Exothermic Side Research Articles

Simultaneous utilization of two different membranes for intensification of ultrapure hydrogen production from recuperative coupling autothermal multitubular reactor

The potential of simultaneous hydrogen production and in situ water removal in a thermally coupled multitubular two-membrane reactor (TCTMR) were studied numerically. Methanol synthesis is carried out in exothermic side with H-SOD membrane 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. Therefore, the proposed reactor consists of two membranes, one for separation of pure hydrogen from endothermic side and another one for separation of water from exothermic side. The motivation for in situ H 2O removal during methanol synthesis by using H-SOD membranes is to displace the water–gas shift equilibrium to enhance conversion of CO 2 to improve methanol productivity. A steady-state 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 TCTMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCTMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. Furthermore, lower water production rate in TCTMR reduces catalyst re-crystallization.

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.

Differential evolution (DE) strategy for optimization of hydrogen production and utilization in a thermally coupled membrane reactor for decalin dehydrogenation and Fischer–Tropsch synthesis in GTL technology

In this study, the operating conditions of a thermally coupled membrane reactor (TCMR) in gas-to-liquid (GTL) technology are optimized via differential evolution (DE) method to maximize the hydrogen mole fraction in the endothermic side as well as the gasoline yield in the exothermic side. TCMR is designed as a double pipe reactor where highly exothermic Fischer–Tropsch synthesis (FTS) reactions in the exothermic side are coupled with decalin dehydrogenation reaction in the endothermic side. The minimum required hydrogen molar flow rate in the recycled stream is optimized to compensate a hydrogen lack at the end of the reactor in the exothermic side. The optimization results show 14.28% increase in the gasoline yield in optimized TCMR compared with conventional tubular reactor (CR). Moreover, 81.49% hydrogen is produced in the endothermic side and about 1% hydrogen is recycled to the exothermic side for utilization in FTS reactions in optimized TCMR.

Enhancement of hydrogen production via coupling of MCH dehydrogenation reaction and methanol synthesis process by using thermally coupled heat exchanger reactor

In the present study, hydrogen and methanol production rates are simultaneously investigated through the process intensification (PI) concept. PI is a strategy for reduction of emissions as well as consumption of energy and materials. Endothermic dehydrogenation of methylcyclohexane is supposed to occur in the shell side of conventional methanol synthesis reactor. The reactor is consisted of two thermally coupled concentric tubular reactors. The rate of the dehydrogenation reaction can be adjusted according to the generated heat in the exothermic side. This is like a smart cooler. By using this new configuration, the equilibrium condition in the methanol synthesis (at the last part of the reactor) can be controlled in order to enhance the production rate. The effect of various operating conditions is investigated through this article. The results of simulation are compared with the corresponded outcome of the conventional methanol reactor. Innovations in reactor configuration, which somehow could be the heart of chemical processes, are often preferred to be the starting point of revamping a process. An investigation in relation to the environmental aspects, commercial viability and economic feasibility of the proposed configuration is necessary in order to consider commercialization of the process.

Optimization of hydrogen production via coupling of the Fischer–Tropsch synthesis reaction and dehydrogenation of cyclohexane in GTL technology

In this study, a thermally-coupled reactor containing the Fischer–Tropsch synthesis reaction in the exothermic side and dehydrogenation of cyclohexane in the endothermic side has been modified using a hydrogen perm-selective membrane as the shell of the reactor to separate the produced hydrogen from the dehydrogenation process. Permeated hydrogen enters another section called permeation side to be collected by Argon, known as the sweep gas. This three-sided reactor has been optimized using differential evolution (DE) method to predict the conditions at which the reactants’ conversion and also the hydrogen recovery yield would be maximized. Minimizing the CO 2 and CH 4 yield in the reactor’s outlet as undesired products is also considered in the optimization process. To reach this goal, optimal initial molar flow rate and inlet temperature of three sides as well as pressure of the exothermic side have been calculated. The obtained results have been compared with the conventional reactor data of the Research Institute of Petroleum Industry (RIPI), the membrane dual – type reactor suggested for Fischer–Tropsch synthesis, and the membrane coupled reactor presented for methanol synthesis. The comparison shows acceptable enhancement in the reactor’s performance and that the production of hydrogen as a valuable byproduct should also be considered.

A novel integrated thermally coupled configuration for methane-steam reforming and hydrogenation of nitrobenzene to aniline

In this work, a novel thermally coupled reactor containing the steam reforming process in the endothermic side and the hydrogenation of nitrobenzene to aniline in the exothermic side has been investigated. In this novel configuration, the conventional steam reforming process has been substituted by the recuperative coupled reactors which contain the steam reforming reactions in the tube side, and the hydrogenation reaction in the shell side. The co-current mode is investigated and the simulation results are compared with corresponding predictions for an industrial fixed-bed steam reformer reactor operated at the same feed conditions. The results show that although synthesis gas productivity is the same as conventional steam reformer reactor, but aniline is also produced as an additional valuable product. Also it does not need to burn at the furnace of steam reformer. The performance of the reactor is numerically investigated for different inlet temperature and molar flow rate of exothermic side. The reactor performance is analyzed based on methane conversion, hydrogen yield and nitrobenzene conversion. The results show that exothermic feed temperature of 1270 K can produce synthesis gas with 26% methane conversion (the same as conventional) and nitrobenzene conversion in the outlet of the reactor is improved to 100%. This new configuration eliminates huge fired furnace with high energy consumption in steam reforming process.

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.

Optimal conditions for hydrogen production from coupling of dimethyl ether and benzene synthesis

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions followed by hydrogen permeation through the Pd/Ag membrane improves the thermal efficiency of processes, achieving the autothermality within the reactor, reduces the size of reactors, produces the pure hydrogen, and achieving a multiple reactants multiple products configuration. This paper focuses on optimization of hydrogen, dimethyl ether (DME) and benzene production in a membrane thermally coupled reactor. A steady-state heterogeneous mathematical model that is composed of three sides is developed to predict the performance of this novel configuration reactor. The catalytic methanol dehydration to DME takes place in the exothermic side that supplies the necessary heat for the catalytic dehydrogenation of cyclohexane to benzene reaction in the endothermic side. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. This novel configuration can decrease the temperature of methanol dehydration reaction in the second half of the reactor and shift the thermodynamic equilibrium. The differential evolution (DE), an exceptionally simple evolution strategy, is applied to optimize membrane thermally recuperative coupled reactor considering the summation of methanol and cyclohexane conversions and dimensionless hydrogen recovery yield as the main objectives. The simulation results have been shown that there are optimum values of initial molar flow rate of exothermic and endothermic sides and inlet temperature of exothermic, endothermic and permeation sides to maximize the objective function. The optimization method has enhanced the methanol conversion by 2.76%. The optimization results are compared with corresponding predictions for a conventional (industrial) methanol dehydration adiabatic reactor operated at the same feed conditions. The results suggest that coupling of these reactions could be feasible and beneficial. An experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.

Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor

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 steady-state 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.

A comparison of conventional and optimized thermally coupled reactors for Fischer–Tropsch synthesis in GTL technology

In this research, the conditions at which a thermally coupled reactor – containing the Fischer–Tropsch synthesis reactions and the dehydrogenation of cyclohexane – operates have been optimized using differential evolution (DE) method. The proposed reactor is a heat exchanger reactor consists of two fixed bed of catalysts separated by the tube wall with the ability to transfer the produced heat from the exothermic side to the endothermic side. This system can perform the exothermic Fischer–Tropsch (F–T) reactions and the endothermic reaction of cyclohexane dehydrogenation to benzene simultaneously which can save energy and improve the reactions' thermal efficiency. The objective of the research is to optimize the operating conditions to maximize the gasoline (C 5 +) production yield in the reactor's outlet as a desired product. The temperature distribution limit along the reactor to prevent the quick deactivation of the catalysts by sintering at both sides has been considered in the optimization process. The optimization results show a desirable progress compared with the conventional single stage reactor. Optimal inlet molar flow rate and inlet temperature of exothermic and endothermic sides and pressure of exothermic side have been calculated within the practicable range of temperature and pressure for both sides.

Mathematical modeling of a multi-stage naphtha reforming process using novel thermally coupled recuperative reactors to enhance aromatic production

In this study, a novel thermally coupled reactor containing the naphtha reforming process in the endothermic side and the hydrogenation of nitrobenzene to aniline in the exothermic side has been investigated. Considering the higher thermal efficiency as well as the smaller size of the reactor, utilizing the recuperative coupled reactor is given priority. In this novel configuration, the first and the second reactor of the conventional naphtha reforming process have been substituted by the recuperative coupled reactors which contain the naphtha reforming reactions in the shell side, and the hydrogenation reaction in the tube side. The achieved results of this simulation have been compared with the results of the conventional fixed-bed naphtha reforming reactors. Acceptable enhancement can be noticed in the performance of the reactors. The production rate of the high octane aromatics and the consumption rate of the paraffins have improved 17% and 72%, respectively. The conversion of the nitrobenzene is acceptable and the effect of the number of the tubes also has been taken into account. However, the performance of the new configuration needs to be tested experimentally over a range of parameters under practical operating conditions.

Differential evolution (DE) strategy for optimization of hydrogen production, cyclohexane dehydrogenation and methanol synthesis in a hydrogen-permselective membrane thermally coupled reactor

In this work a novel reactor configuration has been proposed for simultaneous methanol synthesis, cyclohexane dehydrogenation and hydrogen production. This reactor configuration is a membrane thermally coupled reactor which is composed of three sides for methanol synthesis, cyclohexane dehydrogenation and hydrogen production. Methanol synthesis takes place in the exothermic side that supplies the necessary heat for the endothermic dehydrogenation of cyclohexane reaction. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. A steady-state heterogeneous model of the two fixed beds predicts the performance of this configuration. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol, benzene and hydrogen production in a membrane thermally coupled reactor. The co-current mode is investigated and the optimization results are compared with corresponding predictions for a conventional (industrial) methanol fixed bed reactor operated at the same feed conditions. The differential evolution (DE), an exceptionally simple evolution strategy, is applied to optimize this reactor considering the mole fractions of methanol, benzene and hydrogen in permeation side as the main objectives. The simulation results have been shown that there are optimum values of initial molar flow rate of exothermic and endothermic stream, inlet temperature of exothermic, endothermic and permeation sides, and inlet pressure of exothermic side to maximize the objective function. The simulation results show that the methanol mole fraction in output of reactor is increased by 16.3% and hydrogen recovery in permeation side is 2.71 yields. The results suggest that optimal coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.

A novel configuration for hydrogen production from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions improve the thermal efficiency of processes and reduce the size of the reactors. One type of reactor suitable for such a type of coupling is the heat-exchanger reactor. In this work, a distributed mathematical model for thermally coupled membrane reactor that is composed of three sides is developed for methanol and benzene synthesis. Methanol synthesis takes place in the exothermic side and supplies the necessary heat for the endothermic dehydrogenation of cyclohexane reaction. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. A steady-state heterogeneous model of the two fixed beds predicts the performance of this novel configuration. The co-current mode is investigated and the simulation results are compared with corresponding predictions for an industrial methanol fixed-bed reactor operated at the same feed conditions. The results show that although methanol productivity is the same as conventional methanol reactor, but benzene is also produced as an additional valuable product in a favorable manner, and auto-thermal conditions are achieved within the both reactors and also pure hydrogen is produced in permeation side. This novel configuration can increase the rate of methanol synthesis reaction and shift the thermodynamics equilibrium. The performance of the reactor is numerically investigated for various key operating variables such as inlet temperatures, molar flow rates of exothermic and endothermic streams, membrane thickness and sweep gas flow rate. The reactor performance is analyzed based on methanol yield, cyclohexane conversion and hydrogen recovery yield. The results suggest that coupling of these reactions in the presence of membrane could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.

Influence of Flow Arrangement in Catalytic Plate Reactors for Methane Steam Reforming

A theoretical study of the influence of flow arrangement on the thermal behaviour of a catalytic plate reactor (CPR) for steam reforming of methane using methane catalytic combustion as heat source based on a two-dimensional model is presented. CPR performance and thermal behaviour is strongly affected by overall and local balance between heat generated on the exothermic side and heat consumed on the endothermic one, which in turn is influenced by flow arrangement. Simulations for co-current and counter-current flow were carried out for similar inlet conditions and catalyst loadings. It was found that the reactor is better balanced thermally for co-current operation. For counter-current arrangement, higher conversions and better utilization of the overall heat generated in the exothermic process are achieved at the expense of pronounced temperature extremes. Thus, reforming conversion for counter-current operation is 62.8% compared with 52% for co-current operation, whilst maximum transverse temperature difference for co-current operation is only 16.5K compared with 310K for counter-current operation. This increases the chances of the reactor running away and of homogeneous combustion being initiated. Utilization of a non-uniform catalyst distribution can overcome the heat imbalance by inducing favourable reactant depletion along the reactor during counter-current flow.

2251 小型ニッケル水素電池の急速充放電時の発熱挙動

The nickel/metal hydride battery (Ni/MH) has been developed as a power source for the hybrid electric vehicle (HEV) and the pure electric vehicle (PEV). But the large battery with heavy duty cycle by more rapid charge and discharge than today's is desirable for the diffusion of HEV and PEV. Therefore the thermal behavior of Ni/MH battery must be understood precisely for the battery size enlargement and its performance improvement. In this report the thermal behavior of small Ni/MH battery during rapid charge and discharge cycle has been studied numerically and experimentally by considering the entropy charges by electrochemical reactions, the endothermic reaction by hydrogen occlusion to MH, the heat generation by an exothermic side reaction and by overpotential and the heat transfer to the ambient air. The calculated cell temperature agrees well with the measured under both the charge and discharge cycles below the rated current, but the calculated is larger than the measured above the rated current.

Continuously stirred decanting reactor: Operability and stability considerations

AbstractA continuously stirred decanting reactor (CSDR) is a well‐mixed vessel fed with two immiscible liquid phases, while its effluent consists of a single phase containing the reaction products. We consider a CSDR in which a desired highly exothermic reaction occurs in one phase, while an undesirable exothermic side reaction occurs in the second extracting phase. The holdup of the two phases in the CSDR is sensitive to its temperature. Thus, the reactor has to be kept in a narrow temperature range to avoid break‐through, that is, with effluent containing both phases, and to maintain a high selectivity of the desired product. Pilot‐plant data for a proprietary selective‐oxidation process verified the predictions of the steady‐state model.A high rate of heat generation may lead to various exotic and undesired periodic and aperiodic oscillations, which may shift the reactor out of the region of safe operation and have deleterious impact on the decantation efficiency. In some cases, the oscillations lead to a breakthrough during part of the period. To avoid these oscillatory states, one may have to maintain a sufficiently small difference between the reactor and coolant temperatures. We show how loci of local and global singular points of codimension 1 and 2 can be used to construct maps of parameter regions with qualitatively different steady‐state and dynamic bifurcation diagrams. These maps clearly describe the desirable regions of operation and point out all the potential stability and operability issues in other regions.

Weight Loss Behavior of Straight-Chain Saturated Fatty Acids

Weight loss and characterization of straight chain saturated fatty acids (even-numbered fatty acids : 8 kinds, odd-numbered fatty acids : 7 kinds) were studied by dynamic programmed thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC).1) Initial weight losses and weight loss curves of straight chain fatty acids under air and under nitrogen shifted only to the higher-temperature side with increase in carbon number. Weight loss patterns were simple and essentially the same to each other. The DSC curve of each fatty acid under air differed markedly from that under nitrogen. The curves of fatty acids under nitrogen shifted to the endothermic side. Under air, the DSC curves of fatty acids ranging from heptanoic to tridecanoic acids, also shifted to the endothermic side. However, the curves of fatty acids having carbon numbers exceeding that of tetradecanoic acid shifted to the exothermic side.2) GLC analysis of volatile and residual substances at the temperature corresponding to 25 % weight loss on TG indicated to the weight loss of fatty acid until to possibly be due primarily to evaporation of the fatty acid. However, the residual rate after the peak temperature of DTG increased with carbon number, this being particularly evident in the case of exposure to the air flow. Weight loss in the air flow is thus shown to be accompanied by decomposition.3) The peak temperature of DTG curve was closely correlated to fatty acid boiling point. However, the regression line in the air flow was situated on the lower-temperature side than that in the case of the nitrogen flow, due to accompanying decomposition.

Calorimetric studies of stereoselective vanadyl(IV) tartrate reactions

A ΔH of −1·46±0·10 kcal/mole has been determined for the reaction 1 2 [( VO) 2(d- C 4 H 2 O 6) 2] 4− + 1 2 [( VO) 2(l- C 4 H 2 O 6) 2] 4− → [( VO) 2(d- C 4 H 2 O 6)(l- C 4 H 2 O 6)] 4− (“C 4H 2O 6”=tartrato(4-) ligand) in aqueous solution at 298°K in the concentration region [V(IV)]=0·1 to 0·2 M. That the ΔH value observed for the reaction [(VO) 2( l-C 4H 2O 6) 2] 4− + d-C 4H 4O 6 2− → [(VO) 2( d-C 4H 2O 6)( l-C 4H 2O 6)] 4− + l-C 4H 4O 6 2− in the presence of excess ligand is less negative than that observed for the ligand exchange reaction between the binuclear enantiomeric complexes indicates the presence of an exothermic side reaction—probably [(VO) 2(C 4H 2O 6) 2] 4− + 2C 4H 4O 6 2− → 2[(VO)(C 4H 3O 6) 2] 4−. A barrier to rotation of 3 kcal/mole has been estimated for the tartrato(4-) bridging ligand to account for the enthalpy difference between the active and racemic binuclear vanadyl(IV) tartrate(4-) complexes. A value of 24 is calculated for the equilibrium constant of the ligand exchange reaction between the enantiomeric vanadyl(IV) binuclear complexes from the experimental ΔH and the predicted ΔS of 1·37 cal/mole-deg.