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The Progress of the Research Commission on Continued Development of the Gasoline Synthesis from CO and H2, Especially in the Direction of a Direct Synthesis of Isoparaffins. (SS6132-9798/42)
December 1942.
Translated by W. Oppenheimer
On the Direct Synthesis of Isoparaffins from CO and H2
During the experimental work on the behavior of various oxides as catalysts for the conversion of CO and H2 to hydrocarbons and oxygen-containing organic compounds, it was discovered that catalysts based on thorium are outstandingly well suited for the synthesis of branched hydrocarbons.
The process requires a maximum with increased pressures, and the optimal range of pressure is determined by the nature of the catalyst. As one-component catalysts, the thorium catalysts occupy a special position, because with their existence and with relatively low pressure, for example, 30 atmospheres, branched hydrocarbons have been obtained in large quantities. This paper deals with these thorium catalysts because only the work done in this field.
General.
Water gas with a CO: H2 ratio of 1:1 to 1.2:1 was used generally as the starting gas of the synthesis. Such a gas mixture corresponded to the consumption of both components, under optimal conditions of the synthesis.
A series of experiments have been carried out in which dimethylether and H2 have been used as starting substances. These experiments, which have been carried through chiefly for the clarification of the reaction mechanism are not included in this report.
The synthesis has been carried out in CO-proof pressure pipes, that is, partly in copper-lined unalloyed steel pipes and in another part in unlined alloyed steel pipes, for example V2A or Sicromal (a silica, chromium, aluminum alloy) steel.
The inner width of the reaction pipes was generally 15 mm.; however, pipes with an inner width of 25 mm. could also be used without any noticeable harm to the conversion.
The throughput of gas has been determined by measuring the expanded final gases and by the contraction calculated from the nitrogen values. We operated, generally with a final gas quantity of 10 liters per hour per 28 grams thorium catalyst, (based on experiments on the influence of the flow rate). With a contraction of 50 percent, this corresponds to 20 liters per hour per 28 grams thorium catalyst. Under these conditions, the yield per space and time is about 10 times larger than under normal conditions.
The composition of the gasol hydrocarbons in the resulting reaction products which are removed from the final gas by cooling or by active carbon has always been determined by low temperature distillation and the liquid hydrocarbons (mostly the hydrogenized products) have been determined by fine distillation. From each fraction of the liquid hydrocarbons, the refractive index, density, iodine-thiocyan number aniline-point, etc. have been determined. Moreover, the resulting gasoline products, after the proper distillation and the standardizing of the vapor pressure in the crude and the refined state with and without the addition of lead tetraethyl, have been tested in an I.G. testing motor, according to the motor method, for their resistance to knocking.
The Thorium Catalyst.
The best thorium catalysts are produced by precipitation of thorium salt solutions, generally by precipitation of the basic carbonate by sodium carbonate from the nitrate solutions. The freshly precipitated contact was washed until it was free of alkali, because small amounts of alkali reduce the activity of the thorium catalysts and require a higher reaction temperature. After the washing, the contact was dried first at 110º C., then it was granulated, and finally it was zinterad in an air current at 300º to 400ºC.
The lifetime of the thorium catalyst was very long under the conditions of the iso-synthesis. Catalysts which, after a long operation, exhibited an inner resistance due to the formation of carbon could be regenerated by treating them with air at the con-
The Reaction Products as Dependent on the Conditions of the Synthesis
The kind of the resulting reaction products is dependent on the following conditions: The composition and the method of production of the catalyst, the temperature, the pressure, the time during which the gas stays in the contact space, the operation (CO and H2) in several stages, the material of the reaction pipes, etc. Figure 1 shows the composition of the reaction products as dependent on the synthesis temperature with a pressure of 150 atmospheres and a flow rate of the gases corresponding to 10 liters final gas per hour per 28 grams of the catalyst.
The quantity of the resulting alcohols and of other oxygen-containing organic compounds, which prevail at lower temperature, especially below 375º C., decreases fast with rising temperature. In the region of 375ºC. to 425ºC., mostly liquid branched aliphatic hydrocarbons are formed. With rising temperature, the quantity of naphthenee, which result, increases gradually. Their share in the liquid products is not considerable at 375º C., but reaches 50 percent at at 450º to 500º C., aromatic substances could also be identified in the higher-boiling fractions of the resulting liquid hydrocarbons.
The quantity of gaseous reaction products increases from less than 10 percent at 375ºC. to 50 percent of the reaction products at 440ºC. The greatest quantity among the single hydrocarbons is the isobutane. At 450º to 460ºC., one-third of the butane resulted; for example, in quantities of around 10 percent of the isobutane (0.5 to 3 percent of the total products). The quantity of the normal pentane was only one percent of the liquid hydrocarbons.
Table 1 shows yields of gasoline and gasol after the operation in one stage under different experimental conditions, that is , different pressures and different material of the reaction pipes. With the exception of the last experiment, the temperature was always 450ºC.
With atmospheric pressure, no reaction could be observed, with 6 atmospheres, it was insignificant. With 30 atmospheres and a conversion of 22 percent of the CO, 5.1 grams C3 + n-C4 hydrocarbons, 5.h grams i-C4 hydrocarbons, and 16.1 grams liquid hydrocarbons per normal cubic meter inert-free inlet gas was formed. With rising pressure, the quantity of the products, resulting from one operation, increased. It reached, at 500 atmospheres, 46.5 grams i-C4 hydrocarbons was greater when V2A (stainless steel) pipes instead of copper-lined pipes were used.
Figure 2 shows graphically the influence of pressure on the yield, obtained at 450ºC in one stage. The yields of liquid hydrocarbons and gasol increase with rising pressure; and connected with this, with longer stay of the gases within the catalyst space, the conversion of carbon monoxide also increases. This conversion of carbon monoxide can be increased with rising pressures, since the danger of a carbon formation declines with this increase.
With lower pressure, for example 50 to 100 atmospheres, a similar conversion can be obtained. If the operation takes place in several stages instead of one stage, using a pressure of 300 to 500 atmospheres. This means that the necessary catalyst quantity is so much lower that a higher working pressure is chosen.
Figure 3 shows a typical gasol distillation of an experiment, which can be carried out with a pressure of 150 atmospheres and a temperature of 450ºC. (Th 1C12). The main fraction is an isobutane boiling at -12ºC. Isobutane, in the portions boiling between -10º and 5ºC., was always tested for the treatment with 64 percent sulfuric acid, but was not formed.
Figure 4 shows the result of a distillation (Th 101a, 150 atmospheres, 450ºC.) belonging to the same experiment of the liquid hydrogenized hydrocarbon. In Table 2, the refractive index, the density, the aniline point, and the specific dispersion of the resulting single fractions are compiled. Table 3 shows the result titles of normal paraffins have not been obtained. About one percent of the liquid hydrocarbons was n-pentane, but 12 percent was iso-pentane boiling at 28ºC. Relatively large quantities consisted of 2-methyl-pentane (13.6 percent) and possibly of 2,4 and 2,2 dimethylpentane. The numbers compiled in Table 2 give us an approximate picture of the composition of the hydrocarbons.
Figure 5 and Tables 4 and 5 show analogous results for the experiment at 150 atmospheres and 375ºC., Th 101b. The products of this experiment are different from those obtained at 450ºC. by an essentially lower naphthene content and by a higher content in branched aliybatic hydrocarbons (compare Table 1).
Table 6 shows a classification of a series of measurement for resistance to knocking by the motor method.
The first seven gasoline samples have been washed with a 30-percent calcium chloride solution before starting the determination. The octane numbers are between 78 and 80, that is, rather independent of the boiling limits. (Compare Experiments 3, 4, and 5.) An unwashed raw product had an octane number 84.5 (Experiment 13).
The samples 8, 9, and 10 have been hydrogenized on a nickel catalyst before testing the octane number. The octane numbers of these are between 83 and 85.7.
The gasoline (11) obtained at 450º C. and 150 atmospheres and hydrogenized before testing the resistance to knocking, after.
Conclusion
Operating with thorium catalysts and in one stage, 110 grams gasol, gasoline, and oil, could be obtained per normal cubic meter inter-free inlet gas. Operating in two or more stages, it should be possible to increase the yield still more.
The composition of the reaction products could be varied within large limits by the choice of the synthesis conditions. For example, the yields of isobutane could be increased from about 5 grams per normal cubic meter, when we operated for the highest yield in liquid products to 50 grams per normal cubic, when we operated with a corresponding lower yield in liquid hydrocarbons. With the precise knowledge of the influence of the catalyst composition, it will be possible to favor in a much higher degree the formation of certain desired hydrocarbons.
The octane number of the resulting gasoline, after a hydrogenation and an addition of 0.08 volume percent tetraethyl lead, were up to 95. By using the resulting isobutane for the production of alkylation gasoline, the mixtures of both gasolines could be improved to octane numbers of 100 and over.
Research and Development Division
Office of Synthetic Liquid Fuels
U.S. Department of the Interior
Bureau of Mines
Central Experiment Station
Pittsburgh, Pennsylvania
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