Abstract: This research initially concentrated fermentation broth by forward osmosis (FO) process, and investigated the effects of membrane orientation, type and concentration of draw solution, as well as crossflow velocity on the concentration performance. The results showed that under FO mode, the optimal concentration performance was achieved with 4.0 mol/L MgCl2?6H2O and a flow rate of 1200 mL/min.Under this condition, the caproic acid concentration was increased from 10.2 g/L to 22.9 g/L, and the total acid recovery and caproic acid recovery were 54.8% and 62.9%, respectively. Subsequent secondary concentration was conducted via rotary evaporation under reduced pressure, where the influence of temperature on concentration efficiency was explored. 65℃ was identified as the optimal operating temperature, elevating the caproic acid concentration to 40.6 g/L after this step. Finally, the pH of the secondary concentrated solution was adjusted to investigate its impact on acidification-induced oil separation. The results showed that when the pH was adjusted to 3.5, caproic acid was successfully precipitated as an oil phase, achieving a final concentration of 476.4 g/L and a purity of 68.0%, which realized a substantial improvement in both concentration and purity of caproic acid. It is verified that the coupled process of forward osmosis-vacuum rotary evaporation-acidification oil extraction can effectively enhance the separation and purification of caproic acid, providing a new strategy for the separation and extraction of caproic acid from fermentation broth. However, the purity of caproic acid obtained by this process is still insufficient for the application of fine chemicals. Further research will consider adopting rectification and other methods to further improve the purity of caproic acid.

Key words: caproic acid, separation and purification, forward osmosis, rotary evaporation, concentrate

摘要： 本研究通过正渗透(Forward Osmosis, FO)工艺初步浓缩发酵液，探究了正渗透工艺的膜朝向、汲取液种类、浓度和错流流速对浓缩效果的影响。结果表明，FO模式下，选用浓度4.0 mol/L的MgCl2?6H2O、错流流速1200 mL/min时浓缩效果最佳，可将发酵液中己酸浓度由10.2 g/L提升至22.9 g/L，总酸回收率和己酸回收率分别为54.8%和62.9%。在此基础上，采用负压旋转蒸发工艺开展二次浓缩，探究温度对浓缩效果的影响，确定65℃为最优操作温度，二次浓缩后己酸浓度可达40.6 g/L。最后通过调节二次浓缩液的pH，探究pH对酸化提油效果的影响，结果显示在pH为3.5时，己酸以油状析出，己酸最终浓度达476.4 g/L，纯度为68.0%，实现了己酸浓度与纯度的大幅提升。研究证实，正渗透-负压旋转蒸发-酸化提油耦合工艺可有效强化己酸的分离纯化效果，为发酵液中己酸的分离提取提供了新方案。但该方案所得己酸纯度仍难以满足精细化学品的应用要求，后续研究可考虑精馏等方式进一步提高己酸纯度。

关键词: 己酸, 分离纯化, 正渗透, 旋转蒸发, 浓缩