Membrane filtration: Concentration and purification of hydrolyzates from biomass

Sugars, acetic acid and other chemicals in aqueous biomass hydrolyzate can be separated by Nano-Filtration (NF) membranes. Fractionation of the complex hydrolyzate to platform chemicals is a key step in a biorefinery. Sugars can be concentrated, separated and/or cleaned and then utilized as fermentation feedstock. A mathematical model relating the permeate flow rate and the pressure drop has been derived based on flow through porous media coupled with the osmotic pressure. Experimental data on the filtration of hot-water wood extracts showed good agreement with the model. Experimental data revealed that there is a minimum pressure drop, i.e., the osmotic pressure, at which no permeate flow is found. The permeate flow rate increases with increasing pressure drop and decreases with increasing extract concentration. For the membrane having a molecular weight cut-off of 100 g/mol, sugars, polysaccharides and aromatics are preferentially retained in the concentrate stream. Acetic acid, methanol, furfural, hydrolxymethylfurfural and formic acid are preferentially removed to the permeate stream. Thus, sugars can be cleaned and concentrated with the NF-membrane.