Catalytic method and device for controlling VOC. CO and halogenated organic emissions

A method and device for treating a gas stream comprising at least one non-halogenated carbonaceous compound and optionally at least one halogenated organic compound. The gas stream, at 100.degree. C. to 650.degree. C. and in the presence of oxygen is contacted with a first catalyst in a first catalyst zone. The first catalyst comprises a first catalytic material deposited on a low acidity support material. In this zone, the non-halogenated compound is selectively reacted to form innocuous materials such as water and carbon monoxide. This can be followed by contacting the gas stream with a second catalyst in a second catalyst zone. The second catalyst comprises a second catalytic material deposited on a high acidity support material. In this zone, the halogenated organic compounds are reacted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a novel catalyst device and related method for 
the catalytic oxidation of gaseous carbonaceous emissions, in particular, 
gaseous carbonaceous emissions that include halogen containing compounds. 
2. Description of Related Art 
The treatment of gaseous emissions containing volatile organic compounds 
has been of increasing concern in recent years. Thermal incineration, 
catalytic oxidation and adsorption are commonly used for removing these 
pollutants. Thermal incineration requires high operating temperatures and 
high capital cost facilities. If the gaseous stream also includes 
halogenated compounds, thermal incineration can evolve toxic halogenated 
compounds under certain operating conditions. In some instances, 
adsorption by adsorbents such as carbon is an alterative; however, this 
process does not destroy the pollutants, but merely concentrates them. 
Furthermore, adsorption efficiency can be adversely impacted by 
fluctuating concentrations of the gaseous components. 
Catalytic oxidation is an energy efficient and economical way of destroying 
gaseous organic emissions. It operates at significantly lower temperatures 
and shorter residence time than thermal incineration and requires smaller 
reactors made of less expensive materials. 
Methods for the catalytic oxidation of non-halogenated organic and 
halogenated organic compounds are well known in the art. For example, in 
the article by G. C. Bond and N. Sadeghi, "Catalyzed Destruction of 
Chlorinated Hydrocarbons" J. Appl. Chem. Biotechnol., 1975, 25, 241-248, 
it is reported that chlorinated hydrocarbons are converted to HCl and 
CO.sub.2 over platinum on gamma alumina catalyst. 
U.S. Pat. Nos. 3,972,979 and 4,053,557 describe the decomposition of 
halogenated hydrocarbons by oxidation over chromium oxide or a boehmite 
supported platinum. 
U.S. Pat. Nos. 4,059,675, 4,059,676 and 4,059,683 describe methods for 
decomposing halogenated organic compounds using catalysts containing 
ruthenium, ruthenium-platinum and platinum, respectively, in the presence 
of an oxidizing agent at a temperature of at least 350.degree. C. 
The article by James J. Spivy, "Complete Catalytic Oxidation of Volatile 
Organics", Ind Eng. Chem. Res., 1987, 26, 2165-2180, is a review of the 
literature dealing with the heterogenous catalytic oxidation of volatile 
organic compounds. 
The article by S. Chatterjee and H. L. Green, "Oxidative Catalysis by 
Chlorinated Hydrocarbons by Metal-Load Acid Catalysts", Journal of 
Catalysis, 1991, 130, 76-85, reports on a study of the catalytic oxidation 
of methylene chloride in air using supported zeolite catalysts H--Y, 
Cr--Y, and Ce--Y. 
The article by A. Melchor, E. Garbowski, M. V. Michel-Vital Mathia and M. 
Primet, "Physicochemical Properties and Isomerization Activity of 
Chlorinated Pt/Al.sub.2 O.sub.3 Catalyst", J. Chem Soc., Faraday Trans. 1, 
1986, 82, 3667-3679, reports that chlorination of alumina leads to a very 
acidic solid because of an enhancement of the strength and the number of 
strong Lewis Sites. The chlorination treatment enhances the sintering of 
platinum. 
U.S. Pat. No. 4,983,366 describes a method for the catalytic conversion of 
waste gases containing hydrocarbons and carbon monoxide by passing the 
waste gases through a first zone containing a catalyst such as aluminum 
oxide, silicon dioxide, aluminum silicate and/or a zeolite optionally 
containing oxidic compounds or barium, manganese, copper, chromium, and 
nickel, and then through a second zone containing a catalyst such as 
platinum and/or platinum and/or palladium or platinum and rhodium. 
PCT international application No. PCT/US 90/02386 describes a catalytic 
process for converting or destroying organic compounds including 
organohalogen compounds using a catalyst which contains as a catalytic 
component titania. The preferred catalyst also contains vanadium oxide, 
tungsten oxide, tin oxide, and at least one noble metal selected from the 
group consisting of platinum, palladium, and rhodium characterized in that 
the vanadium oxide, tungsten oxide and noble metals are uniformly 
dispersed on the titania. 
U.S. Pat. No. 5,283,041 (commonly assigned to assignor of the instant 
invention), hereby incorporated by reference, discloses an oxidation 
catalyst for treating a gas stream containing compounds selected from the 
group consisting of halogenated organic compounds, other organic compounds 
and mixtures thereof; the catalyst comprising a core material comprising 
zirconium oxide and one or more oxides of manganese, cerium or cobalt with 
vanadium oxide and, preferably, platinum group metal dispersed on the core 
material. 
There is still a need for catalysts and processes for the oxidative 
destruction of halogenated organics and other organic compounds which 
provide enhanced operating efficiencies. 
SUMMARY OF THE INVENTION 
This invention relates to a catalytic device and method for treating gas 
streams containing at least one carbonaceous compound including compounds 
selected from organic compounds and/or carbon monoxide. In particular, the 
gas streams contain at least one non-halogenated carbonaceous compound and 
optionally at least one halogen containing compound, particularly 
halogenated organic compounds. Inorganic gaseous constituents such as 
nitrogen and minor constituents of air may also be present. 
Non-halogenated organic compounds include carbon-containing molecules such 
as aliphatic and cyclic molecules. Such compounds can include hydrocarbon 
molecules, as well as heteromolecules which contain both carbon and 
non-carbon atoms. 
Halogen containing compounds refer to compounds having at least one halogen 
atom in the molecule. Halogenated organic compounds, also referred to 
organohalogen compounds, refer to any organic compound having at least one 
halogen atom in the molecule. 
For the purpose of the present invention, volatile organic compounds 
(VOC's) are organic compounds with sufficiently high vapor pressure to 
exist as a vapor in ambient air and which react in the atmosphere with 
nitrogen oxides in the presence of heat and sunlight to form ozone, and 
include both halogenated and non-halogenated volatile organic compounds. 
The method of the present invention includes treating a gas stream 
containing at least one non-halogenated carbonaceous compound typically 
selected from a non-halogenated organic compound and/or carbon monoxide 
and at least one halogenated organic compound. The gas stream, in the 
presence of oxygen, is introduced to a first catalyst zone and contacted 
with a first catalyst under conditions sufficient to catalyze the 
oxidation of at least some of the carbonaceous constituents. The first 
catalyst zone comprises a first catalyst comprising a catalytic metal 
deposited on a low acidity support material. The gaseous mixture passes 
through the first catalyst zone and is then introduced to a second 
catalyst zone and contacted with a second catalyst in the second catalyst 
zone. The second catalyst zone comprises a second catalyst comprising a 
catalytic material deposited on a high acidity support material. A 
substantial amount of the carbonaceous constituents of the gas stream are 
converted to CO.sub.2 and H.sub.2 O in the first catalyst zone. The 
halogenated organic compounds are substantially converted to CO.sub.2, 
H.sub.2 O and molecular halogens or haloacids in the second catalyst zone. 
In accordance with the method of the present invention, it has been found 
that by the use of a low acidity support in the first zone the 
non-halogenated carbonaceous compounds are preferentially converted (i.e., 
oxidized) while the halogenated organic remain substantially unreacted. 
This prevents the reaction of the non-halogenated compounds in the first 
zone from being inhibited by a reaction of the halogenated compounds. 
The present invention also includes a method for treating a gas stream 
comprising at least one non-halogenated carbonaceous compound and 
optionally at least one halogen containing compound by contacting the gas 
stream at a temperature of about 100.degree. C. to about 650.degree. C. 
and in the presence of oxygen with a first catalyst comprising a first 
catalytic material deposited on a low acidity support material; and 
non-halogenated compound is substantially converted and the halogen 
compound is substantially unconverted. 
In specific embodiments of this invention using either a first catalyst 
zone or a first and second catalyst zone, the gas stream is introduced to 
the first catalyst zone at a temperature of up to about 650.degree. C., 
preferably about 100.degree. C. to about 550.degree. C., and more 
preferably at a temperature of about 150.degree. C. to about 450.degree. 
C. The ratio of gaseous hourly flow rate to catalyst bed volume, referred 
to as volume hourly space velocity (VHSV), is preferably from about 1,000 
to about 100,000 hr.sup.-1, and more preferably 5,000 to about 50,000 
hr.sup.-1. 
The catalysts useful in the practice of this invention include at least one 
catalytic material which comprises at least one metal or metal compound 
which can include metals and metal oxides known to promote catalytic 
oxidation of carbonaceous compounds, such as the oxides of vanadium, 
chromium, manganese, iron, nickel, cobalt, copper and the platinum group 
metals. In a preferred embodiment, the catalytic material comprises 
platinum and/or palladium. The first catalytic material and the second 
catalytic material may be the same material or may be different catalytic 
materials. 
In accordance with the present invention, the catalytic material is 
deposited upon a support material. The combination is referred to as 
catalyzed support material. Preferably, the support material is in powder 
or particle form. In the first catalyst zone, the support material is 
characterized as a low acidity support material. The second catalyst zone 
support material is characterized as a high acidity support material. 
As used herein, a low acidity support material is characterized as a 
support material that when tested in uncatalyzed, powder form by the 
temperature programmed desorption method (TPD) described below, desorbs 
less than about 0.04 millimoles NH.sub.3 per gram of uncatalyzed support 
material. In a preferred embodiment, the low acidity support materials 
desorb from about 0.005 millimoles to about 0.035 millimoles NH.sub.3 per 
gram, and more preferably from about 0.015 to about 0.03 millimoles 
NH.sub.3 per gram. Preferred low acidity support material include but are 
not limited to at least one metal oxide compound selected from the group 
consisting of SiO.sub.2, TiO.sub.2, ZrO.sub.2, MgO, CaO, La.sub.2 O.sub.3, 
Y.sub.2 O.sub.3, and tin oxide. 
A high acidity support material desorbs more than about 0.04 millimoles 
NH.sub.3 per gram of uncatalyzed support material using the TPD test. 
Preferably, the high acidity support materials desorb from about 0.05 
millimoles NH.sub.3 per gram to about 0.14 millimoles NH.sub.3 per gram; 
and more preferably desorbs in the range of about 0.06 millimoles to about 
0.10 millimoles NH.sub.3 per gram uncatalyzed support material. Preferred 
high acidity support material include but are not limited to at least one 
material selected from the group consisting of gamma alumina, delta 
alumina, theta alumina, transitional forms of alumina, silica-alumina, and 
zeolites. 
In accordance with the present invention, at least some of the organic 
compounds and/or carbon monoxide contained in the introduced gas stream 
are converted in the presence of oxygen to comparatively innocuous 
compounds, such as CO.sub.2 and H.sub.2 O using the catalyst device and 
method of the invention. Preferably, at least 60% based on initial 
concentrations and more preferably substantially all of the organic 
compounds are converted. At least some of the halogenated organic 
compounds and preferably at least 60% based on the initial concentration, 
and more preferably substantially all of the halogenated organic compounds 
contained in the introduced gas stream are converted to compounds such as 
CO.sub.2, H.sub.2 O and halogen molecules (Cl.sub.2, Br.sub.2, etc.) 
and/or halogen acids, such as HCl, HBr, etc. The molecular halogen and 
halogen acids subsequently can be removed from the gas stream by 
conventional scrubbing technology. A gas constituent of the introduced gas 
stream is substantially unconverted when less than about 30% of the 
initial concentration is converted at the stated conditions. 
The present invention includes a catalytic device for treating a gaseous 
stream containing non-halogenated carbonaceous and optionally halogenated 
compounds. The device comprises a reactor, preferably an enclosed reactor, 
having a reactor chamber, an inlet and an outlet. The device comprises a 
first catalyst disposed in a first catalyst zone (or bed). The first 
catalyst comprises a first catalytic material deposited on a low acidity 
support material. There is a second catalyst disposed in a second catalyst 
zone (or bed), positioned downstream from the first catalyst bed. The 
second catalyst comprises a second catalytic material deposited on a high 
acidity support material. The first zone is the first to be contacted when 
the gaseous stream is introduced to the catalyst device. The second 
catalyst zone, or second bed, is disposed in a downstream position from 
the first catalyst bed, and is the second catalyst bed to be contacted by 
the gaseous stream after the stream has been introduced to and passed 
through the first bed. After the gas stream passes through the second bed, 
the stream exits from the outlet. 
In a preferred embodiment, the first and second catalyst beds are disposed 
within a container having an inlet and an outlet, with the first catalyst 
bed disposed between the inlet and the second bed, and the second bed 
disposed between the first catalyst bed and the outlet. Alternatively, it 
is also within the scope of the invention that the first catalyst bed and 
the second bed be in separate containers. 
The present invention includes a catalytic device comprising a first 
catalyst disposed in a single catalyst bed. This device comprises a 
reactor, preferably an enclosed reactor, having a reactor chamber, an 
inlet and an outlet. The single catalyst bed contains a first catalyst 
comprising a catalytic material deposited on a low acidity support 
material. This catalytic device is referred to as the single bed device. 
The gas stream to be treated enters the device through the inlet, contacts 
and passes through the single catalyst bed and subsequently exits the 
device by way of the exhaust outlet. 
Gas streams comprising non-halogenated carbonaceous and halogenated organic 
compounds can be effectively treated by dual bed devices of the invention 
at lower operating temperatures and/or higher space velocities. Both 
single bed and dual bed devices of the invention have a reduced tendency 
for coke formation and a reduced tendency for catalyst poisoning by 
halogen compounds. It is within the scope of the invention to repeatedly 
thermally regenerate the catalysts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be understood by those skilled in the art by 
reference to the accompanying drawings, the following description and 
examples. 
The device of the present invention having a dual bed is illustrated in 
FIGS. 1A and 1B. Common elements in FIGS. 1A and 1B have the same 
reference characters. The dual bed device comprises a reactor 12 which is 
preferably enclosed and has an inlet 14 and an outlet 16. The reactor 
comprises a reactor chamber 18 disposed between the inlet and the outlet. 
A first catalyst bed 20 is disposed in the chamber 18 between the inlet 14 
and the outlet 16. A second catalyst bed 22 is located in the chamber 18 
between the first catalyst bed 20 and the outlet 16. A flow path 24 is 
defined from the inlet 14, through the first catalyst bed 20, to and 
through the second catalyst bed 22 and out of the outlet 16. 
There are means for securing and sealing the first catalyst bed 20 and the 
second catalyst bed 22 within the reactor chamber 18 so that the gas 
stream introduced into reactor chamber 18 through the inlet 14 flows 
substantially through the first catalyst bed 20 and then through the 
second catalyst bed 22 without bypassing the first or second bed. 
FIG. 1A illustrates a dual bed 10 reactor where the first catalyst bed 20 
comprises a first honeycomb carrier 26 located between the inlet 14 and 
the outlet 16 upstream of a second honeycomb carrier 28. The first 
catalyst is coated onto the first honeycomb carrier 26 and the second 
catalyst is coated onto the second honeycomb carrier 28. The honeycomb 26 
comprises longitudinal passages 30 extending through the honeycomb from 
the inlet side to the outlet side. Preferably, the first honeycomb carrier 
passages are coaxial to the flow path 24. The honeycomb carrier extends 
across the cross-section of the reactor so that gases entering inlet 14 
pass through the first honeycomb carrier longitudinal passages 30. The 
reactor 12 is preferably enclosed and has a cross-section which can be any 
suitable shape including circular, square or rectangular or oval. A high 
temperature blanket 32 is located between the outer wall of the first 
honeycomb carrier and the inner wall of reactor 12 to prevent the gaseous 
stream from leaking between the honeycomb and the reactor. In this way, 
substantially all of the gaseous stream entering the inlet 14 passes 
through the passages 30 of the first honeycomb carrier 26. The second 
honeycomb carrier 28 is downstream from the first honeycomb carrier. The 
second honeycomb carrier passages 34 which extend from the inlet side to 
the outlet side of the reactor. Preferably, the second honeycomb passages 
are also coaxial with the gaseous flow path 24. The second honeycomb 
carrier 28 preferably extends across the whole cross-section of reactor 
12. The high temperature blanket 32 which is the same or a separate high 
temperature blanket is located between the inner wall of reactor 12 and 
the outer wall of the second honeycomb carrier. In this way, gases flowing 
from the passages 30 of the first honeycomb carrier pass through the 
passages 34 of the second honeycomb carrier 28 with substantially no 
leakage between the inner wall of reactor 12 and the outer wall of second 
honeycomb carrier 34. The second honeycomb carrier is coated with a second 
catalyst. 
An alternate embodiment of the present invention is illustrated in FIG. 1B. 
As noted, common elements of FIGS. 1A and 1B have the same reference 
characters. FIG. 1B illustrates a dual bed reactor comprising a first 
catalyst bed 20 located between inlet 14 and outlet 16. There is a second 
catalyst bed 22 located upstream of the first catalyst bed 20. The second 
catalyst bed is shown to be adjacent to the first catalyst bed 20 but can 
be spaced apart as the honeycomb beds of FIG. 1A are spaced apart. The 
first and second catalyst beds 20 and 22 respectively comprise first 
catalyst particles 36 and second catalyst particles 38. The particles of 
the first and second catalyst beds 20 and 22 are maintained in place in 
their beds by suitable first and second housings 40 and 42. The housings 
extend across the cross-section of the reactor and have perforations or 
are screened, as by screens 13 to hold the first catalyst particles 36 in 
first catalyst bed 20 and second catalyst particles 38 in second catalyst 
bed 22. The catalyst particles cooperate with the respective housings to 
permit gases to flow from inlet 14 through the first catalyst bed 20 to 
and through the second catalyst bed 22 and out of outlet 16. 
In a specific embodiment where gases flowing through the reactor 12 from 
inlet 14 to outlet 16 comprise at least one non-halogenated carbonaceous 
compound, and optionally one halogenated compound such as a halogenated 
organic compound, and it is desired to preferentially react only the one 
non-halogenated carbonaceous compound in the first catalyst bed. The 
device can be a single bed reactor having only the first catalyst bed 
wherein the first catalyst comprises the first catalytic material 
supported by a low acidity support material. FIG. 2 is an illustration of 
a single catalyst bed reactor 44. Common elements of FIG. 2 and FIG. 1B 
have the same reference characters and reference is made to the above 
discussion of FIG. 1B. As in FIG. 1B, the first catalyst bed of reactor 44 
contains a first catalyst in the form of particles comprising a first 
catalytic material supported by a low acidity support material. 
The first catalyst bed is preferably configured as illustrated comprising 
one bed. However, the first catalyst bed can comprise a plurality of 
catalyst beds containing a first catalyst. Where there is a dual bed, the 
second catalyst is preferably in a single catalyst bed as illustrated in 
FIGS. 1A and 1B. Optionally, the second catalyst can be in more than one 
catalyst bed. The first catalyst bed or plurality of first catalyst beds 
are located upstream of the second catalyst bed or plurality of second 
catalyst beds. 
The first catalyst bed comprises a first catalyst which comprises a first 
catalytic material supported by a low acidity support material and a 
second catalyst bed or zone comprises a second catalyst comprising a 
second catalytic material supported by a high acidity support material. 
The first catalytic material and the second catalytic material can be the 
same or different and comprise any suitable catalytic material useful in 
amounts to catalyze the desired reactions in the first and second catalyst 
beds. It has been found that where the first catalytic material is 
supported by a low acidity support material, a gas stream comprising at 
least one non-halogenated carbonaceous compound will react even in the 
presence of halogenated compounds, including halogenated organic 
compounds. Where it is desired to react halogenated organic compounds in 
the subsequent second bed the appropriate second catalytic material can be 
supported on a high acidity support material. 
Generally, depending on the gas stream composition, the low acidity support 
material can be characterized as a material which enhances the 
preferential catalysis of the reaction of non-halogenated carbonaceous 
compounds to form innocuous materials including carbon dioxide and water 
while any halogenated compounds including organic halogenated compounds 
present remain substantially unreacted at the conditions at which the 
non-halogenated compounds react. A support material is characterized as 
being a high acidity material where the acidity of the material is 
sufficiently high so that halogenated compounds and, in particular, 
halogenated organic compounds will react in the presence of the second 
catalytic material. The second catalyst may also catalyze the reaction of 
some of the unreacted carbonaceous compounds passing through the first 
zone. 
Following is a description of an analytical technique which can be used to 
quantitatively discriminate between low and high acidity catalyst support 
materials. 
The acidity of the support materials can be measured by the temperature 
programmed desorption (TPD) method using NH.sub.3 as the titration gas. In 
this analytical method, NH.sub.3 is preferentially adsorbed on acid sites, 
and the amount of adsorbed NH.sub.3 is therefore a measure of acidity. 
Specifically, a sample of powdered, uncatalyzed material is placed in the 
middle of an open-ended hollow quartz tube. Pure helium gas at a 
temperature of 450.degree. C. is flowed through the tube for one hour. The 
temperature of the helium gas stream is then reduced to 210.degree. C., at 
which point the gas composition is switched over to a 5% NH.sub.3 95% 
helium gas flowing through the tube at a temperature of 210.degree. C. 
After 30 minutes of this treatment, the gas composition is switched back 
to pure helium gas at 210.degree. C. Immediately after switching back to 
pure helium, measurement for NH.sub.3 in the exhaust gases is initiated 
using a calibrated Antek Nitrogen analyzer. Measurement continues as the 
pure helium gas input temperature is increased to 600.degree. C. and the 
cumulative amount of desorbed NH.sub.3 is determined. For purposes herein, 
low acidity support materials can be defined as those that desorb less 
than about 0.04 millimoles NH.sub.3 per gram of uncatalyzed support 
material, whereas high acidity support materials desorb more than about 
0.04 millimoles NH.sub.3 per gram. 
Compounds, preferably oxides of Group 4A and 4B elements (including Si, Ge, 
Sn, Pb, Ti and Zr), lanthanum oxide, yttrium oxide, magnesium oxide, 
calcium oxide and combinations thereof are preferred low acidity support 
materials. These materials are considered effective in facilitating the 
catalytic oxidation of non-halogenated carbonaceous compounds, such as 
carbon monoxide and volatile organic compounds. 
Support material compositions comprised of ZrO.sub.2, SiO.sub.2, TiO.sub.2, 
and combinations thereof are particularly preferred as low acidity support 
materials. Especially preferred is a refractory metal oxide composition 
comprised of ZrO.sub.2 and SiO.sub.2. The especially preferred low acidity 
support material contain from about 1% to about 30% weight percent 
ZrO.sub.2 and about 70% to 99% percent SiO.sub.2. Deeba et al. (U.S. Pat. 
No. 5,145,825, commonly assigned to the assignee of the instant invention) 
discloses useful support materials comprising silica, ZrO.sub.2 and/or 
TiO.sub.2 ; the entire disclosure of U.S. Pat. No. 5,145,825 is hereby 
incorporated by reference. 
In the case of a low acidity support material containing silica and another 
metal oxide compound, the support may be prepared by adding silica 
particles, such as in the form of a finely divided dry powder or in the 
form of a colloidal suspension to a soluble salt solution containing the 
other metal and allowing the solution to coat and/or impregnate the silica 
particles, and then calcining the mixture in air to convert the metal salt 
to the respective metal oxide. The support material prepared is in the 
form of a fine powder. 
Various materials are useful as high acidity support materials. Preferred 
high acidity support materials include gamma, delta or theta alumina and 
transitional forms thereof, acid-treated aluminas, zeolites and 
silica-alumina. Advantageous results have been obtained with the use of a 
commercially available gamma alumina powder with a surface area of 150 
m.sup.2 /g supplied by Condea, which desorbed about 0.07 millimoles 
NH.sub.3 per gram using the TDP test. 
The support materials can be thermally stabilized with oxides of cerium, 
barium, calcium and combinations thereof, using techniques well known in 
the art. Stabilization permits the support material to be subjected to 
more severe thermal conditions without adversely affecting the structure 
or activity of the catalyzed and stabilized support material. 
The support materials used in the practice of this invention may be 
prepared by means well known to those of ordinary skill in the art and 
include physical mixtures, coagulation, coprecipitation or impregnation. 
The preferred techniques for preparing the materials of this invention are 
coagulation and coprecipitation. For further details of these methods see 
U.S. Pat. No. 4,085,193 which is incorporated by reference for its 
teaching of techniques for coprecipitation and coagulation. Typically 
support materials prepared by the methods described are in the form of a 
fine powder. The support material can be used in powdered form. 
Alternatively, the support material in powdered form can be subsequently 
formed into larger particles and particulate shapes. The catalytic 
material may be applied to the support material prior to forming the 
support material into a particulate shape, or alternatively after the 
support is shaped into particulate form. The support material may be 
shaped into particulate or pellet form, such as extrudates, spheres and 
tablets, using methods well known in the art. For example, catalyzed 
support powder can be combined with a binder such as a clay and rolled in 
a disk pelletizing apparatus to give catalyst spheres. The amount of 
binder can vary considerably but for convenience is present from about 10 
to about 30 weight percent. 
The first and second catalyst of the present invention comprises a first 
and second catalytic material respectively. The first catalytic material 
can catalyze the reaction of non-halogenated carbonaceous material; and 
the second catalytic material catalyzes the reaction of at least the 
halogenated compounds. The preferred catalytic material is a catalytic 
metal or metal compound which can be dispersed onto the support materials 
by means well known in the art. A preferred method is impregnation, 
wherein the support material in particulate or powder form is impregnated 
with a solution containing a soluble compound of the catalytic metal or 
metals. The solution may be an aqueous solution, one using an organic 
solvent, or a mixture of the two. An aqueous solution is preferred. The 
soluble compounds of the metal (or metals) should decompose to the metal 
upon heating in air at elevated temperatures. 
Platinum group metals are preferred catalytic materials. Illustrative of 
suitable soluble platinum group compounds are chloroplatinic acid, 
ammonium chloroplatinate, bromoplatinic acid, platinum tetrachloride 
hydrate, platinum dichlorocarbonyl dichloride, dinitrodiamino platinum, 
amine solubilized platinum hydroxide, rhodium trichloride, 
hexaamminerhodium chloride, rhodium carbonylchloride, rhodium trichloride 
hydrate, rhodium nitrate, rhodium acetate, chloropalladic acid, palladium 
chloride, palladium nitrate, diamminapalladium hydroxide and 
tetraamminepalladium chloride. 
One convenient method of impregnation is to place the uncatalyzed support 
material in the form of granules into a rotary evaporator which is 
partially immersed in a heating bath. The impregnating solution which 
contains an amount of the desired metal compound to provide the desired 
concentration of oxide or metal in the finished catalyst is now added to 
the support material and the mixture cold rolled (no heat) for a time from 
about 10 to 60 minutes. Next, heat is applied and the solvent is 
evaporated. This usually takes form about 1 to about 4 hours. Finally, the 
solid is removed from the rotary evaporator and calcined in air at a 
temperature of about 400.degree. C.-600.degree. C. for about 1 to 3 
hours. If more than one catalytic metal is desired, they may be 
impregnated simultaneously or sequentially in any order. 
Alternatively, the support material in powder form is placed into a 
planetary mixer and the impregnating solution is added under continuous 
agitation until a state of incipient wetness is achieved. The powder is 
then dried in an oven for 4-8 hours and calcined from about 400.degree. 
C.-600.degree. C. for 1-3 hours. 
The catalyst of the instant invention may be used in any configuration, 
shape or size which exposes it to the gas to be treated. For example, the 
supported catalyst can be conveniently employed in particulate form or the 
supported catalyst can be deposited as a coating onto a solid monolithic 
substrate. In some applications when the particulate form is used it is 
desirable to provide a screen-like barrier that permits the flow of the 
gas stream but inhibits the movement of the solid particulates from one 
catalyst bed to the other. 
In circumstances in which less mass is desirable or in which movement or 
agitation of particles of catalyst may result in attrition, dusting and 
resulting loss of dispersed metals, or undue increase in pressure drop 
across the particles due to high gas flows, a monolithic substrate is 
preferred. In the employment of a monolithic substrate, it is usually most 
convenient to employ the supported catalyst as a thin film or coating 
deposited on the inert substrate material which thereby provides the 
structural support for the catalyst. The inert substrate material can be 
any refractory material such as ceramic or metallic materials. It is 
desirable that the substrate material be unreactive with the catalyst and 
not be degraded by the gas to which it is exposed. Examples of suitable 
ceramic materials include sillimanite, petalite, cordierite, mullite, 
zircon, zircon mullite, spodumene, alumina-titanate, etc. Additionally, 
metallic materials which are within the scope of this invention include 
metals and alloys as disclosed in U.S. Pat. No. 3,920,583 (incorporated 
herein by reference) which are oxidation resistant and are otherwise 
capable of withstanding high temperatures. For the treatment of gases 
containing halogenated organic ceramic materials are preferred. 
The monolithic substrate can best be utilized in any rigid unitary 
configuration which provides a plurality of pores or channels extending in 
the direction of gas flow. It is preferred that the configuration be a 
honeycomb configuration. The honeycomb structure can be used 
advantageously in either unitary form, or as an arrangement of multiple 
modules. The honeycomb structure is usually oriented such that gas flow is 
generally in the same direction as the cells or channels of the honeycomb 
structure. For a more detailed discussion of monolithic structures, refer 
to U.S. Pat. No. 3,785,998 and U.S. Pat. No. 3,767,453, which are 
incorporated herein by reference. In a preferred embodiment, the honeycomb 
substrate has about 50 to about 600 cells per square inch of 
cross-sectional area. In an especially preferred embodiment, the honeycomb 
has about 100 to about 400 cells per square inch. 
It is also within the scope of the invention that the monolith substrate 
consists of a crossflow-type monolith having a first plurality of passages 
defining a first flow path through the monolith and a second plurality of 
passages defining a second flow path through the monolith, segregated from 
the first flow path. The first and second catalyst beds of the dual bed 
devices of this invention may be disposed in the respective first and 
second flow paths of the crossflow monolith. 
If a monolithic form is desired, the catalyst of this invention can be 
deposited onto the monolithic honeycomb carrier by conventional means. For 
example, a slurry can be prepared by means known in the art such as 
combining the appropriate amounts of the supported catalyst of this 
invention in powder form, with water. The resultant slurry is typically 
ball-milled for about 8 to 18 hours to form a usable slurry. Other types 
of mills such as impact mills can be used to reduce the milling time to 
about 1-4 hours. The slurry is then applied as a thin film or coating onto 
the monolithic carrier by means, well known in the art. Optionally, an 
adhesion aid such as alumina, silica, zirconium silicate, aluminum 
silicates or zirconium acetate can be added in the form of an aqueous 
slurry or solution. A common method involves dipping the monolithic 
carrier into said slurry, blowing out the excess slurry, drying and 
calcining in air at a temperature of about 450.degree. C. to about 
600.degree. C. for about 1 to about 4 hours. This procedure can be 
repeated until the desired amount of catalyst of this invention is 
deposited on said monolithic honeycomb substrate. It is desirable that the 
supported catalyst of this invention be present on the monolithic carrier 
in an amount in the range of about 1-4 grams of supported catalyst per 
in.sup.3 of carrier volume and preferably from about 1.5-3 grams/in.sup.3. 
An alternative method of preparation is to disperse the catalytic metal or 
metals and such other optional components on a monolithic substrate 
carrier which previously has been coated with only uncatalyzed support 
material by the above procedure. The compounds of catalytic metal which 
can be used and the methods of dispersion are the same as described above. 
After one or more of these compounds have been dispersed onto the support 
material coated substrate, the coated substrate is dried and calcined at a 
temperature of about 400.degree. C. to about 600.degree. C. for a time of 
about 1 to 6 hours. If other components are desired, they may be 
impregnated simultaneously or individually in any order. 
An embodiment of this invention is a process for reacting or converting by 
oxidation non-halogenated carbonaceous compounds even in the presence of 
halogenated organic compounds present in a gas stream. The process 
comprises contacting the gas stream at a temperature of about 100.degree. 
C. to about 650.degree. C. and preferably at a temperature of about 
150.degree. C. to about 450.degree. C. with the first catalyst comprising 
a first catalytic material deposited on a low acidity support material. 
Preferably, this is followed by a second catalyst comprising a second 
catalytic material deposited on a high acidity support material. 
Processes of this invention, using either the single or dual bed devices, 
effectively treat, by catalytic reaction using the first catalyst, gaseous 
non-halogenated aliphatic and cyclic organic compounds including alkanes, 
alkenes and hetero compounds. Specific examples of such compounds commonly 
found in the waste gas streams of industrial processes include benzene, 
toluene, xylenes, phenol, ethyl alcohol, methyl acetate, methyl formate, 
isopropyl amine, butyl phthalate, aniline, formaldehyde, methyl ethyl 
ketone, acetone, etc. 
The process of this invention, using either the single or dual bed device, 
may also effectively treat carbon monoxide contained in the introduced gas 
stream. The gas stream may consist essentially of carbon monoxide as the 
sole carbonaceous compound or the CO may be present as a component in a 
gas stream also comprising other carbonaceous compounds and/or halogen 
compounds. 
The organohalogen compounds which can be treated, by catalytic reaction 
using the second catalyst, include halogenated compounds such as 
halogenated organic compounds. Some specific examples of halogenated 
compounds which can be reacted include chlorobenzene, carbon 
tetrachloride, chloroform, methyl chloride, vinyl chloride, methylene 
chloride, ethyl chloride, ethylene chloride, ethylidene dichloride, 
1,1,2-trichloromethane, 1,1,1-trichloromethane, methyl bromide, ethylene 
dibromide, trichloroethylene, tetrachloroethylene, polychlorinated 
biphenyls, chlorotrifluoromethane, dichlorodifluoromethane, 
1-chlorobutane, ethyl bromide, dichlorofluoromethane, chloroformic acid, 
trichloracetic acid and trifluoroacetic acid. 
Many gas streams already contain enough oxygen (O.sub.2) to oxidize all the 
pollutants, and most gas streams contain a large excess. In general, a 
large excess of oxygen greatly facilitates the oxidation reaction. In the 
event that the gas stream does not contain enough oxygen, oxygen, 
preferably as air, may be injected into the gas stream prior to contact 
with the first catalyst. The minimum amount of oxygen which must be 
present in the gas stream is the stoichiometric amount necessary to 
convert the carbon and hydrogen in the compounds present to carbon dioxide 
and water. For convenience and to insure that the oxidation reaction goes 
to completion, it is desirable that an excess of oxygen be present. 
Accordingly, it is preferable that at least two times the stoichiometric 
amount and most preferably at least five times the stoichiometric amount 
of oxygen be present in the waste gas stream. 
It is also understood that the process of the present invention is not 
dependent on the concentration of the organic compounds and/or the 
organohalogen compounds. Thus, gas streams with a very wide concentration 
range of pollutants can be treated by the instant process. The process of 
this invention is also applicable to processes wherein liquid 
organohalogen compounds and organic compounds are vaporized and mixed with 
oxygen. 
Particularly advantageous results are achieved with the dual and single bed 
devices of the invention wherein the feed gas stream comprises up to about 
1% and typically 0.01 to 1% carbon monoxide, up to about 2000 ppm and 
typically 50 to 2000 ppm volatile organic compounds, up to about 2000 ppm 
and typically 50 to 2000 ppm halogenated organic compounds, and about six 
times the stoichiometric amount of oxygen. Water may be present in the gas 
feed in an amount from less than 1% to greater than 15%. 
The invention has been found to be particularly useful in treating vent 
gases derived from industrial processes that make phthalic acid compounds 
such as terephthalic acid (TPA), purified terephthalic acid, isophthalic 
(IPA) acid and alizarinic acid from xylene via catalytic reactions that 
use bromine as an initiator. Similarly, trimellitic anhydride is made by 
catalytic processes from trimethylbenzene using bromine as initiator. 
Further, catalyzed reactions making dicarboxylic acids from dimethyl 
naphthalene also use bromine. The desired acid end-product of these 
reactions typically are recovered by condensation, leaving a vent gas 
waste stream comprised of various volatile organic compounds, such as 
toluene, xylene, benzene, methyl formate, acetic acid, alcohol, carbon 
monoxide and methyl bromide. Conventional treatment of vent gases from 
such industrial processes involve thermal incineration or catalytic 
oxidation comprising a catalytic metal on a high acidity support. Compared 
with conventional catalytic control, the processes and devices of this 
invention provide the advantage of effective catalytic oxidation of the 
vent gas constituents at reduced operating temperatures and/or catalyst 
volume and with a reduced tendency for coke formation. 
Another application of the invention involves treatment of volatile organic 
compounds and halogenated organic compounds, particularly chlorinated 
organic compounds such as chloroform and dioxin, derived from chlorine 
bleaching of pulp. 
The requirement of the catalyst bed volume for a given application is 
normally referred to as volume hourly space velocity (VHSV), which is 
defined as the ratio of gaseous hourly flow rate to the catalyst bed 
volume. In the practice of this invention, the volume hourly space 
velocity (VHSV) can vary substantially preferably from about 1,000 to 
about 100,000 hr..sup.-1 and more preferably from about 5,000 to about 
50,000 hr..sup.-1 based on gas rates calculated at standard temperature 
and pressure. For a fixed flow rate, the VHSV can be controlled by 
adjusting the size of the catalyst bed. 
The bed volume and loading levels of the catalytic components may be 
specifically sized and tailored to particular applications. In dual bed 
configurations, the relative bed volume and catalytically active metal 
loading levels of the first and second catalyst beds may be varied 
according to the specific conversion requirements of the treatment 
application. For example, a dual bed device may have a relatively larger 
volume of the second catalyst than the first catalyst when it is desired 
to have a very high destruction efficiency of halogenated organic 
constituents of the gas feed; whereas a device providing high efficiency 
for non-halogenated compounds and a lesser efficiency for halogenated 
organics may require a larger volume of the first catalyst and a smaller 
bed volume of the second catalyst. The loading levels of the catalytic 
metal material based on the metal (or metal in a metal compound) can 
similarly be varied according to requirements of the application. When 
honeycomb substrate form is used, typical catalytic metal loading can 
range from about 10 to about 200 grams catalytic metal per cubic foot 
substrate. 
Once the gas stream has been contacted with the catalyst and the pollutants 
destroyed, the catalyst treated gas stream may be further treated, if 
desired, to remove the halogen acid and any halogens which are formed 
during the conversion process. For example, the treated gas stream may be 
passed through a scrubber to absorb the acid. The scrubber may contain a 
base such as sodium or ammonium hydroxide which neutralizes the acids and 
solubilizes the halogens as basic hypolhalites and halides. 
The catalysts of the invention are active and stable. The catalysts can be 
thermally regenerated to remove deposits of carbonaceous coke by means 
well known in the art. Typically, oxygen at a temperature of about 
400.degree.-450.degree. C. is introduced to the device by way of the inlet 
duct. The exothermic reaction of coke combustion can increase temperatures 
within the catalyst bed(s) to at least about 600.degree. C. The catalysts 
of the invention and the activity of the catalysts is substantially 
unaffected by successive regeneration treatments. The thermal stability of 
a support material, such as alumina, can be further augmented with 
additions of ceria, barium, calcium and combinations thereof. 
Structural components of the devices of the invention, including the 
reactor chamber, transition cones, ducts and supporting elements are 
designed, using methods and materials well known in the art, to meet the 
severe operating conditions of temperature, pressure, turbulent flow and 
corrosivity encountered during catalytic operations and regeneration. Such 
conditions will vary substantially with the particular application. For 
example, the device may be designed to be subjected to operating pressures 
of ambient pressure (0 psig) to greater than 300 psig. 
The advantage of the present invention is believed to be attributable to 
low acidity materials having little adsorption affinity for halogen 
compounds at temperature of 100.degree. to 600.degree. C. High acidity 
support materials interact with the halogen compounds, and the presence of 
surface acidity and/or surface hydroxy groups on such high acidity 
supports promote the adsorption and breakage of halogen compounds. While 
not being limited to this interpretation, it is considered that in a gas 
stream comprising halogen compounds and other carbonaceous compounds, such 
as volatile organic compounds (VOC's) and/or carbon monoxide, the halogen 
compounds are preferentially adsorbed onto high acidity support materials, 
thus reducing the accessibility of active sites to VOC and CO compounds. 
Additionally, the attachment of halogens to the solid further increases 
surface acidity thereby increasing the tendency for agglomeration of 
catalytic material (sintering) and/or promoting the formation of coke 
deposits, especially if unsaturated hydrocarbons such as aromatic 
compounds, alkenes, alkynes, etc. are present. Both sintering and coking 
contribute to shortening catalyst life. Due to the reduced catalyst 
activity, higher operating temperatures and/or larger amounts of catalyst 
are needed to treat carbonaceous gas streams containing halogenated 
organic compounds with a single bed high acidity catalyst than with the 
dual bed device of the present invention. 
In the examples herein below, the first and second catalyst components in 
the dual bed device have the same substrate volume and metal loading 
levels, however, this is not to be considered as limiting to the device of 
the invention. Various embodiments of the invention are described 
hereinbelow. The description and examples are not intended as limiting, as 
modifications will be apparent to those skilled in the art. 
EXAMPLE I: Preparation of Catalysts 
A first catalyst was prepared from a first catalytic material deposited on 
a low acidity support material, and a second catalyst was prepared from a 
second catalytic material deposited on a second high acidity support 
material. 
The low acidity support material was composed of 25% ZrO2 and 75% SiO2 and 
was prepared by mixing dry SiO2 powder (Davision Syloid 74) into a 
zirconia acetate solution (from MEI). The slurry was then spray dried and 
calcined for about an hour at 1300.degree. F. to produce a powdered 
support material ready for impregnation by the platinum solution. The 
Zr/Si powder had a BET surface area of 208 m.sup.2 /g. The high acidity 
catalyst support was a gamma alumina powder with a BET surface area of 150 
m2/g (supplied by Condea). 
The alumina and Zr/Si uncatalyzed support materials were tested by the 
temperature programmed desorption (TPD) method for acidity; the alumina 
powder desorbed 0.07 moles NH.sub.3 /g and the Zr/Si support desorbed 0.02 
moles/g. Conventional pyridine IR analysis indicates that Lewis acid sites 
are the predominant source of acidity in both the alumina and Zr/Si 
materials. The Bronsted to Lewis acid cites were measured with the 
following results: Zr/Si--0.1, alumina--0.0. 
The batches of low acidity and high acidity catalyst support materials in 
the form of fine powder were each impregnated with an aqueous platinum 
solution (amine solubilized H.sub.2 Pt(OH)6). 
After impregnation by the platinum solution, the supports were treated with 
acetic acid to fix the platinum onto the support, followed by drying at 
100.degree. to 120.degree. C. The catalyzed support material, commonly 
referred to as frit, contained about 1.5 to 4.0 wt % platinum. 
After Pt fixation, the frit was then mixed with deionized water to form a 
25%-35% solids slurry. The slurry was then ball milled to so that about 
90% of the solids (by weight) had a particle size of less than 10 microns. 
Blocks of cordierite honeycomb substrate having 200 cell per square in 
(supplied by Corning) were washcoated with a slurry comprising either the 
catalyzed Zr/Si frit or the catalyzed alumina frit. Target loading levels 
of 1.4 to 2.0 grams frit (dry basis) per cubic inch substrate were 
adjusted to achieve a target platinum metal loading (e.g. 80 grams 
platinum metal) per cubic foot substrate. The catalyzed substrates were 
then dried at 100.degree. C. for two hours and then calcined at about 
450.degree. C. for one hour. Subsequently, the catalyzed substrate blocks 
were then drill cored coaxial to the cell axis to obtain cylindrical 
sections for the tests of Example 2. 
EXAMPLE 2: Performance Tests For Catalysts Systems 
Three catalyst configurations using the materials described in Example 1 
with a target platinum metal loading of 80 grams/cubic foot honeycomb 
substrate were prepared for laboratory testing to determine the 
effectiveness of the configurations. Two of the configurations were single 
bed systems and one configuration was a dual bed configuration. 
One catalyst system, designated Pt/Al, used a 1" diameter by 1.5" long 
cylindrical core of honeycomb substrate wash coated with the frit of 
platinum on the high acidity alumina support material. The second catalyst 
system, designated Pt/Zr/Si, used a 1" diameter by 1.5" long core of 
honeycomb substrate wash coated with the frit of platinum on the ZrO2/SiO2 
support material. 
The third catalyst configuration, the dual bed configuration, included two 
aligned catalyzed substrate cores. The core aligned in the upstream 
position within the bed, thus the first of the two catalyzed components to 
be contacted by the introduced gaseous mixture, was a 1" diameter by 0.75" 
long core of substrate coated with the frit of platinum on the low acid 
ZrO2/SiO2 support. The downstream or second component in the configuration 
was a 1 inch diameter by 0.75 inch long core of substrate washcoated with 
the frit of platinum on the high acid alumina support. This dual catalyst 
system is designated C in Table 1 below. 
In each case, the catalyzed cores were placed in a quartz reactor vessel 
and aligned such that the introduced gaseous stream was constrained to 
flow through the longitudinal passages of the honeycomb substrate. 
Catalytic performance of these three catalyst configurations were 
determined by comparing their effectiveness in decreasing the 
concentrations of carbon monoxide, toluene and methyl bromide in a feed 
gas containing 7000 ppm CO, 1000 ppm toluene, 3% O.sub.2, 1.5% H.sub.2 O 
and 50 ppm methyl bromide. The test space velocity (the ratio of gas flow 
to catalyst volume) was maintained at a constant rate of 30,000 1/hr for 
each of the three configurations through the testing cycle. The 
temperature of the gaseous stream introduced to the reactor was controlled 
by a pre-heating unit. Starting an initial gas temperature of about 
150.degree. C., the temperature of the gaseous stream was incrementally 
increased over a period of about 24 hours to about 450.degree. C. Gas 
temperatures were held constant to allow the composition of the outlet 
gases to stabilize prior to measurement. Gas concentration measurements 
were made by GC analysis of gas samples taken from immediately before and 
after the reactors's inlet and outlet passages, respectively. The 
effectiveness of removing carbon monoxide, toluene and methyl bromide via 
conversion to less harmful compounds was then calculated with the 
following expression: 
% Conversion=(Inlet conc.--outlet conc.)/Inlet conc. * 100 
The data obtained, in % conversion, from this testing are summarized as 
follows: 
TABLE 1 
__________________________________________________________________________ 
PERCENT CONVERSION OF FEED STREAM COMPONENTS 
Pt/Al Pt/Zr/Si C 
.degree.C. 
Tol 
CO MeBr 
Tol CO MeBr 
Tol CO MeBr 
__________________________________________________________________________ 
150 2 36 2 0 37 0 
200 31 93 6 37 93 20 
225 73 95 7 75 97 49 
250 55 44 7 90 98 20 89 98 75 
275 73 77 43 94 99 29 99+ 
99+ 
95 
300 94 97 77 97 99+ 
36 
350 98 99+ 
58 
__________________________________________________________________________ 
Configuration C: Pt on low acidity Zr/Si support followed by Pt on high 
acidity alumina support. 
The data indicate that within the temperature of about 225.degree. C. to 
about 275.degree. C., the Pt/Zr/Si catalyst substantially (at least about 
70%) converts the CO and toluene components of the gas stream, while the 
methyl bromide component remains substantially unconverted (conversion of 
less than about 30%). To achieve a similar level of CO and toluene 
conversion in the presence of methyl bromide as the Pt/Zr/Si catalyst, the 
Pt/Al catalyst must operate at substantially higher operating temperature 
(or lower space velocities). 
It is also noted that Pt/Zr/Si is about as effective as the dual bed 
configuration C in removing carbon monoxide and toluene. However, the dual 
bed, Pt/Zr/Si+Pt/Al, was the most effective in removing all the gaseous 
compounds simultaneously, providing greater than 95% conversion of the 
three gaseous compounds at about 275.degree. C. whereas both single bed 
configurations would require temperatures in excess of 350.degree. C. to 
provide similar conversion levels. 
EXAMPLE 3 
The catalytic performance of single bed Pt/Al and Pt/Zr/Si configuration 
described in Example 1 above, were tested with gas streams consisting of 
7000 ppm carbon monoxide, 1000 ppm toluene, 3% O.sub.2 and 1.5% H.sub.2 O 
both with and without the 50 ppm methyl bromide component. As above, space 
velocities were maintained at 30,000 1/hr through the testing cycle. The 
results are depicted graphically in FIG. 3. With no methyl bromide 
present, both single bed catalyst configurations gave very high 
efficiencies of carbon monoxide removal. With 50 ppm methyl bromide 
present, the activity of the Pt/Al catalyst for CO was substantially 
suppressed and significantly higher operating temperatures were required 
to achieve the same level of CO removal e.g. about 60.degree. C. higher at 
70% conversion level and about 210.degree. C. higher at 99+% conversion 
level. 
The CO activity for the low acidity Pt/Zr/Si catalyst was less affected by 
the presence of methyl bromide, requiring feed gas operating temperatures 
of only about 25.degree. C. higher for 70% conversion, and about 
45.degree. C. higher for 99.sup.+ % conversion, as compared to the feed 
gas lacking methyl bromide. 
Modifications, changes and improvements to the preferred forms of the 
invention herein disclosed, described and illustrated may occur to those 
skilled in the art who come to understand the principles and precepts 
thereof. Accordingly, the scope of the patent to be issued hereon should 
not be limited to the particular embodiments of the inventions set forth 
herein, but rather should be limited by the advance of which the invention 
has promoted the art.