Pyrolysis of cellulose in aromatic solvents: Reactivity, product yield, and char morphology

•Pyrolysis in aromatic solvent retards cellulose degradation.•Aromatic solvents bearing polar >CO groups are effective at suppressing pyrolysis.•Yields of levoglucosan and 5-hydroxymethylfurfural rise in aromatic solvents.•Film-like char is formed from cellulose pyrolyzed in aromatic solvent.•5-Hydroxymethylfurfural is a precursor of solid carbonized products.

Aromatic solvents are known to stabilize levoglucosan (1,6-anhydro-β-d-glucopyranose), the major pyrolysis intermediate of cellulose, against thermal degradation including char formation. In this article, pyrolysis of cellulose, a crystalline component of biomass, was investigated in the aromatic solvents 1,3-diphenoxybenzene, diphenyl sulfide, and benzophenone under nitrogen at 280 °C. Thermal degradation of cellulose (Whatman filter paper) was markedly delayed in the aromatic solvents and gave thin film-like char after the removal of unreacted cellulose through hydrolysis. The yields of levoglucosan and 5-hydroxymethylfurfural were greatly enhanced in the aromatic solvents. These observations are discussed at the molecular level in terms of the interactions of cellulose crystallites and the pyrolysis products with the aromatic solvents. A possible char formation mechanism via 5-hydroxymethylfurfural involving the ultrastructure of the cell wall is also discussed. This study provides insight into the molecular-based cellulose pyrolysis mechanisms and efficient and selective thermochemical production of bio-based materials and chemicals.