Fractionation of sugar beet pulp polysaccharides into component sugars and pre-feasibility analysis for further valorisation

Sugar beet pulp (SBP) is a by-product formed in large amounts during the production of refined sugar and is currently used as a low-cost feed for livestock. The dry SBP comprises largely three polysaccharides (75–85%), cellulose, hemicellulose and pectin, whose component sugars constitute potential valuable feedstock for producing building blocks for chemicals and materials. In the present study, a simple and integrated process for the fractionation of SBP polysaccharides into streams enriched with corresponding sugars is developed. Initial screening of several pectinase preparations (from Novozymes) for the treatment of dry SBP (at initial pH 4.0, 50 °C) showed Pectinase ME to release the maximum amount of galacturonic acid (GalU) along with high amounts of arabinose (Ara). On the other hand, subjecting the SBP to acid hydrolysis using 0.64 M sulphuric acid at 80 °C was relatively selective in solubilising mainly Ara (71.3% of the initial content), and the subsequent treatment with Pectinase ME solubilised 68.5% of the initial GalU content. Treatment of the residual solid fraction with cellulases released 81.9% of the original glucose content. Size-exclusion chromatography revealed the presence of oligomers ranging from dimers to pentamers in the acid and pectinase hydrolysates. Mass-balance based process analysis of 1000 kg_dry/h SBP biorefinery using the three-stage fractionation of sugars and further valorization to arabitol, mucic acid and levulinic acid, respectively, indicated the potential economic feasibility and value addition of SBP, which is currently sold at 200 US$/t as animal feed. Recycling of water and catalysts would be important for reducing waste generation and improving environmental performance.