Synthesis of Dodecylbenzene with Benzene and 1-Dodecene over MCM-22 Zeolite Modified with Phosphorus

A series of MCM-22 zeolite catalysts modified with phosphorus were prepared by incipient wetness impregnation. The effects of phosphorus on the structure and acidity of the MCM-22 were studied using X-ray powder diffraction, solid-state Al-27 and (31) nuclear magnetic resonance, N-2 adsorption, temperature-programmed desorption of ammonia, thermogravimetry and IR spectroscopy of adsorbed pyridine. The alkylation of benzene with 1-dodecene to form dodecylbenzene was evaluated in a fixed-bed reactor. The results showed that the crystal structure was intact after modification, but there was partial breaking of the Al-O-Si bonds, and some tetrahedral aluminum was converted to octahedral aluminum. The formation of aluminum phosphate species and polyphosphate chains led to changes in the pore size and acidity. With an increase in the phosphorus content, the quantity of weak acid sites increased gradually, and the quantity of strong acid sites decreased. The quantities of the total acid sites and Bronsted acid sites increased initially and then decreased, and the quantity of Lewis acid sites decreased. A proper phosphorus content can improve the selectivity for 2-dodecylbenzene and the catalytic stability of the MCM-22 catalyst for the alkylation of benzene with 1-dodecene. For the MCM-22 modified with 0.5% of phosphorous, the maximum yield of 2-dodecylbenzene was obtained.