Dehydration of 1-Octadecanol over H-BEA: A Combined Experimental and Computational Study

Liquid-phase dehydration of 1-octadecanol, which is intermediately formed during the hydrodeoxygenation of microalgae oil on zeolite H-BEA, has been studied, combining experiment and theory. Both the OH group and the alkyl chain of 1-octadecanol interact with zeolite Brønsted acid sites, inducing inefficient utilization in the presence of high acid-site concentrations. The parallel intramolecular and intermolecular dehydration pathways, leading to octadecene and dioctadecyl ether, have different activation energies and pass through different reaction intermediates. The formation of surface alkoxides is the rate-limiting step in the intramolecular dehydration, whereas the intermolecular dehydration proceeds via a bulky dimer intermediate, occurring preferentially at the pore mouth or outer surface of zeolite crystallites. Despite the main contribution of Brønsted acid sites toward both dehydration pathways, Lewis acid sites are also active to form dioctadecyl ether.