Separation of lignocelluloses from spent liquor of NSSC pulping process via adsorption

• Removal of lignocelluloses from spent liquor of NSSC process was investigated via adsorption.
• Optimal conditions for adsorption on activated carbon were SL/AC wt ratio of 30, 30 °C, pH 5.7 and 360 min treatment time.
• A maximum of 0.33 g/g lignin and 0.25 g/g hemicelluloses were adsorbed on activated carbon.
• The turbidity and COD removals were 39% and 11%, respectively.

Hemicelluloses and lignin present in the spent liquor (SL) of neutral sulfite semichemical (NSSC) pulping process can potentially be converted into value-added products such as furfural, hydroxymethylfurfural, levulinic acid, phenols and adhesives. However, the direct conversion of hemicelluloses and lignin of SL into value-added products is uneconomical due to the dilute nature of the SL. To have a feasible downstream process for utilizing lignocelluloses of SL, the lignocelluloses should initially be separated from the SL. In this study, an adsorption process (via applying activated carbon) was considered for isolating the dissolved lignin and hemicelluloses from the SL of an NSSC pulping process. Under the optimal conditions of pH, SL/AC weight ratio, time and temperature of 5.7, 30, 360 min and 30 °C, the maximum lignin and hemicellulose adsorptions were 0.33 and 0.25 g/g on AC. The chemical oxygen demand (COD) and turbidity of the SL were decreased by 11% and 39%, respectively, as a result of lignocellulose adsorption on AC. Also, the incineration behavior of the SL-treated AC was studied with a thermo-gravimetric analysis (TGA).