Water Gas Shift Membrane Reactor Research Articles

Pure H2 production through hollow fiber hydrogen‐selective MFI zeolite membranes using steam as sweep gas

Hollow fiber MFI zeolite membranes were modified by catalytic cracking deposition of methyldiethoxysilane to enhance their H2/CO2 separation performance and further used in high temperature water gas shift membrane reactor. Steam was used as the sweep gas in the MR for the production of pure H2. Extensive investigations were conducted on MR performance by variations of temperature, feed pressure, sweep steam flow rate, and steam‐to‐CO ratio. CO conversion was obviously enhanced in the MR as compared with conventional packed‐bed reactor (PBR) due to the coupled effects of H2 removal as well as counter‐diffusion of sweep steam. Significant increment in CO conversion for MR vs. PBR was obtained at relatively low temperature and steam‐to‐CO ratio. A high H2 permeate purity of 98.2% could be achieved in the MR swept by steam. Moreover, the MR exhibited an excellent long‐term operating stability for 100 h in despite of the membrane quality. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3459–3469, 2015

Water gas shift reaction in membrane reactors: Theoretical investigation by artificial neural networks model and experimental validation

In this work, a theoretical approach via artificial neural networks model has been followed for studying the water gas shift reaction in hydrogen selective membrane reactors, based on an experimental campaign useful for training the aforementioned model. In particular, such parameters as the reaction pressure (from 150 to 300 kPa), reaction temperature (from 300 to 360 °C), gas hourly space velocity (GHSV) between 2000 and 6000 h−1, sweep gas flow rate (between 35.75 and 130.42 mL/min of N2), H2O/CO feed molar ratio (from 1/1to 4.5/1) and feed configuration (co–or counter-current mode with respect to the sweep gas) have been considered from both a modeling and an experimental point of view in order to analyze their influence on the water gas shift performance (in terms of CO conversion, hydrogen recovery, hydrogen permeate purity) in two membrane reactors, allocating dense Pd–Ag membranes, having different active membrane surface areas. As best experimental results, by using a Cu–Zn based catalyst, at GHSV = 3340 h−1, T = 350 °C, H2O/CO feed molar ratio = 2/1 and co-current configuration of sweep gas, CO conversion around 100% and H2 recovery of about 70% were reached. Meanwhile, the artificial neural networks model has been validated by using part of the experimental tests as training values and, then, it was used for optimizing the system to achieve as much as possible high hydrogen recovery. The model predicted the experimental performance of the water gas shift membrane reactors with an error on CO conversion lower than 0.5% and around 10% for the H2 recovery over the experimental tests not used during the model training.

Economic evaluation of pre-combustion CO2-capture in IGCC power plants by porous ceramic membranes

Pre-combustion-carbon-capture is one of the three main routes for the mitigation of CO2-emissions by fossil fueled power plants. Based on the data of a detailed technical evaluation of CO2-capture by porous ceramic membranes (CM) and ceramic membrane reactors (WGSMR) in an Integrated-Gasification-Combined-Cycle (IGCC) power plant this paper focuses on the economic effects of CO2-abatement. First the results of the process simulations are presented briefly. The analysis is based on a comparison with a reference IGCC without CO2-capture (dry syngas cooling, bituminous coal, efficiency of 47.4%). In addition, as a second reference, an IGCC process with CO2 removal based on standard Selexol-scrubbing is taken into account. The most promising technology for CO2-capture by membranes in IGCC applications is the combination of a water gas shift reactor and a H2-selective membrane into one water gas shift membrane reactor. For the WGSRM-case efficiency losses can be limited to about 6%-points (including losses for CO2 compression) for a CO2 separation degree of 90%. This is a severe reduction of the efficiency loss compared to Selexol (10.3% points) or IGCC–CM (8.6% points). The economic evaluation is based on a detailed analysis of investment and operational costs. Parameters like membrane costs and lifetime, costs of CO2-certificates and annual operating hours are taken into account. The purpose of these evaluations is to identify the minimum cost of electricity for the different capture cases for the variation of the boundary conditions. Fixing 90% CO2 separation the analysis identifies clearly that the economic minimum for cost of electricity and maximum thermodynamic efficiencies do not coincide. The cost of electricity for the reference case was 67€/MWh and for the WGSMR integration with 90% CO2 separation 57€/MWh, if certificate costs of 30€/tCO2, membrane costs of 300€/m2 and 8000 operating hours/year are considered. Further studies on the sensitivity of cost of electricity on the technical and commercial boundary conditions will be presented.

Thermal Management of a Water–Gas-Shift Membrane Reactor for High-Purity Hydrogen Production and Carbon Capture

This paper focuses on the thermal management of a hydrogen-selective low temperature water-gas-shift (WGS) membrane reactor for simultaneous high-purity hydrogen production and carbon capture. A ma...

Lab-scale tests of different materials for the selection of suitable sorbents for CO2 capture with H2 production in IGCC processes

In this work two different types of materials, potassium carbonate promoted hydrotalcites and natural dolomites, have been investigated at laboratory scale to select the most promising sorbent to be used in a water gas shift membrane reactor (WGSMR). Sorbents were prepared by calcination in the temperature range of 500–800°C. Two experimental campaigns were carried out, the first one in a thermobalance under dynamic conditions (cooling down in a CO2/N2 stream) and the second one in a fixed bed reactor under isothermal conditions at 300°C. The influence of the preparation method, system pressure and water content in the feed gas on the performance of the sorbents has been investigated and the results obtained are described in this paper.As expected, K-doped hydrotalcite-based sorbents provided higher CO2 capture capacities than natural dolomites, which were found to require a deeper study to optimise their performance. For hydrotalcites, steam partial pressures, Mg/Al ratio and calcination temperature were found to play a crucial role in their CO2 capture capacities. Material Mg61-K2CO3 calcined at 600°C provided an initial CO2 capture capacity of 9mol/kg at PCO2=0.34bar and PH2O=4.55bar so this material was pre-selected to be used in the WGSMR system. Under those operating conditions formation of MgCO3 is suspected to occur so detailed studies are being carried out to confirm this hypothesis. The efficiency of thermal regeneration and depressurisation as regeneration method was explored at 1bar and 5bar in four sorption–desorption cycles and the combination of both approaches was found to provide the best results. Cycling behaviour and optimisation of the regeneration conditions are being carried out before going to the membrane reactor.

CO2 Selective Water Gas Shift Membrane Reactor : Modeling and Simulation

The concept of a CO2 selective water gas shift (WGS) membrane reactor has been modeled and simulated by a one-dimensional reactor and transport process in the membrane. The model was used to investigate the effect of temperature, total pressure, membrane thickness and area on the reactor performance. A Silicalite-1 membrane was considered to be integrated with the WGS reactor. The mass transport through the membrane was described by surface diffusion. Air was used as sweep gas on the permeate side of the membrane. The catalytic WGS kinetics were for a commercial Cu/ZnO catalyst for the lower-temperature WGS reaction. The WGS membrane reactor was sized to produce H2 sufficient for the production of 10 kW electrical power from a fuel cell. The modeling and simulation results showed that the WGS membrane reactor with a silicalite-1 membrane was capable of decreasing the CO concentration to about 675 ppm which is 70% less than that achievable at equilibrium conversion, but it would come at the cost of unacceptable H2 loss. Based on a minimum target of H2 loss, the optimum outlet CO concentration achieved by the silicalite-1 membrane reactor was about 1310 ppm, under a range of limited conditions. The modeling study showed that both the WGS reaction rate and the CO2/H2 selective permeation played an important role on the overall reactor performance.

Effect of Pressure on High-Temperature Water Gas Shift Reaction in Microporous Zeolite Membrane Reactor

A water gas shift (WGS) membrane reactor (MR) has been constructed using a MFI-type zeolite disk membrane packed with a cerium-doped ferrite catalyst. The WGS reaction was performed at high temperatures of 400–550 °C, and the effect of reaction pressure on the MR performance was investigated in a range from 2 to 6 atm with the permeate side swept by nitrogen at atmospheric pressure. Increasing temperature and pressure enhance both the reaction rate and the rate of H2 membrane permeation that in turn significantly enhances the CO conversion. The equilibrium limit of CO conversion can be surpassed in the MR at high pressure and/or high temperature. It has been demonstrated in this study that membranes with moderate H2 selectivity can be effective for enhancing CO conversion at high operation temperature and pressure with the cost of low H2 concentration in the permeate stream. The timely removal of H2 from the catalyst bed dramatically reduced the undesirable methane production because H2 is a reactant for ...

Simulation of Water-Gas Shift Membrane Reactor for Integrated Gasification Combined Cycle Plant with CO2 Capture

The effectiveness of energy conversion and carbon dioxide sequestration in Integrated Gasification Combined Cycle (IGCC) is highly dependent on the syngas composition and its further processing. Water gas shift membrane reactor (WGSMR) enables a promising way of syngas-to-hydrogen conversion with favourable carbon dioxide sequestration capabilities. This paper deals with a numerical approach to the modelling of a water gas shift reaction (WGSR) in a membrane reactor which promotes a reaction process by selectively removing hydrogen from the reaction zone through the membrane, making the reaction equilibrium shifting to the product side. Modelling of the WGSR kinetics was based on Bradford mechanism which was used to develop a code within Mathematica programming language to simulate the chemical reactions. The results were implemented as initial and boundary conditions for the tubular WGSMR model designed with Aspen Plus software to analyze the broader system behaviour. On the basis of selected boundary conditions the designed base case model predicts that 89.1% CO conversion can be achieved. Calculations show that more than 70% of carbon monoxide conversion into hydrogen appears along the first 40% of reactor length scale. For isothermal conditions more than two thirds of the heat released by WGSR should be extracted from the first 20% of the reactor length. Sensitivity analysis of the WGSMR was also performed by changing the membrane’s permeance and surface area.

CFD Simulation of Water Gas Shift Membrane Reactor--Pressure Effects on the Performance of the Reactor

Membrane reactor is a process intensified equipment that carries out both the reaction and separation in a single vessel. The equilibrium limited water gas shift reaction is an ideal reaction to be carried out in a membrane reactor as it improves the conversion of the reaction and reduces the space requirement for the reactor. Computational fluid dynamics offers a virtual prototyping of the reactor and helps in design, optimization, and scale-up of the reactor. To obtain pure hydrogen from the membrane reactor, the pressure of the reactor needs to be optimized. Hence the water gas shift membrane reactor is subjected to computational fluid dynamic analysis to understand the role played by pressure on the performance of the reactor using three different gas mixtures. The CO conversion and H2 recovery for the different operating pressures are simulated and the effects of pressure are discussed in this paper.

Hydrogen enrichment and separation from synthesis gas by the use of a membrane reactor

One of the objectives of the CHRISGAS project was to study innovative gas separation and gas upgrading systems that have not been developed sufficiently yet to be tested at a demonstration scale within the time frame of the project, but which show some attractive merits and features for further development. In this framework CIEMAT studied, at bench scale, hydrogen enrichment and separation from syngas by the use of membranes and membrane catalytic reactors. In this paper results about hydrogen separation from synthesis gas by means of selective membranes are presented. Studies dealt with the evaluation of permeation and selectivity to hydrogen of prepared and pre-commercial Pd-based membranes. Whereas prepared membranes turned out to be non-selective, due to discontinuities of the palladium layer, studies conducted with the pre-commercial membrane showed that by means of a membrane reactor it is possible to completely separate hydrogen from the other gas components and produce pure hydrogen as a permeate stream, even in the case of complex reaction system (H2/CO/CO2/H2O) under WGS conditions gas mixtures. The advantages of using a water-gas shift membrane reactor (MR) over a traditional fixed bed reactor (TR) have also been studied. The experimental device included the pre-commercial Pd-based membrane and a commercial high temperature Fe–Cr-based, WGS catalyst, which was packed in the annulus between the membrane and the reactor outer shell. Results show that in the MR concept, removal of H2 from the reaction side has a positive effect on WGS reaction, reaching higher CO conversion than in a traditional packed bed reactor at a given temperature. On increasing pressure on the reaction side permeation is enhanced and hence carbon monoxide conversion increases.

A process dynamic modeling and control framework for performance assessment of Pd/alloy-based membrane reactors used in hydrogen production

In the present study a comprehensive, insightful and practical process dynamic modeling framework is developed in order to analyze and characterize the transient behavior of a Pd/alloy-based (Pd/Au or Pd/Cu) water-gas shift (WGS) membrane reactor. Furthermore, simple process control ideas are proposed aiming at enhancing process system performance by inducing the desirable dynamic characteristics in the response of the controlled process during start-up as well as in the presence of unexpected adverse disturbances (process upset episodes) or operationally favorable set-point changes that reflect new hydrogen production requirements. Finally, the proposed methods are evaluated through detailed simulation studies in an illustrative example involving a Pd/alloy-based WGS membrane reactor that exhibits complex dynamic behavior and is currently used for lab-scale pure hydrogen production and separation.

CFD analysis of water gas shift membrane reactor

Fuel cell based modular power generation can be achieved by miniaturization and process intensification of equipments in the process. Fuel cells require hydrogen rich gas which can be generated through reforming and water gas shift reaction. The water gas shift reactor being kinetically limited occupies more volume to achieve the required CO conversion. A membrane reactor integrates the reaction and hydrogen separation stages and hence reduces the volume requirement. Computational Fluid Dynamics offers virtual prototyping of the reactor and thus helps in design, optimization and scale up of reactors. In this study customized User Defined Functions (UDFs) were developed to analyze the performance of low temperature water gas shift membrane reactor. The models were validated using literature data for the parameters – synthesis gas compositions, time factor, sweep flow rate and steam to CO ratio. The effect of all these parameters on the reactor was analyzed for CO conversion, H 2 recovery, DaPe, concentration polarization, concentration profiles and conversion index. The simulations have showed that the UDFs developed were capable of simulating the membrane reactor and this can be used for the design and optimization of the membrane reactor for any process conditions.

Performance and economics of a Pd-based planar WGS membrane reactor for coal gasification

Conceptual 300 tonne per day (tpd) H 2-from-coal plants have been the subject of several major costing exercises in the past decade. Incorporating conventional high- and low-temperature water-gas-shift (WGS) reactors, amine-based CO 2 removal and PSA-based H 2 purification systems, these studies provide a benchmark against which alternative H 2-from-coal technologies can be compared. The catalytic membrane reactor (CMR), combining a WGS catalyst and hydrogen-selective metal membrane, can potentially replace the multiple shift and separation stages of a plant based on conventional technology. CMR-based shift and separation offers several major advantages over the conventional approach, including greater-than-equilibrium WGS conversion, the containment of the CO 2 at high-pressure and a reduction in the number of unit processes. To determine capital costs of a WGS CMR-based H 2-from-coal plant, a prototype planar CMR was constructed and tested with varying catalyst bed depth, residence time and membrane type (commercially-sourced 50 μm Pd or 40 μm Pd-25Ag wt%). Experiments to measure CO conversion, and H 2 flux and yield were conducted at 400 °C with a feed pressure of 20 bar H 2O:C ratio of 3 and a H 2 product pressure of 1 bar. Under the optimum conditions examined (with a 40 μm-thick Pd-25Ag membrane and <3 mm-thick catalyst bed), a membrane surface area of ∼25,000 m 2 would be required to provide a throughput of 300 tpd with 85% H 2 yield. The capital cost of the CMR component of the plant would be around $US 180 million (based on current metal prices), of which 73% can be attributed to the cost of the Pd–Ag alloy membranes. Incorporation of a membrane that meets the 2015 US DOE cost and flux targets would offer cost parity, with a plant cost of $US 44 million and a total membrane area of ∼13,000 m 2. Meeting these performance and cost targets would likely require a shift to very thin Pd-alloy membranes or highly-permeable Group IV, V body-centred-cubic alloys.

Multi-tube Pd–Ag membrane reactor for pure hydrogen production

An experimental apparatus carrying out a membrane process for producing pure hydrogen via ethanol steam reforming has been tested in order to measure the hydrogen production by varying operative parameters such as temperature, pressure and membrane sweeping mode. The process consists of a traditional fixed bed reformer, which performs the ethanol steam reforming, and a multi-tube Pd–Ag membrane reactor, where both the water gas shift reaction and the separation of pure hydrogen take place. The water gas shift membrane reactor uses permeator tubes of wall thickness 50–60 μm, diameter 10 mm and length 250 mm. The experiments have been carried out with a reaction pressure in the range 100–250 kPa, while the reformer has been operated at a temperature of 690–890 °C with feed water/ethanol molar ratio of 10.5/1 and flow rates between 200 and 500 g h −1. The hydrogen has been recovered in the shell side of the membrane module by vacuum pumping or inert gas (nitrogen) sweeping at 350–400 °C. The highest hydrogen productions (about 3.5 NL min −1) have been attained by feeding 500 g h −1 of water/ethanol mixture and by recovering the hydrogen through vacuum pumping in the shell side of the membrane module at 400 °C.

Mathematical simulation of WGS membrane reactor for gas from coal gasification

Mathematical model of a membrane reactor for the water-gas-shift (WGS) reaction and results of simulation studies are presented. The physicochemical phenomena and brief description of the model are given. Due to the fact that membranes for CO 2 separation exhibit poor selectivity at the elevated temperature range (indispensable for the desired activity of WGS catalysts), the simulations were carried out only for H 2 selective membranes, containing Pd or its alloys. Comparison of the conventional two-stage WGS reactor with the membrane reactor revealed that operating temperature range of the catalyst used in the membrane reactor unit has to be much wider than that in conventional industrial reactors with separate high- and low temperature catalyst stages and with cooling in between. Thus, the research of new catalysts should accompany development of the membrane reactor technology. Simulations discussed in the present paper were focused on processing the gas derived from the coal gasification plant. Some results of mathematical simulations are presented. They reveal that under some conditions the membrane reactor technology can be promising for the hydrogen production from the coal-derived gas.

A simulation study of the effect of operating and design parameters on the performance of a water gas shift membrane reactor

Abstract The goal of this work is to understand the effect of the relative values of membrane permselectivity, permeation flux and reaction rate on the performance of a water gas shift membrane reactor. This was achieved by simulating the operation of an isothermal tube–shell reactor. Its performance was evaluated based on the CO conversion and H 2 recovery, as well as the permeate and retentate H 2 molar fractions. The maximum enhancement of CO conversion has been observed when the Damkholer number ( Da ) is almost equal to the permeation number ( Pe ). Improvements in CO conversion can be achieved even when membranes with relatively low permselectivity values (∼10) are used. Further increase of permselectivity primarily increased the purity of the H 2 rich stream. The utilization of CO 2 selective instead of H 2 selective membranes could improve CO conversion only if the CO 2 content of the feed is higher than that of H 2 . Finally, simulations using rate expressions that correspond to different detailed reaction mechanisms resulted only in slight differences in reactor performance.

The water‐gas shift reaction: from conventional catalytic systems to Pd‐based membrane reactors—a review

AbstractThe water‐gas shift (WGS) reaction is a well‐known step for upgrading carbon monoxide to hydrogen in the production of synthesis gas. For more than 90 years after its first industrial application, many issues in respect of the catalyst, process configuration, reactor design, reaction mechanisms and kinetics have been investigated. More recently, a renewed interest in the WGS reaction carried out in hydrogen perm‐selective membrane reactors (MRs) has been observed because of the growing use of polymeric electrolyte membrane (PEM) fuel cells that operate using high‐purity hydrogen. Moreover, MRs are viewed as an interesting technology in order to overcome the equilibrium conversion limitations in traditional reactors.This article reviews the most relevant topics of WGS MR technology—catalysis and membrane science. The most used catalysts and relevant progress achieved so far are described and critically reviewed. The effects of the most important parameters affecting the WGS in MRs are detailed. In addition, an overview on the most used membranes in MRs is also presented and discussed. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Effects of system parameters on the performance of CO 2-selective WGS membrane reactor for fuel cells

Performing water gas shift (WGS) reaction efficiently is critical to hydrogen purification for fuel cells. In our earlier work, we proposed a CO 2-selective WGS membrane reactor, developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. Further modeling investigations were made on the effects of several important system parameters, including inlet feed temperature, inlet sweep temperature, feed-side pressure, feed inlet CO concentration, and catalyst activity, on membrane reactor performance. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas. As the inlet feed temperature increased, the required membrane area reduced because of the higher WGS reaction rate. Increasing the inlet sweep temperature decreased the required membrane area more significantly, even though the required membrane area increased slightly when the inlet sweep temperature exceeded about 160 °C. Higher feed-side pressure decreased the required membrane area as a result of the higher permeation driving force and reaction rate. A potentially more active catalyst could make the membrane reactor more compact because of the enhanced reaction rate. The modeling results have shown that a CO concentration of less than 10 ppm is achievable from syngases containing up to 10% CO.

Thermodynamic modelling of the Cu–Pd–H system

Thermodynamic modelling of hydrogen interactions with the Cu–Pd B2 alloys is used to set the stage for the development of membrane alloys with improved thermal and chemical stability for the separation of pure hydrogen from coal gasifier exhaust or syngas within advanced water gas shift membrane reactors. Thermodynamic descriptions of the binary Cu–Pd, Pd–H, Cu–H, and ternary Cu–Pd–H systems are obtained by combining experimental investigation, first-principles calculations, and thermodynamic modeling. The H solubilities in the Cu 0.56Pd 0.44 B2 alloy have been measured from 100 to 350 ∘C up to 7 bar H 2 pressure. The stabilities of the ternary B2 phase at different compositions are predicted by first-principles calculations. The model parameters for the Gibbs energy of individual phases are optimized using experimental phase equilibrium and thermochemical data, and the first-principles predictions. The B2 phase is described with a three-sublattice model, (Cu,Pd) 0.5(Cu,Pd) 0.5(H,V a), which allows for ordering. The Pd–H fcc miscibility gap is well described and the partial H thermodynamic quantities of the Pd–H system are in agreement with experiments. The ternary para-equilibrium and full equilibrium fcc miscibility gap are calculated for the Cu–Pd–H system. Extensive comparisons are presented between the thermodynamic modelling and experimental data.

Hydrogen interactions with the PdCu ordered B2 alloy

Combined experimental and modeling studies on hydrogen interactions with PdCu ordered body-centered cubic (B2) alloys have set the stage for membrane alloy development for advanced water gas shift membrane reactors that separate pure hydrogen from coal gasifier exhaust or syngas. First principles potential energy surface and ground state minimization calculations were used to profile the surface site selectivity of H 2 and H 2S adsorption on the lowest energy PdCu B2 (1 1 0) surface. Finite temperature surface energy calculations for varying H 2 and H 2S coverages were used to estimate the potential for blocking of H 2 adsorption by H 2S physisorption under coal gasification partial pressure and temperature conditions. Experimental measurements of hydrogen solubility in the Pd 0.44Cu 0.56 B2 alloy were made with a Sievert's type apparatus. This data was assessed, along with existing experimental data and first principles predicted finite temperature data for hypothetical end-member phases, to develop a thermodynamic description of the ternary Pd–Cu–H system encompassing the PdCu B2 phase. First principles ground state and lattice dynamics simulations were used to predict favorable pathways for thermally activated hydrogen diffusion within the B2 lattice. The newly derived solubility and diffusivity parameters were evaluated within a mass transfer model to predict the ideal bulk permeability in the absence of other mass transfer contributions.