Hydrogen-permselective Membrane Reactor Research Articles

Development of a novel flowsheet for sulfur–iodine cycle based on the electrochemical Bunsen reaction for hydrogen production

The sulfur–iodine (SI) cycle is one of the promising methods for large-scale hydrogen production. A new flowsheet of SI cycle assembled with electrochemical Bunsen reaction was devised and modeled in this work. Adoption of electrochemical Bunsen reaction simplifies the flowsheet. The high concentrations of H2SO4 and HI, especially the over-azeotropic HI solution, successfully generated in the separated compartments of electrochemical cell without requiring further separation and purification. The enriched HI gas evaporates through flash, eliminating the extra concentration process, and then decomposes into 1 mol/s of H2 in hydrogen perm-selective membrane reactor. A HI separator is employed to maximize the recycle of undecomposed HI. The concentrated H2SO4 after flash decomposes into 0.5 mol/s of O2. The mass and energy balances of the SI cycle were evaluated. The cascade utilization of energy was carried out through internal heat exchange between hot and cold streams in the flowsheet. The surplus waste heat was recovered as electric power to improve the energy utilization efficiency. The overall thermal efficiency of the flowsheet was estimated to be 42–50% and was sensitive to heat recovery ratio. The simplified and energy-efficient flowsheet is competitive to the previous traditional flowsheets and will provide a reference for the industrial utilization of SI cycle.

Modelling and optimization of simultaneous styrene and hydrogen production in an industrial hydrogen‐permselective membrane reactor

Coupling reaction and separation in a membrane reactor improves process efficiency and reduces purification cost in the next stages. In this work, the performance of the hydrogen–permselective membrane reactors to produce styrene and hydrogen through ethylbenzene dehydrogenation is studied at steady state condition. In the proposed configuration, the Pd/Ag membrane tubes have been placed in the adiabatic reactors to remove hydrogen from the reaction zone. Then, the membrane reactors are modelled heterogeneously based on the mass and energy conservation laws considering a detailed thermal and catalytic kinetic model. To prove the accuracy of the considered model and assumptions, the simulation results of the conventional process are compared with the plant data. In addition, the genetic algorithm as a powerful method in the global optimization is applied to maximize the styrene production. The temperature of feed and sweep gas streams are attainable decision variables due to severe effect of temperature on the equilibrium and kinetic constant. This configuration has enhanced styrene production rate about 9.98 % compared to the industrial adiabatic reactor.

Purge gas recovery of ammonia synthesis plant by integrated configuration of catalytic hydrogen-permselective membrane reactor and solid oxide fuel cell as a novel technology

The purge gas emission of ammonia synthesis plant which contains hazardous components is one of the major sources of environmental pollution. Using integrated configuration of catalytic hydrogen-permselective membrane reactor and solid oxide fuel cell (SOFC) system is a new approach which has a great impact to reduce the pollutant emission. By application of this method, not only emission of ammonia and methane in the atmosphere is prevented, hydrogen is produced through the methane steam reforming and ammonia decomposition reactions that take place simultaneously in a catalytic membrane reactor. The pure generated hydrogen by recovery of the purge gas in the Pd–Ag membrane reactor is used as a feed of SOFC. Since water is the only byproduct of the electrochemical reaction in the SOFC, it is recycled to the reactor for providing the required water of the reforming reaction. Performance investigation of the reactor represents that the rate of hydrogen permeation increases with enhancing the reactor temperature and pressure. Also modeling results indicate that the SOFC performance improves with increasing the temperature and fuel utilization ratio. The generated power by recovery of the purging gas stream of ammonia synthesis plant in the Razi petrochemical complex is about 8 MW.

Optimal conditions of isobutane dehydrogenation in radial flow moving bed hydrogen-permselective membrane reactors to enhance isobutene and hydrogen production

In the isobutane dehydrogenation process, coupling reaction and separation and optimization of the intensified process can improve the isobutane conversion and selectivity, reduce operational costs and lets to produce pure hydrogen. In this research, the radial flow moving bed reactors in the Olefex technology have been supported by Pd–Ag membrane plate to remove hydrogen from the reaction zone. The reactions occur in the tube side and the hydrogen is permeated from the reaction zone to the sweep gas stream. The proposed configuration has been modeled heterogeneously based on the mass and energy conservation laws considering reaction networks. To prove the accuracy of the considered model, the simulation results of the conventional process have been compared against available plant data. The Genetic algorithm as an effective method in the global optimization has been considered to optimize the operating condition of membrane reactors to enhance isobutene productivity. In this optimal configuration, the isobutene production has been enhanced about 3.7%.

Modelling of hydrogen perm-selective membrane reactors for catalytic methane steam reforming

Methane steam reforming is one of the most important pathways for producing high purity hydrogen. In this context, the use of fixed-bed catalytic reactors equipped with hydrogen perm-selective membranes is an interesting alternative for producing high purity hydrogen in one single step. In this work, this reactor is studied by means of numerical simulations using a 2D model, consisting of mass, energy and momentum balances. The fixed-bed is considered to be formed by Ru/SiO2 catalyst particles, especially tailored for steam reforming at low temperature and steam-to-carbon ratio, whereas a composite palladium membrane was considered for hydrogen permeation. The model was validated with experimental data, and the adequacy of a simplified 1D model to simulate the membrane reactor was evaluated and discussed in comparison to the 2D model. Then, the model was used to study the influence of the main operating variables (inlet temperature, pressure, space velocity, steam excess and sweep gas rate in the permeate side) on the reactor performance. Finally, the optimum operating conditions, corresponding to a maximum hydrogen permeation rate, were determined, and the behaviour of the optimized reactor is analysed in detail.

Fixed bed membrane reactors for WGSR-based hydrogen production: Optimisation of modelling approaches and reactor performance

The production of high-purity hydrogen using the water–gas-shift reaction in both conventional fixed bed reactor and hydrogen perm-selective membrane reactor at low to medium scale is studied in this work by developing and comparing models with different complexity levels. A two-dimensional rigorous reactor model considering radial and axial variations of properties (including bed porosity), setting mass, energy and momentum differential balances, and nesting a rigorous model for mass transfer within the porous catalyst was considered as reference for comparison. Different simplifications of this model for taking into account mass-transfer effects within the catalyst pellet (Thiele modulus, evaluation of apparent kinetic constants, empirical correlation for effectiveness factors or just neglecting these effects) were tested, being observed that these effects are not negligible and that the first two approaches are accurate enough for taking into account mass transfer within catalyst pellets. Regarding to the reactor model, it was observed that one-dimensional models are not adequate, especially for the membrane reactor. Analogously, neglecting the momentum balances in the reactor (as made is most simulations reported in the literature) leads to important misspredictions in the behaviour of the membrane reactor performance. Finally, the influence of the main operation parameters (inlet temperature, pressure, space velocity, etc.) was studied using the detailed reactor model, concluding that space velocity and pressure are the most important parameters affecting reactor performance for membrane reactors.

Genetic algorithm strategy (GA) for optimization of a novel dual-stage slurry bubble column membrane configuration for Fischer–Tropsch synthesis in gas to liquid (GTL) technology

In this work, a novel configuration of a cascade double membrane assisted slurry bubble column reactor and hydrogen-permselective membrane reactor is proposed (SDMR) for Fischer–Tropsch synthesis (FTS). A one-dimensional heterogeneous model in first reactor and axial dispersion model (AMD) for both gas and liquid–solid suspension as a homogeneous phase for slurry bubble column reactor has been developed. Subsequently, this novel configuration was optimized. Here, genetic algorithm (GA) method was applied as powerful method for optimization of procedure. The proposed model has been used to compare the performance of an SDMR with a Fluidized-bed membrane dual-type reactor (FMDR) and a conventional reactor (CR). The simulation results show an enhancement in the gasoline production, a main decrease in undesirable product formation and a favorable temperature profile along the proposed concept rather than conventional reactor and even FMDR.

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.

The application of membrane reactor technology in hydrogen production using S–I thermochemical process: A roadmap

Thermochemical cycle using water as raw material and nuclear/renewable energies as sources of energy is believed to be a safe, stable and sustainable route of hydrogen production. Amongst the well-studied thermochemical cycles, the sulfur–iodine (S–I) cycle is capable of achieving an energy efficiency of 50%, making it one of the most efficient cycles among all water-splitting processes.The SI cycle is characterized by three basic reactions as shown below.1.I2 + SO2 + 2H2O → 2HIx + H2SO4 (120 °C)2.2H2SO4 → 2SO2 + 2H2O + O2 (830 °C)3.2HIx → I2 + H2 (450 °C)The third section, that is the HIx (HI + I2 + H2O) processing section, is the most intricate step in terms of the process efficiency as it has got the lowest overall rate and very complicated separations. In order to overcome the low efficiency due to the poor equilibrium decomposition of HI, ongoing research is dedicated toward development of a hydrogen-permselective membrane reactor. Proper identification of suitable membranes and introduction of membrane reactor is proposed to improve the efficiency of the overall cycle and make hydrogen production more economical. The experimental procedure has already been optimized toward development of an asymmetric silica membrane. The authors presently intend to use the membrane in the form of a packed bed membrane reactor for the enhancement of equilibrium decomposition of HI. The present paper discusses the challenges and intricacies associated toward development of a membrane reactor which can be applied in highly corrosive environment like HI under a high temperature of about 500 °C.

Inorganic Membranes for Hydrogen Production from the Water-Gas Shift Reaction: Materials, Reactor Design, and Simulation

Inorganic membranes for gas separation and purification have attracted great research interest. One application utilizing these materials is for H2 production from the water-gas shift reactions (WGS). The exothermic, reversible WGS reaction is controlled by thermodynamic equilibrium and exhibits decreased conversion with increasing temperatures. It is envisaged that the reaction conversion will surpass the equilibrium value if the reaction is conducted in a hydrogen-permselective membrane reactor, where the hydrogen product can be continuously removed from the reactor to shift the reaction equilibrium. In this article, the most recent development on material synthesis and fabrication of microporous ceramic membranes and dense palladium-based metal membranes are firstly reviewed according to their performance for H2 permeance and permselectivity over slightly larger molecules. The modification methods for improving membrane structure integrity, hydrophobicity, and stability at high temperature operation are also discussed. Subsequently, inorganic membrane reactors for the WGS reaction are evaluated in terms of CO conversion, hydrogen purity and operation parameters. Finally, modeling on gas transport through inorganic membranes and simulation of membrane reactors are discussed. By comparing the performance of various membranes, future prospective and improvement on membrane preparation and membrane reactor design are proposed.

Production of ultrapure hydrogen via utilizing fluidization concept from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor

In this work, a novel fluidized-bed thermally coupled membrane reactor has been proposed for simultaneous hydrogen, methanol and benzene production. Methanol synthesis is carried out in exothermic side which is a fluidized-bed reactor and supplies the necessary heat for the endothermic side. Dehydrogenation of cyclohexane is carried out in endothermic side with hydrogen-permselective Pd/Ag membrane wall. Selective permeation of hydrogen through the membrane in endothermic side is achieved by co-current flow of sweep gas through the permeation side. A steady-state fixed-bed heterogeneous model for dehydrogenation reactor and two-phase theory in bubbling regime of fluidization for methanol synthesis reactor is used to model and simulate the integrated proposed system. This reactor configuration solves some observed drawbacks of new thermally coupled membrane reactor such as internal mass transfer limitations, pressure drop, radial gradient of concentration and temperature in both sides. The proposed model has been used to compare the performance of a fluidized-bed thermally coupled membrane reactor (FTCMR) with thermally coupled membrane reactor (TCMR) and conventional methanol reactor (CR) at identical process conditions. This comparison demonstrates that fluidizing the catalytic bed in the exothermic side of reactor caused a favorable temperature profile along the FTCMR. Furthermore, the simulation results represent 5.6% enhancement in the yield of hydrogen recovery in comparison with TCMR.

Reduction in CO emissions along a two-stage hydrogen-permselective membrane reactor in methanol synthesis process

Carbon monoxide (CO) is a scentless and invisible gas that is quite poisonous. It is also known to be a major environmental pollutant. Industrial chemical processes contribute to CO pollution levels in the atmosphere. One of the most important processes for controlling the carbon monoxide content is conversion of CO to methanol by catalytic hydrogenation. The present work investigates enhancement of CO conversion in a conventional two-stage methanol synthesis reactor using a hydrogen-permselective membrane. For this membrane system, a one-dimensional dynamic plug flow model was proposed in the presence of long-term catalyst deactivation. This model compares CO removal in a membrane two-stage methanol synthesis reactor with a conventional two-stage methanol synthesis reactor. A conventional two-stage reactor is a vertical shell and tube in which the first reactor coolant is saturated water and the second one is cooled with synthesis gas. In a membrane two-stage reactor, the wall of the tubes in the gas-cooled reactor is coated with a Pd–Ag membrane, which only permits the diffusion of hydrogen. For validation of the recommended dynamic model, the measured daily process data of a methanol plant recorded for a period of 4 years were used and a good agreement was obtained.

Membrane development for applications in hydrogen production using the sulphur-iodine thermochemical route

Careful optimisation of a safe and sustainable route for hydrogen production is a pressing need. Thermochemical processes employing water as raw material and nuclear/renewable energies as energy source are believed to be the best possible option in this direction, while alarming issues such as climate change and global warming are being taken into account. Amongst the well-identified cycles, the sulphur-iodine (S-I) thermochemical route assumes the highest thermal efficiency and the best one as regards its coupling to a high temperature nuclear reactor. Material development is the key issue to be addressed to realise successfully the potential of the S-I cycle. The most important area is development of gas-permeable membranes for enhancement of the equilibrium decomposition of HI, which is the most intricate step as far as the overall process efficiency is concerned. In order to overcome the low efficiency associated with the low equilibrium decomposition of HI, the authors intend to develop a hydrogen permselective membrane reactor. As a first step towards this development, a silica membrane of asymmetric nature was developed using sol-gel processing and dip coating, and characterised using scanning electron microscopy and a BET surface area analyser. A road map towards realising the successful emergence of the membrane reactor is discussed.

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.

Comparison of two different flow types on CO removal along a two-stage hydrogen permselective membrane reactor for methanol synthesis

Carbon monoxide (CO) is a gaseous pollutant with adverse effects on human health and the environment. Industrial chemical processes contribute significantly to CO accumulation in the atmosphere. One of the most important processes for controlling carbon monoxide emissions is the conversion of CO to methanol by catalytic hydrogenation. In this study, the effects of two different flow types on the rate of CO removal along a two-stage hydrogen permselective membrane reactor have been investigated. In the first configuration, fresh synthesis gas flows in the tube side of the membrane reactor co-currently with reacting material in the shell side, so that more hydrogen is provided in the first sections of the reactor. In the second configuration, fresh synthesis gas flows in the tube side of the membrane reactor counter-currently with reacting material in the shell side, so that more hydrogen is provided in the last sections of the reactor. For this membrane system, a one-dimensional dynamic plug flow model in the presence of catalyst deactivation was developed. Comparison between co-current and counter-current configurations shows that the reactor operates with higher conversion of CO and hydrogen permeation rate in the counter-current mode whereas; longer catalyst life is achieved in the co-current configuration. Enhancement of CO removal in the counter-current mode versus the co-current configuration results in an ultimate reduction in CO emissions into the atmosphere.

Hydrogen production from urea wastewater using a combination of urea thermal hydrolyser–desorber loop and a hydrogen-permselective membrane reactor

This work presents novel application of palladium-based membrane in a wastewater treatment loop of urea plant for hydrogen production. Urea wastewater treatment loop is based on combined thermal hydrolysis–desorption operations. The wastewater of urea plant includes ammonia and urea which in the current treatment loop; urea decomposes to ammonia and carbon dioxide. The catalytic hydrogen-permselective membrane reactor is proposed for hydrogen production from desorbed ammonia of urea wastewater which much of it discharges to air and causes environmental pollution. Therefore hydrogen is produced from decomposition of ammonia on nickel–alumina catalyst bed simultaneously and permeates from reaction side to shell side through thin layer of palladium–silver membrane. Also a sweep gas is used in the shell side for increasing driving force. In this way, 4588 tons/yr hydrogen is produced and environmental problem of urea plant is solved. The membrane reactor and urea wastewater treatment loop are modeled mathematically and the predicted data of the model are consistent with the experimental and plant data that show validity of the model. Also the effects of key parameters on the performance of catalytic hydrogen-permselective membrane reactor such as the temperature, pressure, thickness of Pd–Ag layer, configuration of flow and sweep gas flow ratio were examined.

Comparative Study of Two Different Hydrogen Redistribution Strategies along a Fluidized-Bed Hydrogen Permselective Membrane Reactor for Methanol Synthesis

In this work, two different hydrogen redistribution strategies along a bubbling fluidized-bed hydrogen permselective membrane reactor have been compared. In the first strategy, fresh synthesis gas flows in the tube side of the fluidized-bed membrane reactor in cocurrent mode with reacting material in the shell side, so that more hydrogen is provided in the first segments of the reactor. In the second strategy, fresh synthesis gas flows in the tube side of the fluidized-bed membrane reactor in countercurrent mode with reacting material in the shell side, so that more hydrogen is provided in the last segments of the reactor. A dynamic two-phase theory in the bubbling regime of fluidization was developed to model and compare two strategies from different points of view. Comparison between cocurrent and countercurrent modes of operation shows that the reactor in the countercurrent configuration operates with higher conversion of methanol, longer catalyst life, and higher carbon dioxide removal, whereas the reactor in the cocurrent configuration operates with higher carbon monoxide removal, lower water production, and higher hydrogen permeation rate. Enhancement of the carbon dioxide removal in countercurrent mode and the carbon monoxide removal in cocurrent mode causes a lower environmental impact. The lower water production rate in cocurrent mode reduces catalyst recrystallization.

A comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane dual-type FTS reactor in GTL technology

In this work, a comparison of co-current and counter-current modes of operation for a novel hydrogen-permselective membrane reactor for Fischer–Tropsch Synthesis (FTS) has been carried out. In both modes of operations, a system with two-catalyst bed instead of one single catalyst bed is developed for FTS reactions. In the first catalytic reactor, the synthesis gas is partly converted to products in a conventional water-cooled fixed-bed reactor, while in the second reactor which is a membrane fixed-bed reactor, the FTS reactions are completed and heat of reaction is used to preheat the feed synthesis gas to the first reactor. In the co-current mode, feed gas is entered into the tubes of the second reactor in the same direction with the reacting gas stream in shell side while in the counter-current mode the gas streams are in the opposite direction. Simulation results for both co-current and counter-current modes have been compared in terms of temperature, gasoline and CO 2 yields, H 2 and CO conversion, selectivity of components as well as permeation rate of hydrogen through the membrane. The results showed that the reactor in the co-current configuration operates with lower conversion and lower permeation rate of hydrogen, but it has more favorable profile of temperature. The counter-current mode of operation decreases undesired products such as CO 2 and CH 4 and also produces more gasoline.

Production of hydrogen from purge gases of ammonia plants in a catalytic hydrogen-permselective membrane reactor

Abstract The present study investigates hydrogen production in a hydrogen-permselective membrane reactor from purge gases of an ammonia plant. Hydrogen which initially exists in the purge gases and hydrogen that is produced from decomposition of ammonia on nickel–Alumina catalyst bed simultaneously permeate from reaction side to shell side through a thin layer of palladium–silver membrane. A sweep gas can be used in the shell side for increasing driving force. The amount of hydrogen that can be gained annually and effect of pressure, temperature, thickness of Pd–Ag layer, configuration of flow in the membrane reactor and sweep gas flow ratio have been studied. This study shows that the countercurrent mode is better than co-current mode of operation. The rate of hydrogen permeation increases with increasing of temperature, pressure and sweep gas flow rate. This approach produces and separates large amounts of hydrogen and decreases environmental impacts owing to ammonia emission.

Optimization of a novel combination of fixed and fluidized-bed hydrogen-permselective membrane reactors for Fischer–Tropsch synthesis in GTL technology

In this work, a novel combination of fixed and fluidized-bed hydrogen-permselective membrane reactors for Fischer–Tropsch synthesis (FTS) has been optimized using Genetic Algorithm (GA). This novel reactor configuration incorporates a fixed-bed FTS reactor with a membrane assisted fluidized-bed FTS reactor. In the proposed configuration, hydrogen is withdrawn from the fresh feed synthesis gas and is injected to the end segment of reactor in order to control dozing of hydrogen along the reactor and prevention of hydrogen waste. A theoretical investigation was performed in order to optimize the reactor performance, maximizing C 5 + production and at the same time, minimizing the CO 2 yield as an undesired product. The optimization was carried out and the results show there is a favorable profile of FTS products along the optimized combined system relative to the conventional fixed-bed single stage FTS reactor. Optimal ratio of reactors length, H 2/CO ratio, catalyst size, shell and tube pressures of second reactor, hydrodynamic parameters, gas phase velocity and temperature profile along the reactor were obtained and 45.9% additional C 5 + yield was resulted in optimized system relative to conventional fixed-bed single stage FTS reactor.