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
Graphical abstract
Introduction
Due to the rapidly increasing global population and accelerated industrial development, energy demands have soared over the last few decades. Conventional energy production and conversion processes are based on the combustion of fossil fuel feedstocks [1], which cause massive emissions of anthropogenic greenhouse gases resulting in alarming environmental problems. Thus, the development of eco-friendly energy processes is required, but these processes are not easily adopted due to their economic infeasibility. Hydrogen is considered as an alternative energy carrier because it can be easily produced from various feedstocks and also because it possesses a higher energy density than conventional fossil fuels [2]. Approximately 50 million tons of hydrogen are already produced annually, and hydrogen is widely used in a variety of applications including the chemical synthesis of ammonia and urea, hydrocracking and hydrotreating in oil-upgrading, and in fuel for vehicles [3]. Hydrogen can also be used in many ways for power generation, especially in fuel cell systems [4].
Steam methane reforming (SMR) reaction processes are commonly used for bulk hydrogen production. Furthermore, water gas shift (WGS) reaction processes using synthesis gas feeds produced by the gasification of carbonaceous feedstocks, such as coal and biomass, are becoming increasingly common [5], [6], [7]. In the WGS reaction, carbon monoxide and steam react to produce hydrogen and carbon dioxide. Since the hydrogen produced from the WGS reaction contains massive amounts of byproduct CO2, unreacted CO, and steam, the product gas stream is subjected to separation processes such as pressure swing adsorption after steam condensation to obtain high-purity hydrogen [8], [9]. In particular, hydrogen for polymer electrolyte membrane fuel cells must be more than 99.9% pure and contain less than 10 ppm CO. Recently, to improve the performance of the WGS reaction, the sorption-enhanced reaction (SER) concept was applied [10], [11]. In the sorption-enhanced WGS (SE-WGS) reaction, the WGS reaction and CO2 removal by sorption are carried out simultaneously in a single reactor, and the thermodynamic equilibrium limitation of the WGS reaction can be circumvented based on the Le Chatelier principle. Since fuel-cell grade high-purity hydrogen can be directly produced from the SE-WGS reaction, the cost of separation can be reduced, and a more compact process can be developed. The SER process is also considered to be a promising pre-combustion CO2 capture technology, and combined SE-WGS and integrated gasification combined cycle (IGCC) technology has been highlighted as a prominent solution for mitigation of CO2 emissions in coal-based power plants [12], [13]. The application of SE-WGS reaction process in IGCC has benefits in terms of operating costs compared to the combination of IGCC and the conventional Selexol process [14].
For the successful implementation of SE-WGS reactions, sorbents that can capture high-temperature CO2 are crucial. Hydrotalcite, calcium oxide, Na2O-modified alumina, modified MgO, and alkali metal zirconate have been applied as high-temperature CO2 sorbents for the SE-WGS reaction [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Hydrotalcite and modified hydrotalcite-like sorbents have been particularly successfully applied to SE-WGS reaction processes, but their CO2 sorption uptakes are relatively low (0.13–1.4 mol/kg) at high (or intermediate) temperature, resulting in rapid saturation with CO2 and reduced hydrogen productivity. To increase the CO2 sorption uptake of these sorbents, several approaches, such as addition of alkali metals, modification of the synthesis method, and changing the component ratio, were considered [26], [27]. However, these sorbents need further examination before application to SER processes.
Recently, double salt-based sorbents were reported as promising materials for high-temperature CO2 capture, showing characteristic properties for CO2 sorption [28], [29]. In our previous studies, Na-Mg and K-Mg double salt-based sorbents were synthesized and have been tested for high-temperature CO2 capture, and they showed unique and promising CO2 sorption performances [30], [31]. In particular, the Na-Mg double salt-based sorbent exhibited fast sorption kinetics, outstanding cyclic stability, and high CO2 sorption capacity (∼3 mol/kg) between 200 and 400 °C, which corresponds with the temperature required for the WGS reaction.
In this study, the SE-WGS reaction was experimentally investigated using a commercial catalyst and a Na-Mg double salt-based sorbent. The Na-Mg double salt-based sorbent was first applied to the SE-WGS reaction. Pellets of a one-body hybrid solid of catalyst and sorbent, a catalyst-only solid, and a sorbent-only solid, were prepared by compressing the corresponding powder. The prepared pellets were packed into a reactor column at different catalyst-to-sorbent ratios and with different packing methods, and their effects on the SE-WGS reaction performance and hydrogen production were investigated. In particular, the reduced catalytic reactivity and CO2 sorption performance using one-body hybrid solid pellets having direct contact between the catalyst and sorbent are reported for the first time, and the divided section packing concept is suggested and tested as a solution to this problem.
Section snippets
Sample preparation
To experimentally demonstrate WGS and SE-WGS reactions, commercial ShiftMax 210 (Cu/ZnO/Al2O3) catalyst powder manufactured by Clariant (formerly Süd-Chemie) and a Na-Mg double salt-based CO2 sorbent were used. The Na-Mg double salt-based sorbent was prepared by a precipitation method [30]. For the synthesis of this sorbent, appropriate amounts of sodium carbonate (Na2CO3; Sigma-Aldrich, >99.5%) and magnesium nitrate hexahydrate (Mg(NO3)2·6H2O; Sigma-Aldrich, ACS reagent, 99%) were suspended in
Characteristics of prepared samples
Crystalline structures of the catalyst before and after WGS reaction, the pristine Na-Mg double salt-based sorbent, and the one-body hybrid solid having a catalyst-to-sorbent ratio of 0.25 before and after the SE-WGS reaction were identified using XRD analysis. The XRD spectra in Fig. 3a indicates that the pristine commercial catalyst is mainly composed of CuO, ZnO, and Al2O3. The characteristic peaks of CuO in the catalyst were fully converted to those of Cu after the WGS reaction at 375 °C (
Conclusions
A Na-Mg double salt-based CO2 sorbent was applied to the SE-WGS reaction for high-purity H2 production. First, a one-body hybrid solid, a physical admixture of commercial catalyst and CO2 sorbent, was prepared, and its characteristics were analyzed. From XRD analysis, the one-body hybrid solid was confirmed to contain both catalyst and sorbent crystalline components, resulting from the homogeneous mixing of the catalyst and the sorbent by ball-milling. However, the reactivity and CO2 sorption
Acknowledgements
This work was supported by a New & Renewable Energy Core Technology Program (No. 20153030041170) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government’s Ministry of Trade, Industry & Energy, and grants from the Korea Institute of Energy Research (B7-2424).
References (45)
- et al.
Hydrogen production and purification from the water-gas shift reaction on CuO/CeO2-TiO2 catalysts
Appl Energy
(2013) - et al.
Water-gas shift reaction over Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation
Appl Catal A: Gen
(2006) - et al.
Development of catalysts for hydrogen production through the integration of steam reforming of methane and high temperature water gas shift
Energy
(2015) - et al.
Catalytic hydrogen production from fossil fuels via the water gas shift reaction
Appl Energy
(2015) - et al.
Techno-economic comparison between different technologies for CO2-free power generation from coal
Appl Energy
(2017) - et al.
SEWGS technology is now ready for scale-up!
Energy Proc
(2013) - et al.
High-purity hydrogen production through sorption enhanced water gas shift reaction using K2CO3-promoted hydrotalcite
Chem Eng Sci
(2012) - et al.
Sorption-enhanced hydrogen production for pre-combustion CO2 capture: thermodynamic analysis and experimental results
Int J Greenh Gas Con
(2007) - et al.
Application of one-body hybrid solid pellets to sorption-enhanced water gas shift reaction for high-purity hydrogen production
Int J Hydrogen Energy
(2014) - et al.
Sorption-enhanced water gas shift reaction by sodium-promoted calcium oxides
Fuel
(2010)
Kinetics and reactor modeling for CaO sorption-enhanced high-temperature water-gas shift (SE-WGS) reaction for hydrogen production
Appl Energy
Enhanced hydrogen-rich gas production from steam gasification of coal in a pressurized fluidized bed with CaO as a CO2 sorbent
Int J Hydrogen Energy
Synthesis and test of sorbents based on calcium aluminates for SE-SR
Appl Energy
Performance of Na2O promoted alumina as CO2 chemisorbent in sorption-enhanced reaction process for simultaneous production of fuel-cell grade H2 and compressed CO2 from synthesis gas
J Power Sources
Roles of double salt formation and NaNO3 in Na2CO3-promoted MgO absorbent for intermediate temperature CO2 removal
Int J Greenh Gas Control
Characteristics of Na-Mg double salt for high-temperature CO2 sorption
Chem Eng J
Effect of pH-controlled synthesis on the physical properties and intermediate-temperature CO2 sorption behaviors of K-Mg double salt-based sorbents
Chem Eng J
Nitrate reduction by metallic iron
Water Res
Catalytic reduction of nitrate on Pt-Cu and Pd-Cu on active carbon using continuous reactor: the effect of copper nanoparticles
Appl Catal B: Environ
Application of multisection packing concept to sorption-enhanced steam methane reforming reaction for high-purity hydrogen production
J Power Sources
Subsection-controlling strategy for improving sorption-enhanced reaction process
Chem Eng Res Des
Effect of catalyst activity in SMR-SERP for hydrogen production: commercial vs. large-pore catalyst
Chem Eng Sci
Cited by (41)
Recent advances in intermediate-temperature CO<inf>2</inf> capture: Materials, technologies and applications
2024, Journal of Energy ChemistryProduction of high-purity H<inf>2</inf> through sorption-enhanced water gas shift over a combination of two intermediate-temperature CO<inf>2</inf> sorbents
2023, International Journal of Hydrogen EnergySorption-enhanced steam gasification of biomass for H<inf>2</inf>-rich gas production and in-situ CO<inf>2</inf> capture by CaO-based sorbents: A critical review
2023, Applications in Energy and Combustion ScienceMgO promoted by Fe<inf>2</inf>O<inf>3</inf> and nitrate molten salt for fast and enhanced CO<inf>2</inf> capture: Experimental and DFT investigation
2023, Separation and Purification TechnologyEnsemble process for producing high-purity H<inf>2</inf> via simultaneous in situ H<inf>2</inf> extraction and CO<inf>2</inf> capture
2022, Cell Reports Physical Science