Palladium Membrane Reactor Research Articles

Theoretical Investigation of a Pd‐membrane Reactor for Methanol Synthesis

AbstractA numerical study is performed in order to evaluate the performance and optimal operating conditions of a palladium membrane reactor for methanol synthesis. A novel reactor configuration with a Pd wall, which is perm‐selective to hydrogen, has been proposed. In this configuration the reactants are added to the tube side while pure hydrogen is added to the shell side, as a result, the hydrogen diffuses across the membrane from the shell side to the tube side. In this membrane reactor, hydrogen penetrates to the reaction side in order to maintain a suitable hydrogen level in the whole length of the reactor and shift the equilibrium reaction. The effects of different parameters on the methanol output mole fraction were investigated in the co‐current mode. These parameters were membrane thickness, reaction side flow rate, reaction side pressure, shell side pressure and H2/CO2 ratio in the feed.

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.

Effect of incipient removal of hydrogen through palladium membrane on the conversion of methane steam reforming: Experimental and modeling

This paper presents a mathematical model based on the reaction rate expressions to describe the displacement of methane conversion in the steam reforming. The effect of several parameters including weight hourly space velocity (WHSV), load-to-surface ratio, reaction pressure, hydrogen partial pressure in permeate side and reaction temperature were investigated. Simulation and experimental results showed that a conversion higher than 80% could be achieved in a palladium membrane reactor at reaction temperature of 500 °C relative to 850 °C in a conventional fixed bed reactor (FBR). Besides, the yield of CO (<2%) in membrane reactor was much lower than that (>50%) in the FBR, which indicated the significant depression of CO production in use of membrane reactor.

Efficient Hydrogen Production via Methanol Steam Reforming by Preventing Back-permeation of Hydrogen in a Palladium Membrane Reactor

It was found that hydrogen recovery in a palladium membrane reactor is depressed by the back-permeation of hydrogen from the perm-side to the reforming side near the inlet of the reactor, where the partial pressure of hydrogen on the reforming side is lower than that of the perm-side because the reaction has just started. To diminish this phenomenon, three methods, (1) use of a sweep gas, (2) premixing hydrogen into the feed, and (3) extension of the catalyst bed, were examined by simulation as well as experimentally. As a result, it was shown that the first method, if one uses steam as the sweep gas, is useful in a fuel cell system requiring humidified hydrogen. The second one is not as effective because the hydrogen amount recovered is less than that premixed. The third one is the best for obtaining pure hydrogen.

Simulation of Hydrogen Production from Dehydrogenation of Ethanol in a Palladium Membrane Reactor

In this study, we have employed a Runge-Kutta numerical method to simulate the hydrogen production from the dehydrogenation of ethanol in a palladium membrane reactor. The reacting system consists of a double-tube reactor with a palladium membrane coated on the inner porous stainless steel tube. The shell side is loaded an appropriate amount of active catalyst over which the dehydrogenation of ethanol occurs. An empirical rate law from Franckaerts and Froment (1964) is used to describe the ethanol dehydrogenation behavior. One-dimensional plug flow, negligible axial dispersion of heat and mass transfer, and negligible radial gradients of temperature and concentration are assumed before conducting the numerical simulation. The simulation results show that the membrane reactor, which combines reaction and separation in a single unit, not only increases the reaction conversion, but also improves the efficiency of the reactor. When the ethanol feed is 2.37×10-6 mole/s and with a purge gas flow rate of 10-3 mole/s in the permeation side, the conversion will achieve 100% which exceed the equilibrium value of 81.7%. With proper operating conditions, 100% recovery of hydrogen can be achieved either by using a high flow rate of purge gas in the separation side or by reducing the pressure of separation side to nearly vacuum.

Methane Conversion to Syngas in a Composite Palladium Membrane Reactor with Increasing Number of Pd Layers

Syngas is a valuable raw material for the production of higher hydrocarbons, methanol, and ammonia. Currently, this gas mixture is obtained industrially from methane steam reforming. An alternative route could be the partial oxidation of methane. However, both processes have thermodynamic constraints. Membrane reactors offer the possibility of overcoming the equilibrium conversion through the selective removal of one of the products from the reaction zone. In particular, a palladium membrane enables only hydrogen product to permeate through it, shifting equilibrium toward conversions higher than those that can be obtained at thermodynamic equilibrium. This work focuses on the experimental behavior of both a traditional reactor (TR) and a composite ceramic multilayered palladium membrane reactor (MR) having the same geometrical dimensions and the same amount of a Ni-based catalyst. Their performances are compared in terms of methane conversion to syngas and hydrogen selectivity. An analysis of methane conv...

Simulation of a Palladium Membrane Reactor for Dehydrogenation of Ethylbenzene.

Mathematical models taking into account the non-isothermal condition and radial heat and mass transfer for the dehydrogenation of ethylbenzene to styrene in a conventional fixed-bed reactor and a palladium membrane reactor were developed using the kinetic data of a 70 wt% F2O3:20 wt% K2O:5 wt% Ce2O:5 wt% Cr2O3 catalyst and the H2 permeation data through a palladium membrane with 10 μm thickness. The study showed that due to the continuous removal of H2 from the reaction side, both the conversion and the selectivity obtained from the membrane reactor were superior to those of the conventional fixed-bed reactor. It was shown by the theoretical study that the assumptions of isothermal and plug-flow conditions overestimated the performance of the reactors. The membrane reactor with a catalyst packed in the shell side showed superior performance to the one with a catalyst packed in the tube side because the former had lower heat transfer resistance than the latter. The operating modes in the separation side played an important role in determining the reactor performance. The use of reactive sweep gas did not only rapidly consume the permeating H2 but also supplied additional heat to the reaction side; however, the resulting performance may be interior to the other operating modes such as vacuum and inert sweep gas modes.

Application of Palladium Membrane Reactor for Dehydrogenation of Propane

The dehydrogenation of propane in palladium membrane reactors was simulated using two models, i.e. the plug flow and radial diffusion models. The expression of hydrogen permeation through a Pd-Ag membrane was obtained from experiments at 673,773 and 873 K, assuming that the permeation follows Sievert’s law. The simulation results agreed well with the experimental values in the membrane reactor for the dehydrogenation of propane on Pt-Sn-K/γ-Al2O3. The membrane thickness played an important role in the performance of the membrane reactor. The conversion of propane was independent of the N2 sweep flow rate when the membrane thickness was larger than 100 μm. Conversely, when the membrane thickness decreased, the conversion increased and gradually leveled off. The effect of radial diffusion was significant at a membrane thickness of 10 μm.

An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas

Today only a small percentage of methane is used as a chemical feedstock to produce syngas that is a valuable feedstock for the production of higher hydrocarbons or methanol. Currently, the process extensively used in industry for the production of syngas is the steam reforming of methane in large furnaces. The reaction is industrially operated under strong conditions resulting in several undesirable consequences: sintering of the catalyst, danger of explosion, very high carbon deposition and the use of high-temperature resisting materials. A potential alternative technique to steam reforming processes for producing syngas is the partial oxidation of methane with oxygen, having over steam reforming the disadvantage that pure oxygen is required. Utilisation of air instead of pure oxygen is beneficial only if it can be performed by using a membrane reactor in which the membrane is permselective to oxygen. Another route to produce syngas using the partial oxidation of methane is offered by membrane reactors, i.e. engineering systems that combine the separation properties of membrane with the typical characteristics of catalytic reactions. It is well known that the use of dense palladium as membrane enables hydrogen product to permeate out through the membrane, shifting thereby conversions towards the values higher than thermodynamic equilibrium ones and providing pure hydrogen product. In fact, only hydrogen is allowed to permeate through dense palladium membranes. In this work five reactors are investigated with respect to the partial oxidation of methane. In particular, the performance of a traditional reactor (TR), three composite ceramic palladium membrane reactors (MRa, MRb and MRc), and a dense palladium membrane Reactor (PMR), all having the same geometrical dimensions and using the same Ni-based catalyst, are evaluated in terms of experimental results of methane conversion to syngas and in terms of hydrogen selectivity. A comparison between methane conversion at various temperatures and data in literature is also presented.

The partial oxidation of methane to syngas in a palladium membrane reactor: simulation and experimental studies

Among numerous potential applications of inorganic membrane reactors, the partial oxidation of methane (POM) may offer an alternative route, with respect to steam reforming of methane, for producing synthesis gas. Inorganic membrane reactors are considered to be multifunctional reactors because they are able to combine catalytic reactions with membrane separation properties. In particular, dense palladium membranes are characterised by the fact that: (1) only hydrogen might permeate through them; (2) both Arrhenius and Sievert laws are followed. In this investigation, a dense palladium membrane reactor (PMR) concept is analysed referring both to experimental data and to simulation study. The partial oxidation of methane (POM) reaction to produce synthesis gas was chosen as a model reaction to be investigated. A membrane reactor model that includes the membrane, the gas phase and the catalyst activity is proposed. The experimental results in terms of methane conversion obtained by using a pin-hole free palladium membrane permeable to hydrogen only were compared with model predictions. The effect of reaction temperature on methane conversion at different time factors and sweep gas flow rates was considered. In particular, the effects of temperature profiles on the methane conversion are taken into account in the kinetic model.

Study on the hydrogen production from methanol steam reforming in supported palladium membrane reactor

This paper presents the effect of palladium membrane on the conversion of methanol reformed to the hydrogen by steam. A supported palladium membrane, which was electrolessly plated on porous stainless steel tube, was incorporated into the reaction system to configurate the membrane reactor. The reaction was carried out over Cu/ZnO/Al 2O 3 catalysts at 350°C. The stability of the catalyst was affected by the composition of Cu, Zn, and Al. The higher the content of Al, the better the stability of the catalyst. A double-jacketed membrane reactor was used to conduct both reforming and oxidation reactions simultaneously in separate compartments. The heat released from the oxidation compartment can be directly transferred into the reforming compartment to compensate the heat required from the external furnace. The measured heat supply was found to be strongly depending on the recovery yield of hydrogen. Therefore, a heat balance could be obtained at the recovery yield around 74%, which is consistent with the analysis of energy self-balance.

Palladium membrane reactor for the dehydrogenation of ethylbenzene to styrene

The Pd membrane was made by the electroless plating of Pd on the oxidized porous stainless steel (PSS) support with a 0.5 μm grade. The dehydrogenation of ethylbenzene to styrene was carried out in both the Pd membrane reactor and fixed-bed reactor at temperatures from 450 to 625°C and 1.2 atm pressure with a steam/ethylbenzene ratio of 6.8. As the result of the removal of hydrogen, the ethylbenzene conversion in the Pd membrane reactor was about 10% higher than that in the fixed-bed reactor for temperatures above 600°C. More importantly, the styrene selectivity in the Pd membrane reactor was ∼15% higher than that in the fixed-bed reactor.

An economic feasibility study for water gas shift membrane reactor

An economical analysis of palladium membrane reactors for the water gas shift (WGS) reaction is presented and discussed. In particular, a comparison of costs between the conventional apparatus and different membrane systems, for a fixed pure hydrogen recovery, is reported. The effect of the palladium thickness and of the membrane permeability to hydrogen on costs of membrane devices is analysed. Both higher permeabilities and lower thickness improve the hydrogen removal leading to a decrease in membrane area for a fixed hydrogen recovery and, thus, to a cost reduction. While both capital and operating costs are higher than the traditional ones for all the range of permeabilities used, by reducing the palladium thickness, it is possible to determine a range in which membrane reactors might be cost-effective. In particular, for palladium thicknesses equal or lower than 20 μm, membrane reactors could represent a possible alternative to conventional apparatus.

An analysis of the performance of membrane reactors for the water–gas shift reaction using gas feed mixtures

The water–gas shift (WGS) reaction in membrane reactors has been widely studied by several authors. From these works, the increase of the CO conversion above the equilibrium values appears to be possible when hydrogen is removed through the membrane. However, to date, this feasibility has been verified mostly when feeding pure reagents to the reactor, although in an industrial context the feed normally contains several other compounds. The objective of this work has been to analyse the effect of the feed composition on the membrane reactor efficiency in order to determine the best conditions in terms of CO conversion. At this purpose, experimental tests with mixtures of different compositions have been carried out in three different systems of reaction: (1) traditional fixed-bed reactor; (2) membrane reactor with mesoporous ceramic membrane; (3) membrane reactor with palladium membrane. The experiments included permeation (for the membrane reactors) and reaction tests. The experimental results obtained with the various systems of reaction have been compared. A mathematical model has been also formulated for the different type of reactors used in order to verify the experimental results obtained. From the work carried out it can be concluded that by using the palladium membrane reactor it is possible to overcome the equilibrium conversion. Moreover, a complete conversion has been achieved for one of the mixtures fed to the reactor.

Oxidation of isobutane over supported noble metal catalysts in a palladium membrane reactor

Pd membranes are often used to remove the H 2 produced in dehydrogenation reactions, thereby relieving the equilibrium limitations on the product yield. These processes, however, can still be limited by the slow kinetics of the dehydrogenation reaction. If O 2 is added to the system, the reaction proceeds through both the very fast oxidative dehydrogenation route as well as the dehydrogenation route. Thus, the addition of O 2 can suppress a kinetic limitation, while the removal of H 2 through the Pd membrane can alleviate the equilibrium limitation imposed on the system by the dehydrogenation route. In this study, we have examined the oxidative dehydrogenation of isobutane in a Pd membrane reactor over Pt/α-Al 2O 3 and Rh/α-Al 2O 3 monoliths and Pt/γ-Al 2O 3 pellets. We have examined iC 4H 10 : O 2 ratios of 1.0 to 2.0, resulting in operating temperatures ranging from 400 to 700°C. While most of this heat is generated by the exothermicity of the reaction, some additional heating was used to boost conversions. Typical contact times ranged from 0.04 to 0.25 s. By continuously removing the H 2 produced, isobutylene yields increased. Yield improvements depended strongly on the balance of reaction time with H 2 removal time and the importance of the dehydrogenation in the overall reaction scheme.

External Catalytic Packed-Bed Palladium Membrane Reactor with Baffle Rings.

External Catalytic Packed-Bed Palladium Membrane Reactor with Baffle Rings.

Process development for generating high purity hydrogen by using supported palladium membrane reactor as steam reformer

High purity hydrogen has been mainly used as a fuel for low temperature fuel cells such as polymer or alkaline electrolyte fuel cells. Hydrogen is industrially produced by steam reformation of hydrocarbons such as methane, naphtha oil, methanol, etc. Additional purification is invariably required for crude hydrogen and often is a costly step in the whole process. This paper presents an advanced process, in which no additional purification facility is needed, to generate high purity hydrogen (∼99.9%) directly from the supported palladium membrane tube incorporated in a steam reforming reactor. The hydrogen produced and purified from the palladium membrane reactor is free of CO and CO 2 so that it is suitable for polymer or alkaline electrolyte fuel cells. A unique design of a double-jacketed reactor was set up as a pure hydrogen generator with features of clean emission and energy self-balance. Experiments were conducted to illustrate the process for the direct and continuous generation of high purity hydrogen from methanol. The production flux of pure hydrogen obtained was higher than 5 m 3/h-m 2 and the recovery yield of hydrogen from methanol was found to be over 70%. This process has opened up a new possibility of on-board hydrogen generation for electric vehicle fuel cells in use of liquid fuel such as gasoline or methanol, which can be refueled fast and are compatible with the infrastructure of the current fuel system.

Decline in Hydrogen Permeation Due to Concentration Polarization and CO Hindrance in a Palladium Membrane Reactor

Hydrogen separation from binary gas mixtures, Ar−H2 and CO−H2, using a double-tube type of palladium membrane reactor (PMR) was carried out and analyzed by solving mathematical models taking into account mixing diffusion of hydrogen in the radial direction of the catalyst-packed bed. The experiment showed that carbon monoxide prevented hydrogen permeation through the membrane at temperatures less than 280 °C. The decline in hydrogen permeation could be estimated by solving a model describing the concentration polarization and the hindrance by cabon monoxide. Furthermore, the mathematical models were applied to analyze methanol decomposition in the same PMR, showing that a drop in hydrogen permeation due to both the factors had a significant influence on the performance of the PMR.

Dense Palladium and Perovskite Membranes and Membrane Reactors

The development of high-temperature processes and tighter environmental regulations requires utilization of efficient gas-separation processes that will provide high fluxes, high selectivity of separation, and the ability to operate at elevated temperatures. Dense inorganic membranes and membrane reactors are especially well suited for high-temperature reactions and separations, due in part to their thermal stability and high separation selectivity (in theory, infinite). Furthermore, membrane reactors offer an inherent advantage of combining reaction, product concentration, and separation in a single-unit operation for the improvement of process economics and waste minimization.The classification of membrane reactors can either be by membrane material and geometry or by the configuration of the reactor. Porous and dense membranes in both tubular and disk forms have been used for membrane reactors. The membrane can either be catalytically active (catalytic membrane reactor [CMR]) or simply act as a separation medium. In the latter case, the catalyst is packed in the reactor, whose walls are formed by the membrane (packed-bed membrane reactor [PBMR]). In addition, if the membrane is also catalytically active, the reactor is called a packed-bed catalytic membrane reactor (PBCMR).The principal materials from which porous inorganic (ceramic) membranes are made are alumina, zirconia, and glass. Alumina and zirconia membranes are usually asymmetric and composite, with a porous support (0.5–2.0 mm thick) for mechanical strength and one or more thin layers for carrying out separations.On the other hand, glass membranes, such as Vycor and microporous glass, have symmetric pores. Materials commonly used as the porous support are alumina, granular carbon, sintered metal, and silicon carbide.

Modified Simulation of Methane Steam Reforming in Pd-Membrane/Packed-Bed Type Reactor.

Methane Steam Reforming (MSR) is a catalytic process in which methane is reacted with steam to produce hydrogen and carbon dioxide gases. Many experimental and simulation studies have been assumed to be under isothermal conditions using a packed-bed inert membrane reactor (PBIMR). However, the flow fields inside the reactor are complex and a temperature gradient also occurs because of the catalyst particles packed in the reactor. This study suggests a new model considering heat transfer at the reactor wall and pressure drop inside the reactor. The model applies to the MSR reaction using PBIMR with a stainless steel reactor supported by a palladium membrane and packed-bed type reactor. Results are compared with the published experimental and simulation results. The simulation results suggested in the study shows better agreement than the simple model with constant temperature assumption, for both cases of palladium membrane and packed-bed type reactor. In addition, the effects of H2O/CH4, flow rate of sweep gas and particle diameter of catalyst on the methane conversion are investigated. In all cases, the proposed heat transfer model reveals better agreement with the published experimental data than that of the isothermal model.