Sodalite Membrane Research Articles

Modeling of reverse water–gas shift reaction in a membrane integrated microreactor

CO2 hydrogenation to syngas via reverse water–gas shift (RWGS) is modeled in a membrane decorated microchannel reactor. Coated CuO/ZnO/Al2O3 catalyst exists in the reaction channel which is physically separated from the neighboring permeate channel by a layer of supported sodalite (SOD) membrane selective to H2O and H2 transport. Pure H2 is used as the sweep gas. Two–dimensional, steady state, isothermal operation of the reactor is quantified by the momentum and mass conservations in the entire flow domain, membrane material transfer and catalytic reaction. Upon its benchmarking with the literature–based experimental data, the reactor model is used to study the effects of inlet velocities and partitioning of the reactive mixture and sweep streams, reactor pressure, and molar inlet H2:CO2 ratio. At 523 K, 15 bar and H2:CO2 = 3, the per cent CO2 conversion exceeds the thermodynamic limit of 16.8% and can be maximized to 52% when the inlet velocity of the H2 + CO2 mixture is minimized. Decreased dosing of the reactive mixture, however, limits the molar amount of CO2 converted and reduces reactor capacity. Both metrics are positively correlated with reactor pressure and the inlet velocity of the sweep gas but remain insensitive to flow direction. Syngas composition (molar exit (H2 – CO2)/(CO + CO2) ratio) can be varied between 1.7 and 9.8. The proposed reactor can deliver ∼2.5 times higher volume and catalyst mass–based productivity and ∼33% higher CO2 conversion than an equivalently operated packed–bed membrane reactor.

Investigation of NH3 Desorption Kinetics on the LTA and SOD Zeolite Membranes.

The acidity characteristics of zeolite are highly significant, and understanding the acidic properties is essential for developing new types of zeolite catalysts. Zeolite membranes were synthesized using metakaolin, sodium hydroxide, and alumina with a molar ratio of 6Al2Si2O7:12NaOH:2Al2O3 as the starting ingredients. X-ray diffraction, scanning electron microscopy, and infrared spectroscopy were used for this study. N2 adsorption measurements determined the surface areas of the SOD zeolite membrane (115 m2/g) and the LTA membrane (150 m2/g). The units of absorbed water vapor were 40 and 60 wt% for the SOD membrane and the LTA membrane, respectively. The strength and number of acid sites of the synthesized LTA and SOD zeolite membranes were determined by temperature-programmed desorption of ammonia. As a result, the value of the total acidity of the LTA zeolite membrane is in the range of 0.08 × 1019 units/m2 while that of the sodalite membrane is an order of magnitude lower and is 0.006 × 1019 units/m2. The apparent activation energy values for desorption of ammonia from LTA and SOD zeolite membranes were calculated using data on the kinetics of desorption of ammonia at different heating rates. It was found that at temperatures below 250 °C, the degree of conversion of the activation energy values is no more than 35 kJ/mol, which corresponds to the desorption of physically bound ammonia. An increase in the activation values up to 70 kJ/mol (for SOD) and up to 80 kJ/mol (for LTA) is associated with the desorption of chemically bound ammonia from the samples.

Modeling and simulation of a steam-selective membrane reactor for power-to-methanol

The hydrogenation of CO2 to methanol is currently receiving increased attention following the deployment of Power-to-X processes. In this exothermic reversible reaction, the CO2 conversion is strongly limited by the thermodynamic equilibrium and the offer of commercial catalysts is mostly limited to Cu-based materials. Therefore, available options for improving methanol production consider either process design and optimization and/or using multifunctional reactors that provide advantageous features compared to conventional reactors, despite additional complexity. In this work we have modeled and simulated a membrane reactor (MR) featuring steam removal for shifting the reaction equilibrium to the products side and thus not only improving the CO2 conversion but also contributing to the increase of catalyst life span and representing a reliable alternative for heat removal. For this purpose, the proposed model for the MR considered the properties of a hydrophilic sodalite (SOD) membrane and the kinetics of a Cu/ZnO/Al2O3 catalyst. A split feed strategy has been devised to tackle poor membrane selectivity in the temperature range of interest. At 270 °C and 50 atm, the split feed allowed increasing the methanol yield up to 18%, while an ideal membrane (i.e., infinitely selective to steam) up to 31% (both in relative terms), when compared to a traditional reactor. Moreover, using the MR with the SOD membrane in the referred conditions it was obtained a permeate outlet stream containing only reactants and steam, therefore easily recyclable.

Sustainable DME synthesis from CO2–rich syngas in a membrane assisted reactor–microchannel heat exchanger system

One–step syngas–to–dimethyl ether (DME) conversion is modeled in a cascade of packed–bed reactors (PBRs) and microchannel heat exchangers (micro–HEXs). Each reactor, loaded with mixtures of Cu–ZnO/Al2O3 and HZSM–5 for adiabatic syngas hydrogenation and methanol dehydration, respectively, is connected to a micro–HEX for cooling PBR effluent. HEXs involve layers of sodalite membrane allowing selective H2O and H2 exchange between reactive stream and cooling channels. Membraneless and membrane–integrated systems are simulated at inlet syngas conditions of 50 bar, 523 K, and ∼0.8 mol/s, resembling syngas throughput of a pilot–scale gasifier. Although PBR effluents become H2O–lean in syngas–cooled membrane–integrated HEXs, CO2 conversion and DME yield remain almost identical with those of the membraneless (benchmark) case (∼6 and 10 %, respectively), suggesting that reactions are not constrained by steam. Cooling by pure H2 allows its penetration into reactive stream. H2–enriched PBR feeds are transformed under kinetic and thermodynamic promotions giving CO2 conversion and DME yield up to ∼72 and ∼57 %, respectively. Improved metrics occur at elongated contact of the fluids with membrane, necessitating voluminous HEX units. Nevertheless, membrane aided molar DME production and CO2 consumption per volume remain up to 1.6 and 2.3 times higher than the benchmark values. Membrane assistance also improves benchmark catalyst weight–based DME productivity and CO2 utilization by factors up to 7 and 13, respectively. Proposed cascade system allows scalable and sustainable DME production via increased CO2 valorization.

Split feed strategy for low-permselective membrane reactors: A simulation study for enhancing CO2 methanation

A non-isothermal membrane reactor (MR) was simulated to study the production of methane through CO2 hydrogenation. The reaction kinetics of a commercial catalyst and the extrapolated properties of a steam-selective sodalite (SOD) membrane were considered. A traditional fixed-bed reactor (TR) was also simulated and its performance compared with that obtained with a MR in the temperature and pressure range of 250−410 °C and 1−7 atm, respectively. The results indicate that at higher temperatures the SOD membrane removes not only water but also a significant amount of reactants from the reaction medium. It was demonstrated that this can be solved splitting the feed between both chambers (retentate and permeate), reducing the reactants loss due to a lower driving force. However, the methane permeation through the SOD membrane limits the process performance. The simulation of an ideal MR (i.e. membrane with infinite selectivity to water), with the perspective of assessing its potential, allowed reaching a conversion of 89.5 % (at 390 °C and 1 atm), being able not only to improve the catalytic bed conversion of a TR in the same conditions (82.7 %), but also to surpass the chemical equilibrium conversion (85.4 %), showing that the full potential of the MR technology for this application still depends on the development of adequate membranes.

Modeling of a membrane integrated catalytic microreactor for efficient DME production from syngas with CO2

Conversion of syngas (CO + CO2 + H2) to dimethyl ether (DME) with in–situ steam separation is modeled in a membrane integrated, isothermal catalytic microchannel reactor. Reaction channel, involving washcoated form of physically mixed Cu–ZnO/Al2O3 and HZSM–5 catalysts, is separated from the permeate channel by a supported sodalite (SOD) membrane layer. Conservation of momentum and mass within the porous washcoat and the channels, and cross–membrane material transport are modeled in two dimensions at steady–state to elucidate the effects of temperature, pressure, syngas composition and permeate flow properties. Dosing syngas to both channels at 523 K, 50 bar, CO2/COx (COx: CO + CO2) = 0.5 and H2/COx = 2.0 gives CO and CO2 conversions, and DME yield of 33.2, 12.4 and 15.3 %, respectively, which are 29.9, 7.2 and 12.7 % without membrane. These findings are coherent with relaxed thermodynamic limitations on methanol synthesis and dehydration upon selective H2O removal. Higher permeate syngas flow rates promote steam efflux and H2 influx across the membrane and further elevate CO2 conversion and DME yield up to 15.8 and 17.4 %, respectively. These metrics can be improved up to 23.4 and 22.9 %, respectively upon dosing pure H2 as the permeate fluid. However, a positive pressure gradient from reaction to permeate channel does not improve reactor performance. Coherent with its higher dehydration activity, HZSM–5 responds to membrane assistance stronger than γ–Al2O3.

CFD Modeling of Methanol to Light Olefins in a Sodalite Membrane Reactor using SAPO-34 Catalyst with In Situ Steam Removal.

In this work, the performance of a sodalite membrane reactor (MR) in the conversion of methanol to olefins (MTO process) was evaluated for ethylene and propylene production with in situ steam removal using 3-dimensional CFD (computational fluid dynamic) technique. Numerical simulation was performed using the commercial CFD package COMSOL Multiphysics 5.3. The finite element method was used to solve the governing equations in the 3- dimensional CFD model for the present work. In the sodalite MR model, a commercial SAPO-34 catalyst in the reaction zone was considered. The influence of key operation parameters, including pressure and temperature on methanol conversion, water recovery, and yields of ethylene, propylene, and water was studied to evaluate the performance of sodalite MR. The local information of component concentration for methanol, ethylene, propylene, and water was obtained by the proposed CFD model. Literature data were applied to validate model results, and a good agreement was attained between the experimental data and predicted results using CFD model. Permeation flux through the sodalite membrane was increased by an increase of reaction temperature, which led to the enhancement of water stream recovered in the permeate side. The CFD modeling results showed that the sodalite MR in the MTO process had higher performance in methanol conversion compared to the fixed-bed reactor (methanol conversion of 97% and 89% at 733 K for sodalite MR and fixed-bed reactor, respectively).

Modeling and Simulation of a Steam-Selective Membrane Reactor for Enhanced CO2 Methanation

A modelling and simulation study of a hydroxy sodalite (H-SOD) membrane reactor for in-situ water removal during CO2 methanation reaction is presented. A non-isothermal, steady-state, pseudo-homoge...

Separation of Helium from Gases Using the Synthesized Hydroxy Sodalite Membrane

The goals of this work are to synthesize and evaluate the potential of hydroxy sodalite membrane in the separation of helium from natural gas. Sodalite membrane was synthesized via direct hydrothermal method (conventional heating) on tubular alumina support. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation using helium and N2. After drying of the membrane, permeances of single gases were found to be of the order Helium > CH4 > N2 > CO2 at low temperatures and the membrane was impermeable to N2, CO2 and CH4 at high temperatures (>85 °C). In the investigated range of temperature 35-180 °C, membrane performance tended to high selectivity. The maximum separation factors (helium/N2 ~ 8.8, helium/CO2 ~ 16.5 and helium/CH4 ~ 5) with acceptable permeance were observed at 85 °C.

Modeling of Ethylbenzene Dehydrogenation Membrane Reactor to Investigate the Potential Application of a Microporous Hydroxy Sodalite Membrane

In this study the catalytic dehydrogenation of ethylbenzene to styrene was investigated in a simulated tubular sodalite membrane reactor. The high quality microporous sodalite membrane was synthesized by direct hydrothermal method and characterized by single gas permeation measurements. The performance of the prepared membrane showed high potential for application in a dehydrogenation membrane reactor (MR). The performance of the MR was evaluated using a pseudo-homogeneous model of the fixed bed that was developed in this purpose. The obtained results were evaluated in comparison with corresponding predictions for a plug flow reactor (PFR) operated at the same conditions. The modeling results confirmed the high performance of a MR over a conventional PFR. Ethylbenzene conversion and styrene yield increased about 3.45% and 8.99% respectively which is attributed to the effect of hydrogen removal from reaction side. The results demonstrate that the styrene yield in the MR is predicted to be more effective than that of in the conventional PFR.

Simultaneous dimethyl ether synthesis and decalin dehydrogenation in an optimized thermally coupled dual membrane reactor

The efficient coupling of exothermic and endothermic reactions in a membrane reactor reduces the size of reactors and operational costs, improves thermal efficiency and also increases the production rate in the processes. In the present study, a thermally coupled dual-membrane reactor for simultaneous production of hydrogen, dimethyl ether (DME) and naphthalene is proposed. In this configuration, the exothermic DME synthesis reaction is coupled with the endothermic dehydrogenation of decalin to improve the heat transfer between the endothermic and exothermic sides. Furthermore, in order to increase the production rate, a Pd/Ag membrane and a hydroxy sodalite (H-SOD) membrane are assisted for separation of pure hydrogen from the endothermic side and permeation of water from the exothermic side respectively. The operating conditions of thermally coupled dual-membrane reactor are optimized via differential evolution (DE) method to maximize outlet DME mole fraction in the exothermic side as well as outlet hydrogen mole fraction in the endothermic side. Then a comparison is made between the optimized thermally coupled dual-membrane reactor (OTCDMR), the optimized thermally coupled reactor (OTCR) and conventional DME synthesis reactor (CR). The outlet DME mole fraction increases about 34.2% and 3.42% in OTCDMR and optimized thermally coupled reactor respectively, compared with conventional one. Hydrogen mole fraction in the outlet point of OTCDMR also improves about 6.4% in comparison with the one in optimized thermally coupled reactor. In addition to the enhancement of hydrogen and DME mole fractions, a more favorable profile of temperature is achieved in OTCDMR compared with other reactors.

Correction: Daramola, M.O.; Aransiola, E.F.; Ojumu, T.V. Potential Applications of Zeolite Membranes in Reaction Coupling Separation Processes. Materials 2012, 5, 2101-2136.

Due to an oversight by the authors, Table 4 in the aforementioned review article [1] should have been referred to as obtained from reference [2]: Khajavi, S. Separation of Process Water Using Hydroxy Sodalite Membranes. PhD Thesis, Delft University of Technology, Delft, The Netherlands, 2010. Furthermore, an additional affiliation for the first author of this review is added as follows: Catalysis Engineering Section, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands The authors apologize for any inconvenience this may have caused. [...]

Differential Evolution Strategy for Optimization of Hydrogen Production via Coupling of Methylcyclohexane Dehydrogenation Reaction and Methanol Synthesis Process in a Thermally Coupled Double Membrane Reactor

The present paper focuses on optimization of a thermally coupled double membrane methanol reactor (TCDMR). This novel configuration is used in order to increase methanol production and achieve pure hydrogen. To reach this goal, the exothermic methanol synthesis reaction is coupled with endothermic dehydrogenation of methylcyclohexane to improve the heat transfer between the endothermic and exothermic sides. Methylcyclohexane (MCH) has been proposed as a potential candidate among the cycloalkanes to produce gaseous hydrogen and a liquid aromatic product toluene (TOL). Two different membrane layers are assisted in TCDMR to improve mass transfer between the exothermic/endothermic side and both permeation sides. A Pd/Ag membrane is used for separation of pure hydrogen from the endothermic side and a hydroxy sodalite (H-SOD) membrane is used for permeation of water from the exothermic side. It has been shown that in situ water removal from the exothermic side has certain advantages. H2O removal improves the activity and selectivity control of the methanol synthesis as well as inhibits the catalyst recrystallization. A steady state heterogeneous model predicts the performance of this innovative configuration. The optimization results have been compared with corresponding predictions for a conventional methanol reactor, thermally coupled methanol reactor, and thermally coupled double membrane reactor. The differential evolution (DE) is a simple and efficient global optimization algorithm applied to optimize the thermally coupled double membrane reactor considering the summation of methanol, toluene, and H2 recovery yields as the objective function. The simulation results demonstrate that lower water production rate in the optimized TCDMR (OTCDMR) caused 13.8% enhancement in methanol yield in comparison with a conventional reactor and the hydrogen recovery permeation side reaches 2.15 yields.

Production of hydrogen and methanol enhancement via a novel optimized thermally coupled two-membrane reactor

This study focuses on optimum operating conditions for thermally coupled two-membrane reactor (TCTMR) to maximize ultrapure hydrogen and methanol production as alternative environmentally friendly fuels. Hydrogen is used in chemical and petrochemical industries especially applicable in fuel cell technologies, with zero CO2 emission. In the proposed configuration, methanol synthesis is carried out in the exothermic side by hydroxy sodalite membrane and supplies the necessary heat for the endothermic side. Dehydrogenation of cyclohexane is carried out in the endothermic side with hydrogen-permselective Pd/Ag membrane wall. A one-dimensional, steady-state heterogeneous model and the differential evolution method, as a strong and powerful optimization method, are applied to simulate and optimize the proposed reactor configuration. The simulation results have been shown that there are optimal values of the initial molar flow rate of endothermic, outer and the inner permeation stream, inlet temperature of exothermic, endothermic, outer and inner permeation sides and inlet pressure of inner permeation side to maximize the objective function. The optimization results show 5.87 and 10.51% increase in the methanol production in optimized TCTMR compared with TCTMR and a conventional reactor, respectively. Moreover, this novel configuration with optimal conditions raises the hydrogen production rate about 1.1847 ton/day. Copyright © 2012 John Wiley & Sons, Ltd.

Simultaneous hydrogen production and utilization via coupling of Fischer–Tropsch synthesis and decalin dehydrogenation reactions in GTL technology

A thermally coupled membrane dual-type reactor (TCMDR) has been proposed for simultaneous hydrogen production and utilization in gas-to-liquid technology (GTL). Decalin dehydrogenation reaction is coupled with Fischer–Tropsch synthesis (FTS) reaction to improve the heat transfer between endothermic and exothermic sides. Furthermore, Pd–Ag and Hydroxy Sodalite membrane layers are assisted in TCMDR to improve the mass transfer between exothermic/endothermic side and permeation side. Some of the produced hydrogen via decalin dehydrogenation reaction is utilized in FTS reaction and the other is extracted and stored. The modeling results show 95% hydrogen production and 5% hydrogen utilization in FTS reactions in the exothermic reaction side of TCMDR configuration. The performance of TCMDR is compared with the one of conventional reactor (CR) and fluidized-bed membrane dual-type reactor (FMDR). Moreover, the gasoline yield in TCMDR increases about 17% and 29% in comparison with the one in FMDR and CR, respectively. The enhancement in gasoline and hydrogen yields demonstrates the superiority of TCMDR to the previous reactors.

Production of ultra pure water by desalination of seawater using a hydroxy sodalite membrane

Abstract A hydroxy sodalite membrane has been synthesized and employed in pervaporative desalination of seawater at 2.2 MPa feed pressure over a temperature range of 303–473 K. The membrane's performance was also tested with aqueous solutions of NaCl and NaNO 3 at 473 K and 2.2 MPa cross membrane pressure, evaluating the effect of salt concentration on permeation flux and solute rejection. In total the membrane was used for over 100 h. In all cases the membrane showed salt rejection better than 99.99%; the collected permeate was ultra pure water with a resistance of 18.2 MΩ (0.1 μS/cm) at 25 °C. Flux through the membrane in seawater desalination showed a steep increase with feed temperature, exceeding the flux values obtained for pure water. Increasing the salt concentration in NaCl and NaNO 3 aqueous solutions gave opposite trends in flux through the membrane. In case of NaCl, the flux increased with increasing salt concentration in the feed, whereas the opposite was found for NaNO 3 solutions. The latter is attributed to a decreased water activity, i.e. driving force for water permeation, and a blocking effect. It is speculated that in case of NaCl ion exchange between the zeolite and solution brings about compositional changes in the sodalite cage modifying the interaction with water, increasing the water mobility.

Application of a sodalite membrane reactor in esterification—Coupling reaction and separation

A tubular hydroxy sodalite (SOD) membrane was successfully applied in the esterification of acetic acid with ethanol and acetic acid with 1-butanol, to selectively remove water by pervaporation and to overcome the thermodynamic equilibrium limitation of the esterification. The reactions were carried out using equimolar solutions of acetic acid with the appropriate organic alcohol at 363 K using Amberlyst 15 as acid catalyst. The hybrid process drove the esterification reactions almost to completion. The special feature of the SOD-membrane is that it showed absolute selectivity towards water and retained its stability under the reaction conditions. The membrane exhibited a stable water pervaporation performance at pH values above 2.9 for acetic acid–water mixtures.

Performance of hydroxy sodalite membranes as absolute water selective materials under acidic and basic conditions

Abstract Gas tight α-alumina supported hydroxy sodalite membranes were employed in pervaporation, testing the acid and base stability of the membranes through prolonged dehydration of acetic acid/water mixtures and sodium hydroxide solutions with different concentrations at 473 K and 2.2 MPa cross-membrane pressure. Under continuous operation for approximately 320 h, hydroxy sodalite membranes showed good acid and base stability within a feed pH range of 2.9–13.7. Under these conditions the membrane showed absolute selectivity towards water, and the flux through the membrane remained fairly stable. The membranes were also employed in dehydration of acetone/water mixtures at different temperatures and feed compositions. The membrane exhibited a water/acetone separation factor larger than 106.

Application of hydroxy sodalite films as novel water selective membranes

Supported hydroxy sodalite (H-SOD) membranes were prepared on α-alumina disks using direct hydrothermal synthesis at 413 K for 3.5 h. The continuity of the membranes was verified using single gas permeation of He and N 2 at ambient conditions. The membranes were impermeable to N 2 and He, which validated absence of defects in the membrane structure. The membranes were used in dewatering several organic alcohol/water mixtures (organic alcohol being: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, and 2-pentanol). The influence of feed temperature (303–473 K), feed concentration (0–100 mol% alcohol in the feed), and absolute feed pressure (1.6–2.4 MPa) on the water flux were analyzed. The absolute feed pressure had no effect on the water permeance. The membrane exhibited a water/alcohol separation factor larger than 10 6 and showed excellent thermal, mechanical, and operation stability in continuously dehydrating a water/ethanol mixture (72 mol% water) by pervaporation at 473 K and 2.2 MPa for 125 h. The normalized water flux correlated well with the water feed concentration for the primary alcohols. Below 40 mol% water in mixtures with secondary alcohols the water flux was three orders of magnitude lower. The water mobility through the membrane had an activation energy of ∼15 kJ/mol.

Direct crystallisation of a hydroxy sodalite membrane without seeding using a conventional oven

A double layered hydroxy sodalite membrane was synthesised directly onto a tubular α-alumina support without seeding using a conventional hot-air oven. The effect of different synthesis parameters including the water content, ageing period, synthesis time and temperature, on the purity and continuity of the membrane was investigated. The water content was an important factor in controlling the presence of contaminating zeolite phases in the membrane. The optimised membrane which was contaminant free was characterised by XRD, SEM and single gas permeation using He, N 2 and SF 6. The permeance of the three gases through the membrane ranged from 0.8 to 8 × 10 −8 mol m −2 s −1 Pa −1. The selectivity ( α = 2.5–2.7) compared well to the Knudsen diffusion ratio for He/N 2.