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.

Enhanced water gas shift reaction by CeO2 anchored Pt single atom catalyst

Pt/CeO2 were synthesized through the polyvinyl alcohol (PVA) reduction protection method, and the efficacies of the catalysts for water gas shift (WGS) reaction were evaluated. Pt was deposited on CeO2 in different forms of Pt single atoms (0.15Pt1/CeO2) and Pt nanoparticles (0.56Pt/CeO2), respectively. CO conversion (400 °C) and turnover frequency (TOF) (250 °C) of the Pt single atom catalyst 0.15Pt1/CeO2 were 89% and 0.85 s−1, respectively, significantly higher than that of the Pt nanoparticle catalyst 0.56Pt/CeO2 for the WGS reaction. The superior catalytic performance Pt single atom catalyst can be attributed to enhanced low-temperature reducibility and increased oxygen vacancies facilitated. In-situ diffuse reflectance infrared Fourier transform spectroscopy (in-DRIFTS) revealed that Pt single atoms promoted the creation of oxygen vacancies on CeO2, which dissociated H2O to H2 and adsorbed O, that subsequently interacted with the weakly adsorbed CO on these Pt sites to generate CO2. In contrast, the adsorption strength of CO nanoparticles Pt was much higher. CO reacted with the OH groups on the Pt nanoparticle catalyst surface to form formate species, which then decomposed to produce both CO2 and H2. This study presents a promising strategy for designing highly efficient catalysts tailored for WGS.

Effects of synthesis route on the performance of mesoporous ceria-alumina and ceria-zirconia-alumina supported nickel catalysts in steam and autothermal reforming of diesel

Decline in catalyst performance due to coke deposition is the main problem in diesel steam (SR) and autothermal reforming (ATR) reactions. Good redox potential and strong interaction of CeO2 with nickel increase activity and coke resistivity of Ni/Al2O3 catalysts. In this study, mesoporous Al2O3, CeO2/Al2O3, and CeO2/ZrO2/Al2O3 supported nickel catalysts were successfully synthesized. The highest hydrogen yield, 97.7%, and almost no coke deposition were observed with CeO2/ZrO2/Al2O3 catalyst (Ni@8CeO2-2ZrO2-Al2O3-EISA) in SR reaction. The second highest hydrogen yield, 91.4%, was obtained with CeO2/Al2O3 catalyst (Ni@10CeO2-Al2O3-EISA) with 0.3 wt% coke deposition. Presence of ZrO2 prevented the transformation of cubic CeO2 into CeAlO3, which enhanced water gas shift reaction (WGSR) activity. Ni@10CeO2-Al2O3-EISA did not show any decline in activity in a long-term performance test. Higher CeO2 incorporation (20 wt%) caused lower steam reforming activity. Change of synthesis route from one-pot to impregnation for the CeO2 incorporation decreased the number of acid sites, limiting cracking reactions and causing a significant drop in hydrogen production.

Surface modification of g-C3N4-supported iron catalysts for CO hydrogenation: Strategy for product distribution

Surface modified g-C3N4 supported iron catalysts were prepared using ultrasonic-assisted impregnation and employed as model catalysts to investigate the surface modification effects on product distribution in Fischer–Tropsch synthesis. Characterizations evidenced that both hydroxyl and amino groups were grafted on the g-C3N4 surface. Results showed that the selectivity of light olefins in hydrocarbons was increased from 12.3% on pure Fe3O4 to 31.5% on Fe/C3N4 further to 38.4% on Fe/AMC3N4 under same reaction condition as well as elevated activity owing to electron transfer of amino groups. But high CO2 selectivity was inevitable via the enhanced water gas shift reaction. H2O2 treatment increased the hydrophilicity of g-C3N4, resulting in predominance of water-assisted pathway promoted the chain growth. Compared with Fe/C3N4, the CH4 selectivity for Fe/OHC3N4 was significantly reduced from 38.4% to 22.8%. The Fe/OHC3N4 also exhibited lower CO2 selectivity of 11.4% than Fe/AMC3N4 of 24% due to the enrichment of surface hydroxyl. Surface modification played a critical role in tuning the product distribution and promoting the formation of light olefins with low C1 by products (CH4 and CO2).

Thermodynamic analysis of syngas production via chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) for syngas production was studied based on thermodynamic equilibrium analysis under various fuel reactor temperatures and pressures. Fe2O3 was used as the oxygen carrier (OC). Four CL-DRM stages can be identified based on the ratio of circulated Fe2O3 flow rate to fed CH4 flow rate (OC/CH4): combined methane decomposition (MD) and partial oxidation of methane (POM), combined POM and complete oxidation of methane (COM) with POM dominance, combined POM and COM with COM dominance, and COM. For syngas production the OC/CH4 ratio must be small and its value depends on reaction temperature. Based on the results obtained, it was found that CH4 oxidation due to the presence of OC is the key reaction that affects CL-DRM performance. Compared with conventional DRM in which no OC was introduced, CL-DRM has advantages of producing higher CH4 conversion and lower carbon formation. However, lower CO2 conversion results. It was found that both conventional DRM and CL-DRM were not favourable as reaction pressure increases. The CH4 conversion in CL-DRM can be enhanced by increased CO2/CH4 ratio and water addition in the feedstock. However, CO2 conversion decreased due to increased CO2 amount or enhanced water gas shift reaction.

Investigation on the Trace Amount of Released CO in Sorption Enhanced Water Gas Shift Reaction Applied in Pre-combustion CO2 Capture and High Purity H2 Production

Sorption enhanced water gas shift (SEWGS) is a developing technology that combines the water gas shift reaction and pre-combustion CO2 capture. It has the ability to in-situ remove CO2 and produce fuel cell level of hydrogen from coal derived syngas. In this paper, the trace amount of CO and CO2 leakage in SEWGS was analyzed. A SEWGS model was built by coupling the elementary kinetic CO2 adsorption model and the high temperature WGS model. It considered comprehensive coupling effects from mass and momentum transport processes, integrated with dynamic boundary condition and realistic operating procedures. 17 cases with different S/G ratio, feed flow, inlet CO concentration and balanced gas were simulated. The results indicated that the outlet CO concentration in SEWGS could be controlled below 50 ppm, even 10 ppm from the original 1000–30000 ppm of WGS thermodynamic balance concentration.

Producing Hydrogen-rich Gas by Fresh Biomass Co-pyrolysis with Additive

<p>Pyrolysis properties of fresh ficus lacor leaves with moisture content of 70<em>wt</em>. % was investigated in a TGA setup. The effects of different operating parameters on pyrolysis of biomass were studied in a fixed-bed reactor system. With addition of CaO, there showed an additional decrease in weight at temperature range of 382~490 <sup>o</sup>C, but 12<em>wt</em>. % weight was recovered in the first stage (40~220 <sup>o</sup>C). Fresh biomass pyrolysis was calculated to be first order reaction with activation energy about 29.8 kJ mol<sup>-1</sup>. Activation energy was lowered to 20.4 kJ mol<sup>-1</sup> by addition of CaO. With scope of temperature studied, higher temperature was found always favor hydrogen production during pyrolysis of fresh biomass. Carbonation and hydration of CaO enhanced water gas shift reaction (WGS) which led to hydrogen yield increasing. The highest hydrogen content (around 70<em>vol</em>. %) of hydrogen concentration and hydrogen yield (23.2 ml g<sup>-1</sup><sub>-biomass</sub>) were achieved when CaO/biomass mass ratio increased to 0.3. Pyrolysis of fresh biomass without pre-drying showed the potential of hydrogen production.</p>

HYDROGEN PRODUCTION FROM STEAM PYROLYSIS-GASIFICATION OF SUGARCANE LEAVES WITH SORBENT-CATALYSTS

In this work, the hydrogen production during biomass steam pyrolysis-gasification with a combined catalysts and sorbent. The biomass sample was originated from sugarcane leaves. The combined catalyst and sorbent (NiO-MgO-CaO/γ-Al2O3) was prepared by an excess-solution impregnation method and the property of fresh and used catalysts was characterized using XRD. The prepared sorbent-catalysts promoted both tar reforming and CO2 absorption. High hydrogen production was achieved due to the enhanced water–gas shift reaction by the latter. The pyrolysis-gasification experiments were conducted in a drop tube two-stage fixed bed reactor. The effect of operating parameters such as the amount of MgO (3, 5 and 10 wt.%) and CaO (3, 5 and 10 wt.%) on supported catalysts and the gasification temperatures (600, 700 and 800 oC) were investigated. It was found that the highest hydrogen yield of 23.2 mmol H2/gbiomass was attained using the Ni10Mg5Ca5 catalyst at the gasification temperature of 600 oC. However, the maximum of tar conversion was observed around 78 wt.% at gasification temperature up to 800 oC.

Regenerable MgO-based sorbent for high temperature CO2 removal from syngas: 3. CO2 capture and sorbent enhanced water gas shift reaction

Regenerable MgO-based sorbent, which was prepared and evaluated in the thermogravimetric analyzer (TGA) in part 1, was also evaluated in high-pressure packed-bed unit in CO2/N2/H2O mixture and simulated pre-combustion syngas environment. In CO2/N2/H2O environment, the CO2 absorption capacity of the sorbent increases with increasing temperatures from 6.7% at 350°C to 9.5% 450°C. The sorbent is capable of achieving over 95% CO2 capture and 40% conversion in the water gas shift (WGS) reaction, which should be attributed to positive effect of WGS reaction in producing CO2 during the process. The sorbent reactivity and absorption capacity toward CO2, as well as its WGS catalytic activity decreases with increasing temperature. The maximum pre-breakthrough WGS conversion occurs at 350°C, which diminishes as the sorbent is carbonated. The variable diffusivity shrinking core reaction model coupled with the two-fluid computational fluid dynamics (CFD) model was shown to accurately predict the break-through gas compositions at different operating conditions.

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.

Production of fuel-cell grade hydrogen by sorption enhanced water gas shift reaction using Pd/Ni–Co catalysts

It has been demonstrated both thermodynamically and experimentally that fuel-cell grade hydrogen can be produced by a one-step sorption enhanced water gas shift (SEWGS) process at about 500°C, where the water gas shift (WGS) catalyst and the CO2 sorbent are highly integrated. A synthetic CaO-based mixed oxide sorbent was also assessed, which showed a good CO2 capture capacity and stability in the cyclic operation of the SEWGS reaction. Catalysts play a significant role in CO conversion via WGS, methanation and methane steam reforming reactions. A Pd promoted Ni–Co catalyst (1%Pd/20%Ni–20%Co) derived from hydrotalcite-like material (HT) showed a high activity for WGS and methane steam reforming. The methanation activity was further reduced on 30%Ni–10%Co. There exists an optimum temperature (500°C) for hydrogen production by the SEWGS process, where it is kinetically limited by the WGS reaction at lower temperatures (425–475°C) and it is thermodynamically unfavorable at higher temperatures (475–550°C). The challenges for hydrogen production by SEWGS at high CO pressures were also demonstrated, where CO pressure has shown a negative influence on WGS activity. An induction period was observed, which can be reduced by improving catalyst activity and by adding hydrogen to the reactant mixture.

Study of MgO-based dry regenerable sorbent for sorption enhanced water gas shift reaction

CO2 sorption capacities and physical properties of the MgO-based sorbent, and the effect of steam during the sorbent regeneration were studied. Four MgO-based dry regenerable sorbents (P-A ∼ D) were prepared by spray drying method for the application to pre-combustion CO2 capture. Physical properties of the sorbents were measured by standard ASTM methods. MgO-based sorbents satisfied with most of the physical requirements for commercial fluidized-bed process. All sorbents had a spherical shape and an average size of 106 ± 10 μm. Most of the attrition index (AI) of the sorbents except for P-D was below 12%, which was superior, compared to commercial fluidized catalytic cracking (FCC) catalysts. CO2 sorption capacities were evaluated by multi-cycle test in a high pressure bubbling fluidized-bed reactor at 473 K and 20 bar with 37% CO2. The sorption capacities of the sorbents showed 3.3–14.5 wt% during 3 cycle. Particularly, P-A showed a high CO2 sorption capacity of more than 14 wt%. In this study, CO2 sorption capacity of steam-treated sorbent was higher than non-treated sorbent. This result can be explained by the presence of Mg(OH)2 formed by hydroxylation by MgO and increasing surface area of steam-treated sorbent.

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO2 capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO2, and the solid product is CaCO3, and the Ca(OH)2 may be formed from the reaction of CaO with H2O with the presence of steam in gas phase. The effect of Ca(OH)2 and CaCO3 on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO3 did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)2 may be the reason of catalytic reactivity recovery. CaCO3 can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO3 decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.

High-purity hydrogen production through sorption enhanced water gas shift reaction using K2CO3-promoted hydrotalcite

Sorption enhanced water gas shift (SEWGS) reaction is a process concept, which simultaneously carries out the gas phase water gas shift (WGS) reaction (CO+H2O↔CO2+H2) and selective chemisorption of the byproduct CO2 from the gas phase reaction zone for direct production of essentially pure H2 in a single unit operation. A packed bed sorber-reactor containing an admixture of a WGS catalyst and a CO2 chermisorbent is used in the process. The concept circumvents the thermodynamic limitation of the WGS reaction and enhances the rate of reaction for H2 production. In this study, the SEWGS reaction concept was successfully demonstrated by both experiment and numerical simulation using K2CO3-promoted hydrotalcite as the CO2 sorbent. Numerical model simulations were also carried out to investigate the effects of various operating conditions of SEWGS reaction on the process performance. In general, higher H2O/CO feed ratio, higher fraction of sorbent (chemisorbent ratio in the sorber-reactor), and lower operating temperature favor both H2 productivity and CO conversion. Higher reaction pressure increases H2 productivity but decreases CO conversion.

Investigation of the Enhanced Water Gas Shift Reaction Using Natural and Synthetic Sorbents for the Capture of CO2

The water gas shift (WGS) reaction was conducted in the presence of two natural and two synthetic CaO-based sorbents. It was shown that such sorbents can affect the WGS in two ways: (i) by catalysi...