Highly stable hydrophobic SiNCO nanoparticle‐modified silicon nitride membrane for zero‐discharge water desalination

Membrane distillation water desalination can attain a significantly higher water recovery than reverse osmosis, while the lack of stable hydrophobic membranes limits its commercial applications. This article presents the preparation of a new hydrophobic membrane by modifying a porous Si₃N₄ substrate with vesicular SiNCO nano‐particles. The membrane had a water contact angle of 142°, due to the presence of –Si–CH₃ terminal groups and the high surface roughness. The contact angle remained nearly the same after exposures of the membrane to boiling water, aqueous solutions with pH ranging from 2 to 12, and benzene. The membrane exhibited satisfactory water desalination performance on highly concentrated NaCl solutions and simulated seawater. With the highly stable membrane, it is promising to develop a zero‐discharge water desalination process for simultaneous production of fresh water for daily uses and brine for industrial uses. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1272–1277, 2017     

Development of a new asymmetric alloy membrane for water desalination

The preparation of a novel asymmetric membrane cast from a poly (4-vinylpyridine) and cellulose acetate homogeneous mixture is discussed. The two polymers were found to be miscible in concentrated solutions. Asymmetric membranes were cast from a sexted dope mixture containing: chloroform, methanol, acetone and formamide. The as-cast solution, when coagulated in water at ambient temperature, yields a highly plasticized asymmetric matrix which, upon slow diffusion of the chloroform into the water, solidifies into a glassy state. The membranes following this stage, do not require annealing and yield high fluxes and salt rejection when tested in reverse osmosis. The asymmetric morphology was confirmed by scanning electron microscopy studies which revealed a dense skin resting upon a highly porous, open-celled, foam-like structure. This structure retains its original wet dimensions upon drying. Brief attempts to quaternize the matrix are also reported.     

Polyphosphates used for membrane scaling inhibition during water desalination by membrane distillation

The desalination of surface water (lake) was performed using direct contact membrane distillation. The membrane distillation process was carried out at 358 K. As a consequence of water heating the CaCO₃ deposit formed on the membrane surfaces, which resulted in a decrease in module efficiency. The polyphosphate antiscalant was used for restriction of carbonate deposition. In order to increase the scaling potential during the desalination process, the water was additionally enriched with bicarbonates (feed alkalinity 3.1 mmol HCO₃^–/dm³ and 4.5 mmol HCO₃^–/dm³). The membrane distillation with and without antiscalant was carried out to evaluate the scale inhibition effect. Various solution compositions (2–20 ppm) of the commercial polyphosphate based antiscalant (destined for reverse osmosis) and laboratory-grade sodium polyphosphate was used. SEM–EDS was used to investigate the chemical composition and morphology of the precipitate formed on the membrane surface. It was found that the formation of CaCO₃ crystallites was almost eliminated as a result of using antiscalant. However, a thin layer of amorphous deposits on the membrane surface was observed. As a results, a decline of the permeate flux was still observed. The initial module efficiency was restored by periodical rinsing of the membranes with diluted HCl solutions. The application of antiscalant minimized the penetration of deposit into the pores, and a high permeate flux was maintained over a period of 260 h of performed investigations when periodical rinsing with HCl solution was used.     

Water permeation and solute rejection behaviors of a novel hydrophilic polyamide membrane

Summary The poly(BOL) membrane prepared by casting polymerization exhibited an excellent fractional solute-rejection behavior in the aqueous solution, having a comparatively sharp boundary region at the molecular weight range of about 200 to 1400, together with an extremely high water permeability. These conspicuous behaviors, as well as a great capacity for water absorption, may result from some delicate arrangement of polar hydrophilic and nonpolar hydrophobic microdomains probably formed along and between the polymer chains.     

Low-pressure RO membrane desalination of agricultural drainage water

Agricultural drainage water is a complex mixture of dissolved and suspended chemical species and may contain a wide variety of microorganisms. The application of membrane systems for desalination of agricultural drainage (AD) water requires careful consideration of feed water quality, suitable membrane selection and operating conditions. In order to evaluate the potential applicability of low-pressure reverse osmosis (RO) to the treatment of AD water, a diagnostic approach to membrane selection and process evaluation was undertaken in support of a pilot field study in the California San Joaquin Valley. Five candidate membranes were evaluated in a diagnostic laboratory membrane system which provided an initial selection based on salt rejection and product water flux performance for model salt solutions of univalent and divalent cations. Biofouling potential of the selected membranes was also evaluated using two standards strains of bacteria. Preliminary pilot plant performance, based on the selected membranes, was encouraging and has provided the basis for long-term pilot plant testing at higher recoveries to assess the impact of fluctuating AD water feed composition.     

RO membrane autopsy of Zarzis brackish water desalination plant

Tunisia, located in a semi-arid zone, has limited water resources. The shortage of good water quality in particular at the south regions required a brackish water desalination to supply these regions with potable water. Zarzis desalination plant, working since 1999, has revealed difficulties related to the loss of membrane performances. In the aim to determine the reason of membrane fouling, foulant layer were analysed. The membrane autopsy has achieved by different methods, such as TOC (total organic carbon) measurement, SEM (scanning electron microscopy), AFM (atomic force microscopy), FTIR (fourier transform infrared spectroscopy) analysis, diffraction by X-ray. Results show that the foulant layer composed mostly of SiO₂, clay, organic matter (polysaccharide, protein), CaSiO₃, Fe₃O₄, AlPO₄, and CaSO₄. The characteristics bonds obtained by IR indicate the presence of polysaccharides and proteins that constitute a source for further microbiological growth; this is the problem of biofouling. The metallic elements results of corroded stainless steel and internal coating of cartridges filter that are damaged by the silica particle rejected by sand filters. The scale of CaSO₄ and CaSiO₃ deposition is owing to the bad antiscaling efficiency. The results are presented and discussed in the light of new trends in material.     

Hydrophobizing polyether sulfone membrane by sol-gel for water desalination using air gap membrane distillation

ABSTRACT

The hydrophobic polyether sulfone membranes were prepared by the sol-gel method to be applied in an air gap membrane distillation setup for desalination. The surface modifications were carried out using Trimethylsilyl chloride (TMSCl) and Methyltrimethoxysilane (MTMS) solutions. The membranes were characterized using Attenuated Total Reflection Infrared (ATR-IR) spectroscopy, Scanning Electron Microscopy (SEM), and Optical Contact Angle (OCA) methods. The effects of membrane preparation as well as operating conditions such as temperature difference, salt concentration, feed rotation speed, and cold-side temperature on membrane performance were investigated using central composite design method. It was found that feed temperature has the largest effect among the parameters on the permeation flux. The flow rate and salt rejection of the membrane in the optimum conditions were 4.47 Kg m^?2 h^?1 and 99.37%, respectively.     

Synthesis and evaluation of aromatic polyamide membranes for desalination in reverse-osmosis technique

Reverse-osmosis membrane-grade aromatic polyamides have been synthesized by reacting 3,5-diaminobenzoic acid separately with three different acylchlorides, viz. isophthaloyl chloride, terephthaloyl chloride, and 4,4′-diphenyldicarboxylic acid chloride. Using these polyamides, asymmetric membranes were developed and characterized for various physical parameters, such as Staverman coefficient, membrane potential, and percent salt rejection using sodium chloride solution under high pressure. The effects of pressure, feed concentration, and feed flow rate have been studied on membrane transport parameters, viz. pure water permeability constant, product rate, solute transport parameter, and separation factor. The effects of annealing temperature and solvent evaporation time on the performance of the membranes were also studied. The analysis of the reverse-osmosis data revealed that the membranes prepared from the 3,5-diaminobenzoic acid and 4,4′-diphenyldicarboxylic acid chloride are superior to the membranes prepared from other polymeric materials. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 643–653, 1997     

A computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program is developed for predicting desalinating performance of a batch electrodialysis process. The program includes the principle of ① mass transport, ② current density distribution, ③ cell voltage, ④ mass balance/energy consumption and ⑤ limiting current density. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc., ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length in a desalting cell etc. and ③ electrodialytic conditions such as voltage, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.The following phenomena were computed and discussed; ① Changes of electrolyte concentration and current density with operation time. ② Influence of cell voltage on operation time (batch duration), water recovery and energy consumption. ③ Influence of volume of an electrolyte solution prepared at first on operation time. ④ Influence of cell voltage, electrolyte concentration and standard deviation of solution velocity ratio in desalting cells on limiting current density. ⑤ Energy consumption in a reverse osmosis process. ⑥ Excepting limiting current density, the performance of an electrodialyzer is never influenced by the standard deviation of normal distribution of solution velocity ratio in desalting cells. ⑦ Energy consumption in electrodialysis is less than that in reverse osmosis at feeding saline water concentration less than about 2000 mg/l.     

A computer simulation of continuous ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program including the principle of ① mass transport, ② current density distribution, ③ energy consumption and ④ limiting current density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as current density, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and current density distribution. Solution velocities in desalting cells vary between the cells, and give rise to solution velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of solution velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, current density distribution, and limiting current density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.     

反渗透海水淡化膜法预处理技术研究进展

简要论述了反渗透海水淡化的各种新型膜法预处理技术研究进展情况及其在国内外的具体运用情况,内容主要涵括连续微滤技术(CMF)、浸没式帘式膜过滤、超滤技术、纳滤技术以及陶瓷膜过滤.并指出膜法预处理将成为今后反渗透海水淡化预处理的主要发展方向.     

Feed water pretreatment for desalination plants

Effective membrane pretreatment is a crucial requirement for trouble free and cost effective RO desalination. Pretreatment construction costs are significant and may reach as much as 10%-20% of the total desalination plant capital costs. This paper presents a general review of the central factors involved in assessing raw water quality. The main foulant categories are described and the various unit operations commonly applied are reviewed. Pretreatment aspects of desalination offer fertile grounds for advancing desalination technologies. Promising research directions are highlighted.     

Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. I. Pure water permeation and membrane characterization by sorption measurements

The pervaporation of pure water through homogeneous aromatic polyamide membranes was investigated. The structure of the prepared membranes was controlled by varying the solvent evaporation times before the gelation step from 5 min to 240 min. The permeation flux of pure water decreased rapidly when the solvent evaporation time increased from 5 min to 30 min, and the decrease was rather moderate at higher evaporation times. Vapor and liquid sorption measurements were used to characterize the membranes. The amount of vapor sorption at a given relative pressure increased with an increase in the solvent evaporation time. The specific surface area of the membranes, calculated from the vapor sorption isotherm, increased with evaporation time up to 30 min, and remained constant thereafter. Liquid sorption volume, on the other hand, decreased monotonically with an increase in evaporation time. The formation of channels in the membrane is used to explain the morphology change during the solvent evaporation. The increase in the solvent evaporation time gradually increases the number of the channels in the membrane and decreases their average size. Good correlation was observed between the average size of the channels (represented by the ratio of specific volume to the specific surface area) and the parameters associated with pervaporation transport. © 1995 John Wiley & Sons, Inc.     

Gas permeation property of polyaniline films

We examined the influence of polyaniline (PAn)'s unit sequence and doping with low molecular weight dopants or polymer dopants on permeation property. It was found that CO₂ permeability was increased by the formation of a quinonediimine unit in PAn with the oxidation. CO₂ sorption amount of PAn was decreased by oxidation. The increase of CO₂ permeability with oxidation, therefore, resulted from the increase of diffusivity, which was attributable to morphological variation by the increase of a quinonediimine unit. The permselectivity of PAn films was found to be remarkably improved by doping. In particular, the selectivity value of the PAn film doped with polyvinyl sulphonic acid as a polymer dopant went up to over 2,000. This remarkable increase of selectivity was found to result in the increase of selectivity, depending on diffusivity. It was also found that the permselectivity of the PAn film doped by polymer dopants was surpassed, as compared with that doped by low molecular dopants. © 1995 John Wiley & Sons, Inc.     

Charged ultrafiltration membrane for permeation of proteins

Polyacrylonitrile-g-poly(N,N-dimethylaminoethyl methacrylate) was synthesized photochemically and quaternized. The positively charged membranes made from the quaternized graftcopolymer showed high ultrafiltration rate for water by adding poly(vinyl alcohol) to casting solution and washing it out after the casting. In buffered saline solution, the permeability of the membranes was very small at pH below isoelectric point of albumin but increased markedly at higher pH. On the other hand, the permeability for γ-globulin was very small and did not show any pH dependence.     

Energy-saving electro dialyzer for sea water desalination

Tokuyama Soda Co. ltd. has developed an energy-saving skid mounted electrodialyzer for sea water desalination. This equipment is suitable for making fresh water for drinking and industrial use. To desalinate 25°C sea water and turn out one ton of product water. This equipment consumes only 8.5 KWH of electricity and 0.09 Kg of concentrated sulfuric acid. Low energy consumption is achieved by adoption of low electric resistance membranes, new spacer and new designed one pass type system. Low running cost, easy maintenance and low initial installment cost place the equipment good position in the desalination field. And also we applied high temperature electrodialysis up to 50°C of sea water and get figure 6.0 KWH for one ton of product water.