PET recycling via gasification - Influence of operating conditions on product distribution

Abstract

EU plans to achieve 100% plastic packaging reuse in 2040, and some new technologies have been proposed. Gasification is one of the promising technologies to convert plastic into syngas for heat production or chemicals synthesis process. This project focused on the thermoplastic that is widely used in textile fibre, film, and bottles – PET. Although PET bottle recycling is reliable, gasification could be an option for recycling contaminated and other PET products. Proximate analysis was carried out by Thermogravimetric Analysis (TGA) to comprehend its thermal decomposition, obtaining volatiles and char. Gasification experiments were conducted in a lab scale bubbling fluidized bed with batch and continuous feeding operation. The batch experiments compared different plastics and gasifying agents. It was found that CO2 dominated the gas production at all agents, and steam can motivate H2 production. However, air cannot reduce tar formation significantly as literature stated. After that, continuous feeding experiments for steam gasification were designedtoinvestigatehowtemperature, residence time and steam/fuel ratio affect the distribution of gas and tar products in PET steam gasification. The results show the temperature is an essential condition parameter for gas and tar yield. The increasing temperature improved the gas yield and tar cracking. The application of syngas produced by PET steam gasification was evaluated based on the experimental results. The highest energy conversion efficiency from PET and reacted steam to cold syngas was 29% at 800 ◦C, meaning that most of heat energy was lost. Fuel synthesis was analyzed by H2/CO ratio, and syngas products are more likely to be produced fuels by FT synthesis. Besides, the tar limitation of both power generation and fuel synthesis are very strict, but the tar concentrations in all cases are extremely high. Mixing with other plastics or biomass and better bed material could be solutions to promote syngas quality. Moreover, the mass balance analysis suggests 35% - 40% carbon was not detected, so sampling and measurement methods should be improved in the future research.