Comparative analysis on sorption enhanced steam reforming and conventional steam reforming of hydroxyacetone for hydrogen production: Thermodynamic modeling

The chemical thermodynamics of sorption enhanced steam reforming (SESR) of hydroxyacetone for hydrogen production were investigated and contrasted with hydroxyacetone steam reforming (SR) by means of Gibbs free energy minimization principle and response reactions (RERs) method. Hydrogen is mainly derived methane steam reforming reaction from and water gas shift reaction. The former reaction contributes more than the latter one to hydrogen production below 550 °C and at higher temperature the latter one tends to dominate. The maximum hydrogen concentration is 70% in SR, which is far below hydrogen purities required by fuel cells. In SESR, hydrogen purities are over 99% in 525–550 °C with a WHMR greater than 8 and a CHMR of 6. The optimum temperature for SESR is approximately 125 °C lower than that for SR. In comparison with SR, SESR has the advantage of almost complete inhibition of coke formation in 200–1200 °C for WHMR ≥ 3.     

Comparative exergy analysis of sorption enhanced and conventional methane steam reforming

Exergy efficiency analysis tool is used to evaluate sorption enhanced steam reforming in comparison with the industrial hydrogen production route, steam reforming. The study focuses on hydrogen production for use in high pressure processes. Thermodynamic sensitivity analysis (effect of reforming temperature on hydrogen yield and reforming enthalpy) was performed to indicate the optimum temperature (650 °C) for the sorption enhanced reforming. The pressure was selected to be, for both cases, 25 bar, a typical pressure used in the industrial (conventional) process. Atmospheric pressure, 1000 °C and CO₂ as inert gas were specified as the optimum operating parameters for the regeneration of the sorbent after performing exergy efficiency analysis of three realistic case scenarios. Aspen Plus simulation process schemes were built for conventional and sorption enhanced steam reforming processes to attain the mass and energy balances required to assess comparatively exergy analysis. Simulation results showed that sorption enhanced reforming can lead to a hydrogen purity increase by 17.3%, along with the recovery of pure and sequestration-ready carbon dioxide. The exergy benefit of sorption enhanced reforming was calculated equal to 3.2%. Analysis was extended by adding a CO₂ separation stage in conventional reforming to reach the hydrogen purity of sorption enhanced reforming and enable a more effective exergy efficiency comparison. Following that analysis, sorption enhanced reforming gained 10.8% in exergy efficiency.     

Techno-economic analysis of the Ca-Cu process integrated in hydrogen plants with CO2 capture

In this work, a techno-economic analysis of a hydrogen production plant based on the Ca-Cu process has been carried out. The simulation of the whole hydrogen production plant has been performed, including the calculation of the Ca-Cu fixed bed reactors system using a sharp front modelling approach. From the analyses carried out, it has been demonstrated that the optimal operation point from the energy performance point of view is reached when fuel needed for sorbent regeneration is entirely supplied by the off-gas from the PSA hydrogen purification unit, which corresponds to operating the plant with the minimum steam-to-carbon ratio in the reforming step. Moreover, lowering the operating pressure of the Ca-Cu system results beneficial from the hydrogen production efficiency, but the CO₂ emissions and the economics worsen.The Ca-Cu based hydrogen production plant operating at a high pressure has been demonstrated to be cost efficient with respect to a benchmark hydrogen production plant based on conventional fired tubular reformer and CO₂ capture by MDEA absorption. A hydrogen production cost of 0.178 €/Nm³ and a CO₂ avoided cost of 30.96 €/ton have been calculated for this Ca-Cu hydrogen production plant, which are respectively 8% and 52% lower than the corresponding costs of the benchmark.     

MnFe2O4 nanopowder synthesised via a simple hydrothermal method for promoting hydrogen sorption from MgH2

The effects of MnFe₂O₄ nanopowder synthesised via a simple ‘hydrothermal’ method on the hydrogen storage properties of MgH₂ are investigated for the first time. The particle size of the as-synthesised MnFe₂O₄ nanoparticles is determined to be about 10 nm. We observe that MnFe₂O₄ catalyst decreases the decomposition temperature of MgH₂ and enhances the sorption kinetics. Interestingly, the onset hydrogen desorption temperature of 10 wt% MnFe₂O₄-doped MgH₂ sample gets lowered from 350 °C to 240 °C with faster kinetics, and the sample shows an average dehydrogenation rate 8–9 times faster than that of the as-milled MgH₂ sample. By adding 10 wt% of as-prepared MnFe₂O₄ to MgH₂, approximately 5.5 wt% hydrogen can be absorbed in 10 min at 200 °C. In contrast, the un-doped MgH₂ sample absorbed only 4.0 wt% hydrogen in the same period of time. From the Kissinger analysis, the apparent activation energy for hydrogen released in the MnFe₂O₄-added MgH₂ composite is found to be 108.42 kJ/mol, which is much lower than the activation energy for hydrogen released in the as-milled MgH₂ (146.57 kJ/mol). It is believed that the in situ formed Fe particle and Mn-containing phases together play a synergistic role in remarkably improving MgH₂ storage properties.     

Thermodynamic analysis of aqueous phase reforming of three model compounds in bio-oil for hydrogen production

Thermodynamic analysis with Gibbs free energy minimization was performed for aqueous phase reforming of methanol, acetic acid, and ethylene glycol as model compounds for hydrogen production from bio-oil. The effects of the temperature (340-660 K) and pressure ratio Psys/PH₂O (0.1-2.0) on the selectivity of H₂ and CH₄, formation of solid carbon, and conversion of model compounds were analyzed. The influences of CaO and O₂ addition on the formation of H₂, CH₄, and CO₂ in the gas phase and solid phase carbon, CaCO₃, and Ca(OH)₂ were also investigated. With methanation and carbon formation, the conversion of the model compounds was >99.99% with no carbon formation, and methanation was thermodynamically favored over hydrogen production. H₂ selectivity was greatly improved when methanation was suppressed, but most of the inlet model compounds formed solid carbon. After suppressing both methanation and carbon formation, aqueous phase reforming of methanol, acetic acid and ethylene glycol at 500 K and with Psys/PH₂O = 1.1 gave H₂ selectivity of 74.98%, 66.64% and 71.38%, respectively. These were similar to the maximum stoichiometric hydrogen selectivity of 75.00% (methanol), 66.67% (acetic acid), and 71.43% (ethylene glycol). At 500 K and 2.90 MPa, as the molar ratio of CaO/BMCs increased, the normalized variation in H₂ increased and that for CH₄ decreased. Formation of solid carbon was effectively suppressed by addition of O₂, but this was at the expense of H₂ formation. With the O₂/BMCs molar ratio regulated at 1.0, oxidation and CO₂ capture increased the normalized variation in H₂ to 33.33% (methanol), 50.00% (acetic acid), and 60.00% (ethylene glycol), and the formation of solid carbon decreased to zero.     

Hydrogen-rich gas production by air–steam gasification of rice husk using supported nano-NiO/γ-Al2O3 catalyst

The air–steam catalytic gasification of rice husk for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor with the newly developed nano-NiO/γ-Al₂O₃ catalyst. A series of experiments have been performed to explore the effects of catalyst presence, catalytic reactor temperature, the equivalence ratio (ER), and steam to biomass ratio (S/B) on the composition and yield of gasification gases. The experiments demonstrated that the developed nano-NiO/γ-Al₂O₃ catalyst had a high activity of cracking tar and hydrocarbons, upgrading the gas quality, as well as yielding a high hydrogen production. Catalytic temperature was crucial for the overall gasification process, a higher temperature contributed to more hydrogen production and gas yield. Varying ER demonstrated complex effects on rice husk gasification and an optimal value of 0.22 was found in the present study. Compared with biomass catalytic gasification under air only, the introduction of steam improved the gas quality and yield. The steam/biomass ratio of 1.33 was found as the optimum operating condition in the air–steam catalytic gasification.     

Synthesis,characterization and photocatalytic performances of Cu2MoS4

A novel visible-light-driven Cu₂MoS₄ photocatalyst was prepared by a facile hydrothermal method using Ammonium Tetrathiomolybdate reacting with cuprous chloride in aqua ammonia. The synthetic catalysts were characterized by XRD, UV–vis spectra, XRF and SEM techniques. The influence of the reaction temperature and time on the activities of the catalysts and the morphology of particles was investigated. The results showed that the catalysts exhibited strong absorption in visible light region. It was found that the photocatalyst prepared under hydrothermal condition at 140 °C for about 24 h showed good crystallinity with regular shape, and the highest activity for hydrogen production under visible light irradiation in an aqueous Na₂S–Na₂SO₃ solution. The reason for its better performance has been discussed in detail.     

Hydrogen production by sorption enhanced steam reforming of propane: A thermodynamic investigation

Thermodynamic features of hydrogen production by sorption enhanced steam reforming (SESR) of propane have been studied with the method of Gibbs free energy minimization and contrasted with propane steam reforming (SR). The effects of pressure (1-5 atm), temperature (700-1100 K) and water to propane ratio (WPR, 1-18) on equilibrium compositions and carbon formation are investigated. The results suggest that atmospheric pressure and a WPR of 12 are suitable for hydrogen production from both SR and SESR of propane. High WPR is favourable to inhibit carbon formation. The minimum WPR required to eliminate carbon production is 6 in both SR and SESR. The most favourable temperature for propane SR is approximately 950 K at which 1 mol of propane has the capacity to produce 9.1 mol of hydrogen. The optimum temperature for SESR is approximately 825 K, which is over 100 K lower than that for SR. Other key benefits include enhanced hydrogen production of nearly 10 mol (stoichiometric value) of hydrogen per mole of propane at 700 K, increased hydrogen purity (99% compared with 74% in SR) and no CO₂ or CO production with the only impurity being CH₄, all indicating a great potential of SESR of propane for hydrogen production.     

Hydrogen production by sorption enhanced steam reforming of oxygenated hydrocarbons (ethanol, glycerol, n-butanol and methanol): Thermodynamic modelling

Thermodynamic analysis of steam reforming of different oxygenated hydrocarbons (ethanol, glycerol, n-butanol and methanol) with and without CaO as CO₂ sorbent is carried out to determine favorable operating conditions to produce high-quality H₂ gas. The results indicate that the sorption enhanced steam reforming (SESR) is a fuel flexible and effective process to produce high-purity H₂ with low contents of CO, CO₂ and CH₄ in the temperature range of 723-873 K. In addition, the separation of CO₂ from the gas phase greatly inhibits carbon deposition at low and moderate temperatures. For all the oxygenated hydrocarbons investigated in this work, thermodynamic predictions indicate that high-purity hydrogen with CO content within 20 ppm required for proton exchange membrane fuel cell (PEMFC) applications can be directly produced by a single-step SESR process in the temperature range of 723-773 K at pressures of 3-5 atm. Thus, further processes involving water-gas shift (WGS) and preferential CO oxidation (COPROX) reactors are not necessary. In the case of ethanol and methanol, the theoretical findings of the present analysis are corroborated by experimental results from literature. In the other cases, the results could provide an indication of the starting point for experimental research. At P = 5 atm and T = 773 K, it is possible to obtain H₂ at concentrations over 97 mol% along with CO content around 10 ppm and a thermal efficiency greater than 76%. In order to achieve such a reformate composition, the optimized steam-to-fuel molar ratios are 6:1, 9:1, 12:1 and 4:1 for ethanol, glycerol, n-butanol and methanol, respectively, with CaO in the stoichiometric ratio to carbon atom.     

Techno-economic analysis and life cycle assessment of hydrogen production from different biomass gasification processes

The paper presents techno-economic analyses and life cycle assessments (LCA) of the two major gasification processes for producing hydrogen from biomass: fluidized bed (FB) gasification, and entrained flow (EF) gasification. Results indicate that the thermal efficiency of the EF-based option (56%, LHV) is 11% higher than that of the FB-based option (45%), and the minimum hydrogen selling price of the FB-based option is $0.3 per kg H₂ lower than that of the EF-based option. When a carbon capture and liquefaction system is incorporated, the efficiencies of the EF- and FB-based processes decrease to 50% and 41%, respectively. The techno-economic analysis shows that at a biomass price of $100 per tonne, either a minimum price of $115/tonne CO_2e or a minimum natural gas price of $5/GJ is required to make the minimum hydrogen selling price of biomass-based plants equivalent to that of commercial natural gas-based steam methane reforming plants. Furthermore, the LCA shows that, biomass as a carbon-neutral feedstock, negative life cycle GHG emissions are achievable in all biomass-based options.     

Sustainable hydrogen production options from food wastes

In this study, two thermochemical processes, namely steam gasification and supercritical water gasification (SCWG), were comparatively studied to produce hydrogen from food wastes containing about 90% water. The SCWG experiments were performed at 400 and 450 °C in presence of catalyst (Trona, K₂CO₃ and seaweed ash). The maximum hydrogen yield was obtained at 450 °C in presence of K₂CO₃ catalyst. In second process, hydrothermal carbonization was used to convert food wastes into a high-quality solid fuel (hydrochar) that was further gasified in a dual-bed reactor in presence of steam. The steam gasification of hydrochar was carried out with and without catalysts (iron?ceria catalyst and dolomite). The maximum hydrogen yield obtained from steam gasification process was 28.08 mmol/g dry waste, about 7.7 times of that from SCWG. This study proposed a new concept for hydrogen production from wet biomass, combination of hydrothermal carbonization following steam gasification.     

Process simulation and techno-economic assessment of SER steam gasification for hydrogen production

In the SER (sorption enhanced reforming) gasification process a nitrogen-free, high calorific product gas can be produced. In addition, due to low gasification temperatures of 600–750 °C and the use of limestone as bed material, in-situ CO₂ capture is possible, leading to a hydrogen-rich and carbon-lean product gas. In this paper, results from a bubbling fluidised bed gasification model are compared to results of process demonstration tests in a 200 kW_th pilot plant.Based upon that, a concept for the hydrogen production via biomass SER gasification is studied in terms of efficiency and feasibility. Capital and operational expenditures as well as hydrogen production costs are calculated in a techno-economic assessment study. Furthermore, market framework conditions are discussed under which an economic hydrogen production via SER gasification is possible.     

Improvement of steam methane reforming via in-situ CO2 sorption over a nickel-calcium composite catalyst

Optimization of steam methane reforming (SMR) reaction by CO₂ sorption enhancement was investigated. In this study, the sorption-enhanced steam methane reforming reaction (SESMR) was conducted to maximize hydrogen production via suitable adjustments in the operating conditions of the reaction, which include the molar ratio of steam to CH₄, space velocity, and temperature. The reforming catalysts were prepared by a physical mixture of 20 wt% Ni/Al₂O₃ and CaO. The results reveal that there are significant differences in CH₄ conversion between the SMR and the SESMR from 18% to 108%; this conversion strongly depended on the reaction conditions. High-purity H₂ products (98.9%) with <0.1 ppmv CO were obtained by SESMR under the suitable conditions of 2600 cm³/g/h, steam/CH₄ molar ratio of 4 and 823 K. This implies that the high-quality H₂ produced through the SESMR process could be directly used for the proton-exchange membrane fuel cell.     

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

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

Improvement of reaction kinetics by metal chloride on ammonia and lithium hydride system

Ammonia NH₃ and lithium hydride LiH system releases hydrogen even at room temperature to form lithium amide LiNH₂. LiNH₂ is recycled back to NH₃ and LiH below 300 °C under hydrogen H₂ flow condition. However, the reaction rate of the system is slow for a practical application. In this work, various kinds of transition metal chlorides were examined as a potential catalyst to improve the kinetics. For hydrogen desorption reaction, the reaction kinetics of titanium chloride TiCl₃ dispersing LiH was about 8 times faster than the raw LiH, suggesting that TiCl₃ possessed an excellent catalytic effect. In the case of the regeneration reaction, the reaction kinetics was also improved by the addition of TiCl₃. It was mainly caused by physical effects in contrast to the hydrogen desorption process, in other words, the small crystallite and/or particle were formed by the milling with the additive.