Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.     

Chemical looping steam reforming of ethanol without and with in-situ CO2 capture

Chemical looping steam reforming (CLSR) of ethanol using oxygen carriers (OCs) for hydrogen production has been considered a highly efficient technology. In this study, NiO/MgAl₂O₄ oxygen carriers (OCs) were employed for hydrogen production via CLSR with and without CaO sorbent for in-situ CO₂ removal (sorption enhanced chemical looping steam reforming, SE-CLSR). To find optimal reaction conditions of the CLSR process, including reforming temperatures, the catalyst mass, and the NiO loadings on hydrogen production performances were studied. The results reveal that the optimal temperature of OCs for hydrogen production is 650 °C. In addition, 96% hydrogen selectivity and a 'dead time' (the reduced time of OCs) less than 1 minute is obtained with the 1 g 20NiO/MgAl₂O₄ catalysts. The superior catalytic activity of 20NiO/MgAl₂O₄ is due to the maximal quantity of NiO loadings providing the most Ni active surface centers. High purity hydrogen is successfully produced via CLSR coupling with CaO sorbent in-situ CO₂ removal (SE-CLSR), and the breakthrough time of CaO is about 20 minutes under the condition that space velocity was 1.908 h^?1. Stability CLSR experiments found that the hydrogen production and hydrogen selectivity decreased obviously from 207 mmol to 174 mmol and 95%–85% due to the inevitable OCs sintering and carbon deposition. Finally, stable hydrogen production with the purity of 89%～87% and selectivity of 96%～93% was obtained in the modified stability SE-CLSR experiments.     

Optimization of two bio-oil steam reforming processes for hydrogen production based on thermodynamic analysis

Thermodynamics of hydrogen production from conventional steam reforming (C-SR) and sorption-enhanced steam reforming (SE-SR) of bio-oil was performed under different conditions including reforming temperature, S/C ratio (the mole ratio of steam to carbon in the bio-oil), operating pressure and CaO/C ratio (the mole ratio of CaO to carbon in the bio-oil). Increasing temperature and S/C ratio, and decreasing the operating pressure were favorable to improve the hydrogen yield. Compared to C-SR, SE-SR had the significant advantage of higher hydrogen yield at lower desirable temperature, and showed a significant suppression for carbon formation. However excess CaO (CaO/C > 1) almost had no additional contribution to hydrogen production. Aimed to achieve the maximum utilization of bio-oil with as little energy consumption as possible, the influences of temperature and S/C ratio on the reforming performance (energy requirements and bio-oil consumption per unit volume of hydrogen produced, Q_D/H2 (kJ/Nm³) and Y_Bio-oil/H2 (kg/Nm³)) were comprehensively evaluated using matrix analysis while ensuring the highest hydrogen yield as possible. The optimal operating parameters were confirmed at 650 °C, S/C = 2 for C-SR; and 550 °C, S/C = 2 for SE-SR. Under their respective optimal conditions, the Y_Bio-oil/H2 of SE-SR is significant decreased, by 18.50% compared to that of C-SR, although the Q_D/H2 was slightly increased, just by 7.55%.     

Steam reforming of shale gas in a packed bed reactor with and without chemical looping using nickel based oxygen carrier

The catalytic steam reforming of shale gas was examined over NiO on Al₂O₃ and NiO on CaO/Al₂O₃ in the double role of catalysts and oxygen carrier (OC) when operating in chemical looping in a packed bed reactor at 1 bar pressure and S:C 3. The effects of gas hourly space velocity GHSV (h^?1), reforming temperatures (600–750 °C) and catalyst type on conventional steam reforming (C-SR) was first evaluated. The feasibility of chemical looping steam reforming (CL-SR) of shale gas at 750 °C with NiO on CaO/Al₂O₃ was then assessed and demonstrated a significant deterioration after about 9 successive reduction-oxidation cycles. But, fuel conversion was high over 80% approximately prior to deterioration of the catalyst/OC, that can be strongly attributed to the high operating temperature in favour of the steam reforming process.     

Combined autothermal and sorption-enhanced reforming of olive mill wastewater for the production of hydrogen: Thermally neutral conditions analysis

A thermodynamic study and an energy analysis are performed on the autothermal reforming (ATR) and sorption-enhanced autothermal reforming (SE-ATR) of olive mill wastewater (OMW) to produce green hydrogen. For comparative purposes, the traditional reforming (TR) and sorption-enhanced reforming (SER) are also assessed. The thermodynamic equilibrium compositions are calculated by using the Gibbs free energy minimization method. The effect of temperature, pressure and steam-to-carbon molar ratio (S/C) is assessed for the different reactor configurations. The energy analysis is done by determining the level of oxygen needed to operate under thermally neutral conditions.The results show a reduced hydrogen yield for ATR and SE-ATR compared to their non-autothermal counterparts, but a decreased energy requirement per mole of hydrogen produced. For the ATR, the thermally neutral operation requires a high amount of oxygen, which reduces the hydrogen yield. However, for SE-ATR, the exothermal sorption reaction provides nearly enough energy for the process to be thermally neutral by itself.     

A combined thermodynamic and experimental study on chemical‐looping ethanol reforming with carbon dioxide capture for hydrogen generation

Chemical‐looping ethanol reforming with carbon dioxide capture is proposed. It combines chemical‐looping reforming and carbon dioxide capture for pure hydrogen generation from ethanol with inherent separation of carbon dioxide. A thermal analysis of the process using NiO oxygen carrier is performed by simulating reactions using the Gibbs energy minimization method. The promising systems are investigated further with respect to temperature, NiO/C₂H₅OH molar ratio, CaO/C₂H₅OH molar ratio and pressure changes as well as possible carbon formation in the reformer. Favorable operation conditions in the presence of CaO are: pressures around 3 atm, reactor temperatures around 850 K, NiO/C₂H₅OH molar ratio = 3 and CaO/C₂H₅OH = 3. The H₂ yield and thermal efficiency with CaO addition are higher than that without CaO addition, showing that the addition of a CO₂ sorbent in the process increases the H₂ production. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrogen production from bio-oil aqueous fraction with in situ carbon dioxide capture

This paper presents the results of the investigation on steam reforming bio-oil aqueous fraction coupled with in situ carbon dioxide capture for hydrogen production. Experiments were carried out in a bench-scale fixed-bed reactor with calcined dolomite as the sorbent. The effects of temperature and water to bio-oil ratio on hydrogen production are reported. In the presence of calcined dolomite, maximum hydrogen yield of 75% was obtained among without sorbent, with CaO and with calcined dolomite at 600 °C, whereas hydrogen content was 83%, a little lower than that of 85% when CaO was used. Hydrogen content varies little at different water to bio-oil ratios and hydrogen yield was the greatest at the water to bio-oil ratio of 1:1. After regeneration of the sorbent, hydrogen content was back to the initial level but the hydrogen yield dropped.     

Biohydrogen production from Imperata cylindrica bio-oil using non-stoichiometric and thermodynamic model

This paper presents a non-stoichiometric and thermodynamic model for steam reforming of Imperata cylindrica bio-oil for biohydrogen production. Thermodynamic analyses of major bio-oil components such as formic acid, propanoic acid, oleic acid, hexadecanoic acid and octanol produced from fast pyrolysis of I. cylindrica was examined. Sensitivity analyses of the operating conditions; temperature (100–1000 °C), pressure (1–10 atm) and steam to fuel ratio (1–10) were determined. The results showed an increase in biohydrogen yield with increasing temperature although the effect of pressure was negligible. Furthermore, increase in steam to fuel ratio favoured biohydrogen production. Maximum yield of 60 ± 10% at 500–810 °C temperature range and steam to fuel ratio 5–9 was obtained for formic acid, propanoic acid and octanol. The heavier components hexadecanoic and oleic acid maximum hydrogen yield are 40% (740 °C and S/F = 9) and 43% (810 °C and S/F = 8) respectively. However, the effect of pressure on biohydrogen yield at the selected reforming temperatures was negligible. Overall, the results of the study demonstrate that the non-stoichiometry and thermodynamic model can successfully predict biohydrogen yield as well as the composition of gas mixtures from the gasification and steam reforming of bio-oil from biomass resources. This will serve as a useful guide for further experimental works and process development.     

Continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production

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.     

Utilization of NiO/porous ceramic monolithic catalyst for upgrading biomass fuel gas

Catalytic steam reforming for producing high quality syngas from biomass fuel gas was studied over monolithic NiO/porous ceramic catalysts in a fixed-bed reactor. Effects of reaction temperature, steam to carbon (S/C) ratio, and nickel loading content on catalyst performance were investigated. Results indicated that the NiO/porous ceramic monolith catalyst had a good ability to improve bio-fuel gas quality. H₂ yield, H₂ + CO content, and H₂/CO ratio in produced gas were increased when reaction temperature was increased from 550 to 700 °C. H₂ yield was increased from 28.1% to 40.2% with S/C ratio increased from 1 to 2. And the yield of hydrogen was stabilized with the further increase of S/C ratio. Catalyst activity was not always enhanced with increased nickel content, when NiO loading content reaches 5.96%, serious aggregation and sintering of active composition on catalyst surface occur. The best performance, in terms of H₂ yield, is obtained with 2.50% NiO content at reaction temperature of 700 °C and S/C ratio of 2.     

Steam reforming of propionic acid: Thermodynamic analysis of a model compound for hydrogen production from bio-oil

The thermodynamic equilibrium of steam reforming of propionic acid (HPAc) as a bio-oil model compound was studied over a wide range of reaction conditions (T = 500–900 °C, P = 1–10 bar and H₂O/HPAc = 0–4 mol/mol) using non-stoichiometric equilibrium models. The effect of operating conditions on equilibrium conversion, product composition and coke formation was studied. The equilibrium calculations indicate nearly complete conversion of propionic acid under these conditions. Additionally, carbon and methane formation are unfavorable at high temperatures and high steam to carbon (S/C) ratios. The hydrogen yield versus S/C ratio passes a maximum, the value and position of which depends on temperature. The thermodynamic equilibrium results for HPAc fit favorably with experimental data for real bio-oil steam reforming under same reaction conditions.     

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O₂/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.     

Development of a Fe/Mg-bearing metallurgical waste stabilized-CaO/NiO hybrid sorbent-catalyst for high purity H2 production through sorption-enhanced glycerol steam reforming

In this work, a Fe/Mg-bearing metallurgical waste (upgraded slag oxide, UGSO) was, for the first time, investigated as a stabilizer for increasing the cyclic stability of CaO-based sorbents. The sorbents were prepared through the wet mixing of the ball-milled UGSO particles with the limestone-derived calcium citrate under sonication. The sorption capacity of samples containing different waste loadings (5, 10, 15, and 25 wt%) was studied for 18 carbonation/regeneration cycles under conditions similar to the sorption-enhanced glycerol steam reforming process. A significant improvement of the cyclic stability was observed for all doped sorbents; however, the sample with 10 wt% UGSO showed the highest sorption capacity among all tested samples. This optimum sorbent was further used to synthesize a UGSO stabilized CaO–NiO hybrid sorbent-catalyst material (20 wt% NiO loading), whose performance was tested in sorption-enhanced steam reforming of glycerol. A H₂ purity of around 95% was obtained in the pre-breakthrough period that lasted for about 30 min. In summary, the results showed a better stability of UGSO stabilized sorbents compared to pure CaO and a good performance of the CaO-UGSO10/NiO sorbent-catalyst hybrid material in the sorption-enhanced reforming process.     

Hydrogen-rich syngas production of urea blended with biobutanol by a thermodynamic analysis

Both biobutanol and urea are the environment-friendly hydrogen carrier. This study is to compare hydrogen production between steam reforming of biobutanol and autothermal reforming of biobutanol feed using pure steam and vaporization of aqueous urea (VAU) by a thermodynamic analysis. Hydrogen-rich syngas production, carbon formation, thermal neutral temperature (TNT), and hydrogen production cost are analyzed in both steam reforming and autothermal reforming. The results show that hydrogen-rich syngas production with the use of VAU is higher than that with pure steam not only in steam reforming but also in autothermal reforming. When the VAU/butanol molar ratio is 8, and the O₂/butanol molar ratio equals 3, the reforming efficiency reaches up to 81.42%. At the same condition, the hydrogen production cost is lower than that without blending urea. Therefore, using VAU to replace pure steam in biobutanol reforming leads to benefits of increasing the hydrogen-rich syngas yield and lowering cost.     

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.     

Autothermal sorption-enhanced steam reforming of bio-oil/biogas mixture and energy generation by fuel cells: Concept analysis and process simulation

A concept of sorption-enhanced steam reforming of bio-oil/biogas for electricity and heat generation by phosphoric acid fuel cells is investigated. The process is modeled using SIMSCI Pro II process simulator. Sorptive removal of the carbon dioxide from the reaction site results in low CO and _CO2${\mathrm{CO}}_2$ concentrations (<1%$<1\%$) in the reformate, as a result it can be used in the phosphoric acid fuel cell without any further fuel cleanup. High hydrogen concentration and calorific value of the reformate enable the operation of the fuel cell at a high-efficiency mode despite of the high carbon/hydrogen ratio of the bio-fuel. Addition of biogas to the reformer enables autothermal operation of the reformer, as well as significantly improves the efficiency of the process. The simulation shows that the overall efficiency of the proposed system is compatible with the efficiency of the system using “classical” steam reforming of the fuel. The process exhibits 6% lower electrical efficiency compared to the system utilizing natural gas, and 4.6% higher efficiency compared to a system using bio-oil as a fuel.     

Hydrogen production by sorption-enhanced steam reforming of acetic acid over Ni/CexZr1−xO2-CaO catalysts

The production of high purity hydrogen via the sorption-enhanced steam reforming of acetic acid, a model compound of bio-oil, was investigated in this work. A bi-functional catalyst with stable catalytic activity and CO₂-capture ability, Ni/Ce_xZr_1−xO₂-CaO, was prepared by a sol–gel method and characterized in details by BET, XRD, TPR and SEM-EDX analytic techniques. The characterization of these materials showed that the catalysts were mainly composed of Ni, Ce_xZr_1−xO₂ and CaO. As CaO loading increased, a new species, CaZrO_3, with a perovskite structure was formed. The presence of CaZrO₃ in the catalysts acted as a barrier to CaO grain growth at high temperatures and thus improved the CO₂-capture stability. These catalysts exhibited good CO₂ sorption capacity in 15 consecutive carbonation–calcination cycles, even at a high calcination temperature of 900 °C. Particularly, in case of the Ni/CZC-2.5 catalyst, 98% high purity H₂ could be obtained during the prebreakthrough stage when the catalysts were tested in the SESR of acetic acid at 550 °C with an S/C ratio of 4. In addition, high hydrogen purity was maintained over 15 cyclic reaction-calcination operations, which was mainly attributed to the uniform distribution of Ni, CaO, Ce_xZr_1−xO₂ and CaZrO₃ in the catalysts. These results indicated the great potential of the SESR technique for hydrogen production from bio-oil.     

Renewable hydrogen production concepts from bioethanol reforming with carbon capture

This paper is assessing the hydrogen production from bioethanol at industrial scale (100000 Nm³/h hydrogen equivalent to 300 MW thermal) with carbon capture. Three carbon capture designs were investigated, one based on pre-combustion capture using chemical gas–liquid absorption and two based on chemical looping (one based on syngas and one using direct bioethanol looping). The carbon capture options were compared with the similar designs without carbon capture. The designs were simulated to produce mass and energy balances for quantification of key performance indicators. A particular accent is put on assessment of reforming technologies (steam and oxygen-blown autothermal reforming) and chemical looping units, process integration issues of carbon capture step within the plant, modelling and simulation of whole plant, thermal and power integration of various plant sub-systems by pinch analysis. The results for chemical looping designs (either syngas-based or direct bioethanol) show promising energy efficiency coupled with total carbon capture rate.     

Thermodynamic analysis of hydrogen generation via oxidative steam reforming of glycerol

A thermodynamic analysis of the oxidative steam reforming of glycerol (OSRG) for hydrogen production has been carried out with Aspen plus ^TM. The reaction was investigated at ambient pressure within the carbon-to-oxygen (C/O) ratio of 0.5–3.0, steam-to-carbon (S/C) ratio of 0.5–8.0 and temperature of 400–850 °C. Higher C/O and S/C ratios favor the production of hydrogen from glycerol. The highest hydrogen selectivity is obtained at 600–700 °C. To predict the potential technical obstacles in the glycerol reforming process, the OSRG process was compared with oxidative steam reforming of ethanol (OSRE) in terms of hydrogen production, autothermal condition and carbon deposition. The selectivity to hydrogen via OSRG is lower than that via OSRE under identical conditions. To achieve autothermal reforming, higher S/C and C/O ratios are required for reforming of glycerol than for ethanol due to the higher oxygen content in a glycerol molecule. From the viewpoint of thermodynamics, the glycerol reforming is more resistant to the carbon deposition. On the basis of the thermodynamic analysis and the preliminary experimental study, suggestions were proposed to guide the development of the glycerol reforming technique.     

Ethanol steam reforming on Ni/CaO catalysts for coproduction of hydrogen and carbon nanotubes

Catalytic steam reforming of ethanol is considered as a promising technology for producing H₂ in the modern world. In this study, using a fixed‐bed reactor, steam reforming of ethanol was performed for production of carbon nanotubes (CNTs) and H₂ simultaneously at 600°C on Ni/CaO catalysts. Commercial CaO and a synthetic CaO prepared using sol‐gel were scrutinized for ethanol's catalytic steam reforming. Analysis results of N₂ isothermal adsorption indicate that the CaO synthesized by sol‐gel has more pore volume and surface area in comparison with the commercial CaO. When Ni was loaded, the Ni/CaO catalyst shows an encouraging catalytic property for H₂ production, and an increase in Ni loading could improve H₂ production. The Ni/CaO catalyst with sol‐gel CaO support has presented a higher hydrogen production and better catalytic stability than the catalysts with the commercial CaO support at low Ni loading. The highest hydrogen yield is 76.8% at Ni loading content of 10% for the Ni/sol‐gel CaO catalyst with WHSV of 3.32/h and S/C ratio of 3. The carbon formed after steam reforming primarily consists of filamentous carbons and amorphous carbons, and CNTs are the predominant type of carbon deposition. The deposited extent of carbon on the used Ni/CaO catalyst lessen upon more Ni loading, and the elongated CNTs are desired to be formed at the surface of the Ni/sol‐gel CaO catalyst. Thus, an efficient process and improved economic value is associated with prompt hydrogen production and CNTs from ethanol steam reforming.