Oxidative Liquefaction, an Approach for Complex Plastic Waste Stream Conversion into Valuable Oxygenated Chemicals

Abstract

Various waste streams including municipal solid waste (MSW), polymer waste from personal protective equipment (PPE) used in medical fields, and composite waste from wind turbine blades (WTBs) demand modern waste management and recycling approaches. Ultimate and proximate analysis of mentioned samples revealed a higher content of carbon—28.2 ± 8.0, 80.1 ± 2.3, and 50.3 ± 2.3, respectively—exhibiting sufficient potential to be converted into secondary carbon-based compounds. For this purpose, oxidative liquefaction of selected waste materials was carried out following a detailed experimental plan, a centred composite design for WTBs, and a central composite face-centred plan for MSW and PPEs. Temperature, pressure, oxidant concentration, reaction time, and waste-to-liquid ratio were the parameters of key interest, and their values were tested at a range of 200–350 °C, 20–40 bar, 15–60%, 30–90 min, and 3–25%, respectively, depending upon the type of waste. As a result, total polymer degradation (TPD) was recorded for three types of waste and the results were satisfactory, encouraging the decomposition of primary waste in liquid oxygenated chemical compounds (OCCs). Gas Chromatography with Flame Ionisation Detection (GC-FID) helped us quantify the number of OCCs for each waste sample. Energy consumption during the process was also recorded and optimisation of the experimental plan based on maximum TPD and OCCs yields against the minimum energy consumption was performed to make the process tech-economic.