Hydrothermal catalytic cracking of fatty acids with HZSM-5

We explored the hydrothermal cracking of palmitic acid by HZSM-5 zeolite in a batch reactor. The major liquid products were aromatic hydrocarbons (e.g., xylenes, toluene) and alkanes (e.g., 2-methyl-pentane, heptane). The major gaseous products were CO and CO₂, but appreciable yields of propane and butane were also obtained. The effects of batch holding time, temperature, hydrogen pressure, and water density on product yields were elucidated. Total yields of gas and liquid products exceeding 90 wt % are available at reaction conditions of 400 °C, 180 min, and either with no added H₂ and a water density of 0.1 g/mL or less or with added H₂ and a water density of 0.15 g/mL. The activation energy for palmitic acid disappearance is 31 ± 1 kJ/mol. The zeolite catalyst undergoes some modest structural changes under the hydrothermal reaction conditions employed, but the catalyst can be regenerated by controlled oxidation to remove coke and calcination to restore the structure. These results demonstrate the technical feasibility of using HZSM-5 under hydrothermal conditions to produce valuable chemicals from renewable fatty acid feedstocks.