NBSIR 73-258

A Gas Dilution System for Acrolein

Eugene P. Scheide, Ernest E. Hughes and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

October 1973

Final Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

NBSIR 73-258

A GAS DILUTION SYSTEM FOR ACROLEIN

Eugene P. Scheide, Ernest E. Hughes and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

October 1973

Final Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

A Gas Dilution System for Acrolein

ABSTRACT

A system capable of producing well-definedtest atmospheres of acrolein in air (or any other

desired diluent) and an analytical system for the

analysis of these gas mixtures is described. Using

a bulk mixture of 9.0 ppm acrolein in nitrogen, and

accurately blending this with a stream of clean,

dry air, concentrations between 0.05 and 0.50 ppm

can be produced. This system provides a means of

calibration of the various analytical systems for

acrolein now in use.

1. INTRODUCTION

This report describes a system capable of producing welldefined test atmospheres containing concentrations of acrolein

(CH2=CHCH0) for the calibration of analytical instruments and

evaluation of analytical methodology. The system developed

and described was designed to produce concentrations in the

industrial hygiene range of 0.05 to 0.5 ppm, but other concentrations could be achieved by suitable adjustment of the

operational parameters.

2 . EXPERIMENTAL

Acrolein is a relatively stable substance so that

little difficulty is encountered in preparing low concentration mixtures of it in air by dilution of high concentration

mixtures. Furthermore, high concentration mixtures of

acrolein in air prepared at high pressure in gas cylinders

appear to have sufficient stability so that frequent re

analysis is not required. Consequently, the simplest system

for providing a variety of concentrations of acrolein in air

consists of a cylinder at high pressure containing a known

concentration of acrolein and a system for diluting this high

concentration with accurately measured volumes of air.

Systems for the accurate blending of gas mixtures have been

built and evaluated and it is intended that such systems will

be used for the dilution of acrolein.

The dilution system is described in detail elsewhere [1]

and is shown schematically in Figure 1. It consists of two
controlled flow systems, one for the diluent air and one for

the bulk mixture of acrolein, flow meters for measuring the

flow of each gas stream, a mixing chamber where the two

streams are combined, and a manifold from which the mixture

may be withdrawn for analysis or for calibration purposes.

2 . 1 Gases, Gas Mixtures

A pressurized cylinder containing a bulk mixture of

acrolein in nitrogen was prepared by the manometric method to

have an acrolein concentration of 9.0 ppm. The cylinder was

pressurized to a total pressure of 1200 psi corresponding to

approximately 3600 liters of the 9.0 ppm mixture at ambient

conditions. The mixture also contained 2.1 ppm of propane as an internal calibrant. The source of diluent air can be

either a pressurized cylinder of "breathing" air or "house"

air from the bench. In either case, the air is passed through

a silica gel-charcoal dryer to remove major contaminants.

2 . 2 Analysis "

A gas chromat ograph equipped with a flame ionization

detector can be used to analyze the concentration of either

the bulk mixture of acrolein or any of the dilutions produced

with the system. The dilution, sampling and analytical systems

are shown diagramatically in Figure 2. Sampling is accomplished

by inserting a Teflon tube, connected at one end to a gas

sampling valve, into one port of the sampling manifold.

Samples are drawn through the gas sampling valve by applying

a moderate vacuum, and are then injected into the gas chromatograph by the carrier gas.

The recommended gas chromatographic operating parameters

are as follows:

Column 6 ft X 1/4 in Porapak Q,

80-100 mesh, #5750

Column temp. 145 °C

De tec tor FID at 225 °C

He flow 50 ml/min

Samp le 10 ml

Sampling rate 40 ml/min

2
Precautions should be taken to optimize the gas chromatograph sensitivity before each set of analyses using the

manufacturer's recommended procedure. A significant decrease

in the detector signal for samples of the same concentration

is an indication that the gas chromatograph must be optimized

again

.

2 . 3 Calculation of Bulk Mixture Concentration

The bulk mixture concentration is calculated using the

following equation:

^ _/Acrolein g.c. peak area\

b yPropane g.c. peak area ) x R x propane concentration Eq. (Ij

where

,

C^ = bulk concentration of acrolein (ppm)

.

R = g.c. response factor (ratio of signals for equal

concentrations) - 1.69 (experimental value).

For example, using a bulk mixture of acrolein containing

2.1 ppm propane, if the propane g.c. peak area - 1690 and the

acrolein peak area - 4235, then the bulk mixture concentration

of acrolein would be 8.9 ppm, i.e.,

42 35

^b

~

-[^^ QQ

X 1.69 X 2*1 = 8 .

9

ppm.

The acrolein concentration for various dilutions is

calculated using Equation (2)

.

F • C^

X air

whe re ,

C = acrolein concentration produced in the manifold (ppm).

F = measured flow rate of acrolein-N2 mixture (cm /min)

.

I F . = measured flow rate of dilution air (cm^/min).

C^ = concentration of bulk mixture (ppm)

.

3
Equation 2, rearranged, may be used to calculate the flow

rates required to produce a given concentration of acrolein

in the manifold. For example, using a 9.0 ppm bulk mixture of

acrolein and a acrolein flow of 30 crnVmin, an air flow of

5370 cc/min would be needed to porduce a 0.05 ppm mixture in

the manifold: i.e.,

F

=

' _ _ (30) (9.0) . . . air C ^x ToTOSl ^^^^

5370 cmVmin .

It is recommended to maintain the sample flow at a fixed value

and to vary only the air flow in producing various acrolein

concentrations

;, 3. PERFORMANCE EVALUATION

3 . 1 Conditioning of Gas Cylinders

Mixtures of acrolein in nitrogen placed in pressurized

steel cylinders will show a small but significant decrease

in concentration with time. This decrease can be slowed down

considerably by conditioning the cylinder by prior exposure

to a high-concentration acrolein mixture. The cylinder is

then evacuated and filled in the normal manner. This conditioning effect is shown in Figure 3.

3.2 Tank Stability

Once the cylinder is conditioned and allowed to reach

equilibrium, the acrolein concentration will remain relatively

constant. But, because a change may occur, analysis of the

bulk mixture is advised before each day's operation.

Since the propane concentration has been found to be stable

it serves as an internal standard by which the concentration

of the acrolein may be determined at any time.

3 . 3 Analysis of Bulk Mixture and Dilutions

The bulk mixture and dilutions were analyzed by gas

chromatography as described earlier. Table 1 shows the results

of replicate analyses of one of the dilutions taken from the

sampling manifold. The precision of these analyses is very

good indicating that the analytical system and sampling

technique are reliable.

Various mixtures of acrolein in air were prepared and

analyzed by gas chromatography. Figure 4 shows a plot of g.c.
signal versus acrolein concentration. The plot is linear over

the range of 0.05 to 0.5 ppm and the g.c. sensitivity is sufficient to analyze all of the dilutions directly.

3 . 4 Standards and Calibration

Calibration standards accurate to 1 percent were made

volumetrically consisting of solutions of acrolein in benzene.

These gave a linear plot from which the bulk mixture of acrolein

in nitrogen was calibrated.

4. CONCLUSIONS

The system described in this report is capable of producing

well-defined test atmospheres of varying concentration of

acrolein in air by blending a bulk mixture of acrolein in nitrogen

from a pressurized cylinder with a stream of diluent air.

Analysis of the bulk mixture and the dilutions can be easily

performed by gas chromatography. This gas generation system

should provide a means of calilDrating analytical systems for

acrolein now in use.

5 . REFERENCE

1. E. E. Hughes, W. D. Dorko , E. P. Scheide, J. K. Taylor,

Gas Generating Systems for the Evaluation of Gas Detecting

Devices, NBS Report NBSIR 73-292, October 1973.

. TABLE 1 Precision of Gas Chromatographic

Analysis of Acrolein

0.292 ppm Sample

Run Propane signal Acrolein signal Aero le in /propane

1 1150 1304 1.134

2 1179 1212 1.028

3 1121 1203 1.073

4 1202 1302 1.083

Ave . 1163 1255 1.080

Std. Dev. 35 55 .043

Rel. Std. Dev. 3.01% 4.381 3.9 8"^

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Acrolein Concentration (ppm)

Figure 4. Measured response of gas chromat ograph to various

concentrations of acrolein.

9

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7. Ai iiiDiuM g^p^ Scheide, E.E. Hughes and J.K. Taylor 8. l'iTU)rnntiK_ "ri;,m. Kr(>oi; Xo. NBSIR 73-258

9. IM-.KI-OKMINt, t)KCi AX I/A XAMI' AXI1 ADDUI SS NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMAAERCE

WASHINGTON, D.C. 20234

10. Pro|c Lt, T.isk. Work 1 mt X...

1). (.ontrait Cirant No.

12. Spoiisorinj; I.V >; .in i / at i . ti N.iiiu' .xul < onipi'ti- A.j.lrc.s (Slrect. City. Si^jie. ZIP)

National Institute for Occupational Safety and Health

Cincinnati, Ohio

13. I vpc of Kc port & l'i rl.).i Covered

Final

14. Sponsoring Agency C.oilc15. sl^ppi.i:mi;xtarv xoths

16. ARSTRACl (A 200-\vord or /ess Uistiial nummary ot most significant inforwJtion. If doLtimt-nl includes a significant

biblios^raphy or literature survey, mention it here.)

U.S. 0^ t^T . -J ' • 'f-'M . BIBLIOGRAPHIC DATA

SHFFT

1. n |i \ I I'K H\ I t iK I Xi). NBSIR 73-2582. Uov'l .\. c I ,.,•,,,11 Xo.

4. I II I.I 1. 1 I II I A Gas Dilution System for Acrolein

3. K ; p u n I

' s .Ai 1. 1- ., s I, 111

5. I 'ii 111 II .11 Ion n.in- October 1973

6. I '< r for 111 1 11 g Org. nil /.It mil * i'

A system capable of producing well-defined test atmospheres of acrolein

in air (or any other desired diluent) and an analytical system for the

analysis of these gas mixtures is described. Using a bulk mixture of

9.0 ppm acrolein in nitrogen, and accurately blending this with a stream

of clean, dry air, concentrations between 0.05 and 0.50 ppm can be produced. This system provides a means of calibration of the various

analytical systems for acrolein now in use.

17. KEY Vl'ORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Acrolein; gas Chromatography analysis; gas dilution

system; occupational safety.

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