Co-pyrolysis of polyethylene terephthalate and poplar wood: influence of zeolite catalyst on coke formation

In this study, poplar wood and PET were co-pyrolysed in a fixed-bed reactor in the absence/presence of zeolite (A4 type), aiming to understand the migration pathway of oxygen from both oxygen-containing feedstocks into products. The results indicated that both co-pyrolysis and the zeolite catalyst affected the properties of the products. Comparing to single feedstock, the co-pyrolysis enhanced the yields of tar, while reduced the formation of char, and wax. In addition, the co-pyrolysis decreased the abundance of oxygen-containing and unsaturated species in the tar, and oxygen migrated from feedstock mainly into gas phase in the form of CO and CO2. Zeolite further enhanced the rate of cracking, reducing the yield of char and wax, while increasing the formation of gases. The high rate of cracking/deoxygenation reactions over the zeolite catalyst led to the formation of more light organics, which were mainly saturated aliphatics or aromatics, in the tar. In addition, the zeolite catalyst changed the structure of char, but it did not affect the structure of wax significantly. Little amount of oxygen-containing coke with mainly organized aromatic structure was formed. Zeolite enhanced the migration of oxygen into char and coke. A substantial amount of monoaromatics were formed inside the tar.