(302d) Investigating the Separation Performance of Carboxylic Acids in a Pilot-Scale Membrane System

Carboxylic acids (CAs) are valuable platform chemicals widely used in the production of pharmaceuticals, cosmetics, polymers, and biofuels. While the predominant way of producing CAs remains reliant on traditional petrochemical processes, producing CAs from biomass enables a more resilient and domestically sourced energy supply with milder operating conditions.¹ For example, Wu et al. reported that CAs from organic waste via anaerobic fermentation (i.e., arrested methanogenesis) can be used to produce low-cost synthetic aviation fuels.² However, the complex composition of biomass feedstocks often leads to the production of a mixture of organic compounds (e.g., lactic acid, butyric acid, ethanol, etc.) during fermentation. Due to the high solubility and typically low concentrations of organic acids in the fermentation broth, selectively separating them is particularly challenging and can contribute to as much as 60% of the total bioprocessing costs.³

Pressure-driven membrane separation is a promising low-cost separation method and can reportedly separate CAs such as acetic, butyric and lactic acids under conditions commonly associated in fermentation effluents.^4,5 However, previous bench-scale studies have not adequately captured the mass transfer effects on acid separation that occur within membrane cartridges at larger scales. In this study, pilot-scale membrane separation experiments were conducted using a commercial spiral-wound membrane cartridge (NF90-2540) to evaluate the separation behavior of CA solutions. Acetic, butyric, and lactic acids were tested under fermentation broth conditions (pH 6.0, 0.2 mol/L) in single- and multi-component solutions across a range of transmembrane pressures. The results showed that in a ternary acid mixture with equal molar concentrations, high rejections (>90%) were achieved for all acids at a transmembrane pressure of 21 bar. Lactic acid exhibited the highest rejection (~98%), while acetic acid had the lowest (~91%). In addition, established membrane separation models (e.g., solution-diffusion model) were employed to predict permeate flux and solute rejection at pilot scale. This talk will compare model predictions to pilot-scale experimental results. These findings demonstrate that membrane separation is a scalable and effective method for recovering CAs from aqueous dilute solutions under fermentation conditions and highlight the importance of considering transport phenomena within membrane cartridges when modeling large-scale systems.

Reference:

(1) Holtzapple, M. T.; Wu, H.; Weimer, P. J.; Dalke, R.; Granda, C. B.; Mai, J.; Urgun-Demirtas, M. Microbial Communities for Valorizing Biomass Using the Carboxylate Platform to Produce Volatile Fatty Acids: A Review. Bioresource Technology 2022, 344, 126253. https://doi.org/10.1016/j.biortech.2021.126253.

(2) Wu, H.; Kim, T.; Ferdous, S.; Scheve, T.; Lin, Y.; Valentino, L.; Holtzapple, M.; Hawkins, T. R.; Benavides, P. T.; Urgun-Demirtas, M. Sustainable Aviation Fuel from High-Strength Wastewater via Membrane-Assisted Volatile Fatty Acid Production: Experimental Evaluation, Techno-Economic, and Life-Cycle Analyses. ACS Sustainable Chem. Eng. 2024, 12 (18), 6990–7000. https://doi.org/10.1021/acssuschemeng.4c00167.

(3) Hamid, U.; Hsieh, C.-J.; Wu, H.; Valentino, L.; Urgun-Demirtas, M.; Chen, C.-C. Adsorption Equilibrium, Kinetics, and Column Breakthrough Data for Aqueous Solutions of Binary-Acid and Ternary-Acid Mixtures of Acetic Acid, Butyric Acid, and Lactic Acid on IRN-78 Ion-Exchange Resin at Initial pH Levels of ∼3–7 and at 25–55 °C. J. Chem. Eng. Data 2024, 69 (11), 4230–4246. https://doi.org/10.1021/acs.jced.4c00380.

(4) Wu, H.; Valentino, L.; Riggio, S.; Holtzapple, M.; Urgun-Demirtas, M. Performance Characterization of Nanofiltration, Reverse Osmosis, and Ion Exchange Technologies for Acetic Acid Separation. Separation and Purification Technology 2021, 265, 118108. https://doi.org/10.1016/j.seppur.2020.118108.

(5) Anjum, N.; Wu, H.; Lomax, A.; Valentino, L.; Urgun-Demirtas, M.; Chen, C.-C. Experimental Investigation of Nanofiltration Separation Performance for Aqueous Organic Acid Solutions; AIChE, 2024.