Microwave-assisted pyrolysis spent bleaching clay for aromatic bio-oil production: Exploration of heating pathway based on microwave response characteristics of feedstock

Spent bleaching clay (SBC) is a waste generated from the refining process of edible oils. SBC contains some residual oils, with excellent potential to produce aromatic bio-oil. For the first time, microwave-assisted pyrolysis was used to treat SBC, which has unique microwave response characteristics. The products of microwave heating and electric heating were investigated, under three conditions: no catalyst, in-situ catalysis, and ex-situ catalysis. Microwave heating saved 50% of the reaction time and up to 53% of the energy consumption, compared to electric heating. Microwave heating facilitated the formation of aromatic hydrocarbons by promoting hydrogen transfer and cyclization reactions. In comparison with electric heating, the aromatic hydrocarbons relative content was increased by 15.46% under no catalyst. In addition, the optimal pyrolysis temperature, catalytic temperature, feedstock to catalyst mass ratio (F/C) and nitrogen flow rate based on microwave heating pathway were 500 °C, 500 °C, 10/1, and 50 mL/min, respectively. Under these conditions, the relative content of aromatic hydrocarbons was 87.89%. Microwave-assisted catalytic pyrolysis is a fast and energy efficient pathway to produce aromatic bio-oil from SBC, which can provide a theoretical basis for resource utilization of SBC.