Degenerate Non-primary Products in Catalytic Cracking of Isoalkanes

Abstract

Product distributions in catalytic cracking of a series of C10-C17 isoalkanes over two acidic catalysts, a Y-zeolite-based commercial catalyst and SiO2-Al2O3, were studied at 250 and 350°C. The cracked products from a Cn alkane belong to two distinct groups, primary products (isomerized Cn alkanes), and degenerate non-primary products, isoalkanes ranging from C3 to Cn−1. Degeneration of the non-primary products is expressed in two ways: 1. In each carbon number range, the non-primary products from alkanes are the mixtures of isoalkanes containing mostly monomethyl- and dimethyl-branched alkanes. The compositions of the mixtures are practically independent of the structures of feed alkanes, and the relative yields of isoalkanes with different skeletons are mostly determined by the thermodynamic stabilities of respective isomers. 2. The distributions of the non-primary products with respect to their carbon numbers have the inverted-U shapes with the maxima at C4-C5. These distributions also do not depend on the skeleton structure of the feeds. The main reason for the cracked product degeneration is high reactivity of a part of the reaction products, light olefins, in reactions over acidic catalysts. This conclusion is based on the experimental cracking study of a series of C3-C14 olefins with the same catalysts under mild conditions (100-250°C).