Characterization, Evaluation, and Fouling Analysis of Reverse Osmosis and Nano-Filteration Membranes for Sugar Concentration and Inhibitor Separation Using Complex Lignocellulosic Biomass Hydrolysate within a Biorefinery

The U.S. Renewable Fuels Standard (RFS) mandates the production of 36 billion gallons of biofuels (mainly ethanol and biodiesel) annually by 2022.  Of this, 16 billion gallons is expected to be from “cellulosic biofuels,” which are derived from plant sources such as trees and grasses. The Black Hills of South Dakota is rich in ponderosa pine.  This feedstock for bioethanol production, which is widely available due to recent pine beetle infestation,  will not only add to the RFS requirement, it will also have a positive impact on rural economies in South Dakota. From the wood chips of pine, after acid pretreatment and enzymatic hydrolysis, the fermentable sugars obtained are relatively dilute in concentration (~20-30 g/L). Hence, within a biorefinery, to increase the fermentation efficiency and decrease downstream processing cost of the biofuels, concentrating the sugars can be beneficial.  In this study, RO and NF membranes were tested with complex lignocellulosic hydrolysate samples for their ability to concentrate sugars prior to fermentation. Fouling analysis and membrane characterization for both RO and NF membranes were performed by SEM, AFM, BET, contact angle and FTIR spectroscopy. Efficiency of membranes for their ability to separate fermentation inhibitors (e.g., organic and mineral acids, furans and phenolic compounds) from sugars, while simultaneously concentrating the sugars was studied to make the bio-ethanol production process cost and energy efficient. In addition, the molecular modeling software Material Studio 5.0 was used to theoretically evaluate the interactions between different membrane chemistries and the components present in a lignocellulosic enzymatic hydrosylate.  Molecular modeling was also used to guide the design of membrane modifications that could be used to potentially improve performance.