Haflich Holly M, Singleton Joshua W, Coronell Orlando
Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7431.
J Memb Sci. 2024 Nov;711. doi: 10.1016/j.memsci.2024.123204. Epub 2024 Aug 12.
Economically valuable volatile fatty acids (VFAs) are sustainably produced via fermentation processes. To use VFAs downstream, they must be recovered using technologies like electrodialysis (ED). Solute transport properties (i.e., partition coefficient (K), diffusion coefficient (D), and permeability (P=KD)) govern flux in ED. Therefore, to advance understanding of VFA flux through anion exchange membranes (AEMs) in ED, we aimed to elucidate the relative contributions of VFA partitioning and mobility to their flux. Accordingly, for VFAs of different sizes (C1-C5) and inorganic anions (Cl, Br), we measured their fluxes during ED, permeabilities, and partition coefficients, and calculated the diffusion coefficients. We then evaluated the correlations between flux and transport properties and between transport properties and anion physicochemical properties. Results showed VFA flux had a strong correlation with permeability (R=0.94, <0.01), consistent with flux described by the Nernst-Planck equation. Further, while there was a negative correlation between VFA flux and partition coefficient (R=0.46, =0.21), there was a positive correlation between VFA flux and diffusion coefficient (R=0.95, <0.01) which showed VFA mobility governed VFA flux. We observed a negative correlation between VFA diffusion coefficient and carbon-chain length which was attributed to steric hindrance, and a positive correlation between partition coefficient and carbon chain-length which we attributed to hydrophobicity and polarizability. This work provides fundamental insight on interactions between VFAs and AEMs which affect anion flux during ED.
具有经济价值的挥发性脂肪酸（VFAs）可通过发酵过程可持续生产。为了在下游使用VFAs，必须使用电渗析（ED）等技术对其进行回收。溶质传输特性（即分配系数（K）、扩散系数（D）和渗透率（P = KD））决定了ED中的通量。因此，为了深入了解VFAs在ED中通过阴离子交换膜（AEMs）的通量，我们旨在阐明VFA分配和迁移率对其通量的相对贡献。相应地，对于不同大小的VFAs（C1 - C5）和无机阴离子（Cl、Br），我们测量了它们在ED过程中的通量、渗透率和分配系数，并计算了扩散系数。然后，我们评估了通量与传输特性之间以及传输特性与阴离子物理化学性质之间的相关性。结果表明，VFA通量与渗透率有很强的相关性（R = 0.94，<0.01），这与能斯特 - 普朗克方程描述的通量一致。此外，虽然VFA通量与分配系数之间存在负相关（R = 0.46，=0.21），但VFA通量与扩散系数之间存在正相关（R = 0.95，<0.01），这表明VFA迁移率决定了VFA通量。我们观察到VFA扩散系数与碳链长度之间存在负相关，这归因于空间位阻，而分配系数与碳链长度之间存在正相关，我们将其归因于疏水性和极化率。这项工作为影响ED过程中阴离子通量的VFAs与AEMs之间的相互作用提供了基本见解。
