Catalytic Pyrolysis of Pinyon–Juniper Using Red Mud and HZSM-5

Abstract

Pinyon and juniper are invasive woody species in the western United States that occupy over 30 million hectares of land. The U.S. Bureau of Land Management (BLM) has embarked on harvesting these woody species to make room for range grasses for grazing. The major application of harvested pinyon–juniper (PJ) is low-value firewood. Thus, there is a need to develop new high value products from this woody biomass to reduce the cost of harvesting. We investigated the fractional catalytic pyrolysis of PJ using both HZSM-5 catalyst and red mud at 475 °C in a fluidized bed reactor at atmospheric pressure. Both the HZSM-5 and the red mud were effective catalysts for producing low-viscosity pyrolysis oils. Oils that were catalyzed with red mud had a lower viscosity (96 cP @40 °C) than oils that were catalyzed with HZSM-5 (213 cP @40 °C). In both cases, the yields of liquids ranged from 42 wt % to 49 wt %. The mechanisms of catalysis by the two catalysts were quite different. The HZSM-5 rejected oxygen mostly as carbon monoxide (CO) and produced lower amounts of carbon dioxide (CO2); in contrast, the red mud produced more CO2 and less CO. However, both catalysts produced similar amounts of water. The char/coke yields from both catalysts were similar but the total gas yields were slightly different. The higher heating value of the red mud catalyzed oil (HHV = 29.46 MJ/kg) was slightly higher than that catalyzed by HZSM-5 (HHV = 28.55 MJ/kg). Thus, red mud can be used to achieve similar catalytic pyrolysis results as HZSM-5 catalysts.