Co-pyrolysis of dyeing sludge and pine sawdust in a fluidized bed: Characterization and analysis of pyrolytic products and investigation of synergetic effects.

Co-pyrolysis of dyeing sludge (DS) and pine sawdust (PS) was carried out in a fluidized bed pyrolyser. The results revealed that addition of PS increased the yields of condensate and gas, and dramatically improved pore structure of co-pyrolysis char, enhancing immobilization of the metals, nutrient and pollution elements. Catalysts (Na-ZSM-5 and HZSM-5) significantly reduced tar and coke, strengthened the integrity of pore structure. Yield of nitrogen-containing compounds declined sharply from 88.66% to 8.14% when 25% of PS was added. Addition of 50% PS promoted ring opening to generate chain compounds and abundant oxygenates (such as ketones, aldehydes and carboxylic acids) in pyrolysis oil (PO) at 650 °C. Correspondingly, yield of gaseous products was inhibited except CO2 and H2 when PS content was dominant. The catalysts greatly increased yield of gaseous products by enhancing primary and secondary cracking depending on different feedstocks and catalysts (e.g., DS over Na-ZSM-5 and PS over HZSM-5). The maximum energy efficiency (69.75%) was obtained at 650 °C when 75% PS was added.