Chemical hot gas cleaning concept for the “CHRISGAS” process

The aim of the CHRISGAS project was the development of a gasification technique to produce clean hydrogen-rich synthesis gas from biomass. In order to improve the process efficiency, this work presents a gas cleaning concept, which combines chemical hot gas cleaning with hot (1 MPa, 900 °C) and warm (1 MPa, 300 °C) filtration. As the focus is set on the removal of H₂S, HCl and KCl, calculations on chemical gas cleaning for the hot and warm gas filter were done using a thermodynamic process model using SimuSage? (GTT-Technologies). The calculations show that Ca-based and Fe-based sorbents are not suitable H₂S sorbents under the conditions of the hot gas filter. For Cu-based sorbents, H₂S concentration below 100 cm³ m^?3 is achievable, if the temperature is reduced below 810 °C. Additional calculations of KCl sorption on alumosilicates under the conditions of the hot gas filter show that the alkali concentration in gasifier-derived gases can be limited to 100 mm³ m^?3. Thus, the condensation temperature of KCl can be decreased down to 580 °C. The results of HCl sorption calculations show that Na- and K-based sorbents are only suitable for temperatures below 600 °C. Therefore, the HCl sorption is transferred to the warm gas filter. The KCl sorption results were confirmed by experiments using bauxite, bentonite, kaolinite and naturally occurring zeolite as sorbents.     

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.     

Release and transformation characteristics of Na/Ca/S compounds of Zhundong coal during combustion/CO2 gasification

Zhundong (ZD) coal from northwest China is a high quality steam coal with reserves of more than 390 billion tons. However, the utilization of ZD coal is limited due to the high content of alkali and alkaline earth metals. This study aimed at revealing the release and transformation mechanism of Na/Ca/S compounds during combustion/gasification of ZD coal. The results demonstrate that Na was primarily influenced by temperature, mostly releases at 600–800 °C. The transformation of Ca compounds was affected by both temperature and atmosphere. The high temperature of the combustion process could accelerate the decomposition of CaCO₃ and CaSO₄, and the high content of CO₂ during gasification prolonged the decomposition of CaCO₃. The transformation of S was primarily influenced by atmosphere. SO₂ could react with CaO and form CaSO₄ during the combustion process. While S compounds were mainly released as S (g) and H₂S (g) during gasification process. There was a significant interaction among Na/Ca/S compounds during combustion, original CaSO₄ in coal could adsorb Na compounds with SO₂ at 600–800 °C and then reacted with aluminosilicates, by this reaction, Na could be fixed above 1000 °C.     

Calcium species evolution mechanism during coal pyrolysis and char gasification in H2O/CO2

The release mechanism of Ca during coal pyrolysis and char gasification in H₂O, CO₂ and their mixtures was studied. Sequential chemical extraction was used to determine the modes of occurrence of Ca in coal and char. The released Ca from coal pyrolysis and char gasification were captured and analyzed by activated carbon adsorption and X-ray photoelectron spectroscopy (XPS). Model compounds CaS and CaSO₄ were adopted to further reveal the released form of Ca under different atmospheres. The results indicate that Ca in coal is mainly released as CaCl₂ during the pyrolysis process, and the possible migration mechanism of Ca during pyrolysis was proposed. Ca in coal is mainly released in the form of CaCl₂, CaCO₃, and CaSO₄ during the gasification, and Ca is released as CaCl₂ under all conditions. In addition, Ca will be released as CaCO₃ under CO₂ atmosphere, as CaSO₄ under H₂O and H₂O/CO₂ atmospheres at 800 °C and 900 °C, released as CaSO₄ under all conditions at 1000 °C. This is closely related to the formation of CaO₂ intermediates during the gasification process.     

Influence of CaO precursor on CO2 capture performance and sorption-enhanced steam ethanol reforming

This work presents the effect of calcium and carbonate precursors on properties of CaCO₃. The synthetic CaCO₃ samples were transformed into CaO and tested their application to high-temperature CO₂ capture. Four different sorbent precursors were investigated in this work, including calcium chloride (CaCl₂) and calcium acetate (CaAc₂) as calcium precursor, and sodium carbonate (Na₂CO₃) and urea (CO(NH₂)₂) as carbonate precursor. The results show that both calcium and carbonate precursors affect morphologies of CaCO₃; CaCO_3,Cl-Urea, and CaCO_3,Cl-Na have calcite phase, whereas mixed-phases of calcite (30%) and vaterite (70%) are observed with CaCO_3,Ac-Na, and aragonite is found with CaCO_3,Ac-Urea. CaCO_3,Cl-Na exhibits small cubic (rhombohedral) particle, CaCO_3,Cl-Urea possesses spherical particle with rough surface, CaCO_3,Ac-Na has spherical-like morphology with smooth surface, and CaCO_3,Ac-Urea possesses aggregated form of CaCO₃ particles. For application to CO₂ capture, CaO derived from CaCO_3,Ac-Urea provides the highest CaO conversion of 80% at 700 °C. The synthetic CaO-based sorbents were further incorporated with nickel oxide to form one-body bi-functional catalysts for H₂ production from sorption-enhanced steam ethanol reforming. The results show that 87%H₂ purity could be obtained with pre-breakthrough period of 60 min. Sorbent reactivity can be maintained the production of H₂ for at least 10 consecutive cycle tests.     

Hydrogen production by biomass gasification in supercritical or subcritical water with Raney-Ni and other catalysts

Gasification of peanut shell, sawdust and straw in supercritical or subcritical water has been studied in a batch reactor with the presence of a series of Raney-Ni and its mixture with ZnCl₂ or Ca(OH)₂. The main gas products were hydrogen, methane, carbon dioxide, and a small amount of carbon monoxide. Different types of Raney-Ni, containing different metal components such as Fe, Mo or Cr, have different influences on the gasification yield and hydrogen selectivity. The catalysis effect can be improved obviously by adding ZnCl₂ or Ca(OH)₂. Increasing the reaction temperature or adding ZnCl₂ and Ca(OH)₂ could improve the mass of H₂ in gas products and reduce the mass of CH₄ and CO₂ at the same time. The possible mechanism is that ZnCl₂ can decompose the biomass particle by accelerating cellulose hydrolyzation in high-temperature water, increasing more specific surface to admit catalysts, while Ca(OH)₂ can absorb CO₂ to produce CaCO₃ deposit, which can drop out from the reactant system, and which will drive the reaction to get more hydrogen. With respect to the biomass conversion to gas product and selectivity of H₂ at low temperature, the series of Raney-Ni has shown many advantages over other catalysts; thus, this kind of catalyst has great potential to be utilized in the hydrogen industry for the gasification of biomass.     

The synergistic effect of Ca(OH)2 on the process of lignite steam gasification to produce hydrogen-rich gas

The synergistic effect of Ca(OH)₂ prepared by the wet-mixing method on lignite steam gasification process at different temperatures (700–900 °C) was analyzed in a spout-fluid bed reactor. Firstly, to avoid disturbance of volatile and tar, active carbon was used as a model compound. On the one hand, Ca(OH)₂ effectively catalyzed the water-gas shift (WGS) reaction to improve H₂ concentration, but the performance was weaker at higher temperature due to the enhancement of boudouard reaction and the weakening of WGS reaction. On the other hand, it was found that the (CO+2CO₂)/H₂ ratio of syngas produced at 700 °C in the presence of Ca(OH)₂ was 0.82, which was much lower than that of the other cases, owning to the absorption of CO₂. The synergistic effect was observed at this temperature, for the adsorption of CO₂ altered equilibrium of the WGS reaction and further improved H₂ concentration. Then two kinds of Chinese lignite (HLH and XM) were selected to further study the performance of Ca(OH)₂ on optimizing the lignite steam gasification process. In the presence of Ca(OH)₂, tar and char yields greatly reduced at the same reaction temperature, whereas the gas yields significantly increased. As a catalyst, Ca(OH)₂ can not only promote solid–gas reaction to decrease char yield, but also accelerate tar decomposition to reduce its yield in syngas. Based on GC–MS data, it can be deduced that Ca(OH)₂ has different catalytic activity on the steam reforming of tar with different molecular structures. Contrast to Class 4, tars of aliphatic hydrocarbons, Class 2 and Class 5 were clearly catalytic reformed. Hydrogen-rich gas can be produced at 800 °C and 900 °C owning to the catalytic effect of Ca(OH)₂, but the highest H₂ concentration was found at 700 °C due to the additional effect of CO₂ absorption, which was supported by the results of thermogravity experiments.     

High quality syngas production from pressurized K2CO3 catalytic coal gasification with in-situ CO2 capture

The enhanced K-catalytic coal gasification by CO₂ sorption reaction (EKcSG) was proposed to produce syngas with high content of H₂ and CH₄ and perform in-situ CO₂ capture. CO₂ is reduced dramatically with the introduction of the CaO into the reactor under typical K-catalytic coal gasification condition (3.5 MPa, 700 °C). The carbonation reaction of CaO can promote the syngas production by improving the equilibrium of the water-gas shift reaction and supplying heat for coal gasification reaction. In the presence of the CaO sorbent (Ca/C = 0.5), the CO₂ concentration in the product gas decreased from 25.61% to 12.80% compared with that without CaO. Correspondingly, the total concentration of H₂ and CH₄ is improved from 65.61% to 82.99% and the carbon conversion reached above 95%. The effect of Ca/C ratio and reaction temperature was investigated during the EKcSG process. It is considered that Ca/C ratio of 0.5 is the best proportion in terms of carbon conversion and CO₂ absorption in our experimental conditions.     

HCl emission and capture characteristics during PVC and food waste combustion in CO2/O2 atmosphere

The emission and capture characteristics of HCl during PVC and food waste combustion in CO₂/O₂ atmospheres were studied. Replacement of N₂ by CO₂ decreased the dechlorination rate of limestone at 600–700 °C but increased dechlorination rate at 800–900 °C. The chlorine species and temperature highly influenced the HCl emission and capture efficiency of limestone for HCl in CO₂/O₂ atmospheres. Compared with inorganic chloride in food waste, organic chlorine in PVC had much greater Cl–HCl conversion percent (75.0–93.9%), and higher dechlorination rate (20.4–44.9%) with 10% limestone in 80CO₂/20O₂ atmosphere. The increment of O₂ partial pressure in CO₂/O₂ atmospheres promoted Cl–HCl conversion. Sulphur in the fuel suppressed the formation of HCl but decreased the dechlorination rate at 700–1000 °C in CO₂/O₂ atmospheres. The dechlorination efficiency of limestone was better than magnesium based additive and could be improved by modification with NaOH. This research helps control HCl and manages MSW oxy-fuel incineration.     

Pyrolysis characteristics of Turkish lignites in N2 and CO2 environments

Pyrolysis characteristics and kinetic parameters of two Turkish lignites having different ash contents (Orhaneli as low ash and Soma as high ash sample) were studied under N₂ and CO₂ atmospheres by means of thermogravimetric analysis. The isoconversional kinetic methods of Flynn?Wall??Ozawa, Kissinger??Akahira??Sunose, and Friedman were employed to estimate the activation energy and pre-exponential factors. The experiments were conducted at four different heating rates of 5, 10, 15, and 20°C/min within the temperature range of 50??950ºC. The obtained results indicated that changing the pyrolysis ambient had no significant effect on the devolatilization region up to 700°C. The char formation region in N₂ atmosphere was due to the CaCO₃ decomposition and was more significant for Soma lignite due to its high ash content. However, in CO₂ atmosphere, the gasification reaction took place at temperatures higher than 700°C. The decomposition process of CaCO₃ in CO₂ atmosphere was hampered up to temperatures higher than 900°C. The estimated activation energies were found to have approximately similar trends under different atmospheres. For Orhaneli lignite, the average activation energy values were higher in CO₂ environment. However, for Soma lignite due to decomposition of CaCO₃, the activation energy values were higher in N₂ atmosphere. The mean uncertainty values were assessed for the activation energy values obtained for all test cases.     

Molten salt synthesis of high-entropy alloy AlCoCrFeNiV nanoparticles for the catalytic hydrogenation of p-nitrophenol by NaBH4

High-entropy alloy (HEA) AlCoCrFeNiV nanoparticles were prepared from oxide precursors using a molten salt synthesis method without an electrical supply. The oxide precursor was directly reduced by CaH₂ reducing agent in molten LiCl at 600°C-700°C or molten LiCl–CaCl₂ at 500°C-550°C. When the reduction was conducted at 700°C, a face-centered cubic (FCC) structure produced, as identified by X-ray diffraction analysis. With lower reduction temperatures, the FCC structure was absent, replaced by a body-centered cubic (BCC) structure. With a reduction temperature of 550°C, the resulting sample was composed of highly pure HEA AlCoCrFeNiV nanoparticles with a BCC structure of 15 nm. Analyses by scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy confirmed the formation of homogeneous HEA AlCoCrFeNiV with a nanoscale morphology. In the hydrogenation reaction of p-nitrophenol by NaBH₄, the AlCoCrFeNiV nanoparticles (produced at 550°C) exhibited a catalytic activity with ～90% conversion and 16 kJ/mol activation energy.     

Study on SO2-Absorption Behavior of Composite Materials for DeSOx Filter From Diesel Exhaust

NO_x emitted from diesel engines is one of the major air pollutants in most countries. To reduce NO_x emission, NO_x storage/reduction (NSR) catalysts have been developed for diesel systems. The catalyst for NSR is strongly poisoned with sulfur. This paper reports the synthesis of Na-doped CaCO₃ as a new material for SO₂ adsorption. Measurements of the desulfurization breakthrough characteristics using monolith washcoated Na-doped CaCO₃ were investigated at 450°C. The Na-doped CaCO₃ absorbed ～77.6–90.6 mg_-SO₂/g_-material of SO₂ at 450°C (where CaCO₃ is 8 mg_-SO₂/g_-material). Investigation of the source of the improved sulfur absorption capacity of the Na-doped CaCO₃ relative to the parent material via x-ray diffraction (XRD) and scanning electron microscopy–energy-dispersive x-ray spectroscopy (SEM-EDX) analyses revealed that the new material forms a composite partially composed of Na₂Ca(CO₃)₂. The enhanced SO₂ absorption capacity derived from the formation of composite materials is demonstrated herein. SO₂ contained in the exhaust gas is absorbed at a lower temperature than with previously reported systems. In order to elucidate the SO₂ absorption mechanism of the composite materials, further studies and synthesis of materials with greater absorption capacity are required.     

Municipal Solid Waste Leachates Destruction and Metals Recovery by Supercritical Water Oxidation

Municipal solid waste leachate dissolved with nitrates of Cr, Pb, and Cu was investigated using a supercritical water oxidation process in this study. The destruction efficiency of chemical oxygen demand increased with the higher temperature and longer reaction time. A first-order expression applied for chemical oxygen demand was determined with a pre-exponential factor of 318 s^–1 and activation energy of 58 kJ/mol. Recovery efficiency of Cr, Pb, and Cu from initial solution into solid product increased with the higher temperature and longer reaction time. X-ray diffraction of solid products showed that the metal species were found to be Cu₂O, HCrO₂, and CaCO₃ at temperature 400°C, while the structure were identified as CuO, Cr₂O₃, PbCrO₄, and CaCO₃ at temperature 500°C.     

Combined ethanol and methane production from switchgrass (Panicum virgatum L.) impregnated with lime prior to steam explosion

Pretreatments are crucial to achieve efficient conversion of lignocellulosic biomass to soluble sugars. In this light, switchgrass was subjected to 13 pretreatments including steam explosion alone (195 °C for 5, 10 and 15 min) and after impregnation with the following catalysts: Ca(OH)₂ at low (0.4%) and high (0.7%) concentration; Ca(OH)₂ at high concentration and higher temperature (205 °C for 5, 10 and 15 min); H₂SO₄ (0.2% at 195 °C for 10 min) as reference acid catalyst before steam explosion. Enzymatic hydrolysis was carried out to assess pretreatment efficiency in both solid and liquid fraction. Thereafter, in selected pretreatments the solid fraction was subjected to simultaneous saccharification and fermentation (SSF), while the liquid fraction underwent anaerobic digestion (AD). Lignin removal was lowest (12%) and highest (35%) with steam alone and 0.7% lime, respectively. In general, higher cellulose degradation and lower hemicellulose hydrolysis were observed in this study compared to others, depending on lower biomass hydration during steam explosion. Mild lime addition (0.4% at 195 °C) enhanced ethanol in SSF (+28% than steam alone), while H₂SO₄ boosted methane in AD (+110%). However, methane represented a lesser component in combined energy yield (ethanol, methane and energy content of residual solid). Mild lime addition was also shown less aggressive and secured more residual solid after SSF, resulting in higher energy yield per unit raw biomass. Decreased water consumption, avoidance of toxic compounds in downstream effluents, and post process recovery of Ca(OH)₂ as CaCO₃ represent further advantages of pretreatments involving mild lime addition before steam explosion.     

Performance predictions for a new zeolite 13X/CaCl2 composite adsorbent for adsorption cooling systems

Composite adsorbents synthesized from zeolite 13X and CaCl₂ were investigated for applications in solar adsorption cooling systems. The effects of Ca ion exchange on the adsorption properties of zeolite 13X were studied. Ca ion exchange was found to decrease the specific surface area of the zeolite while increasing the total pore volume. Soaking zeolite 13X in 46 wt.% CaCl₂ solution for 24 h gave the optimum Ca ion exchange. The increase in the total pore volume facilitated further impregnating the zeolite with CaCl₂. In all, 41.5 mol% of CaCl₂ was impregnated in the Ca-ion-exchanged zeolite from a 40 wt.% CaCl₂ solution to form the zeolite 13X/CaCl₂ composite adsorbent. A 0.4 g/g difference in equilibrium water uptake between 25 and 75 °C at 870 Pa was recorded for the composite adsorbent. This was 420% of that of zeolite 13X under the same conditions. Numerical simulation predicts that an adsorption cooling system using the composite adsorbent could be powered by a low grade thermal energy source using the temperature range 75–100 °C. Greatly improved efficiency is predicted compared to a system using pure zeolite 13X or impregnated silica gel.     

Turning glycerol surplus into renewable syngas through glycerol steam reforming over a sol-gel Ni–Mo2C-Al2O3 catalyst

In this work, a sol-gel Ni–Mo₂C–Al₂O₃ catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H₂ yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h⁻¹.g_cat⁻¹), shows high catalyst stability, up to 30 h, with final conversion, H₂ yield, and H₂/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N₂-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H₂ production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H₂ production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H₂ production. The H₂/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H₂ production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.     

Experimental investigation of improved calcium-based CO2 sorbent and Co3O4/SiO2 oxygen carrier for clean production of hydrogen in sorption-enhanced chemical looping reforming

In this study, highly pure hydrogen is produced in sorption enhanced chemical looping steam methane reforming (SE-CLSMR) using cobalt-based oxygen carrier (OC) and cerium promoted CaO-based sorbent. In addition, the CO₂ removal from a gas stream at high temperatures is investigated via calcium looping process prior to SE-CLSMR process. The prepared samples are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and energy dispersive X-ray spectroscopy (EDX) techniques. The effect of Ca/Ce molar ratio (100/0.00–0.91/0.09), sorption temperature (550–650 °C) and sorbent lifetime are studied to find the optimal sorbent. The characterization results show the uniform and orderly CeO₂ dispersed sorbent nanoparticles that notably improved the sorbent morphology compared with blank CaO. The sorption results revealed the negative effect of temperature on CO₂ uptake of all the samples. In addition, the CO₂ sorption evaluations indicate that the molar ratio of cerium to calcium plays a significant role in the stability of sorbent and improved the CO₂ sorption capacity significantly. The high CO₂ removal efficiency in the cerium modified sorbents could be due to decrease in diffusion resistance of CO₂ through the sorbent structure during the carbonation reaction. Furthermore, results show that the addition of cerium to the sorbent structure, effectively improves the thermal resistance of synthesis sorbents. The SE-CLSMR results showed that the H₂ purity could be increased up to about 95% considering Co₃O₄/SiO₂ oxygen carrier and cerium promoted calcium-based sorbent at relatively low temperature of 550 °C, which is comparable with 84% in CLR process.     

CO2 separation during hydrocarbon gasification

Hydrocarbon can be gasified with steam into fuel gas, including CO, CO₂, H₂, CH₄, etc. For H₂ production, it is necessary to separate the other gases from hydrogen. In this study, hydrogen production by removal of carbon oxides during hydrocarbon gasification with CaO and other metal oxides was examined theoretically and experimentally.It was experimentally confirmed that when the hydrocarbon, water, and Ca(OH)₂ were set in a micro-autoclave at a temperature of 973 K and a pressure of 25 MPa, the only gas products were hydrogen along with a small amount of methane. CO was converted to CO₂, and CO₂ was absorbed by Ca(OH)₂ to form CaCO₃ completely. CaOSiO₂ can absorb CO₂ to form CaCO₃ under the same experimental conditions. Others such as MgO, SnO, and Fe₂O₃ were found to be unsuitable sorbents for CO₂ absorption in the gasifier at high temperature.By calcination, CaCO₃ can reform to CaO. Because the chemical energy contained in CaO can be released during hydrocarbon gasification, H₂ production efficiency as high as 70–80% can be expected.