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.     

Thermodynamic analysis of the autothermal reforming of glycerol using supercritical water

Hydrogen can be produced by autothermal reforming of glycerol using supercritical water (SCW). With the aid of AspenPlus™, a systematic thermodynamic analysis of this process has been carried out by the total Gibbs free energy minimization method, which computes the equilibrium composition of synthesis gas (syngas). The predictive Soave-Redlich-Kwong equation of state (EOS) has been used as thermodynamic method in the simulation of the supercritical region. A sensitivity analysis has been conducted both for a pure glycerol feed and pretreated crude glycerol feed coming from biodiesel production. Simulations run so as to calculate the O₂ needed to enter the Gibbs reactor (reformer) for achieving the thermoneutral condition (no external heat to sustain the reformer operation is required). Thus, the effect of the main operating parameters (reforming temperature, water to glycerol mole ratio, glycerol purity in the feed of crude glycerol, oxygen to glycerol mole ratio and the inlet feed temperature) aimed to the hydrogen production has been investigated, by obtaining the mole fraction and molar flow-rate of components in syngas, as well as the hydrogen yield. By this way, the most thermodynamic favorable operating conditions at which glycerol may be converted into hydrogen by autothermal reforming using SCW have been identified. As a second part of the study, a conceptual design and an energy and exergy analysis of the overall process will be performed later.     

Thermodynamic analysis of hydrogen production by autothermal reforming of ethanol

Ethanol steam reforming (ESR) is a strong endothermic reaction and ideally it only produces hydrogen and carbon dioxide.     

Dry autothermal reforming of glycerol with in situ hydrogen separation via thermodynamic evaluation

On the basis of the Gibbs free energy minimization principle, the dry autothermal reforming performance of crude glycerol in situ hydrogen separation is investigated via thermodynamic analysis. The impact of hydrogen separation fraction on gas composition in product, carbon formation and reaction heat is studied. It can be found that the hydrogen separation promotes the hydrogen production and hinders methane formation. The hydrogen removal is selective to the reduction of carbon deposition, which improves the carbon formation at a low feed CO₂ to glycerol molar ratio and the impact is reverse for high feed CO₂ to glycerol molar ratio. When the reaction temperature varies from 850 K to 900 K, the required oxygen to glycerol molar ratio of thermal neutral condition is obviously increased from 0.15 to 0.4 with hydrogen removal. Meanwhile, the glycerol impurities evaluation indicates that the syngas yield is significantly reduced with the increase of the glycerol impurities. At a high temperature, the hydrogen removal is in favor of the achievement of autothermal process.     

Hydrogen production via steam and autothermal reforming of beef tallow: A thermodynamic investigation

A thermodynamic analysis of hydrogen production via steam and autothermal reforming of beef tallow has been carried out via the Gibbs free energy minimization method. Equilibrium calculations are performed at atmospheric pressure with a wide range of temperatures (400–1200 °C), steam-to-beef tallow ratios (1–15) and oxygen-to-beef tallow ratios (0.0–2.0).     

Effect of mode of operation on hydrogen production from glycerol at thermal neutral conditions: Thermodynamic analysis

Thermodynamic analysis of hydrogen production from glycerol under thermal neutral conditions is studied in this work. Heat requirement from the process can be achieved from the exothermic reaction of glycerol with oxygen in air fed to the system. Two modes of operation for air feeding are considered including (i) Single-feed mode in which air is fed in combination with water and glycerol to the reformer, and (ii) Split-feed mode in which air and part of glycerol is fed to a combustor in order to generate heat. The thermal neutral conditions are considered for two levels including Reformer and System levels. It was found that the H₂ yield from both modes is not significantly different at the Reformer level. In contrast, the difference becomes more pronounced at the System level. Single-feed and Split-feed modes offer high H₂ yield in low (600–900 K) and high (900–1200 K) temperature ranges, respectively. The maximum H₂ yields are 5.67 (water to glycerol ratio, WGR = 12, oxygen to glycerol ratio, OGR = 0.37, T = 900 K, Split-feed mode), and 3.28 (WGR = 3, OGR = 1.40, T = 900 K, Single-feed mode), for the Reformer and System levels, respectively. The difference between H₂ yields in both levels mainly arises from the huge heat demand for preheating feeds in the System level, and therefore, a higher amount of air is needed to achieve the thermal neutral condition. Split-feed mode is a favorable choice in term of H₂ purity because the gas product is not diluted with N₂ from the air. The use of pure O₂ and afterburner products (ABP) stream were also considered at the System level. The maximum H₂ yield becomes 3.75 (WGR = 5.21, OGR = 1.28, T = 900 K, Split-feed mode) at thermal neutral condition when utilizing heat from the ABP stream. Finally comparisons between the different modes and levels are addressed in terms of yield of by-products, and carbon formation.     

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.     

Thermodynamic evaluation of hydrazine assisted glycerol reforming for syngas production and coke inhibition

Thermodynamic investigation of glycerol reforming has been performed to study hydrogen production, carbon dioxide evolution and coke formation. Gibb's free energy direct minimization procedure was used to calculate the concentration of different components at equilibrium. The analysis was performed at temperatures from 300K to 1000K under unit atmospheric pressure. A comparative study on steam reforming of glycerol (SRG) and glycerol reforming reaction with hydrazine has been conducted in the presence of hydrazine that act as a suitable reducing agent. Incorporation of hydrazine into glycerol reforming system helped in minimizing coke formation, maximizing hydrogen and syn-gas production. A complete conversion of glycerol with coke free products, along with reduced level of carbon dioxide and maximum hydrogen generation was obtained when glycerol steam reforming process (S/G = 1) was combined with higher moles of hydrazine. Reformation at higher temperatures could enhance the hydrogen production and decrease carbon generation due to methanation reaction and hence optimum results were accomplished at 1000K and atmospheric pressure.     

Thermodynamic analysis and heat integration for hydrogen production from bio-butanol for SOFC application: Steam reforming vs. autothermal reforming

Thermodynamic analysis of hydrogen production by steam reforming and autothermal reforming of bio-butanol was investigated for solid oxide fuel cell applications. The effects of reformer operating conditions, e.g., reformer temperature, steam to carbon molar ratio, and oxygen to carbon molar ratio, were investigated with the objective to maximize hydrogen production and to reduce utility requirements of the process and based on which favorable conditions of reformer were proposed. Process flow diagram for steam reforming and autothermal reforming integrated with solid oxide fuel cell was developed. Heat integration with pinch analysis method was carried out for both the processes at favorable reformer conditions. Power generation, electrical efficiency, useful energy for co-generation application, and utility requirements for both the processes were compared.     

Autothermal steam reforming of glycerol for hydrogen production over packed-bed and Pd/Ag alloy membrane reactors

In this study, glycerol, with its high H/C ratio feature, was steam reformed with oxygen to produce hydrogen in packed-bed and Pd/Ag membrane reactors. The addition of oxygen, which causes the partial oxidation, was to achieve thermal neutral for the energy saving purposes.     

Hydrogen production by glycerol steam reforming with in situ hydrogen separation: A thermodynamic investigation

Thermodynamic features of hydrogen production by glycerol steam reforming with in situ hydrogen extraction have been studied with the method of Gibbs free energy minimization. The effects of pressure (1–5 atm), temperature (600–1000 K), water to glycerol ratio (WGR, 3–12) and fraction of H₂ removal (f, 0–1) on the reforming reactions and carbon formation were investigated. The results suggest separation of hydrogen in situ can substantially enhance hydrogen production from glycerol steam reforming, as 7 mol (stoichiometric value) of hydrogen can be obtained even at 600 K due to the hydrogen extraction. It is demonstrated that atmospheric pressure and a WGR of 9 are suitable for hydrogen production and the optimum temperature for glycerol steam reforming with in situ hydrogen removal is between 825 and 875 K, 100 K lower than that achieved typically without hydrogen separation. Furthermore, the detrimental influence of increasing pressure in terms of hydrogen production becomes marginal above 800 K with a high fraction of H₂ removal (i.e., f = 0.99). High temperature and WGR are favorable to inhibit carbon production.     

Thermodynamic analysis of hydrogen production from methane via autothermal reforming and partial oxidation followed by water gas shift reaction

Reaction characteristics of hydrogen production from a one-stage reaction and a two-stage reaction are studied and compared with each other in the present study, by means of thermodynamic analyses. In the one-stage reaction, the autothermal reforming (ATR) of methane is considered. In the two-stage reaction, it is featured by the partial oxidation of methane (POM) followed by a water gas shift reaction (WGSR) where the temperatures of POM and WGSR are individually controlled. The results indicate that the reaction temperature of ATR plays an important role in determining H₂ yield. Meanwhile, the conditions of higher steam/methane (S/C) ratio and lower oxygen/methane (O/C) ratio in association with a higher reaction temperature have a trend to increase H₂ yield. When O/C ≤ 0.125, the coking behavior may be exhibited. In regard to the two-stage reaction, it is found that the methane conversion is always high in POM, regardless of what the reaction temperature is. When the O/C ratio is smaller than 0.5, H₂ is generated from the partial oxidation and thermal decomposition of methane, causing solid carbon deposition. Following the performance of WGSR, it suggests that the H₂ yield of the two-stage reaction is significantly affected by the reaction temperature of WGSR. This reflects that the temperature of WGSR is the key factor in producing H₂. When methane, oxygen and steam are in the stoichiometric ratio (i.e. 1:0.5:1), the maximum H₂ yield from ATR is 2.25 which occurs at 800 °C. In contrast, the maximum H₂ yield of the two-stage reaction is 2.89 with the WGSR temperature of 200 °C. Accordingly, it reveals that the two-stage reaction is a recommended fuel processing method for hydrogen production because of its higher H₂ yield and flexible operation.     

Thermodynamic analyses of adsorption-enhanced steam reforming of glycerol for hydrogen production

A non-stoichiometric thermodynamic analysis is performed on the adsorption-enhanced steam reforming of glycerol for hydrogen production based on the principle of minimising the Gibbs free energy. The effects of temperature (600–1000 K), pressure (1–4 bar), water to glycerol feed ratio (3:1–12:1), percentage of CO₂ adsorption (0–99%) and molar ratio of carrier gas to feed reactants (1:1–5:1) on the reforming reactions and carbon formation are examined. The results show that the use of a CO₂ adsorbent enhances glycerol conversion to hydrogen and the maximum number of moles of hydrogen produced per mole of glycerol can be increased from 6 to 7 due to the CO₂ adsorption. The analyses suggest that the most favourable temperature for steam–glycerol reforming is between 800 and 850 K in the presence of a CO₂ adsorbent, which is about 100 K lower than that for reforming without CO₂ adsorption. Although high pressures are favourable for CO₂ adsorption, a lower operating pressure gives a higher overall hydrogen conversion. The most favourable water to glycerol feed ratio is found to be 9.0 above which the benefit becomes marginal. Carbon formation could occur at low water to glycerol feed ratios, and the use of a CO₂ adsorbent can suppress the formation reaction and substantially reduce the lower limit of the water to glycerol feed ratio for carbon formation.     

Thermodynamic analysis of steam reforming of ethanol and glycerine for hydrogen production

In the past few years there has been a growing interest in environmentally clean renewable sources for hydrogen production. In this context new technologies have been developed for ethanol and glycerine reforming. Hydrogen production varies significantly according to the operating conditions such as pressure, temperature and feed reactants ratio. The thermodynamic analysis provides important knowledge about the effects of those variables on the process of ethanol and glycerine reforming. The present work was aimed at analyzing the thermodynamic steam reforming of ethanol and glycerine, using Gibbs free energy minimization using actual temperature and pressure data found in the literature. The nonlinear programming model was implemented in GAMS^® and the CONOPT2 solver was used to solve the equations. The ideality in gaseous phase and the formation of solid carbon was considered. The methodology used reproduced the most relevant papers involving experimental studies and thermodynamic analysis.     

Thermodynamic analysis of hydrogen production for fuel cell via oxidative steam reforming of propane

A thermodynamic analysis of hydrogen production from propane by oxidative steam reforming (OSR) is performed with a Gibbs free energy minimization method. Addition of oxygen reduces the enthalpy of the system and facilitates the heat supply. Equilibrium compositions of OSR as a function of temperature (300, 500, 700 and 900 °C), H₂O/C₃H₈ ratio (1.0–20.0) and O₂/C₃H₈ ratio (0.0–2.0) under oxidative and thermo-neutral (TN) conditions are evaluated. The results for oxidative conditions demonstrate that at 700 °C with H₂O/C₃H₈ ratios above 7.0 and/or O₂/C₃H₈ ratios higher than 1.3 are beneficial for hydrogen production which facilitates superior hydrogen yield, i.e. close to 9.0 mol/mol propane, with coke and methane formation reactions being suppressed effectively. For TN condition, autothermal temperature and equilibrium composition have a stronger dependence on O₂/C₃H₈ ratio than on H₂O/C₃H₈ ratio. Further calculations show that the condition at 700 °C with an appropriate H₂O/C₃H₈ ratio between 7.0 and 13.0 is favorable for achieving a high hydrogen yield and a low carbon monoxide yield. Therefore, a favorable operational range is proposed to ensure the most optimized product yield.     

A review on reforming bio-ethanol for hydrogen production

Bio-ethanol is a prosperous renewable energy carrier mainly produced from biomass fermentation. Reforming of bio-ethanol provides a promising method for hydrogen production from renewable resources. Besides operating conditions, the use of catalysts plays a crucial role in hydrogen production through ethanol reforming. Rh and Ni are so far the best and the most commonly used catalysts for ethanol steam reforming towards hydrogen production. The selection of proper support for catalyst and the methods of catalyst preparation significantly affect the activity of catalysts. In terms of hydrogen production and long-term stability, MgO, ZnO, _CeO2${\mathrm{CeO}}_2$, and _La2O3${\mathrm{La}}_2{\mathrm{O}}_3$ are suitable supports for Rh and Ni due to their basic characteristics, which favor ethanol dehydrogenation but inhibit dehydration. As Rh and Ni are inactive for water gas shift reaction (WGSR), the development of bimetallic catalysts, alloy catalysts, and double-bed reactors is promising to enhance hydrogen production and long-term catalyst stability. Autothermal reforming of bio-ethanol has the advantages of lesser external heat input and long-term stability. Its overall efficiency needs to be further enhanced, as part of the ethanol feedstock is used to provide low-grade thermal energy. Development of millisecond-contact time reactor provides a low-cost and effective way to reform bio-ethanol and hydrocarbons for fuel upgrading. Despite its early R&D stage, bio-ethanol reforming for hydrogen production shows promises for its future fuel cell applications.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Hydrogen production by autothermal reforming of LPG for PEM fuel cell applications

Indirect partial oxidation, or oxidative steam reforming, tests of a bimetallic Pt–Ni catalyst supported on δ$\delta$-alumina were conducted in propane–n  -butane mixtures (LPG) used as feed. _H2${\mathrm{H}}_2$ production activity and _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity were investigated in response to different S/C, C/_O2$\mathrm{C}/{\mathrm{O}}_2$ and W/F ratios. It was confirmed that higher steam content in the reactant stream increases both the activity and the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt–Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for different propane-to-n-butane ratios in the LPG feed indicated that the Pt–Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

Hydrogen production by autothermal reforming of methane over NiPd catalysts: Effect of support composition and preparation mode

NiPd/Ce_0.5Zr_0.5O₂/Al₂O₃ and NiPd/La₂O₃/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts were prepared by incipient wetness co-impregnation method or sequential impregnation method for autothermal reforming of methane (ATR of CH₄). The influence of the preparation mode, Ce_0.5Zr_0.5O₂ and La₂O₃ additives on the physicochemical properties of NiPd supported catalysts and the effect on their activity to produce hydrogen by ATR of CH₄ were investigated. Characterization of fresh and spent Ni-based catalysts by X-ray fluorescence spectroscopy, N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were performed. It was demonstrated that support composition determines NiO dispersion as well as reducibility of Ni species through different strength of Ni-support interaction. The preparation method modifies the phase composition and catalyst ability for reduction. The catalyst evolution under reaction conditions was studied. The NiO (∼15 nm) and NiPd alloy (∼18 nm) phases were observed in the spent catalysts. It was found that the Ni^o/NiO ratio can be regulated by support composition and preparation mode of catalysts. It is demonstrated that studied catalysts provide high methane conversion of 90–100%, CO yield of 55–85% and H₂ yield of 55–75% in ATR of CH₄ at 750–950 °C. The optimal composition and preparation method of catalyst were selected. The best ATR of CH₄ performance is provided by 10 Ni_0.5Pd/10Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst prepared by Pd/Ni sequential impregnation method that can be associated with peculiarity of NiPd particles structure and the optimal ratio between NiO species with different ability for reduction.