Application of Box-Behnken design in optimizing product properties of supercritical methanol co-liquefaction of rice straw and linear low-density polyethylene

Abstract

Co-processing of plastic and biomass wastes to produce high-quality fuel has been attracting considerable interest in energy recovery. This work employed Box-Behnken Design (BBD) to optimize yield and properties of oil from supercritical methanol (scMeOH) co-liquefaction of rice straw (RS) and linear low-density polyethylene (LLDPE). Three independent variables of reaction temperature (270, 300, and 330°C), holding time (60, 90, and 120 mins), and RS/LLDPE mass ratio (0.15, 0.50, and 0.85) were selected for experiments. A maximum oil yield of 34.17 wt% was achieved at 303°C, 96 mins, and RS/LLDPE ratio of 0.59 according to BBD. Temperature and RS/LLDPE ratio dominated the oil yield and synergistic effects during co-liquefaction, whereas time was an insignificant factor. Optimum oil from co-liquefaction contained substantial hydrocarbons content of 32.91% compared to that from single RS-derived oil of 7.77%. Solid product obtained at the optimum condition could be used as solid fuel, due to its relatively high HHV of 43.08 MJ/kg compared to the other solid fuels (13.90–32.14 MJ/kg). This work provides a deep understanding of the co-processing of solid biomass and plastic wastes.