Aromatic Hydrocarbons from Pure Fatty Acids and Renewable Triglyceride Feedstocks via Hydrothermal Zeolite Catalysis.

Abstract

Triglycerides and fatty acids are attractive renewable feedstocks, because they are the major components of many types of biomass. There are several proposed chemical processes that generate aqueous streams rich in fatty acids. Thus, fatty acids in aqueous streams represent a renewable feedstock available for the production of chemicals. Zeolite catalysis is applied because these catalysts promote aromatization reactions, and aromatics are the targeted chemical products.

I investigated the reactions of saturated (palmitic and stearic acids) and unsaturated fatty acids (oleic and linoleic acids) in water near the critical point at 400 Celsius, at 12.5, 20, and 24 MPa, and over zeolites Y, beta, and ZSM-5. Zeolite ZSM-5 was found to be the most promising catalyst for producing aromatics from fatty acids in water among the different types of zeolite we have tested. The major liquid products were aromatics (e.g., xylenes, toluene), and alkanes (e.g., 2-methyl-pentane, heptane). Reaction conditions of 400 Celsius, 20 MPa, and 180 minutes gave the highest total product yield. Additional hydrogen and water density have effects on the product distribution. The lowest silica/alumina ratio (23) we tested generated the most aromatics. The catalyst can be regenerated and reused. ZSM-5 with a silica/alumina ratio of 23 gave a total product yield of 76 ± 3 wt% at its third use, after undergoing regeneration twice previously. Finally, this methodology has been applied to fatty acid-rich lipids extracted directly from biomass, including algal oil, coconut oil, peanut oil, and lard, to assess the technical feasibility of the approach with real plant-derived feedstocks. Peanut oil (53 ± 15 wt%) and lard (48 ± 4 wt%) showed comparable major aromatic yields to pure fatty acids (42 ± 4 wt%).

This research confirms the technical feasibility of producing appreciable yields of aromatic products from fatty acids in water over consecutive uses. Examining the influence of different process variables has revealed methods to tune the product distribution in order to favor desired products. Taken together, this work lays the foundation for an aromatics production process using renewable feedstocks.