Water Vapor Separation Research Articles

SI‐ATRP Polymer‐Functionalized Graphene Oxide for Water Vapor Separation

AbstractGraphene oxide is functionalized with poly(2‐diethylaminoethyl) methacrylate (PDEAEMA), and the resulting material is used as a selective layer of a thin‐film composite membrane (TFCM). The polymer synthesis is carried out by surface‐initiated atom transfer radical polymerization (SI‐ATRP) from bulk and also from single‐layer graphene oxide (GO). The polymer brushes synthesized by the “grafting from” method are characterized by size exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), Fourier‐transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and TGA‐FTIR. The TFCMs are prepared by the deposition of the selective layer from a stable polymer solution. The molecular weight of the polymer is sufficiently high to obtain a continuous defect‐free layer on a porous support. The thickness of the selective layer is ≈400 nm, as found in morphological investigations by scanning electron microscopy (SEM). The obtained membranes are utilized for gas and water vapor transport experiments in a wide temperature range. The water vapor permeability coefficient of the investigated materials is up to 4500 Barrer; this value increases threefold upon quaterization of the amine. The high permeance and selectivity for water vapor make this type of thin‐film membranes a potential candidate for membrane distillation.

NEXARTM-coated hollow fibers for air dehumidification

Air conditioning is one of the essential requirements for households as well as work stations. Dehumidification in air conditioning is the highest energy-consuming component, where membranes could play a crucial role. In this work, we propose the coating of NEXARTM, a commercial pentablock copolymer in tetrahydrofuran on polyetherimide hollow fiber support for separation of water vapor from humidified air. The block copolymer in tetrahydrofuran forms a lamellar/parallel cylindrical structure separated by equidistance during the morphological transformation process giving its unique characteristics with higher water vapor transfer efficiency. Both vacuum and sweep gas modes of membrane dehumidification strategies are investigated along with the detailed study of the morphological transformation process under a controlled environment, which is supported by comprehensive scanning electron microscopic and atomic force microscopic imaging. The membrane has shown water vapor permeance up to 9089 GPU with water vapor to nitrogen selectivity up to 3870. The membrane can reduce the relative humidity from 80% to 41% proving one of the competitive materials for membrane dehumidification.

Pyridinium based Poly(Ionic Liquids) membranes with exceptional high water vapor permeability and selectivity

Removing water vapor from gas streams via condensation is an energy-intensive process. Membrane-based technology is an attractive alternative for water vapor separation over other conventional dehumidification technologies, reducing the energy consumption and the overall operational cost. Polymeric membranes exhibiting high water vapor permeability and selectivity are promising candidates for water removal from applications including compressed air drying and flue gas dehydration. In this work, a precursor polymeric membrane based on aromatic polyether copolymer containing main chain pyridine units (PY-APE) and its pyridinium-based polymeric ionic liquids (PILs) films containing different counter anions (MeSO4−, BF4−, TFSI−) were prepared and evaluated as dehumidification membranes. Single gas and water vapor measurements were carried out and the selectivity of different gas pairs (H2O/H2, Η2Ο/Ν2, H2O/CO2, H2O/CH4) was measured. Among all membranes, PIL-MeSO4 had the highest water vapor permeability of 1.84 × 105 Barrer combined with the highest H2O/gas selectivity (e.g.H2O/CO2 selectivity is 2.0 × 105), which is one of the highest reported in the literature. The activation energies of water vapor and single gases (H2, CO2, CH4) permeation through the PIL-MeSO4 membrane were calculated suggesting that water vapor permeation is controlled by solubility while diffusion is the main transport mechanism for the other gases. The study of the water vapor effect on gas permeation under process gas streams conditions using a mixture of 3% H2O-24.25% CO2-72.75% H2 revealed that gas permeability increased one or two orders of magnitude. As a consequence, the separation factors decreased in comparison with the ideal selectivities obtained in dry conditions. This marked improvement in permeability is related to the presence of water vapor which causes swelling of the hydrophilic matrix thus producing water like domains that mainly govern gas permeation.

Analysis of pressure-driven water vapor separation in hollow fiber composite membrane for air dehumidification

A two-dimensional axisymmetric mathematical model was established to describe the pressure-driven water vapor separation in the hollow fiber composite membrane for air dehumidification. The developed transport model considered the permeation in the dense layer and the diffusion in the porous membrane substrate, in which the mass and momentum balance equations were coupled. The predicted results by the simulation model was consistent well with the experimental data. The velocity, pressure and concentration profiles and the mass transfer process in a single hollow fiber membrane were then solved and analyzed in detail, including the effects of feed velocity, feed humidity and transmembrane pressure on the dehumidification performance. The results show that the amount of water vapor separation (outlet humidity) is more sensitive to the medium feed velocity with the separation amount about twice than that of high and low velocities. The separated amount of water vapor by the membrane is less dependent on the feed inlet humidity. And the air dehumidification performance of the membrane could be realized effectively until the transmembrane pressure over a critical value, which is 1.0 bar in this model. The findings deliver an insight into the mass transport in the membrane-based dehumidification process, with the aims to provide a useful reference to the design, process optimization and module development using hollow fiber membrane.

Comparative thermodynamic analysis of membrane-based vacuum air dehumidification systems

Recently, membrane-based vacuum air dehumidification (MVD) systems have been studied as an advanced cooling scheme. In general, the working principle of these systems is based on the separation of water vapor from air caused by a vapor pressure gradient between the feed and permeate side of a membrane when humid air passes over the membrane. After permeating, the vapor is discharged to the atmosphere through a vacuum compressor or pump. Several types of MVD systems with different operation drivers have been introduced recently, but the comparative analyses with the working properties were limited. In this study, three promising MVD systems of the sweep air mixed (S-MVD) type, water vapor discharge (W-MVD) type, and condenser combined (C-MVD) type, are analyzed comparatively with an idealized membrane with infinite selectivity on H2O. From the simulation, the W-MVD system exhibited the best dehumidification performance because of the lowest compression ratio and water vapor flow rate. However, the C-MVD system, which is relatively simple to implement, practically exhibited better performance under limited conditions of a hot and humid climate. After the comparison of the three MVD systems, the applicability of each MVD system for different climates was discussed in detail.

Feasibility Analysis of a Membrane Desorber Powered by Thermal Solar Energy for Absorption Cooling Systems

In absorption cooling systems, the desorber is a component that separates the refrigerant fluid from the liquid working mixture, most commonly completed by boiling separation; however, the operation temperature of boiling desorbers is generally higher than the low-enthalpy energy, such as solar, geothermal, or waste heat. In this study, we used a hydrophobic membrane desorber to separate water vapor from an aqueous LiBr solution. Influencing factors, such as the H2O/LiBr solution and cooling water temperatures, were tested and analyzed. With the experimental data, a solar collector system was simulated on a larger scale, considering a 1 m2 membrane. The membrane desorber evaluation shows that the desorption rate of water vapor increased as the LiBr solution temperature increased and the cooling water temperature decreased. Based on the experimental data from the membrane desorber/condenser, a theoretical heat load was calculated to size a solar system. Meteorological data from Emiliano Zapata in Mexico were considered. According to the numerical result, nine solar collectors with a total area of 37.4 m2 provide a solar fraction of 0.797. The membrane desorber/condenser coupled to the solar system can provide an average of 16.8 kg/day of refrigerant fluid that can be used to produce a cooling effect in an absorption refrigerant system.

Boron geochemistry of the geothermal waters from two typical hydrothermal systems in Southern Tibet (China): Daggyai and Quzhuomu

The Tibetan plateau is characterized by a widely and intensively distributed geothermal activity and an extreme enrichment of boron in some geothermal waters. Twenty-five hot spring samples were collected from the Daggyai and Quzhuomu geothermal areas in Tibet to determine their boron concentrations and isotope composition. The boron concentrations and δ11B values for the neutral geothermal waters in Daggyai range from 72.5 to 106.9 mg/L and −16.4‰ to −12.3‰ while the Daggyai acid waters have much lower boron concentrations (1.1–1.2 mg/L) and slightly higher δ11B values (−12.9‰). The hot spring samples from the Quzhuomu geothermal area have boron concentrations varying from 21.9 to 44.6 mg/L and δ11B values from −11.3‰ to −7.1‰. The hydrochemical and B isotopic evidence imply that the boron in Daggyai geothermal waters is contributed by both magmatic fluid input and host rock leaching. In contrast, marine carbonates and granites, especially the former, are confirmed as the major boron sources for the Quzhuomu geothermal waters. In addition, there also exist some secondary processes affecting the boron isotope fractionation in geothermal waters, e.g. water-vapor separation and absorption or incorporation of B into hydrothermally altered minerals. Finally, based on the analysis of B geochemistry in these two typical geothermal areas in Southern Tibet with different heat sources and reservoir lithology, the mechanisms for the accumulation of boron in the Daggyai and Quzhuomu geothermal waters are suggested. This study is promising to provide insight into the sources of boron in the geothermal waters in other Tibetan geothermal areas.

Analysis of design parameter effects on gas dehumidification in hollow fiber membrane contactor: Theoretical and experimental study

Tri-ethylene glycol (TEG) solution is an appropriate solvent for the effective separation of water vapor from the gas stream. In this study, a comprehensive two-dimensional axisymmetric mathematical modeling has been performed for simulation of water absorption into tri-ethylene glycol solution in a hollow fiber membrane contactor. The obtained governing equations for different sections of membrane contactor (tube side, membrane and shell side) along with the proper boundary conditions have been solved with the aid of COMSOL Multiphysics software. The experiment has been conducted to validate the proposed model and confirm the calculated values by the model. The effects of different parameters such as gas flow rate, desiccant solvent flow rate, TEG concentration, flow direction and wetting on membrane performance have been investigated using the model. The experimental data and predicted values are in excellent agreement with an error of only 2%, indicating the validation of CFD model for process simulation. The results reveal that the resistance in the liquid phase is not the limiting factor for this system. Also, membrane wetting by tri-ethylene glycol could decrease the absorption flux significantly.

Water vapor transport properties of interfacially polymerized thin film nanocomposite membranes modified with graphene oxide and GO-TiO2 nanofillers

Graphene oxide (GO) and its composite with TiO2 (GT) were utilized as nano-filler materials to prepare highly permeable and water vapor selective nanocomposite membranes. The nano-fillers were characterized using different analytical tools to determine their physicochemical properties. Nanocomposite membranes were prepared by dispersing the nano-fillers in aqueous phase monomer solution for interfacial polymerization reaction on the inner surface of Polysulfone hollow fiber membrane. Surface morphology and bonding chemistry of the nanocomposite membrane was analyzed using various analytical tools. The two types of nano-fillers were compared for their compatibility with the polyamide matrix, and consequently, the water vapor separation performance of the resulting membrane. Results revealed that both the nano-fillers are firmly attached to the polyamide layer via hydrogen and covalent bonds. GT based membranes have higher surface roughness and better hydrophilicity as compared to GO. In addition, GT membranes have more carboxyl groups and lesser degree of cross-linking due to the interference with interfacial polymerization reaction. This leads to a higher permeance (2820 GPU) and a water vapor/nitrogen selectivity when compared to other TFN membranes reported in literature. The nano-fillers act as active sites for preferential transport of water vapor molecules through the membrane thereby, significantly improving water vapor permeance.

A new approach for drying moist air: The ideal Claridge-Culp-Liu dehumidification process with membrane separation, vacuum compression and sub-atmospheric condensation

The Claridge-Culp-Liu Dehumidification Process is a novel and efficient approach to removing water vapor from air using a combination of membrane separation, vacuum compression and sub-atmospheric condensation. The basic theory of this process is to separate water vapor from moist air flowing across one side of a membrane by applying a partial vacuum to the opposite side of the membrane and then compressing the water vapor to its saturation pressure at the wet-bulb temperature of the ambient air so as to facilitate condensation. This process has a fundamental efficiency limit that approximates the Carnot limit, but for eight different ideal dehumidification-only cases examined herein, the process requires only 26–56% the energy required by a Carnot vapor-compression system. Furthermore, the limiting energy required by an ideal 5-stage membrane system is 16–31% that of a Carnot system for the same cases. Of special importance, the ideal Claridge-Culp-Liu Dehumidification Process requires less than 5% of the energy required by an ideal desiccant process for all cases treated. The Claridge-Culp-Liu Dehumidification Process can also be combined with evaporative cooling to provide dehumidification and sensible cooling with the temperature and humidity controlled independently. Of special importance, this system uses no HFC refrigerants, and it generates pure water as a by-product.

Efficient prediction of water vapor adsorption capacity in porous metal–organic framework materials: ANN and ANFIS modeling

Optimum design of water vapor separation process (dehumidification) using adsorption process mostly depends on the selection of appropriate porous materials or adsorbents with the highest equilibrium storage capacity of the vapor. Equilibrium capacity is generally evaluated through cost-demanding experiments via direct measurement of the vapor isotherm. Reliable prediction of the vapor adsorption capacity in porous materials provides a robust tool to a quick screening of porous materials appropriating for dehumidification process. In this article, adsorption capacity of water vapor in metal–organic framework (MOF) materials is predicted using two robust “artificial neural network (ANN)” and “Adaptive network-based fuzzy inference system (ANFIS)” methods. The three parameters of the surface area, pore volume and pore diameters are selected as input and the water vapor adsorption capacities of MOFs were computed as the output of the models. Comparison of the obtained results and real experimental data implied the superiority of the ANFIS and ANN models to predict the water vapor adsorption capacity into MOFs with a mean squared error (MSE) of 0.005 and 0.002, respectively. This clearly indicates a great potential for the application of both ANN and ANFIS methods to rapid screen MOFs suitable for water vapor adsorption.

Dehydration of paddy rice in a chitosan membrane drier

A chitosan membrane was used to separate water vapor evaporated from moist paddy rice out of the apparatus, called the “membrane drier”. It was aimed as an alternative method to dry harvested paddy instead of the traditional open air technique that can encounter rain or flooding problems. The prototype membrane drier was designed from a mathematical air flow pattern analysis, where it was found that a horizontal flow mode with a baffle plate and triangle air flow path (HFwBF&TFP) was the most appropriate feature. The chitosan membranes studied in this research were uncrosslinked dense (UCD), crosslinked dense (CD), uncrosslinked composite-on-spunbond (UCC) and crosslinked composite-on-spunbond (CC) membranes. The highest drying rate of the membrane drier equipped with UCD, CD, UCC and CC membranes occurred in the first hour of operation at 46.4 ± 0.4, 51.7 ± 6.7, 57.8 ± 0.9 and 71.5 ± 4.9 g-water/kg-moist-paddy/h, respectively. Compared to the drying rate by the open air technique and a hot air oven at 40 °C (52.7 ± 0.7 and 40.2 ± 0.7 g-water/kg-moist-paddy/h, respectively), the chitosan membrane drier could be used as an alternative method for drying biomass, such as paddy rice. The CC chitosan membrane drier could reduce the moisture content of harvested paddy rice from 22.8 ± 0.4 to 15.7 ± 0.9% within 1 h.

Investigating the structural effect of electrospun nano-fibrous polymeric films on water vapor transmission

Abstract Electrospun polymers have many applications in the industry. However, the structure of these polymers has been less widely considered by researchers. In this work, the structural effect of electrospun and casted films of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) polymers on water vapor transmission were investigated. Sorption of water vapor was measured at 35, 60 and 80 °C and different relative humidities. The diffusion coefficients were calculated based on mass changes of the polymer sample. The water vapor transmission rate (WVTR) was also measured at 35 °C and 90% relative humidity. The results indicated that electrospun nano-fibrous polymers (ESNPs) absorb much higher water vapor compared to non-porous casted polymers. The interaction of water molecules with mentioned polymers was investigated based on Flory-Huggins theory. The Flory-Huggins interaction parameter of electrospun films was less than casted films, suggesting much better interaction of water molecules with electrospun films. It was also found that electrospun films have anomalous kinetic behavior and do not obey the Fickian diffusion model. Finally, it was revealed that ESNPs show less resistance to water vapor transmission and they are good candidates for the applications of water vapor separation using membranes.

Preliminary study on the feasibility of using a zeolite A membrane in a membrane reactor for methanol production

Abstract The permeation of a mixture containing H2, CO2 and water through a zeolite membrane was studied under several operating conditions. The aim was to obtain insight on the feasibility of using such membrane in a zeolite membrane reactor for CO2 hydrogenation to methanol. The effects of total pressure (100–270 kPa), water partial pressure (10–18 kPa) and temperature (160–260 °C) were studied. Promising water-permanent gas separation factors were obtained up to 240 °C. A surprisingly high water partial pressure was found in the permeate in some cases, which is explained by the radial temperature gradient in the experimental system. The good capability of this zeolite A membrane to selectively separate water vapor makes it a promising material for its use in a zeolite membrane reactor.

Development of thin film nanocomposite membranes incorporated with sulfated β-cyclodextrin for water vapor/N2 mixture gas separation

In this work, thin film nanocomposite (TFN) membranes incorporated with sulfated β-cyclodextrin (sb-CD) were fabricated by interfacial polymerization using aliphatic diethylene triamine (DETA) and trimesoyl chloride (TMC) for water vapor separation. Aromatic m-phenylenediamine (MPD) was used for performance comparison with DETA. The intrinsic properties of fabricated TFN membranes were investigated by Attenuated total reflectance-Fourier transformed infrared (ATR-FTIR), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and water contact angle (WCA). The contact angle (35°) of the TFC membranes with DETA was very lower than that (59°) of The TFC with MPD. Moreover, the TFN membrane with sb-CD loading of 0.15wt% showed the lowest contact angle of 14°, implying that many hydrophilic sulfonic acid groups of sb-CD nanoparticles contributed to decreased contact angle. The effect of sb-CD loading on water vapor permeance and selectivity was studied. Increase in sb-CD loading caused synergistic increase in both permeance and selectivity below the agglomeration point due to its hydrophilic and packable nature. The maximal selectivity of 503 along with 1597 GPU in permeance was obtained with the sb-CD loading of 0.15wt%. In addition, the structural characteristics were found to have a bigger impact on TFN membrane performance than intrinsic properties.

Synthesis of superhydrophilic Nafion based nanocomposite hollow fiber membranes for water vapor separation

Mesoporous SiO2 nanoparticles are explored as a potential hydrophilic inorganic filler to recognize nanocomposite membranes with Nafion and ionic liquid (IL) tetramethylammonium hydroxide (TMAOH) for water vapor removal applications under condensed relative humidity. Nanocomposite membranes are obtained by inserting SiO2 nanoparticles in Nafion–ionic liquid coating solution in different concentrations of Nafion, thereby providing increased adsorption sites for water vapor. These nanocomposite membranes are prepared on the surface of polysulfone (PSf) hollow fiber membranes. The main objective of this study was to prepare Nafion–IL–SiO2 nanocomposite membranes for direct water vapor mixture gas separation in applications with the aim of increasing water vapor permeance and keeping up the selectivity. The application of the Nafion–IL–SiO2 nanocomposite membranes in water vapor mixture gas separation was demonstrated. As a result, the high water vapor permeance of 2131GPU was achieved for the PSf–Nafion–IL–SiO2-M2 membrane and high H2O/N2 selectivity of 130 was obtained for the PSf–Nafion–IL–SiO2-M3 membrane at pressure 3bar and temperature 30°C.

Membrane dehumidification process using defect-free hollow fiber membrane

Water vapor removal by the polymeric membrane to reduce the energy cost during the water–gas shift reaction in a catalytic membrane reactor was investigated. In this study, polyamideimide (PAI) defect-free hollow fiber membranes were produced by a dry/wet phase inversion method. The purpose of this study was to investigate the water vapor removal efficiency under high pressure and high temperature. The morphologies of the hollow fiber membranes were characterized by SEM. The water vapor and hydrogen mixed gas separation properties were used to verify the performance of a defect-free membrane. The water vapor removal efficiency increased from 54% to 90% (at 120 °C) as a function of the operating conditions because of the enhanced water vapor flux. However, the H2 retention ratio was negatively related to the water removal efficiency.

Enhancement of water vapor separation using ETS-4 incorporated thin film nanocomposite membranes prepared by interfacial polymerization

In this work, microporous Engelhard titanosilicate-4 (ETS-4) incorporated thin film nanocomposite (TFN) membranes for water vapor separation were fabricated via interfacial polymerization. ETS-4 particles were synthesized and ground by an attrition mill to reduce particle size. The ground ETS-4 nanoparticles were well dispersed in 3,5-diaminobenzoic acid (DABA) solution followed by reacting with trimesoyl chloride (TMC) to get embedded in the polyamide selective layer on the outer surface of polysulfone (PSf) hollow fibers. The intrinsic properties of ETS-4 as well as TFN membranes were investigated by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), atomic force microscopy (AFM) and water contact angle (WCA). The effect of ETS-4 concentration on water vapor permeance and selectivity was investigated. Increase in ETS-4 concentration during interfacial polymerization causes significant increase in selectivity due to its molecular sieving effect by sacrificing little permeance till 0.5wt%, above which the selectivity deteriorates due to the agglomeration of ETS-4 nanoparticles. The maximum selectivity of 346 was obtained with 1377 GPU in permeance for the TFN membrane (DTE-0.5) with ETS-4 concentration of 0.5wt%. Additionally, the effect of concentration polarization was examined and individual resistances from the overall resistance were calculated.

Experimental investigation of multi-effect regenerator for desiccant dehumidifier: Effects of various regeneration temperatures and solution flow rates on system performances

We have experimentally measured the thermal performances (PR) of vacuum assisted multi-effect regenerator, which employs hydrophobic membrane to separate water vapor from LiCl solution with higher evaporation rates. We have modified the working principles of the conventional multi-effect membrane distillation (MEMD) by the transfer of heat from one stage to the other stage of regenerating module such that more energy can be recovered through multi-effect evaporation generated in each regenerating module with enhanced liquid vapor separation in the membrane. The PR and percentage change in desiccant concentration are measured for the temperatures ranging from 50 °C to 75 °C. The experimental results show that the conventional MEMD is not suitable for dehumidification applications due to higher feed concentration. We have modified the conventional MEMD system employing (i) one-steam-three-solution passes and (ii) two-steam-four-solution passes, which handles higher feed concentrations. The PR is found 0.7 for one steam three solution passes system.

Scalable Production Method for Graphene Oxide Water Vapor Separation Membranes

ABSTRACTMembranes for selective water vapor separation were assembled from graphene oxide suspension using techniques compatible with high volume industrial production. The large-diameter graphene oxide flake suspensions were synthesized from graphite materials via relatively efficient chemical oxidation steps with attention paid to maintaining flake size and achieving high graphene oxide concentrations. Graphene oxide membranes produced using scalable casting methods exhibited water vapor flux and water/nitrogen selectivity performance meeting or exceeding that of membranes produced using vacuum-assisted laboratory techniques. (PNNL-SA-117497)