This study examined the behavior and penetration mechanisms of typical phenolic (benzoic) acids, which determine their observed penetration rates during membrane separation, focusing on the influence of electrostatic and hydrophobic solute/membrane interactions. To understand the effects of hydrophobicity and electrostatic interaction on membrane filtration, the observed penetration of five structurally similar phenolic acids was compared with regenerated cellulose (RC) and polyamide (PA) membranes at different solute concentrations and solution pHs. Variation partitioning analysis (VPA) was performed to calculate the relative contributions of electrostatic and hydrophobic effects. The penetration of phenolic acids was mainly influenced by the electrostatic interaction, with salicylic acid having the highest penetration. Penetration of phenolic acids through the PA membrane decreased from 98% at pH 3.0 to 30–50% at pH 7.4, indicating the dominance of the electrostatic interaction. Moreover, based on its hydrophobicity and greater surface charge, the PA membrane could separate binary mixtures of protocatechuic/salicylic acid and 4-hydroxybenzoic/salicylic acid at pH 9.0, with separation factors of 1.81 and 1.78, respectively. These results provide a greater understanding of solute/membrane interactions and their effect on the penetration of phenolic acids through polymeric ultrafiltration membranes.

Macroporous resin is an efficient separation technology that plays a crucial role in the separation and purification of traditional Chinese medicine (TCM). However, the application of macroporous resins in TCM pharmaceuticals is hindered by serious fouling caused by the complex materials used in TCM. This study examines the impact of ultrafiltration (UF) membrane technology on the macroporous resin adsorption behavior of TCM extracts. In this paper, Bupleurum chinense DC. (B. chinense) water extracts were included as an example to study the effect of UF pretreatment on the macroporous resin adsorption of total saponins. The study results indicated that the adsorption of total saponins constituents from the water extracts of B. chinense on the macroporous resin followed the pseudo-second-order kinetic model and the Langmuir model. The thermodynamic parameters of adsorption, including enthalpy changes and Gibbs free energies, were negative, while entropy changes were positive. These results demonstrated that the total saponin components form a monolayer adsorption layer by spontaneous thermal adsorption on the macroporous resin, and that the adsorption rate is not determined by the rate of intraparticle diffusion. Following treatment with a UF membrane with an average molecular weight cut-off of 50 kDa, the protein, starch, pectin, tannin, and other impurities in the water extracts of B. chinense were reduced, while the total saponin content was retained at 82.32%. The adsorption kinetic model of the saponin constituents on the macroporous resin remained unchanged and was consistent with both the second-order kinetic model and the Langmuir model; the adsorption rate of the second-order kinetic model increased by 1.3 times and in the Langmuir model at 25 °C, the adsorption performance improved by 1.16 times compared to the original extracts. This study revealed that UF technology as a pretreatment method can reduce the fouling of macroporous resin by TCM extracts and improve the adsorption performance of macroporous resin.

This study used polyacrylonitrile (PAN) and heat-treated polyacrylonitrile (H-PAN) membranes to enrich nutmeg essential oils, which have more complex compositions compared with common oils. The oil rejection rate of the H-PAN membrane was higher than that of the PAN membrane for different oil concentrations of nutmeg essential oil-in-water emulsions. After heat treatment, the H-PAN membrane showed a smaller pore size, narrower pore size distribution, a rougher surface, higher hydrophilicity, and higher oleophobicity. According to the GC-MS results, the similarities of the essential oils enriched by the PAN and H-PAN membranes to those obtained by steam distillation (SD) were 0.988 and 0.990, respectively. In addition, these two membranes also exhibited higher essential oil rejection for Bupleuri Radix, Magnolia Officinalis Cortex, Caryophylli Flos, and Cinnamomi Cortex essential oil-in-water emulsions. This work could provide a reference for membrane technology for the non-destructive separation of oil with complex components from oil-in-water emulsions.

Ceramic membrane has an important application prospect in industrial acid solution treatment. Enhancement of the acid resistance is the key strategy to optimize the membrane treatment effect. This work reports a core–shell structured membrane fabricated on alumina ceramic substrates via a one-step in situ hydrothermal method. The acid resistance of the modified membrane was significantly improved due to the protection provided by a chemically stable carbon layer. After modification, the masses lost by the membrane in the hydrochloric acid solution and the acetic acid solution were sharply reduced by 90.91% and 76.92%, respectively. Kinetic models and isotherm models of adsorption were employed to describe acid adsorption occurring during the membrane process and indicated that the modified membrane exhibited pseudo-second-order kinetics and Langmuir model adsorption. Compared to the pristine membrane, the faster adsorption speed and the lower adsorption capacity were exhibited by the modified membrane, which further had a good performance with treating various kinds of acid solutions. Moreover, the modified membrane could be recycled without obvious flux decay. This modification method provides a facile and efficient strategy for the fabrication of acid-resistant membranes for use in extreme conditions.