Performance of microchannel reactor combined with combustor for methanol steam reforming

The microchannel reactor with combustor for methanol steam reforming was fabricated to produce hydrogen for onboard proton exchange membrane (PEM) fuel cell device. A commercial copper-containing catalyst (Cu/ZnO/Al₂O₃) and Pt/ZrO₂ were used as a catalyst for methanol steam reforming and combustion reaction, respectively. It was found that catalyst layer with zirconia sol solution in microchannel showed no crack on the surface of catalyst layer and an excellent adherence to stainless steel microchannel even after reaction. The temperature of combustor could be controlled between 200 and 300 °C depending on the methanol feed rate. The hydrogen flow of 3.9 l h⁻¹ hydrogen was obtained with the reforming feed flow rate of 3.65 ml h⁻¹ at 270 °C.     

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.     

A hybrid adsorbent-membrane reactor (HAMR) system for hydrogen production

Design characteristics and performance of a novel reactor system, termed a hybrid adsorbent-membrane reactor (HAMR), have been investigated for hydrogen production. The recently proposed HAMR concept couples reactions and membrane separation steps with adsorption on the membrane feed-side or permeate-side. Performance of conventional reactors has been significantly improved by this integrated system. In this paper, an HAMR system has been studied involving a hybrid-type packed-bed catalytic membrane reactor undergoing methane steam reforming through a porous ceramic membrane with a CO₂ adsorption system. This HAMR system is of potential interest to pure hydrogen production for fuel cells for various mobile and stationary applications. Reactor behaviors have been investigated for a range of temperature and pressure conditions. The HAMR system shows enhanced methane conversion, hydrogen yield, and product purity, and provides good promise for reducing the hostile operating conditions of conventional reformers, and for meeting the product purity requirements.     

Computation of reacting electrokinetic flow in microchannel geometries

Devices using an electric field to produce flow in microchannel networks have application to precise chemical reaction, analysis and separation. There is a need for accurate computational design tools that can be used with the physically and geometrically complex conditions of practical devices. The equations governing electrokinetic reacting flow are presented together with classical one-dimensional cases that are directly relevant to the flows in electrokinetic devices. This provides the background for an order of magnitude study of the importance of the various terms in each governing equation, both for the conditions of the double-layer flow and for the main flow in the channel outside the double-layer regions. In agreement with previous studies, for channel widths in the range from several microns to hundreds of microns, it is found that representing the double layer using a local one-dimensional solution to produce the boundary conditions at the walls for the main flow is a good approximation. The ‘layer model’ that emerges is consistent with models proposed in previous studies under more restricted conditions than those considered here, where the role of non-uniform ion species concentration is analysed. The model is applied to the example of alternating reacting flow in a tee junction, both for a two-dimensional and a three-dimensional channel section. The case of the same flow driven by pressure instead of electric field is computed for comparison.     

A composite catalytic polymer membrane reactor using heteropolyacid-blended polymer membrane

The vapor-phase MTBE decomposition was examined in a shell and tube-type catalytic membrane reactor (CMR). 12-Tungstophosphoric acid (PW) was used as a catalyst and poly-2,6-dimethyl-1,4-phenylene oxide (PPO) was used as a polymer material. A single-phase CMR (PW-PPO/Al₂O₃, type-1) and a composite CMR (PW-PPO/ PPO/ Al₂O₃, type-2) were successfully designed and characterized. It was revealed that the single-phase PW-PPO/ Al₂O₃ showed perm-selectivities for reaction products. The selective removal of methanol through the catalytic membrane shifted the chemical equilibrium toward the favorable direction in the MTBE decomposition. The PWPPO/ PPO/ Al₂O₃ showed the better performance than PW-PPO/ Al₂O₃. The enhanced performance of PW-PPO/ PPO/ Al₂O₃ CMR was due to the intrinsic perm-selectivity of PW-PPO and the additional separation capability of sub-layered PPO membrane.     

Propyne hydrogenation in a continuous polymeric catalytic membrane reactor

Propyne hydrogenation was studied in a continuous polymeric catalytic membrane reactor (pCMR), both experimentally and theoretically. It was used a poly(dimethylsiloxane) (PDMS) composite membrane with an average thickness of , loaded with 5 wt% of 9 nm diameter Pd clusters. The reaction was conducted at 308 K and several feed compositions at a fixed flow rate were tested.The mathematical model proposed includes the mass balances to the retentate and permeate chambers and the mass balance and transport kinetics through the catalytic membrane. The pCMR model also considers a reaction rate equation composed of two terms: the propyne to propylene and the propylene to propane hydrogenations. The selectivity between these two reactions is described by the bicomponent adsorption of propyne and propylene obtained by the IAST model (thermodynamic selectivity). The proposed model represents quite well the experimental data regarding the flow rates and mixture compositions of the permeate and retentate streams.     

Hydrogen recovery from cyclohexane as a chemical hydrogen carrier using a palladium membrane reactor

A palladium membrane reactor was applied to recover the hydrogen from cyclohexane as one of the promising chemical hydrogen carriers. The operation conditions of the palladium membrane reactor to obtain a higher hydrogen recovery were predicted by computer simulation. As a result, it was shown that the hydrogen recovery rate becomes higher as the pressure on the hydrogen permeation side is lowered below atmospheric pressure or as the reaction pressure increases. This was confirmed experimentally. As the perm-side pressure was lowered, the conversion as well as the hydrogen recovery rate at 573 K was found to increase. About 80% of the hydrogen contained in cyclohexane, depending on the operation condition was successfully recovered.     

Influence of the operating conditions on yield and selectivity for the partial oxidation of ethane in a catalytic membrane reactor

In this study, simulation results are presented for the partial oxidation of ethane to ethylene in a Catalytic Membrane Reactor (CMR) under isothermal and non-isothermal conditions. Considering the importance of the transport processes, a 2D model was developed and implemented in FLUENT^® using self-designed program modules for reaction kinetics, transport properties and post-processing. An analysis of significance of the influencing variables is carried out on the basis of a reference case. The number of parameters were minimized by the dimensionless formulation of the model. One of the most important variables is the oxygen dosage through the membrane. Both velocity and oxygen concentration of the trans-membrane stream were varied with the aim of attaining maximum ethylene yield. The results of the different simulations clearly show the advantages of the CMR compared to the Catalytic Wall Reactor (CWR). The numerical simulations are essential in order to reduce the experimental costs and to evaluate different reactor concepts.     

Hydrogen generation and purification in a composite Pd hollow fiber membrane reactor: Experiments and modeling

“Pd nanopore” composite membranes are a novel class of H₂ permselective membranes in which a thin layer of Pd is grown within the pores of a supported nanoporous layer. In this work, Pd nanopore membranes and conventional Pd top-layer membranes were used in the generation of high-purity H₂ from the catalytic decomposition of anhydrous NH₃. An effective 4 μm thick Pd nanopore membrane and 13 μm thick Pd top-layer membrane were synthesized on 2 mm O.D. α-Al₂O₃ hollow fibers. The permeation features of the membranes were determined and the membranes were then employed in a single fiber packed-bed membrane reactor in which Ni-catalyzed NH₃ decomposition served as the test reaction, with conditions spanning a range of conditions (500–600 °C; 3–5 bar total retentate pressure; 60–1200 scc/h g cat space velocity). The NH₃ conversions in both the PBMRs were approximately 10% higher than in a packed-bed reactor (PBR) under similar conditions. The increase in conversion with the PBMR was attributed to the removal of H₂, which has an inhibitory effect on the forward kinetics of the reaction as per the Temkin-Pyzhev type rate mechanism. Reactor productivities in the range of 2 mol/s m³ (at 85% H₂ utilization) to 7 mol/s m³ (at 50% H₂ utilization) were obtained. The permeate stream purity exceeded 99.2% H₂. A two-dimensional pseudo-homogeneous model was successfully used to simulate the experimental results and to interpret the findings. Permeation and kinetic parameters were estimated in permeation and PBR experiments, respectively. Without any data fitting the PBMR model predictions demonstrated very good agreement with experimental trends. Together with an analysis of the characteristic times, the model determined that transverse transport of hydrogen in the catalyst bed limited PBMR performance. The model was used to determine the rate limiting step and to suggest ways in which the reactor productivities could be further improved.     

Mass transfer measurements and modeling in a microchannel photocatalytic reactor

The main objective of this paper was to evaluate the influence of mass transfer on the photocatalytic efficiency at a low flow rate in the order of several mL per hour. Several continuous flow microchannel reactors have been used to study the degradation of salicylic acid (SA) taken as a model pollutant. The photocatalytic degradation of salicylic acid, under UV illumination of 1.5 mW cm⁻², was assessed from the outlet concentration measured by liquid chromatography HPLC. It was shown that the degradation of SA by UV was limited by mass transfer. Numerical simulations have allowed establishing a relationship of the Sherwood number valuable for all the microchannel geometries. Computational fluid dynamics with Comsol Multiphysics is useful for predicting the degradation yield for a given geometry of the microreactor. The best representation of the experimental data is obtained by introducing a kinetic law taking into account mass transfer limitation.     

Optimal design conditions for dehydrogenation of cyclohexane in a membrane reactor

The design variables of a membrane reactor, such as the permeation rate through the membrane and catalyst loading in the membrane, have received little attention in comparison with the operating conditions. A non-dimensionalized model for a membrane reactor was developed to account for the effects of permeation rate and catalyst loading. The increased permeation rate did not always increase the exit conversion and there existed a maximum point of exit conversion. At isothermal conditions, the exit conversion was saturated as catalyst loading was increased; however, when the reactor was under non-isothermal condition along the axial direction, there existed an optimum catalyst loading at which the exit conversion was maximum. With this model, the optimal configuration of permeation rate and catalyst loading could be determined.     

Photochemical heterogeneous catalytic reaction at recirculated reactor system

A study was undertaken to examine the possibility of combining a batch-recirculated photoreactor with a ceramic membrane filter for heterogeneous photocatalysis applications. D-cargo red GS (GS) was used as the test substrate and titanium dioxide was used as photocatalyst for this study. The dark adsorption of GS on the TiO₂ particle surface was also analyzed. The adsorption trends of GS at various initial concentrations followed the Langmuir isotherm trend. The GS were decolorized from 20% to 70% by the dark adsorption with various concentrations. The photodegradation of GS after the dark adsorption showed the behavior of Langmuir-Hinshelwood model. The variation of recirculation flow rate did not much influence photocatalysis. Variation tendencies of GS concentration were almost similar after about 90 minutes illumination in spite of the flow rate change. The values ofk (apparent first order rate constant) also varied with increase of the recirculation flow rate, but there were no observable significant differences between them. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Hydrogen production via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system

Hydrogen production was prepared via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system. Low-cost catalyst dolomite was chosen for the primary steam reforming of bio-oil in consideration of the unavoidable deactivation caused by direct contact of metal catalyst and bio-oil itself. Nickel-based catalyst Ni/MgO was used in the second stage to increase the purity and the yield of desirable gas product further. Influential parameters such as temperature, steam to carbon ratio (S/C, S/CH₄), and material space velocity (W_BHSV, GHSV) both for the first and the second reaction stages on gas product yield, carbon selectivity of gas product, CH₄ conversion as well as purity of desirable gas product were investigated. High temperature (> 850 °C) and high S/C (> 12) are necessary for efficient conversion of bio-oil to desirable gas product in the first steam reforming stage. Low W_BHSV favors the increase of any gas product yield at any selected temperature and the overall conversion of bio-oil to gas product increases accordingly. Nickel-based catalyst Ni/MgO is effective in purification stage and 100% conversion of CH₄ can be obtained under the conditions of S/CH₄ no less than 2 and temperature no less than 800 °C. Low GHSV favors the CH₄ conversion and the maximum CH₄ conversion 100%, desirable gas product purity 100%, and potential hydrogen yield 81.1% can be obtained at 800 °C provided that GHSV is no more than 3600 h^− 1. Carbon deposition behaviors in one-stage reactor prove that the steam reforming of crude bio-oil in a two-stage fixed bed reaction system is necessary and significant.     

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogena-tion method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and significant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.     

Hydrogen separation from the H2/N2 mixture by using a single and multi-stage inorganic membrane

The separation characteristics of hydrogen from a gas mixture were investigated by using a single and two-stage inorganic membrane. Three palladium impregnated membranes were prepared by using the sol-gel, hydrolysis, and soaking-and-vapor deposition (SVD) techniques. A two-stage gas separation system without a recycling stream was constructed to see how much the hydrogen separation factor would be increased. Numerical simulation for the separation system was conducted to predict the separation behavior for the multi-stage separation system and to determine the optimal operating conditions at which the highest separation factor is obtained. Gas separation through each prepared membrane was achieved mainly by Knudsen diffusion. The real separation factor for the H₂/ N₂ mixture was increased with the pressure difference and temperature for a single stage, respectively. For the twostage separation system, there was a maximum point at which the highest separation factor was obtained and the real hydrogen separation factor for H₂/N₂ mixture was increased about 40 % compared with a single stage separation. The numerical simulation for the single and two-stage separation system was in a good agreement with the experimental results. By numerical simulation for the three-stage separation system, which has a recycle stream and three membranes that have the same permeability and hydrogen selectivity near to the Knudsen value, it is clear that the hydrogen separation factors for H₂/N₂ mixture are increased from 1.8 to 3.65 and hydrogen can be concentrated up to about 80 %. The separation factors increased with increasing recycle ratio. Optimal operating conditions exist at which the maximum real separation factor for the gas mixture can be obtained for three-stage gas separation and they can be predicted successfully by numerical simulation.     

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al₂O₃ catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al₂O₃ catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion.

The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.     

The effect of operating conditions on acylation of 2-methylnaphthalene in a microchannel reactor

Acylation of 2-methylnaphthalene(2-MN) is a very important reaction in organic synthesis,and the effiency of the continuous reactor is more than one of the batch reactor.Considering that the Friedel–Crafts acylation is a rapid exothermic reaction,in this study,we perform the acylation of 2-MN in a stainless steel microchannel flow reactor,which is characterized by high mass and heat transfer rates.The effect of reactant ratio,mixing temperature,reaction temperature,and reaction time on product yield and selectivity were investigated.Under the optimal conditions,2-methyl-6-propionylnaphthalene(2,6-MPN) was obtained in 85.8% yield with 87.5% selectivity.Compared with the conventional batch system,the continuous flow microchannel reactor provides a more efficient method for the synthesis of 2,6-MPN.     

旋叶动态膜分离式酶解反应器酶解糊精的实验研究

研究了旋叶动态膜分离式酶解反应器的主轴转速、底物浓度和循环量等操作参数对糖化酶酶解糊精反应的影响 ,测定固定化酶反应的动力学参数 ,并对其适宜操作条件进行了探索     

Catalytic combustion assisted methane steam reforming in a catalytic plate reactor

A theoretical study of methane steam reforming coupled with methane catalytic combustion in a catalytic plate reactor (CPR) based on a two-dimensional model is presented. Plates with coated catalyst layers of order of micrometers at distances of order of millimetres offer a high degree of compactness and minimise heat and mass transport resistances. Choosing similar operating conditions in terms of inlet composition and temperature as in industrial reformer allows a direct comparison of CPRs with the latter. It is shown that short distance between heat source and heat sink increases the efficiency of heat exchange. Transverse temperature gradients do not exceed across the wall and across the gas-phase, in contrast to difference in temperature of outside wall and mean gas phase temperature inside the tube usually observed in conventional reformers. The effectiveness factors for the reforming chemical reactions are about one order of magnitude higher than in conventional processes. Minimisation of heat and mass transfer resistances results in reduction of reactor volume and catalyst weight by two orders of magnitude as compared to industrial reformer. Alteration of distance between plates in the range 1- does not result in significant difference in reactor performance, if made at constant inlet flowrates. However, if such modifications are made at constant inlet velocities, conversion and temperature profiles are considerably affected. Similar effects are observed when catalyst layer thicknesses are increased.     

Test results of a catalytic combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. Combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected. A combustor for multi-can type gas turbine of 10 MW class was designed and tested at high-pressure conditions using liquefied natural gas (LNG) fuel. This combustor is composed of a burner system and a premixed combustion zone in a ceramic type liner. The burner system consists of catalytic combustor segments and premixing nozzles. Catalyst bed temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to catalytic combustion gas and lean premixed combustion is carried out in the premixed combustion zone. As a result of the combustion tests, NO_x emission was lower than 5 ppm converted at 16% O₂ at a combustor outlet temperature of 1350°C and a combustor inlet pressure of 1.33 MPa.