Study on the polystyrene plastic degradation in supercritical water/CO2 mixed environment and carbon fixation of polystyrene plastic in CO2 environment

Through the degradation of organic waste, the carbon can be extracted and converted into syngas with calorific value, and the CO2 generated can also be used after fixed. In this work, the gasification of polystyrene (PS) in supercritical water with CO2 was studied in the temperature range of 400 °C-700 °C and time range of 0-30 min. In addition, PS containing only carbon and hydrogen can react with CO2 to generate CO in CO2 atmosphere. Therefore, the degradation of PS plastics in CO2 atmosphere was also studied. The results showed that PS plastic was hardly gasified at 400 °C, and as the temperature rose, the liquid composition changed. In supercritical water, under certain feedstock conditions, reacting for 20 min, the carbon conversion efficiency of PS plastic reached 47.6% at 700 °C. Under all CO2 atmosphere conditions in this experiment, the highest proportion of CO2 consumed by PS degradation was 12.5%. Moreover, the higher the temperature, the smaller the average diameter of carbon microspheres in the solid product. The morphology of carbon microsphere was also related to the reaction time, and the main change came from the gasification of carbon microspheres and the precipitation and adhesion of carbon element in liquid product.