Energy Recovery From Composite Acetate Polymer-Biomass Wastes via Pyrolysis and CO2-Assisted Gasification

Abstract

Abstract Discarded cigarette butts contain polymers, biomass, and a variety of toxins that cause an adverse effect to the human health and environment for years. The cigarette residuals are not recyclable and often get mixed with other kinds of wastes so that much of this waste ends up in landfills. This study investigates the safe disposal of cigarette butts by the thermochemical pathways using pyrolysis and gasification. Mass loss during its thermal decomposition was examined first using a thermogravimetric analyzer. The effect of temperature on the pyrolysis and CO2-assisted gasification was then conducted using a semi-batch reactor with a focus on the flowrate of total syngas and its gas components. Syngas yield, energy recovery, as well as energy efficiency were calculated and compared. The effect of temperature on the CO2 consumption during the gasification process was also examined. The thermal decomposition of cellulose acetate, tar, and wrapping paper were the main contributors during the pyrolysis of cigarette butt. However, the gasification process mainly consisted of the pyrolysis, cracking, and reforming reactions in the gas phase and gasification of char derived from wrapping paper. An increase in temperature enhanced the syngas flowrate, syngas yield, and gas efficiency while decreasing the char yield and reaction time for both the processes. Energy recovery from gasification was higher than pyrolysis due to added CO generation. The maximum syngas energy of 13.0 kJ/g under the gasification condition at 1223 K was 67.2% higher as compared with the pyrolysis. High temperature strongly affected the gasification reaction, while it was negligible at a temperature lower than 1023 K. Complete conversion occurred during gasification at 1223 K that provided only ash residue. The CO2 gasification of cigarette butts provided an effective pathway to utilize 0.5 g CO2/g feedstock at 1223 K to form valuable CO by the Boudouard reaction. Compared with the gasification of other solid wastes, syngas energy yield from cigarette butts was found to be higher than syngas from polystyrene and polyethylene terephthalate. These results support the effectiveness of thermochemical pathways in the rapid conversion of cigarette butts to valuable syngas along with CO2 utilization.