Pyrolysis and ex-situ vapor upgrading of pine nut shells over Ni- and Co-modified HZSM-5 catalysts to high-quality bio-oil and syngas

The ex-situ catalytic upgrading of pine nut shell pyrolysis vapor was conducted over Ni/HZSM-5 and Ni-Co/HZSM-5 catalysts using a fixed bed reactor. The effects of the catalytic temperature (500-800 °C) and pressure (0.1-0.6 MPa) on the yield and composition of the products were investigated. The physicochemical properties of bio-oil were visibly improved by increasing the temperature and pressure, and the products mainly contained light aromatic hydrocarbons, aliphatic hydrocarbons and phenolic compounds. The addition of Co significantly enhanced the deoxidation ability of the Ni-Co/HZSM-5 catalyst, and the BTXEN yield of the upgraded bio-oil increased to 15.3 mg/g with a heating value of 36.80 MJ/kg. Less water was generated in pressurized catalysts, and the syngas yield significantly increased with increasing pressure. Based on mechanistic considerations, atmospheric pressure catalysis favors alkylation, and high-pressure catalysis increases the syngas yield.