(336k) Coupling of Membranes and Chromatographic Separation for the Production of Fermentable Monosaccharides in a Wood-Based Biorefinery

Integration of a wood-based biorefinery to existing pulp mills has recently received considerable attention both in Europe and in North America. According to the process schemes presented, the two products with largest volumes are ethanol and acetic acid. Ethanol can be produced by extracting hemicellulose from wood, converting it into monosaccharides with acid hydrolysis (or enzymes), and fermenting the monosaccharides. Acetic acid is formed as a by-product in the acid hydrolysis stage.

Several separation steps are required in such a process. Chromatographic separation with ion exchange resins has recently been applied to separate the hydrolysis acid (for recycling) and fermentable sugars. Also simultaneous recovery of acetic acid is possible. In general, the drawback of adsorptive separations is dilution of the products. Although dilution is not excessive in continuous chromatographic SMB processes, both cost efficiency and sustainability considerations call for optimized process schemes. One benefit of membrane separations is that, when the product is the retentate, it is concentrated compared to the feed.

In the present work, various possibilities to couple chromatography and membrane separation for the production of fermentable monosaccharides and acetic acid in a wood-based biorefinery were investigated. Authentic hydrolysates from lignocellulosic biomass (spruce), as well as synthetic solutions, were used. Hemicellulose was extracted from swollen wood chips with water at 430 K, and the solution was treated with sulphuric acid to hydrolyze the dissolved polysaccharides. Concentration and purification of the hydrolysate by cross-flow filtration was investigated with different UF membranes (Microdyr Nadir, Koch, GE Osmonics). Several strong acid cation exchange resins with varying cross-link densities and particle sizes were used in the chromatographic acid-sugar separation. The influence of the concentration of the feed solution of the maximum loading of the column was of particular interest.