Microwave pyrolysis of textile dyeing sludge in a continuously operated auger reactor

Abstract

Textile dyeing sludge (DS) was pyrolysed using an auger pyrolyser under microwave irradiation. It showed the non-condensable gas yield was increased as reactor temperature increased and the char yield decreased with temperature. The condensate and oil yields reached maximum at 650°C (i.e. 12.86wt% and 0.84wt%, respectively). The content of C, H and N in DS and sludge char (SC) decreased with temperature while S increased. The SC and sorbents (e.g. CaO) showed positive effects on sulfur retention. The maximum BET surface area of 91.9m2/g was observed for SC at 550°C. Addition of catalysts such as CaO and Fe decreased pyrolysis oil yield and increased the H2 yield. Oxygenates were mainly formed at 450–650°C. The relative content of aromatic compounds in the pyrolysis oil increased as temperature increased, up to 88.38% (GC–MS area) at 750°C. Heterocyclic aromatic compounds containing nitrogen accounted for 20%–58% of the pyrolysis oil. The H2 content increased from 25.39vol% without catalyst to 64.17vol% with addition of 30wt% CaO. As concentration in DS and SC was beyond the control standards for forestland use in China and should be further treated and disposed. The electricity consumption for pyrolysing DS of 60wt% water content were 0.76–2.59kWh/kg wet DS in the temperature range of 450–750°C and auger speed range of 1–9rpm. Higher pyrolysis temperature and lower auger speeds increased electricity consumptions.