BACKGROUND Spent sulfite liquor is a by‐product obtained in the process of manufacturing dissolving pulp by the acid sulfite method. A full physico‐chemical characterization of this waste has been developed in order to determine if it is susceptible to valorization by means of biorefinery processes. RESULTS The main components present in this spent liquor are sugars from hemicelluloses (25.9%), mainly xylose (18.2%) because hardwood is used as a raw material, and lignosulfonates (50.6%). Taking into account the results obtained, a literature search has been done in order to establish the biorefinery options for this lignocellulosic waste, giving lignosulfonates, xylitol, ethanol, polyhydroxybutyrate or polybutylene‐succinate, hydrogen and furfural as the best options. However, other compounds present in the liquor such as furans, acids and inorganic pollutants can complicate the valorization options. CONCLUSIONS Spent sulfite liquor can be a good feedstock for biomass based processes. This paper will be useful for future work regarding the potential biorefinery opportunities of the sulfite mill. © 2014 Society of Chemical Industry

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BACKGROUND: Spent sulfite liquor, a by-product obtained in the process of manufacturing dissolving pulp, contains 26% of sugars that can be valorized in order to obtain high value-added products by means of biorefinery processes. A technoeconomic assessment of three options, furfural, xylitol and ethanol, has been developed with the purpose of identifying which alternative is the best for the case study mill. RESULTS: Different techniques of fractionation/detoxification of the spent liquor such as ultrafiltration, resins or adsorptionwere tested; anionic resins were selected as the most feasible. A technical evaluation of the three biorefinery options producing 19.92, 15.84 or 14.64 t day −1 of furfural, xylitol and ethanol, respectively, was performed. The study was pursued with the sizing and costing of the equipment. For the economic evaluation, the fixed capital invested and the manufacturing costs for each valorization option were computed as well as the return period and the net present value. In addition, a sensitivity analysis was performed for the most promising option. CONCLUSIONS: Spent sulfite liquor can be profitably processed in the considered mill. According to the data obtained by simulation and the analysis performed, the best valorization option is the production of xylitol.

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