On the Role of Water in Natural-Zeolite-Catalyzed Cracking of Athabasca Oilsands Bitumen

Water addition to natural-zeolite-catalyzed reactions significantly improves cracking of oilsands bitumen compared to analogous reactions in the absence of water. We report that the addition of 3% water to the catalyzed cracking reactions results in samples with lower viscosities and average molecular weights, less residue, olefin, and coke formation, and higher C-2+ gas production compared to analogous reactions in the absence of water. Our study suggests that untreated natural zeolites undergo self-acidification by hydrolysis reactions in the presence of water. Fourier transform infrared spectroscopy and solid-state NMR analyses detected the presence of acid -OH groups on the raw untreated chabazite and clinoptilolite surfaces that are capable of supplying protons to initiate carbocation reactions. Stable isotopic mass spectrophotometric analyses on bitumen on D2O-doped catalytic reactions confirm up to similar to 56% hydrogen incorporation from added water to the liquid products. Aromaticity and proton and deuterium distribution of products by liquid NMR indicate the occurrence of a number of catalytic reactions, including aromatization, rearrangement and substitution in the aliphatic chains, beta-scission, dehydrogenation, and increased hydrogen enrichment at beta- and gamma-positions. On the basis of our findings, we postulate that water addition to natural zeolites generates catalytic reactions that involve carbocation on acid sites. Studies with model compounds such as cumene and hexadecane also demonstrated significant cracking activity with water addition.