Thermodynamic and mechanistic studies on recovering phenol crystals from dilute aqueous solutions using pervaporation–crystallization coupling (PVCC) system

Application of a biodegradable poly(butylene adipate-co-terephthalate) membrane for phenol pervaporation recovery

In the field of membrane separation, the environmental concerns caused by spent membranes are becoming increasingly serious, which contradicts the concept of sustainable development. Based on this, a biodegradable poly(butylene adipate-co-terephthalate) (PBAT) membrane was used for the first time in the pervaporation separation of phenol, a high boiling point organic compound (HBOC). By using the PBAT membrane, outstanding separation efficiency was achieved, and environmental pollution and disposal issues were also avoided. The separation process and mechanism of the PBAT membrane were systematically studied through the experiment together with molecular dynamics (MD) simulation. The swelling experiment and intermolecular interaction energy calculation demonstrated that the PBAT membrane had a strong affinity for phenol. Further simulation concluded that higher phenol concentration increased the number of hydrogen bonds so that the membrane was more greatly swollen. Meanwhile, the simulations on the adsorption, diffusion and permeation predicted that the PBAT membrane had excellent separation performance for phenol. Besides MD simulation, the influences of feed concentration and temperature on pervaporation performance were also investigated by experiment. The results showed that the flux of each component increased with the feed concentration. This phenomenon was attributed to the preferential adsorption of phenol by the PBAT membrane, which resulted in large free volumes and cavities within the membrane, accelerating the diffusion of molecules. In addition, it was found that the optimal operating temperature was 333 K with the best separation performance. This study confirms that the biodegradable PBAT membrane is valuable for the recovery of high boiling point organic compounds (HBOCs) such as phenol.

Application of polyurethane membrane with surface modified ZSM-5 for pervaporation of phenol/water mixture

In the present work, β-cyclodextrin was grafted to the surface of ZSM-5 via 2,3-epoxypropyl trimethylammonium chloride (ETMAC) and epichlorohydrin (EPI) as the bridging agent by ion exchange and sequential grafting. The mixed matrix membranes were prepared using polyurethane (PU) and ZSM-5 before and after modification. Modified ZSM-5 and corresponding MMM were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). These membranes were applied for the removal of phenol from aqueous solution in pervaporation process. The results showed that modified ZSM-5 dispersed homogeneously in polymer. The flux and pervaporation separation index of PU increased greatly with a limited decrease in selectivity by the addition of modified ZSM-5. The increased feed temperature enhanced both the flux and separation factor of PU and modified PU membranes.

Polyurethane membrane with a cyclodextrin-modified carbon nanotube for pervaporation of phenol/water mixture

Polyurethane (PU) membrane has great potential in pervaporation recovery of phenol from water. In order to improve the permeability of the membrane, cyclodextrin was attached onto carboxylic and hydroxylate carbon nanotubes (CNTs) by physical and chemical methods, with which modified CNTs/PU membranes were prepared. The results showed that the addition of modified CNTs greatly increases the permeability and comprehensive performance of PU membranes in the pervaporation separation of a phenol/water mixture. With 0.5% phenol content in feed at 80°C, the flux and pervaporation separation index of blank PU are 6.10 and 324 kg·μm·m−2·h−1, while those of chemically modified carboxylic CNTs/PU membranes are 156.1 and 655.8 kg·μm·m−2·h−1, respectively.