Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 3, 1978 255
w = weight of catalyst, g x = mole fraction conversion
Subscripts H = hydrogen T = thiophene S = hydrogen sulfide Literature Cited Chakraborty, P., Kar, A. K., lndian J. Techno/., 14, 340 (1976). Frost, A. V., Vestn. Mosk. Gos. Univ., No. 3-4, 111 (1946). Griffith, R. H., Marsh, J. D. F., Newling, W. S.,Proc. Roy. SOC.London, Ser. A, 194 (1949). Hoog, H., J. Inst. Pet., 36, 738 (1950).
Kolboe, S., Amberg, C. H., Can. J. Chem., 44, 2623 (1966). Kronig, W., "Die Katalytische Druckhydrierung Von Kohlen, Teeren and Mineralolen", Springer-Verlag. Berlin, 1950. Obolentsev, R. D., Mashkina, A. V., Gidrogenoliz Seraorg, Soedinenii Nefti, Gos Nauch-Tekhn. Izd. Neft. i Gorno-Toplivoi Lit., Moscow (1961). Owen. P. J., Amberg, C. H., Adv. Chem. Ser., No. 33, 182 (1961). Pease, R. N., Keighton, W. B., Jr., hd. Eng. Chem., 25, 1012 (1933). Satterfield, C. N., Roberts, G. W., AIChEJ., 14, 159 (1967). Sherwood. T. K., Reid, R. C., "The Properties of Gases and Liquids", p 264, McGraw-Hill, New York, N.Y., 1966. Watanabe. T., Echigoya, E., Morikawa, K., Sekiyn Gakkai Shi, 10(12), 882 (1967).
Received for review December 30,1976 Accepted January 9,1978
Process Studies on the Conversion of Methanol to Gasoline Clarence D. Chang,' James C. W. Kuo, William H. Lang, Solomon M. Jacob, John J. Wise, and Anthony J. Silvestri Mobil Research and Development Corporation, Princeton and Paulsboro, New Jersey 08540
Process studies on the conversion of methanol to high quality gasoline are described. Exploratory process variable studies were carried out in single-pass fixed bed reactors. Process design and catalyst aging studies were conducted using a two-stage fixed bed reactor system with light gas recycle to the second reactor. The thermochemistry of the reaction is discussed.
Introduction The production of gasoline from coal and other nonpetroleum carbon sources will likely become a necessity in the United States before the turn of the century. Until now, only two coal conversion processes have attained any measure of commercial significance. These are the Bergius and FischerTropsch processes. In the Bergius process (Kirk-Othmer, 1972),finely divided coal is slurried with recycle oil containing a small amount of iron catalyst and hydrogenated at 900 O F and 3000-10 000 psi. The product is a synthetic crude. This process was practiced extensively in Germany during World War 11, achieving a peak annual production of four million tons of oil by 1944. However, no Bergius plants survive today. The Fischer-Tropsch process (Kirk-Othmer, 1972) is an indirect method for hydrocarbon manufacture from coal, involving coal gasification and the subsequent catalytic conversion of synthesis gas to hydrocarbons at moderate pressure and temperature. Iron-based catalysts are used. The Fischer-Tropsch process is commercially practiced a t Sasolburg, South Africa. The major shortcoming of the Bergius and Fischer-Tropsch processes is poor gasoline selectivity and quality. Products encompass a wide spectrum of molecular weights ranging from methane to heavy residue in the Bergius process and from methane to waxes and large amount of hydrocarbon oxygenates in the Fischer-Tropsch process. Downstream processing entails elaborate separation steps. Naphthas from these processes are generally low in octane and need extensive upgrading for automotive use. Mobil Research is developing a new process for converting coal or natural gas to high quality gasoline with high selectivity (Meisel et al., 1976; Chang and Silvestri, 1977). As shown in Figure 1, coal or natural gas can be converted to synthesis gas. After purification, the synthesis gas can be converted to methanol. By using the Mobil process, crude methanol can 0019-7882/78/1117-0255$01.00/0
then be converted to gasoline and water with small amounts of LPG and high Btu fuel gas as by-products. It is not necessary to remove the water or the small amounts of oxygenates present in the crude methanol. All the upstream steps from coal or natural gas to crude methanol are established technologies (Kirk-Othmer, 1972) while the last step is a simple catalytic step. Methanol can also be directly blended into gasoline or used by itself as an automotive fuel (Reed and Lerner, 1973). However, methanol's affinity for water, its corrosiveness, toxicity, low volumetric energy content, and unusual volatility, present formidable obstacles to its use either alone or as a component of gasoline (Lindquist and Ingamells, 1974). Large investments would be required to modify engines, storage and distribution facilities, and to develop new fuel and lube additive formulations (Kant, 1974). We calculate that it is more economical to convert methanol into gasoline than to use it alone or blend it with conventional gasoline. Methanol synthesis is known to proceed with high selectivity (Danner, 1970). As shown later, high selectivities also typify the newly discovered methanol-to-gasoline conversion represented by the reaction The first reported observation of hydrocarbon formation from methanol may be credited to Mattox (1962),who found minor amounts of c 2 - C ~olefin during methanol dehydration to dimethyl ether over NaX zeolite. Similar results have been reported later by various investigators using various catalysts (Heiba and Landis, 1964; Venuto and Landis, 1968; Topchieva et al., 1972; Swabb and Gates, 1972). Higher yields of hydrocarbons, including substituted aromatics, were observed by Pearson (1974) from methanol dehydration over P205 a t elevated temperature. No processes have been previously reported for the selective direct synthesis of high octane gasoline from methanol.
0 1978 American Chemical Society
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Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 3, 1978
BY
t
~
PRODUCTS
i
WATER
Figure 1. Simplifiedflow scheme for the manufacture of gasoline from coal or natural gas. Table I. Typical Hydrocarbon Distributionn Wt%
+
+
Methane ethane ethylene Propane Isobutane n-Butane Propylene and butenes C5+ Nonaromatics Aromatics
1.5 5.6 9.0 2.9 4.7 49.0 27.3 100.0 76.3 88.8
c5+ Gasoline including alkylate (9 Reid vapor pressure) a Fixed-bed recycle reactor: space velocity (WHSV), 0.5 h-l; 2nd reactor pressure, 205 psig; inlet temperature, 700 OF; pure methanol feed. The conversion of methanol to hydrocarbons is made possible by Mobil's discovery of a new class of shape-selective zeolites. These zeolites are members of the ZSM-5 class (Meisel et al., 1977). The conversion of methanol and dimethyl ether to gasoline hydrocarbons is reported in a number of patents (Chang et al.), which describe potential catalysts. The ZSM-5 class zeolites possess a unique channel structure (Meisel et al., 1976), with apertures intermediate between small pore zeolites and faujasites. This results in selective penetrability by molecules of intermediate size. An important consequence of this shape-selectivity is that only small amounts of hydrocarbons boiling above 400 OF, the end point of conventional gasoline, are produced. Typical production distribution obtained from the fixed bed pilot plant is detailed in Table I. As described later, this is a two-stage reactor system with recycle to the second stage. Very little methane and ethane (
