(380f) Experimental Investigation of Nanofiltration Separation Performance for Aqueous Organic Acid Solutions

The emissions from conventional sources of energy actively contribute to the imminent threat of climate change. Curbing these emissions requires transitioning to clean energy technologies with low carbon footprint. Harnessing sustainable energy and materials from renewable sources like biomass provides a promising path to diversify the U.S. energy supply, reducing petroleum reliance for biofuel and renewable chemical production¹. Organic acids obtained from anaerobic fermentation are becoming popular intermediates for the synthesis of bio-based products (e.g., sustainable aviation fuel, bioplastics)² . However, the high emissions and costs associated with their separation and purification pose significant barriers to widespread adoption of this platform. One of the solutions to this problem is membrane separation technology. In comparison to other techniques, membrane separation processes are widely explored due to their low energy consumption, greater separation efficiency, reduced number of processing steps, and high quality of final products³.

The current study examines the separation performance of a nanofiltration membrane for aqueous solutions containing acetic, butyric, and lactic acid, both individually and in combination. This investigation aims to elucidate real-world complexities and offer insights for optimizing membrane separation processes in practical applications. Experiments are carried out using dilute aqueous solutions of single acids (10 – 30g/L), binary acid mixtures (0.1 – 0.2 mol/L), and ternary acid mixtures (0.1 – 0.2 mol/L) with different acid concentrations to simulate fermenter effluents at different applied pressures (3.44 – 27.57 bar) and different solution pH (3 – 10). The results suggest that increasing solution pH enhanced acid rejection while reducing permeate flux (e.g., for acetic-butyric acid mixture, rejection increased by 60% while flux decreased by 40% as pH increased from 3 to10). In contrast, higher solution concentration decreased both permeate flux and rejection (e.g., for acetic-butyric acid mixture, rejection and flux decreased by 50% and 10%, respectively as concentration increased from 0.1 to 0.2 mol/L). This trend is common for all three acids while the rejection is highest for lactic acid and lowest for acetic acid (e.g. for 0.1 mol/L concentration for each acid in a ternary mixture at pH 3 and pressure 20.68 bar, Rejection is 45 % for acetic acid and 90% for lactic acid). The results from this experimental work are modeled using solution diffusion model to understand the efficacy of membrane separation technique to purify bio-based chemicals and the deficiencies in the model are identified to lay a groundwork for an enhanced thermodynamic model.

References:

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2. Holtzapple, M.T., Wu, H., Weimer, P.J., Dalke, R., Granda, C.B., Mai, J. and Urgun-Demirtas, M., 2022. Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: A review. Bioresource Technology, 344, p.126253.
3. He, Y., Bagley, D.M., Leung, K.T., Liss, S.N. and Liao, B.Q., 2012. Recent advances in membrane technologies for biorefining and bioenergy production. Biotechnology advances, 30(4), pp.817-858.