Sorption-enhanced Hydrogen Production Research Articles

Calcium-based pellets for continuous hydrogen production by sorption-enhanced steam methane reforming

Sorption-enhanced steam methane reforming (SESMR) can produce high-purity H2 in one step, while removing CO2 to reduce carbon emissions. The sorbents, catalysts or bifunctional composite used in this system typically exist in powder form, which is difficult to use in industrialized fluidized bed reactors. Granulation can effectively avoid reactor clogging, increase practicality and operability of the system. In this work, Al-modified CaO-based sorbents were granulated using the graphite-casting method and test its sorption-enhanced hydrogen production effects during methane steam reforming. The effects of granulation on the microstructure, carbonation reactivity and mechanical properties were characterized. The reaction conditions (temperature and water-gas ratio) and the combination method of catalyst and sorbent (powder mixing, pellets mixing, layered placement and bifunctional materials mixed evenly at the molecular level) on hydrogen yield were investigated. Results showed that CaO-based pellets after granulation had a fluffy and porous structure, exhibited excellent adsorption performance under low CO2 partial pressure. The average crushing load of 75Ca25Al and 15Ni70Ca15Al pellets exceeded 6 N, showing good mechanical strength. The optimal reaction temperature range was found to be 550–600 °C. Increasing the water-gas ratio and reducing the flow rate were effective ways of improving CH4 conversion and H2 purity. The bifunctional 15Ni70Ca15Al powder prepared by sol-gel method had no catalytic effect on CH4–H2O reforming at 600 °C. After granulation, the catalytic performance was improved and the purity of H2 reached 95%, but it declined rapidly during multiple SESMR cycles. In the case of mixed of two pellets (catalyst and sorbent), the outlet H2 reached almost 100% with no decay observed over 15 cycles. When the switching time of feed gas was set to 60 min, high-purity (>96%) hydrogen can be produced continuously for 600 min on the parallel two fixed-bed reactors.

Investigation of sorption-enhanced hydrogen production by glycerol steam reforming in bubbling fluidized bed

Sorption-enhanced glycerol steam reforming process is numerically investigated by the multiphase particle-in-cell model within the Eulerian-Lagrangian framework in the bubbling fluidized bed with the aim of exploring the particle-level fundamentals of the binary particles. After the verification, the particle-scale evaluations and gas thermal properties are comprehensively presented. The results reveal that the size- and density-induced segregation results in the preferential distribution of CaO particles in the bottom zone of the bed. The particles in the bottom, freeboard, wake vortex and bubbling regions have a comparatively large heat transfer coefficient, velocity and slip velocity. At the same volume fraction, slip velocity and time instant, the heat transfer coefficient of sorbent is lower than that of catalyst. Increasing the superficial velocity elevates the heat transfer coefficient while reduces the C3H8O3 consumption and H2 yield. The probed results are of profound significance to the in-depth comprehension about complex gas–solid reacting flow and the process optimization of the sorption-enhanced hydrogen production system.

Bi-functional particles for integrated thermo-chemical processes: Catalysis and beyond

Particulate materials possessing dual functionalities have received tremendous investigations in many fields, owing to their superiority over mono-functional counterparts and their potential for process integration and intensification. This review focuses on bi-functional catalytic particles which also serve as sorbents/adsorbents or heat suppliers in the scheme of various thermo-chemical processes, enabling inherent separation or energy conservation within single-step operation. Bi-functional particles applied for integration of reaction and separation including sorption-enhanced hydrogen production and integrated capture and catalytic conversion processes are reviewed in detail, providing insights into material design and key performance indicators. On the other hand, bi-functional particles applied for integration of reaction and non-thermal radiation heating, including electrothermal and photothermal assisted heterogeneously catalyzed reactions, are also reviewed, with emphasis on the material property and energy efficiency improvement. These bi-functional particles show broad adaptability and feasibility in various reactions operated in integrated and intensified schemes, affording huge potentials for further improving productivity and efficiency in thermo-chemical processes.

Enhancing hydrogen production from propane partial oxidation via CO preferential oxidation and CO2 sorption towards solid oxide fuel cell (SOFC) applications

Under the demand of distributed power sources, solid oxide fuel cell (SOFC) has attracted considerable interest for its high efficiency. However, non-carbon neutral and CO poisoning limit the applications of SOFC when converting hydrocarbons to hydrogen-rich gas by thermally incorporating an external/internal processor. In this work, an external reformer and SOFC system is established to improve hydrogen production therefore enhancing power density by CO preferential oxidation and CO2 sorption-enhanced methods. The prepared CoxMgyCa(1-x-y)Oz sorbents are observed to provide porous structures, and Co0.110Mg0.204Ca0.686Oz presents the most uniform pore size distribution and the highest CO2 sorption capacity by lowering the CO2 sorption activation energy via kinetic analysis. By using the mixture of Ni/Al2O3–SiC catalyst and the synthesized CoxMgyCa(1-x-y)Oz sorbents, sorption-enhanced hydrogen production from propane partial oxidation is achieved for a higher hydrogen production and lower CO, CO2 productions. The produced hydrogen is served as a fuel of the proposed SOFC system, and a maximum output power density of 513 mW/cm2 at 1.2 A/cm2 is reached, which is equivalent to 160 mL/min of pure H2. This work might offer a novel insight for developing low-cost processes towards indirect hydrogen production for fuel cells.

Synthetic CaO-based sorbent for high-temperature CO2 capture in sorption-enhanced hydrogen production

Calcium precursor and surfactant addition on properties of synthetic alumina-containing CaO-based for CO2 capture and for sorption-enhanced steam methane reforming process (SE-SMR) were investigated. Results showed that the sorbent derived from calcium d-gluconic acid (CG-AN) offered CO2 sorption capacity of 0.38 g CO2/g sorbent, which is greater than 0.17 g CO2/g sorbent of the sorbent derived from calcium nitrate (CN-AN). Addition of CTAB surfactant during synthesis was found to enhance CO2 sorption capacity for CG-AN but not for CN-AN sorbents. Stability tests of the modified sorbents for 10 cycles showed that CG-AN-CTAB provided higher CO2 sorption capacity than CN-AN-CTAB for each corresponding cycle. Incorporation of CG-AN with Ni catalyst (Ni-CG-AN) using wet-mixing technique offered the longest pre-breakthrough period of 60 min for average maximum H2 purity of 88% at 600 °C and a steam/methane molar ratio of 3.

Synergistic study between CaO and MgO sorbents for hydrogen rich gas production from the pyrolysis-gasification of sugarcane leaves

Abstract This study focused on investigating the sorption-enhanced hydrogen (H2)-rich gas production during the pyrolysis-steam gasification of biomass in a two-stage fixed-bed reactor. The mixed CaO/MgO sorbents were employed in order to enhance the H2 production through the water-gas shift reaction associated with the capturing of CO2. The CaO/MgO sorbents prepared by dry- and wet-physical mixing with different molar ratios were examined. In addition, the effect of different devolatilization temperatures (400–800 °C) and gasification temperatures (600–800 °C) on the H2 yield were explored. It was found that the dry-mixed CaO/MgO sorbent exhibited a synergistic effect in the pyrolysis-steam gasification of the biomass, where a CaO:MgO molar ratio of 2:1 gave the highest H2 yield (16.8 mmol/gbiomass) and H2 concentration (75.0%). The wet-mixed sorbent gave superior results, affording a higher H2 yield (21.2 mmol/gbiomass) and H2 concentration (79.8%) with the same CaO: MgO molar ratio of 2:1. The CO2 yield was also reduced to 1.14 mmol/gbiomass compared to that with the dry mixed sorbent (1.72 mmol/gbiomass). The oxygenated compounds mainly derived at the devolatilization temperature of 600 °C were conceivably preferable to the sorption-enhanced hydrogen production in the gasification, leading to the highest yield and concentration of H2. Increasing the gasification temperature above 600 °C provided a higher H2 yield but caused a lower H2 concentration. A comprehensive discussion on these aspects related to volatile components released from different temperatures and reactivity of sorbents is provided.

Green Synthesis of Nanosilica from Coal Fly Ash and Its Stabilizing Effect on CaO Sorbents for CO2 Capture.

High-temperature sorption of CO2 via calcium looping has wide applications in postcombustion carbon capture, sorption-enhanced hydrogen production, and inherent energy storage. However, fast deactivations of CaO sorbents and low CO2 uptake in the fast carbonation stage are major drawbacks of this technology. For the first time, we developed a green approach through the reuse of nanosilica derived from coal fly ash (CFA) to enhance both the cyclic CO2 uptakes and the sorption kinetics of CaO sorbents. The as-synthesized nanosilica-supported CaO sorbent showed superior cyclic stability even under realistic carbonation/calcination conditions, and maintained a final CO2 uptake of 0.20 g(CO2) g(sorbent)-1 within short carbonation time, markedly increased by 155% over conventional CaO sorbent. Significantly, it also exhibited very fast sorption rate and could achieve almost 90% of the total CO2 uptake within ∼20 s after the second cycle, which is critical for practical applications. These positive effects were attributed to the formation of larnite (Ca2SiO4) and the physical nanostructure of silica, which could yield and keep abundant reactive small pores directly exposed to CO2 throughout multiple cycles. The proposed strategy, integrating the on-site recycling of CFA, appears to be promising for CO2 abatement from coal-fired power plants.

Hydrothermal Fabrication of High Specific Surface Area Mesoporous MgO with Excellent CO2 Adsorption Potential at Intermediate Temperatures

In this work, we report on a novel sodium dodecyl sulfate (SDS)-assisted magnesium oxide (MgO)-based porous adsorbent synthesized by hydrothermal method for intermediate CO2 capture. For industrial MgO, its CO2 adsorption capacity is normally less than 0.06 mmol g−1, with a specific surface area as low as 25.1 m2 g−1. Herein, leaf-like MgO nanosheets which exhibited a disordered layer structure were fabricated by the introduction of SDS surfactants and the control of other synthesis parameters. This leaf-like MgO adsorbent showed an excellent CO2 capacity of 0.96 mmol g−1 at moderate temperatures (~300 °C), which is more than ten times higher than that of the commercial light MgO. This novel mesoporous MgO adsorbent also exhibited high stability during multiple CO2 adsorption/desorption cycles. The excellent CO2 capturing performance was believed to be related to its high specific surface area of 321.3 m2 g−1 and abundant surface active adsorption sites. This work suggested a new synthesis scheme for MgO based CO2 adsorbents at intermediate temperatures, providing a competitive candidate for capturing CO2 from certain sorption enhanced hydrogen production processes.

Sorption-enhanced hydrogen production by steam reforming of ethanol over mesoporous Co/CaO[sbnd]Al2O3 xerogel catalysts: Effect of Ca/Al molar ratio

A series of multifunctional Co/CaOAl2O3 catalysts (Co/XCA, X = 0, 0.25, 0.5, 0.75, and 1.0) with different Ca/Al molar ratio (X) were prepared for use in the sorption-enhanced hydrogen production by steam reforming of ethanol. Mesoporous structure was successfully formed in all the calcined catalysts, and surface area of the catalysts decreased with increasing Ca/Al molar ratio. Co3O4, CaCO3, and γ-Al2O3 phases were dominantly formed in the calcined catalysts. It was revealed that addition of Ca neutralized support acidity, resulting in a decrease of C2H4 selectivity. Addition of Ca also increased strong base sites which were related to sorption-enhanced hydrogen production at the initial reaction stage. In the XRD and H2-TPD analyses, Co/0.5CA catalyst retained the smallest crystallite size of metallic cobalt and the highest cobalt surface area among the catalysts. Catalytic activity in the steam reforming of ethanol exhibited a volcano-shaped trend with respect to Ca/Al molar ratio. Hydrogen yield increased with increasing cobalt surface area. Among the catalysts tested, Co/0.5CA catalyst with the highest cobalt surface area showed the best catalytic performance. Thus, cobalt surface area served as a crucial factor determining the catalytic activity for ethanol steam reforming. Low acidity and high surface area were also responsible for stable catalytic activity of Co/0.5CA catalyst in the steam reforming of ethanol.

Fe-Ca interactions in Fe-based/CaO catalyst/sorbent for CO2 sorption and hydrogen production from toluene steam reforming

After biomass gasification, tar can be removed by steam reforming and additional hydrogen production. This latter can be enhanced by CO2 sorption using the global process known as sorption enhanced hydrogen production (SEHP). Toluene was studied as tar model compound and its reforming was carried out at a compromise temperature (700°C) to permit simultaneous activation of iron based catalyst and CO2 sorption on CaO based sorbent.Fe-Ca interactions on Fe-based/CaO catalyst/sorbent performances occur during steam reforming of toluene. In order to determine the specific conditions for the formation of the different iron species, Fe-based/CaO bi-functional materials have been prepared following three different methods with various calcium and iron precursors. The characterizations (XRD, Mossbauer spectroscopy, TGA, TPR, SEM, and BET/BHJ) performed before and after steam reforming of toluene provide information about the evolution of the iron species and Fe-Ca interactions during catalytic tests. The results suggest that the activity of Fe/CaO materials depends not only on the presence of Fe2O3 but also on the stability of the interactions between iron and calcium under reaction conditions.The bi-functional material prepared from iron acetate and calcium acetate by mechanical mixing (FeAc/CaO (M)) has properties (large specific surface area, appropriate sorption capacity at 700°C, and the lowest deactivation) that play an important role for CO2 capture. Moreover, the presence of the α-Fe2O3 phase, precursor of the active phase in steam reforming of tar, reducible at 700°C, intervenes in the hydrogen production rate by enhancing the Water Gas Shift reaction. Finally, its higher availability of iron (Fe2O3) limit the selectivity towards undesirable products such as benzene.

Sorption enhanced coal gasification for hydrogen production using a synthesized CaO[sbnd]MgO-molecular sieve sorbent

This study tends to investigate sorption enhanced hydrogen production process using MgO-molecular sieve modified CaO-based sorbents in a horizontal fixed bed reactor. The synthesized sorbents were prepared using a wet mixing method for enhancing H2 yields and concentration as well as capturing CO2. The sorbents were characterized by means of X-ray diffraction (XRD), nitrogen adsorption and desorption isotherms test, and scanning electron microscopy (SEM)/energy dispersive spectrometer (EDS). The ash content of coal and the calcined mixture were analyzed by the method of energy dispersive X-ray fluorescence (EDXRF). The CaOMgO-molecular sieve sorbents were investigated during 20 adsorption and calcination cycles using thermogravimetric analyzer (TGA). The effects of different kinds of CaO-based sorbents, the molar ratio of Ca/C, and diverse coal species on gas yields and concentration were investigated. The experimental results verified that the presence of modified sorbents in the steam coal gasification process enhanced the concentration of hydrogen to more than 80%, with lower concentration of CO2 emission. The highest hydrogen concentration were obtained using the modified CaOMgO-5A molecular sieve at the condition that the temperature is 650 °C, the N2 flow rate is 0.5 L/min, and the water injection rate is 0.3 L/min.

Simulation of the calcium looping process (CLP) for hydrogen, carbon monoxide and acetylene poly-generation with CO2 capture and COS reduction

In this paper, a novel poly-generation system is proposed for hydrogen, carbon monoxide, and acetylene production with inherent CO2 capture and COS reduction. It is based on calcium looping coal gasification and oxygen-thermal CaC2 preparation. The system is comprised of calcium looping gasification reactors, preheaters, oxygen-thermal CaC2 furnace, and carbide slag modifier. Modified carbide slag and fresh CaCO3 are used as raw materials for sorption enhanced hydrogen production (SEHP). The cycled CaO-based sorbent is fed into oxygen-thermal CaC2 furnace for CaC2 production after calcination. CO-rich gas is generated from the furnace simultaneously. A portion of CO-rich gas which includes COS is fed into calcium looping gasification system to generate extra hydrogen. In addition, CO2 and COS are captured through the CaO-based sorbent. To maintain the heat balance of the system, a portion of CO-rich gas is fed into the regenerator for combustion. The entire process is modeled and simulated using Aspen Plus software. The proposed system efficiency could reach 81.62%. Parameters that affect the target products (H2, CO, C2H2, and CaC2) are investigated in the sensitive analysis, including steam/CO/CaO ratio, riser temperature, coke/CaO/O2 ratio, and coal species.

Unexpected highly reversible topotactic CO2 sorption/desorption capacity for potassium dititanate

Potassium dititanate (K2Ti2O5) was revealed to possess an unexpected, highly reversible CO2 sorption/desorption capacity at ca. 750 °C, which is promising as a high-temperature CO2 adsorbent for sorption enhanced hydrogen production (SEHP) processes.

Sorption enhanced hydrogen production using one-body CaO–Ca12Al14O33–Ni composite as catalytic absorbent

Catalytic absorbents containing CaO and Ca12Al14O33 and metallic Ni in one body were prepared in combination of precipitation and hydration and tested for sorption enhanced hydrogen production (SEHP). Adding aluminum precursor in the precipitation step induced the formation of Ca12Al14O33 and FIB-TEM analysis revealed that Ca12Al14O33 provides spacious pathway for CO2 diffusion by forming porous structure. In thermogravimetric analysis, Ca12Al14O33 was identified as an excellent support material providing superior cyclic stability for Ca-based sorbent. Catalytic absorbents were prepared with adding various amount of Ni precursor (3, 5, 7, and 10 wt %). The SEHP test with the catalytic absorbents showed that 7wt% of Ni loading resulted in excellent performance in terms of H2 production and CH4 conversion. Ni agglomeration was observed when 10 wt% of Ni is loaded on the catalytic absorbent.

Effects of preparation method on cyclic stability and CO 2 absorption capacity of synthetic CaO–MgO absorbent for sorption-enhanced hydrogen production

A novel and economical method for preparing CaO-based high-temperature CO 2 absorbents for sorption-enhanced hydrogen production is introduced. CaO–MgO absorbents prepared by the co-precipitation method show excellent cyclic stability but poor absorption capacity (∼8–14 g CO 2/100 g absorbent). An additional hydration process provided spacious CO 2 pathways resulting in a significant increase of the absorption capacity (∼17.4–47.8 g CO 2/100 g absorbent) with excellent cyclic stability. As the MgO content increased, the absorption ratio of the absorbent and the degree of CaO conversion also increased. In addition, XRD analysis revealed that the hydration process followed by calcination at 900 °C led to the formation of a partial solid solution in the CaO–MgO absorbent containing 25 wt% MgO.

Dispersed Calcium Oxide as a Reversible and Efficient CO2−Sorbent at Intermediate Temperatures

Dispersion of calcium oxide on high surface area γ-Al2O3 creates a stable and reversible CO2−sorbent that overcomes the problems associated with bulk CaO, such as limited long-term stability, slow uptake kinetics, and energy-intensive regeneration. This sorbent is a candidate for the sorption-enhanced hydrogen production via steam reforming and/or water-gas shift reactions. CO2 uptake tests were performed in a 15% CO2/N2 atmosphere to evaluate the efficacy at typical hydrocarbon reformer gas partial pressure. CO2 uptake kinetics and capacities are investigated in TGA studies, while the long-term stability is shown in multicycle experiments. The dispersed CaO is an active sorbent at low temperatures and binds CO2 at 300 °C up to 1.7 times as efficiently as compared to bulk CaO powder. Furthermore, the sorbent can be regenerated in a CO2-free atmosphere at intermediate temperatures between 300 and 650 °C. Multicycle CO2 uptake and release has been tested for 84 cycles at a constant temperature of 650 °C and...

Low temperature catalytic methane steam reforming over ceria–zirconia supported rhodium

This paper presents an experimental study of the catalytic steam reforming of methane over newly developed ceria–zirconia supported rhodium as an active candidate catalyst for low temperature sorption enhanced hydrogen production from methane. The kinetic experiments are performed in a tubular fixed bed reactor over a temperature range of 475–725 °C and a total pressure of 1.5 bar in the absence of mass transport limitations. The over all reaction orders in methane and steam are determined to be less than 1 from 475 to 625 °C. At low temperature, most of the gas product is composed of CO 2 and H 2 due to the pronounced influence of the water–gas shift reaction. At higher temperature and low steam/carbon ratio (S/C), this influence is diminished. Inhibitory effects of H 2, CO, and CO 2 on the methane conversion rates are detected. Temperature-programmed steam reforming experiments over ceria–zirconia support revealed insignificant methane adsorption on the surface from 550 to 725 °C. Catalyst deactivation and steady state stability over time were examined. A molecular reaction mechanism is proposed to qualitatively explain the kinetic observations. Two distinct sites are thought to be responsible for the dissociative adsorption of methane and steam on the catalyst and the support surfaces. Methane is dissociatively adsorbed on the rhodium active metal sites and steam is dissociatively adsorbed on the support surface. Surface reactions of carbon containing methane precursors on the interface between the active metal and the support are considered to be the rate determining steps.

Sorption-Enhanced Hydrogen Production: A Review

In the sorption-enhanced hydrogen production process, hydrocarbon reforming, water gas shift, and CO2 separation reactions occur simultaneously in a single reaction step over a reforming catalyst mixed with a CO2 sorbent. Transferring CO2 as it is formed from the gas to the solid phase shifts the normal equilibrium restrictions and allows both the reforming and water gas shift reactions to approach completion. Depending on reaction conditions, the product (dry basis) may contain as much as 98% H2 and only ppmv levels of CO and CO2, thereby minimizing the final H2 purification step or even eliminating it for some applications. A number of CO2 sorbents have been studied including calcium-based oxides, K-promoted hydrotalcite, and mixed metal oxides of lithium and sodium. The sorbent is consumed during H2 production so that the process is intrinsically unsteady state. Process economics requires that the sorbent be regenerable and used in many reaction−regeneration cycles. Regeneration may occur via temperatu...

Modeling of Multiple Cycles for Sorption-Enhanced Steam Methane Reforming and Sorbent Regeneration in Fixed Bed Reactor

Mathematical models of multiple cycles for sorption-enhanced steam methane reforming and Ca-based sorbent regeneration in a fixed bed reactor are developed. Empirical correlations are used to describe steam methane reforming, the water−gas shift, and CO2 capture kinetics. The processes of multiple carbonation/calcination cycles of a Ca-based sorbent are taken into account to describe the sorption-enhanced hydrogen production process with the simultaneous removal of carbon dioxide by a Ca-based sorbent. The mathematical models are validated through comparing simulated results with experimental data. The model results qualitatively agree with experimental data. The effect of reactivity decay of dolomite, CaO/Ca12Al14O33, and limestone sorbents on sorption-enhanced hydrogen production and sorbent regeneration processes was studied through numerical simulation. The simulated results indicated that the operation time of producing high-purity hydrogen (that is defined as the time for the start of breakthrough, ...

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.