Formation of reaction intermediates and primary volatiles during acid-catalysed fast pyrolysis of cellulose in a wire-mesh reactor

Abstract

This study aims to understand the fundamental reaction mechanisms during fast pyrolysis of the acid-impregnated cellulose in a wire-mesh reactor at 40–450 °C and 20 °C/s, via quantifying key compounds in the reaction intermediates and primary volatiles. Acid impregnation reduces the onset reaction temperature of cellulose pyrolysis. During acid-catalysed cellulose pyrolysis, 1,6-anhydro-β-d-glucofuranose (AGF), levoglucosenone (LGO) and 5-hydroxymethylfurfural (5-HMF) are identified as major products in the primary volatiles, and the formation of levoglucosan is greatly suppressed. At temperatures < 100 °C, acid catalyses hydrolysis reactions to produce glucose, which is further dehydrated to AGF at 120 °C. At temperatures > 160 °C, acid enhances the dehydration of glucose, levoglucosan and AGF to produce 5-HMF and LGO as major primary products. Once produced, those products can be easily released into the vapour phase, as either aerosols via thermal ejection or vapours via evaporation. As the pyrolysis temperature increases to 240 °C, aromatic compounds can be identified in the primary volatiles, indicating condensation reactions also play important roles during acid-catalysed cellulose pyrolysis under the conditions. As a result, char formation becomes the favoured pathway during acid-catalysed cellulose pyrolysis at temperatures > 300 °C.