Bio-oil production via catalytic microwave pyrolysis of model municipal solid waste component mixtures

Abstract

In this study, microwave assisted co-pyrolysis of mixtures of cellulose, paraffin oil, kitchen waste and garden waste that closely mimic municipal solid wastes (MSW) is conducted at different reaction conditions. Experiments were conducted in a multimode microwave reactor using ten different microwave absorbing materials (or susceptors) such as aluminium, activated carbon, garnet, iron, silica beads, cement, SiC, TiO₂, fly ash and graphite. Pyrolysis was conducted up to 600 °C, and the effects of feed to susceptor ratio and composition of the model MSW mixture on (i) overall bio-oil, gas and char yields, (ii) heating value of the bio-oil, and (iii) composition of the bio-oil and gases, were evaluated. Besides greatly affecting the yields of bio-oil, gases and char, the susceptors played a catalytic role in altering the selectivity of the various components in bio-oil. The bio-oil contained oxygenated compounds (furans, phenolics, cyclo-oxygenates), aliphatic and aromatic hydrocarbons (mono and polycyclics). Aromatic hydrocarbons were the key products of interaction among the model components. Highest bio-oil yield of 53 wt% was achieved with an equal composition mixture at 1 : 1 wt/wt of MSW : graphite. This corresponded to nearly 95% energy recovery and 85% deoxygenation in bio-oil. High selectivities of monoaromatics such as benzene, toluene, xylene and styrene, and C8–C20 aliphatic hydrocarbons, and low selectivity of polycyclic aromatics were obtained with a majority of the susceptor–MSW combinations. Methane, ethylene, propylene, isobutylene and hydrogen were the major gaseous products, whose selectivities varied with MSW composition. This study shows that microwave assisted pyrolysis is a promising strategy to derive value added organics from MSWs.