Search

[Display omitted] • A coupled chemical looping conversion of glycerol, CO 2 and H 2 O is achevied. • High-purity H 2 and syngas are one-step produced by GO, GDR and WS using OC. • Co-Fe interaction in OC inhibits the formation of carbon. • FeCoCe OC achieve excellent oxygen storage and redox reactions. • OC with 7:5:10 of Co: Fe: Ce presents high activity and stability. A coupled chemical looping conversion of glycerol and CO 2 with thermochemical water splitting (WS) cycle is substantially researched due to its potential for one-step renewable H 2 and syngas production. The major challenge lies on having good controls of redox reactions of the oxygen carriers (OCs) used and its unusual sensitivity to the changes of the compositions, chemical states and structure, etc. Here, we develop the OCs that consists of Fe 2 O 3 -Co 3 O 4 supported on the mesoporous CeO 2 structure (Fe 2 O 3 -Co 3 O 4 /CeO 2), which simultaneously promote glycerol oxidization (GO), dry reforming of glycerol (GDR), and WS processes. The easy migration and activation of lattice oxygen by Fe 2 O 3 -Co 3 O 4 /CeO 2 greatly improved the GO and GDR to produce syngas at the first step, and the pure H 2 production by the reduced Fe 2 O 3 -Co 3 O 4 /CeO 2 achieved excellent WS and oxygen storage at 750℃. The low-content Fe dopant in the OC presented a beneficial effect on the anti-sintering performance, and increase of Co-doping indicated a high activity to WS as well as enhanced GDR. The Fe 2 O 3 -Co 3 O 4 /CeO 2 with 7:5:10 of Co: Fe: Ce molar ratio presented the highest glycerol and CO 2 conversions and the highest H 2 yield, also illustrated the excellent activity and stability in 40 consecutive redox cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integrated design of in-situ H 2 sorption/storage in WGS to H 2 production is proposed. • H 2 production from supercritical CO 2 , steam, air gasification of biomass is compared. • Energy analysis for H 2 production with in-situ H 2 sorption/storage is studied. The novel process on in-situ hydrogen sorption/storage during water gas shift (WGS) was proposed and the enhanced hydrogen production in supercritical CO 2 gasification (CG), air gasification (AG), and steam gasification (SG) from biomass was integrated. Pure hydrogen was obtained by regeneration from the material (Mg 2 Ni) used for in-situ H 2 absorption during WGS. The effects of temperature, pressure, steam-to-carbon (S/C) ratio, and the quantity of adsorbent for the enhanced hydrogen production with in-situ hydrogen sorption/storage were determined. When Mg 2 Ni was added as the in-situ H 2 adsorbent, the hydrogen conversion in WGS reaction was improved. The increase of temperature reduced the hydrogen yield. SG presented the highest hydrogen yield and AG showed the highest hydrogen conversion. The steam-to-carbon (S/C) had a positive effect on the hydrogen production for all the processes and the methanation reaction was greatly inhibited by AG. The energy efficiencies reached 22.98 %, 26.31 %, and 27.149.51 %, and the exergy efficiencies reached 61.66 %, 64.19 %, and 83.62 %, for CG, AG and SG, respectively. The system energy can be supplied by in-situ hydrogen sorption/storage and the energy requirement order was SG > CG > AG. [ABSTRACT FROM AUTHOR]

Under the high attention of the international community to CO 2 emissions, the capture utilization and storage (CCUS) and the CO 2 hydrogenation fuel production have become two popular directions, especially for the combination of the two processes. In this paper, the production of liquid fuels via the methanol synthesis pathway in an integrated CCUS system based on Aspen Plus models was studied. The NH 3 -CO 2 -H 2 O absorption was used to capture CO 2 and hydrogen was provided by water electrolysis using renewable energy sources. A two-stage reactor with a recirculating stream was specified for the process of CO 2 hydrogenation to synthesize methanol, and the liquid fuel dimethyl ether (DME) was reproduced by dehydrating methanol (Power-to-Liquid). The amount of absorbent used for the carbon capture process was determined and the yield differences due to the number of cycles in the intermediate methanol synthesis reaction were analyzed. It is possible to convert 4.15 t of CO 2 per tonne of DME produced at the mass material balance of the process. The optimization of the heat exchange network and the energy requirements for the total process were evaluated. It is calculated that the energy involved in producing 1 ton of DME in the process model is 176 GJ. The analysis of the overall process and the evaluation of models could provide options for the possibility of CCUS engineering application. [Display omitted] • An integral process model converts CO 2 to liquid fuels by methanol synthesis. • Treatment options are proposed for emissions that accumulate in the cycle of the process. • The model offers energy requirement assessment for possible engineering applications. [ABSTRACT FROM AUTHOR]

A series of multifunctional catalysts were derived from lamellar montmorillonite (MMT) via ultrasound-assisted cation-exchange method. They were characterized by N 2 adsorption-desorption, X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), H 2 pulse chemisorption, inductively coupled plasma optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). The characterization results show that metal-support interaction (MSI) together with Ni and Ca dispersion interrelates with confinement effect of montmorillonite. The CO 2 absorption capacity of CAT-5 (Ca/MMT molar ratio is 5) was still above 20.0% at the tenth cycle. The steam to glycerol molar ratio (S/G) and reaction temperature were investigated, and an S/G = 3 and a temperature of 600 °C were optimized. The hydrogen purity was significantly enhanced by the equilibrium shift of insitu CO 2 removal at 600 °C. CAT-5 presents the best performance considering the synchronized absorption capacity and catalytic activity. Compared with CAT-M, CAT-5 shows higher stability in the multiple reaction-decarbonation cycles, which is due to the elevated sintering resistance of CaO derived from the confinement effect of lamellar structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • SECLSR proposed realizes CO 2 in-situ capture & utilization to H 2 and syngas. • Conversion of CO 2 from in-situ extraction of dolomite using MDR at 850 °C is feasible. • NiO/NiAl 2 O 4 of 15% NiO presented good activity and stability in SECLSR and MDR. • The process is no need for separating catalyst and sorbent for SECLSR. Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO 2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO 2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO 2 in one integrated chemical looping hydrogen production process. The process is characterized to use the oxidized NiO/NiAl 2 O 4 as a steam reforming catalyst, the reduced NiO/NiAl 2 O 4 as a CO 2 -CH 4 dry reforming catalyst, and the inexpensive dolomite as a CO 2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO 2 -CH 4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO 2 in-situ capture, dolomite decomposition and CO 2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO 2 was decreased to zero in the pre-CO 2 breakthrough periods. The reduced NiO/NiAl 2 O 4 catalysts favored the CO 2 -CH 4 dry reforming at 850 °C. The syngas of H 2 -to-CO molar ratios of 0.8–1.1 through the conversion of CO 2 from in-situ extraction of the absorbed CO 2 dolomite, was produced. The NiO/Al 2 O 4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles. [ABSTRACT FROM AUTHOR]

Hydrogen production from sorption enhanced aqueous phase reforming (APR) of biodiesel byproduct glycerol was studied by Ni-based monometallic and bimetallic catalysts supported on gelatinous MgO supports. Compared with Ni-based monometallic catalyst, the H 2 selectivity and glycerol conversion of the Cu–Ni bimetallic catalyst were found to be increased more than 3% and 30%, respectively. Meanwhile, higher reaction temperature was found to have higher H 2 yield with lower H 2 selectivity. The H 2 yield using the catalyst with gelatinous MgO support was 1.25 times higher than that of calcined support. Through in-situ CO 2 capture, the addition of CaO to the Cu–Ni bimetallic catalyst increased more than 58.3% and 14.4% of the H 2 yield and selectivity, respectively. An analysis about liquid product component indicate that the presence of CaO promote the further cleavage of the C–C bond, which further increased the conversion of glycerol. Furthermore, it was found that the presence of CaO could also improve the stability of the catalyst through the control experiments. [Display omitted] • Sorption enhanced APR to H 2 with in-situ CO 2 capture was studied. • Monometallic and bimetallic supported on MgO were developed. • Cu–Ni supported on gelatinous MgO exhibited good APR performance. • H2 yield by gelatinous MgO support was 1.25 times higher than that of calcined MgO. • Presence of CaO in APR improved conversion, selectivity, and stability. [ABSTRACT FROM AUTHOR]

Hydrogen production by chemical looping steam reforming of ethanol using oxygen carriers was carried out in a fixed-bed reactor. NiO/montmorillonite prepared by ultrasound assisted cation exchange impregnation method was used as oxygen carriers. The synthesized NiO/montmorillonite was characterized by N 2 adsorption–desorption, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), transmission electron microscopy (TEM), H 2 temperature-programmed reduction (H 2 -TPR), H 2 pulse chemisorption, temperature-programmed reduction (TPO) and thermal gravimetric analysis (TGA). The characterization results showed the particle size, metal-support interaction, nickel dispersion interrelated with cation exchange capability and confinement effect of montmorillonite’s lamellar structure. Activity and stability tests were conducted at 550 °C with a steam to carbon ratio of 4. The results showed that 20Ni–MMT possessed the best performance due to its strong sintering and coking resistance, and also presented the shortest ‘dead time’ due to its larger active surface area. Moreover, 20Ni–MMT exhibited the excellent coke elimination ability in the air feed step. [ABSTRACT FROM AUTHOR]

Hydrogen production from chemical looping steam reforming (CLSR) of glycerol was studied by Ni-based oxygen carrier in a fixed-bed reactor. For the fixed-bed reactor configuration, solid Ni-based oxygen carrier is stationary and alternatively exposed to reducing and oxidizing conditions by periodically switching the feed gases. The Ni-based oxygen carrier was prepared by a liquid-state co-precipitation method with rising pH technique and the characterization was performed by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N 2 adsorption–desorption. Gaseous products and temperature variety during CLSR process by Ni-based oxygen carrier in a fixed-bed reactor were measured, and the thermodynamic equilibrium calculation was also carried out. The results showed that the Ni-based oxygen carrier synthesized has a dual function and can efficiently convert glycerol and steam to H 2 by redox reactions. The coexisting reactions of glycerol oxidization (or NiO reduction) and steam reforming occurred before the steady stage of hydrogen production in the fuel feed step, and the conversion of NiO to Ni was obtained. Alternating reduction and oxidation reactions enabled Ni-based oxygen carrier to produce H 2 with a concentration of 85% of the equilibrium value at 600 °C, and glycerol conversion was up to 99%. The increase of temperature related to the exothermic reactions by Ni-based oxygen carrier in CLSR process was observed in redox cycles. [ABSTRACT FROM AUTHOR]

In this study, renewable hydrogen production was achieved by coupling of water splitting and glycerol oxidation reforming by chemical looping technology (CLWS-GOR) using the novel Ce–Ni modified Fe-based oxygen carriers (OCs). The OCs were developed by combining metal chelating sol-gel and isometric impregnation method, which exhibited anti-sintering characteristic and lattice oxygen migration ability in CLWS-GOR. The amount of hydrogen between 12.49 and 12.96 mmol in the steam stage was produced from all the OCs with different ratios of Fe, Ce and Ni. However, with the increase of Ce and Ni doping, the production of H 2 and CO in the fuel stage increased, as well as the probability of carbon deposits released in the subsequent steam stage. The H 2 /CO ratio in syngas were easily adjusted by steam to carbon molar ratio (S/C) in chemical looping steam reforming (CLSR), but the effects of steam introducing led to gradual deterioration of OCs. The results proved the OCs prepared by the combination method has high activity and stability for renewable hydrogen production from coupling of CLWS-GOR. [Display omitted] • Coupling of water splitting and glycerol oxidation reforming by chemical looping. • Ce–Ni modified Fe-based OCs were synthesized by combined method. • Pure H 2 was achieved from CLWS-GOR by reduced OCs. • WGS enhancement and the H 2 /CO ratio adjustment were achieved. [ABSTRACT FROM AUTHOR]

Abstract: About 10wt.% of glycerol can be produced during the conversion of vegetable oils or animal fats into biodiesel fuel by the transesterification process. To make use of glycerol and increase its values, H2 production from catalytic steam reforming of glycerol by Ni–Mg–Al based catalysts was evaluated experimentally in a fixed-bed reactor under atmospheric pressure within a temperature range of 450–650°C. The thermodynamic analysis was conducted by using a non-stoichiometric methodology based on the minimization of Gibbs free energy. The Ni–Mg–Al based catalysts were synthesized by the co-precipitation method with rising pH technique. The synthesized catalysts were characterized by the elemental analysis, BET, XRD and SEM methods. All the metals in the catalyst remained in oxide forms and the catalysts had the specific surface areas from 98.542 to 126.777m2/g for different compositions. The results showed that glycerol conversion and H2 selectivity were increased with increasing temperatures from 450 to 650°C. The formations of CH4 and CO in the glycerol steam reforming were almost negligible. Carbon formation in glycerol steam reforming was serious in low temperatures. The catalyst containing NiO of 24.1wt.%, MgO of 26.1wt.% and Al2O3 of 49.8wt.% performed appreciable catalytic activity, and the H2 selectivity was found to be 78.5% and conversion of glycerol was up to 88.0% at 650°C. The effects of the operating conditions including temperature, the ratio of steam to carbon (S/C), glycerol inlet concentration and flow rate of carrier gas on glycerol steam reforming by the optimized catalyst were tested. Based on a kinetic model assuming the power law with a first reaction order, the activation energy and the frequency factor for glycerol steam reforming by the Ni–Mg–Al based catalysts were calculated. [Copyright &y& Elsevier]

Abstract: The adsorption and photocatalytic reduction of toxic Hg(II) in aqueous solutions were investigated at different temperatures using synthesized TiO2 nanoparticles and TiO2/montmorillonite. The synthesized materials were tested by TGA, BET, TEM and XRD methods. High-purity anatase TiO2 nanoparticles with an average diameter of 9.10nm were produced by the acid catalyzed sol–gel method at 500°C, and the specific surface area of synthesized TiO2 nanoparticles was in excess of 200m2 g−1. TiO2/montmorillonite was prepared by slurry reactions, resulting in average pore size of 3.10nm with TiO2 nanoparticles on the montmorillonite surface. TiO2/montmorillonite with a 22wt% TiO2 load exhibited a specific surface area of 239m2 g−1. Removal of Hg(II) in aqueous solutions at 25, 35 and 45°C in darkness and under UV illumination showed that the photocatalytic reduction of Hg(II) increased with increasing temperature, and a decline in adsorption was observed for a rise in temperature from 25 to 45°C, following the exothermicity of the adsorption process. The adsorption behavior of Hg(II) on TiO2 nanoparticles was well described by the Langmuir isotherm model, and the rates were simulated by the Elovich equation. A first-order reaction model was used to simulate the photocatalytic reduction reaction of Hg(II) in aqueous solutions, and a good fit was obtained with the experimental data. [Copyright &y& Elsevier]

[Display omitted] • Hydrogen was efficiently produced from CLSR of biodiesel byproduct glycerol. • Well-order mesoporous CeNiO/MCM-41 and CeNiO/SBA-15 were synthesized for CLSR. • High feeding conversion and H 2 selectivity was achieved by mesoporous OCs. • High loading NiO and CeO 2 on mesoporous OCs achieved excellent CLSR redox cycles. The selection of metal oxides and supports to improve catalytic activity and stability of oxygen carriers (OCs) is crucial for chemical looping steam reforming (CLSR) to hydrogen production. In this study, the Ni-based MCM-41 and SBA-15 OCs with and without CeO 2 promoter were prepared by direct synthesis and impregnation methods. The BET, XRD, TEM, ICP-AES, H 2 -TPR and DSC-TGA were used to analyze the synthesized OCs. Hydrogen production by CLSR using biodiesel byproduct glycerol was studied in a fixed-bed reactor with fuel and air stages. The DSC-TGA experiments were carried out to determine the thermal decomposition of biodiesel byproduct glycerol and the results indicated the exothermic and/or endothermic reactions as a result of secondary reactions and, the main degradation with the mass loss of 85.5 wt% occurred in the stages of 150–500 °C. The mesoporous OCs presented high specific surface area, large pore volume, and uniform pore size. It was found that the NiO and CeO 2 in the mesoporous OCs were first reduced by fuels and the reduced OCs was responsible of steam reforming and water gas shift (WGS) to hydrogen production, and hydrogen selectivity was up to 90% using CeNiO/SBA-15. The mesoporous OCs with Ce promoter greatly shortened 'dead time' (the reduce time of OCs), and effectively suppressed carbon deposited on OCs. High loading of NiO and CeO 2 on SBA-15 improved oxygen transfer and achieved excellent cyclic stability. These findings provide the fundamental understanding and principle of design on the conventional Ni-based OCs with room for further developments in chemical looping process. [ABSTRACT FROM AUTHOR]

• Non-isothermal pyrolysis of bituminous coal were studied by coupling TG-MS/DSC. • Improved Coats-Redfern kinetics method to improve kinetics accuracy was developed. • Catalytic steam-assisted pyrolysis of bituminous coal by CaO was enhanced. • The addition of CaO and water feeding rates significantly promoted the H 2 production. The non-isothermal characteristics and pyrolysis kinetics of bituminous coal at different heating rates of 10, 20, and 30 ℃/min were studied by coupling TG-MS/DSC techniques. A fixed-bed reactor was used to investigate the coal-CaO-H 2 O reactions to understand hydrogen production and the effects of CaO under different water feeding rates. The pyrolysis phase, the maximum mass loss rate, the characteristic peak temperature, and the release of the main volatile gases were studied. Based on the improved Coats-Redfern method by introducing the function of Q (E/RT), the activation energies and pre-exponential factors of non-isothermal pyrolysis of bituminous coal were estimated iteratively by regression to enhance their accuracy. The values of E were calculated as 22, 22, 19 kJ/mol in the first stage, 67, 75, 78 kJ/mol in the second stage, 114, 96, 133 kJ/mol in the third stage at the heating rates of 10, 20, and 30 ℃/min. Finally, the concentration and selectivity of gaseous products from the pyrolysis of bituminous coal were studied. The concentrations of H 2 , CO, and CO 2 in the gas products increased with the addition of CaO and the increase of water feeding rate. Besides, the concentration of CH 4 increases with the increase of water feeding rate but decreases significantly with the addition of CaO. It is also worth noting that the pyrolysis process was enhanced by CaO addition to in-situ CO 2 captured and catalytic cracking reactions at the initial stage of the pyrolysis process. [ABSTRACT FROM AUTHOR]

• The mathematical model can accurately predict the melting heat transfer process of PCMs. • The Rayleigh number increased with the heat flux, and the higher the heat flux, the larger the amplitude. • Increasing the heat flux improved the integrated heat transfer coefficient and thermal storage performance of the CPCMs. • Conduction was the primary heat transfer mechanism; however, the proportion of natural convection increased with the heat flux. To investigate the effect of heat flux on the enhanced heat transfer in phase change materials (PCMs) composed of copper metal foam (CMF) and paraffin wax (PX), a semi-cylindrical visualized heat storage device with a varied heat flux of 7.3 kW/m2, 8.5 kW/m2, 9.7 kW/m2, and 10.9 kW/m2 was established in this paper. Moreover, a 3-D mathematical model of composite phase change materials (CPCMs) was established using hybrid grid to study the temperature distribution, imbalance effect, flow, heat transfer mechanisms, and heat storage performance during the melting process. The results showed that the melting time of the CPCMs decreased as the heat flux increased. Compared with a heat flux of 7.3 kW/m2, the melting time was shortened by 10.05 %, 20.71 %, and 27.21 %, respectively. In addition, the Rayleigh number (Ra) increased with the increase in heat flux, and the amplitudes of Ra were 1.45×108,1.54×108,1.61×108, and 1.74×108, respectively, which indicated that the higher the heat flux, the larger the amplitudes. Moreover, the heat transfer mechanism during the melting process was dominated by conduction; however, with the increase in heat flux, the maximum flow velocity of the liquid paraffin increased, which caused the proportion of natural convection to increase from 27.80 % to 31.30 %. Hence, the integrated heat transfer coefficient of CPCMs increased from 5.69 W/(m·K) to 5.81 W/(m·K). However, the temperature imbalance effect of the CPCMs was exacerbated, as evidenced by the increased maximum temperature difference in the vertical direction of the center of the CPCMs from 24.7 K to 35.6 K. Besides, the heat storage performance was enhanced. Compared with a heat flux of 7.3 kW/m2, the heat storage capacities of the CPCMs increased by 4.21%, 9.46%, and 12.66 % with increasing heat flux, and the heat storage rates of the CPCMs increased by 15.3 %, 34.9 %, and 52.3 %, respectively. Furthermore, the relative error of the overall melting time was 3.4 %, indicating that the model provided reasonable predictions. [ABSTRACT FROM AUTHOR]

SO 2 -depolarized electrolysis (SDE) is the key process in the hybrid sulfur cycle for green hydrogen production, but the detailed SDE characteristics including products generation, current efficiency variation, and side reactions are unclear. Herein, a continuous SDE process was experimentally conducted and theoretically modelled. The H 2 and H 2 SO 4 production was accelerated and the current efficiency for both electrodes was improved with a proper increase in current density (50−100 mA/cm2) or temperature (293−318 K), but further increasing current density to 150 mA/cm2 or temperature to 333 K led to a negative trend because of the anode corrosion or declined SO 2 solubility. The increasing initial H 2 SO 4 concentration (10−40 wt%) facilitated the cathodic H 2 production and current efficiency, while negatively influenced the anodic SO 2 conversion. The parasitic reactions occurred at cathode consumed H 2 and resulted to the cathodic current efficiency well below 100%. A rigorous mathematical regression model correlating the production rates of H 2 and H 2 SO 4 with current density, temperature, and initial H 2 SO 4 concentration was developed, and combined with the analysis of variance, current density was suggested the biggest factor affecting products generation in SDE process. These findings demonstrate a practical avenue for efficient SO 2 conversion and H 2 production in SDE process of hybrid sulfur cycle. [Display omitted] • H 2 and H 2 SO 4 production, current efficiency, and side reactions during SDE process were characterized. • Influence of current density, temperature, and initial H 2 SO 4 concentration on SDE process were emphasized. • Rigorous mathematical regression models concerning H 2 and H 2 SO 4 production rates were developed. • Current density was the biggest influencing factor toward products generation during SDE process. [ABSTRACT FROM AUTHOR]

• A flowsheet of SI cycle considering the Bunsen reaction kinetics was developed. • A user-defined Fortran module concerning Bunsen reaction kinetics was established. • Internal heat exchange network was created using pinch point temperature difference analysis. • The theoretical thermal efficiency of SI system was obtained in the range of 14.0–57.4 %. Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H 2 SO 4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle. [ABSTRACT FROM AUTHOR]

• Condensation heat transfer and pressure drop were investigated experimentally with R410A and R32 in four different tubes. • The surface structures inside tubes were smooth, hydrophobic, herringbone and hydrophobic/herringbone, respectively. • The performance enhancement factor and specific sensitivity factor were used to evaluate the influence of overall heat transfer performance. An experimental investigation was performed to evaluate the condensation heat transfer characteristics for R32 and R410A inside four horizontal round tubes with 12.7 mm outer diameter. The saturation temperatures were 35 °C and 45 °C, the vapor qualities ranged from 0.2 to 0.8, and the mass flux ranged from 50 kg m−2 s−1 to 200 kg m−2 s−1. Different inside surface structures of the four tubes were smooth (ST), hydrophobic (HYD), herringbone (HB) and hydrophobic/herringbone (HYD/HB), respectively. Effects of mass flux, vapor quality, refrigerant and saturation temperature on condensation heat transfer in different tubes were discussed with the aid of flow pattern visualizations. Experimental results show that the heat transfer coefficient of R32 was higher than that of R410A due to different physical properties of the refrigerant. HB tube had the highest heat transfer coefficient at low vapor quality and HYD tube was the best at high vapor quality. The performance enhancement factors (PEF) of HB tube and HYD tube were better, ranging from 1.07 to 1.4 and from 1.02 to 1.31, respectively. However, as the composite of HB and HYD, the HYD/HB tube had the lowest overall performance, with the PEF ranged from 0.94 to 1.12. Additionally, the specific sensitivity factor (SSF) was used to evaluate the influence of various parameters on heat transfer and pressure drop. [ABSTRACT FROM AUTHOR]

Transition from bulk surfactant solution to gelatinous surfactant dry solution and the behavior of the methane uptake in GDS droplets during the repeated hydrate formation. • GDS droplets have the merits of the dry water, the surfactant solution and the gelling agent. • The droplets can provide abundant gas channels, considerable gas–liquid contact area and stable gel-like structure. • The droplets facilitate rapid and reversible methane storage in clathrate hydrate. • The droplets maintained relatively high methane storage capacities until the ninth cycle. A gelatinous dry solution (GDS) was prepared by blending sodium dodecyl sulfate solution, gellan gum powder, and hydrophobic silica nanoparticles in air at a high speed. It is essentially a pile of free-flowing micro surfactant droplets supported by a gelling agent. The GDS has the dispersion characteristics of dry water, activity of the surfactant solution and stability of the gel. The flour-like droplets can provide abundant micro channels for gas transfer, a considerable surface area for gas–liquid contact and stable gel-like structure for repeated hydrate formation. Multi-cycle methane consumption experiments were conducted in a stainless steel vessel at 5.0–8.1 MPa and 273.2 K, in order to study the repeated kinetics of methane hydrate formation in GDS. The results demonstrated that the dispersed GDS facilitated rapid and reversible methane storage in clathrate hydrate by enhancing the gas–liquid contact and the stability of the regular droplets. Methane uptake (152.2–163.2 m3·m−3) and maximum uptake rates (4.522–5.690 m3·m−3·min−1) were achieved in the first storage cycle at the experimental pressures. GDS maintained relatively high methane storage capacities (114.3–118.0 m3·m−3) until the ninth cycle, and the capacities only were attenuated by 24.92–27.70% with respect to the first cycle at the above pressures. A hypothesis of "droplets breakage by released gas" was proposed to illustrate the attenuation of gas storage capacity of the droplets. [ABSTRACT FROM AUTHOR]

In this study, a critical comparison between two low metal (Ni) loading catalysts is presented, namely Ni/Al2O3 and Ni/AlCeO3 for the glycerol steam reforming (GSR) reaction. The surface and bulk properties of the catalysts were evaluated using a plethora of techniques, such as N2 adsorption/desorption, Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP–AES), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDX, Transmission Electron Microscopy (TEM), CO2 and NH3– Temperature Programmed Desorption (TPD), and Temperature Programmed Reduction (H2–TPR). Carbon deposited on the catalyst's surfaces was probed using Temperature Programmed Oxidation (TPO), SEM, and TEM. It is demonstrated that Ce-modification of Al2O3 induces an increase of the surface basicity and Ni dispersion. These features lead to a higher conversion of glycerol to gaseous products (60% to 80%), particularly H2 and CO2, enhancement of WGS reaction, and a higher resistance to coke deposition. Allyl alcohol was found to be the main liquid product for the Ni/AlCeO3 catalyst, the production of which ceases over 700 °C. It is also highly significant that the Ni/AlCeO3 catalyst demonstrated stable values for H2 yield (2.9–2.3) and selectivity (89–81%), in addition to CO2 (75–67%) and CO (23–29%) selectivity during a (20 h) long time-on-stream study. Following the reaction, SEM/EDX and TEM analysis showed heavy coke deposition over the Ni/Al2O3 catalyst, whereas for the Ni/AlCeO3 catalyst TPO studies showed the formation of more defective coke, the latter being more easily oxidized. [ABSTRACT FROM AUTHOR]

To explore the effect of metal foam(MF)pore density on the melting and heat transfer of phase-change materials(PCMs), a semi-cylindrical visualization experimental setup was established to experimentally study copper MFs with different pore densities coupled with paraffin wax. The results showed that as pore density increases, the melting time of the composite PCMs decreases compared to that of pure paraffin wax by 11.5%, 16.2% and 18.1% for pore densities of 5, 20, and 30 PPI, respectively. Composite PCMs with a pore density of 30 PPI exhibited fastest melting and lowest maximum temperature difference during melting. Considering the relative thermal energy storage(TES) capacity and relative TES rate, composite PCMs with a pore density of 30 PPI exhibited optimal overall thermal storage performance. Furthermore, heat conduction was the primary means of thermal transmission during the melting of the bottom paraffin. However, the melting of the upper paraffin was nevertheless influenced by natural convection, Hence, as pore size decreased, the influence on the weakening of natural convection became more significant. The results of the study provide guidance for the optimal design of latent heat storage devices for semi-cylinders. • The metal foam's pores are smaller the more effectively it transfers heat. • The copper foam with a 30 PPI pore density exhibited the best thermal storage performance. • The natural convection effect was less noticeable as pore size decreased. • The rate of heat storage increased as pore density continued to rise. [ABSTRACT FROM AUTHOR]

Chemical looping reforming (CLR) of ethanol is a novel method to produce hydrogen. It’s vital to select an appropriate oxygen carrier (OC) with favorable catalytic activity and high stability for successive redox processes. In current research, the intelligent perovskites La 2- x M x NiO 4- λ ( M = Ca, Sr and Ce) were used as OCs and prepared by co-precipitation method. The ‘intelligence’ was embodied in exceptional self-recovery ability of perovskite during oxidation stage of CLR process, which was confirmed by the movement that Ni ions escaped and regained back to original position during oxidation step. The experimental result indicated that the movement effectively restrained the growth of metallic Ni and resulted in high activity of OC during life-time service and aging. Furthermore, the influence of promoters doping on the regeneration characteristics of OCs was investigated by BET, TEM, XRD, ICP-OES, TG and a fixed-bed experiment. From the perspective of catalytic performance, the addition of promoter strongly improved the reducibility of OCs, and the optimal substitution is Ca. The LNO-Ca OC exhibited favorable reducibility of nickel ions, shorter ‘dead time’, higher yield of hydrogen, superior ethanol conversion, stronger anti-carbon ability and excellent reproducibility of perovskite during successive redox reactions. [ABSTRACT FROM AUTHOR]

• The condensation heat transfer characteristics of R410A on the outside of three enhanced tubes were experimentally investigated. • Effect of surface structure, mass flux, average vapor quality, and saturation temperature on HTC and frictional pressure drop. • The six correlations are evaluated and the correlation with the highest accuracy is selected and modified to obtain a predictive correlation suitable for the enhanced tubes. Condensation heat transfer characteristics on the outer annular walls of double-sided horizontal tubes having three different enhancement geometries are investigated experimentally. The enhancement geometries are (1) a fine fin array, (2) a rectangular convex platform array, and (3) a T-shaped column array. The inner surface geometries are threads of various pitches. The experiments are with various mass fluxes, average vapor qualities, and saturation temperatures. They were conducted with refrigerant R410A. The results show the effects of enhancement geometry. Six correlations are used to predict the heat transfer coefficients of smooth tube, and the correlation with the highest accuracy is selected and corrected to obtain a new correlation suitable for the enhanced tubes. The new correlation can predict 92% of the data points within a prediction error of +22% to -30%. Frictional pressure drops are correlated with mass flux, average vapor quality, and saturation temperature. The heat transfer performances of the three experimental tubes are compared using a performance evaluation factor and the enhancement geometries with better condensation heat transfer performances are identified. [ABSTRACT FROM AUTHOR]

Dewatering of sewage sludge (SS) was the prerequisite for saving its drying energy and sustaining its stable combustion. Hydrothermal treatment (HT) has been a promising technology for improving SS dewaterability with high energy efficiency. However, the knowledge of phosphorus (P) transformation and heavy metals (HMs) behaviors in the combined HT and incineration process was still lack. P fractions, P-bioavailability, HMs speciation, and their environmental risk in the ash samples from this combination process were evaluated and compared with those from the co-incineration of SS and CaO. The combination process was superior to the latter one in the light of P and HMs. CaO preferred to enhance the transformation of non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP) initially with enriched P and increased P-bioavailability in the resultant ash samples. The combination process further reduced the values of risk assessment code and individual contamination factor with the increment of the stable F4 fraction in HMs. Significant reduction of potential ecological risk was observed with the lowest global risk index of 43.76 in the combination process. Optimum CaO addition of 6% was proposed in terms of P and HMs. The work here can provide theoretical references for the potential utilization of P from SS to mitigate the foreseeable shortage of P rocks. [Display omitted] • Hydrothermal treatment combined with incineration of sewage sludge was studied. • P enrichment and bioavailability in ash were enhanced by combination process. • Reduced mobility and ecological risk of heavy metals were observed in ash. • Combination process was superior to co-incineration of sewage sludge and CaO. • CaO preferred to enhance the transformation of NAIP to AP in combination process. [ABSTRACT FROM AUTHOR]

• A greater proportion of copper metal foam (CMF) can enhance the heat transfer of paraffin wax and reduce the temperature gradient. • A theoretical model was built to calculate the comprehensive heat transfer coefficient of composite PCMs and to determine the intensity change of heat conduction and natural convection of PCMs with different CMF proportions. • Melting time and heat storage capacity of CMF composite PCMs first increased and then decreased with increasing CMF proportion. • Heat storage rate and comprehensive heat transfer coefficient first decreased and then increased with increasing CMF proportion. • Composite PCMs with a CMF proportion of 0.86% exhibit the best heat storage performance. Phase-change materials (PCMs) can overcome the low energy density and utilization efficiency of solar energy. However, the low thermal conductivity of PCMs significantly affects the thermal efficiency of solar devices; thus, improving the thermal conductivity of PCMs has been the focus of many recent studies. In this study, copper metal foam (CMF) composite PCMs were prepared using paraffin wax and high-pore-density CMF. The effect of the CMF proportion on heat transfer enhancement in the PCM melting process was analyzed using experimental equipment for heat storage visualization. Comprehensive heat transfer coefficients of CMF composite PCMs were obtained. The experimental results showed that as the CMF proportion increased from 0 to 2.15%, the melting time of the CMF composite PCMs and their heat storage capacity first increased and then decreased, whereas the heat storage rate and comprehensive heat transfer coefficient first decreased and then increased. The minimum temperature gradient of 8.09 K was reached when the CMF proportion was 2.15%. More importantly, as the proportion of CMF increased from 0.43 to 2.15%, the proportion of natural convection decreased from 87.90 to 17.69%, and natural convection was the major heat transfer mechanism in the melting process of composite PCMs with a low CMF proportion. The composite PCMs with a CMF proportion of 0.86% has the best heat storage performance when the heat storage capacity and heat storage rate were both considered. [ABSTRACT FROM AUTHOR]

The purpose of this study was to obtain the characteristics of CO 2 hydrate formation and dissociation by using different experimental modes and pressures with glass beads. From the experiments, it was found that hydrate forms rapidly in each cycle, especially at high pressure. Hydrate blockage rarely appeared during hydrate formation and dissociation when applying gas flow (Case 2); this approach was significantly better than the other two experimental modes. The maximum hydrate saturations for the three experimental modes were 28%, 24% and 67.5%. The overall hydrate saturation of Case 3 was significantly better than those of the other two cases. When a heating process was applied to induce hydrate dissociation, the rapid backpressure decrease led to migration of the pore solution during depressurization. The minimal residual water after hydrate formation resulted in consistent residual water saturation after hydrate dissociation for Case 2. Considering hydrate saturation and operating pressure, 5.00 MPa is a better choice for hydrate-based desalination and CO 2 capture. If the initial residual solution can be completely converted to hydrate, this technology has potential for industrial applications. [ABSTRACT FROM AUTHOR]

The SO 2 -depolarized electrolysis (SDE) is one of the main processes in the hybrid sulfur cycle for hydrogen production, the microscopic characteristics of which are still not clear. In this work, a numerical analysis of SDE was conducted. The steady-state, laminar and incompressible 2D model of the electrolytic cell (EC) for carrying out SDE was first developed and verified. Physical field characterization indicated that the velocity was almost uniformly distributed in the flow channel, but higher pressure drops and pumping power consumption existed in the anode channel than in the cathode channel. Meanwhile, the continuous conversion of SO 2 to H 2 SO 4 at anode and generation of H 2 at cathode along the channel length were determined. Further exploring the impacts of three main operating parameters implied that an appropriate higher electrolytic potential, lower inlet flow rate (not less than 0.005 m/s) and operating temperature were favorable for improving the SDE. After comprehensive consideration of SDE performance and energy consumption, a feasible operating condition of 0.8 V, 303 K, and 0.005 m/s was proposed for SDE process. The developed model and microscopic characterization of SDE will favor the design and optimization of EC for SDE process. [Display omitted] [ABSTRACT FROM AUTHOR]

• Obvious kinetic compensation effects were found during hydrochar gasification. • Formation of fixed carbon by HTC lowered char-CO 2 gasification reactivity. • HTC treatment had determinant impact on chemical composition of pyrolytic volatiles. • Positive correlation of carbon functionality and volatile aromatics was found. • Mild HTC pretreatment is encouraging in combination with gasification. Hydrothermal carbonization (HTC) combined with subsequent thermochemical conversion is an effective approach for sewage sludge (SS) to energy. In this work, HTC pretreatment of SS was performed. Then the properties of released volatiles and the remaining char-CO 2 gasification after pyrolysis were evaluated via the multiple kinetic model and combined instrumental analyses. The gasification behavior of these samples exhibited slightly different due to high ash content and limited fixed carbon, although the aromatic structure in the hydrochars developed as HTC proceeded. Kinetic analysis indicated that volume reaction model (VRM) with chemical reaction order of 1.5 showed high correlation coefficients (R 2>0.99) for all carbonized samples. There was an obvious kinetic compensation effect in the char gasification step, and activation energy (E) and pre-exponential factor (A) of these samples followed a positive correlation relationship as lnA = 0.1037 × E + 0.3579. The formation of fixed carbon in the hydrochar samples was conserved during pyrolysis, which lowered the average gasification reactivity of char. Py-GC/MS demonstrated that the chemical composition of pyrolytic volatiles was found to be mainly determinant by HTC conditions. The share of aromatics in the volatiles was in a positive correlation with the evolution of carbon functionality in the hydrochar samples. Above in all, HTC temperature exerted a more significant effect on the fuel properties of hydrochar samples than HTC duration did, which also indicated by their subsequent thermochemical conversion. These findings can provide essential knowledge on the thermochemical conversion of hydrochar samples and favor the designing, optimization, and scaling up of the process. [ABSTRACT FROM AUTHOR]

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use. [ABSTRACT FROM AUTHOR]

The SO 2 -depolarized electrolysis (SDE) is a promising method for SO 2 capture and hydrogen production. But the SDE is limited by the high overpotential and slow kinetics of anodic SO 2 oxidation reaction (SOR). Herein, to boost SDE process, we add hydroiodic acid (HI) to the anolyte and form HI-assisted SO 2 -depolarized electrolysis (HASDE). The mechanism of HI assisted SOR is explored, the existence of HI reduces the onset potential and impedance, but increases current density and reaction rate of SOR. HI is supposed to change the single-step SOR into three-step reactions, without changing the overall anodic reaction. A HI concentration of less than or equal to 0.02 mol/L and an operating temperature of 50 °C or less are recommendable. The comparison of SDE and HASDE processes indicates that HASDE delivers a lower cell voltage than SDE during continuous constant-current electrolysis, and has negligible effect on cathodic H 2 evolution, while it achieves 27.03–48.65% reduction in electric energy consumption compared with SDE. The present work provides an innovative strategy for improving SDE and energy-saving production of value-added chemicals like H 2 SO 4 and H 2. Image 1 • HI-assisted SO 2 -depolarized electrolysis (HASDE) was proposed. • Anodic HI assisted SO 2 oxidation reaction (SOR) was more favorable than SOR. • Mechanism of anodic oxidation reaction in HASDE was elucidated. • HASDE was more efficient and energy-saving than SDE. [ABSTRACT FROM AUTHOR]

The relatively slow gas storage rate as well as poor storage capacity of the static hydration system are still major challenges in the large-scale practical application of hydrate technology. Sodium dodecyl sulfate (SDS) solutions containing suspended copper particles (CP) and stainless steel fibers (SSF) were used for natural gas storage in clathrate hydrates at 4.0–7.0 MPa and 274.15 K. The particles and fibers in the suspension provided a large number of metal nuclei for crystallization, especially the fibers acted as metal pathway for crystallization heat transfer. The enhanced effect of CP and SSF on gas capture in hydrates was concluded through kinetics comparison of hydrates formation in the suspension and in a simple surfactant solution. In the SDS/CP–SSF system, the time required to reach the storage capacity of 100 cm3·cm−3 was shorter not only than that in the SDS solution but also than that in the CP suspension at each pressure. The hybrid suspension exhibited higher gas storage capacities (112.6–149.2 m3·m−3) and larger storage rates (7.54–39.47 cm3·cm−3·min−1) at the applied pressures, increasing by 35.6–173.0% and 19.8–26.2%, respectively, over those of the simple surfactant solution. A "point (CP)–line (SSF) model" was proposed to illustrate the synergetic enhancement effect of the CP and SSF on hydrate nucleation and heat transfer. Synergetic enhancement of gas hydrates heat removal in suspension with stainless steel fibers (SSF) and copper particles (CP). Unlabelled Image • The suspension with metal fibers and particles provides numerous nucleation sites for gas hydrate crystallization. • SSF served as heat transfer "highway" for enhancing hydrate heat removal. • SDS/CP–SSF system exhibited higher gas storage capacities and larger storage rates compared with SDS solution. • A "point (CP)–line (SSF) model" was proposed to illustrate synergetic enhancement of nucleation and heat transfer. [ABSTRACT FROM AUTHOR]