A slow–fast phase separation (SFPS) process to fabricate dual-layer hollow fiber substrates for thin-film composite (TFC) organic solvent nanofiltration (OSN) membranes

Hollow Fiber Membrane for Organic Solvent Nanofiltration: A Mini Review

Organic solvents take up 80% of the total chemicals used in pharmaceutical and related industries, while their reuse rate is less than 50%. Traditional solvent treatment methods such as distillation and evaporation have many disadvantages such as high cost, environmental unfriendliness, and difficulty in recovering heat-sensitive, high-value molecules. Organic solvent nanofiltration (OSN) has been a prevalent research topic for the separation and purification of organic solvent systems since the beginning of this century with the benefits of no-phase change, high operational flexibility, low cost, as well as environmental friendliness. Especially, hollow fiber (HF) OSN membranes have gained a lot of attention due to their high packing density and easy scale-up as compared with flat-sheet OSN membranes. This paper critically reviewed the recent research progress in the preparation of HF OSN membranes with high performance, including different materials, preparation methods, and modification treatments. This paper also predicts the future direction of HF OSN membrane development.

Thin-Film Composite Membranes with a Carbon Nanotube Interlayer for Organic Solvent Nanofiltration

Compared to the traditional chemical-crosslinking-based polymer, the porous polytetrafluoroethylene (PTFE) substrate is considered to be an excellent support for the fabrication of thin-film composite (TFC) organic solvent nanofiltration (OSN) membranes. However, the low surface energy and chemical inertness of PTFE membranes presented major challenges for fabricating a polyamide active layer on its surface via interfacial polymerization (IP). In this study, a triple-layered TFC OSN membrane was fabricated via IP, which consisted of a PA top layer on a carbon nanotube (CNT) interlayer covering the macroporous PTFE substrate. The defect-free formation and cross-linking degree of the PA layer can be improved by controlling the CNT deposition amount to achieve a good OSN performance. This new TFC OSN membrane exhibited a high dye rejection (the rejection of Bright blue B > 97%) and a moderate and stable methanol permeated flux of approximately 8.0 L m−2 h−1 bar−1. Moreover, this TFC OSN membrane also exhibited an excellent solvent resistance to various organic solvents and long-term stability during a continuous OSN process.

Organic Liquid Mixture Separation Using an Aliphatic Polyketone-Supported Polyamide Organic Solvent Reverse Osmosis (OSRO) Membrane

Energy-efficient membrane technology has received tremendous attention for the separation of organic molecules; however, the separation of molecules of less than 100 Da has remained challenging. Herein, a membrane fabricated from interfacial polymerization on a polyketone support was used as an organic solvent reverse osmosis (OSRO) membrane for the separation of organic liquid mixtures. The chemically stable and highly cross-linked selective layer exhibited outstanding separation factors toward large nonpolar molecules from small polar ones with high fluxes. For example, separation factors of 8.4, 11.1, 14.9, and 38.0 were achieved toward toluene, pentane, hexane, and heptane (10 wt % in mixtures), respectively, from methanol solution at 3 MPa, with fluxes around 5 LMH. This membrane outperformed the currently available reverse osmosis membrane and organic solvent nanofiltration membranes in terms of stability and separation factor. This work promotes the development of OSRO separation of organic liquid mixtures without phase change.

Pharmaceutical concentration using organic solvent forward osmosis for solvent recovery

The organic solvent forward osmosis (OSFO) process can simultaneously concentrate the active pharmaceutical ingredients (APIs) and recover the organic solvents. Here we demonstrate and evaluate an OSFO process for solvent recovery. In this demonstration, OSFO was conducted in different solvents with different draw solutes. The OSFO process shows rejections >98% when recovering organic solvents from different feed solutions, even when the feed concentration is as high as 20 wt%. More importantly, all systems exhibit relatively low ratios of reverse solute flux to solvent flux, indicating that the adverse effects of using hazardous draw solutions could be minimized. Nevertheless, the use of non-hazardous draw solutes such as citric acid is highly recommended to remove any potential risk, and it has been demonstrated. Herein, the OSFO process is a promising technology for solvent recovery as it possesses a reasonable solvent flux, low reverse solute flux and requires no external pressure.

One-step fabrication of polyamide 6 hollow fibre membrane using non-toxic diluents for organic solvent nanofiltration

We developed new polyamide 6 hollow fibre membranes using a green process to fabricate cutting-edge “organic solvent nanofiltration” membranes by one-step spinning process for organic solvent separation. This economic and sustainable membrane showed good rejection and durability performance in various organic solvents.

We developed new polyamide 6 hollow fibre membranes using a green process to fabricate cutting-edge “organic solvent nanofiltration” membranes by one-step spinning process for organic solvent separation.

The Selectivity Challenge in Organic Solvent Nanofiltration: Membrane and Process Solutions

Recent development of organic solvent nanofiltration (OSN) materials has been overwhelmingly directed toward tight membranes with ultrahigh permeance. However, emerging research into OSN applications is suggesting that improved separation selectivity is at least as important as further increases in membrane permeance. Membrane solutions are being proposed to improve selectivity, mostly by exploiting solute/solvent/membrane interactions and by fabricating tailored membranes. Because achieving a perfect separation with a single membrane stage is difficult, process engineering solutions, such as membrane cascades, are also being advocated. Here we review these approaches to the selectivity challenge, and to clarify our analysis, we propose a selectivity figure of merit that is based on the permselectivity between the two solutes undergoing separation as well as the ratio of their molecular weights.