Butane isomerization catalyst life

Pentane isomerization was used to increase the critical supply of aviation gasoline toward the end of the war. Two processes—one developed by Shell and one by Standard Oil Company (Indiana)—were commercialized. The pentane processes differ from butane isomerization mainly in the use of somewhat milder conditions and an inhibitor to suppress side reactions. In general, the problems of the butane processes are inherent also in pentane isomerization, but the quality of the feed stock is less important. Olefins can be as high as 0.2 %, although 0.05 % is preferable. The hexane content should not exceed about 5%, and sulfur and water contents should be as low as in the butane process. Catalyst life is much shorter than in the butane processes only about 30-50 gallons of isopentane are produced per pound of aluminum chloride. 

The butanes show little tendency to crack or disproportionate (7) thus butane isomerization is fairly straightforward. However, the suppression of side reactions becomes more difficult as the molecular weight increases. With pentanes, disproportionation to isobutane and hexane is pronounced, amounting to as much as 63%. A typical composition of pentane disproportionation products is shown in Table III. Besides lowering the yield of isopentane, such side reactions shorten the life of the catalyst. Adding small amounts of cyclic hydrocarbons (7,15,18)... 

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