Organic solvent nanofiltration membrane cascades for solvent exchange and purification

Imperial Users onl

Organic solvent nanofiltration (OSN) modelling - from pure solvents to highly rejected solutes

Imperial Users onl

Mixed-matrix membranes

Article In Press title was: New directions for mixed-matrix membranes. Also published in German in Angewandte Chemie, 2017; 129(32):9420-9439.Research into extended porous materials such as metal-organic frameworks (MOFs) and porous organic frameworks (POFs), and their molecular analogues, metal-organic polyhedra (MOPs) and porous organic cages (POCs), has blossomed over the last decade. Given their chemical and structural mutability and notable porosity, MOFs have been proposed as novel adsorbents for industrial gas separations. In this context they have also been identified as promising filler components for high-performance mixed matrix membranes (MMMs). Research in this area has focused on enhancing the chemical compatibility between the MOF and polymer phase by judiciously functionalising the organic linkers of the MOF, modifying the MOF surface chemistry and, more recently, exploring how particle size, morphology and distribution enhance separation performance. Other filler materials, including POFs, MOPs and POCs, are also being explored as additives for MMMs and have shown, unexpectedly, remarkable anti-aging performance and excellent chemical compatibility for commercially available polymers. This review briefly outlines the state-of-the-art in MOF-MMM fabrication, and the more recent use of porous organic frameworks and molecular additives for MMMs.Janina Dechnik, Jorge Gascon, Christian J. Doonan, Christoph Janiak and Christopher J. Sumb

Hybrid and mixed matrix membranes for separations from fermentations

Fermentations provide an alternative to fossil fuels for accessing a number of biofuel and chemical products from a variety of renewable and waste substrates. The recovery of these dilute fermentation products from the broth, however, can be incredibly energy intensive as a distillation process is generally involved and creates a barrier to commercialization. Membrane processes can provide a low energy aid / alternative for recovering these dilute fermentation products and reduce production costs. For these types of separations many current polymeric and inorganic membranes suffer from poor selectivity and high cost respectively. This paper reviews work in the production of novel mixed matrix membranes (MMMs) for fermentative separations and those applicable to these separations. These membranes combine a trade-off of low-cost and processability of polymer membranes with the high selectivity of inorganic membranes. Work within the fields of nanofiltration, reverse osmosis and pervaporation has been discussed. The review shows that MMMs are currently providing some of the most high-performing membranes for these separations, with three areas for improvement identified:1. Further characterization and optimization of inorganic phase(s). 2. Greater understanding of the compatibility between the polymer and inorganic phase(s).3. Improved methods for homogeneously dispersing the inorganic phase<br/

Solution-processable polymer membranes with hydrophilic subnanometre pores for sustainable lithium extraction

Membrane-based separation processes hold great promise for sustainable extraction of lithium from brines for the rapidly expanding electric vehicle industry and renewable energy storage. However, it remains challenging to develop high-selectivity membranes that can be upscaled for industrial processes. Here we report solution-processable polymer membranes with subnanometre pores with excellent ion separation selectivity in electrodialysis processes for lithium extraction. Polymers of intrinsic microporosity incorporated with hydrophilic functional groups enable fast transport of monovalent alkali cations (Li+, Na+ and K+) while rejecting relatively larger divalent ions such as Mg2+. The polymer of intrinsic microporosity membranes surpasses the performance of most existing membrane materials. Furthermore, the membranes were scaled up and integrated into an electrodialysis stack, demonstrating excellent selectivity in simulated salt-lake brines. This work will inspire the development of selective membranes for a wide range of sustainable separation processes critical for resource recovery and a global circular economy. </p

Thin film composite membranes by interfacial polymerization for organic solvent nanofiltration

One of the challenges of current organic solvent nanofiltration (OSN) membranes is to improve permeability in polar and non-polar solvents without compromising selectivity. Here, the development of a new generation of OSN membranes: High flux Thin Film Composite membranes (TFC) via interfacial polymerization (IP), is proposed. This thesis offers a comprehensive study that analyses the relationship of OSN high flux TFC membrane formation and post-formation parameters, morphology, structure and surface polarity, to membrane functional performance in both polar and non polar solvents. The dissertation starts with the development of novel high flux TFC membranes for polar aprotic solvents to address the trade-off between permeability and selectivity. This is accomplished by using two different approaches: (a) incorporation of polyethylene glycol inside the pores of the support prior to the IP reaction, and; (b) post-treatment of the TFC membranes with an “activating solvent”. Subsequently, a detailed analysis of membrane performance and morphology, considering the aforementioned approaches was conducted, resulting in dramatically increased solvent fluxes without compromising rejection. Additionally, a detailed study to manipulate molecular weight cut-off (MWCO) of these TFC membranes was carried out and successfully achieved by using different amines in the IP reaction. Next, novel high flux hydrophobic TFC membranes via IP with tuned MWCO for non-polar solvents were developed, elucidated and studied. The surface properties of hydrophilic TFC OSN membranes were modified by capping the free acyl chloride groups on their surface with different monomers containing hydrophobic groups. A detailed study on surface polarity and membrane performance was undertaken, suggesting that surface chemistry plays an important role in solvent permeation. The membrane performance was compared to commercial OSN integrally skinned asymmetric (ISA) and TFC rubber-coated membranes. In the next stage of this thesis, the effects of different support membranes on TFC membrane formation and functional performance were studied for both polar and non-polar solvents. It was found that support membranes have an effect on TFC membrane formation and solvent permeation. Finally, to increase permeability even further without a requirement for treating the TFC membrane with an activating solvent, highly porous TFC membranes have been developed via IP by controlling the structure of the top layer at a molecular level. This was achieved by incorporating a monomer with a contorted structure during the IP reaction, resulting in a highly porous polymer network. It is believed high flux TFC OSN membranes prepared by interfacial polymerization may offer new degrees of freedom in membrane design, which could lead to the next generation of high performance OSN membranes

Advances in biopolymer-based membrane preparation and applications

Membrane technology has had a continue growth for the last 40 years. The forecast is that the membrane market will reach US$10.8 billion by the end of 2019. Unfortunately, it is also recognized as having a low sustainability with respect to membrane fabrication as this involves fossil-based polymers. It is well known that the environmental impact of plastic wastes represents a general global problem, and disposal technologies are limited. The growing environmental pollution has been the starting point for researching potential natural polymers able to substitute the conventional ones for membrane preparation. Biopolymers derived from animal (polylactic acid, polyhydroxyalcanoates, polybutylene succinate) or vegetable sources (cellulose-based polymers, alginate, polyisoprene, starch), as well as from bacterial fermentation products (chitin, chitosan, collagen, sericin), fascinated the research along with the growing worldwide trend towards sustainability. The use of biopolymers for the preparation of membranes, in fact, is very well documented in literature even if their application on a larger scale is still a challenge. This review addresses on the current (bio)plastic and membrane market with a look on the trend for the next years. Moreover, biopolymers used in membrane preparation are critically reviewed in terms of their synthesis, main properties and applications with particular emphasis on the main results of bio-based membranes during the last decades in the different fields of membrane technology including micro- and ultrafiltration, pervaporation, gas separation and medical applications