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Alkylation and Isomerization W. L. LAFFERTY, JR. and R. W. STOKELD
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Texaco Inc., Beacon, Ν. Y.
The histories of alkylation, a widely accepted commercial process, and isomerization, a process with fewer commercial applications, are traced from their early stages of develop ment to their present position in the petroleum refining in dustry. The factors which have affected the growth of these processes are reviewed along with recent advances in tech nology and developments in processing equipment which have improved their status in the industry. The various types of alkylation and isomerization processes based on different catalyst systems and equipment configurations are compared. The general effects of operating variables, charge stock compositions, and charge stock purification systems are also discussed. The future roles of alkylation and isomeriza tion in petroleum refining are considered with respect to the continued growth of the gasoline market and the possible changes in gasoline specifications which may be required for automotive emission control.
Τ η petroleum refining the term alkylation generally applies to the catalytic reaction of isobutane with various light olefins to produce highly branched paraffins for use in high octane gasoline. Alkylation processes have attained exceptional importance in the petroleum industry over the past 30 years. The rapid growth of alkylation created large demands for isobutane, and to help supply these demands, butane isomerization proc esses were developed. The isomerization technology was later applied to higher molecular weight paraffins, and as a result, various isomeriza tion processes were developed to complement alkylation as a tool for gasoline manufacture. This paper reviews the development history of the alkylation and isomerization processes, considers their present status in the industry, and predicts their future role in the manufacture of petroleum products. A
130 In Origin and Refining of Petroleum; McGrath, H., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.
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LAFFERTY, JR. AND STOKELD
Alkyhtion and Isomenzation
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Alkylation Development and Growth. Alkylation became commercially feasible when thermal and catalytic cracking processes began to be used widely in the 1930s. In cracking the heavy components of crude oil to supply the growing demand for gasoline, substantial quantities of light hydrocarbons, such as ethylene, propylene, and butylènes, and isobutane, were produced. Only limited quantities of these light hydrocarbons could be used in gasoline because of their high vapor pressure. Consequently, these compounds had to be used largely for fuel gas, but their availability set chemists and engineers to working on the classical task of finding more profitable uses for the by-products from the cracking processes. Consequently, alkylation was developed (1). Most of the petroleum companies were experimenting with the alkylation reaction following the discovery of the reaction by Ipatieff and co-workers using an aluminum chloride catalyst. Texaco Inc., Shell Development in the Hague, Netherlands, and the Anglo Iranian Oil Co., Ltd. in England each experimented independently with a sulfuric acid catalyst at about the same time. Following a publication by Anglo Iranian (2) in 1938, Humble Oil and Refining Co., with the cooperation of Anglo Iranian, put in a commercial plant at Baytown, Tex. by converting and adapting a polymerization unit to alkylation. Texaco Inc. designed a completely new plant and put in a commercial plant at Port Arthur, Tex. Five companies—Anglo-Iranian Oil Co., Ltd., Humble Oil and Refining Co., Shell Development Co., Standard Oil Development Co., and Texaco Inc. issued a joint report and introduced the sulfuric acid alkylation process to the industry at the Chicago meeting of the Petroleum Institute, Nov. 17, 1939. Other companies participating in some of the early development work on alkylation processes were Union Oil Co., Stratford Engineering Corp., The M . W. Kellogg Co., Universal Oil Products, and Phillips Petroleum Co. (2, 3). By the end of 1939, six commercial sulfuric acid alkylation units were on stream making 3525 BPD of aviation alkylate. Eight more units were under construction or contracted for, which would make an additional 9000 BPD of alkylate (3). The early experimental work showed that the alkylation reactions could be carried out thermally and by using hydrofluoric acid or aluminum chloride as catalysts. Successful processes were developed with the hydrofluoric acid catalyst, and the first commercial H F unit started up on Christmas Day 1942, having a capacity of 1950 BPD (3). Other commercial H F alkylation units followed quickly. The thermal and aluminum chloride-catalyzed alkylation processes had limited commercial acceptance.
In Origin and Refining of Petroleum; McGrath, H., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.
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ORIGIN A N D REFINING OF P E T R O L E U M
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The excellent characteristics of alkylate were quickly recognized. It had a high octane rating, a high heat of combustion per pound, a low vapor pressure, and a desirable boiling range (1,3). In addition, alkylate had good lead susceptibility with low or, in some cases, negative sensi tivity (RON-MON). Thus, alkylate was found to be extremely well suited for use in aviation fuel or motor gasoline blending. World War II caused a tremendous increase in the demand for fuels, and the ability of the petroleum industry to gear up and supply these demands played an important part in the outcome of the war (3). The alkylation processes provided the basic ingredient of the huge quantities of aviation fuel which were used by the military forces, and, as shown in Figure 1, alkylation capacity increased rapidly through the war years. Between 1939 and 1946, 59 alkylation units were built. By the end of the war capacity had reached 169,000 PBD (5). When World War II ended, the demand for aviation alkylate dropped, and refiners had excess alkylate which they started using in motor gasoline. About half of the alkylation units were soon shut down, and some of the units were dismantled because the octane levels of motor gasoline were not high enough to justify the continued use of this rela tively expensive process (6). The Korean War caused the demand for aviation alkylate to jump again in 1950, but only about 35 alkylation units were in operation at the 700 • £
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