Bipolar reverse osmosis membrane for separating mono-and divalent ions

Bipolar reverse osmosis membranes that have both negatively and positively charged layers have been prepared to enhance the selectivity towards mono- and divalent ions in respect of both cations and anions. Positively charged layers are formed on low pressure reverse osmosis membranes having negative charge (NTR-7410 and 7450) by an adsorption method using polyethyleneimine (PEI) or a quaternary ammonium polyelectrolyte (QAP). These layers attach to the membrane's dense layer, which is made of sulfonated polyether sulfone. The selectivity of mono- and divalent ions is proven by experimental results for single electrolytes (NaCl, Na₂SO₄ and MgCl₂). Although negatively charged membranes repulse divalent anions more strongly than cations and monovalent anions, bipolar reverse osmosis membranes reject both divalent cations and divalent anions better than monovalent ions. An optimal preparation method for bipolar membranes showing selectivity towards mono- and divalent ions were developed. The bipolar membranes showed good ion selectivity for artificial sea water.     

Electrodialysis of acetate fermentation broths

Electrodialysis (ED) shows good potential for downstream processing of acetate fermentation broths, to separate acetic acid while unreacted glucose and other nutrients are partially recycled back to the fermenter. With conventional anion- and cation-exchange membranes, higher current increased acetate flux, water flux, and energy consumption. Multiple ED stacks connected in series with unequal initial volumes for a batch process maximized acetate concentration in the concentrating stream to 134g/L calcium-magnesium acetate (CMA) in the fermentation broth at pH 6.8. Back-transport of acetate from the product into the feed stream and water transport limit the maximum concentration possible. Cost of ED is about $295/ton acetate for the CMA broth.     

发酵过程与双极膜电渗析的集成操作——介绍一个分离与反应技术一体化的化学工程实验

介绍一个分离与反应技术一体化的化学工程实验,实验中需进行发酵过程与双极膜电渗析过程的集成操作,可使学生在了解分离与反应技术一体化基本理论的基础上,改变传统的化学工程反应观念,激发对新型化学工程学科的学习兴趣。     

Electrodialysis of Amino Acid Solutions with Bipolar Ion-Exchange Membranes

Bipolar membranes intended for the generation of hydrogen and hydroxyl ions in order to convert bipolar ions of amino acid into cations or anions migrating through cation- or anion-exchange membranes under a gradient of electric potential applied to the electromembrane system are studied. The transport processes occurring in glycine and sucrose solutions under electrodialysis with bipolar and unipolar ion-exchange membranes are examined. The proposed method permits the separation of a mixture of amino acids and sugars.     

Electrodialysis with Bipolar Membranes: Principles,Optimization, and Applications

This paper is an overview of the bipolar membrane technology. The process of electrodialysis with bipolar membrane (EDBM) along with the different EDBM process configurations are presented. Some ways of optimization of both the bipolar membranes and the EDBM technology are envisaged. Most of the applications relate to the production or recovery of organic acids while the first plant has been commissioned by 1986 at Washington Steel (USA) for the recovery of HF/HNO₃ from waste pickling liquors. In the last few years, there has been increasing interest in using bipolar electrodialysis stacks in chemical and agro industrial processes to directly acidify or basify process streams without the addition of chemicals. This attractive feature of this technology has contributed to the implementation of several plants in fermentation process for the production of organic and amino acids.     

阴阳离子双隔膜三室电解槽电渗析处理垃圾渗滤液

采用阴阳离子双隔膜三室电解槽,将电渗析技术与Ｆｅｎｔｏｎ试剂法结合,去除垃圾渗滤液中氨氮和ＣＯＤ_Ｃｒ。垃圾渗滤液中的氨氮通过电渗析技术富集到阴极液中,随后用化学沉淀法加以去除。同时,在铁阳极上生成的Ｆｅ^２＋离子,与滴加入阳极液中的Ｈ_２Ｏ_２反应生成Ｆｅｎｔｏｎ试剂,降解有机物,降低ＣＯＤ_Ｃｒ。实验结果表明,模拟废水中的氨氮透过率达８０％,垃圾渗滤液中氨氮浓度和ＣＯＤ_Ｃｒ由原来的１９８２和２２４８ ｍｇ／Ｌ分别降至２００和１２７ ｍｇ／Ｌ。     

Recovery of Acid and Alkaline from Industrial Saline Wastewater by Bipolar Membrane Electrodialysis under High-Chemical Oxygen Demand Concentration

Actual high saline wastewater containing concentrated organics and sodium chloride is a bioenergy and renewable resource. This study compared two different bipolar membrane electrodialysis membranes from two companies’ stacks to recover HCl and NaOH from sodium chloride solution and actual chemical wastewater. The results demonstrated that the electrolysis rates were around 1.5 kg/m²h, the HCl and NaOH production rates were about 0.9 kg/m²h, energy consumption was in the range of 1.05–1.27 kWh/kg, and the economic benefits were above 1 yuan/h in BMED systems. From analyzing the performance of seven different BMED membrane stacks, the B2 stack was chosen for electrolyzing actual high salt wastewater to observe the effect of chemical oxygen demand on BMED systems, where electrolytic salt performance, HCl-NaOH alkali production rates, and energy consumption show linear dependence on time for 5000 mg/L chemical oxygen demand wastewater. It illustrated chemical oxygen demand can enhance energy consumption and reduce electrolytic salt performance and the acid and alkali production rates, due to improving the membrane area resistance. In this study, the effect of high COD saline wastewater on the performance of a BMED membrane stack was clarified and the mechanism was analyzed for its practical application in treating chemical high salt wastewater.     

Physicochemical Properties of Profiled Heterogeneous Ion-Exchange Membranes

Optimum values of parameters of hot pressing of heterogeneous ion-exchange membranes MK-40 and MA-40 (temperature, pressure, exposure duration) with the aim of creating geometrical profiles on their surfaces are determined. A method of optical visualization of membrane profiles and a diffusion technique of diagnostics of through pores in the membranes are developed and substantiated. Most important physicochemical and physicomechanical characteristics of profiled membranes are investigated. It is shown that the major obstacle in the production of profiled cation-exchange heterogeneous membranes is encapsulation of grains of the ion-exchange resin by an inert polyethylene film, which leads to an increase in the surface resistance of the membranes and to a decrease in the fraction of their active surface areas. The profiling of heterogeneous anion-exchange membranes is accompanied by an increase in their microscopic porosity and diffusion penetrability.     

Transport of Na2SO4 and MgSO4 solutions through a composite membrane

Retention curves with a composite membrane (HR 95) have been measured for different solutions of Na₂SO₄ and MgSO₄. Salt permeabilities in the skin and the porous layer of the composite membrane have been calculated. The results show that the salt permeability in the skin layer is 15% of that corresponding to the porous layer. Electrical resistances for the composite membrane and another membrane similar to the supported membrane (without skin layer) have been measured using both direct and alternating current. From the a.c. values, assuming that no concentration polarization exists at the skin-porous layer interface, the electrical resistance for the skin layer at different concentrations was estimated. The membrane resistance values were also determined by impedance spectroscopy measurements, and the results agree with those previously found by a.c. measurements.     

Inorganic Membranes for Hydrogen Separation

Hydrogen, one of the most promising energy carriers for the future, is currently produced mainly by natural gas reforming or coal gasification, where mixtures containing H₂, CO₂ and contaminants like CO, H₂S and CH₄ are obtained. Among other methods, membrane technology has received special attention due to its potential efficiency for hydrogen separation, simplicity of operation, low energy consumption, and because it is environmentally friendly. For this application, the inorganic membranes can be essentially divided into five main families: metallic and proton conducting (dense phases), and silica, zeolite and carbon molecular sieve (porous solids). Over the past 20 years, palladium-based membranes have been the most studied and implemented at industrial level; however, recent advances in other membrane types have received a great deal of attention. This article critically reviews more than 520 publications, highlighting the latest research developments on inorganic membranes for the recovery and purification of hydrogen, with emphasis on their structural characteristics, synthesis, commercial application, drawbacks and challenges. Furthermore, a large compilation of data is provided in Supplementary Material divided according to membrane type.     

Scalable Antifouling Reverse Osmosis Membranes Utilizing Perfluorophenyl Azide Photochemistry

We present a method to produce anti‐fouling reverse osmosis (RO) membranes that maintains the process and scalability of current RO membrane manufacturing. Utilizing perfluorophenyl azide (PFPA) photochemistry, commercial reverse osmosis membranes were dipped into an aqueous solution containing PFPA‐terminated poly(ethyleneglycol) species and then exposed to ultraviolet light under ambient conditions, a process that can easily be adapted to a roll‐to‐roll process. Successful covalent modification of commercial reverse osmosis membranes was confirmed with attenuated total reflectance infrared spectroscopy and contact angle measurements. By employing X‐ray photoelectron spectroscopy, it was determined that PFPAs undergo UV‐generated nitrene addition and bind to the membrane through an aziridine linkage. After modification with the PFPA‐PEG derivatives, the reverse osmosis membranes exhibit high fouling‐resistance.

     

Quantum Mechanical Calculations for Biomass Valorization over Metal-Organic Frameworks (MOFs)

Metal-organic framework (MOF) in biomass valorization is a promising technology developed in recent decades. By tailoring both the metal nodes and organic ligands, MOFs exhibit multiple functionalities, which not only extend their applicability in biomass conversion but also increase the complexity of material designs. To address this issue, quantum mechanical simulations have been used to provide mechanistic insights into the catalysis of biomass-derived molecules, which could potentially facilitate the development of novel MOF-based materials for biomass valorization. The aim of this review is to survey recent quantum mechanical simulations on biomass reactions occurring in MOF catalysts, with the emphasis on the studies of the catalytic activity of active sites and the effects of organic ligand and porous structures on the kinetics. Moreover, different model systems and computational methods used for MOF simulations are also surveyed and discussed in this review.     

Tuning the Electrochemical Properties of Novel Asymmetric Integral Sulfonated Polysulfone Cation Exchange Membranes

In this study, novel asymmetric integral cation exchange membranes were prepared by the wet phase inversion of sulfonated polysulfone (SPSf) solutions. SPSf with different degrees of sulfonation (DS) was synthesized by variation in the amount of chlorosulfonic acid utilized as a sulfonating agent. The characterization of SPSf samples was performed using FTIR and ¹H-NMR techniques. SPSf with a DS of 0.31 (0.67 meq/g corresponding ion exchange capacity) was chosen to prepare the membranes, as polymers with a higher DS resulted in poor mechanical properties and excessive swelling in water. By a systematic study, the opportunity to tune the properties of SPSf membranes by acting on the composition of the polymeric solution was demonstrated. The effect of two different phase inversion parameters, solvent type and co-solvent ratio, were investigated by morphological and electrochemical characterization. The best properties (permselectivity of 0.86 and electrical resistance of 6.3 Ω∙cm²) were obtained for the membrane prepared with 2-propanol (IPA):1-Methyl-2-pyrrolidinone (NMP) in a 20:80 ratio. This membrane was further characterized in different solution concentrations to estimate its performance in a Reverse Electrodialysis (RED) operation. Although the estimated generated power was less than that of the commercial CMX (Neosepta) membrane, used as a benchmark, the tailor-made membrane can be considered as a cost-effective alternative, as one of the main limitations to the commercialization of RED is the high membrane price.     

Current progress in membranes for fuel cells and reverse electrodialysis

The deterioration of the environmental situation has led to the need to restructure the world’s power industry, and clean renewable power sources are coming to the forefront. This review deals with recent advances in the development of promising ion-exchange membrane materials for two types of application that have been intensely developing recently, namely, hydrogen energy and reverse electrodialysis. Special attention is paid to the comparison of two properties of membranes, conductivity and selectivity, that are competing but fundamentally important in both areas. Perfluorinated sulfonic acid membranes now play a dominant role in hydrogen power engineering, as they provide not only high proton conductivity but also chemical stability and low gas permeability. The review also covers other types of membrane materials, including anion exchange membranes, polybenzimidazoles and hybrid membranes containing inorganic nanoparticles that have been actively developed in recent years. The milder operating conditions of membranes in reverse electrodialysis units allow one to use less expensive non-perfluorinated membranes, including grafted ones. It is of note that in devices of this type, the selectivity of membranes to the transfer of oppositely charged ions is a more important parameter.     

Valorization of Rice Straw via Hydrotropic Lignin Extraction and Its Characterization

Rice straw hydrotropic lignin was extracted from p-Toluene sulfonic acid (p-TsOH) fractionation with a different combined delignification factor (CDF). Hydrotropic lignin characterization was systematically investigated, and alkaline lignin was also studied for the contrast. Results showed that the hydrotropic rice straw lignin particle was in nanometer scopes. Compared with alkaline lignin, the hydrotropic lignin had greater molecular weight. NMR analysis showed that β-aryl ether linkage was well preserved at low severities, and the unsaturation in the side chain of hydrotropic lignin was high. H units and G units were preferentially degraded and subsequently condensed at high severity. High severity also resulted in the cleavage of part β-aryl ether linkage. ³¹P-NMR showed the decrease in aliphatic hydroxyl groups and the increasing carboxyl group content at high severity. The maximum weight loss temperature of the hydrotropic lignin was in the range of 330–350 °C, higher than the alkaline lignin, and the glass conversion temperature (T_g) of the hydrotropic lignin was in the range of 107–125 °C, lower than that of the alkaline lignin. The hydrotropic lignin has high β-aryl ether linkage content, high activity, nanoscale particle size, and low T_g, which is beneficial for its further valorization.     

MembrFactory: A Force Field and composition Double Independent Universal Tool for Constructing Polyamide Reverse Osmosis Membranes

The topmost polyamide (PA) layer of the thin-film-composite reverse osmosis (RO) membrane is the most important part in the membrane-based RO technology. With the aid of molecular dynamics simulations, many PA layer-related features in the RO process can be revealed. With many novel types of PA RO membranes out of trimesoyl chloride/m-phenylenediamine monomers developed in the laboratory, a convenient model building tool for these PA layer systems is urgently needed to conduct the theoretical analysis. Here, we develop a new universal toolkit for constructing PA RO membranes, named as MembrFactory, which combines flexibility of force fields and membrane compositions. A key characteristic of our approach is the use of monomers as the starting state, and the final membrane model was obtained automatically by stepwise reaction between the functional groups on the monomers. The reliability of MembrFactory has been validated by constructing several common PA RO membranes. © 2019 Wiley Periodicals, Inc.     

Electrodialysis of Binary Electrolyte Mixtures with Membranes Modified by Organic Species

The modification of anion-exchange membranes MA-40 by lauric acid and sodium polystyrenesulfonate is studied. By measuring the wetting angle and using IR spectroscopy, the mechanism of sorption of the modifiers by the membranes is established. The membrane modification is accompanied by hydrophobization of a surface layer and the formation of strong bonds between functional groups of membranes and modifiers. The concentration dependence of the ion separation coefficients in electrodialysis of binary electrolyte mixtures with modified and nonmodified membranes is studied. The selectivity of modified membranes to less-hydrated ions increases and the smaller the solution concentration, the larger the ions.     

Influence of Substitutional Defects in ZIF-8 Membranes on Reverse Osmosis Desalination: A Molecular Dynamics Study

In this study, molecular dynamics simulation is used to investigate the effects of water-based substitutional defects in zeolitic imidazolate frameworks (ZIF)-8 membranes on their reverse osmosis (RO) desalination performance. ZIF-8 unit cells containing up to three defect sites are used to construct the membranes. These substitutional defects can either be Zn defects or linker defects. The RO desalination performance of the membranes is assessed in terms of the water flux and ion rejection rate. The effects of defects on the interactions between the ZIF-8 membranes and NaCl are investigated and explained with respect to the radial distribution function (RDF) and ion density distribution. The results show that ion adsorption on the membranes occurs at either the nitrogen atoms or the defect sites. Complete NaCl rejection can be achieved by introducing defects to change the size of the pores. It has also been discovered that the presence of linker defects increases membrane hydrophilicity. Overall, molecular dynamics simulations have been used in this study to show that water-based substitutional defects in a ZIF-8 structure reduce the water flux and influence its hydrophilicity and ion adsorption performance, which is useful in predicting the type and number of defect sites per unit cell required for RO applications. Of the seven ZIF-8 structures tested, pristine ZIF-8 exhibits the best RO desalination performance.     

Valorization of Byproducts of Hemp Multipurpose Crop: Short Non-Aligned Bast Fibers as a Source of Nanocellulose

Nanocellulose was extracted from short bast fibers, from hemp (Cannabis sativa L.) plants harvested at seed maturity, non-retted, and mechanically decorticated in a defibering apparatus, giving non-aligned fibers. A chemical pretreatment with NaOH and HCl allowed the removal of most of the non-cellulosic components of the fibers. No bleaching was performed. The chemically pretreated fibers were then refined in a beater and treated with a cellulase enzyme, followed by mechanical defibrillation in an ultrafine friction grinder. The fibers were characterized by microscopy, infrared spectroscopy, thermogravimetric analysis and X-ray diffraction after each step of the process to understand the evolution of their morphology and composition. The obtained nanocellulose suspension was composed of short nanofibrils with widths of 5–12 nm, stacks of nanofibrils with widths of 20–200 nm, and some larger fibers. The crystallinity index was found to increase from 74% for the raw fibers to 80% for the nanocellulose. The nanocellulose retained a yellowish color, indicating the presence of some residual lignin. The properties of the nanopaper prepared with the hemp nanocellulose were similar to those of nanopapers prepared with wood pulp-derived rod-like nanofibrils.