Conversion of methanol into hydrogen and carbon monoxide

A gas stream containing methanol is contacted with a catalyst including nickel and potassium supported on an alumina carrier, whereby the methanol is converted into hydrogen and carbon monoxide.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the catalytic conversion of 
methanol into hydrogen and carbon monoxide. 
There are increasing demands for hydrogen and carbon monoxide in many 
fields and methanol is now an important starting material therefor in that 
it can give hydrogen and carbon monoxide through catalytic decomposition. 
In an internal combustion engine, the waste heat generated therefrom can 
be utilized for the catalytic conversion of methanol into hydrogen and 
carbon monoxide, the mixed gas product being introduced into the engine as 
at least a part of the fuel. This method has advantages not only from an 
economic point of view but also from the standpoint of preventing 
pollution since the discharge of nitrogen oxides and carbon monoxide may 
be significantly reduced. 
Catalytic conversion of methanol is also utilized in a fuel cell, in which 
an oxygen-containing gas is supplied to the anode and a fuel, preferably 
hydrogen, is supplied to the cathode. The reaction between the anode and 
cathode can produce an electrical energy. The hydrogen may be produced 
from methanol. Thus, methanol is catalytically converted into hydrogen and 
carbon monoxide, the latter being further reacted with water to yield 
hydrogen and carbon dioxide by water gas reaction. The hydrogen obtained 
in the two-stage process is separated from carbon dioxide for introduction 
to the cathode. 
In addition, hydrogen and carbon monoxide are used in a wide variety of 
chemical plants. For example, hydrogen is utilized for hydrogenation of 
organic compounds, hydrotreatment of heavy hydrocarbon oils, etc., and 
carbon monoxide is utilized for the production of carbonyl 
group-containing organic compounds. 
There is, therefore, a great demand for an effective process capable of 
converting methanol into hydrogen and carbon monoxide. A process is 
proposed in which a catalyst containing nickel, lanthanum and ruthenium 
supported on silica gel is used. Although the catalyst can exhibit a 
relatively high activity for the decomposition of methanol at an initial 
stage, the catalytic activity is gradually lowered as the reaction at 
about 300.degree. C. proceeds and the catalyst is considerably 
deteriorated after about several hours. A process is also known wherein a 
catalyst having copper and/or nickel supported on silica gel is used. This 
catalyst, however, is poor in resistance to heat and, moreover, is 
defective because with it undesirable by-products such as water and 
methane are formed at about 400.degree. C. or more. The term "formation of 
by-products" herein and hereinafter means the case where compounds other 
than methanol, hydrogen and carbon monoxide are contained in the reaction 
product in an amount of 10 vol % or more. The formation of by-products 
requires an additional step for the removal thereof and is not acceptable 
in practice. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a process 
which is devoid of the drawbacks of the prior art process. 
Another object of the present invention is to provide an effective process 
by which methanol may be decomposed into hydrogen and carbon monoxide 
while minimizing the formation of undesirable by-products such as dimethyl 
ether, methane, water, carbon dioxide and methyl formaldehyde. 
It is a further object of the present invention to provide a process in 
which the catalytic conversion of methanol can be performed in a stable 
manner for a long period of process time. 
In accomplishing the foregoing objects, there is provided in accordance 
with the present invention a process of decomposing methanol for the 
production of hydrogen and carbon monoxide, which comprises contacting a 
gas stream containing methanol with a catalyst including a carrier 
material of alumina, and nickel and potassium supported on the carrier 
material. The content of Ni is in the range of about 1-12 mg-atom per one 
gram of the carrier and the content of K is in the range of about 1-12 
mg-atom per one gram of the carrier. 
Other objects, features and advantages of the present invention will become 
apparent from the detailed description of the invention to follow. 
DETAILED DESCRIPTION OF THE INVENTION 
The process of this invention includes contacting a methanol-containing gas 
with a catalyst comprised of alumina as a carrier material and nickel and 
potassium carried on the carrier material. 
Any activated alumina may be suitably used as the carrier material. 
Illustrative of such activated alumina are .gamma.(gamma)-alumina, 
.kappa.(kappa)-alumina, .delta.(delta)-alumina, .eta.(eta)-alumina, 
.theta.(theata)-alumina, .rho.(rho)-alumina and .chi.(chai)-alumina. The 
alumina carrier preferably has a specific surface area of about 150-300 
m.sup.2 /g. 
Supported on the alumina carrier are nickel and potassium. The content of 
the nickel in the catalyst should fall within the range of about 1-12 
mg-atom (i.e. 58.7-704.4 mg) per 1 g of the alumina carrier. An amount of 
Ni below 1 mg-atom is insufficient to impart practically acceptable 
activity to the catalyst and, moreover, causes a danger of the formation 
of by-products. Above 12 mg-atom Ni, the catalytic activity is 
considerably lowered. The Ni content is preferably about 2-8 mg-atom. The 
content of the potassium in the catalyst should also fall within the range 
of about 1-12 mg-atom (i.e. 39.1-469.2 mg) per 1 g of the alumina carrier. 
An amount of K below 1 mg-atom causes the formation of by-products. Above 
12 mg-atom K, the catalyst becomes poor in activity. The K content is 
preferably about 2-8 mg-atom. 
The catalyst of this invention may be prepared in any known manner. For 
example, a water soluble nickel salt such as nickel nitrate is dissolved 
in water, with which an alumina carrier material is impregnated. The 
impregnated material is then dried and calcined in an atmosphere of 
oxygen. The calcination is preferably conducted while elevating the 
temperature stepwise from 100.degree. to 500.degree. C. The carrier 
material thus loaded with nickel is then impregnated with a solution 
containing a potassium compound such as potassium nitrate. The resulting 
impregnated material is subsequently dried and calcined in the same manner 
as described above to obtain a catalyst containing nickel and potassium 
carried on the carrier material. The catalyst may also be prepared by 
impregnating a carrier material with a solution containing both nickel and 
potassium compounds, followed by drying and calcination. 
In order to stabilize the catalytic performance, it is preferred that the 
thus obtained catalyst be subjected to a pretreatment with a reducing gas. 
The pretreatment, which may be performed either just after the calcination 
step or before conducting the methanol conversion process, includes 
heating the catalyst at a temperature of 200.degree.-500.degree. C., 
preferably 300.degree.-400.degree. C., for 1-15 hours in the atmosphere of 
a reducing gas such as hydrogen or methanol. 
The step of contacting a methanol-containing gas stream with the catalyst 
is carried out at a temperature of 200.degree.-600.degree. C., preferably 
250.degree.-500.degree. C. for 0.1-12 sec, preferably 1-10 sec. The 
content of the methanol in the gas stream can be 100%. The gas stream may 
contain an inert gas such as argon or nitrogen, however.

The following examples will further illustrate the present invention. 
EXAMPLE 1 
Nickel nitrate was dissolved in water to obtain an aqueous solution having 
a Ni content of 1 g/l. With the solution was impregnated a .gamma.-alumina 
carrier to obtain nickel-impregnated alumina. The impregnated alumina was 
dried and calcined at 500.degree.C. for 4 hours to obtain a 
nickel-carrying alumina having a Ni content of 2 mg-atom per one gram of 
the alumina carrier. The nickel-carrying alumina was then impregnated with 
an aqueous solution containing potassium nitrate and having a K content of 
1 g/l to obtain an impregnated material. The impregnated material was then 
dried and calcined in the same manner as above to obtain a nickel and 
potassium-carrying alumina catalyst having a Ni content of 2 mg-atom and a 
K content of 2 mg-atom per 1 g of the carrier. 
0.5 g of the thus obtained catalyst were packed in a reaction tube having 
an inner diameter of 9 mm, through which was streamed first a hydrogen gas 
at 500.degree. C. for 2 hours and then a mixed gas containing methanol 
vapor (partial pressure: 0.8 atm.) and argon (partial pressure: 0.2 atm.) 
at a flow rate of 12.4 ml/hour in terms of liquid methanol at 
300.degree.-350.degree. C. for 15 hours to stabilize the catalyst 
performance. After this pretreatment, a feed gas containing methanol vapor 
(0.5 atm.) and argon (0.5 atm.) was introduced into the reaction tube for 
contact with the packed catalyst layer at 350.degree. C. for 12 sec. The 
effluent gas was sampled for analyzing the conversion (decomposition) rate 
and the composition thereof. The results of the analysis are shown in 
Experiment No. 1 of Table 1. 
COMATIVE EXAMPLE 1 
Thirteen types of catalysts were prepared using nitrates of the metal 
components shown in Experiment Nos. 2-14 of Table 1 in the same manner as 
that in Example 1. The content of each of the catalyst metal components 
was 2 mg-atom per one gram of the alumina carrier. However, rhodium was 
contained in an amount of 0.05 mg-atom per one gram of the alumina carrier 
(Experiment No. 14) and no catalyst metal component was contained in the 
catalyst of Experiment No. 2. Each catalyst was subjected to pretreatment 
conditions in the same manner as that in Example 1 and, with the use of 
the pretreated catalyst, methanol was decomposed in the same manner as 
that in Example 1. The results were as shown in Experiment Nos. 2-14 of 
Table 1. 
TABLE 1 
__________________________________________________________________________ 
Catalytic 
Experiment 
metal Conversion of 
Composition of product (vol %) 
No. component 
methanol (%) 
Hydrogen 
Carbon monoxide 
Dimethyl ether 
Methane 
Water 
__________________________________________________________________________ 
1 Ni, 
K 52 65 35 0 0 0 
2 None 92 0 0 51 0 49 
3 K 9 4 2 47 0 47 
4 Ni 90 36 20 22 0 22 
5 Ti, 
K 2 
6 V, K 3 
7 Cr, 
K 5 70 30 0 0 0 
8 Mo, 
K 4 
9 Mn, 
K 1 
10 Fe, 
K 2 70 30 0 0 0 
11 Co, 
K 24 67 33 0 0 0 
12 Cu, 
K 5 70 30 0 0 0 
13 Zn, 
K 5.5 70 30 0 0 0 
14 Rh, 
K 20 67 33 0 0 0 
__________________________________________________________________________ 
As will be appreciated from the results shown in Table 1, whilst a high 
methanol conversion is attained when alumina is used by itself as catalyst 
(Experiment No. 2), the majority of the product is dimethyl ether and 
water and neither hydrogen nor carbon monoxide is produced. With a 
catalyst containing potassium alone as catalyst metal component 
(Experiment No. 3), methanol conversion is significantly lowered and no 
improvement in selectivity is seen as compared with the case of Experiment 
No. 2. With a catalyst containing nickel alone as catalyst metal component 
(Experiment No. 4), on the other hand, undesirable by-products are formed 
in large amounts. In contrast, the catalyst of the present invention 
containing both nickel and potassium (Experiment No. 1) exhibits both a 
high methanol conversion and an excellent selectivity to hydrogen and 
carbon monoxide. When the nickel is substituted with other metals 
(Experiment Nos. 5-14), satisfactory conversion is not obtained. 
EXAMPLE 2 
Methanol decomposition was conducted in the same manner as that in Example 
1 except that the pretreatment conditions were varied. Thus, in 
Experiments Nos. 15 and 16, Table 2 argon and hydrogen were used, 
respectively, in place of the hydrogen used in the pretreatment step of 
Example 1. In Experiment No. 17, the pretreatment was carried out by 
feeding a hydrogen gas to the reaction tube at 310.degree.-350.degree. C. 
for 15 hours. In Experiment No. 18, the pretreatment was performed by 
feeding the same mixed gas as used in Example 1 at 300.degree.-350.degree. 
C. for 15 hours. The results are shown in Table 2, together with those of 
Experiment No. 1. 
TABLE 2 
______________________________________ 
Conver- 
Experi- sion of Composition of product (vol %) 
ment Treatment methanol Carbon By- 
No. gas (%) Hydrogen 
monoxide 
products 
______________________________________ 
1 hydrogen, 52 65 35 0 
methanol 
15 argon, 79 67 33 0 
methanol 
16 oxygen, 55 67 33 0 
methanol 
17 hydrogen 61 64.5 35.5 0 
18 methanol 75 68 32 0 
______________________________________ 
The results in Table 2 indicate that pretreatment conditions have an 
influence upon the activity of the catalyst. It is seen that when the 
treatment with methanol is to be preceded by the high temperature 
treatment with other gases (Experiment Nos. 1, 15 and 16), the use of 
argon is preferable. 
EXAMPLE 3 
A catalyst having a Ni content of 4 mg-atom and a K content of 4 mg-atom 
per one gram of alumina was prepared in the same manner as described in 
Example 1. With the use of this catalyst, methanol was decomposed in the 
same manner as that in Example 1 except that argon was used in place of 
hydrogen in the pretreatment step and the catalytic conversion was 
performed at temperatures of 300.degree. C. (Experiment No. 19) and 
430.degree. C. (Experiment No. 20). The results are shown in Table 3. 
COMATIVE EXAMPLE 2 
Using silica gel as a carrier material, two types of catalysts were 
prepared in the same manner as that in Example 1. One of the catalysts 
contained nickel as its catalytic metal component in an amount of 4 
mg-atom per one gram of the silica gel carrier. The other catalyst 
contained nickel and potassium each in an amount of 4 mg-atom per one gram 
of the carrier. With the use of these catalysts, methanol was decomposed 
in the same manner as that in Example 3. The results are summarized in 
Experiment Nos. 21-24 of Table 3. 
TABLE 3 
__________________________________________________________________________ 
Conversion 
Catalytic Reaction 
of Composition of product (vol %) 
Experiment 
metal temperature 
methanol Carbon Carbon 
Dimethyl 
No. component 
Carrier 
(.degree.C.) 
(%) Hydrogen 
monoxide 
Methane 
Water 
dioxide 
ether 
__________________________________________________________________________ 
19 Ni, K alumina 
300 53 65 35 0 0 0 0 
20 430 100 59 32 5 0 4 0 
21 Ni Silica 
300 70 62 37 1 0 0 0 
22 gel 430 100 35 10 27 13 15 0 
23 Ni, K Silica 
300 32 70 30 0 0 0 0 
24 gel 430 100 46 15 15 12 12 0 
__________________________________________________________________________ 
As will be seen from Table 3, the nickel-carrying silica gel catalyst 
exhibits outstanding activity at 300.degree. C. (Experiment No. 21). With 
this catalyst, however, when the reaction temperature is raised so as to 
increase the conversion, the selectivity to hydrogen and carbon monoxide 
becomes considerably lowered and the yield of by-products increases 
(Experiment No. 22). This tendency is also observed in the case of the 
catalyst having both nickel and potassium carried on silica gel 
(Experiments Nos. 23 and 24). In contrast thereto, the catalyst of this 
invention can exhibit good catalytic activity even at a low temperature 
(Experiment No. 19) and excellent selectivity to hydrogen and carbon 
monoxide even at a high temperature (Experiment No. 20). 
EXAMPLE 4 
Catalysts having the various Ni and K contents indicated in Table 4 were 
prepared in the same manner as that in Example 1. Tests of catalytic 
conversion of methanol were carried out with these catalysts in the same 
manner as described in Example 1 at temperatures of 300.degree., 
350.degree., 400.degree. and 450.degree. C. The test results were as shown 
in Table 4. 
TABLE 4 
______________________________________ 
Content of catalytic 
metal component 
Conversion of methanol (%) 
Experiment 
(mg-atom/g-alumina) 
Reaction temperature (.degree.C.) 
No. Ni K 300 350 400 450 
______________________________________ 
25 0 2 2 9 24 -- 
26 1 2 29 75 95 -- 
27 2 2 34 79 98 -- 
28 4 0 58 83 93 98 
29 4 0.5 24 50 74 99 
30 4 1 28 67 98 100 
31 4 2 51 91 100 100 
32 4 3 51 89 99 100 
33 4 4 53 89 98 100 
34 4 5 40 79 96 96 
35 4 6 42 81 96 99 
36 4 8 44 81 96 97 
37 4 12 33 71 94 99 
38 6 2 60 91 100 100 
39 8 2 51 87 100 100 
40 8 8 44 78 93 97 
41 12 4 45 85 100 100 
______________________________________ 
It will be appreciated from the results in Table 4 that the catalyst 
containing potassium alone (Experiment No. 25) fails to show practically 
acceptable methanol conversion activity at any temperatures. Moreover, as 
shown in Table 1, Experiment No. 3, considerably large amounts of 
by-products are produced. While the catalyst having nickel alone 
(Experiment No. 28) can show high methanol decomposition activity, the 
yield of by-products is very high as shown in Table 1, Experiment No. 4. 
This is also the case with the catalyst having a K content of 0.5 mg-atom 
(Experiment No. 29). The other catalysts shown in Table 4 can exhibit 
practically acceptable methanol decomposition activity at suitably 
selected temperatures and can show good selectivity to hydrogen and carbon 
monoxide. Especially, the catalysts having 2-8 mg-atom each, of Ni and K 
contents are very advantageous because they can exhibit satisfactory 
activity at a temperature of 350.degree. C. while substantially preventing 
the formation of by-products (Experiments Nos. 27, 31-36 and 38-40). 
EXAMPLE 5 
The same type of catalyst as employed in Example 4, Experiment No. 33, was 
used in this example. The catalyst was subjected to the same pretreatment 
conditions as those in Example 4, except that the treatment with the mixed 
gas was continued for an additional 145 hours, i.e. 160 hours total. 
Thereafter, a methanol decomposition test was performed in the same manner 
as that in Example 1 at temperatures of 300.degree., 350.degree. and 
400.degree. C. The results are shown in Experiment No. 42 Table 5 together 
with those of Experiment No. 33. 
TABLE 5 
______________________________________ 
Experiment 
Pretreatment time 
Conversion of methanol (%) 
No. (with methanol) 
300.degree. C. 
350.degree. C. 
400.degree. C. 
______________________________________ 
33 15 hours 53 89 98 
42 160 hours 50 84 99 
______________________________________ 
The results in Table 5 show that the catalyst used for 160 hours can still 
exhibit excellent catalytic performance comparable to the catalyst after 
15 hours process time. The analysis of the product revealed that the 
product consisted of 65% of hydrogen and 35% of carbon monoxide. These 
facts indicate that the catalyst of this invention has a sufficiently long 
catalyst life.