Increasing Feed Pressure Research Articles

Performance of thin film composite membranes for ammonium removal and reuse of ammonium-enriched solution for plant growth

Abstract Ammonium is known to be one of the most significant pollutants in water bodies. The presence of ammonium in water is mainly originated from agricultural activities, domestic sewage and industrial effluent. This study evaluates the performance of two commercial thin film composite (TFC) membranes, i.e., NF270 and XLE from FilmTec™ for ammonium removal using synthetic wastewater and domestic sewage. The filtration experiment was conducted at different feed ammonium concentrations, humic acid concentrations, pHs and pressure. Results showed that the membrane rejection against ammonium increased dramatically with increasing ammonium concentration. However, the membrane flux was slightly compromised at higher ammonium concentration. With respect to pH, highest ammonium removal rate was able to be achieved at an optimum pH of 10. Besides, the permeation flux increased gradually with increasing feed pressure. From the results, the XLE membrane outperformed the NF270 membrane in terms of ammonium rejection. The retentate of XLE membrane filtration process was found to be useful as liquid fertiliser for plant growth. The results indicated that the TFC membrane process is not only able to produce permeate with an ammonium concentration below the acceptable limit of 10 mg/L but also able to produce retentate with enriched ammonium for plant growth.

Intensification and optimization of the characteristics of polyacrylonitrile nanofiltration membranes with improved performance through experimental design and statistical analysis

AbstractThe present study aims to employ experimental design and statistical analysis in order to investigate in detail the effect of various prominent parameters on the characteristics and performance of polyacrylonitrile nanofiltration membranes for the treatment of electroplating wastewaters targeting Ni, Cr, and Zn ions. Incorporation of TiO2 into the membrane matrix was effective in improving pure water flux (PWF) by ~16%. Also, PWF and Ni rejection of membranes escalated to 118.55 L m−2 h−1 and 90.79%, respectively upon addition of 1.5 wt% citric acid to the dope. Variation in coagulation bath temperature from 25°C to 45°C led to the formation of membranes having higher porosity with enhanced PWF by about 25% at the expense of only 5% reduction in Ni rejection. Parameters were optimized by analysis of variance (ANOVA). In contrast to the effect of feed concentration, an increase in feed pressure and pH enhanced permeate flux and total ion rejection. Similarly, permeate flux increased at higher operational temperatures without change in total rejection. A mathematical model was developed by applying ANOVA and the best combination of operating parameters was obtained by optimization.

Development of high performance amine functionalized zeolitic imidazolate framework ( ZIF ‐8)/cellulose triacetate mixed matrix membranes for CO 2 / CH 4 separation

High cost and complex fabrication process of inorganic membranes and lower position of pristine polymeric membranes in the Robeson upper bound curve urged the researchers to develop mixed matrix membranes (MMMs). Cellulose acetate being most commercially used polymer, dominates the market of CO2 separation mainly because of low cost and environmental friendly resource. In the present study, MMMs consists of amine functionalized zeolitic imidazolate framework (NH2-ZIF-8) and cellulose triacetate were fabricated for the first time. NH2-ZIF-8 was used as a filler because the pore size of ZIF-8 is between the kinetic diameter of separating gases (CO2 and CH4). Moreover, NH2 group attached on the surface of ZIF-8 has affinity with condensable gases like CO2. Morphology, crystallinity, tensile strength and functional groups of fabricated membranes were investigated using different analytical techniques. Results revealed that the increase of feed pressure has increased CO2 permeability and decreased permselectivity. However, improvements in gas separation performance were observed with the addition of nanofiller. Best position in Robeson's upper bound curve at 4 bar was obtained with 10 wt% loading with CO2 permeability and CO2/CH4 permselectivity of 218 barrer and 13.84, respectively. The improvement in the gas separation performance with loading is attributed to the increased diffusion coefficients as well as solubility coefficients, which was increased to 33% and 3.8%, respectively.

Mixed matrix membranes on the basis of Matrimid and palladium-zeolitic imidazolate framework for hydrogen separation

Gas separation membranes with enhanced performance were developed by the introduction of nanosized palladium particles. In this study, gas separation performance of Matrimid membrane incorporated with palladium-zeolitic imidazolate framework-8 (Pd@ZIF-8) particles, prepared by solution casting method, has been investigated. ZIF-8 nanoparticles were first synthesized using rapid room-temperature method and Pd@ZIF-8 nanoparticles were prepared through an assembly approach. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD), and Fourier transform infrared equipped with attenuated total reflection (FTIR-ATR). TEM images exhibited that the incorporated Pd nanoparticles are well confined within the ZIF-8 crystals. The prepared mixed matrix membranes (MMMs) with various Pd@ZIF-8 contents (0–30 wt%) were characterized by SEM and XRD. All the modified membranes exhibited enhanced gas separation performance for selected gas pairs compared to a neat Matrimid membrane. The highest performance was observed for nanocomposite membranes with incorporation of 30 wt% of Pd@ZIF-8 into Matrimid which resulted in 72% increase in H2 permeability. The separation factors of H2/CO2, H2/CH4 and H2/N2 were improved from 3.25, 126.13, 95.21 for Matrimid/ZIF-8 to 5.82, 228.2 and 169.1 for Matrimid/(Pd@ZIF-8) membranes, respectively. Finally, the increase in feed pressure significantly improved the separation performance quality in all the membranes.

Thermodynamic study on carbon dioxide and methane permeability in polyvinylchloride/ionic liquid blends

In the present study, to improve separation proficiency of polyvinyl chloride (PVC) membrane, polyvinyl chloride is combined with 1–butyl–4–methylpyridinium ionic liquids ([B4MPyr][X]) with different anions bromide, [Br]−, chloride, [Cl]−, thiocyanate, [SCN]−, and tetrafluoroborate, [BF4]. The prepared PVC/[B4MPyr][X] blend membranes were characterized by differential scanning calorimetry (DSC) analyses. The prepared membrane morphology was investigated by Scanning Electron Microscope (SEM). The effects of feed pressure, temperature and, different of anions on the performance of blend membrane were surveyed. The results reveal that the permeability of methane and carbon dioxide gases in the PVC/[B4MPyr][X] blevapournd membranes were reduced with an increase in feed pressure while the ideal selectivity of CO2/CH4 was increased with an increase in feed pressure. Moreover, the permeability of CH4 and CO2 gases in the PVC/[B4MPyr][X] blend membranes are increased with an increase in temperatures while the ideal selectivity of CO2/CH4 was decreased with increasing temperatures. Also, the PVC/[B4MPyr][SCN] membrane has a higher performance for the separation of CO2 and CH4 gases in comparing with others membranes.

Separation of C1–C4 Hydrocarbon Mixtures Using Fe-Containing Siloxane Composition

Polymer composition has been prepared on the basis of commercial siloxane rubber SKTN-D and tris-(methyldiethoxysiloxy)iron with the reagent ratio 60 : 40 wt %, respectively. Transport parameters of individual hydrocarbons C1–C4 have been shown to be comparable with those for polydimethylsiloxane published previously. Permeability coefficients P of single hydrocarbons C2–C4 increase with an increase in the penetrant feed pressure. It has been demonstrated for n-butane that such increase in P resulted from both a higher diffusion coefficient and solubility coefficient of the penetrant. For mixed gas permeation of C1–C4, an increase in P of methane and a decrease in P of n-butane are observed with increasing the feed pressure. These trends may be explained by the plasticization of the polymer compound and the presence of “rigid” polycyclic structures based on the iron-siloxane component. Similar behavior has been observed for methane and C2+ components with separating quaternary mixture of C1–C4 hydrocarbons. Separation selectivities with respect to methane decreased with increasing feed pressure; however, they become comparable with corresponding results for previously studied substituted polytricyclonones.

Study on the effect of process parameters on CO2/CH4 binary gas separation performance over NH2-MIL-53(Al)/cellulose acetate hollow fiber mixed matrix membrane

The aim of current work is to study the interaction of process parameters including, temperature, CO2 feed composition and feed pressure were towards CO2 separation from CO2/CH4 binary gas mixture over hollow fiber mixed matrix membrane using design of experiment (DoE) approach. The hollow fiber mixed matrix membrane (HFMMM) containing NH2-MIL-53(Al) filler and cellulose acetate polymer was successfully spun and fibers with outer diameter of approximately 250–290 nm were obtained. The separation results revealed that the increment of temperature from 30 °C to 50 °C reduced the CO2/CH4 separation factor while, increasing feed pressure from 3 bar to 15 and increment of CO2 feed composition from 15 to 42.5 vol% increased the separation factor of HFMMM. The DoE results showed that the feed pressure was the most significant process parameter that intensely affected the CH4 permeance, CO2 permeance and CO2/CH4 separation factor. Based on the experimental results obtained, maximum CO2 permeance of 3.82 GPU was achieved at feed pressure of 3 bar, temperature of 50 °C and CO2 feed composition of 70 vol%. Meanwhile, minimum CH4 permeance of 0.01 GPU was obtained at feed pressure of 15 bar and temperature of 30 °C and CO2 feed composition of 70 vol%. Besides, maximum CO2/CH4 separation factor of 14.4 was achieved at feed pressure of 15 bar and temperature of 30 °C and CO2 feed composition of 15 vol%. Overall, the study on the interaction between separation processes parameters using central composite design (CCD) coupled with response surface methodology (RSM) possesses significant importance prior to the application of NH2-MIL-53(Al)/Cellulose Acetate HFMMM at industrial scale of natural gas purification.

A preferential CO2 separation using binary phases membrane consisting of Pebax®1657 and [Omim][PF6] ionic liquid

Pebax®1657 and [Omim][PF6] ionic liquid (IL) were used to fabricate a blend membrane and applied for CO2 separation. The changes upon adding ionic liquid into the polymer matrix as well as the membrane characteristics were studied through SEM, FTIR, DSC and TGA analysis. The obtained gas permeation results indicated that the CO2 permeability in all membranes was much higher than the other studied gases. CO2 permeability of Pebax containing 8 wt% IL increased from 82.3 Barrer up to 125.6 Barrer at a pressure of 2 bar, which showed a 53% increment compared to the neat Pebax membrane. Furthermore, as the [Omim][PF6] loading within the polymer matrix was increased, the CO2/CH4 and CO2/N2 selectivities improved. In addition, the permeability and selectivity of gases was enhanced as the feed pressure increased. Upon increasing feed pressure to 10 bar, the CO2 permeability of Pebax containing 8 wt% IL reached 185.3 Barrer, which was approximately 48% higher than the permeability at a pressure of 2 bar. Moreover, the selectivity of CO2/CH4 and CO2/N2 for the Pebax/8wt% IL membrane at pressure of 2 bar was 15.3 and 46.5, respectively, which improved to 19.7 and 59.8 as the pressure increased to 10 bar.

CFD-based genetic programming model for liquid entry pressure estimation of hydrophobic membranes

Wetting phenomenon inside the pore is a significant obstacle hindering membrane distillation (MD) from being fully industrialized. Herein, a new equation is provided for the users, using the combination of computational fluid dynamics (CFD) and genetic programming (GP) tools for estimation of liquid entry pressure (LEP), a parameter closely related to pore wetting. CFD was applied to model the wetting process inside the pore during the gradual increase in feed pressure at different scenarios in which contact angle, pore radius and membrane thickness were changed. Afterwards, GP as an intelligent method was employed to provide a computer program estimating LEP in the whole ranges in which CFD modeling was carried out. Moreover, validation was done using experimental data and then the influence of effective parameters on LEP was studied. This work provides an explicit formula for estimation of LEP in a closer agreement with the experimental data in comparison to the Young-Laplace equation. In addition, the influence of the membrane thickness was added to the equation, providing a more realistic formula for LEP estimation.

The effect of supercritical CO2 on the permeation of dissolved water through PDMS membranes

Water vapor permeation under supercritical carbon dioxide (scCO2) conditions through dense polydimethylsiloxane (PDMS) was investigated up to pressure of 185 bars to evaluate the regenerability of scCO2 as desiccant to dehydrate fresh products that are prone to product deterioration during conventional drying. This study experimentally examined the impact of concentration polarization on the H2O vapor permeation through dense PDMS membranes in the presence of sub- and supercritical CO2. The results were compared to a system containing N2 instead of CO2.For the CO2 system, the residual mass transfer resistance, which excludes the membrane layer resistance, decreased down to zero with increasing feed pressure, at 90 bar. This is the result of the convergence of the H2O contents of the feed bulk and permeate, which leads to a change of the main H2O transport mechanism within the feed boundary layer from diffusion to convection. Here the H2O and CO2 molecules are transported with comparable speed towards the membrane surface. For the system with N2, the opposite trend was found, due to the maintained significant difference in transport speed between H2O and N2 even at elevated pressures. Consequently, the water vapor transport rate through the PDMS membrane is governed by the type of matrix fluid (CO2 or N2).

A Computational Fluid Dynamics Approach for the Modeling of Gas Separation in Membrane Modules

Natural gas demand has increased rapidly across the globe in the last decade, and it is set to play an important role in meeting future energy requirements. Natural gas is mainly produced from fossil fuel and is a side product of crude oil produced beneath the earth’s crust. Materials hazardous to the environment, like CO2, H2S, and C2H4, are present in raw natural gas. Therefore, purification of the gaseous mixture is required for use in different industrial applications. A comprehensive computational fluid dynamics (CFD) model was proposed to perform the separation of natural gas from other gases using membrane modules. The CFD technique was utilized to estimate gas flow variations in membrane modules for gas separation. CFD was applied to different membrane modules to study gas transport through the membrane and flux, and to separate the binary gas mixtures. The different parameters of membrane modules, like feed and permeate pressure, module length, and membrane thickness, have been investigated successfully. CFD allows changing the specifications of membrane modules to better configure the simulation results. It was concluded that in a membrane module with increasing feed pressure, the pressure gradient also increased, which resulted in higher flux, higher permeation, and maximum purity of the permeate. Due to the high purity of the gaseous product in the permeate, the concentration polarization effect was determined to be negligible. The results obtained from the proposed CFD approach were verified by comparing with the values available in the literature.

Permeability behavior of polyvinyl chloride-ionic liquid ionomer for CO2/CH4 separation

To modification of polyvinylchloride membranes for separation of methane and carbon dioxide gases, 1–vinyl–3-butyilimidazolium halide with three different anions (bromide, [Br]-, thiocyanate, [SCN]-, and tetrafluoroborate, [BF4]-) was grafted onto the polyvinylchloride by free radical graft copolymerization. The prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analyzer (CHN) technique. The permeability of methane and carbon dioxide gases was performed using constant pressure/variable volume method. The effects of variation of anions, feed pressure, and temperature on the membrane performance were investigated. The results indicate that the 1–vinyl–3-butyilimidazolium with [SCN]-anion has better performance to separation of carbon dioxide and methane gases. Also, the enhancement of temperature led to decrease the selectivity of membrane for carbon dioxide/methane gases; whereas, the selectivity of membranes was increased with increasing feed pressure. Also, to confirm the obtained results, the interaction energy between carbon dioxide gas and ionomer membrane with different anions was investigated by density functional theory calculations.

Enhancing plasticization-resistance of mixed-matrix membranes with exceptionally high CO2/CH4 selectivity through incorporating ZSM-25 zeolite

Partially Li+ exchanged Na-ZSM-25 zeolites (LNZ25) were incorporated into the commercial polymer Matrimid® 5218 to yield a mixed-matrix membrane (MMM) via solvent-casting. ZSM-25 has exclusive admission of CO2 and complete exclusion of CH4 and is therefore an ideal candidate for MMMs. The fillers were evenly dispersed in the polymer matrix with good adhesion. The separation performance of the fabricated MMMs with 0–15 wt% filler loadings are determined by both single and binary gas permeability using a constant pressure variable volume apparatus. Single gas permeation tests on the MMM with 5 wt% filler loading show exceptionally high CO2/CH4 selectivity (169 at 5 bar) and a plasticization-resistance-like behaviour, i.e. the selectivity increases as the feed pressure increases. Binary gas measurements indicate the CO2/CH4 selectivity of the MMM is constant with an increase of pressure while the selectivity of the pristine Matrimid decreases with increased pressure. The exclusive admission of CO2 and the rejection of CH4 of the LNZ25 contributes to enhanced permeability and plasticization-resistance-like performance of the MMM.

Phosphorylated nanocellulose fibrils/PVA nanocomposite membranes for biogas upgrading at higher pressure

ABSTRACTHigh moisture uptake and excellent mechanical properties of cellulose nano-fibril (CNF) make it an interesting material to use as an additive in facilitated transport membranes. The objective of this work is to develop novel phosphorylated nanocellulose fibrils (PCNF)/polyvinyl alcohol (PVA) nanocomposite membranes for biogas upgrading. Results showed that the thickness of membrane increases with increasing concentration of PCNF. The addition of PCNF to pristine PVA membranes has beneficial effect for CO2/CH4 separation. However, maximum performance was achieved with 1 wt.% PCNF in 2% PVA at pH 12. Furthermore, increasing feed pressure caused a decrease in both permeability and selectivity.

Synthesis of NaX zeolite-graphite amine fiber composite membrane: Role of graphite amine in membrane formation for H2/CO2 separation

Pore surface modification of zeolite membrane is a challenging area to combat the trade-off between the high flux and high selectivity of the gas separation membrane. Herein we report facile method of pore along with defects modification of NaX zeolite membrane by incorporating graphite amine (Ga) into the membrane structure. Permeation properties of different membranes were evaluated by single gas permeance of H2, CO2 and separation factors for mixed gas H2-CO2 with different mixture ratio. These studies were done at room temperature and 100–300 kPa feed pressure. The results show that Ga is not only active for defect removal of NaX membrane but also enhanced the formation of NaX zeolite from mother sol. In addition, presence of graphite amine into NaX zeolite membrane increase the permeance of H2 from 5.1 × 10−7 mol m−2 s−1 kPa−1 to 36.5 × 10−7 moll m−2 s−1 kPa−1 with increase of feed pressure 100–300 kPa feed pressure due to its hydrophobic properties and separation factor of H2-CO2 enhanced up to 31 for H2-CO2 mixture gas compared to literature reported value 6.5 for FAU membrane over 3-aminopropyltriethoxysilane functionalized alumina. Herein for the first time we report that graphite amine catalyzes for the formation of NaX zeolite in addition to pore modification in zeolite membrane.

Permeation of supercritical CO2 through dense polymeric membranes

Supercritical carbon dioxide (scCO2) is used in the food industry as a water-extracting drying agent. Once saturated with water, the scCO2 needs to be regenerated. A promising way of drying scCO2 is by using H2O permeable membranes. Ideally, these membranes demonstrate low CO2 permeability. Here, we investigated the CO2 permeability of three types of dense membranes, Nafion, Natural Rubber and PDMS, of which the latter in more detail because of its ease of handling. The experimental conditions, temperature and pressure, resulting in minimum CO2 permeability (=losses) were explored. Even though the absolute CO2 permeability depends on the intrinsic membrane material properties, its trend with increasing feed pressure is defined by the (supercritical) behavior of CO2, notably its density as a function of temperature and pressure. The data points to transitions within the supercritical regime, from the gaseous-like supercritical state to the liquid-like supercritical state, graphically visualized by the Widom line for CO2 density. Sorption measurements with PDMS membranes confirm this behavior that follows the diffusion-solution theory. In the gaseous state, the (normalized) permeability follows the (normalized) solubility, indicating a constant CO2 diffusivity. With increasing pressure and when entering the liquid-like (supercritical) regime, the diffusivity drops, resulting in a (normalized) permeability that starts to lag behind the (normalized) solubility.

Assessment of gas separation properties and CO2 plasticization of polysulfone/polyethylene glycol membranes

In the current paper, the effect of various concentrations of polyethylene glycol (PEG) on properties of PEG-blended polysulfone (PSU) gas separation membranes was investigated. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and x-ray diffraction analysis were applied to assess membrane morphology as well as chemical and phase structure, respectively. The obtained results confirmed the dense asymmetric structure in membrane cross sectional morphology. Moreover, the PSU/PEG membranes were found to be consisted of amorphous regions without any crystalline structure. In addition, gas permeability and selectivity of obtained membranes were investigated with respect to pure gases of N2, O2, CH4, and CO2 and membrane CO2 plasticization was studied at varying pressures. According to the results, CO2 accounted for the highest gas permeability at all PEG concentrations while CH4 and N2 represented the lowest gas permeability through the pure PSU and PEG-blended PSU membranes, respectively. CO2 permeability was found to decrease and then increase with increasing feed pressure at various PEG concentrations with the highest variation of permeability at 20 wt % PEG.

Effect of High Pressure Carbon Dioxide Exposure on the Permeation Properties of Asymmetric Polysulfone Membranes for Gas Separation

In this study, the dependence of permeability on the feed pressure for glassy asymmetric polysulfone membranes has been investigated. Pure CO2 and CH4 were used as test gases. In pure gas experiments with CO2, the untreated membrane showed that the carbon dioxide permeation rate increased with increasing feed pressure from one bar onwards. This is because carbon dioxide behaves as a plasticizing agent by expanding the polymer lattice and increased the frequency of molecular motions of the polymer. Moreover, high carbon dioxide concentration in the polymer film disrupts the chain packing, thereby leading to a larger free volume and enhanced rates of segmental motions. Due to swelling of the polymer matrix, the structure of the polymer matrix is loosened and consequently polymer chains become more flexible. For the treated membrane, the permeability of carbon dioxide does not increase with feed pressure but gives a steady state value over the feed pressure ranges investigated. This was in agreement with scanning electron microscopy studies, which revealed that heat treatment densified the membrane skin layer. Thus, a subsequent heat treatment to the membrane is necessary in suppressing the plasticization effect.

Polar/nonpolar gas transfer through PEO-based copolymers membranes

ABSTRACTTwo PEG-based copolymers containing two different chain extenders, as hard segments, were synthesized by 4,4′-methylenediphenyl diisocyanate (MDI). The chain extenders were 1,4-butane diol (BDO) and 1,2-ethane diamine (EDA). The application of the polyurethane (PU) and poly(urethane-urea)s (PUU)s synthesized polymers, which were characterized by Fourier transform infrared spectrometer (FTIR), differential scanning calorimetry (DSC) and atomic Force Microscopy (AFM), in the gas permeability was investigated. The obtained results indicated that by replacing the urea linkage in the polymers, the microphase separation of hard and soft segments increased. The synthesized PEG-based copolymers were semi-crystalline at room temperature. According to the DSC results, the crystallinity of the synthesized polyurethanes decreased as temperature increased. In addition, a reduction in mean surface roughness could be seen based AMF information. The gas (carbon dioxide and methane) separation properties of the polymers revealed that by replacing the urea linkage, the diffusivity, permeability and selectivity of the gases increased slightly.The solubility and diffusivity of gases indicated he solubility domination of gas transport in these membranes. However, the sorption coefficient (S) of a particular gas was surprisingly constant for the two synthesized polymers. The CO2 permeability increased with increasing feed pressure, while CH4 permeability remained almost constant at both temperatures of 25°C and 35°C. The increase in temperature led to an increase in the permeability of the gases and a decrease in the gas selectivity for the both synthesized polyurethanes.

BRACKISH WATER DESALINATION USING REVERSE OSMOSIS SYSTEM

Desalination technologies of brackish water have become a great concern. Reverse osmosis (RO) membranes are the leading technology for desalination because of their strong separation capabilities and a great potential for treatment of waters worldwide. Performance evaluation of RO for brackish water desalination was studied under Four feed pressures (20, 25, 30 and 35 bar), Five levels of water salinity (1200, 5000, 10000, 15000 and 20000 ppm) and number of RO membranes (two and three stages). RO system evaluation was carried out in terms of water quantity and quality according to World Health Organization guidelines. The major results could be summarized as follow: - Increasing feed pressure, increased salt rejection and permeate flux, while the permeate salinity and specific energy was decreased. Increasing feed water salinity, decreased the permeate flux, while the salt rejection was increased up to 5000 and then decreased. Using three RO membranes were sufficient to give the required quality water specification and lower specific energy consumption. For household and agricultural uses: Operate RO desalination system under 20 bar pressure for 1200, 5000 and 10000 ppm water salinity, while use 25 bar for 15000 ppm and 30 bar for 20000 ppm salinity. For industrial uses (Hatching): Operate RO desalination system under 35 bar pressure for 1200 ppm water salinity to obtain the desired limits of water quality for disinfection (5 – 10 ppm).