Carboxylic Acid Concentration in Downstream Bioprocessing Using High-Pressure Reverse Osmosis

During the production of many bio-based chemicals from fermentation and enzymatic processes, product separations frequently represent the most expensive and energy-intensive unit operations in an integrated process, often due to the low concentrations of target bioproducts. In this study, we integrated high-pressure reverse osmosis (HPRO) to concentrate an exemplary fermentation product, butyric acid, prior to downstream extraction. Through both modeling and experimental measurements, we identified the major factors limiting the maximum achievable concentration factor (CF) of 4.0 for butyric acid concentration with an HPRO membrane compared to the 2.6-3.2 range for conventional reverse osmosis (RO) membranes. The resulting concentrated aqueous stream underwent liquid-liquid extraction with an organic solvent and distillation for butyric acid purification and solvent recycling. The integration of HPRO product concentration into an in situ product recovery (ISPR) process leads to >5-fold increase in the final butyric acid concentration in the organic phase, and a concomitant 76% reduction in organic solvent usage. These improvements lead to an estimated 53 and 46% reduction in ISPR butyric acid production cost and greenhouse gas (GHG) emissions, respectively, considerably exceeding the process performance when integrating conventional RO product concentration. Overall, the integration of an HPRO membrane for product concentration enables more economical and sustainable bioproduct recovery from dilute aqueous streams.