13-05: Performance evaluation and fouling analysis of reverse osmosis membranes and evaporator heating surfaces during concentration of enzymatic hydrolysate sugars

Within the biorefinery paradigm for production of renewable fuels and chemicals, concentrating the sugar-rich hydrolysate stream by evaporation and/or reverse osmosis (RO) prior to fermentation can enhance the fermentation productivity and reduce downstream separation costs.  However, fouling of the evaporator surface or reverse osmosis membrane by soluble and suspended solids within the process steams can become problematic.  In this study we analyzed the performance and fouling characteristics of an evaporator surface and RO membranes using a pine wood enzymatic hydrolysate.  During evaporation, the rate and severity of fouling, along with the induction period for scale deposition, depended strongly on temperature and the concentration of soluble and suspended solids, with maximum fouling occurring at the highest temperatures with no suspended solids present. Characterization of the fouling deposits has been studied using FTIR, SEM-EDS and ICP analysis.  For RO, five different membranes were tested at a constant operating temperature and pressure.  In this case, osmotic pressure limitations, due to the high concentration of soluble compounds, were found to be a major source of flux reduction.  However, fouling of the membrane, due to interactions between soluble and insoluble compounds with the membrane surface, also contributed to poor performance.  Systematic evaluation and characterization of membranes by BET, SEM, AFM, surface contact angle and FTIR were used to understand the fouling mechanisms of each membrane.  Based on these investigations, economic comparisons were made and fouling reduction techniques were suggested to improve the process efficiencies when using either evaporation or RO for concentrating enzymatic hydrolysate sugars.