Effect of the two-stage process comprised of ether extraction and supercritical hydrodeoxygenation on pyrolysis oil upgrading

In this research, Ni-based catalysts with different supports (HBeta and HZSM-5) were prepared via the impregnation method and subsequently tested for the catalytic hydrodeoxygenation (HDO) of crude pyrolysis oil (CPO) using supercritical methanol (MeOH). The Ni/HBeta showed a better catalytic performance than Ni/HZSM-5, resulting in a 43.81% deoxygenation degree of CPO. In addition, the ether extraction of CPO was carried out to remove its heavy fraction and improve the efficiency of the upgrading process. A high-quality refined oil was achieved after using the combined physicochemical treatments of ether extraction and supercritical catalytic HDO. The upgrading efficiency was evaluated in terms of the degree of deoxygenation, carbon residue value, water content, higher heating value, and distribution of products. The effect of the type of supercritical solvent on the catalytic HDO performance of Ni/HZSM-5 was evaluated by replacing MeOH with ethanol (EtOH). The results showed that when MeOH was substituted with EtOH, the yields of the gaseous and solid products were significantly reduced, while the yield of liquid products was considerably increased. Meanwhile, the content of coke deposited on the catalysts was analyzed using thermogravimetric analysis, and the coke compositions were evaluated using Fourier-transform infrared (FTIR) spectroscopy. While the minimum catalytic coke content was obtained using Ni/HBeta in the supercritical HDO of CPO, the minimum coke content was observed using Ni/HZSM-5 in the upgrading of ether-extracted pyrolysis oil (EEPO). The FTIR results revealed that the coke deposited on the catalysts was mainly formed through condensation, rearrangement, and hydrogen transfer mechanisms.