Techno-economic evaluation for the process optimization of galactoglucomannan and lignin recovery by ultrafiltration

Galactoglucomannans (GGM) can be used as a precursor for the production of surfactants, plastics, hydrogels etc. However, separation of galactoglucomannan (GGM) from lignin and lignin-carbohydrate-complexes using membrane filtration is difficult. Precipitation of GGM with anti-solvents is an approach that has been previously studied. A membrane filtration step prior to precipitation is economically beneficial to decrease anti-solvent requirements with increasing concentration of GGM. However, previous studies have shown that membrane fouling is a problem that can have a large impact on the life-time of the membranes but also the overall yield of the products.

The raw material used in this study was a sodium-based spent-sulfite-liquor (SSL) provided by Domsjö Fabriker (Örnsköldsvik, Sweden) and is the outtake after the first pulping step of softwood (60 % Picea abies and 40 % Pinus sylvestris). The SSL was concentrated with a 50 kDa polysulfone membrane (hydrophobic) and four regenerative cellulose membranes (30, 20, 10 and 5 kDa) (hydrophilic) to a volume reduction of 90 %. The resulting retentate was analyzed for the composition and the product yields were calculated. Membrane data, such as, flux, trans-membrane pressure, cross-flow velocity and degree of fouling were used together with the GGM yields in a techno-economic evaluation to find a cost-efficient process for the separation and purification of GGM and lignin from SSL.