Sorption Enhanced Water Gas Shift Research Articles

Testing of hydrotalcite based sorbents for CO2 and H2S capture for use in sorption enhanced water gas shift

The sorption enhanced water-gas shift technology is attractive for pre-combustion decarbonisation of power production based on IGCC, but only when the SEWGS technology can be applied for sour syngas. To this extend, it was recently demonstrated that 2000 ppm of H2S did not influence the CO2 sorption behaviour of a potassium promoted hydrotalcite material at a relatively low pressure of 5 bar. This paper highlights ongoing sorbent testing at pressure swing operation between 30 bar adsorption and 2 bar regeneration, crucial for the successful development of the technology. The sorbent has good catalytic activity for the water-gas shift reaction during SEWGS conditions. At 30 bar pressure and 400 °C feed temperature, a CO, CO2 and H2S free H2-product is obtained when feeding a syngas containing 200 ppm H2S. This implies that mixing in a separate WGS catalyst is not needed, which significantly simplifies the technology. Moreover, multi-cyclic testing at 30 bar and 400 °C for 110 cycles shows good sorbent stability in the presence of 200 ppm H2S. Deliberately induced slips of CO2 and H2S stabilize within a limited number of cycles. By simply reducing the adsorption period, the mass-transfer zones for both CO2 and H2S are readily pushed back into the column, again producing a product free of CO2 and H2S. These observations suggest that reversibility of sorption processes on the material that have been tested is fully appropriate for the further development of the long-term operation of sour-SEWGS technology.

Improved sorbent for the sorption-enhanced water-gas shift process

Abstract For the sorption-enhanced water-gas shift (SEWGS) process, a new sorbent material has been developed. The sorbent is a potassium-carbonate promoted hydrotalcite-based material. The material has been tested under realistic process conditions in an experimental rig of 2 m length. The cyclic capacity of the material is 27% higher than the cyclic capacity of the reference sorbent, which was used in CACHET, a previous R&D project. Moreover, 36% less steam is required for its regeneration. The sorbent pellets also have a 65% higher crush strength than the reference sorbent. Contrary to the reference material, the novel material does not form notable amounts of MgCO 3 under relevant operating conditions. Due to the absence of this slow CO 2 uptake process, the sorbent remains mechanically stable, the cyclic steady state is reached rapidly, CO 2 slip in the product gas is reduced, and steam requirements are lowered. It is demonstrated that the sorbent remains mechanically stable during operation of at least 1200 adsorption–desorption cycles. With this new, higher density material, carbon capture levels exceeding 95% can be obtained more efficiently and vessels will be smaller.

Integration of SEWGS for carbon capture in Natural Gas Combined Cycle. Part B: Reference case comparison

This two part-paper investigates the performance of different integration possibilities in a Natural Gas Combined Cycle of an innovative reactor for CO 2 capture named SEWGS (Sorption Enhanced Water Gas Shift). This activity is carried out under the FP7 project CAESAR financed by the EU community. In part A, several plant layouts starting from completely decoupled hydrogen island and power section up to very tight integration are investigated in order to show the different advantages and performance differences. A sensitivity analysis on main parameters is also carried out. Part B presents three reference cases selected for electricity production: without carbon capture, with post-combustion carbon capture by MEA and with pre-combustion carbon capture by MDEA. These cases are compared with three different SEWGS plants presented in part A. A tight integration between power and hydrogen island allows SEWGS to achieve a lower efficiency penalty than MEA and MDEA (7.5% for SEWGS, 8.4% for MEA and 8.0% for MDEA) with a higher CO 2 avoided (95.2% for SEWGS, 90.2% for MEA and 91.0% for MDEA). Decoupling the hydrogen and power islands brings about higher efficiency penalty (12.5%) with 95.3% of CO 2 avoided. Finally, an exergy comparison among all the cases is carried out in order to explain the performance differences, outlining the main advantages of SEWGS in high temperature CO 2 separation with limited energy consumption.

Integration of SEWGS for carbon capture in natural gas combined cycle. Part A: Thermodynamic performances

This two part-paper investigates the performance of different integration options of an innovative reactor for CO 2 capture named SEWGS (Sorption-Enhanced Water Gas Shift) in a natural gas combined cycle. This activity was carried out under the FP7 project CAESAR financed by the EU community. In Part-A, several plant layouts starting from a completely decoupled hydrogen island and power section, up to very tight integration are investigated in order to outline mutual advantages and performances. Decoupling the hydrogen island from the power plant is beneficial to system flexibility but penalizes the net electric efficiency (45.9% with a CO 2 capture of 95.3%). The best overall performance is achieved by a tight integration of the two sections that increases efficiency up to 50.9% with a CO 2 capture of 95.2%, thanks also to the possibility of expanding the CO 2–steam stream from the SEWGS unit. A sensitivity analysis on the main parameters is also carried out. Part B presents three reference cases selected for electricity production with and without CO 2 capture in order to benchmark the innovative solution including by exergy analysis.

Testing of hydrotalcite-based sorbents for CO 2 and H 2S capture for use in sorption enhanced water gas shift

The feasibility of the sorption enhanced water gas shift (SEWGS) process under sour conditions is shown. The sour-SEWGS process constitutes a second generation pre-combustion carbon capture technology for the application in an IGCC. As a first critical step, the suitability of a K 2CO 3 promoted hydrotalcite-based CO 2 sorbent is demonstrated by means of adsorption and regeneration experiments in the presence of 2000 ppm H 2S. In multiple cycle experiments at 400 °C and 5 bar, the sorbent displays reversible co-adsorption of CO 2 and H 2S. The CO 2 sorption capacity is not significantly affected compared to sulphur-free conditions. A mechanistic model assuming two different sites for H 2S interaction explains qualitatively the interactions of CO 2 and H 2S with the sorbent. On the type A sites, CO 2 and H 2S display competitive sorption where CO 2 is favoured. The type B sites only allow H 2S uptake and may involve the formation of metal sulphides. This material behaviour means that the sour-SEWGS process likely eliminates CO 2 and H 2S simultaneously from the syngas and that an almost CO 2 and H 2S-free H 2 stream and a CO 2 + H 2S stream can be produced.

Sorption-enhanced water gas shift reaction by sodium-promoted calcium oxides

The water gas shift reaction was evaluated in the presence of novel carbon dioxide (CO 2) capture sorbents, both alone and with catalyst, at moderate reaction conditions (i.e., 300–600 °C and 1–11.2 atm). Experimental results showed significant improvements to carbon monoxide (CO) conversions and production of hydrogen (H 2) when CO 2 sorbents are incorporated into the water gas shift reaction. Results suggested that the performance of the sorbent is linked to the presence of a Ca(OH) 2 phase within the sorbent. Promoting calcium oxide (CaO) sorbents with sodium hydroxide (NaOH) as well as pre-treating the CaO sorbent with steam appeared to lead to formation of Ca(OH) 2, which improved CO 2 sorption capacity and WGS performance. Results suggest that an optimum amount of NaOH exists as too much leads to a lower capture capacity of the resultant sorbent. During capture, the NaOH-promoted sorbents displayed a high capture efficiency (nearly 100%) at temperatures of 300–600 °C. Results also suggest that the CaO sorbents possess catalytic properties which may augment the WGS reactivity even post-breakthrough. Furthermore, promotion of CaO by NaOH significantly reduces the regeneration temperature of the former.

Carbon Capture by Sorption-Enhanced Water−Gas Shift Reaction Process using Hydrotalcite-Based Material

A novel route for precombustion decarbonization is the sorption-enhanced water−gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water−gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tablets of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400 °C, the material shows a breakthrough capacity of 1.4 mmol/g. The sharp adsorption front is accompa...

Selection of CO2 chemisorbent for fuel-cell grade H2 production by sorption-enhanced water gas shift reaction

Abstract New experimental data are reported to demonstrate that high purity H2 can be directly produced by sorption-enhanced water gas shift (WGS) reaction using synthesis gas (CO + H2O) as sorber-reactor feed gas. An admixture of a commercial WGS catalyst and a proprietary CO2 chemisorbent (K2CO3 promoted hydrotalcite or Na2O promoted alumina) was used in the sorber-reactor for removal of CO2, the WGS reaction by-product, from the reaction zone. The promoted alumina was found to be a superior CO2 chemisorbent for this application because (a) it could directly produce a fuel-cell grade H2 product (

Performance of Water–Gas Shift Catalysts under Sorption-Enhanced Water–Gas Shift Conditions

Abstract The second pre-combustion decarbonisation technology Sorption Enhanced Water-Gas Shift (SEWGS) combines the WGS reaction with simultaneous CO 2 capture by using a mixture of WGS catalyst and CO 2 sorbent. Accordingly, the WGS catalyst is exposed to all conditions encountered in the cyclic SEWGS process, such as exposure to steam in the regeneration step. This paper shows that commercial precious metal, FeCr, and CoMo WGS catalysts are robust towards periodic exposure to these atypical conditions. Catalyst behavior is reported to periodic exposure to these atypical conditions at a temperature of 400 ∘ C, pressures up to 5 bara and H 2 S contents from 1 ppm to 2,000 ppm. Although additional experiments need to be performed at increased pressure, it appears that all catalysts can potentially be used in the SEWGS process.

Performance of sorption-enhanced water-gas shift as a pre-combustion CO2 capture technology

Abstract The sorption-enhanced water-gas shift (SEWGS) process is a promising technology for pre-combustion decarbonisation. It is well suited for decarbonising syngas produced from natural-gas and coal based fuels in combined-cycle power production schemes. Higher capture rates could be obtained by SEWGS at lower efficiency penalties and at lower costs than by absorption. In the SEWGS process, multiple reactor vessels are packed with mixtures of CO 2 sorption pellets and water-gas shift catalyst pellets. The technology is developed using potassium promoted hydrotalcite-based materials as the CO 2 sorbent. In a first series of experiments, the performance of this material is investigated under typical SEWGS process conditions. The sorbent was loaded in 2 m and 6 m tall fixed-bed reactor vessels. Breakthrough capacities of 1.3–1.4 mmol/g are reported. After breakthrough the sorbent continues to take up CO 2 , albeit at a much lower rate. Total sorption capacities exceeding 8 mmol/g are observed. This capacity is attributed to the formation of MgCO 3 in the bulk of the sorbent material and requires moderate to high partial pressures of CO 2 and steam. The stability of the sorbent material during cyclic operation was demonstrated for more than 4,000 adsorption and desorption cycles. A stable and low slip of CO 2 was established, corresponding to a carbon capture ratio of well above 90%. After investigation of the relevant sorbent characteristics, the reactor was loaded with sorbent and catalyst material in order to provide a proof-of-principle of the SEWGS technology and establish the performance and stability of sorbent and catalyst material. When the reactor was fed with a gas mixture that simulated a syngas typically produced by auto-thermal reforming of natural gas, it was demonstrated that carbon monoxide conversion can be enhanced from 55% in absence of a sorbent to 100% in the presence of a sorbent. Neither the change of gas composition nor the mixing of sorbent with catalyst did significantly impact CO 2 breakthrough capacity. In a cyclic duration test, the carbon capture rate and carbon monoxide conversion were confirmed to be above 98% without excessive steam demand, and reasonably stable for at least 500 cycles. The experimental data will be used for modelling, cycle optimization, and scale-up to a pilot unit.

Reduction in the cost of pre-combustion CO2 capture through advancements in sorption-enhanced water-gas-shift

Abstract Sorption-enhanced water-gas-shift (SEWGS) is a pre-combustion decarbonisation technology combining adsorption of CO2 with the water-gas-shift reaction. This process maximises the production of hydrogen from syngas whilst simultaneously capturing and separating CO2. Simulations have been completed to evaluate the use of SEWGS for power generation from natural gas with carbon capture. The modelling results show that using the SEWGS process could significantly reduce the cost of capturing CO2 versus a reference design that uses amine absorption. Work has also been completed to show that using a counter-current steam-rinse step may be an improvement over a co-current CO2-rinse cycle proposed previously.

Effect of Reaction Temperature on the Performance of Thermal Swing Sorption-Enhanced Reaction Process for Simultaneous Production of Fuel-Cell-Grade H2 and Compressed CO2 from Synthesis Gas

A novel cyclic thermal swing sorption-enhanced reaction (TSSER) process concept was recently proposed for the simultaneous production of fuel-cell-grade H2 and compressed CO2 from synthesis gas containing CO and H2O. The process carried out the catalytic water−gas shift (WGS) reaction (CO + H2O ↔ CO2 + H2) with simultaneous removal of CO2 from the reaction zone by a reversible, water-tolerant, CO2-selective chemisorbent in order to circumvent the thermodynamic limitation of the WGS reaction and enhance the rate of the forward reaction. The chemisorbent was periodically regenerated using the principles of thermal swing adsorption by purging the sorber−reactor with superheated steam at different pressures and temperatures. Several intermediate process steps were employed to produce a pure and compressed CO2 byproduct during the thermal desorption process. The present work reports (a) new experimental data demonstrating the concept of the sorption-enhanced WGS reaction at different temperatures using a commercial WGS catalyst and Na2O-promoted alumina as the CO2 chemisorbent and (b) the effect of the sorption−reaction temperature on the TSSER process performance estimated by model simulation. Relatively slower kinetics of the sorption-enhanced WGS reaction imposes a lower bound (∼200 °C), whereas the thermal stability of the chemisorbent and the use of carbon steel sorber−reactors set the upper bound (∼550 °C) of temperatures for practical operation of the TSSER process. Simulated process performances (sorption−reaction at 200 and 400 °C and regeneration at 550 °C) show that the operation of the sorption−reaction step at 200 °C increases the H2 and CO2 productivities of the process by ∼38% and 35%, respectively, without changing (a) the number of moles of H2 produced per mole of CO in the feed gas or (b) the net CO2 recovery as a compressed byproduct gas. The total steam duty for the sorbent regeneration increases by ∼14% for operation at the lower sorption−reaction temperature. Another major benefit of operation at the lower reaction temperature is a very large increase in the pressure of the CO2 byproduct (e.g., 40 and 21 atm at 200 and 400 °C, respectively) when the reactor feed gas contained 20% CO + 80% H2O at a total pressure of 15 atm.

The Crucial Role of the K+–Aluminium Oxide Interaction in K+‐Promoted Alumina‐ and Hydrotalcite‐Based Materials for CO2 Sorption at High Temperatures

CO(2)-free hydrogen can be produced from coal gasification power plants by pre-combustion decarbonisation and carbon dioxide capture. Potassium carbonate promoted hydrotalcite-based and alumina-based materials are cheap and excellent materials for high-temperature (300-500 degrees C) adsorption of CO(2), and particularly promising in the sorption-enhanced water gas shift (SEWGS) reaction. Alkaline promotion significantly improves CO(2) reversible sorption capacity at 300-500 degrees C for both materials. Hydrotalcites and promoted hydrotalcites, promoted magnesium oxide and promoted gamma-alumina were investigated by in situ analytical methods (IR spectroscopy, sorption experiments, X-ray diffraction) to identify structural and surface rearrangements. All experimental results show that potassium ions actually strongly interact with aluminium oxide centres in the aluminium-containing materials. This study unambiguously shows that potassium promotion of aluminium oxide centres in hydrotalcite generates basic sites which reversibly adsorb CO(2) at 400 degrees C.

Thermodynamic Analysis for the Production of Hydrogen through Sorption Enhanced Water Gas Shift (SEWGS)

A thermodynamic analysis for the process concept of hydrogen production based on the combination of the water gas shift (WGS) and CO2 capture reactions (Absorption Enhanced Water Gas Shift, SEWGS) is presented. The chemical equilibrium analysis of this reaction system was performed to select the proper CO2 absorbent among: calcined dolomite (CaO•MgO), Li4SiO4 and Na2ZrO3 to be used in the process. Results indicate that the use of Na2ZrO3 produced the highest hydrogen concentration among absorbents studied. Results also revealed that the maximum hydrogen concentration (97% mol) can be achieved with a feed molar ratio of CO/Na2ZrO3/H2/O = 1/1/2 at 500°C at atmospheric conditions. The use of a catalyst for such processes may not be needed, since the high temperature at which these reactions are proposed may promote homogeneous non-catalyzed reactions. However, if the combination of both reaction kinetics (WGS and carbonation) are not fast enough to reach equilibrium, a new non-conventional WGS catalyst may be needed.

Performance of Na 2O promoted alumina as CO 2 chemisorbent in sorption-enhanced reaction process for simultaneous production of fuel-cell grade H 2 and compressed CO 2 from synthesis gas

The performance of a novel thermal swing sorption-enhanced reaction (TSSER) concept for simultaneous production of fuel-cell grade hydrogen and compressed carbon dioxide as a by-product from a synthesis gas feed is simulated using Na 2O promoted alumina as a CO 2 chemisorbent in the process. The process simultaneously carries out the water gas shift (WGS) reaction and removal of CO 2 from the reaction zone by chemisorption in a single unit. Periodic regeneration of the chemisorbent is achieved by using the principles of thermal swing adsorption employing super-heated steam purge. Recently measured equilibrium and kinetic data for chemisorption and desorption of CO 2 on the promoted alumina using conventional column dynamic tests as well as new experimental data demonstrating the concept of sorption-enhanced WGS reaction using the material are reviewed. The simulated performance of the TSSER process employing this material as a chemisorbent is compared with the process performance using K 2CO 3 promoted hydrotalcite as the chemisorbent. The promoted alumina exhibited (i) ∼15% lower H 2 productivity at a slightly reduced CO to H 2 conversion, and (ii) comparable compressed CO 2 productivity at a higher CO 2 recovery, albeit at a relatively lower product pressure. However, the steam duty for regeneration of the chemisorbent was reduced by ∼50% for the promoted alumina.

Sorption-enhanced hydrogen production for pre-combustion CO 2 capture: Thermodynamic analysis and experimental results

Hydrotalcite-based materials have been identified as suitable materials for high temperature (400 °C) adsorption of CO 2. In pre-combustion decarbonisation processes for natural gas based power cycles, it should be possible to use this material to improve conversions in the water-gas shift (WGS) and steam-reforming (SMR) reaction. The efficiencies for electricity production from natural gas have been calculated for some different system configurations, in which hydrotalcite-based material could be used. The calculated efficiency penalties ranged from 5.5 to 8.6 percentage points. The assumptions made in the system study have been tested on the laboratory scale. Hydrotalcite-based materials are found to be an excellent choice for use in the sorption-enhanced WGS reactor. The requirements for very low residual concentrations of CO 2 at 400 °C and large amounts of catalyst in the sorption-enhanced SMR reactor make its application less likely. Suggestions are made to how the SE-SMR could be improved.

99/03641 High-temperature coal gas desulfurization using CuMnO based sorbent. I. Sulfidation of CuMnO based sorbent: Wan., C. et al. Ranliao Huaxue Xuebao, 1998, 26, (5), 400–405. (In Chinese)

Sorption-enhanced water-gas-shift (SEWGS) is a pre-combustion decarbonisation technology combining adsorption of CO2 with the water-gas-shift reaction. This process maximises the production of hydrogen from syngas whilst simultaneously capturing and separating CO2.Simulations have been completed to evaluate the use of SEWGS for power generation from natural gas with carbon capture. The modelling results show that using the SEWGS process could significantly reduce the cost of capturing CO2 versus a reference design that uses amine absorption. Work has also been completed to show that using a counter-current steam-rinse step may be an improvement over a co-current CO2-rinse cycle proposed previously.