Dehydrocyclodimerization and concomitant reactions of piperylene on alkali-containing alumina

Abstract

1. Piperylene on Al2O3 (500°C) is completely converted to cracking and condensation products, n- and iso-pentene, and, to a small extent, to cyclopentane and cyclopentadiene. Addition of alkali to Al2O3 greatly increases the yield of n-pentenes and simultaneously reduces the yield of isoamylenes and of cracking and condensation products. 2. Piperylene on Al2O3.10%K2O (500°C) is mainly converted to n-pentenes, alkenylcyclohexenes, C6-C9 aromatic hydrocarbons, C10 alkenyl- and alkylaromatic hydrocarbons, and also higher-molecular condensation products. We have obtained results that suggest that n-pentenes are formed by hydrogenation of piperylene by hydrogen liberated in concomitant dehydrogenation reactions. 3. We have made a comparison of the reactions of piperylene with those of hexadiene on Al2O3 and alkali-containing Al2O3, as described in the literature. Piperylene undergoes cyclization more sluggishly but is cyclodimerized more reasily than hexadiene. The intermediate cycloolefins are dehydrogenated to form aromatic hydrocarbons (benzene from hexadiene and C10 aromatics from piperylene) while the liberated H2 hydrogenates the starting dienes to the corresponding olefins.