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Methanol production in an optimized dual-membrane fixed-bed reactor
mohammad farsi
Chemical Engineering and Processing: Process Intensification, 2011
Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the following stages. This paper focuses on modeling and optimization of methanol production in a dual-membrane reactor. In this configuration, conventional methanol reactor is supported by Pd/Ag membrane tubes for hydrogen permeation and alumina-silica composite membrane tubes for water vapor removal from the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed to predict the performance of this novel configuration. In order to verify the accuracy of the model, simulation results of the conventional reactor is compared with available industrial plant data. The main advantages of the optimized dual-membrane reactor are: higher CO 2 conversion, the possibility of overcoming the limitation imposed by thermodynamic equilibrium, improvement of the methanol production rate and its purity. Genetic algorithm as an exceptionally simple evolution strategy is employed to maximize the methanol production as the objective function. This configuration has enhanced methanol production rate by 13.2% compared to industrial methanol synthesis reactor.
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Application of water vapor and hydrogen-permselective membranes in an industrial fixed-bed reactor for large scale methanol production
Mohammad Farsi
Chemical Engineering Research & Design, 2000
Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the next stages. In this work a novel reactor consisting two membrane layers has been proposed for simultaneous hydrogen permeation to reaction zone and water vapor removal from reaction zone in the methanol synthesis reactor. In this configuration conventional methanol reactor is supported by a Pd/Ag membrane layer for hydrogen permeation and alumina–silica composite membrane layer for water vapor removal from reaction zone. In this reactor syngas is fed to the reaction zone that is surrounded with hydrogen-permselective membrane tube. The water vapor-permselective membrane tube is placed in the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed for simulation of the proposed reactor. To verify the accuracy of the model, simulation results of the conventional reactor is compared with the available plant data. The membrane fixed bed reactor benefits are higher methanol production rate, higher quality of outlet product and consequently lower cost in product purification stage. This configuration has enhanced the methanol yield by 10.02% compared with industrial reactor. Experimental proof-of-concept is needed to establish the safe operation of the proposed configuration.
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Enhancement of Methanol Production in a Membrane Dual-Type Reactor
M. R. Rahimpour
Chemical Engineering & Technology, 2007
In this study, a dynamic model for a membrane dual-type methanol reactor was developed in the presence of long term catalyst deactivation. The proposed model is used to compare the performance of a membrane dual-type methanol reactor with a conventional dual-type methanol reactor. A conventional dual-type methanol reactor is a shell and tube heat exchanger reactor in which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. In a membrane dual-type reactor, the wall of the tubes in the gas-cooled conventional reactor is covered with a palladium-silver membrane, which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. The proposed dynamic model was validated against measured daily process data of a methanol plant recorded for a period of four years and a good agreement was achieved. The simulation results show that there is a favorable profile of temperature and activity of the membrane dual-type reactor relative to single and conventional dual-type reactor systems. Therefore, the performance of methanol reactor systems improves when a membrane is used in a conventional dual-type methanol reactor.
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Reduction in CO emissions along a two-stage hydrogen-permselective membrane reactor in methanol synthesis process
Mohammad Mazinani
Journal of Industrial and Engineering Chemistry, 2011
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.
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Verification of the membrane reactor concept for the methanol synthesis
Samuel Stucki
Applied Catalysis A-general, 2001
The experimentally observed rise in the single pass methanol production with CO 2 and H 2 (T = 200 • C, P = 4.3 bar) by in situ product removal over a perm-selective Nafion ® membrane is verified by model simulations. For this purpose, software was developed which addresses the two rivalling processes (synthesis and permeation) for given catalyst activity and permeation performance of the membrane. The program predicts the production rate of all the reactor gas components leaving the reactor by explicit integration of the gas component and (reactor and mantle) space specific differential rate equations along the symmetry axes of the tubular membrane reactor. The activity of the CO 2 -tolerant catalyst used was characterized independently by kinetic model analysis; the experimentally determined permeation performance of the membrane for the various reactant gas components by Arrhenius type temperature dependencies. The model confirmed the membrane reactor results satisfactorily well. It was estimated that with 10 m thin membrane surfaces implemented in commercial methanol synthesis plants and operated under technically relevant conditions (T = 200 • C, P = 40 bar, GHSV = 5000 h −1 ), the single pass reactor yield improves by 40% and that the additional costs for the membrane material are two production months only.
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A Comprehensive Model for Catalytic Membrane Reactor
Surendra Kumar
International Journal of Chemical Reactor Engineering, 2000
Catalytic membrane reactors are multifunctional reactors, which provide improved performance over conventional reactors. These are used mainly for conducting hydrogenation/ dehydrogenation reactions, and synthesis of oxyorganic compounds by using inorganic membranes. In this paper, comprehensive model has been developed for a tubular membrane reactor, which is applicable to Pd or Pd alloys membrane, porous inorganic membranes. The model accounts for the reaction on either side, tube or shell, isothermal and adiabatic conditions, reactive and non reactive sweep gas, multicomponent diffusion through gas films on both sides of membrane, and pressure variations. Equations governing the diffusion of gaseous components through stagnant gas film, and membranes have been identified and described. The model has been validated with the experimental results available in literature. By using the developed model catalytic dehydrogenation of ethylbenzene to produce styrene in a tubular membrane r...
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Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor
Farhad Rahmani
International Journal of Hydrogen Energy, 2011
Coupling the methanol synthesis with the dehydrogenation of cyclohexane to benzene in a co-current flow, catalytic fixed-bed double-membrane reactor configuration in order to simultaneous pure hydrogen and methanol production was considered theoretically. The thermally coupled double-membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from feed synthesis gas side (inner tube) into exothermic side. A steadystate heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCDMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCDMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. The influence of some operating variables is investigated on hydrogen and methanol yields. The results suggest that utilizing of this reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the recuperative reactor.
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On the modeling of one-dimensional membrane reactors: Application to hydrogen production in fixed packed bed
Hugo Jakobsen
Fuel, 2017
Hydrogen production by steam-methane reforming in membrane-assisted reactors has attracted substantial interest over the years. A variety of models for membrane-assisted reactors have been developed and suggested in the literature. In particular, examining the membrane models applied to the fixed packed bed reactor concept, there is no consensus or guidelines in the literature regarding the formulation of the heat balances (in terms of temperature). Thus, in the present study, different mathematical models for a fixed packed bed reactor with an integrated membrane have been compared in order to elucidate the effects of different model assumptions formulating the heat balance. The model formulations were examined by application to the steam-methane reforming process with hydrogen removal. The main findings of the present theoretical study are: With an increased temperature difference between the reaction and permeation zones, the enthalpy associated with the mass flux across the membrane has an increased effect on the temperature in the permeation zone. The temperature profile in the reaction zone is not influenced by the enthalpy difference across the membrane. Hence, in cases where it is not required with an accurate model prediction of the sweep gas temperature, the membrane reactor model can be simplified assuming isothermal condition in the permeation zone. The present study presents a rigorous derivation and examination of cross-sectional averaged models for membrane-assisted fixed packed bed reactors. Considering the level of details in the model formulations analyzed in this study, there exists currently no appropriate experimental data for model validations.
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A Novel Fluidized-Bed Membrane Dual-Type Reactor Concept for Methanol Synthesis
M. R. Rahimpour
Chemical Engineering & Technology, 2008
A novel fluidized-bed membrane dual-type methanol reactor (FBMDMR) concept is proposed in this paper. In this proposed reactor, the cold feed synthesis gas is fed to the tubes of the gas-cooled reactor and flows in counter-current mode with a reacting gas mixture in the shell side of the reactor, which is a novel membrane-assisted fluidized bed. In this way, the synthesis gas is heated by heat of reaction which is produced in the reaction side. Hydrogen can penetrate from the feed synthesis gas side into the reaction side as a result of a hydrogen partial pressure difference between both sides. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed bed reactor and the chemical reaction is initiated by the catalyst. The partially converted gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. This reactor configuration solves some drawbacks observed from the new conventional dual-type methanol reactor, such as pressure drop, internal mass transfer limitations, radial gradient of concentration, and temperature in the gas-cooled reactor. The two-phase theory of fluidization is used to model and simulate the proposed reactor. An industrial dual-type methanol reactor (IDMR) and a fluidized-bed dual-type methanol reactor (FBDMR) are used as a basis for comparison. This comparison shows enhancement in the yield of methanol production in the fluidized-bed membrane dual-type methanol reactor (FBMDMR).
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Effect of In-situ Membrane Removal of H2O on Methanol Conversion during Dimethyl Ether Synthesis Reaction
Mohammed Albager
An adiabatic tubular fixed bed reactor with and without a membrane was modeled and simulated to study the effect of in-situ H2O membrane removal on methanol conversion during dimethyl ether (DME) synthesis. An optimization approach was implemented to determine the best feed conditions for maximum conversion. A steady state one dimensional reactor model was used to process 100,000 tons per year of methanol over γ-Al2O3 pellets as reaction catalyst using a novel kinetic model. Pressure, temperature, conversion, and components molar flow rates profiles along the reactor were predicted. Results showed that methanol conversion exceeded the thermodynamic equilibrium limits when a membrane fixed bed reactor is used instead of a traditional fixed bed reactor. Methanol conversion reached 96% at optimum feed conditions in the fixed bed reactor with a membrane.
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