Importance of char-volatiles interactions during co-pyrolysis of polypropylene and biomass components

This study reports the importance of plastic volatiles on char-volatiles interactions during co-pyrolysis of polypropylene (PP) and biomass components under non-catalytic conditions in a two-stage reactor. PP-volatiles were generated and interacted with biochar from cellulose and lignin downstream at different temperatures. Different experiment configurations were designed in order to explore the contribution of the tarry and waxy materials in PP-volatiles to the char-volatiles interactions. Experimental results showed that the char-volatiles interactions altered the yield and the chemical structure of PP-oil and biochar. The O-containing and aromatic species in biochar acted as active sites during interactions. Large aromatic rings in the biochar were predominant during the cracking of the tarry materials in PP-volatiles, while the O-containing species dominated during the recombination and polymerization of the waxy material in PP-volatiles. At higher temperatures, waxy and tarry materials released H-radicals inside the cellulose-char matrix, and strengthened the ring aromatic condensation reactions, while waxy and tarry materials were involved in heavier aromatic structures in lignin-char, leading to the fragmentation of lignin. In addition, even at low temperatures (e.g. 500 °C), waxy material can provide hydrogen and slightly enhance the condensation of the aromatic ring systems in lignin-char.