formaldehyde

concentrations.

2. e. Linear regression analysis

Ca-concentrations were compared to pa-concentrations by a best fit linear

regression line of the form ca-concentration = slope * pa-concentration.

Similarly, ca-concentrations were compared to gr-concentrations by a best

fit linear regression line of the form ca-concentration = slope ' grconcentration.

3. Results

Comparisons between several mean ca-concentrations and mean paconcentrations of particleboard underlayment, and between ca-concentrations

and gr-concentrations of two different span gases are shown in table 1 and

figures 4-5. The formaldehyde concentrations covered a pa-concentration

range of 50-400 ppb, and a gr-concentration range of 70-100 ppb. The

deviation of each of the two ca-concentrations from their mean was less than

121 for concentrations less than 100 ppb, and less than 5% for

concentrations greater than 100 ppb. The standard deviation of paconcentrations ranged between 8-21%, with no evident dependence on concentration. As discussed in the methods section above, the relative

errors in the gr-concentrations were estimated to be under 5%. Double

impinger tests were discontinued when no formaldehyde was found in the

second impinger.

Figure 4 shows the line of identity between ca- and pa-concentrations, and

the best-fit linear regression line of the form ca-concentration = slope

pa-concentration. Table 1 shows that the regression line has a slope of

0.91, with an error of 0.02 and r^ = 0.99. Table 1 also shows ratios of cato pa-concentration. These are all between 0.89 and 1.14. Every caconcentration except one is within 1 pa-concentration standard deviation

unit of the pa-concentration. The remaining ca-concentration, 53 ppb, is

within 2 standard deviation units of the pa-concentration, 46 ppb. The

conclusion is that ca- and pa-concentrations of the pressed-wood products

tested are nearly indistinguishable from each other.

Figure 5 shows the line of identity between ca- and gr-concentrations. The

best-fit linear regression line of the form ca-concentration = slope ‘ grconcentration is not shown in the figure because it nearly coincides with

the line of identity. Table 1 shows that the regression line has a slope of

0.99, with an error of 0.07 and r^ = 0.82. This means that the ca- and grconcentrations are nearly identical to each other.

78
Table 1

Comparison between formaldehyde concentrations determined by chromotropic

acid with concentrations determined by pararosaniline or gravimetrically

board date CA dif dif/CA* PA SD SD/PA CA/PA

B3 5/1/86 60 2 0.03 61 6 0.11 0.99

B8 5/1/86 53 3 0.05 46 6 0.12 1.14

B2 5/2/86 116 4 0.04 127 27 0.21 0.91

B3 5/2/86 123 5 0.04 124 25 0.20 0.99

B8 5/2/86 122 3 0.02 126 25 0.20 0.97

Gil 5/7/86 366 5 0.01 410 64 0.16 0.89

slope; of linear regression line of CA = slope * PA 0.91

standard error of slope 0.02

r

z 0.99

GR date CA dif dif/CA* CA/GR

69 5/1/86 71 8 0.11 1.03

95 5/16/86 101 0 0.00 1.05

69 5/30/86 57 4 0.07 0.83

slope of linear regression line of CA = slope * GR 0.99

standard error of slope 0.07

r

2 0.82

CA = average of 2 formaldehyde concentrations determined by chromotropic

acid, ppb

dif = absolute value of the difference between either formaldehyde

concentration determined by chromotropic acid and CA, ppb

PA = average formaldehyde concentration determined by pararosaniline, ppb

SD = standard deviation of PR, ppb

AER = air exchange rate, h

-1

GR = span gas concentration determined gravimetrically, ppb

k . , , , ...

The two quantities m this expression were not rounded before division.

Discussion

Agreement between mean ca- and gr-concentrations, their small errors, and

the inability to detect higher than background concentrations in the second

impinger of a double impinger test, show that formaldehyde collection

efficiency by the first impinger was nearly 100%. Since the automated

procedure is based on permeation tubes, the results of the experiment

reported here suggest that the pararosaniline and chromotropic acid methods

would agree on "pure" formaldehyde atmospheres produced by heating

polyoxymethylene permeation tubes. Preliminary experiments further suggest

that pa- and ca-concentrations agree with each other on the pressed-wood

products tested. Further tests are needed to expand these results to a wider variety of pressed-wood products from different manufacturers.

One question of interest is whether processes used in the manufacture of

pressed-wood products may result in the emission of substances that are

79
HCHO

cone.,

chromotropic

acid,

ppb

.aa

a, 2

u

o

a,o

L©

E

o

h. JC

w>

u

c

0

aO

X

0

1

Figure 4. Ca- vs. pa-concentrations of particleboard. The line is the line

of identity.

HCHO cone., apcm gaaea, ppb

Figure 5. Ca- vs. gr-concentrations of span gases. The line is the line of

identity.

80
interferences for the pararosaniline or chromotropic acid methods. Higher

molecular weight aldehydes give positive interference for both methods, but

only if their concentrations are far in excess of formaldehyde

concentration, which is most unlikely [4-5] . Phenol, ethanol, higher

molecular weight alcohols, olefins, and sulfur dioxide give negative

interferences for the chromotropic acid method [5, 12] . It is possible that

some of these compounds may be emitted by underlayment . The present study

shows that any interfering substances emitted by the boards did not

differentially affect the two analytical methods.

Acknowledgment

This project was made possible by support from the U. S. Consumer Product

Safety Commission.

References

[1] Versar, Inc., "Formaldehyde Exposure in residential settings: sources,

levels, and effectiveness of control options," prepared for U. S.

Environmental Protection Agency, Springfield, VA, 1986.

[2] R. A. Grot, S. Silberstein, and K. Ishiguro, "Validation of Models for

Predicting Formaldehyde Concentrations in Residences due to Pressed

Wood Products — Phase I," National Bureau of Standards Interagency

Report No. 85-3255, Gaithersburg, MD, 1985.

[3] T. G. Matthews, T. J. Reed, B. J. Tromberg, K. W. Fung, C. V.

Thompson, J. 0. Simpson, and A. R. Hawthorne, "Modeling and Testing of

Formaldehyde Emission Characteristics of Pressed-Wood Products,"

Report no. 18 to CPSC, Oak Ridge National Laboratory Report no. TM

9867, 1985.

[4] R. R. Miksch et al., "Modified Pararosaniline Method for the

Determination of Formaldehyde in Air," Anal. Chem. 53, 2118-2123,

1981.

[5] National Institute for Occupational Safety and Health, Manual of

Analytical Methods, 3rd ed.; P. M. Eller, Ed., NIOSH Publication No.

84-100, Method 3500, Cincinnati, 1984.

[6] National Research Council, "Formaldehyde and Other Aldehydes,"

National Academy Press, 1981, Washington.

[7] G. R. Lyles, F. B. Dowling and V. J. Blanchard, "Quantitative

Determination of Formaldehyde in Parts Per Hundred Million

Concentration Level," J. Air Pollut. Control Assoc. 15, 106-108, 1965.

[8] CEA Instruments, Inc., "Low Level Formaldehyde in Air (Mercury-Free

Procedures)," Emerson, NJ, 1984.

81
[ 9 ] F. P. Scaringelli, A. E. O'Keefe, E. Rosenberg and J. P. Bell,

"Preparation of Known Concentrations of Gases and Vapors with

Permeation Devices Calibrated Gravimetrically, " Anal . Chem. 42, 871-

816, 1970 o

[10] R. A. Grot, D. Me Burch, S. Silberstein, and L. Galowin, "Measurement

Methods for Evaluation of Thermal Integrity of Building Envelopes,"

National Bureau of Standards Interagency Report 82-2605, Gaithersburg,

MD, 1982.

[11] S. Silberstein, R. A. Grot, K. Ishiguro, and W. S. Dols, "Validation

of Models for Predicting Formaldehyde Concentrations in Residences due

to Pressed Wood Products — Final Report," in preparation.

[12] E. R. Kennedy, A. W. Teass, and Y. T. Gagnon, "Industrial Hygiene

Sampling and Analytical Methods for Formaldehyde: Past and Present,"

pp. 3-12 in V. Turoski, ed., "Formaldehyde, " Advances in Chemistry

Series 210, American Chemical Society, Washington, 1985.

82
Discussion and Conclusions - Preston E. McNall, NBS

After the prepared presentations, an open discussion was held for one and

one-half hours, led by the editor. The purpose was to summarize what was

known about test methods, and to outline future directions. The editor

presents his impressions here. It is impossible to attribute statements

here to the individuals who took part in the discussion.

Challenge materials. It was agreed that a number of challenge materials

should be used to represent the wide range of materials expected to be

encountered in practice. It was felt that seven to ten different

materials might suffice, for example:

Acrolein

Ammonia

Carbon monoxide

Carbon disulfide

Carbon tetrachloride

Formaldehyde

Hydrogen sulfide

Ozone

These materials, except ozone and formaldehyde, could be prepared in

various concentrations in cylinders, and form a standard "cocktail" to be

supplied to candidate devices. More work is needed to determine the

challenge materials to be usetL, but this appeared to be the most

practical approach.

Other contaminants could be added by the user, if such contaminants were

handled similarly, as appropriate to the individual equipment in

application. The user would need to show the importance of the added

contaminants

.

Challenge Concentrations

.

Because the performance of most commonly used

devices is affected drastically by concentration, the challenge

concentrations must be kept close to those expected to be encountered in

the field. High concentrations could cause non-representative results.

Test time and cost problems for loading tests were recognized.

Ambient Test Conditions. Obviously, test conditions should approach

those encountered in practice. It was noted that humidity, as well as temperature, often affect performance significantly. Since most

equipment will be installed in return air ducts, and since high

humidities are usually detrimental to performance, it was agreed that

conditions of about (21° C) , (70° F) and 50% RH be used. Options might

be considered for including other conditions for special equipment, but

much of the time 70° F and 50% RH will be appropriate.

83
Equipment Type. Several types of equipment may be used. Adsorption,

absorption, chemisorption, catalysis and electric fields are known

methods. While these operate differently on contaminants, it was

concluded that all should be evaluated similarly. Special

considerations, involving breakthrough, selective off-gassing of

previously retained materials, and penetration or off-gassing of

chemically-changed materials could be included in tests for different

types of equipment if appropriate. However, similar challenge materials

seemed to be most representative of field conditions, and should be used

for all types of filters.

Types of Tests

.

Two general types of tests are necessary. First, a test

of the performance of a new or regenerated filter should be performed.

For this purpose, the efficiencies (or penetrations) of the new equipment

should be reported on each of the challenge materials. These should be

measured at test conditions reasonably expected in the field, as

described elsewhere. Second, the performance life, or loading must be

established under reasonable conditions representative of those to be

encountered in the field.

Detailed Test Procedures

General . Filter evaluations have generally been made in two ways.

First, a test duct has been employed, in which the equipment can be

mounted. Measurements are made on the filters on a single-pass mode.

Efficiencies, etc. are then single-pass for the filter. Second, a roomsize, or smaller chamber has been used, and the filters placed in a recirculating airflow arrangement. Concentrations are measured in the

chamber. It was decided to employ the single-pass method, because the

filter field application requires the single-pass parameters to predict

field performance. In the chamber tests, the single-pass efficiency must

be calculated from the chamber system measurements. Another important

factor was that the ASHRAE Standard 52 for particulate filter evaluation

employs a test duct, which could probably be used for gaseous and

vaporous evaluation as well.

In conclusion, a test duct similar to that of ASHRAE Standard 52 seemed

to be the most appropriate choice.

Contaminant Feeding Methods. A "cocktail" of contaminants as described

earlier could be prepared and packaged in cylinders of various sizes.

The entrance section of the test duct should be equipped with suitable

prefilters to condition the outside, or laboratory air. Heaters, coolers

and humidity contol would also be necessary. The conbtaminants would be

introduced from the cylinders at a controlled rate to provide the desired

upstream concentrations. Mixing baffles would probably be required.

Nonstorable contaminants, such as ozone, would require different feeding

systems as appropriate. Formaldehyde would have to be kept separate from

ozone and NH 3

.

Measuring Means . Upstream and downstream concentrations need to be

84
measured so that single-pass efficiencies (or penetrations) can be

evaluated directly. Gas chromatography seemed to be the most appropriate

choice. Other methods for specific contaminants may also be required.

Weighing of filters to obtain retention values would not usually be

appropriate due to spurious retention of moisture and other unknown

contaminants

.

"Clean" Efficiency Tests . "As received" filters need efficiency

evaluations as important parameters. Approximately 2' x2' sample filters

representative of field models are needed (consistent with ASHRAE

Standard 52) . Evaluations would be reported on the cocktail contaminants

separately for each. As previously mentioned, concentrations would be

low and representative of field use.

The face velocity would be representative of field use, about 500 ft/min

corresponding to about 2000 cfm. Higher and lower velocities may also be

appropriate to cover ranges of field use. "Clean" pressure drop results

are needed for application and economics.

Loading Tests . An appropriate loading test is needed to determine filter

life. To save challenge gases and time it was decided, for practical

reasons, to feed concentrations at perhaps 10 times the "clean" test

rate, to representative smaller filter samples. A 3" x 3" section or

even smaller was thought appropriate. Of course, practical filter

sections may not lend themselves to sections this small, and larger

sections for those filters would be necessary. If this procedure worked,

a test of 100-200 hours might be appropriate.

Pressure drop vs. loading information would also be obtained several

times throughout the test. Breakthrough information on these challenge

contaminants would be measured and reported several times also.

There was much discussion of when to terminate such a loading test. For

general ventilation purposes, clean efficiencies of 90% or so would be

particularly useful (penetration 10%) . Perhaps the test could be

terminated at a doubling of "clean" penetration of 1/2 the number

challenge materials. More research and consensus are necessary.

Chemisorption filters would also have to be monitored for off-gassing of

other unwanted materials.

Conclusions

In application the designer needs to know answers to four important

questions

1. What does the "clean" filter do?

2. How long does it last?

3. What penalty, energy, etc. is associated with its pressure drop?

85
4. What are its first cost, regeneration or replacement costs, and

product life?

With this information the designer can estimate, for field application,

the value (performance) of the filter and its life-cycle cost. The test

procedures should answer the first three questions and the manufacturer

must establish the answer to question 4.

The workshop was successful in helping to describe the state of the art,

and to set a framework for future test development and research.

Although all of the appropriate experts could not participate, it is

hoped that this document will stimulate more public presentations of

important research results.

86
S«T 14A (REV. 2.80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS IR 88-3716

2. Performing Organ. Report No. 3. Publication Date

MARCH 1988

TITLE AND SUBTITLE

Proceedings of the Symposium on Gaseous

Removal Equipment Test Methods

and Vaporous

AUTHOR(S)

P. E. McNall

PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No.

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

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NBS

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[ H Document describes a computer program; SF-185, FIPS Software Summary, is attached.

. ABSTRACT (A 200- word or less factual summary of most si gn i fi cant in formation. If document includes a si gn i fi cant

bi bl iography or literature survey, mention it here)

his symposium proceedings summarizes the current state-of-the-art on gaseous and

aporous removal test methods for equipment designed for use in the general ventilation

f buildings. Papers by the ten (10) invited authors are included. A discussion

ection outlines the conclusions reached concerning the future direction of test

lethod development.

!. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) absorption; adsorption; air cleaning; catalysis, chemisorption; gaseous;

validation; vapors

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