Catalysts and method

An improved catlayst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HC1 and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

BACKGROUND OF THE INVENTION 
The present invention relates generally to catalysts and methods for 
converting light hydrocarbons into monohaloalkanes and other useful 
products. In particular, the invention is directed to the production of 
monochloromethane and formic acid from methane. As has been described in 
the inventors' prior U.S. Pat. No. 4,769,504, entitled "Process for 
Converting Light Alkanes to Higher Hydrocarbons", issued Sept. 6, 1988, 
monochloromethane so produced can be further processed to form gasoline 
boiling range hydrocarbons. This prior U.S. patent is hereby incorporated 
by reference for describing this process. 
The need to supplement petroleum supplies has stimulated research and the 
production of chemicals and fuels from other sources. Methane from natural 
gas and from the conversion of coal is a source of considerable interest 
for such production. 
It is well known that methane can be converted to methanol by reformation 
with steam and that the methanol thus produced can be further processed 
over a crystalline aluminosilicate catalyst to form gasoline boiling range 
hydrocarbons. Such a process is described in U.S. Pat. No. 3,928,483 to 
Chang et al. 
Monohalomethanes can be prepared as disclosed in European Patent 
Application No. 0117731 and as suggested in PCT Publication No. 
W085102608, converted to higher hydrocarbons over crystalline 
aluminosilicates. It has long been thought that the monohalides are much 
preferred in such processes with only low levels of polyhalogenated 
alkanes tolerated for effective conversion. Such monohalomethanes can be 
produced by reaction of chlorine or other halogens with methane which 
requires elevated temperatures above 450.degree. C. or by the 
oxyhalogenation of methane using a suitable catalyst such as the halide 
salts of copper, nickel, iron or palladium. Such procedures as are 
described in the above cited European Patent Application are characterized 
by low conversions, generally less than about 35%. 
An oxyhydrochlorination catalyst containing copper chloride, potassium 
chloride and a rare earth chloride is disclosed in U.S. Pat. No. 4,123,389 
to Pieters et al. This catalyst is reported to provide substantially 
higher values of methane conversion, but to result in substantial 
polychlorination. Previously, this catalyst was of particular interest in 
the production of carbon tetrachloride as a feed stock for 
chlorofluorocarbon-refrigerants. 
This invention also relates to the production of formic acid as a 
co-product to monohalide alkanes. Typically, formic acid is produced by 
the reaction of sulfuric acid with sodium formate in the presence of 
85-90% formic acid. Adequate cooling of the reaction mixture and the 
presence of the added formic acid as a reaction medium limits 
decomposition of the product. Sodium formate is formed by the reaction of 
sodium hydroxide and carbon monoxide, such as from producer gas that is 
carefully cleaned and compressed to 12-18 atmospheres. The sodium formate 
crystals are obtained by drying the reaction product prior to reaction 
with the sulfuric acid. 
The major commercial use of formic acid is in the textile and leather 
industries as an effective disinfectant and preservative. It acts as a dye 
exhausting agent for various fabrics and for other functions in dying and 
treating textiles. Formic acid serves as an intermediate in the 
preparation of various esters and amides. Methyl and ethyl formate have 
value as solvents, fumigants and pesticides. Formamide is of particular 
interest as it has considerable value in the manufacture of 
pharmaceuticals, agricultural chemicals and dyes. 
SUMMARY OF THE INVENTION 
Therefore, in view of the above, it is an object of the present invention 
to provide a process for the coproduction of monohalomethanes and formic 
acid. 
It is also an object of the invention to provide a method for the 
production of monochloromethane with recoverable concentrations of formic 
acid. 
It is a further object of the invention to provide a catalyst for the 
production of monochloromethane with limited production of 
polychloromethanes. 
It is likewise an object of the invention to provide a two-stage conversion 
process of methane to gasoline range hydrocarbons with a co-product of 
formic acid. 
It is a further object of the invention to provide oxyhydrochlorination 
catalysts for the co-production of monochloromethane and formic acid. 
It is also an object of the invention to provide an improved 
oxyhydrochlorination catalyst for the conversion of methane to 
monochloroalkanes with enhanced methane conversion and reduced production 
of polychloromethanes. 
In accordance with the present invention, a catalytic method for the 
production of monochloromethane with recoverable concentrations of formic 
acid in aqueous solution with limited polychloromethane production 
includes providing an oxyhydrochlorination catalyst with a pyrogenic 
support material carrying a first layer of catalyst including a metal 
chloride deposited on the support. The metal chloride selected is from the 
group of chlorides including cobalt, lead, nickel and silver. A second 
catalyst layer includes alkali metal chlorides and permissibly a rare 
earth chloride deposited on the support. The catalyst is contacted with a 
reactant gas mixture containing methane, HCl and oxygen at reactant 
conditions to produce a normalized carbon-product distribution of at least 
20 mol % formic acid and with monochloromethane in excess of the total 
polychloromethane production. 
In other aspects of the invention, the formic acid is separated from other 
carbon products by condensation in a formic acid-water solution and 
concentrated to a constant boiling composition of formic acid and water. 
Concentrations in the range of 75-90% formic acid are obtained by 
fractional distillation, azeotropic distillation and solvent extraction. 
In one other aspect of the invention, the gas mixture contacts a catalyst 
at a temperature of about 300.degree. C. to 450.degree. C. for a residence 
time of about 7-10 seconds. 
After separating the monochloromethane from aqueous formic acid, it can be 
dried and reacted over a crystalline aluminosilicate catalyst to produce 
hydrocarbons in the C5 to C10 gasoline boiling point range. HCl produced 
in the second reaction can be recycled to the oxyhydrochlorination 
catalysts for further production of monochloromethane. 
The invention also comprehends an oxyhydrochlorination catalyst for the 
co-production of monochloromethane and formic acid from methane. The 
catalyst in major proportion is a metal chloride selected from the 
chlorides of cobalt, nickel, lead and silver along with a minor proportion 
of alkali metal chlorides permissibly including a rare earth chloride. The 
active catalyst materials are supported on a pyrogenic carrier selected 
from silica titania and alpha alumina. Preferably, the catalyst employs 
cobaltous chloride in about 40-60 weight % along with 10-20 weight % of a 
mixture of potassium chloride and lanthanum chloride supported on a silica 
carrier at about 20-40 % by weight.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1 wherein oxyhydrochlorination reactor 11 is provided 
with a feed of HCl 13, methane 15 and oxygen 17 for reaction over an 
oxyhydrochlorination catalyst. The catalyst is selected particularly for 
the co-production of monochloromethane and formic acid with limited 
production of polychloromethanes such as dichloromethane, trichloromethane 
and carbon tetrachloride. The inventors have found that the chlorides of 
cobalt, nickel, lead and silver are particularly advantageous for this 
purpose. Preferably, for the balanced production of monochloromethane and 
formic acid, cobaltous chloride is selected as the catalyst. The active 
metal chloride is supported on a pyrogenic oxide such as silica, titania 
or alpha alumina as a first layer and is coated with a second layer of an 
alkali metal chloride such as potassium chloride and permissively a minor 
proportion of the rare earth chloride. The resulting product containing 
monochloromethane, formic acid and water in principal amounts along with 
minor amounts of dichloromethane, trichloromethane and carbon dioxide is 
passed into a separator 19 wherein the formic acid and water is condensed 
from the monochloromethane and other carbon containing products. 
As is described in the above cited U.S. Pat. No. 4,769,504, the 
monochloromethane is thoroughly dried and passed on to a second reactor 21 
containing a zeolite catalyst for producing gasoline boiling range 
fraction products 23 (within the C-5 and C-10 range) and light 
hydrocarbons 25 (C-3 and C-5 range). HCl released in this reaction is 
separated and recycled to the oxyhydrochlorination reactor 11 for reaction 
with additional methane and oxygen. Permissibly, the light hydrocarbons or 
a portion thereof, also may be recycled to the oxyhydrochlorination 
reactor for further processing. 
It is advantageous to include minor proportions of polychloromethanes or 
other polychloroalkanes to be condensed over the zeolite catalysts as they 
may promote formation of aromatic and branched-chain hydrocarbons in the 
product. However, the inventors have found that polychloroalkanes 
approaching the concentration of the monochloromethane can have a 
deleterious effect on the zeolite catalyst. This has been a disadvantage 
of the copper based oxyhydrochlorination catalysts as they tend to produce 
polychlorinated alkanes up to and in excess of the monochloromethane 
product. Accordingly, it is preferred that the normalized product 
distribution based on carbon include monochloromethane in excess of the 
total molar concentration of the more highly chlorinated hydrocarbons. 
Water and formic acid separated from the chlorinated hydrocarbons at 29 are 
passed on to a fractionation process 31 in which water 33 is separated 
from the more highly concentrated formic acid product 35. Typically, 
formic acid concentration of 20-30% in water can be separated by 
condensation from the reaction products produced with a cobalt chloride 
catalyst. In contrast, the condensation product corresponding to flow 29 
in a process using a copper-based oxyhydrochlorination catalyst will 
include economically unrecoverable concentrations of formic acid of only 
about 0.5-2%. With the copper catalyst not only is less formic acid 
produced, but also a greater proportion of water is produced in the 
reactions leading to the polychloroalkanes. 
The following four reactions show the conversion of methane to 
monochloromethane, dichloromethane, trichloromethane and to formic acid. 
It is seen that the production of the polychloromethanes adds increasing 
amounts of water into the product stream that must subsequently be 
removed. 
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METHANE CONVERSION REACTIONS 
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CH.sub.4 + HCl + 1/2 0.sub.2 .fwdarw. CH.sub.3 Cl + H.sub.2 O 
CH.sub.4 + 2HCl + 0.sub.2 .fwdarw. CH.sub.2 Cl.sub.2 + 2H.sub.2 O 
CH.sub.4 + 3HCl + 3/2 0.sub.2 .fwdarw. CHCl.sub.3 + 3H.sub.2 O 
CH.sub.4 + 3/2 O.sub.2 .fwdarw. CH.sub.2 O.sub.2 + H.sub.2 O 
______________________________________ 
Advantageously, nickel, lead and silver catalysts provide even higher 
concentrations of formic acid typically in excess of 40 mol %. 
These aqueous solutions of formic acid can be readily concentrated to 
constant boiling mixtures of formic acid containing between 75 and 85% 
acid depending on the pressure of fractionation. Azeotropic distillation 
with propyl formate gives a non-aqueous phase which can be further 
distilled to yield anhydrous formic acid. The separated aqueous phase 
typically will contain less than about 1% formic acid. Such methods for 
separating formic acid are described in Louderback, Formic Acid and 
Derivatives, KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, 2nd ED., 
Vol. 10, pages 99-113. 
The following examples are presented merely by way of illustration and are 
not intended to limit the invention beyond that defined in the claims. 
EXAMPLE I 
An oxyhydrochlorination catalyst containing cobalt chloride was prepared by 
thoroughly dissolving cobaltous chloride, CoCl.sub.2 in acetonitrile, 
CH.sub.3 CN. Particulate silicon dioxide (Cab-O-Sil.RTM. HS-5) was added 
to the solution with swirling followed by standing overnight to thoroughly 
impregnate the cobaltous chloride into the silicon dioxide support. The 
acetonitrile was then slowly evaporated under aspiration with slow 
rotation over a period of about four hours. The temperature was increased 
slowly to 60.degree. C. and then held to prevent any rapid boiling that 
could interfere with the uniform distribution of the catalyst into the 
support. The resulting blue solid was then slowly dried under vacuum 
overnight at a temperature of 90.degree.-110.degree. C. Potassium chloride 
(KCl) and lanthanum chloride (LaCl.sub.3) were dissolved in 98% formic 
acid and this solution was added to the cobaltous chloride-silica powder 
and allowed to stand overnight. The formic acid was then evaporated under 
aspiration with rotation until a tacky solid was formed. The rotation was 
stopped and the temperature slowly increased to 60.degree. C. and held 
until all of the formic acid was removed. The resulting blue solid was 
dried overnight under vacuum at a temperature of 90 .degree. to 
110.degree. C. The blue powder as thus formed included a first layer of 
crystalline cobaltous chloride uniformly distributed on the silica support 
with a second layer of potassium chloride and lanthanum chloride deposited 
over the cobaltous chloride. 
Scanning Electron Photomicrography has shown that the catalysts in their 
most active forms have crystalline materials on their surfaces and that 
catalysts of the same chemical composition with lesser activities have 
less crystalline materials on their surfaces. It has been found that the 
surface topography of these catalysts, and thus their activities, is 
directly related to the method of preparation. In order to make the more 
active catalysts with highly crystalline surfaces, great care must be 
taken during the evaporation of the various solvents when layering the 
supports with the metal chlorides. High solvent evaporation rates and 
rapid tumbling during evaporation lead to materials with lower surface 
crystallinity and lower catalytic activity. 
EXAMPLE II 
A lead oxyhydrochlorination catalyst was prepared in much the same way 
Example I except lead acetate (Pb(OAc).sub.2) was dissolved in methanol to 
be deposited onto the silica support. After drying the resulting white 
solid it was exposed to gaseous hydrochloric acid (HCl) for sufficient 
time to convert the lead acetate to lead chloride (PbCl.sub.2). A second 
catalytic layer of potassium chloride and lanthanum chloride was then 
deposited in much the same manner as described in Example I. 
Various other oxychlorination catalysts in accordance with the present 
invention as well as copper chloride and blank catalysts were prepared for 
comparison in a manner similar to that described in Examples I and II. The 
catalysts compositions are given below in Table I. 
TABLE I 
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CONSTITUENTS BY WEIGHT 
% METAL 
CATALYST CHLORIDE % SiO.sub.2 
% KCl % LaCl.sub.3 
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Cu 41.66 37.50 11.46 9.38 
Co 55.17 28.82 8.81 7.20 
Ni 58.46 26.70 8.16 6.68 
Pb 66.96 21.24 6.49 5.31 
Ag 44.73 35.53 10.86 8.88 
Pt 41.66 37.50 11.46 9.38 
Cr 56.24 28.12 8.61 7.03 
BLANK 0.00 64.29 19.64 16.07 
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EXAMPLE III 
An oxyhydrochlorination catalyst as described in Example I with cobaltous 
chloride in an amount of about 3 grams was exposed to equal flows of 
methane and HCl (4.0 milliliters/minute) and about one half that flow (2.0 
milliliters/minute) of oxygen diluted with 2 milliliters per minute of 
nitrogen at about 340.degree. C. and a residence time of 8.3 seconds. The 
flow was continued for over 48 hours resulting in a methane conversion of 
about 61%, HCl conversion of about 53% and an oxygen conversion of about 
85%. 
Similar runs made with various other catalysts were conducted and the 
reactant conversions given below in Table II. 
TABLE II 
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REACTANT CONVERSION 
% CH.sub.4 % HCl % O.sub.2 
CATALYST CONV CONV CONV 
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Cu 47.69 80.08 83.86 
Co 61.03 52.54 85.48 
Ni 19.31 19.81 11.11 
Pb 5.51 14.86 9.41 
Ag 4.54 7.95 14.03 
Pt.sup.a 54.34 0.01 3.10 
Pt.sup.b 7.36 3.29 6.56 
Cr 13.15 3.54 33.21 
BLANK 16.16 6.63 25.31 
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Each of the catalysts, other than platinum, maintained nearly constant 
conversion over the full period. The platinum catalyst was found to 
degrade substantially after 48 hours of reaction. Subsequent tests with 
the other catalysts conducted for over 400 hours showed the cobalt, 
nickel, lead and silver catalysts to be stable over the full time period. 
FIG. 5 illustrates the constant conversion rates for the cobaltous 
chloride catalyst. The lower conversion percentages are attributed to a 
more rapid stripping of the acetonitrile than that described in Example I 
resulting in less crystalline CoCl.sub.2 deposited. 
Unexpectedly, the cobalt chloride catalyst was found to have higher 
selectivity for monochloromethane in preference to polychloromethanes of 
any of the catalysts tested. In addition, this catalyst produced 
substantial amounts of formic acid within the aqueous phase. 
Nickel, lead and silver catalysts also produced advantageous results with 
high selectivity for formic acid and good selectivity of monochlormethane 
over the polychloromethanes. The performance of the PbCl.sub.2 catalyst is 
illustrated in FIGS. 7 and 8 where increased conversion of methane with 
good selectivity for monochloromethane is obtain at temperatures of 
350.degree.-450.degree. C. 
The results of the normalized carbon distribution of he various catalysts 
are listed below in Table III. 
TABLE III 
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NORMALIZED CARBON PRODUCT DISTRIBUTION 
CATALYST 
CH.sub.3 Cl 
CH.sub.2 Cl.sub.2 
CHCl.sub.3 
CCl.sub.4 
CO CO.sub.2 
HCOOH 
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Cu 30.03 
39.42 
9.39 
0.14 
0.00 
12.44 
8.58 
Co 44.31 
12.44 
1.32 
0.00 
0.00 
3.67 
38.26 
Ni 23.0 3.78 0.00 
0.00 
0.00 
0.00 
73.19 
Pb 20.97 
3.49 0.37 
0.00 
0.00 
0.00 
75.17 
Ag 12.71 
1.37 0.09 
0.00 
0.00 
14.52 
71.31 
Pt.sup.a 
31.26 
3.49 0.30 
0.18 
0.00 
17.35 
47.42 
Pt.sup.b 
28.96 
3.28 0.42 
0.14 
0.00 
10.75 
56.45 
Cr 10.92 
2.66 0.60 
0.00 
64.77 
21.05 
0.00 
BLANK 10.10 
0.45 0.09 
0.00 
69.55 
7.02 
12.78 
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.sup.a After 24 hours. 
.sup.b After 48 hours. 
As stated above, it is of advantage to minimize the polychloromethane 
production in order to protect the catalysts. It is also of note that 
limiting the polychloromethane production also limits water production 
that must be removed in recovering the formic acid product. 
It is therefore seen that the present invention provides an improved method 
for the production of monochloromethane and other chlorinated alkanes from 
methane. The methane can be provided from natural gas supplies or from 
that which ordinarily is removed in a coal gasification process. Through 
use of one of the selected oxyhydrochlorination catalysts in accordance 
with the invention increased selectively of monochloromethane over 
polychloromethanes is achieved along with the production of economically 
recoverable quantities of formic acid. Using a straight forward 
condensation separation, formic acid concentrations of 20-30% and higher 
can be obtained for subsequent further concentration by fractionation or 
azeotropic distillation. Improved conversions of the methane are achieved 
through use of the cobaltous chloride catalyst to enhance productivity in 
a second reaction over zeolite for the production of gasoline boiling 
fractions with recycle of release HCl. 
Although the invention is described in terms of specific embodiments and 
process parameters, it will be clear to one skilled in the art that 
various modifications in the procedures and materials can be made within 
the scope of the following claims.