THE SYNTHESIS OF HYDROCARBONS AND CHEMICALS FROM CO AND H2
SECTION VI
LOW PRESSURE METHANOL SYNTHESIS
SUMMARY
The attached report covers the development of a new synthesis of methanol which is carried out at 30 atmospheres as compared with the usual operation at 250 atmospheres. The work was carried out on a laboratory scale and had resulted in the assembly of a pilot plant at the Degussa laboratory at Wolfgang near Hanau.
In view of the large saving in equipment and operation this synthesis, if carried through to commercial realization, may be of great interest to the producers of methanol in the United States.
1. Low Pressure Methanol Synthesis.
The following information on the synthesis of methanol, by utilization of pressures not in excess of 30 atmospheres, was obtained during an interrogation of Dr. Brendlein of the Deusche Gold-und Silber Scheideanstalt (Degussa) at the Wolfgang bei Hanau plant of the company. This synthesis uses as raw materials carbon monoxide and hydrogen. In this respect it is similar to the commonly used high pressure synthesis of methanol. The net reactions involved are shown in the following of methanol. The net reactions involved are shown in the following equations:
The catalyst for reaction I is sodium methylate dissolved in methanol, the catalyst for the second reaction is a typical hydrogenation catalyst described by Adkins, made up of copper, chromium and barium oxide. From the above set of equations it can be seen that although two molecules of methanol are formed, one is recycled for reaction I and one is product so that the result is the combination of one molecule of carbon monoxide and two of hydrogen to give one methanol. Overall yields of 95% to methanol are claimed for the process.
Enclosed with this description are four reports which give in detail the experimental findings of this work. Report (a) gives the results of experimental batch processes; (b) confirms the findings of (a) and although other alcohols such as ethanol and butanol can be used in the synthesis in place of methanol, methanol is selected as the optimum reaction medium; (c) discusses methods of continuous operation with both counter current and parallel flow of raw material through the reaction vessels; (d) describes the hydrogenation step (II) of the synthesis. In addition there are also enclosed two charts of which one shows in scheme the arrangement of the experimental equipment and the other shows in detail, the equipment and arrangement for a proposed plant to produce 28 tons per month of methyl formate or its equivalent of 15 tons of methanol.
2. Details.
Reaction I above is conducted as follows for a batch process:
Sodium metal,, 5.8 grams, is dissolved in 100 grams of methanol; this makes approximately a 13% solution of sodium methylate. The solution is charged to an autoclave and air is removed by displacement with carbon monoxide, and then a pressure of 30 atmospheres is produced by feeding carbon monoxide. The temperature is raised to 80° C and as the carbon monoxide reacts the pressure is maintained at 30 atmospheres by feeding carbon monoxide. The temperature is held at 80° C. The yield of methyl formate in this step is about 38% of the theoretical. In continuous operation the yield of methyl formate is approximately 25% (see Report (c) above). The heat of reaction for step I is approximately 9 kilo Cal/mol. of methanol.
It is essential in this operation that the reactants be free of water and carbon dioxide, as either of these react with the catalyst as indicated below, so that if present in sufficient quantity, they will prelude the desired reaction”
(a) CH3 ONa + H2O → Na OH + CH3OH
|
Ester Fed. |
Pressure Atm. |
Temp. C° |
Catalyst load M/l/h |
Ester fed g/h |
Length of Expt., |
% of Ester converted based on Ester fed |
Yield of Methanol in % theoretical based on Formic acid |
|
Ethyl Formate |
30 |
210 |
3.68 |
41.0 |
7.0 |
90.5 |
85.0 |
|
Methyl Formate |
30 |
215 |
4.74 |
42.6 |
5.75 |
97.8 |
58.4 |
|
Methyl Formate |
30 |
200 |
5.42 |
48.8 |
7.1 |
97.7 |
62.9 |
|
Methyl Formate |
30 |
200 |
4.34 |
39.0 |
8.0 |
96.3 |
66.2 |
|
Methyl Formate |
30 |
180 |
4.41 |
39.8 |
7.75 |
96.3 |
83.5 |
|
Methyl Formate |
30 |
160 |
4.34 |
39.0 |
7.5 |
97.4 |
94.5 |
|
Methyl Formate |
30 |
160 |
13.43 |
121.0 |
7.1 |
95.7 |
95.5 |
|
Butyl Formate |
30 |
208 |
2.65 |
42.0 |
7.0 |
87.6 |
80.0 |
|
Butyl Formate |
30 |
200 |
2.94 |
44.7 |
7.0 |
92.8 |
90.0 |
The presence of hydrogen in the carbon monoxide used in this step tends to decreased the yield of methyl formate. It is not essential, however, that the hydrogen be removed completely, because experiments with acceptable yields have been made with carbon monoxide containing 30 volume percent hydrogen.
The crude product from the addition of carbon monoxide to methanol is separated from the catalyst salts by distillation of methanol and methyl formate and is then hydrogenated. The apparatus used in the hydrogenation was a silver plated tube of 175 cc volume containing 150 cc. of Adkins catalyst of copper-chromium-barium oxide. The tube was 40 cm. in length. Thermocouples were placed along the tube. The temperature in this step is closely controlled between 175 and 185° Centigrade. Higher temperatures give rise to two side reactions, one of which decreases the yield of methanol but does not decrease the efficiency in that the products are methanol and carbon monoxide which can be recycled in a large installation. this reaction is indicated as follow:
The second reaction, which results from too high a hydrogenation temperature, not only decreases the yield but also decreases the efficiency in that the products are not adaptable to further utilization.
The yields obtainable in the hydrogenation step are indicated in the following table taken from Enclosure (A) mentioned above.
The products of the hydrogenation are separated by fractional distillation. The distillation is not complicated in that the products boil at widely different temperatures, methyl formate 31.8° C, and methanol 64.7° C. No azeotropes are formed in the fractionation.
3. List of References.
The German documents listed below are available in the library of the Bureau of Ships in Washington, D.C.