The effect of hydrothermal treatment of FCC catalysts and ZSM-5 additives in catalytic conversion of biomass

Abstract

Fresh fluid catalytic cracking (FCC) catalysts and ZSM-5 additives were hydrothermally treated with 100% steam at 732°C (1350°F) and 788°C (1450°F) for 4h in a fluidized bed reactor. The catalytic pyrolysis of hybrid poplar wood with fresh and steam treated catalysts was conducted in a 50mm bench scale bubbling fluidized bed reactor at 475°C and a weight hourly space velocity (WHSV) of 2h−1. BET surface area measurements showed a reduction of 24% and 34% in the surface area of the FCC catalyst after steam treatment at 732°C and 788°C respectively. The non-phosphorus based ZSM-5 additive lost about 15% of its surface area after mild steaming at 732°C. However, the phosphorus impregnated ZSM-5 additive was not affected at both steaming conditions. The hydrothermal treatment of the catalysts influenced the catalytic product distribution and the quality of the bio-oil. The steamed FCC catalyst produced higher organic liquid and gas yields and lower formation of coke and water. The viscosity and the density of the bio-oils produced from the steamed FCC catalyst were lower than those produced with the fresh FCC catalyst. In the case of the ZSM-5 additives, the steam treatment affected only the organic liquid and gas yields. The organic liquid yield increased and the gas yield decreased. Steaming of the ZSM-5 additive did not show any effect on the char/coke yield as was seen with the FCC catalyst due to the lower tendency of ZSM-5 to form coke. The GC analysis of the product gases suggested that steam treatment influenced the catalyst selectivity in the formation of CO, CO2, H2, CH4 and C2C5 hydrocarbons. The 13C NMR analysis of the bio-oil showed generally that steaming of the FCC catalyst increased the selectivity for the production of aromatic hydrocarbons.