Thermal properties of lignocellulosic precipitates from neutral sulfite semichemical pulping process

In a neutral sulfite semichemical (NSSC) pulping process, wood chips are pretreated with sodium sulfite and sodium carbonate solution. This pretreatment dissolves a part of hemicellulose and lignin from wood chips. The spent liquor (SL) that is produced in the pretreatment process contains a considerable amount of lignosulfonate and hemicelluloses, but SL is generally treated in the wastewater effluent system of the mills (i.e. lignocelluloses are wasted). In this paper, these lignocelluloses were separated from SL with organic solvents, and their thermal properties were determined. The results showed that the precipitates isolated from SL/acetone, SL/ethanol or SL/isopropyl mixtures with the weight ratio of 67/33 had the highest heating values of 18.61, 17.59 and 17.05 MJ/kg, respectively. The precipitates made from mixing acidified SL and solvents had lower heating values than those made from mixing untreated SL and solvents, which is likely due to the relatively high ash content of the precipitates made from mixing acidified SL and solvent. The theoretical and experimental heating values of precipitates were compared in this work. The precipitates displayed lower ignition temperatures compared with other biomass-based solid fuels, implying that the combustion of precipitates would require lower activation energies.