Fractionation of Pre‐Hydrolysis Products from Lignocellulosic Biomass by an Ultrafiltration Ceramic Tubular Membrane

Abstract

Development of the lignocellulosic‐biomass‐based biorefinery for making transportation fuels requires the production of valuable byproducts, minimizing the chemical consumables, and efficient water recovery and reuse. Our focus is on a liquid stream containing a variety of soluble lignin species and alkalinity that is produced by a novel extrusion reactor that was used to break down corn stover to cellulose, sugar acids, and lignin. We report on the ambient temperature fractionation of this byproduct stream with a γ‐alumina ceramic tubular membrane. There are four primary figures‐of‐merit investigated in this study: permeance decline, total organic carbon recovery (TOC) and sodium recovery, and the average molecular mass of organic compounds rejected and permeated. These fractionation results are compared relative to differing feed compositions, recovery, and flux. There was definite fractionation between organic (mostly soluble lignin) compounds. The average molar mass of the organic compounds in the permeate remained around 1000 g/mol; however, they ranged from 1500–4000 g/mol in the retentate. In contrast to the TOC, there was no rejection of sodium ions by the membrane (a desirable objective.) With respect to flux decline, the primary form of resistance (>99%), causing significant permeance decline, was a gel/deposition layer formed on the membrane surface. However, this could be flushed away with periodic rinses using water and/or 0.1 M NaOH. After operation at a cumulative filtration load of ∼4.9 Mg/m2 with various soluble lignin containing streams, 70% of the membrane's virgin pure water permeance could be recovered by a more vigorous cleaning with 0.1 M NaOH including soaking and permeation. Our results seem very consistent with those previously observed for membrane applications within the pulp and paper industry.