ALFRED R. POWELL Ė "THE FISCHER-TROPSCH PROCESS-
THE OPERATION OF PLANTS USING COBALT CATYST."
A. R. Powell. In the very few minutes that I have, I will have to assume that all of you know the principles of the Fischer-Tropsch process, and simply hit the high spots of what we found in our investigations of the Fischer-Tropsch plants located in the western part of Germany.
(Following is the outline of this presentation that was prepared before the meeting.)
THE FISCHER-TROPSCH PROCESS
The Operation of Plants Using Cobalt Catalyst.
1. Synthesis Gas. Made from coke means of water-gas reaction in most plants, supplemented in some cases by cracked coke-oven gas. In East from brown coal by special gasification processes, described by Mr. Odell.
2. Purification. (1) Removal of H2S by ordinary iron-oxide process (Grobreinigung). (2) Removal of organic sulfur by catalyst containing 70% Fe203 and 30% Na2C03 (Feinreinigung). Two towers in series with No. 1 at 200 Ė 380oC, and No. 2 at 130oC with heat exchanger between. About 0.2% oxygen in gas to oxidize organic sulfur, converting Na2C03, to Na2SO4. (3) Where synthesis gas made from coal or cracked coke-oven gas, an active carbon absorption tower before Feinreinigung to remove hydrocarbons that would effect catalyst of Feinreinigung (Feinstreinigung).
3. Catalyst. All commercial plants used cobalt catalyst to be described by Dr. Horne.
4. Catalyst chambers. (1) Plate type for atmospheric-pressure operations, and (2) concentric-tube type for medium pressure operation (10 atmospheres). Few chambers at Wanne-Eichel (Krupp) of "Taschenrohr"
5. Operation. Temperature in catalyst chambers, 180-200oC. Usually two stages of operation with two-thirds of chambers in first and one-third in second stage. Sometimes third stage. Each chamber contains one metric ton cobalt and produces 1.5 metric tons primary products per day, including chambers in all stages. Average yield 150 g. primary products per cubic meter ideal synthesis gas. Usual chamber rotation is fresh catalyst in last stage and old catalyst in first stage. Regeneration of catalyst by either hydrogen or solvent treatment, first period 4 weeks, followed by 2-week intervals. Catalyst life averages about 5 months.
6. Gas recycle operation. Not in commercial operation, only on pilot-plant scale, but Ruhrchemie had plant ready before destruction by bombing. Both Lurgi and Ruhrchemie had low recycle cobalt catalyst processes. Increased throughput of plant.
7. Products. At Sterkrade, with 3-stage operation at medium pressure, products as follows:
|C3 + C4||10%||
|C5 Ė 170oC||25%||
(olefins 24%) Octane No. 45
(soft wax or "gatsch")
hard wax M.P. 90oC.
Olefins of C3 Ė C4 to alcohol and paraffins for motor fuel; gasoline blended for motor fuel; middle fraction for Diesel oil; wax to fatty acids, etc.
J. P. Allen. What was the difference in yields of various products as between atmospheric-pressure and medium-pressure operation?
A. R. Powell. Well, in general the atmospheric-pressure operation gave considerably smaller quantities of waxes and somewhat greater yields of the motor-fuel fraction. The C3 and C4 yields were about the same with both types of operation. Also the Diesel-oil fraction was about the same with both types of operation, being about 25% to 30% of the total primary products. Dr. Martin told me that all efforts to increase yield of the Diesel-oil fraction above this figure had failed. There was, of course, a great incentive to secure greater yields of the excellent high-cetane-number Diesel oil at the expense of the low-octane-number motor fuel which found use only as a poor blending material with other gasoline of high octane number.
V. Haensel. Iíd like to ask what other uses the Germans had for this wax?
A. R. Powell. Well, a great deal of the wax was oxidized to fatty acids and other than that and using it as a feed stock for manufacture of lubricants and other materials, I really donít know of any other use that was made of it.
J. P. Allen. What , in the last analysis, would be the advantage of the intermediate pressure?
A. R. Powell. The intermediate pressure gave a higher throughput per chamber. Also, as stated above, the medium-pressure process gave a higher yield of the waxes, which were important in the German was economy. They were short of fatty acids and fats of all kinds, and I think that the waxes appealed to them very much as a valuable product to make. On the other hand, if they had gone more extensively to the low-pressure process they would have made more of the motor-fuel fraction, which even in Germany was not very good, as stated before. Dr. Martin also told me during the interrogation in Brussels, that he would recommend the medium-pressure process for any postwar Fischer-Tropsch project, since its economy was better than the original atmospheric-pressure process.
A. C. Fieldner. What would be the essential difference in the character of the products if they had developed commercially the iron catalysts?
A. R. Powell. Well, Dr. Fieldner, I think Mr. Atwell is going to take up operation with the iron catalyst, which was entirely experimental and never put into commercial operation. With your permission, Iíll pass that on.
A. C. Fieldner. I should have thought of that. Have any calculations been made as to the yield per unit of coal, that is, per ton of coal?
A. R. Powell. Yes, there are calculations on that basis. It is relatively easy to calculate. From a good coking coal there can be obtained a total of about 1,270 cubic meters of ideal synthesis gas per metric ton, or 1.27 cubic meters of ideal synthesis gas per metric ton, or 1.27 cubic meters per kg. The medium-pressure Fischer-Tropsch process yields 150 g. primary product per cubic meter of gas. This means 190 g. product per kg. of coal, or a weight yield of 19%. However, the heating value of the hydrocarbons in the primary product is considerably higher than that of the coal, weight for weight, so that the thermal efficiency of the process, from coal to primary product, is between 25% and 30%. Of course there is also some heating value in the tail gas, in addition to that in the liquid products, but this tail gas is usually used right in the Fischer-Tropsch plant for heating purposes.
W. C. Schroeder. Dr. Peck, is that figure approximately correct? It seems very low in comparison with other processes.
E. B. Peck. My recollection is that including the tail gas, it is up around the 30-odd percent.
W. C. Schroeder. It seems to me itís higher than that.
E. B. Peck. Including the tail gas, it is somewhere around 33%, but the thermal efficiency based on primary liquid product only is about 25%.
W. C. Schroeder. We are again a little behind in time, and if there arenít any direct and most important questions, I think we will go on to the next topic "Acetylene Chemistry (Reppe)," by Mr. Irwin Jones.