A Novel Pressure-Assisted Isothermal Membrane Distillation Process for the Enhanced Selective Recovery of Mixed Volatile Fatty Acids

초록

While isothermal membrane distillation (IMD) offers a selective method for volatile fatty acid (VFA) separation, its performance is hindered by declining feed concentrations during operation, which reduces the concentration gradient, thereby limiting mass transfer efficiency. To address this limitation, we propose a novel pressure-assisted isothermal membrane distillation (PaIMD) process for enhanced VFA recovery, which can compensate for the loss of the partial pressure of VFAs during IMD operation through continuous pressurization. Hydrophobic modification of mixed cellulose ester (MCE50) membranes with a pore size of 50 nm resulted in high wetting resistance and liquid entry pressures of up to 25 bar. The modified MCE50 membrane exhibited approximately half the VFA flux across the broad isothermal temperature range (35–55 °C) compared to the conventional PVDF450 membrane under IMD conditions. However, the MCE50 membrane successfully overcame its limitations of the initial low VFA flux even at a low applied pressures, achieving 1.5 times higher VFA flux at an applied pressure of 5 bar and 5.5 times higher flux at an applied pressure of 20 bar through the introduction of the PaIMD process, with a maximum acid/water separation factor of 268.4 achieved at an applied pressure of 5 bar. However, as water vapor transport occurs in the PaIMD process, maintaining water vapor flux below 1 L/m2/h is critical for sustaining a high SF. This successful demonstration highlights the potential of the PaIMD process to overcome the limitations of the conventional IMD process, facilitating efficient resource recovery from organic wastewater. © 2025 American Chemical Society

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