A study on the performance of a dense polymeric catalytic membrane reactor (original) (raw)
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Modeling a catalytic polymeric non-porous membrane reactor
Journal of Membrane Science, 2001
A theoretical study on a catalytic polymeric non-porous membrane reactor is performed. The conversion enhancement over the thermodynamic equilibrium is studied when conducting an equilibrium gas-phase reaction of the type A+B ⇔ C+D. The model used considers perfectly mixed flow patterns and isothermal operation for the retentate and permeate. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the reactants' diffusion coefficients are lower and/or sorption coefficients are higher than the products'. This happens for Thiele modulus and contact time over certain threshold values. It was also observed that it is preferable to enhance conversion through an increase in the reactants' sorption coefficients, since this leads to lower reactor dimensions. Since the performance of a non-porous membrane reactor depends on both the sorption and diffusion coefficients, a study of such system cannot be based exclusively on the permeabilities of the components. Favorable combinations of diffusion and sorption coefficients can provide a coupled effect over the reactor's conversion.
Modeling a dense polymeric catalytic membrane reactor with plug flow pattern
Catalysis Today, 2003
A theoretical study on a tubular membrane reactor assuming isothermal operation, plug flow pattern and using a dense polymeric catalytic membrane is performed. The reactor conversion for an equilibrium gas-phase reaction generically represented by A B is analyzed, considering the influence of the product's sorption and diffusion coefficients. It is concluded that the conversion of such a reaction can be significantly improved when the overall diffusion coefficient of the reaction product is higher than the reactant's one and/or the overall sorption coefficient is lower, and for Thiele modulus and contact time values over a threshold. Though a sorption coefficient of the reaction product lower than that of the reactant may leads to a conversion enhancement higher than that one obtained when the reaction product diffusion coefficient is higher than that of the reactant, the contact time value for the maximum conversion is much higher in the first case. In this way, a higher diffusion coefficient for the reaction product should be generally preferable, because it leads to a lower reactor size. The performance of a dense polymeric catalytic membrane reactor depends in a different way on both sorption and diffusion coefficients of reactants and products and then a study of such a system cannot be based only on their own permeabilities. Favorable combinations of diffusion and sorption coefficients can affect positively the reactor's conversion.
Simulation study of a dense polymeric catalytic membrane reactor with plug–flow pattern
Chemical Engineering Journal, 2003
A theoretical study on a tubular membrane reactor, assuming isothermal operation, plug-flow pattern and using a dense polymeric catalytic membrane, is performed. The reactor conversion for an A B equilibrium gas-phase reaction is analyzed, considering the influence of the reactants and products diffusion and sorption coefficients, the influence of the total pressure gradient and the influence of the ratio between the membrane thickness and its internal radius as well as the influence of the feed location (tube side or shell side) and the co-current, counter-current and cross-flow operation modes. One of the most unexpected conclusion is that for a set of conditions where the co-current and counter-current flows leads to differences in the reactor performance, the co-current flow is always better than the counter-current flow, exactly the reverse of what takes place when the membrane performs only gas separation. It is also concluded that the relative permeate pressure favors or penalizes the conversion, depending on the relative permeabilities of each reaction component. It is also concluded that the best reactor's feed location and the optimum r t /δ ratio depend on the relative sorption and diffusion coefficients of the reaction components as well as on the range of the Thiele modulus and contact time operation values.
Theoretical analysis of conversion enhancement in isothermal polymeric catalytic membrane reactors
Catalysis Today, 2006
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Catalysis Today, 2005
The scope of this paper is to present a theoretical study of a catalytic polymeric dense membrane reactor (CPDMR) assuming isothermal conditions, plug flow pattern without pressure drop in both retentate and permeate sides, shell side feed and cocurrent operation. The conversion enhancement over the thermodynamic equilibrium value is studied for a gas-phase reaction of the type aA Ð bB, considering two different stoichiometric ratios: Dn > 0 and Dn < 0, where Dn = b À a. For each of these cases, the influence of the relative sorption and diffusivity of the reaction species is studied. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the diffusivity of the reaction products is higher than that of the reactants and/or the sorption is lower. It is also concluded that, even for equal sorption and diffusion coefficients, the conversion could also be improved for reactions with Dn 6 ¼ 0. The extension of this enhancement depends on the reaction stoichiometry, the overall concentration inside the membrane, the Thiele modulus, and the contact time.
Consecutive-Parallel Reactions in Nonisothermal Polymeric Catalytic Membrane Reactors
Industrial & Engineering Chemistry Research, 2006
This work reports the development of a nonisothermal and nonadiabatic pseudo-homogeneous model to study a completely back-mixed membrane reactor with a polymeric catalytic membrane, for conducting the consecutive hydrogenation of propyne to propene and then to propane. The performance of the reactor is analyzed in terms of the propyne concentration in the permeate stream (the only outlet stream from the reactor), the conversion of propyne and hydrogen, and the selectivity and overall yield to the intermediate product propene. The operating and system parameters considered are the Thiele modulus, the dimensionless contact time, the Stanton number, and the effective hydrogen sorption and diffusion coefficients. To define the regions where the catalytic membrane reactor may perform better than a conventional reactor, a comparison between both reactors is made. For the range of parameter values considered, the reactor model in this study demonstrates that the catalytic membrane reactor performs better than the conventional catalytic reactor in some regions of the Thiele modulus parametric space, for medium to high Stanton number values and for the total flowthrough configuration (total permeation condition). Concerning the effective sorption and diffusion coefficients of hydrogen, they shall be higher than the ones of the hydrocarbons.
High-temperature membrane reactor for catalytic gas-solid reactions
AIChE Journal, 1992
A mathematical model, based on the dusty-gas model extended with surface diffusion, is presented that describes mass transport owing to molecular diffusion and viscous flow, as well as an instantaneous reversible reaction inside a membrane reactor. The reactants are fed to opposite sides of the membrane, considering masstransfer resistances in the gas phase outside the membrane. The Claus reaction is chosen us u model reaction to study this membrane reactor.
A Comprehensive Model for Catalytic Membrane Reactor
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...
Catalytic Membrane Reactors: The Industrial Applications Perspective
Catalysts
Catalytic membrane reactors have been widely used in different production industries around the world. Applying a catalytic membrane reactor (CMR) reduces waste generation from a cleaner process perspective and reduces energy consumption in line with the process intensification strategy. A CMR combines a chemical or biochemical reaction with a membrane separation process in a single unit by improving the performance of the process in terms of conversion and selectivity. The core of the CMR is the membrane which can be polymeric or inorganic depending on the operating conditions of the catalytic process. Besides, the membrane can be inert or catalytically active. The number of studies devoted to applying CMR with higher membrane area per unit volume in multi-phase reactions remains very limited for both catalytic polymeric and inorganic membranes. The various bio-based catalytic membrane system is also used in a different commercial application. The opportunities and advantages offer...
Performance of catalytic membrane reactor in multiphase reactions
Chemical Engineering Science, 2004
Single-channel catalytic membranes were prepared using an evaporation-crystallization Pt deposition method and characterized by employing SEM, EDX and EPMA techniques. Their activity was tested by conducting liquid-phase formic acid oxidation, and effects of trans-membrane pressure difference, catalyst loading and re-circulation rate on their performance is reported. The results obtained have revealed that the measured conversions are preferentially determined by diffusion of formic acid through the top and intermediate layers to the reaction zone on one hand, and by concentration gradient of gaseous reactant on the other hand. Which effect prevails, depends on the position of gas-liquid interface and the instantaneous molar ratio of reactants. Finally, thickness and reactants' concentrations in the reaction zone established within the membrane wall were calculated.