Liu Can, Zhang Xueyao, Qiao Qi, Wang Zhiwu, Shao Qing, Shi Jian
Department of Biosystems and Agricultural Engineering, University of Kentucky, Lexington, KY, 40546, USA.
Department of Biological Systems Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA.
J Biol Eng. 2025 Jul 31;19(1):73. doi: 10.1186/s13036-025-00544-6.
Volatile fatty acids (VFA) derived from acidogenic fermentation can be recovered as precursors for synthesizing value-added chemicals to replace those from fossil fuels. However, separating VFAs from the fermentation broth with complex constituents and a high-water content is an energy-intensive process.
This study developed an innovative membrane extraction technology, utilizing hydrophobic deep eutectic solvents (HDESs) as the acceptor phase along with an omniphobic membrane contactor for efficient extraction of anhydrous VFAs. All tested HDESs, three terpene-based type V HDESs and two tetraalkylammonium halide-based type III HDESs, were found to effectively extract VFAs at pH 3, with extraction recovery percentages (ERPs) up to 80% and 92% for 4 C- and 5 C- VFAs, respectively. However, the ERP of type V HDESs decreased significantly when the aqueous phase was adjusted to pH 6. Molecular simulations suggest that the VFA-HDES interactions vary with VFA dissociation, where the ion-dipole interactions between VFA conjugate bases and hydrogen bond donors at near-neutral pH conditions may destabilize the type V HDES structure and lead to reduced extraction efficiency. The temperature increases from 25 °C to 55 °C did not significantly impact VFA distribution, but a higher temperature could enhance cross-membrane mass transfer.
This study demonstrated a novel continuous VFA extraction technology based on HDESs and elucidates the impact of temperature, pH, impurities in real fermentate and the applicability of an integrated membrane system through combined experimental and computational approaches.
产酸发酵产生的挥发性脂肪酸（VFA）可作为合成增值化学品的前体进行回收，以替代来自化石燃料的化学品。然而，从成分复杂且含水量高的发酵液中分离VFA是一个能源密集型过程。
本研究开发了一种创新的膜萃取技术，利用疏水性深共熔溶剂（HDESs）作为接受相，并结合全疏液膜接触器来高效萃取无水VFA。所有测试的HDESs，三种基于萜烯的V型HDESs和两种基于卤化四烷基铵的III型HDESs，在pH值为3时都能有效萃取VFA，对于4碳和5碳VFA，萃取回收率（ERP）分别高达80%和92%。然而，当水相pH值调至6时，V型HDESs的ERP显著下降。分子模拟表明，VFA与HDES的相互作用随VFA离解而变化，在接近中性pH条件下，VFA共轭碱与氢键供体之间的离子偶极相互作用可能会破坏V型HDES结构并导致萃取效率降低。温度从25℃升高到55℃对VFA的分配没有显著影响，但较高温度可增强跨膜传质。
本研究展示了一种基于HDESs的新型连续VFA萃取技术，并通过实验和计算相结合的方法阐明了温度、pH值、实际发酵液中的杂质以及集成膜系统的适用性的影响。
