Zongli Xie

Ammonia removal by sweep gas membrane distillation.

Wastewater containing low levels of ammonia (100 mg/L) has been simulated in experiments with sweep gas membrane distillation at pH 11.5. The effects of feed temperature, gas flow rate and feed flow rate on ammonia removal, permeate flux and selectivity were investigated. The feed temperature is a crucial operating factor, with increasing feed temperature increasing the permeate flux significantly, but reducing the selectivity. The best-performing conditions of highest temperature and fastest gas flow rate resulted in 97% removal of the ammonia, to give a treated water containing only 3.3 mg/L of ammonia.

A review of water recovery by vapour permeation through membranes.

In vapour permeation the feed is a vapour, not a liquid as in pervaporation. The process employs a polymeric membrane as a semi-permeable barrier between the feed side under high pressure and the permeate side under low pressure. Separation is achieved by the different degrees to which components are dissolved in and diffuse through the membrane, the system working according to a solution-diffusion mechanism. The materials used in the membrane depend upon the types of compounds being separated, so water transport is favoured by hydrophilic material, whether organic or inorganic. The process is used for the dehydration of natural gas and various organic solvents, notably alcohol as biofuel, as well as the removal of water from air and its recovery from waste steam. Waste steam can be found in almost every plant/factory where steam is used. It is frequently contaminated and cannot be reused. Discharging the spent steam to the atmosphere is a serious energy loss and environmental issue. Recycling the steam can significantly improve the overall energy efficiency of an industry, which is responsible for massive CO(2) emissions. Steam separation at high fluxes and temperatures has been accomplished with a composite poly(vinyl alcohol) membrane containing silica nanoparticles, and also, less efficiently, with an inorganic zeolite membrane.

Structure retention in cross-linked poly(ethylene glycol) diacrylate hydrogel templated from a hexagonal lyotropic liquid crystal by controlling the surface tension

Retaining hexagonal lyotropic liquid crystal (LLC) structures in polymers after surfactant removal and drying is particularly challenging, as the surface tension existing during the drying processes tends to change the morphology. In this study, cross-linked poly(ethylene glycol) diacrylate (PEGDA) hydrogels were prepared in LLC hexagonal phases formed from a dodecyltrimethylammonium bromide (DTAB)/water system. The retention of the hexagonal LLC structures was examined by controlling the surface tension. Polarized light microscopy, X-ray diffraction and small angle X-ray scattering results indicate that the hexagonal LLC structure was successfully formed before polymerization and well retained after polymerization and after surfactant removal when the surface tension forces remained neutral. Controlling the surface tension during the drying process can retain the nanostructures templated from lyotropic liquid crystals which will result in the formation of materials with desired nanostructures.

Hyper-Cross-Linked Additives that Impede Aging and Enhance Permeability in Thin Polyacetylene Films for Organic Solvent Nanofiltration

Membrane materials with high permeability to solvents while rejecting dissolved contaminants are crucial to lowering the energy costs associated with liquid separations. However, the current lack of stable high-permeability materials require innovative engineering solutions to yield high-performance, thin membranes using stable polymers with low permeabilities. Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) is one of the most permeable polymers but is extremely susceptible to physical aging. Despite recent developments in anti-aging polymer membranes, this research breakthrough has yet to be demonstrated on thin PTMSP films supported on porous polymer substrates, a crucial step toward commercializing anti-aging membranes for industrial applications. Here we report the development of scalable, thin film nanocomposite membranes supported on polymer substrates that are resistant to physical aging while having high permeabilities to alcohols. The selective layer is made up of PTMSP and nanoporous polymeric additives. The nanoporous additives provide additional passageways to solvents, enhancing the high permeability of the PTMSP materials further. Through intercalation of polyacetylene chains into the sub-nm pores of organic additives, physical aging in the consequent was significantly hindered in continuous long-term operation. Remarkably we also demonstrate that the additives enhance both membrane permeability and rejection of dissolved contaminants across the membranes, as ethanol permeability at 5.5 × 10-6 L m m-2 h-1 bar-1 with 93% Rose Bengal (1017.6 g mol-1) rejection, drastically outperforming commercial and state-of-the-art membranes. These membranes can replace energy-intensive separation processes such as distillation, lowering operation costs in well-established pharmaceutical production processes.

Synergistic effect of combined colloidal and organic fouling in membrane distillation: Measurements and mechanisms

We examined the synergistic effect of combined fouling in MD process with three organic foulants – alginate, bovine serum albumin (BSA), and humic acid – in the presence of colloidal silica particles. Membrane fouling profiles were quantified by water flux decline and permeate conductivity. Mechanisms of the synergistic effect of combined fouling were revealed by light scattering measurements and infrared spectra of foulant–foulant interaction and foulant–membrane interaction. Membrane fouling morphology and element mapping provided further details of transport of colloidal silica particles and elucidated the mechanisms for silica-induced pore wetting. Specially, gelation of alginate formed an alginate layer on membrane surface and prevented penetration of silica particles into the membrane matrix, which was confirmed by silicon element mapping as well as infrared spectra. Adsorption of BSA protein by colloidal silica aggregates led to a sharp water flux decline and a partial pore wetting. Humic acid, forming a coil structure in high salinity, exhibited limited interaction with colloidal silica that penetrated into the membrane matrix and wetted membrane pores, thereby compromising the product water quality. Results showed that the combined organic fouling with colloidal silica particle not only deteriorated water production, but also compromised product quality by partial membrane wetting.

Porous aromatic frameworks impregnated with fullerenes for enhanced methanol/water separation.

Molecular simulation techniques have revealed that the incorporation of fullerenes within porous aromatic frameworks (PAFs) remarkably enhances methanol uptake while inhibiting water uptake. The highest selectivity of methanol over water is found to be 1540 at low pressure (1 kPa) and decreases gradually with increasing pressure. The adsorption of water is very small compared to methanol, a useful material property for membrane and adsorbent-based separations. Grand canonical Monte Carlo (GCMC) simulations are utilized to calculate the pure component and mixture adsorption isotherms. The water and methanol mixture simulations show that water uptake is further inhibited above the pure component results because of the dominant methanol adsorption. Molecular dynamics (MD) simulations confirm that water diffusivity is also inhibited by strong methanol adsorption in the mixture. Overall, this study reveals profound hydrophobicity in C60@PAF materials and recommends C60@PAFs as suitable applicants for adsorbent and membrane-based separations of methanol/water mixtures and other alcohol/water separation applications.

Organic Microporous Nanofillers with Unique Alcohol Affinity for Superior Ethanol Recovery toward Sustainable Biofuels

To minimize energy consumption and carbon footprints, pervaporation membranes are fast becoming the preferred technology for alcohol recovery. However, this approach is confined to small-scale operations, as the flux of standard rubbery polymer membranes remain insufficient to process large solvent volumes, whereas membrane separations that use glassy polymer membranes are prone to physical aging. This study concerns how the alcohol affinity and intrinsic porosity of networked, organic, microporous polymers can simultaneously reduce physical aging and drastically enhance both flux and selectivity of a super glassy polymer, poly-[1-(trimethylsilyl)propyne] (PTMSP). Slight loss in alcohol transportation channels in PTMSP is compensated by the alcohol affinity of the microporous polymers. Even after continuous exposure to aqueous solutions of alcohols, PTMSP pervaporation membranes loaded with the microporous polymers outperform the state-of-the-art and commercial pervaporation membranes.

Building Additional Passageways in Polyamide Membranes with Hydrostable Metal Organic Frameworks To Recycle and Remove Organic Solutes from Various Solvents

Membrane separation is a promising technology for extracting temperature-sensitive organic molecules from solvents. However, a lack of membrane materials that are permeable toward organic solvents yet highly selective curtails large-scale membrane applications. To overcome the trade-off between flux and selectivity, additional molecular transportation pathways are constructed in ultrathin polyamide membranes using highly hydrostable metal organic frameworks with diverse functional surface architectures. Additional passageways enhance water permeance by 84% (15.4 L m-2 h-1 bar-1) with nearly 100% rose bengal rejection and 97.6% azithromycin rejection, while showing excellent separation performance in ethyl acetate, ketones, and alcohols. These unique composite membranes remain stable in both aqueous and organic solvent environments. This immediately finds application in the purification of aqueous mixtures containing organic soluble compounds, such as antibiotics, during pharmaceutical manufacturing.

Desalination by pervaporation

Abstract Desalination by pervaporation has the potential to be an efficient way of getting freshwater from nonpotable saline sources with the advantage in its excellent salt rejection and capability of handling high-salinity solution. It is a combination of diffusion of water through a membrane and then its evaporation into the vapor phase on the other side of the membrane. This chapter covers the principle, transport mechanism, process design and operation, and techno-economic analysis of pervaporation for desalination, with the main focus on membrane development including polymers, inorganic materials, and their hybrids. By far, the best reported pervaporation membranes are with hybrid organic-inorganic membranes, followed by ZSM-5, cellulose membranes, silica, ionic polyethylene and various polyether membranes, with a breakthrough water flux being reported for a GO/PAN membrane. Feed temperature and permeate vapor pressure are critical process parameters affecting the transmembrane flux. Pervaporation technology and the urgent problems to be resolved are emphasized and future trends are discussed. The future growth of the process will still be strongly dependent on the improvement of current membranes or development of novel membrane materials. The possibility of integrating pervaporation with other existing processes such as RO and suggestions for improvement of pervaporation membranes and module design are also proposed.

Microporous carbon from fullerene impregnated porous aromatic frameworks for improving the desalination performance of thin film composite forward osmosis membranes

Porous additives and polymer modifications are becoming increasingly common routes to address some of the current challenges faced by membrane technologies. Here, using carbonization and pre-impregnation of fullerene to enhance the performance of a porous aromatic framework, we have developed a novel hydrophobic porous membrane additive (C60@PAF900) for enhancing the performance of forward osmosis (FO) water purification membranes. We examined the influence of C60@PAF900 loading on the polyamide (PA) layer in the fabrication of novel thin film nanocomposite (TFN) FO membranes and subsequently investigated the desalination performance of the resulting TFN FO membranes. The results showed that the addition of nanoporous C60@PAF900 greatly enhanced the water flux and water permeability of TFN FO membranes. Using 2 mol L−1 NaCl as the draw solution and 10 mmol L−1 NaCl as the feed solution, adding 0.01 w/v% C60@PAF900 into the FO membrane increased the water flux from 7.4 LMH to 12.4 LMH in the ALFS mode (active layer facing the feed solution) and from 12.6 LMH to 21.3 LMH in the ALDS mode (active layer facing the draw solution). To understand these results, the effect of C60@PAF900 on the surface morphology and chemistry of TFN FO was also investigated. Compared to the pristine FO membranes, the TFN FO membranes possessed a less dense crosslinked network due to the influence of C60@PAF900 on the interfacial polymerization process, and the interfacial repulsion between C60@PAF900 and polyamide. Together, this study provides an insight into the performance and potential effects of C60@PAF900 on advanced TFN FO membranes.