Aromatics from saturated and unsaturated fatty acids via zeolite catalysis in supercritical water

• The highest total yield of aromatics achieved at 42 wt%.
• The lowest silica/alumina ratio tested gave the highest product yield.
• An increasing degree of saturation of fatty acid led to a decreasing of liquid to gaseous product ratio.
• Reactant-to-catalyst ratio influences the reaction liquid and gaseous product yield.

We investigated the reactions of saturated (palmitic and stearic acids) and unsaturated fatty acids (oleic and linoleic acids) in supercritical water at 400 °C, 240 bar, over zeolites Y, beta, and ZSM-5. The highest total yield of liquid and gaseous products, 97 ± 2 wt%, was obtained from palmitic acid by applying ZSM-5 with a silica/alumina ratio of 23. The liquid products had a high concentration of single-ring aromatics, and the total molar yield of aromatics was 102% (42 wt% yield). This catalyst could be regenerated and reused. ZSM-5 with silica/alumina ratio of 23 gave a total product yield of 76 ± 3 wt% (which includes 40 ± 5 molar yield of xylenes) at its third use, after undergoing regeneration twice previously. We also report herein the effects of different zeolites, catalyst loadings, degrees of unsaturation in the fatty acids, and silica/alumina ratios of zeolite ZSM-5 on the product yields.

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