Quantification of degree of interactions during co-pyrolysis of nine typical carbonaceous wastes

Organic municipal waste is a mixture of carbonaceous feedstock and cross-interaction of volatiles in their co-pyrolysis has been well documented, but quantifying their extent of interactions in co-pyrolysis is difficult. In this study, the ratio of char yield from co-pyrolysis to calculated average of pyrolysis of single feedstock was used as an indicator to probe the interaction in co-pyrolysis of every two typical carbonaceous wastes (sawdust, rice, spinach, chicken manure, office paper, corrugated paper, plastic bottles/films, fiber towel) at 550 °C. The results indicated that the co-pyrolysis of sawdust and corrugated paper had the highest degree of interaction (0.44). Sawdust and rice with ash-rich feedstock (spinach, chicken manure and office paper) resulted in dominance of gasification reactions to reduce char production in co-pyrolysis process. In comparison, the organics from the degradation of spinach and corrugated/office paper could react with the derivatives (mostly radicals) of plastic bottle (PET), plastic film (PE) or fiber towel (polyesters) via secondary condensation to generate more char. The chicken manure with high ash content hardly forms char of enhanced yield during its co-pyrolysis with other feedstocks. The enhancing char yield through secondary condensation generally resulted in additional oxygen-containing deposit on char and reduced thermal stability, which was the opposite to the formation of char with dominance of gasification. Co-pyrolysis of varied feedstock also led to change of morphologies of char via filling mechanism or formation of organics.