Simulated Countercurrent Moving Bed Chromatographic Reactor Research Articles

Numerical simulation and optimisation of unconventional three‐section simulated countercurrent moving bed chromatographic reactor for oxidative coupling of methane reaction

AbstractThe simulated countercurrent moving‐bed chromatographic reactor (SCMCR) has been reported to significantly enhance methane conversion and C2 product yield for oxidative coupling of methane (OCM) reaction, which is otherwise a low per pass conversion reaction. A mathematical model of an unconventional three‐section SCMCR for OCM was first developed and solved using numerically tuned kinetic and adsorption parameters. The model predictions showed good agreement with available experimental results of SCMCR for OCM. Effects of several process parameters on the performance of SCMCR were investigated. A multi‐objective optimisation problem was solved at the operating stage using state‐of‐the‐art AI‐based non‐dominated sorting genetic algorithm with jumping genes adaptations (NSGA‐II‐JG), which resulted in Pareto Optimal solutions. It was found that the performance of the SCMCR could be significantly improved under optimal operating conditions. © 2011 Canadian Society for Chemical Engineering

Modeling and simulation of simulated countercurrent moving bed chromatographic reactor for oxidative coupling of methane

Oxidative coupling of methane (OCM) is a reaction of industrial importance but per pass equilibrium conversion and product yield in a single reaction column is severely low. The simulated countercurrent moving bed chromatographic reactor (SCMCR) has been reported to significantly improve the methane conversion and C 2 -product yield. This paper addresses the mathematical modeling of a five section SCMCR for OCM, which is particularly important for understanding the operation of this SCMCR system. In order to obtain the various process parameters, a realistic and rigorous kinetics was adopted in reactors for OCM and subsequently a kinetic model was developed which can best describe the associated kinetics of OCM in SCMCR. Adsorption isotherm parameters were then derived based on the experimental breakthrough curves acquired using single adsorption column. The proposed mathematical model demonstrated extremely good predictions of the experimental results. Finally, effects of operating parameters, such as switching time, methane/oxygen feed ratio, raffinate flow rate, eluent flow rate, etc., on the behavior of the SCMCR were studied systematically.

Multi-objective optimization of simulated countercurrent moving bed chromatographic reactor for oxidative coupling of methane

A comprehensive optimization study on a simulated countercurrent moving bed chromatographic reactor (SCMCR) is reported in this article for oxidative coupling of methane (OCM) reaction. The selection of the operating parameters such as the switching time, make-up feed rate, methane to oxygen ratio in feed, length of columns and flow rates in different sections are not straightforward in an SCMCR. In most cases, conflicting requirements and constraints govern the optimal choice of the decision (operating or design) variables. An experimentally verified mathematical model was selected to optimize the performance of the SCMCR for OCM. A few multi-objective optimization problems were solved for both existing setup and at design stage. The optimization was performed using a state-of-the-art AI-based non-traditional optimization technique, non-dominated sorting genetic algorithm with jumping genes (NSGA-II-JG), which resulted in Pareto optimal solutions. It was found that the performance of the SCMCR could be improved significantly under optimal operating conditions.

Enhanced Methanol Yields from the Direct Partial Oxidation of Methane in a Simulated Countercurrent Moving Bed Chromatographic Reactor

A laboratory-scale simulated countercurrent moving bed chromatographic reactor (SCMCR) for the direct, homogeneous partial oxidation of methane to methanol has been constructed and tested. Reaction conditions were evaluated from independent experiments with a single-pass tubular reactor. Separation was effected by gas−liquid partition chromatography with 10% Carbowax on Supelcoport. At the optimal reaction conditions of 477 °C, 100 atm, and feed methane-to-oxygen ratio of 16, the methane conversion in the SCMCR was 50%, the methanol selectivity was 50%, and the methanol yield was 25%. Factors affecting methane conversion were investigated. Possible ways to improve the methane conversion, and hence the methanol yield, are discussed.

Multiobjective Optimization of Simulated Countercurrent Moving Bed Chromatographic Reactor (SCMCR) for MTBE Synthesis

The paper addresses the multiobjective optimization of a simulated moving-bed chromatographic reactor (SCMCR). The selection of the operating parameters such as the length and number of columns, switching time, and liquid flow rates in different sections is not straightforward in an SCMCR. In most cases, conflicting requirements and constraints govern the optimal choice of the decision (operating or design) variables. A mathematical model that predicts single-column experimental results well was modified for MTBE synthesis in an SCMCR. Thereafter, a few simple multiobjective optimization problems were solved that included both existing and designstage SCMCRs using a nondominated sorting genetic algorithm (NSGA). Optimal design and operating conditions for three cases of practical relevance are studied in this work, namely, (a) simultaneous maximization of the purity and yield of MTBE; (b) simultaneous maximization of the purity and yield of MTBE, together with minimization of the total amount of adsorbent/ catalyst required; and (c) maximization of the purity of MTBE with simultaneous minimization of the eluent consumption, to illustrate the procedures and interpret the results obtained. Paretooptimal solutions were obtained in all cases, and moreover, it was found that the performance of the SCMCR could be improved significantly under optimal operating conditions.

Application of Simulated Countercurrent Moving-Bed Chromatographic Reactor for MTBE Synthesis

Synthesis of MTBE directly from methanol and tert-butyl alcohol is considered in a separative chemical reactor, which can be used to simulate a countercurrent chromatographic moving bed. A mathematical model is developed for a reactor configuration consisting of multiple columns connected in series in a circular arrangement with ports that can serve either as inlets or as outlets. The columns are packed with Amberlyst 15 ion-exchange resin, which acts as both adsorbent and catalyst. Experimentally determined adsorption and kinetic parameters are used in the mathematical model to predict the concentration profiles of the reactant and products. The effects of the switching time; the feed, solvent, and product flow rates; and the number of columns on the yield, selectivity, and purity of the desired product (MTBE) and the conversion of the limiting reactant (TBA) were studied systematically. The sensitivity study reveals that it is not possible to maximize the yield and selectivity of MTBE simultaneously, as some of the operating parameter act in conflicting manners.

A simple adsorber dynamics approach to simulated countercurrent moving bed reactor performance

The design and performance of a simulated countercurrent moving bed chromatographic reactor (SCMCR) for high temperature reactions are investigated for both reversible and irreversible reactions of a single reactant. From an analysis of the solid phase and gas phase flow ratios in each of the SCMCR sections, the flow conditions necessary for optimizing the conversion and yield are obtained. Reactor performance is not evaluated from typical material balance equations, but rather by considering the separation of reactant and product waves as they flow through the sections of the SCMCR, and as the feed point is cycled under the assumption of dispersionless plug flow. The additional assumptions of linear adsorption equilibria and infinite gas–solid mass transfer rates permit the expressions for exit molar flow profiles during the initial transient period, and of the ultimate periodic steady state, to be readily obtained. Simple algebraic expressions for the production rate of the reaction product as a function of the adsorption equilibrium constants, the per pass conversion, the number of switching periods, and the molar flow rate of the reactant, are presented.

Optimization of the simulated countercurrent moving-bed chromatographic reactor for the oxidative coupling of methane

This work deals with the further development and optimization of a simulated countercurrent moving bed chromatographic reactor (SCMCR) for the oxidative coupling of methane (OCM). To optimize the adsorptive separation of OCM products from unreacted methane, different adsorbents were selected and tested. Hydrophobic carbon molecular sieve, examined along with other adsorbents (activated charcoal and zeolite with high silica/alumina ratio), appears to be the most suitable choice, both for methane storing and for efficient handling of the OCM separation. Three catalysts, Sm 2O 3, Y 1Ba 2Zr 3O 9.5, and Y 1Ba 2Ge 1O 3.5 have been studied in microcatalytic reactor experiments. The Y 1Ba 2Zr 3O 9.5 catalyst proved to be the best, giving 84% selectivity to C 2-products at a CH 4 O 2 ratio of 11 and nearly complete oxygen conversion. A detailed model of the SCMCR employing experimental information about the catalyst and adsorbent properties was developed to analyze the complex cyclic behavior of the SCMCR. It was found that observed methane loss, and therefore decreased conversion, are caused by incomplete desorption of methane in the carrier section of the SCMCR. This effect can be minimized by selecting a better adsorbent. The influence of the switching time and CH 4 O 2 ratio in the make-up feed, the two most important parameters in this system, on reactor performance was analyzed. It was shown that for the best catalyst (Y 1Ba 2Zr 3O 9.5) at optimal operating conditions the SCMCR can give 55% yield for C2 products at 75% methane conversion. Adaptive flow switching and the use of a non-uniform make-up feed appear to be promising methods for further optimization of the SCMCR.

Numerical simulation of a simulated countercurrent moving bed chromatographic reactor

A mathematical model of a simulated countercurrent moving bed chromatographic reactor (SCMCR) has been developed. The model represents a multiple column reactor consisting of a series of either four or five tubular fixed beds packed with a mixture of catalyst and adsorbent, with a port that can serve either as an inlet or an outlet between each. A reversible first order reaction, A / ag B, with rate coefficients and rate parameters taken from the hydrogenation of 1,3,5-trimethylbenzene is incorporated into the model. The partial differential equations governing the isothermal reactor at 463 K are solved by an adaptive finite element method with uneven grid points. Model predictions of concentration profiles in the columns, and overall reactor performance, are obtained. It is shown that reaction and separation occur simultaneously, and that the conversion of this equilibrium limited reaction is greatly increased over the 0.62 that would be the maximum obtainable in a non-separative system. Under appropriate operating conditions, the model calculations predict that high product purity streams (98–99%) and nearly unit conversions can be obtained.

Experimental study of a laboratory-scale simulated countercurrent moving bed chromatographic reactor

An experimental investigation of the catalytic hydrogenation of 1,3,5-trimethylbenzene to 1,3,5-trimethylcyclohexane in a simulated countercurrent moving-bed chromatographic reactor is reported. A multiple column configuration of the simulated countercurrent moving-bed chromatographic reactor has been designed and assembled. A microcomputer has been interfaced with the reactor and an analytical gas chromatograph for computer control, data acquisition and analysis. This separative reactor gives a reaction product that contains relatively small amounts of unconverted reactant, and conversions that are considerably in excess of the thermodynamic equilibrium that would be the maximum achieved in non-separative reactors. With appropriate operating conditions, a product purity of 96% and reactant conversion of 0.83 was obtained. Under the conditions of the experiment the equilibrium conversion is 0.4.

Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane

The oxidative coupling reaction of methane (OCM) is a potential industrial reaction for the efficient production of ethylene. Replacement of current technologies requires significant product yield improvements. A novel experimental reactor, the simulated countercurrent moving-bed chromatographic reactor (SCMCR), has reported OCM yields which exceed conventional reactors [ Tonkovich et al., 1993, Science 262, 221 ; Tonkovich and Carr, 1995, Chem. Engng Sci. (in press) ]. An understanding of the SCMCR operation is aided by concurrent mathematical modeling. The model mimics the experimental reactor configuration and operation. Four sections are used in the SCMCR, each containing one reaction column and two separation columns connected in series. The feed is switched from section to section at a rate less than a single section breakthrough time, and a make-up feed is used after the first cycle. Reaction occurs in the first column and is followed by rapid product and reactant separation in the ensuing section columns. The model does not incorporate the realistic and complex kinetics arising from the OCM, rather a simplified reaction term is used to qualitatively gain insight into the operation of the SCMCR. The effects of the feed switching time and the make-up feed rate are investigated. The reactant conversion has a maximum at intermediate values of both parameters. This agrees with experimental trends, where the methane conversion and the C 2 yield are also maximized at similar intermediate values of the switching time.

A simulated countercurrent moving-bed chromatographic reactor for the oxidative coupling of methane: Experimental results

The simulated countercurrent moving-bed chromatographic reactor (SCMCR) is applied to the oxidative coupling reaction of methane (OCM). A four-section experimental apparatus, each section containing a reaction column and two separation columns, is used to quickly separate the reactants and products using the principles of simulated countercurrent flow. Rapid product separation inhibits side reactions. Microreactor trials with a samarium oxide catalyst give yields between 2% and 10%. Yields as high as 50% are observed with the same catalyst and run conditions in the SCMCR. The effects of temperature, feed switching time, and methane to oxygen feed ratio have been investigated. The reactor, while not fully optimized, does give promise as an alternative production method for ethylene.

Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane

The oxidative coupling reaction of methane (OCM) is a potential industrial reaction for the efficient production of ethylene. Replacement of current technologies requires significant product yield improvements. A novel experimental reactor, the simulated countercurrent moving-bed chromatographic reactor (SCMCR), has reported OCM yields which exceed conventional reactors [ Tonkovich et al. , 1993, Science 262 , 221 ; Tonkovich and Carr, 1995, Chem. Engng Sci. (in press) ]. An understanding of the SCMCR operation is aided by concurrent mathematical modeling. The model mimics the experimental reactor configuration and operation. Four sections are used in the SCMCR, each containing one reaction column and two separation columns connected in series. The feed is switched from section to section at a rate less than a single section breakthrough time, and a make-up feed is used after the first cycle. Reaction occurs in the first column and is followed by rapid product and reactant separation in the ensuing section columns. The model does not incorporate the realistic and complex kinetics arising from the OCM, rather a simplified reaction term is used to qualitatively gain insight into the operation of the SCMCR. The effects of the feed switching time and the make-up feed rate are investigated. The reactant conversion has a maximum at intermediate values of both parameters. This agrees with experimental trends, where the methane conversion and the C 2 yield are also maximized at similar intermediate values of the switching time.

The simulated countercurrent moving bed chromatographic reactor: a novel reactor—separator

The simulated countercurrent moving bed chromatographic reactor (SCMCR) is a device for carrying out chemical reaction and separation simultaneously in a fixed bed. This is a novel reactor type in which separation takes place at the site of chemical reaction to improve product purities and conversions beyond those prescribed by thermodynamic equilibrium. The simulated countercurrent system mimics the behavior of a countercurrent moving bed by periodically changing feed and product locations sequentially along a fixed bed. The present investigations endeavor to determine to what extent the moving bed reactor advantages of high product purity and favorable equilibrium shifts are retained in SCMCR operations. An equilibrium stage model of the SCMCR consisting of a single fixed bed having series of inlets and outlets along its length is considered. The mass balance equations are discretized to give an equilibrium plate model. Predictions of the concentration profiles in the column(s) are obtained for the 1,3,5-trimethylbenzene hydrogenation reaction at 463 K. It is shown that reaction and separation can be achieved simultaneously and that the yield of the reversible reaction can be improved greatly. Under appropriate operating conditions, the model calculations predict high-purity product streams and nearly complete conversion of a reaction which would otherwise be limited by equilibrium to 62%.

Methanol synthesis in a simulated countercurrent moving-bed adsorptive catalytic reactor

The continuous chromatographic reactor is a device for carrying out chemical reactions and separations simultaneously in a fixed bed to improve product conversions beyond those predicted by thermodynamic equilibrium. In the simulated countercurrent moving-bed chromatographic reactor a countercurrent moving-bed operation is mimicked by periodically changing feed and product locations sequentially along a fixed bed. In the present work the synthesis of methanol from syngas in a simulated countercurrent moving-bed adsorptive catalytic reactor (SCCMBR) is studied by means of numerical modeling. Two different reactor configurations are considered. In the first, operating under adiabatic conditions, the fixed bed consists of a catalyst and a selective product adsorbent, mixed together. In the other one, operating isothermally, the catalyst and adsorbent are alternately packed in beds containing catalyst or adsorbent, and only adsorber sections participate in a discrete countercurrent movement. The present paper analyzes and compares the performance of these two reactors. In addition, a stripping section is introduced to increase the process conversion by blowing unconverted reactants back to the reaction zone before the product removal step. It is shown that there is a range of operating conditions for which very high carbon monoxide conversions (96–99%) are attainable in a single-pass operation due to adsorption of methanol and its continuous withdrawal with solid adsorbent from reaction zone. The reactors have been simulated for conditions that may be used in a commercial operation. Experimental data from the literature have been used for the calculations to describe reaction kinetics over low-pressure catalyst Cu/ZnO/Al 2 O 3 and adsorption of methanol onto silica-alumina adsorbent.

Methanol synthesis in a simulated countercurrent moving-bed adsorptive catalytic reactor

The continuous chromatographic reactor is a device for carrying out chemical reactions and separations simultaneously in a fixed bed to improve product conversions beyond those predicted by thermodynamic equilibrium. In the simulated countercurrent moving-bed chromatographic reactor a countercurrent moving-bed operation is mimicked by periodically changing feed and product locations sequentially along a fixed bed. In the present work the synthesis of methanol from syngas in a simulated countercurrent moving-bed adsorptive catalytic reactor (SCCMBR) is studied by means of numerical modeling. Two different reactor configurations are considered. In the first, operating under adiabatic conditions, the fixed bed consists of a catalyst and a selective product adsorbent, mixed together. In the other one, operating isothermally, the catalyst and adsorbent are alternately packed in beds containing catalyst or adsorbent, and only adsorber sections participate in a discrete countercurrent movement. The present paper analyzes and compares the performance of these two reactors. In addition, a stripping section is introduced to increase the process conversion by blowing unconverted reactants back to the reaction zone before the product removal step. It is shown that there is a range of operating conditions for which very high carbon monoxide conversions (96–99%) are attainable in a single-pass operation due to adsorption of methanol and its continuous withdrawal with solid adsorbent from reaction zone. The reactors have been simulated for conditions that may be used in a commercial operation. Experimental data from the literature have been used for the calculations to describe reaction kinetics over low-pressure catalyst Cu/ZnO/Al 2O 3 and adsorption of methanol onto silica-alumina adsorbent.

A simulated countercurrent moving-bed chromatographic reactor for the oxidative coupling of methane: Experimental results

A simulated countercurrent moving-bed chromatographic reactor for the oxidative coupling of methane: Experimental results

The simulated countercurrent moving bed chromatographic reactor

The simulated countercurrent moving bed chromatographic reactor (SCMCR) is a device for carrying out chemical reaction and separation simultaneously in a fixed bed. It mimics the behavior of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past a stationary reactant inlet, by periodically changing feed locations sequentially along a fixed bed. True countercurrent motion is thus replaced by a periodic motion, while overcoming the problems of solids handling and attrition inherent in moving bed operations, as well as avoiding the flow channeling that would be attendant with scaleup to large column diameters. The present investigations seek to determine to what extent the moving bed reactor advantages of high product purity and favorable equilibrium shifts are retained in SCMCR operations. Two configurations of the SCMCR, a single fixed bed having a series of inlets and outlets along its length, and a series of columns with an inlet or outlet between each, are considered. Model calculations predict that both configurations give high purity product streams and nearly unit conversions of the equilibrium limited reaction.