Preliminary safety evaluation of solvothermal liquefaction of plastic wastes using toluene as solvent

Solvothermal liquefaction (STL) is a promising thermochemical process to produce biocrudes from plastic wastes. In the STL process, solvents, other than water, play a significant role in increasing overall biocrude yield and its properties. However, many of the STL solvents as well as the resulting biocrudes are flammable and hazardous in nature, especially when STL is operated at sub- and supercritical conditions. Therefore, safety evaluation of the STL process is a vital component of the technology advancement. In this study, a STL process with a capacity of 200 tonnes/day feed (1:10 wt/wt plastic wastes to toluene) has been considered. The plant was assumed to be operated at a subcritical temperature of toluene (318 °C) and its autogenous vapor pressure (about 41 bar). A conceptual process flow diagram was constructed, and complete hazard identification along with preliminary risk assessment was performed. Moreover, a consequence model was developed to study the formation of flammable and toxic clouds, potential radiation thermal energy, and over-pressurization on the surrounding area due to a simulated incident of the plant. Based on the preliminary risk assessment, this study proposed a piping and instrumentation diagram (P&ID) with necessary preventive and mitigative safeguards that could minimize the incident occurrence and severity of the post-incident, respectively. Graphical abstract