SECTION I(b)
11. “Schaumfahrweise” Process-I.G. Farben.
(See reference I(b/18 to I(b)/22 at end of this section).
This process was developed by Dr. Michael after abandoning the gas-recycle principle.
It is quite similar to the “Oelkreislauf” process except for the handling of the catalyst. The later is here held in suspension in the liquid by the gas bubbling up through the reactor. It was desired to operate in a system where the catalyst was dispersed widely and in direct contact with the gas is possible. An attempt to obtain this result by dispersing the gas to give a regular froth was made using the product of the synthesis as liquid phase and forcing the gas through a ceramic disc or nozzles with very fine pores to give the necessary dispersion.
The heat of reaction is removed by circulating the slurry through an outside cooler. For this purpose the reactor is allowed to overflow into the settling vessel where the unreacted gas carrying the light product, vapor is released and with drawn. The slurry is then passed through the cooler and then picked up by the circulating pump. The net excess product boiling within the range of the circulating oil is withdrawn.
Preliminary tests were carried out in a reactor 500 mm. Diameter x 8.0 m. high (1.5 m3 reactor volume). Some initial difficulties, such as wear in the slurry pump, could be overcome by use of flushing oil in the stuffing box. The oil velocity required for good operation was such as to give 20 changes of oil per hour in the reactor.
Some difficulty was also encountered with the dispersion plate. The feed gas had to be heated to prevent thermal stress and rupture of the disc. A chamotte plate showed good stability. A disc with 0.1 mm. pore size gave good reactor output but resulted in 5 atm. pressure drop. A 0.2 mm. pore size was substituted resulting in a pressure drop of 1 atm. but causing at the same time a drop in output of 25%. Apparently the dispersion depends greatly on the pore size.
No emulsifiers were used in the system but certain of the liquid oxygenated compounds gave such an effect.
In one test the catalyst, after 8 weeks, began to produce increased amounts of low boiling products and less wax. This could have been caused by sulphur, but it could have been due to the extraction of the alkali in the catalyst by the fatty acid formed in the synthesis.
Upon continued operation (3 months) increased losses of catalyst were noted, which could not be explained by the mechanical losses such as pump leaks or entrainment. Upon inspection it was found that the catalyst had formed a solid cake around the wall of the oven (4cm. thick) particularly in the upper section of the vessel. The catalyst had also settled out in the gas separator. The deposit was thoroughly analyzed and was found to have the following composition:
|
FeCO3 |
48.20% wt |
|
FeO |
13.40% wt |
|
Fe2O3 |
0.25% wt |
|
Fe2C |
8.50% wt |
|
Fe metal |
20.30% wt |
|
Free carbon |
5.10% wt |
|
S (Sulfide) |
0.03% wt |
|
Other |
8.81% wt |
|
Total |
100.00% wt |
The high Fe CO3 content is due to the high CO2 content of the exit gas (partial pressure PCOg=6-8 atm) reacting with FeO. It was further concluded, that some gum-forming substance had served as a glue to hold the catalyst on the wall. Studies to analyze this material were under way.