Sorption-enhanced Water Gas Shift Reaction Research Articles

Investigations to intensified hydrogen production via sorption enhanced water gas shift reaction

Sorption enhanced water gas shift (SEWGS) reaction for the equilibrium enhanced hydrogen production is investigated using lithium orthosilicate (Li4SiO4) sorbents mixed with 1 wt% Pt/Al2O3 catalysts. The Li4SiO4 sorbents, synthesized using novel surfactant-mediated method, are characterized by ultra-fast CO2 capture rates with CO2 absorption capacity in the range of 319–333 mgCO2·g−s1. The thermogravimetric analysis results show ∼ 26 wt% of the carbonation sites are participating in the fast CO2 absorption (∼ 298 mgCO2·g−s1·min−1). The use of these sorbents with 1 wt% Pt/Al2O3 catalysts in the water gas shift reaction show a 103% increase in the hydrogen yield compared to the equilibrium concentration at 600◦C. The Li4SiO4 sorbent-catalyst combination show a shift in the equilibrium by preventing the reverse reaction in the temperature range of 600–650◦C. The SEWGS experiments show that the CO2 absorption capacities, and consequently the hydrogen yields, are affected by the diffusional resistance across Li2CO3 and Li2SiO3 product domains in the sorbent. The Li4SiO4 conversion rates during the SEWGS reaction are measured by sampling at different points in the SEWGS reaction and subsequent Rietveld analysis of the XRD patterns. The XRD results suggest the decrease in CO2 absorption rates as a result of the formation of additional Li2CO3 and Li2SiO3 fractions with decreasing Li4SiO4 phase in this nano-structured composite.

Sorption-Enhanced Water Gas Shift Reaction over a Mechanical Mixture of the Catalyst Pt/Ce0.75Zr0.25O2 and the Sorbent NaNO3/MgO

Sorption-Enhanced Water Gas Shift Reaction over a Mechanical Mixture of the Catalyst Pt/Ce0.75Zr0.25O2 and the Sorbent NaNO3/MgO

Probing the mechanism of H2 production in water gas shift reaction over Ce-modified CaO: A DFT study

The sorption-enhanced water gas shift reaction (WGSR) using CaO-based materials is a promising technology for H2 production, which can be further improved with the Ce-modified CaO material. However, the underlying mechanism for WGSR with the assistance of Ce-modified CaO remains unclear. A Ce-modified CaO periodic slab model was established in this paper, and the density functional theory (DFT) simulations for WGSR characteristics on Ce-modified CaO surface were performed. The results demonstrate that the Ce-modified CaO exhibits higher electron density, and the electron transfer between Ce and adjacent O is observed. The Ce doping obliterates the band gap of CaO, and the Fermi level is penetrated by O 2p orbit of Ce-modified CaO. The intermediates involved in WGSR exhibit obvious mutual promotion for co-adsorption with Ce-modification, and the H2 desorption is facilitated by the absorbed CO2. Ce doping avoids the generation of an additional intermediate, and the energy barriers of H2 generation and CO2 adsorption are reduced. The rate-limiting step on Ce-modified CaO is altered to the cleavage of O–H bond and formation of CO2 radical, and the energy barrier is 2.15 eV, which is 34.6% lower than that on CaO. Therefore, the enhancement mechanism on H2 production in WGSR resulted by Ce-modified CaO was determined.

Revealing the effects of Ni on sorption-enhanced water-gas shift reaction of CaO for H2 production by density functional theory

The sorption-enhanced water-gas shift (SE-WGS) reaction promoted by Ni-doped CaO (Ni-CaO) was sufficiently investigated by experiments that only displayed macroscopic results instead of microscopic reaction mechanisms. In this work, density functional theory (DFT) was employed to clarify the mechanisms of SE-WGS reaction which was catalyzed by Ni in the presence of CaO. The SE-WGS reaction only promoted by CaO was used as a comparison to clarify the catalysis of Ni. The analysis of electron differential densities, the partial density of states, and formation energy indicate that Ni causes the higher stability and reactivity of the Ni-CaO model than the CaO model. The Ni promotes the release of H2* by rising the adsorption energy of H2*(−0.05 eV) and retains the efficient CO2 capture with the adsorption energy of −1.56 eV. The transient state calculations indicate the SE-WGS reaction prefers to proceed along with the redox mechanism compared with the carboxyl and formate mechanisms on the Ni-CaO surface. The energy barriers for the CO2* generation, H2* generation and desorption are respectively 0.74, 1.77 and 0.10 eV on the Ni-CaO surface, which are lower than those on the CaO surface. Therefore, Ni helps to improve CO conversion and H2 productivity which is consistent with the previous experimental results.

Sorption-Enhanced Water-Gas Shift Reaction for Synthesis Gas Production from Pure CO: Investigation of Sorption Parameters and Reactor Configurations

A sorption-enhanced water-gas shift (SEWGS) system providing CO2-free synthesis gas (CO + H2) for jet fuel production from pure CO was studied. The water-gas shift (WGS) reaction was catalyzed by a commercial Cu/ZnO/Al2O3 catalyst and carried out with in-situ CO2 removal on a 20 wt% potassium-promoted hydrotalcite-derived sorbent. Catalyst activity was investigated in a fixed bed tubular reactor. Different sorbent materials and treatments were characterized by CO2 chemisorption among other analysis methods to choose a suitable sorbent. Cyclic breakthrough tests in an isothermal packed bed microchannel reactor (PBMR) were performed at significantly lower modified residence times than those reported in literature. A parameter study gave an insight into the effect of pressure, adsorption feed composition, desorption conditions, as well as reactor configuration on breakthrough delay and adsorbed amount of CO2. Special attention was paid to the steam content. The significance of water during adsorption as well as desorption confirmed the existence of different adsorption sites. Various reactor packing concepts showed that the interaction of relatively fast reaction and relatively slow adsorption kinetics plays a key role in the SEWGS process design at low residence time conditions.

Performance and dynamic behavior of sorption-enhanced water-gas shift reaction in a fluidized bed reactor for H2 production and CO2 capture

A multi-scale dynamic model for a sorption-enhanced water-gas shift (SE-WGS) fluidized bed reactor was developed and the reactor performance in terms of hydrogen production and carbon dioxide capture was analyzed. K2CO3-promoted hydrotalcite sorbent was used as a reference in the SE-WGS fluidized bed reactor and steam methane reforming gas was used as the feed. The sensitivity analysis of the performance was carried out by varying the temperature, pressure, and sorbent circulation rate. The CO conversion achieved at low pressures in the SE-WGS fluidized bed reactor was much higher than the catalytic equilibrium conversion. However, the advantages of the SE-WGS reactor were lost at pressures of over 7 bar. The desired sorption capacity and rate of the CO2 sorbent were suggested to enhance the performance of the SE-WGS fluidized bed reactor at 30 bar. At a five-time higher sorption capacity, the CO conversion and carbon capture efficiencies could be achieved to 95.0% and 86.4%, respectively. In addition, with a simultaneous increase of 1.5 times in the sorption rate, the CO conversion and carbon capture efficiency could be achieved to 99.3% and 98.2%, respectively. Because the CO2 sorption capacity is mainly determined in the mixing zone, the operating conditions need to be finely controlled for the maximum utilization of the sorbent capacity. The study demonstrates the advantages of the SE-WGS fluidized bed reactor for simultaneous H2 production and CO2 capture. In addition, the optimization of the sorption capacity and rate of the CO2 sorbent can provide guidance for the development of high-performance sorbents for application in SE-WGS fluidized bed reactors.

Development of an effective bi-functional Ni–CaO catalyst-sorbent for the sorption-enhanced water gas shift reaction through structural optimization and the controlled deposition of a stabilizer by atomic layer deposition

Bi-functional Ni–hollow CaO stabilized by ALD-grown Al2O3 overcoat for sorption-enhanced water-gas shift reaction producing high purity hydrogen.

CO2 utilization for combined gasification and sorption enhanced water-gas shift for syngas production of biochar

Searching for alternative renewable energy to serve high demand of energy consumption has been of interest for decades. However, the production of energy comes with an emission of large amount of CO2, the main cause of global warming problem. As a consequence, improvement of energy production process in terms of increasing high efficiency and reducing CO2 emission are required [1]. This research verified the combined systems: biochar gasification and sorption-enhanced water gas shift reaction for the production of synthesis gas. The effect of calcium precursor on CaO-based sorbents, type of metal on multifunctional materials, and amount of co-feed CO2 as gasifying agent on process performances were focused on this work. Fixed-bed reactors were used for both gasification and sorption-enhanced water-gas shift experiments. Performances of the system were analyzed in terms of %biochar conversion, H2/CO ratio, and CO2 emission. The temperature used in the gasification process was fixed at 900°C and sorption-enhanced water-gas shift was 600°C at 1 atm. The results showed the sorbent CaO/Caj2Alj4O33 derived from calcium nitrate displayed the best performance for CO2 capture, whose CO2 capture capacity is 0.34 gCO2/g sorbent at 30%CO2v/v at 600°C. For the combined gasification and sorption-enhanced water-gas shift reaction, 98% biochar conversion can be obtained. Ni/CaO-Caj2Ali4O33 offered higher H2/CO ratio and CO2 emission when compared to Cu/CaO-Ca12Al14O33 at fixed feed molar ratio of H2O:CO2:O2:C = 0.5:0.5:0.125:1. The utilization of CO2 as gasifying agent at feed molar ratio of H2O:CO2:O2:C = 0.5:0.1:0.125:1 demonstrated the reduction of CO2 emission with the production of H2/CO ratio = 0.23.

Syngas Production from Combined Steam Gasification of Biochar and a Sorption-Enhanced Water–Gas Shift Reaction with the Utilization of CO2

This research aims at evaluating the performance of a combined system of biochar gasification and a sorption-enhanced water–gas shift reaction (SEWGS) for synthesis gas production. The effects of mangrove-derived biochar gasification temperature, pattern of combined gasification and SEWGS, amount of steam and CO2 added as gasifying agent, and SEWGS temperature were studied in this work. The performances of the combined process were examined in terms of biochar conversion, gaseous product composition, and CO2 emission. The results revealed that the hybrid SEWGS using one-body multi-functional material offered a greater amount of H2 with a similar amount of CO2 emissions when compared with separated sorbent/catalyst material. The gasification temperature of 900 °C provided the highest biochar conversion of ca. 98.7%. Synthesis gas production was found to depend upon the amount of water and CO2 added and SEWGS temperature. Higher amounts of H2 were observed when increasing the amount of water and the temperature of the SEWGS system.

Sorption-enhanced water gas shift reaction by in situ CO2 capture on an alkali metal salt-promoted MgO-CaCO3 sorbent

CO2 capture and sequestration is one of the viable solutions to reduce the CO2 emissions from fossil fuel combustion, and sorption-enhanced water gas shift (SEWGS) is a promising technology for pre-combustion CO2 capture. In this study, a novel alkali metal salt (AMS)-promoted MgO-CaCO3 sorbent was applied to the SEWGS process, and this sorbent exhibited fast sorption rate, high capacity and good stability in 30 CO2 capture cycles. Catalyst and sorbent particles were arranged in a layer-by-layer alternating configuration in the reactor. The effects of operating conditions such as temperature, pressure and initial H2O/CO molar ratio were investigated, and the thermodynamic equilibrium analyses of the CO2 sorption on AMS-promoted MgO-CaCO3 and the SEWGS process in the layered configuration were carried out, based on which the optimization of the reactor configuration was performed. A high-purity H2 (99.4% in dry basis) was experimentally achieved in the SEWGS process at 573 K, 12 atm and an initial H2O/CO molar ratio of 1.5 with a three catalyst/sorbent layered configuration, and the cyclic stability was demonstrated over 10 consecutive SEWGS cycles.

Integration of calcium looping technology in combined cycle power plants using co-gasification of torrefied biomass and coal blends

To comprehensively understand the impact of calcium looping (CaL) technology on a co-gasification of torrefied biomass and coal power plant, two kinds of proposed configurations (pre- and post-CaL), including a co-gasification system, a CaL system, and a combined heat and power system, are studied and compared with each other in the present work. In the CaL process, the kinetic modeling of the carbonation reaction and CaO sorption-enhanced water gas shift (SE-WGS) reaction are developed in a fast fluidized bed reactor (carbonator) to predict the performance of hydrogen production and CO2 capture. The influences of torrefied biomass blending ratios (BRs) and CaO to fuel mass flow rate ratios (CaO/F) on various performance indicators such as hydrogen enhancement factor, hydrogen thermal efficiency (HTE), CO2 capture efficiency, specific CO2 emissions, and overall system efficiency are evaluated. A comparison of pre- and post-CaL schemes reveals that the SE-WGS reaction has a markedly profound effect on the former, causing the hydrogen production and HTE to be higher than those in the latter, whereas the latter is much more conducive to CO2 capture and specific CO2 emissions. Under optimal operating conditions (BR = 40 wt%, CaO/F = 3.5), the values of CO2 capture efficiency and overall system efficiency of both schemes are higher than 90% and 50%, respectively. Overall, the pre-CaL case is suitable to design as a highly efficient co-generation of hydrogen production and electricity plant with low CO2 emissions, whereas the post-CaL case is recommended for a co-gasification power plant with nearly zero CO2 emissions.

GRAMS: A general framework describing adsorption, reaction and sorption-enhanced reaction processes

We present a generalized reaction-adsorption modeling and simulation (GRAMS) framework that captures both reaction and adsorption dynamics in columns with solid catalysts, porous adsorbents or both. It is based on a 1-dimensional, pseudo-homogeneous, non-isothermal, non-adiabatic and non-isobaric model that is extensively validated using experimental data from literature for different adsorption-reaction systems. For demonstrating the capabilities of the high-fidelity framework, simulations are performed for several configurations of a packed-column system containing (i) pure catalyst as in a fixed bed reactor, (ii) pure adsorbent as in a multi-step pressure swing adsorption (PSA) process, (iii) homogeneously-distributed uniform mixture of adsorbent and catalyst as in a cyclic sorption enhanced reaction process (SERP), and (iv) heterogeneously-compartmentalized adsorbent and catalyst as in a layered SERP. The model predictions show good agreement with experimental observations for sorption-enhanced steam methane reforming (SE-SMR), sorption-enhanced water gas shift reaction (SE-WGSR), PSA processes and conventional SMR. The framework is also used for evaluating the performance of a novel process with integrated SE-SMR and reverse water gas shift reaction (RWGSR) for direct natural-gas-to-syngas conversion. GRAMS is implemented such that it can be used for optimal design and intensification of novel, modular and multi-functional processes by combining multiple phenomena within a single unit.

Optimal synthesis of periodic sorption enhanced reaction processes with application to hydrogen production

A systematic design and synthesis framework for multi-step, multi-mode and periodic sorption-enhanced reaction processes (SERP) is presented. The formulated nonlinear algebraic and partial differential equation (NAPDE)-based model simultaneously identifies optimal SERP cycle configurations, design specifications and operating conditions. Key modeling contributions include a generalized boundary-condition formulation and a representation that enables the selection of discrete operation modes and flow directions using continuous pressure variables. A simulation-based constrained grey-box optimization strategy is employed to obtain optimal cycles and design parameters. The framework has been used for designing two SERP systems, namely sorption-enhanced steam methane reforming (SE-SMR) and sorption-enhanced water gas shift reaction (SE-WGSR), for maximizing hydrogen productivity and minimizing hydrogen-production cost. Specifically, a cyclic SE-SMR process is designed that obtains 95% pure hydrogen from natural gas with 35% higher productivity and 10.86% lower cost compared to existing small-scale, distributed systems. The developed synthesis framework can also be applied for other applications.

Thermodynamic equilibrium analysis of water-gas shift reaction using syngases-effect of CO2 and H2S contents

Abstract Thermodynamic equilibrium of water-gas shift reaction (WGSR) under various temperatures, pressures and steam-to-CO (S/C) ratios was analyzed by Gibbs free energy minimization method. Coal-derived syngases with various CO2 and H2S contents were used as the feedstock. Based on the obtained results, it was found that CH4 and carbon formations were enhanced when syngas CO2 content increases. Carbon-free WGSR can be resulted using high S/C ratio. However, CH4-free WGSR cannot be resulted even with low S/C ratios. From the H2O conversion and H2 yield variations, the temperature at which reverse WGSR occurs can be identified and found to decrease with the increase in S/C ratio. Solid CaO sorbent was employed for both CO2 and H2S removals in WGSR when sour syngas was used as the feedstock. It was found that WGSR performance was enhanced due to the CO2 and H2S removals by CaO. The H2S concentration can be decreased with decreased S/C ratio while increasing the reaction pressure was not favourable for H2 production and H2S removal in WGSR with CaO. Because WGSR performance enhancement due to CO2 and H2S removals occurred at high temperature, catalysts can be eliminated in sorption-enhanced WGSR.

Synthesis gas adjustment by low temperature sorption enhanced water-gas shift reaction through a copper-zeolite 13X hybrid material

Water-gas shift reaction (WGSR) and sorption enhanced water-gas shift reaction (SE-WGSR) were studied over Cu-zeolite 13X hybrid material (containing the catalyst and CO2 sorbent) in the temperature range between 398 and 548K. The copper phase was deposited by wet impregnation of binderless beads of 13X zeolite. The catalysts were characterized by N2 sorption, XRD, He pycnometry and SEM-EDX techniques. In addition, the Cu-zeolite 13X hybrid material was also compared with a previously prepared and examined hybrid material, Cu-hydrotalcite hybrid material, used for the same purpose, the SE-WGSR.

Sorption-enhanced water gas shift reaction for high-purity hydrogen production: Application of a Na-Mg double salt-based sorbent and the divided section packing concept

Hydrogen is considered a promising environmentally benign energy carrier because it has high energy density and produces no pollutants when it is converted into other types of energy. The sorption-enhanced water gas shift (SE-WGS) reaction, where the catalytic WGS reaction and byproduct CO2 removal are carried out simultaneously in a single reactor, has received considerable attention as a novel method for high-purity hydrogen production. Since the high-purity hydrogen productivity of the SE-WGS reaction is largely dependent on the performance of the CO2 sorbent, the development of sorbents having high CO2 sorption capacity is crucial. Recently, a Na-Mg double salt-based sorbent has been considered for high-temperature CO2 capture since it has been reported to have a high sorption capacity and fast sorption kinetics. In this study, the SE-WGS reaction was experimentally demonstrated using a commercial catalyst and a Na-Mg double salt-based sorbent. However, the SE-WGS reaction with a one-body hybrid solid, a physical admixture of catalyst and sorbent, showed poor reactivity and reduced CO2 sorption uptake. As a result, a divided section packing concept was suggested as a solution. In the divided section packing method, the degree of mixing for the catalyst and sorbent in a column can be controlled by the number of sections. High-purity hydrogen (<10ppm CO) was produced directly from the SE-WGS reaction with divided section packing, and the hydrogen productivity was further improved when the reactor column was divided into more sections and packed with more sorbent.

Study of sour water gas shift using hydrotalcite based sorbents

One of the most promising alternatives to the use of liquid amines and pressure swing adsorwption (PSA) for H2 production and CO2 capture in pre-combustion processes is the so called sorption-enhanced water gas shift reaction concept (SEWGS). This study presents the performance in SEWGS of two sorbents, a K-promoted hydrotalcite with Mg/Al ratio=2, which based on our previous work was selected as the most promising CO2 capture sorbent tested under sweet water gas shift (WGS) operating conditions, and a bi-functional material prepared by impregnation of the K-promoted hydrotalcite with Co and Mo in order to enhance the catalytic properties of the material.Short term sour CO2 capture tests and WGS tests at similar operating conditions (T=300–350°C; P=15bar) were carried out in order to study the effect of the presence of H2S in the feed gas stream in the CO2 capture capacity and catalytic activity of both sorbent materials as well as to compare their performance in developed tests. Finally, the feasibility of using the bifunctional material for sour SEWGS processes was also studied.Impregnation with Co-Mo did not adversely affect the adsorption capacity of the K-promoted hydrotalcite and enhanced catalytic activity, allowing total CO conversion even after adsorption capacity had been reached.

Novel method for investigation of a K–Mg-based CO2 sorbent for sorption-enhanced water–gas shift reaction

CO2 sorption reactions at 20 bar and two different temperatures (i.e., 180 and 220 °C) using a K–Mg-based CO2 sorbent were carried out in a custom-designed high-pressure thermogravimetric analyzer (pressurized bubbling fluidized bed reactor on a scale) coupled with a gas chromatograph. The experimental apparatus, including the thermogravimetric analyzer, was custom-designed to measure weight changes caused by either CO2 sorption or water sorption or both. Analysis of the CO2 sorption reaction revealed that water sorption takes place rapidly with a moderate CO2 sorption rate at the early stage of the reaction. Then, the reaction migrates to CO2 sorption with simultaneous water desorption. Therefore, the mechanism of the CO2 sorption reaction is assumed to consist of fast hydration of K2CO3 and MgO, formation and decomposition of KHCO3, and finally carbonation of Mg(OH)2 resulting in MgCO3 as the main product. K2CO3 is assumed to provide an efficient pathway for CO2 and water to travel into the core region of the sorbent via a reversible reaction between K2CO3 and KHCO3.

Application of one-body hybrid solid pellets to sorption-enhanced water gas shift reaction for high-purity hydrogen production

Interest in hydrogen, regarded as a new clean energy carrier, has been increasing with expectation of the approaching hydrogen economy. In the hydrogen economy, hydrogen will replace the conventional fuels that have caused pollution problems. As one of the methods for the mass production of hydrogen, water gas shift (WGS) reaction (CO + H2O ↔ H2 + CO2) has been highlighted for synthesis gas feed, which is produced by coal and biomass gasification. Recently, the performance of WGS reaction has been improved significantly through application of the sorption-enhanced WGS (SE-WGS) reaction concept, where WGS reaction and CO2 sorption are carried out simultaneously. High-purity hydrogen can be directly produced through the SE-WGS reaction, without need for further purification processes. In the SE-WGS reaction, uniform packing of the mixture of catalyst and sorbent is important; however, this is difficult to manage with conventional catalyst and sorbent pellets. In this study, novel one-body hybrid solid pellets consisting of the mixture of catalyst and sorbent were prepared to address this shortcoming and applied to SE-WGS reactions. From experiments, the effect of different ratio of catalyst/sorbent in one-body hybrid solid pellets was studied. A novel multi-section packing concept was also applied to SE-WGS reaction with one-body hybrid solid pellets. The experimental results showed that one-body hybrid solid pellets can be successfully used and that multi-section packing can increase the hydrogen productivity in SE-WGS reaction.

Production of High-Purity Hydrogen and Carbon Dioxide Capture by Sorption Enhanced WGS Reaction Process

Global warming has become more and more serious, which is caused by greenhouse gases. Cutting down the emission of CO2 has already become one of the major research target in the world. This study is numerically investigating Thermal Swing Sorption Enhanced Reaction Process on water gas shift (WGS) reaction by Na2O-promoted alumina. According to Le Chateliers law, the forward reaction rates and conversion can be increased by removing some products selected. Therefore, this concept can be used to generate product of high-purity hydrogen. The purified H2 can be sent to gas turbine for generating electrical power or can be used for other energy source. Carbon dioxide can also be recovered and sequestrated to reduce greenhouse gas effects. The method of lines is utilized in simulation, combined with upwind differences, cubic spline approximation and LSODE of ODEPACK software to solve the problem. The concentration, temperature, and adsorption quantity in the bed are integrated with respect to time by LSODE of ODEPACK software. The simulation is stopped when the system reaches a cyclic steady state. In this study, we first simulate breakthrough curve of Na2O-promoted alumina cited from literatures to prove the accuracy of simulation program. The optimal operating conditions of the WGS TSA (temperature swing adsorption) single-bed six-process is obtained by varying operating variables, such as feed time and rinse time. Furthermore, WGS TSA single-bed six-process could achieve 99.89% purity of H2 (dry-basis) as the top product and 90.95% purity and 98.22% recovery of CO2 (dry-basis) as the bottom product.