Water Permselective Membrane Research Articles

Water Permselective Membrane Reactors for Methanol Synthesis from Co2

Water Permselective Membrane Reactors for Methanol Synthesis from Co2

A new concept for control and orientation of the distribution of clean hydrocarbons produced by Fischer–Tropsch synthesis over an industrial iron catalyst

In this work, the performance of the Fischer–Tropsch reaction over iron catalyst in three reactor configurations was theoretically studied and analyzed. Indeed, the control and the guidance of produced hydrocarbons composition were done using a new concept of membrane separation reactor. Our findings show that the composition can be imposed by the nature of the integrated membrane. Depending on the used membrane, the water gas shift reaction equilibrium can be shifted towards hydrogen production or towards carbon monoxide production and consequently, the H2/CO ratio was changed in situ for giving olefins or paraffin according to our requirements specification. Finally, it was found that using a water permselective membrane can boost the composition to C3–C5 olefin compounds, whereas the separation of carbon dioxide can enhance the formation of paraffins.

Green Methanol Production Process from Indirect CO2 Conversion: RWGS Reactor versus RWGS Membrane Reactor

Herein, two different scenarios for indirect CO2 conversion process to produce methanol via reverse water gas shift (RWGS) reaction were investigated and compared. In the first scenario, CO2 is converted to synthesis gas over Fe2O3/Cr2O3/CuO catalyst in a RWGS reactor and then after passing a condenser to eliminate water, as an inhibitor of methanol synthesis catalyst, the product is sent to the methanol production reactor. While in the second, although the process is totally as the same as the previous one, a water permselective membrane was applied in the RWGS reactor. In this scenario, the produced water during the RWGS reaction is separated by the membrane; therefore, the free of water product no longer needed a separator before the methanol synthesis reactor. Both processes were numerically modeled and differential evolution (DE) method was employed to optimize the processes in order to achieve high methanol productivity. Also, the methanol production reactor from these two scenarios were compared with the conventional route (CR), in which methanol is produced from coal and natural gas. The results indicate that, in addition to water removal in the RWGS membrane reactor, a higher CO2 conversion and CO yield and subsequently a more proper synthesis gas composition are obtained. More importantly, methanol production rate increases 13 ton/day (% 4.15 increase) and 109 ton/day (% 50.23 increase) in this scenario compared to the first scenario and CR. Also lower water is produced (17% reduction) in the methanol synthesis reactor of the second scenario respect to the first one.

Green methanol synthesis process from carbon dioxide via reverse water gas shift reaction in a membrane reactor

In the present work, carbon dioxide hydrogenation to methanol via reverse water gas shift reaction (CAMERE) in an industrial scale was modeled and optimized. In this process, syngas is first produced by CO2 hydrogenation through reverse water gas shift (RWGS) reaction over Ni/Al12O19 catalyst and next the syngas is conveyed to a reactor as the feedstock to produce methanol. The inner tubes of methanol synthesis reactor were coated by a water perm-selective membrane for removal of H2O, as the cause of catalyst poisoning. A precise two-dimensional model solved by finite-difference procedure was employed to evaluate both RWGS and methanol synthesis membrane reactors performance. Also, the operating conditions of the RWGS reactor were optimized by differential evolution (DE) technique to gain a maximum methanol production rate. Moreover, the results of the methanol production reactor from the CAMERE process were compared with the conventional route (CR) in which methanol is produced from coal and natural gas. In the case of methanol synthesis membrane reactor, CAMERE process was superior to CR due to achieving 20.8% increase in methanol production rate. The results of this process modeling provide a good initial insight for green methanol production form indirect CO2 conversion.

Enhanced dehydration performance of hybrid membranes by incorporating fillers with hydrophilic-hydrophobic regions

In this study, sulfonated pitch (SP), composed of hydrophilic sulfonate groups and hydrophobic polycyclic aromatic hydrocarbons, was incorporated into sodium alginate (SA) membranes for ethanol dehydration via pervaporation. The morphologies and structures of the SP and hybrid membranes were confirmed by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), positron annihilation lifetime spectroscopy (PALS) and water contact angle measurement. Hydrophilic sulfonate groups in SP formed hydrophilic regions which can bind water molecules, ensuring sufficient water occupancy in the membranes, while the hydrophobic polycyclic aromatic hydrocarbons provided continuous transport “highways” for the water molecules. Meanwhile, the introduction of SP created more polymer-filler interface cavities, rendering the membrane with suitable free volume property for separation. Consequently, the membrane demonstrated a maximum permeation flux of 1879 ± 80 g/m2 h coupled with an optimal separation factor of 1913 ± 69 in separating 90 wt% ethanol aqueous solution. These resulted in an increase over the SA control membrane of 1.5-fold and 4-fold respectively. Moreover, the hybrid membranes exhibited good operation stability. The results suggested that incorporating fillers with hydrophilic-hydrophobic regions in the membranes can be an effective strategy to improve the performance of water-permselective membranes.

Development of an Efficient Methanol Production Process for Direct CO2 Hydrogenation over a Cu/ZnO/Al2O3 Catalyst

Carbon capture and utilization as a raw material for methanol production are options for addressing energy problems and global warming. However, the commercial methanol synthesis catalyst offers a poor efficiency in CO2 feedstock because of a low conversion of CO2 and its deactivation resulting from high water production during the process. To overcome these barriers, an efficient process consisting of three stage heat exchanger reactors was proposed for CO2 hydrogenation. The catalyst volume in the conventional methanol reactor (CR) is divided into three sections to load reactors. The product stream of each reactor is conveyed to a flash drum to remove methanol and water from the unreacted gases (H2, CO and CO2). Then, the gaseous stream enters the top of the next reactor as the inlet feed. This novel configuration increases CO2 conversion almost twice compared to one stage reactor. Also to reduce water production, a water permselective membrane was assisted in each reactor to remove water from the reaction side. The proposed process was compared with one stage reactor and CR from coal and natural gas. Methanol is produced 288, 305, 586 and 569 ton/day in CR, one-stage, three-stage and three-stage membrane reactors (MR), respectively. Although methanol production rate in three-stage MR is a bit lower than three stage reactors, the produced water, as the cause of catalyst poisoning, is notably reduced in this configuration. Results show that the proposed process is a strongly feasible way to produce methanol that can competitive with a traditional synthesis process.

Manipulation of confined structure in alcohol-permselective pervaporation membranes

Alcohol-permselectivity pervaporation has been arousing increasingly more attention in bioalcohol production due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. With the intrinsic feature of larger molecules preferentially permeating and the consequent inferiority in selective diffusion, the development of alcohol-permselective membrane is relatively retarded compared with water-permselective membrane. This review presents the prevalent membrane materials utilized for alcohol-permselective pervaporation and emphatically expatiates the representative and important developments in the past five years from the aspect of tuning confined structure in membranes. In particular, the diverse structure tuning methods are described with the classifications of physical structure and chemical structure. The corresponding structure-performance relationships in alcohol-permselective pervaporation membranes are also analyzed to identify the objective of structure optimization. Furthermore, the tentative perspective on the possible future directions of alcohol-permselective pervaporation membrane is briefly presented.

Preparation of Water-Selective Polybutadiene Membranes and Their Use in Drying Alcohols by Pervaporation and Vapor Permeation Technologies

Separating azeotrope-forming solvent–water mixtures by conventional distillation poses technical, economic, and environmental challenges. Pervaporation and vapor permeation membrane technologies using water-permselective membranes provide an efficient alternative for water removal from solvents. We present here new water-selective materials, based on 1,2-polybutadiene, that address two problems reported for traditional hydrophilic membrane materials under high water activities: swelling and hydrolysis. Exposure to UV radiation and/or heat converted portions of the vinyl groups in the polybutadiene to cross-links and hydrophilic functional groups, including alcohols, ketones, and carboxylic acids. In testing with a series of alcohols, such materials displayed high water permeabilities and stable performance over several months even at the extremes of 100% water, low water (2%), and an ethanol/water vapor at 115 °C and 2.5 bar.

Investigation of thermally double coupled double membrane heat exchanger reactor to produce dimethyl ether and methyl formate

Owing to concerns associated with energy consumption and energy intensive methods in the chemical industries, the present study aims to investigate production of some downstream products of natural gas in a recuperative configuration. Accordingly, simultaneous production of dimethyl ether from methanol and syngas and also methyl formate from methanol is investigated in a catalytic heat-exchanger reactor assisted with water perm-selective membranes. Dimethyl ether synthesis from methanol and syngas are exothermic reactions supplying required energy for the methanol dehydrogenation reaction. Produced waters in both exothermic sides are eliminated from reaction media by permeation through the perm-selective membranes equipped on the inner and outer surfaces of the reactor. A feasibility study is implemented through a mathematical model based on mass and energy balance. Genetic algorithm as a powerful method in nonlinear optimization problems is applied to obtain optimum operating conditions. 97% methanol conversion to dimethyl ether, 66% methanol conversion to methyl formate and 17% hydrogen conversion are the advancements of the proposed thermally double-coupled double-membrane reactor working under optimum conditions.

Comparative Study of the Performance of Fischer–Tropsch Synthesis in Conventional Packed Bed and in Membrane Reactor Over Iron- and Cobalt-Based Catalysts

A comparative study of Fischer–Tropsch synthesis for synthesizing liquid hydrocarbons from syngas was carried out in a conventional packed bed reactor and in a water perm-selective membrane reactor over iron and cobalt catalysts. The process was performed under different operating conditions, such as inlet syngas feed molar ratio, total pressure, gas velocity, temperature, reactor dimensions and sweep fluid ratio. The main simulation results show that the use of the concept of membrane reactor can improve the process performance compared to that obtained in the case of the conventional packed bed reactor. Furthermore, under certain operating conditions, the process could be intensified by a reduction of carbon monoxide conversion magnitude via the water–gas shift reaction. This is possible by using a hydrophilic membrane. Our findings indicate that the membrane reactor provides a quasi-complete conversion of carbon monoxide over iron- or cobalt-based catalysts.

Batch reactor coupled with water permselective membrane: Study of glycerol etherification reaction with butanol

Etherification of glycerol with (bio)butanol was investigated in order to obtain glycerol ethers usable as oxygenated additives for diesel fuel. Experiments were carried out using a batch reactor assisted by a tubular water-permselective membrane. A-15 resin was used as solid acid catalyst at a reaction temperature ranging from 70 to 160°C in view of maximizing the glycerol conversion. The water formed during the reaction was continuously removed by recirculation the gas phase through the membrane and this allowed to enhance reactions kinetics reaching both a total glycerol conversion and the formation of poly-substituted ethers not obtainable without the membrane. The alcohol dehydration and self-etherification of glycerol or alkyl alcohols give rise to the formation of several side products at moment hardly to identify.

Catalytic production of oxygenated additives by glycerol etherification

Abstract In this work the etherification reaction of glycerol with isobutene (IB) and tert-butyl alcohol (TBA) has been studied with the aim of preparing mixtures with high content of poly-substituted ethers. The results obtained using solid acid catalysts have shown that the reaction with IB proceeds at a high rate but the formation of undesired di-isobutene (DIB) represents a serious problem when catalysts with high density of acid sites, such as Amberlyst, are used. When using TBA as a reactant, the main problem is the formation of water that, due to thermodynamic reasons, prevents the formation of poly-substituted ethers regardless of the catalyst used. Some preliminary experiments carried out with a water permselective tubular membrane have demonstrated that the yield of poly-substituted ethers significantly increases once water was selectively removed from the reaction medium by recirculation of the gas phase.

The optimal operating conditions of a thermally double coupled, dual membrane reactor for simultaneous methanol synthesis, methanol dehydration and methyl cyclohexane dehydrogenation

In this study, the concept of thermally double coupled reactor is proposed as an alternative configuration to mix the energy efficient concept of coupling two exothermic with one endothermic reaction. In this multi-tubular fixed bed reactor, methanol synthesis and methanol dehydration, as two exothermic reactions occur in the inner and outer tubes while the methyl cyclohexane dehydrogenation, as an endothermic reaction takes place in the middle tube. Two water permselective membranes are also applied in the inner and outer tubes to remove water from both exothermic sides. Extraction of water as one of the main byproducts in the DME (dimethyl ether) and methanol synthesis processes increases the production rate and the catalyst life time. In this configuration, the operating conditions are optimized using a differential evolution method in order to maximize the outlet methanol and DME mole fractions of the inner and outer exothermic sides respectively. Then the optimized results of the thermally double couple dual membrane reactor are compared with the optimized thermally double couple reactor and the ones in conventional methanol and DME synthesis reactors. This comparison shows the superiority of this configuration to the conventional ones owing to the enhancement of methanol and DME mole fractions (10.9% and 19.5% increase compared with conventional ones respectively). Hydrogen and toluene, as two valuable products, are also produced in a favorable mode.

Glycerol etherification with TBA: high yield to poly-ethers using a membrane assisted batch reactor.

In this work, a novel approach to obtain high yield to poly-tert-butylglycerolethers by glycerol etherification reaction with tert-butyl alcohol (TBA) is proposed. The limit of this reaction is the production of poly-ethers, which inhibits the formation of poly-ethers potentially usable in the blend with conventional diesel for transportation. The results herein reported demonstrate that the use of a water permselective membrane offers the possibility to shift the equilibrium toward the formation of poly-ethers since the water formed during reaction is continuously and selectively removed from the reaction medium by the recirculation of the gas phase. Using a proper catalyst and optimizing the reaction conditions, in a single experiment, a total glycerol conversion can be reached with a yield to poly-ethers close to 70%, which represents data never before reached using TBA as reactant. The approach here proposed could open up new opportunities for all catalytic reactions affected by water formation.

A novel axial-flow spherical packed-bed membrane reactor for dimethyl ether synthesis: Simulation and optimization

In order to improve the performance of conventional tubular reactors, the concept of spherical membrane reactors has been proposed as an alternative to eliminate the problem of pressure drop and to increase the production rate. Regarding this, a novel axial-flow spherical packed-bed membrane reactor (AF-SPMR) has been developed for dehydration of methanol. This configuration consists of two concentric spheres in which dimethyl ether (DME) synthesis occurs in the inner sphere coated by a water perm-selective membrane. The operating conditions as well as length per radius for the AF-SPMR were optimized using differential evolution (DE) method to maximize the mole fraction of DME in the outlet point of the reactor. A comparison was made between the optimized AF-SPMR (OAF-SPMR), AF-SPMR, axial-flow spherical packed-bed reactor (AF-SPR) and the conventional reactor (CR). The optimization results indicate the superiority of OAF-SPMR to all previous configurations due to achieving 13.5% increase in the mole fraction of DME. In addition to much lower pressure drop in AF-SPR (nearly 98% reduction); considerably higher production of DME in AF-SPMR represents the main advantages of this configuration in comparison with CR.

Integrated aqueous-phase glycerol reforming to dimethyl ether synthesis—A novel allothermal dual bed membrane reactor concept

Dimethyl ether (DME) production from glycerol via an integrated process involving aqueous-phase glycerol reforming to biosyngas combined with DME synthesis into an allothermal dual-bed membrane reactor was analyzed numerically. The system combines two separate enclosures, a fixed-bed water perm-selective membrane DME synthesis unit and a gas–liquid–solid fixed-bed aqueous-phase glycerol reforming unit. Exothermic DME synthesis provides heat to endothermic aqueous-phase glycerol reforming which in return produces biosyngas for DME synthesis. The two-scale, non-isothermal, unsteady-state model developed for the integrated system accounts for a detailed gas/gas–liquid dynamics whereupon DME synthesis/aqueous-phase glycerol reforming kinetics, thermodynamics, thermal effects and variable gas flow rate due to chemical/physical contractions were accounted for. The integrated process is intended to minimize abundant glycerol by-product streams via an energy efficient alternative for producing DME. It presents an opportunity to improve the economics of green DME synthesis by cost reduction of biosyngas production while improving thermal efficiency of DME synthesis.

A comparative study between a fluidized-bed and a fixed-bed water perm-selective membrane reactor with in situ H 2O removal for Fischer–Tropsch synthesis of GTL technology

In order to eliminate the pressure drop problem and mal distribution of the temperature profile along the reactors, fluidized-bed membrane reactors are proposed as an alternative for Fischer–Tropsch synthesis (FTS) in gas-to-liquid (GTL) technology. Regarding this, a novel cascading fluidized-bed membrane reactor (CFMR) is proposed in this study and compared with a fixed-bed membrane cascading with fluidized-bed membrane reactor (FMFMR). The CFMR configuration consists of a fluidized-bed water perm-selective membrane reactor followed by a fluidized-bed hydrogen perm-selective membrane reactor. The performance of CFMR is compared with FMFMR in order to investigate the effect of fluidization concept on the reactor performance. Unlike CFMR where a fluidized-bed concept is applied in the first reactor, a fixed-bed concept is used in the first reactor of FMFMR. The modeling results show 5.3% increase in the gasoline yield and 12% decrease in CO 2 yield in CFMR in comparison with FMFMR owing to applying a fluidized-bed concept instead of a fixed-bed concept in which more effective temperature management is achieved. According to the modeling results, CFMR is superior to FMFMR for FTS in GTL technology owing to achieving excellent temperature control and a small pressure drop and consequently higher gasoline yield and lower CO 2 yield.

A novel water perm-selective membrane dual-type reactor concept for Fischer–Tropsch synthesis of GTL (gas to liquid) technology

Abstract The present study proposes a novel configuration of Fischer–Tropsch synthesis (FTS) reactors in which a fixed-bed water perm-selective membrane reactor is followed by a fluidized-bed hydrogen perm-selective membrane reactor. This novel concept which has been named fixed-bed membrane reactor followed by fluidized-bed membrane reactor (FMFMDR) produces gasoline from synthesis gas. The walls of the tubes of a fixed-bed reactor (water-cooled reactor) of FMFMDR configuration are coated by a high water perm-selective membrane layer. In this new configuration, two membrane reactors instead of one membrane reactor are developed for FTS reactions. In other words, two different membrane layers are used. In order to investigate the performance of FMFMDR, a one-dimensional heterogeneous model is taken into consideration. The simulation results of three schemes named fluidized-bed membrane dual-type reactor (FMDR), FMFMDR and conventional fixed-bed reactor (CR) are presented. They have been compared in terms of temperature, gasoline and CO 2 yields, H 2 and CO conversions and the water permeation rate through the membrane layer. Results show that the gasoline yield in FMFMDR is higher than the one in FMDR. The FMFMDR configuration not only decreases the undesired product such as CO 2 but also produces more gasoline.

Structure optimization of water-permselective membrane surfaces by reconstruction

The pervaporation performance with operating time through poly(vinyl alcohol) (PVA) membrane for the separation of various alcohol/water (methanol–water, ethanol–water, isopropanol–water) mixtures was investigated. The water selectivity through the air-side surface of a PVA membrane increased and finally reached an equilibrium value, which was lower than that through the glass-side surface, implying the structure on the glass-side surface of PVA membrane is favorable towards the enhancement of the water permselectivity compared to that on the air-side surface. This phenomenon was attributed to the reconstruction occurred at the air-side surface of the membrane, hence a more hydrophilic membrane surface was formed when it was in contact with the feed mixtures. In order to optimize the water permselective structure on the air-side surface of PVA membrane, the membrane was pre-treated in 80% methanol/water mixtures. For dehydration ethanol and isopropanol, the separation factor through the air-side surface of the pre-treated PVA membrane was improved greatly, approaching that through the glass-side surface. Our results indicate that a desirable structure at the air-side surface can be optimized by surface reconstruction in various environments, which is very useful for the industrial applications of pervaporation membranes because their air-side surfaces are usually in contact with the feed.

Isopropanol dehydration by pervaporation

Pervaporation, a membrane process for separation liquid mixtures, is becoming recognized as an energy efficient alternative of distillation and other separation methods. The performance of a pervaporation membrane can be characterized in terms of permeation flux and separation factor, which are determined by feed temperature and feed composition. The influence of these parameters on isopropanol dehydration by pervaporation will be discussed in this study, by using different water permselective membranes (CMC-CE-01, CMC-CA-01, CMC-CE-02). The experiments were carried out in a laboratory pervaporation unit with various operating temperature (45∼65°C) and feed isopropanol concentration (70∼99.48). The permeate flux, isopropanol and water content in the permeate and in the concentrate fractions were measured during the experimental runs. Comparing the separation behavior of the membranes it was found that all the three types of membrane are suitable for isopropanol dehydration by pervaporation and anhydrous isopropanol can be achieved. The permeation characteristics are obviously dependent on the feed concentration and temperature. The permeation rate significantly increases and the selectivity is strongly decreases with increasing temperature.