Green and Sustainable Membranes: A review

Membranes are ubiquitous tools for modern water treatment technology that critically eliminate hazardous materials such as organic, inorganic, heavy metals, and biomedical pollutants. Nowadays, nano-membranes are of particular interest for myriad applications such as water treatment, desalination, ion exchange, ion concentration control, and several kinds of biomedical applications. However, this state-of-the-art technology suffers from some drawbacks, e.g., toxicity and fouling of contaminants, which makes the synthesis of green and sustainable membranes indeed safety-threatening. Typically, sustainability, non-toxicity, performance optimization, and commercialization are concerns centered on manufacturing green synthesized membranes. Thus, critical issues related to toxicity, biosafety, and mechanistic aspects of green-synthesized nano-membranes have to be systematically and comprehensively reviewed and discussed. Herein we evaluate various aspects of green nano-membranes in terms of their synthesis, characterization, recycling, and commercialization aspects. Nanomaterials intended for nano-membrane development are classified in view of their chemistry/synthesis, advantages, and limitations. Indeed, attaining prominent adsorption capacity and selectivity in green-synthesized nano-membranes requires multi-objective optimization of a number of materials and manufacturing parameters. In addition, the efficacy and removal performance of green nano-membranes are analyzed theoretically and experimentally to provide researchers and manufacturers with a comprehensive image of green nano-membrane efficiency under real environmental conditions.

Novel Polyelectrolyte Complex Membranes Containing Carboxymethyl Cellulose-Gelatin for Pervaporation Dehydration of Azeotropic Bioethanol for Biofuel

Polyelectrolyte complex membranes (PECMs) were prepared by combining sodium carboxymethyl cellulose (NaCMC) and gelatin (Ge) with variations in the Ge content in the NaCMC matrix. Characterization methods, such as infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), contact angle analysis (CA), and universal testing machines (UTM) were used to investigate the physicochemical studies of the prepared membranes. The pervaporation characteristics of membranes with Ge content were investigated using an azeotropic mixture of water and bioethanol. The obtained data revealed that the membrane with 15 mass% of Ge (M-3) showed a maximum flux of 7.8403 × 10^-2 kg/m²·h with separation selectivity of 2917 at 30 °C. In particular, the total and water flux of PECMs are shown as very close to each other indicating that the fabricated membranes could be employed to successfully break the azeotropic point of water-bioethanol mixtures. Using temperature-dependent permeation and diffusion data, the Arrhenius activation parameters were calculated, and the obtained values of water permeation (E_pw) were considerably smaller than bioethanol permeation (E_pE). Developed membranes showed the positive heat of sorption (ΔH_s), suggesting that Henry's sorption mode is predominant.

Exploring the potential of highly selective deep eutectic solvents (DES) based membranes for dehydration of butanol via pervaporation

N-butanol has unique physicochemical and combustion properties, similar to gasoline, which makes it an environmentally friendly alternative to conventional fuels. To improve the efficiency, the dehydration of butanol is necessary. This paper aims to investigate the performance of Deep Eutectic Solvents (DESs) based membranes for the dehydration of n-butanol by the pervaporation process. Three DES with different combinations of hydrogen bond donors and acceptors, i.e., DL-menthol: Lauric acid (DES), DL-menthol-Palmitic acid (DES), and [TETA] Cl: Thymol (DES), were used. We hypothesized that (i) incorporation of hydrophobic DES would increase the hydrophobicity of the membranes; (ii) specific functional groups (phenolic group, amine group) in DESs would enhance the butanol-philic character of membranes, and (iii) hydrophobic DESs would increase the butanol separation efficiency and permeability of membranes. FTIR analysis and physicochemical parameters of the resultant liquid mixture validated the DESs' production. The DESs were then filled into the permeable support, resulting in supported liquid membranes (SLMs). An additional layer of polydimethylsiloxane (PDMS) was coated directly on the DES-PSf layer to prevent leaching out of DES. A feed containing a 6 wt % aqueous solution of butanol under varying temperatures was studied. The results showed that among all membranes, [TETA] Cl: Thymol DES-based membrane showed the highest sorption of 36% at room temperature. The introduction of DES in membranes resulted in a remarkable increase in the separation factor while sustaining a reasonable flux. Among all the membranes, the DL-menthol: Lauric acid (DES) based membrane exhibited the highest separation factor of 57 with a total flux of 0.11 kg/m². h. Significantly high butanol-water separation was attributed to the low viscosity and high butanol solubility of the chosen DES, which makes it a suitable substitute to conventional ILs.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Development of Novel Membranes Based on Polyvinyl Alcohol Modified by Pluronic F127 for Pervaporation Dehydration of Isopropanol

Membrane methods are environmentally friendly and can significantly improve the design and development of new energy consumption processes that are very important nowadays. However, their effective use requires advanced membrane materials. This study aims to improve the performance of pervaporation polyvinyl alcohol (PVA)-based membrane for isopropanol dehydration. To achieve this goal, two methods were applied: (1) bulk modification of PVA by Pluronic F127 and (2) development of supported PVA-based membrane using polyphenylene isophthalamide (PA) as a substrate with a various porosity. Developed membranes were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), contact angle measurement, and swelling experiments. The concentration influence of PA casting solution (12–20 wt.%) on the performance of porous PA membranes (substrates) was investigated in ultrafiltration of pure water and bovine serum albumin (BSA) solution as well as by microscopic methods (SEM and atomic force microscopy). The developed dense and supported PVA-based membranes were tested in the pervaporation dehydration of isopropanol. Optimal transport characteristics were obtained for a supported membrane with a PVA-based selective layer containing 3 wt.% Pluronic F127 onto an ultrafiltration PA (17 wt.%) substrate: improved permeation flux 0.100–1.164 kg/(m2 h) and 98.8–84.6 wt.% water content in the permeate in pervaporation dehydration of isopropanol (12–80 wt.% water).

Biobased composites from agro-industrial wastes and by-products

The greater awareness of non-renewable natural resources preservation needs has led to the development of more ecological high-performance polymeric materials with new functionalities. In this regard, biobased composites are considered interesting options, especially those obtained from agro-industrial wastes and by-products. These are low-cost raw materials derived from renewable sources, which are mostly biodegradable and would otherwise typically be discarded. In this review, recent and innovative academic studies on composites obtained from biopolymers, natural fillers and active agents, as well as green-synthesized nanoparticles are presented. An in-depth discussion of biobased composites structures, properties, manufacture, and life-cycle assessment (LCA) is provided along with a wide up-to-date overview of the most recent works in the field with appropriate references. Potential uses of biobased composites from agri-food residues such as active and intelligent food packaging, agricultural inputs, tissue engineering, among others are described, considering that the specific characteristics of these materials should match the proposed application.

Asymmetric Mass Transport through Dense Heterogeneous Polymer Membranes: Fundamental Principles, Lessons from Nature, and Artificial Systems

Many organisms rely on directional water transport schemes for the purpose of water retention and collection. Directional transport of water and other fluids is also technologically relevant, for example to harvest water, in separation processes, packaging solutions, functional clothing, and many other applications. One strategy to promote mass transport along a preferential direction is to create compositionally asymmetric, multi-layered, or compositionally graded architectures. In recent years, the investigation of natural and artificial membranes based on this design has attracted growing interest and allowed researchers to develop a good understanding of how the properties of such membranes can be tailored to meet the demands of particular applications. Here a summary of theoretical works on mass transport through dense asymmetric membranes, comprehensive reviews of biological and artificial membranes featuring this design, and a discussion of applications, remaining questions, and opportunities are provided.

Review on technologies to separate and purify ethyl alcohol from dilute aqueous solutions

Ethyl alcohol (ethanol) is viewed upon as a fuel additive or even as an alternative fuel. Fermentation is used to produce dilute (<20 mass%) ethanol. This is needed to be concentrated to almost anhydrous, fuel grade ethanol (>99.5 mass%). The technologies used for concentration from dilute grade to fuel grade ethanol are summarized in this review. Thus, extraction; distillation; use of membranes; adsorption and some miscellaneous methods are discussed in detail. For each technique, the inlet and outlet concentrations; merits and demerits and scope for future work are indicated. Hybrid separations are discussed. In addition to technical feasibility, economic viability of the techniques is also discussed. A brief discussion on current industrial practice is also presented.

A Review on Mixed Matrix Membranes for Solvent Dehydration and Recovery Process

Solvent separation and dehydration are important operations for industries and laboratories. Processes such as distillation and extraction are not always effective and are energy-consuming. An alternate approach is offered by pervaporation, based on the solution-diffusion transport mechanism. Polymer-based membranes such as those made of Polydimethylsiloxane (PDMS) have offered good pervaporation performance. Attempts have been made to improve their performance by incorporating inorganic fillers into the PDMS matrix, in which metal-organic frameworks (MOFs) have proven to be the most efficient. Among the MOFs, Zeolitic imidazolate framework (ZIF) based membranes have shown an excellent performance, with high values for flux and separation factors. Various studies have been conducted, employing ZIF-PDMS membranes for pervaporation separation of mixtures such as aqueous-alcoholic solutions. This paper presents an extensive review of the pervaporation performance of ZIF-based mixed matrix membranes (MMMs), novel synthesis methods, filler modifications, factors affecting membrane performance as well as studies based on polymers other than PDMS for the membrane matrix. Some suggestions for future studies have also been provided, such as the use of biopolymers and self-healing membranes.

Organophosphorus Polyurethane Ionomers as Water Vapor Permeable and Pervaporation Membranes

Organophosphorus polyurethane ionomers (AEPA-PU) based on aminoethers of ortho-phosphoric acid (AEPA) were obtained and studied as pervaporation membrane materials for separating isopropanol/water mixtures. The regularities of the change in the water vapor permeability of AEPA-PU were also investigated. It has been established that an increase of solute content in the composition of the urethane-forming system and the content of ionogenic groups in AEPA leads to a noticeable increase in the vapor permeability of the resulting film materials. An increase in water vapor permeability values is accompanied by a significant increase in the pervaporation characteristics of AEPU-PU. It was shown that the conditions promoting clustering of phosphate anions cause an increase in the values of the vapor permeability coefficient of AEPA-PU obtained using polyoxypropylene glycol. However, the hydrophobicity of the polypropylene glycol surrounding the clusters makes it difficult for water to move through the polymer matrix. Due to the hydrophilicity of polyoxyethylene glycol, the highest values of water vapor permeability and pervaporation characteristics are achieved for AEPA-PU synthesized using PEG.

Pervaporation Zeolite-Based Composite Membranes for Solvent Separations

Thanks to their well-defined molecular sieving and stability, zeolites have been proposed in selective membrane separations, such as gas separation and pervaporation. For instance, the incorporation of zeolites into polymer phases to generate composite (or mixed matrix) membranes revealed important advances in pervaporation. Therefore, the goal of this review is to compile and elucidate the latest advances (over the last 2-3 years) of zeolite applications in pervaporation membranes either combining zeolites or polymers. Here, particular emphasis has been focused on relevant insights and findings in using zeolites in pervaporative azeotropic separations and specific aided applications, together with novel concepts of membranes. A brief background of the pervaporation process is also given. According to the findings of this review, we provide future perspectives and recommendations for new researchers in the field.

Novel PVDF-PVP Hollow Fiber Membrane Augmented with TiO2 Nanoparticles: Preparation, Characterization and Application for Copper Removal from Leachate

High proportion of copper has become a global challenge owing to its negative impact on the environment and public health complications. The present study focuses on the fabrication of a polyvinylidene fluoride (PVDF)-polyvinyl pyrrolidone (PVP) fiber membrane incorporated with varying loading (0, 0.5, 1.0, 1.5, and 2.0 wt%) of titanium dioxide (TiO₂) nanoparticles via phase inversion technique to achieve hydrophilicity along with high selectivity for copper removal. The developed fibers were characterized based on scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), permeability, porosity, zeta potential, and contact angle. The improved membrane (with 1.0 wt% TiO₂) concentration recorded the maximum flux (223 L/m²·h) and copper rejection (98.18%). Similarly, 1.0 wt% concentration of TiO₂ nanoparticles made the membrane matrix more hydrophilic with the least contact angle of 50.01°. The maximum copper adsorption capacity of 69.68 mg/g was attained at 1.0 wt% TiO₂ concentration. The experimental data of adsorption capacity were best fitted to the Freundlich isotherm model with R² value of 0.99573. The hybrid membrane developed in this study has considerably eliminated copper from leachate and the concentration of copper in the permeate was substantially reduced to 0.044 mg/L, which is below standard discharge threshold.

Exploring the Effect of Iron Metal-Organic Framework Particles in Polylactic Acid Membranes for the Azeotropic Separation of Organic/Organic Mixtures by Pervaporation

A microporous carboxylate metal-organic framework MIL-100 Fe was prepared as submicron particles by microwave-assisted hydrothermal synthesis (Fe-MOF-MW). This product was explored, for the first time, for the preparation of polylactic acid (PLA) mixed matrix membranes. The produced MOF was characterised by powder X-ray diffraction (PXRD), environmental scanning electron microscopy (ESEM) as well as by thermogravimetric analysis (TGA) and nitrogen adsorption/desorption. The effect of different Fe-MOF-MW concentrations (0.1 and 0.5 wt%) on the membrane properties and performance were evaluated. These membranes were used in the pervaporation process for the separation of methanol/methyl tert-butyl-ether mixtures at the azeotropic point. The influence of the feed temperature and vacuum pressure on the membrane performance was evaluated and the results were compared with PLA pristine membranes. Moreover, the produced membranes have been characterised in terms of morphology, MOF dispersion in the polymeric membrane matrix, wettability, thickness, mechanical resistance and swelling propensity. The presence of Fe-MOF-MW was found to have a beneficial effect in improving the selectivity of mixed matrix membranes towards methanol at both concentrations. The highest selectivity was obtained for the PLA membranes embedded with 0.5 wt% of Fe-MOF-MW and tested at the temperature of 25 °C and vacuum pressure of 0.09 mbar.

Membranes for bioethanol production by pervaporation

BACKGROUND

Bioethanol as a renewable energy resource plays an important role in alleviating energy crisis and environmental protection. Pervaporation has achieved increasing attention because of its potential to be a useful way to separate ethanol from the biomass fermentation process.

RESULTS

This overview of ethanol separation via pervaporation primarily concentrates on transport mechanisms, fabrication methods, and membrane materials. The research and development of polymeric, inorganic, and mixed matrix membranes are reviewed from the perspective of membrane materials as well as modification methods. The recovery performance of the existing pervaporation membranes for ethanol solutions is compared, and the approaches to further improve the pervaporation performance are also discussed.

CONCLUSIONS

Overall, exploring the possibility and limitation of the separation performance of PV membranes for ethanol extraction is a long-standing topic. Collectively, the quest is to break the trade-off between membrane permeability and selectivity. Based on the facilitated transport mechanism, further exploration of ethanol-selective membranes may focus on constructing a well-designed microstructure, providing active sites for facilitating the fast transport of ethanol molecules, hence achieving both high selectivity and permeability simultaneously. Finally, it is expected that more and more successful research could be realized into commercial products and this separation process will be deployed in industrial practices in the near future.

Facile Preparation of a Laponite/PVA Mixed Matrix Membrane for Efficient and Sustainable Pervaporative Dehydration of C1-C3 Alcohols

The exfoliation method was applied for the preparation of high-water selective mixed matrix membranes (MMMs), especially for the dehydration of C1-C3 alcohol-water solutions. Herein, a facile and easy method was employed to fabricate physically cross-linked Laponite nanosilicate clay-PVA MMMs without additional cross-linking by a one-step synthesis route for water dehydration from methanol, ethanol, and isopropanol aqueous solutions. The morphologies, chemical structures, thermal stabilities, and surface hydrophilicity of Laponite-PVA MMMs were investigated properly by different characterization techniques. The Laponite concentration has affected the fractional free volume of the membranes, as proven by positron annihilation lifetime spectroscopy analysis. The MMMs displayed both a significant improvement in the separation factor and remarkable enhancement in the permeation fluxes for the three alcohol systems. The influence of the operating temperature on the MMM performance was investigated for the methanol/water solution. The methanol permeability was 100-fold lower than that of the water, indicating that the membranes are more water selective. Particularly, the Laponite-PVA membrane with 5 mg/mL Laponite loading exhibits excellent separation efficiency for C1-C3 dehydration having water permeabilities higher than most other polymeric membranes from the other literature studies of 2.82, 2.08, and 1.56 mg m^-1 h^-1 kPa^-1 for methanol, ethanol, and isopropanol/water systems, respectively. This membrane development allows a more efficient and sustainable separation of aqueous alcoholic mixtures.

Pervaporative Dehydration of Methanol Using PVA/Nanoclay Mixed Matrix Membranes: Experiments and Modeling

Encouraged by the industrial problem of removing water from methanol solutions, a simple exfoliation method is applied to prepare polyvinyl alcohol (PVA)/laponite nanoclay mixed matrix membranes (MMMs). The membranes are used for the pervaporative dehydration of the methanol-water solution. The influence of the nanoclay content on the pervaporation performance is investigated. The results show that the PVA10 membrane containing 10 wt% Laponite loading exhibits excellent separation efficiency; therefore, all the experimental work is continued using the same membrane. Additionally, the effects of feed concentration and temperature on methanol dehydration performance are thoroughly investigated. The temperatures are ranging from 40–70 °C and the water feed concentrations from 1–15 wt% water. A maximum separation factor of 1120 can be observed at 40 °C and the feed water concentration of 1 wt%. Remarkably, two solution–diffusion models, the Rautenbach (Model I) and modified method by Valentínyi et al. (Model II), are used and compared to evaluate and describe the pervaporation performance of the mixed matrix membrane. Model II proves to be more appropriate for the modeling of pervaporative dehydration of methanol than Model I. This work demonstrates that PVA/nanoclay mixed matrix membranes prepared can efficiently remove water from methanol aqueous solution with pervaporation and the whole process can be accurately modeled with Model II.

A highly hydrophilic benzenesulfonic-grafted graphene oxide-based hybrid membrane for ethanol dehydration

A new type of hybrid membrane was prepared by blending sodium alginate (SA) with benzenesulfonic-grafted graphene oxide (BS@GO), which showed higher hydrophilicity and more defects or edges than GO to create channels for the transfer of water molecules. BS@GO was synthesized by reacting aryl diazonium salts with graphene oxide (GO). The BS@GO sheets were aligned parallelly to the membrane surface and affected the interactions between the SA chains. BS@GO could improve the hydrophilicity and pervaporation properties of SA-based hybrid membranes. Also, compared to GO fillers, BS@GO fillers could supply higher water permeance to improve the pervaporation flux and separation factor. For the pervaporation of 90 wt% aqueous ethanol at 343 K, the optimum hybrid membrane with 1.5 wt% BS@GO in the SA matrix showed the maximum permeate flux of 703 ± 89 g m^-2 h^-1 (1.4 times higher than that of an SA membrane), and the highest separation factor was 5480 ± 94 (5.6 times higher than that of the SA membrane). Moreover, the hybrid membrane exhibited good stability and separation ability during long-term testing.

High-performance pervaporation chitosan-based membranes: new insights and perspectives

Today, the need of replacing synthetic polymers in the membrane preparation for diverse pervaporation (PV) applications has been recognized collectively and scientifically. Chitosan (CS), a bio-polymer, has been studied and proposed to achieve this goal especially in specific azeotropic water-organic, organic-water, and organic-organic separations, as well as in assisting specific processes (e.g. seawater desalination and chemical reactions). Different concepts of CS-based membranes have been developed, which include material blending and composite and mixed matrix membranes which have been tested for different separations. Hereby, the goal of this review is to provide a critical overview of the ongoing CS-based membrane developments, paying a special attention to the most relevant findings and results in the field. Furthermore, future trends of CS-based membranes in PV technology are presented, as well as concluding remarks and suggested strategies for the new scientist in the field.

Tuning of Nano-Based Materials for Embedding Into Low-Permeability Polyimides for a Featured Gas Separation

Several concepts of membranes have emerged, aiming at the enhancement of separation performance, as well as some other physicochemical properties, of the existing membrane materials. One of these concepts is the well-known mixed matrix membranes (MMMs), which combine the features of inorganic (e.g., zeolites, metal–organic frameworks, graphene, and carbon-based materials) and polymeric (e.g., polyimides, polymers of intrinsic microporosity, polysulfone, and cellulose acetate) materials. To date, it is likely that such a concept has been widely explored and developed toward low-permeability polyimides for gas separation, such as oxydianiline (ODA), tetracarboxylic dianhydride–diaminophenylindane (BTDA-DAPI), m-phenylenediamine (m-PDA), and hydroxybenzoic acid (HBA). When dealing with the gas separation performance of polyimide-based MMMs, these membranes tend to display some deficiency according to the poor polyimide–filler compatibility, which has promoted the tuning of chemical properties of those filling materials. This approach has indeed enhanced the polymer–filler interfaces, providing synergic MMMs with superior gas separation performance. Herein, the goal of this review paper is to give a critical overview of the current insights in fabricating MMMs based on chemically modified filling nanomaterials and low-permeability polyimides for selective gas separation. Special interest has been paid to the chemical modification protocols of the fillers (including good filler dispersion) and thus the relevant experimental results provoked by such approaches. Moreover, some principles, as well as the main drawbacks, occurring during the MMM preparation are also given.

New Trends in Biopolymer-Based Membranes for Pervaporation

Biopolymers are currently the most convenient alternative for replacing chemically synthetized polymers in membrane preparation. To date, several biopolymers have been proposed for such purpose, including the ones derived from animal (e.g., polybutylene succinate, polylactic acid, polyhydroxyalcanoates), vegetable sources (e.g., starch, cellulose-based polymers, alginate, polyisoprene), bacterial fermentation products (e.g., collagen, chitin, chitosan) and specific production processes (e.g., sericin). Particularly, these biopolymer-based membranes have been implemented into pervaporation (PV) technology, which assists in the selective separation of azeotropic water-organic, organic-water, organic-organic mixtures, and specific separations of chemical reactions. Thereby, the aim of the present review is to present the current state-of-the-art regarding the different concepts on preparing membranes for PV. Particular attention is paid to the most relevant insights in the field, highlighting the followed strategies by authors for such successful approaches. Finally, by reviewing the ongoing development works, the concluding remarks and future trends are addressed.

Chemical and bio-chemical reactions assisted by pervaporation technology

Since several decades ago, the application of pervaporation (PV) technology has been mainly aimed at the separation of different types of water-organic, organic-water and organic-organic mixtures, reaching its large-scale application in industry for the dehydration of organics. Today, the versatility and high selectivity toward specific compounds have led its consideration to other types of application such as the assisted chemical and bio-chemical reactions. The focus of this review is to provide a compelling overview on the recent developments of PV combined with chemical and bio-chemical reactions. After a general introduction of PV and its theoretical background, particular emphasis is given to the results obtained in the field for different reactions considered, identifying the key features and weak points of PV in such particular applications. Furthermore, future trends and perspectives are also addressed according to the latest literature reports.

Membrane Technology in Catalytic Carbonylation Reactions

In this review, the recent achievements on the use of membrane technologies in catalytic carbonylation reactions are described. The review starts with a general introduction on the use and function of membranes in assisting catalytic chemical reactions with a particular emphasis on the most widespread applications including esterification, oxidation and hydrogenation reactions. An independent paragraph will be then devoted to the state of the art of membranes in carbonylation reactions for the synthesis of dimethyl carbonate (DMC). Finally, the application of a specific membrane process, such as pervaporation, for the separation/purification of products deriving from carbonylation reactions will be presented.

Mixed matrix membranes for hydrocarbons separation and recovery: a critical review

The separation and purification of light hydrocarbons are significant challenges in the petrochemical and chemical industries. Because of the growing demand for light hydrocarbons and the environmental and economic issues of traditional separation technologies, much effort has been devoted to developing highly efficient separation techniques. Accordingly, polymeric membranes have gained increasing attention because of their low costs and energy requirements compared with other technologies; however, their industrial exploitation is often hampered because of the trade-off between selectivity and permeability. In this regard, high-performance mixed matrix membranes (MMMs) are prepared by embedding various organic and/or inorganic fillers into polymeric materials. MMMs exhibit the advantageous and disadvantageous properties of both polymer and filler materials. In this review, the influence of filler on polymer chain packing and membrane sieving properties are discussed. Furthermore, the influential parameters affecting MMMs affinity toward hydrocarbons separation are addressed. Selection criteria for a suitable combination of polymer and filler are discussed. Moreover, the challenges arising from polymer/filler interactions are analyzed to allow for the successful implementation of this promising class of membranes.

Pervaporation-based membrane processes for the production of non-alcoholic beverages

Nowadays, the interest in manufacturing non-alcoholic or low alcoholic content beverages from alcoholic beverages is a current challenge for food technologists; this is due to the fact that huge consumption of alcoholic beverages may produce health problems in the costumers. In principle, the post-fermentation ethanol removal from alcoholic beverages is carried out by means of evaporation or distillation. Such current dealcoholization methodologies are efficiently removing the ethanol, however, some organoleptic compounds can also be lost during the process. This makes the dealcoholization process highly sensitive in order to preserve the quality properties of the beverages. Thereby, membrane-based technologies, which use perm-selective barriers for the separation, have been highly promoted for such purpose. Pervaporation (PV) technology is indeed one of these technologies aimed for ethanol removal. Herein, the goal of this review is to provide a compelling overview of the most relevant findings for the production of non-alcoholic beverages (such as beer and wine) by means of PV. Particular attention is paid to experimental results which provide compelling feedback about the accurate ethanol removal and minimal changes on physicochemical properties of the beverages. Moreover, some theoretical basis of such technology, as well as key criteria for a more efficient dealcoholization, are also given.

Progress on Incorporating Zeolites in Matrimid®5218 Mixed Matrix Membranes towards Gas Separation

Membranes, as perm-selective barriers, have been widely applied for gas separation applications. Since some time ago, pure polymers have been used mainly for the preparation of membranes, considering different kinds of polymers for such preparation. At this point, polyimides (e.g., Matrimid^&reg;5218) are probably one of the most considered polymers for this purpose. However, the limitation on the performance relationship of polymeric membranes has promoted their enhancement through the incorporation of different inorganic materials (e.g., zeolites) into their matrix. Therefore, the aim of this work is to provide an overview about the progress of zeolite embedding in Matrimid^&reg;5218, aiming at the preparation of mixed matrix membranes for gas separation. Particular attention is paid to the relevant experimental results and current findings. Finally, we describe the prospects and future trends in the field.