Effect of reaction parameters and catalyst type on waste plastics liquefaction and coprocessing with coal

Abstract

The effect of reaction conditions and catalyst type on the liquefaction behavior of model waste plastics and on the coprocessing of model waste plastics with coal was evaluated. Individual model plastics and mixtures of these plastics were catalytically reacted at temperatures of 400 to 440 °C with an initial H 2 pressure of 5.6 MPa using fluid catalytic cracking catalysts and a zeolite HZSM-5. Higher conversions to tetrahydrofuran-soluble material were achieved in the reactions of individual model plastics than in the reaction with various mixtures of model plastics, while higher hexane soluble yields and lower gas yields were obtained with the mixtures. A base plastics mixture composed of 50% high density polyethylene (HDPE), 30% polyethylene terephthalate (PET), and 20% polystyrene (PS) was used to evaluate the effect of reaction time and initial H 2 pressure on the conversions and product distributions achieved. Reaction times of 120 min produced high and similar conversions and product distributions from HZSM-5 and two fluid catalytic cracking catalysts; however, the differences in the three catalysts' activities were much larger for converting the plastics at shorter reaction times of 30 and 60 min. The highest conversion of the base plastics mixture occurred when the initial H 2 pressure was low. Addition of aromatic, hydroaromatic, cycloalkane, and straight chain aliphatic solvents to the base plastics mixture influenced the conversion and product distribution obtained. For all three catalysts, the straight chain aliphatic solvents were the most effective for solvating the cracked polymer products and promoting higher conversions. Coprocessing reactions of the base plastics mixture with coal yielded the highest conversion when they were reacted catalytically without a solvent. Introduction of a solvent required higher severity conditions to achieve equivalent conversions as reactions without solvent.