In this study, the Li2ZrO3 based sorbents with different compositions were synthesized by the solid-state reaction method from the mixtures of Li2CO3, K2CO3 and ZrO2. CO2 sorption properties of Li2ZrO3 based sorbents were investigated by analyzing the phases and microstructure changes with the help of thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. The thermodynamic calculations were carried out based on the second law of thermodynamics. Li2CO3/K2CO3-doped Li2ZrO3 sorbent with the composition of 36.23 wt % Li2CO3, 55.12 wt % ZrO2 and 8.65 wt % K2CO3 was considered to achieve excellent capability for high temperature CO2 sorption and presented the maximum sorption rate at 525 °C and 0.15 atm of CO2 partial pressure. The sorbent kept rather stable for multicycles sorption and regeneration, and maintained its original capacity during 12 cycle processes. There were three distinct phases in the nonisothermal CO2 sorption process while the main CO2 sorption occurred during the second phase. An improved iterative Coats–Redfern method was used to evaluate nonisothermal kinetics of the CO2 sorption process, and the kinetic parameters were derived by the MATLAB model. The Fn nth-order reaction model predicted accurately the main phases and differences in the activation energies and the frequency factors for different sorbents in the sorption phases corroborated different mechanism integral functions and reaction orders.

•A novel diffuser that improves the thermal stratification performance of a thermal storage tank is designed.•3D unsteady CFD simulations are validated with experimental measurements.•The influence of operating parameters on thermal stratification is analyzed.•The fill efficiency is used as a measurement index to judge the performance of a thermal storage tank.Heat storage is an important task in the use of solar energy; in particular, the use of water as the thermal storage medium is one of key technologies in solar thermal energy utilization. With the purpose of improving the thermal stratification of a heat storage tank, a novel equalizer was designed in this paper. To investigate the influence factor of thermal stratification in hot water storage tank, numerical analyses based on the three-dimensional (3D) unsteady Computational Fluid Dynamics (CFD) model were performed using the commercial software ANSYS. The initial and inlet temperatures were considered along with various flow rates. The performance parameters, such as the Richardson number, the MIX number and exergy, were involved in the evaluation. This study was further extended to explore the fill efficiency as the performance parameters of thermal stratification within a storage tank. The numerical model was validated with the experimental data; the results were determined to be in good agreement. The results demonstrate that with the growth of flow rate, the Richardson number decreases, fill efficiency and exergy increased first and later decreased, but the MIX number decreased first and later increased. When the flow rate was 3 L/min, the equalizer performs best, and the storage tank had a better thermal stratification. The RMS error increased first and subsequently decreases before increasing again with the growth of the flow rate. Furthermore, the MIX number reaches a minimum at the dimensionless time of 0.5 in the numerical results, whereas it is 0.4 in the experimental results. It was also observed that the contribution of the equalizer on the flow-suppressing of influent results in a decrease of mixing process between the hot and cold water, which could lead to improvement of the thermal stratification.

•Effect of supports on OCs performance of CLSR to H2 was determined.•Confinement effect achieved small partial size, high dispersion and strengthen MSI.•Metal sintering and coke deposition were inhibited by superior confinement effect.•Redox performance order: Ni/SBA-15, Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3.•Mesoporous Ni/SBA-15 OCs exhibited higher activity and stability in CLSR.The Ni-based oxygen carriers (OCs) with different supports including alloy Ni/Al2O3, lamellar Ni/MMT, mesoporous Ni/Al-MCM-41 and mesoporous Ni/SBA-15 were synthesized. The effect of support on hydrogen production from chemical looping steam reforming (CLSR) of ethanol was investigated in a fixed-bed reactor. The oxygen carriers were characterized by some techniques, including N2 adsorption–desorption, XRD, TEM, ICP-OES, H2 pulse chemisorption, H2-TPR, and TG-DTG. It was observed that Ni/SBA-15 exhibited most efficient confinement effect followed by Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3 via: 1) small nickel particle size and high dispersion as well as strengthened metal-support interaction; 2) sintering resistance due to spatial restriction of support; 3) anti-coke capability derived from small nickel particles and ordered diffusion routes for reactants and products. In addition, the silica supported OCs were conductive to promote water gas shift (WGS) reaction but the supports containing Al atoms were prone to coke deposition due to the formation of acid sites. The ‘dead time’ and oxygen transfer capacity reflected that the redox performance of oxygen carriers was listed in the following order: Ni/SBA-15, Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3. Ni/Al-MCM-41 exhibited excellent activity in initial cycle of CLSR but the collapse of the Ni/Al-MCM-41 structure for its weak thermo stability leaded to the deactivation and sintering of active phase. The Ni/SBA-15 and lamellar Ni/MMT OCs exhibited superior activity and stability but the performance of Ni/Al2O3 OCs was mediocre.

•Novel OCs for CLSR were prepared by Ce–Ni nanoparticles encapsulated in SBA-15.•Synthesized OCs have well-ordered mesostructure and high specific surface area.•Ce–Ni in SBA-15 effectively control particles distribution and enhance OT and WGS.•Activity and stability of 12CeNi/SBA-15 for multi-cycles CLSR were found to be high.Chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers was carried out at 650 °C under atmospheric pressure in a fixed-bed reactor. The mesoporous support SBA-15 was synthesized via hydrothermal method and the xCeNi/SBA-15 oxygen carriers were prepared by encapsulating CeO2 and NiO nanoparticles in SBA-15 using surfactant-assisted iso-volumetric impregnation method. Some techniques were conducted to characterize the oxygen carriers, including N2 adsorption–desorption, XRD, TEM, H2-TPR, ICP-OES, and DSC-TGA. It was observed that all the oxygen carriers exhibited high specific surface area (>435 m2/g) and large pore volume (>0.64 cm3/g). Small NiO particle size (e.g. 3.2 nm for 12CeNi/SBA-15), high dispersion and strengthened metal-support interaction were achieved by the CeO2 promotion. The ceria promoter not only inhibited the coke formation but facilitated the removal of coke deposition, and the coke deposition could be further eliminated in the air feed step, both of which resulted in long-term stability. Meanwhile, superior redox performance and shorter ‘dead time’ (e.g. 30 s for 12CeNi/SBA-15) were achieved on account of easier reducibility of NiO particles with increasing amount of CeO2. The oxygen carriers exhibited superior sinter resistance capacity and high activity and stability in CLSR process. The highest ethanol conversion (90.0%) and hydrogen selectivity (84.7%) were obtained for 12CeNi/SBA-15 even after 14 cycle stability test.

•Novel approach on FBGSERP system for H2 production from WP was proposed.•Effects of temperatures on raw gas of FBG and H2 of SERP were evaluated.•H2 produced by integrating WP FBG, SR, WGS with removal of CO2 and HCl was feasible.•88.4% of H2 with small amounts of HCl and CO2 from WP was achieved by FBGSERP system.This paper proposes a novel system for continuous hydrogen production from waste plastic (WP) by fluidized-bed gasification (FBG) combined sorption-enhanced steam reforming process (SERP). The system was operated in successive processes of several sections: (a) gasifying a WP into a raw gas comprising CO, H2, CH4, total hydrocarbons (THC), and small amount of HCl contaminant, etc.; (b) passing the raw gas to hydrogen production through two moving-bed reactors by continuous SERP process over Ni-based catalyst mixed CaO sorbent for in-situ CO2 capture and HCl removal; (c) simultaneously regenerating CaCO3 formed and catalyst with carbons deposited in other moving-bed reactor at the regeneration condition selected; and (d) carrying the particles of catalyst and sorbent to continuous steam reforming and their regeneration between two moving-bed reactors by riser. Gradually expanding chamber design of FBG reactor suitable for different particles flow to prolong the residence times of gas and solid phases makes high carbon conversion and the maximum value is up to 83.6% at 880 °C during FBG stage. The combination of FBG and SERP has produced a stream of high-purity hydrogen at some certain conditions, and about 88.4 vol % of hydrogen (H2O- and N2-free basis) was obtained at 818 °C of FBG temperature with 706–583 °C of SERP temperature. Reduced Ni-based catalyst efficiently converted raw gas from FBG and steam to H2, and CaO sorbent in the moving-bed reactor are capable of reducing the HCl and CO2 to low levels at all the temperatures tested.

•Periodically switching feed gases for SERP was conducted in a fixed-bed reactor.•High-purity H2 was produced by SERP using spinel Ni/NiAl2O4 and CaO based sorbent.•Experimental products in SERP were compared with thermodynamic calculations.•Enhancement of H2 production in SERP was depended on in-situ CO2 removal.•SERP for multi-cycles reaction/regeneration achieved simultaneously in a reactor.For the fixed-bed reactor configuration in the sorption-enhanced steam reforming process (SERP), solid mixture of catalyst and sorbent is stationary and alternatively exposed to reaction and regeneration conditions for multi-cycles by periodically switching the feed gases for enhanced hydrogen production with in-situ CO2 removal. A NiO/NiAl2O4 catalyst was synthesized by the co-precipitation method with rising pH technique and the crystalline spinel phase of NiAl2O4 was formed under the calcination temperature of 900 °C. The catalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), thermo-gravimetric analysis (TGA), and N2 adsorption–desorption. The non-stoichiometric thermodynamic calculation was carried out to determine the effects of temperature and in-situ CO2 removal on the enhancement of hydrogen production by SERP from glycerol at 425–700 °C. The multi-cycles on reaction and regeneration for hydrogen production by SERP from glycerol were performed by NiO/NiAl2O4 catalyst and CaO based sorbent in a fixed-bed reactor. The results showed that hydrogen production by SERP can be clearly divided into three periods, and the experimental gaseous products were compared with non-stoichiometric thermodynamic calculations. It is obvious that H2 purity was greatly increased, and CO2, CO and CH4 concentrations were reduced by in-situ CO2 removal during the pre-breakthrough period. It is found that enhanced hydrogen production was mainly depended on in-situ CO2 removal. The operation durations for producing high-purity hydrogen of more than 90% were decreased with the increase of the cycles. It may due to the decrease in the reactivity of CaO based sorbent after multi-cycles reaction and regeneration.

•Novel OCs for CLSR were prepared by nanoparticles encapsulated in MCM-41 from MMt.•Direct-synthesis OCs have well-ordered mesostructure with 4–6 nm nanoparticles.•Ce in Ni/Al-MCM-41 effectively control particles distribution and enhance OT and WGS.•Activity and stability of CeNi/Al-MCM-41 for multi-cycles CLSR were found to be high.This paper describes the synthesis of a series of Ni based Al-MCM-41 oxygen carriers with and without Ce promoter and their application in chemical looping steam reforming of glycerol. The Al-MCM-41 is derived from montmorillonite. The oxygen carriers were prepared by direct-synthesis and post-synthesis method. A variety of technologies including N2 adsorption-desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), H2 temperature-programmed reduction (H2-TPR), and transmission electron microscopy (TEM) were conducted to characterize the fresh and used oxygen carriers. The results show the direct-synthesis oxygen carrier possesses excellent textual properties, such as high Ni loading, small particle size, large pore volume, and uniform pore size. The incorporation of Ce could effectively control particle size via strong metal support interaction, promote the homogeneous distribution of Ni, and enhance oxygen mobility capability and water gas shift reaction. And thus shorten ‘dead time’ during the fuel feed step. The CeNi/Al-MCM-41 displayed the superior activity and excellent long-term stability, which could be due to the strengthened anti-sintering and coke capability.Download high-res image (130KB)Download full-size image

This paper describes the synthesis and application of a NiO/NiAl2O4 catalyst and Li2ZrO3-based sorbent in sorption-enhanced glycerol steam reforming. A NiO/NiAl2O4 catalyst was prepared by an incipient wetness impregnation and co-precipitation method using a rising pH technique, and the NiAl2O4 crystalline spinel in the catalyst was formed under a high calcination temperature of 900 °C. The K-doped Li2ZrO3 sorbent was prepared by the solid-state method. The synthesized catalyst and sorbent were evaluated for H2 production and CO2 removal, respectively. Sorption-enhanced reforming (SER) hydrogen production possessing high initial H2 purity with CO2 removal was carried out during a multi-cycle reaction/regeneration process under 550 °C and a steam/carbon ratio of 3. CO2 sorption capacity of the Li2ZrO3 sorbent was decreased with an increasing cycle number in SER. A kinetic model was proposed to understand the isothermal kinetics for multi-cycle SER CO2 sorption over a K–Li2ZrO3 sorbent, and the breakthrough curves for each cycle were fitted on the basis of the derived kinetic parameters.

•Multifunctional catalysts for SERP with simultaneous CO2 removal were synthesized.•Catalyst with 41.21% NiO, 28.02% Al2O3 and 30.77% CaO presented high activity.•Desorption and sorption temperatures for CO2 removal in SERP were determined.•Multi-cycles SERP and regeneration for high-purity H2 depended on catalyst activity.The Ni-based multifunctional catalysts for the sorption-enhanced steam reforming process (SERP) with simultaneous in-situ CO2 removal were synthesized by the co-precipitation method with rising pH technique, and the crystalline spinel phases of NiAl2O4 and MgAl2O4 in the catalysts were formed under the calcination temperature of 900 °C. The catalysts were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), and N2 adsorption-desorption. Nonisothermal and isothermal CO2 sorption experiments were carried out to evaluate the activity of catalysts for CO2 removal. Desorption and optimum sorption temperatures for CO2 removal were determined. Hydrogen production from SERP of glycerol over the multifunctional catalysts has been experimentally evaluated under 550 °C and steam to carbon (S/C) ratio of 3. The multifunctional catalyst with the composition of 41.21 wt% NiO, 28.02 wt% Al2O3 and 30.77 wt% CaO presented satisfactory hydrogen purity in the multi-cycles of reforming and regeneration processes. Enhanced hydrogen production was mainly depended on in-situ CO2 removal, and the operation durations for producing high purity hydrogen in the initial 30 min were relatively stable. The multifunctional catalyst possesses uniform distribution of Ni, Ca and Al, contributing significantly to the excellent CO2 sorbent capacity and reforming activity. This multifunctional catalyst synthesized offers a new scheme other than the conventional mixture of sorbent and catalyst for SERP.

In this study, the pyrolysis characteristics of sucrose biomass were investigated with a thermogravimetric analysis coupled with gas chromatography (TGA–GC) system at different temperatures and various heating rates. The gas products from sucrose pyrolysis were measured, and the results showed that the gas product consisted of a major amount of CO, CO2, H2, and CH4. The temperature and addition of CaO could greatly affect the gaseous product yields. The distinct phases in the pyrolysis process of sucrose biomass were discussed. An improved iterative Coats–Redfern method was used to evaluate non-isothermal kinetic parameters for sucrose pyrolysis with/without the addition of CaO in different phases, and the activation energies and pre-exponential factors were calculated by means of linear regressions. The calculated results showed that the model with an Avrami–Erofeev mechanism could accurately be used to predict the main phase as well as the other phases for the pyrolysis processes.

H2 production from glycerol steam reforming by the Ni–Cu–Al, Ni–Cu–Mg, Ni–Mg catalysts was evaluated experimentally in a continuous flow fixed-bed reactor under atmospheric pressure within a temperature range from 450 to 650 °C. The catalysts were synthesized by the co-precipitation methods, and characterized by the elemental analysis, BET, XRD and SEM. The GC and FTIR were applied to analyze the products from steam reforming of glycerol. The coke deposited on the catalysts was measured by TGA experiments during medium temperature oxidation. The results showed that glycerol conversion and H2 production were increased with increasing temperatures, and glycerol decomposition was favored over its steam reforming at low temperatures. The Ni–Cu–Al catalyst containing NiO of 29.2 wt%, CuO of 31.1 wt%, Al2O3 of 39.7 wt% performed high catalytic activity, and the H2 selectivity was found to be 92.9% and conversion of glycerol was up to 90.9% at 650 °C. The deactivation of catalysts due to the formation and deposition of coke was observed. An improved iterative Coats–Redfern method was used to evaluate the non-isothermal kinetic parameters of coke removal from catalysts, and the results showed the reaction order of n = 1 and 2 in the Fn nth order reaction model predicted accurately the main phase in the coke removal for the regeneration of Ni–Mg and Ni–Cu–Al catalysts, respectively.Highlights► Catalysts synthesized by co-precipitation performed high H2 selectivity and yield. ► Glycerol decomposition was favored over its steam reforming at low temperatures. ► Deactivation of catalysts due to coke deposition was observed during reforming. ► Coke deposited was measured by TGA experiments during medium temperature oxidation. ► Improved iterative Coats–Redfern method was applied to kinetics of carbon removal.

•High-purity H2 from glycerol steam reforming with in-situ CO2 capture is evaluated.•New approach on continuous high-purity H2 production with long time is proposed.•Simultaneous flow of catalyst and sorbent for reaction-regeneration is feasible.•Catalyst and sorbent are always run in nearly fresh state for H2 production.•Same regeneration conditions of catalyst and sorbent does not lead to great decay.In this study, the continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production by a simultaneous flow concept of catalyst and sorbent for reaction and regeneration using two moving-bed reactors has been evaluated experimentally. A Ni-based catalyst (NiO/NiAl2O4) and a lime sorbent (CaO) were used for glycerol steam reforming with and without in-situ CO2 removal at 500 °C and 600 °C. The simultaneous regeneration of catalyst and sorbent was carried out with the mixture gas of N2 and steam at 900 °C. The product gases were measured by a GC gas analyzer. It is obvious that the amounts of CO2, CO and CH4 were reduced in the sorption-enhanced steam reforming of glycerol, and the H2 concentration is greatly increased in the pre-CO2 breakthrough periods within 10 min both 500 °C and 600 °C. The extended time of operation for high-purity hydrogen production and CO2 capture was obtained by the continuous sorption-enhanced steam reforming of glycerol. High-purity H2 products of 93.9% and 96.1% were produced at 500 °C and 600 °C and very small amounts of CO2, CH4 and CO were formed. The decay in activity during the continuous reaction-regeneration of catalyst and sorbent was not observed.

To solve the problems of high cost and low efficiency of conventional co-production system of hydrogen and electricity with low hydrogen-to-electricity ratio, a novel co-production system based on coal partial gasification with CO2 capture is proposed and thermodynamically analyzed. The new system integrates the conceptions of cascade conversion of coal and cascade utilization of syngas to realize the system with high efficiency, low cost, environmental friendliness and flexible hydrogen-to-electricity ratio. The performance of the new system is evaluated by an Aspen Plus model and effects of the operating conditions are also studied. It is found that the system with capturing CO2 of 59.7% and hydrogen-to-electricity ratio of 4.76 holds a high exergy efficiency of 54.3% when the carbon conversion ratio of the pressurized fluidized bed (PFB) gasifier is equal to 0.7. The carbon conversion ratio of the PFB gasifier is a dominant factor to decide the performance of system. In comparison with the series-type co-production system, the parallel-type co-production system and separate production system, the new system proposed in this study has exergy-saving efficiency of 17.7%, 15.1% and 8.9%, respectively.Highlights► A new H2-electricity system based on coal partial gasification with CO2 capture. ► An Aspen plus model is developed to evaluate the performance of system. ► The system has a high exergy-saving efficiency. ► Carbon conversion ratio of the PFB gasifier is found to be the dominant factor.

In this paper, the pyrolysis characteristics of sucrose biomass were investigated in a tubular reactor at different temperatures and also using a thermogravimetric analyzer at the heating rate of 10 °C min−1 from room temperature to 1200 °C. The gas products in the pyrolysis process were measured using an Agillent 6890N GC analyzer. The results showed that the temperature greatly affected the product yields. The pyrolysis gas consisted of a major amount of CO, CO2, H2, and CH4, and its yield increased greatly with increasing temperature. Tars occurred mainly at 200–300 °C under isothermal measurements in tubular reactor. The amounts of solid residue and tars decreased with increasing temperature. The presence of CaO responsible for the pyrolysis phase was shown to increase the conversion of sucrose and capture the CO2 produced. The kinetic analysis indicated that the reaction order model (first order) predicted accurately the conversion of 0.102–0.901 during the isothermal pyrolysis of sucrose in tubular reactor, and Arrhenius parameters and prediction of the pyrolysis time were obtained from isothermal kinetic results.Highlights► The pyrolysis characteristics of sucrose in a tubular reactor were different from those obtained by the TG method. ► CaO greatly enhanced the rates of pyrolysis. ► The products and kinetics of sucrose pyrolysis in a tubular reactor were studied.

New porous heterostructured nanohybrid of MgO–TiO2–Al2O3/montmorillonite has been successfully synthesized by an inflating, intercalation, and reassembling method under the ultrasonic vibration. The synthesized material was characterized by TGA–DTG, XRD, TEM and elemental analysis. The results showed that the material had a specific surface area of 156 m2 g−1 with an average pore diameter of 2.68 nm and pore volume of 0.6627 cm3 g−1, and that the MgO, TiO2 and Al2O3 nanoparticles were introduced in the montmorillonite by the heat treatment of 500 °C. It was found that the intercalation and deposition of mixed oxides nanoparticles expanded the basal spacing of montmorillonite, and the crystallites of the nanohybrids were assembled to form a heterostructured composite.Highlights► Heterostructured nanohybrid of MgO–TiO2–Al2O3/montmorillonite was successfully synthesized. ► The synthesized material was characterized by TGA–DTG, XRD, TEM and elemental analysis. ► Formation mechanism of MgO–TiO2–Al2O3/montmorillonite was discussed.

Hydrogen production from steam reforming of glycerol in a fluidized bed reactor has been simulated using a CFD method by an additional transport equation with a kinetic term. The Eulerian–Eulerian two-fluid approach was adopted to simulate hydrodynamics of fluidization, and chemical reactions were modelled by laminar finite-rate model. The bed expansion and pressure drop were predicted for different inlet gas velocities. The results showed that the flow system exhibited a more heterogeneous structure, and the core-annulus structure of gas–solid flow led to back-mixing and internal circulation behaviour, and thus gave a poor velocity distribution. This suggests the bed should be agitated to maintain satisfactory fluidizing conditions. Glycerol conversion and H2 production were decreased with increasing inlet gas velocity. The increase in the value of steam to carbon molar ratio increases the conversion of glycerol and H2 selectivity. H2 concentrations in the bed were uneven and increased downstream and high concentrations of H2 production were also found on walls. The model demonstrated a relationship between hydrodynamics and hydrogen production, implying that the residence time and steam to carbon molar ratio are important parameters. The CFD simulation will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor.