117.    AYRES, E., MONTGOMERY, C. W., AND HIRSCH, J. H.  Some Problems Associated With the Fischer-Tropsch Process.  Oil Gas Jour., vol. 47, No. 25, 1948, pp. 112, 115; Petrol. Refiner, vol. 27, No. 11, 1948, pp. 583-585.

                 Abs. of a paper presented at a meeting of the Am. Soc. Mech. Eng. at Amarillo, Texas.  Due to the fact that about 2,000 vol. of synthesis gas plus recycle gas must be processed to make 1 vol. of liquid motor-fuel product, the latter has to bear a disproportionate part of the cost of amortizing and maintaining the plant and equipment.  Because of this characteristic and to obtain greater economic space-time yields, more severe operating conditions have been imposed, with the result that the catalyst has become overloaded and undesirable side reactions have been set up, which have greatly aggravated the catalyst problem.  The problem of C deterioration of the catalyst is also a serious one.  In the formation of carbides (which by the way are no longer regarded as essential intermediates in the synthesis of hydrocarbons) at synthesis temperatures and above, CO will deposit C on the transition metals of the catalyst far in excess of the stoichiometric amounts indicated by the formulas for the carbides M₂C or M₃C.  As the rates of decomposition of the carbides increase, the C, which was uniformly distributed through the metal lattice in the carbide form, tends to diffuse and accumulate in inclusions, thus freeing lattice sites for the addition of more C.  As this excess C accumulates, the lattices are forced to expand, with the result that the catalyst structure is broken down, and excessive pressure drops through the catalyst ensue.  The formation of high-molecular-weight wax in the synthesis is another serious problem, particularly in fluid operation.  A study of product distribution suggests that certain thermodynamic equilibria are operative and determine the relative amounts of n-paraffins of each molecular-weight range, the relative amounts of the different n-1-olefins, the degree of branching, etc.  Operation of these equilibria impose certain limitations on the flexibility of the process.  Generally speaking, the modern Fischer-Tropsch process yields a disproportionately large amount of gaseous hydrocarbons, while, at the other end of the product range, relatively small amounts of extremely high molecular weight wax paraffins are found.  On account of the equilibria involved, it is impossible to reduce the gas yield without simultaneously increasing the wax yield.  Likewise, the ratio of diesel fuel to gasoline, normally about 1:6, cannot be increased without a corresponding increase in wax.  Only relatively small amounts of wax deposited on the catalyst in fluid operation are enough to cause catalyst agglomeration and incomplete fluidization with consequent localized overheating and C deposition.  The Fischer-Tropsch process is peculiar not only in its abnormal volume shrinkage but also in its loss of heat value.  The power requirements are also considerable.  Economically, it is essential that synthesis processes be developed that do not depend upon credits for byproducts that have limited market.  The oxygenated compounds offer attractive possibilities as chemicals on a relatively small scale, but while synthesis plants of 70,000 bbl./day capacity would produce less than 3% of the country’s motor fuel, the byproduct EtOH would amount to almost 100 million gal./yr., or about half the estimated demand for this material.