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.     

Thermodynamic analysis of propane dry and steam reforming for synthesis gas or hydrogen production

Thermodynamics was applied to investigate propane dry reforming (DR) and steam reforming (SR). Equilibrium calculations employing the Gibbs free energy minimization were performed upon a wide range of pressure (1–5 atm), temperature (700–1100 K), carbon dioxide to propane ratio (CPR, 1–12) and water to propane ratio (WPR, 1–18). From a thermodynamic perspective, it is demonstrated that DR is promising for production of synthesis gas with low hydrogen content, as opposite to SR which favours generation of synthesis gas with high hydrogen content. Complete conversion of propane was obtained for the range of pressure, temperature, CPR and WPR considered in this study. Atmospheric pressure is shown to be preferable for both DR and SR. Approximately 10 mol of synthesis gas can be produced per mole of propane at a temperature greater than 1000 K from DR when CPR is higher than 6. The optimum conditions for synthesis gas production from DR are found to be 975 K (CPR = 3) for a H₂/CO ratio of 1 and 1100 K (CPR = 1) for a H₂/CO ratio of 2. The greatest CO₂ conversion (95%) can be obtained also at 1100 K and CPR = 1. Preferential conditions for hydrogen production from SR are achieved with the temperatures between 925 and 975 K and WPRs of 12–18. The maximum number of moles of hydrogen produced is 9.1 (925 K and WPR = 18). Under conditions that favour hydrogen production, methane and carbon formation can be eliminated to negligible level.     

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 carbon formation boundary and reforming performance for steam reforming of dimethyl ether

Thermodynamic analysis of dimethyl ether steam reforming (DME SR) was investigated for carbon formation boundary, DME conversion, and hydrogen yield for fuel cell application. The equilibrium calculation employing Gibbs free minimization was performed to figure out the required steam-to-carbon ratio (S/C = 0–5) and reforming temperature (25–1000 °C) where coke formation was thermodynamically unfavorable. S/C, reforming temperature and product species strongly contributed to the coke formation and product composition. When chemical species DME, methanol, CO₂, CO, H₂, H₂O and coke were considered, complete conversion of DME and hydrogen yield above 78% without coke formation were achieved at the normal operating temperatures of molten carbonate fuel cell (600 °C) and solid oxide fuel cell (900 °C), when S/C was at or above 2.5. When CH₄ was favorable, production of coke and that of hydrogen were significantly suppressed.     

Thermodynamic equilibrium analysis of combined dry and steam reforming of propane for thermochemical waste-heat recuperation

The thermochemical waste-heat recuperation is one for perspective way of increasing the energy efficiency of the fuel-consuming equipment. In this paper, the thermochemical waste-heat recuperation (TCR) by combined steam-dry propane reforming is described. To understand the influence of technological parameter such as temperature and composition of inlet gas mixture on TCR efficiency, thermodynamic equilibrium analysis of combined steam-dry propane reforming was investigated by Gibbs free energy minimization method upon a wide range of temperature (600–1200 K) and different feed compositions at atmospheric pressure. The carbon and methane formation was also calculated and shown. From a thermodynamic perspective, the TCR can be used for increasing energy efficiency at temperatures above 950 K because in this range the maximum conversion rate is reached (from 1.22 to 1.30 for the different feed composition). Approximately 10 mol of synthesis gas can be generated per mole of propane at the temperatures greater than 1000 K. Furthermore, the propane conversion rate and yield of hydrogen are increased with the addition of extra steam to the feed stock. Also, undesirable carbon formation can be eliminated by adding steam to the feed. The thermodynamic equilibrium analysis was accomplished by IVTANTHERMO which is a process simulator for thermodynamic modeling of complex chemically reacting systems and several results were checked by Aspen-HYSYS.     

Thermodynamic analysis of H2 production by oxidative steam reforming of butanol-ethanol-water mixture recovered from Acetone:Butanol:Ethanol fermentation

Thermodynamic equilibrium analysis has been adopted for oxidative steam reforming of butanol-ethanol mixture (B-E) as renewable source obtained from Acetone:Butanol:Ethanol (ABE) fermentation to produce H₂ by using Gibbs free energy minimization method. The effects of pressure (1–10 atm), temperature (573–1473 K), steam/fuel molar feed ratio (f_O1 = 9 and 12), O₂/fuel molar feed ratio (f_O2 = 0–3), and B-E mixture compositions (50–90%B) on equilibrium compositions of H₂, CO, CO₂, CH₄, and carbon are performed. The maximum H₂ yield (65.456% for f_O2 = 0 and 58% for f_O2 = 0.75) has been achieved at f_O1 = 9, 90% B mixture, 1 atm, and 973 K. The yields of CO, CO₂, and CH₄ with respect to maximum H₂ are 53.390%, 44.384%, and 2.225% for f_O2 = 0, and 45.677%, 53.269%, and 1.053% for f_O2 = 0.75, respectively. Energy required per mol of H₂, thermal and exergy efficiencies for the process are also evaluated to utilize the potential of B–E mixture for H₂ production.     

Thermodynamic analysis of methanol steam reforming to produce hydrogen for HT-PEMFC: An optimization study

A statistical modeling and optimization study on the thermodynamic equilibrium of methanol steam reforming (MSR) process was performed by using Aspen Plus and the response surface methodology (RSM). The impacts of operation parameters; temperature, pressure and steam-to-methanol ratio (H₂O/MeOH) on the product distribution were investigated. Equilibrium compositions of the H₂-rich stream and the favorable conditions within the operating range of interest (temperature: 25–600 °C, pressure: 1–3.0 atm, H₂O/MeOH: 0–7.0) were analyzed. Furthermore, ideal conditions were determined to maximize the methanol conversion, hydrogen production with high yield and to minimize the undesirable products such as CO, methane, and carbon. The optimum corresponding MSR thermodynamic process parameters which are temperature, pressure and H₂O/MeOH ratio for the production of HT-PEMFC grade hydrogen were identified to be 246 °C, 1 atm and 5.6, respectively.     

Biogas steam and oxidative reforming processes for synthesis gas and hydrogen production in conventional and microreactor reaction systems

In this work, a renewable source, biogas, was used for synthesis gas and hydrogen generation by steam reforming (SR) or oxidative reforming (OR) processes. Several Ni-based catalysts and a bimetallic Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO₂ and ZrO₂ were used. For all the experiments, a synthetic biogas which consisted of 60% CH₄ and 40% CO₂ (vol.) was fed and tested in a fixed bed reactor system and in a microreactor reaction system at 1073 K and atmospheric pressure. The catalysts which achieved high activity and stability were impregnated in a microreactor to explore the viability of process intensification. For the SR process different steam to carbon ratios, S/C, varied from 1.0 to 3.0 were used. In the case of OR process the O₂/CH₄ ratio was varied from 0.125 to 0.50. Comparing conventional and microreactor reaction systems, one order of magnitude higher TOF and productivity values were obtained in the microreactors, while for all the tested catalysts a similar activity results were achieved. Physicochemical characterization of catalysts samples by ICP-AES, N₂ physisorption, H₂ chemisorption, TPR, SEM, XPS and XRD showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.     

Exergy analysis of hydrogen production via steam methane reforming

The performance of hydrogen production via steam methane reforming (SMR) is evaluated using exergy analysis, with emphasis on exergy flows, destruction, waste, and efficiencies. A steam methane reformer model was developed using a chemical equilibrium model with detailed heat integration. A base-case system was evaluated using operating parameters from published literature. Reformer operating parameters were varied to illustrate their influence on system performance. The calculated thermal and exergy efficiencies of the base-case system are lower than those reported in literature. The majority of the exergy destruction occurs due to the high irreversibility of chemical reactions and heat transfer. A significant amount of exergy is wasted in the exhaust stream. The variation of reformer operating parameters illustrated an inverse relationship between hydrogen yield and the amount of methane required by the system. The results of this investigation demonstrate the utility of exergy analysis and provide guidance for where research and development in hydrogen production via SMR should be focused.     

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.     

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

This work presents thermodynamics analysis of hydrogen production via steam reforming of bio-oil components. The model compounds, acetic acid, ethylene glycol and acetone, representatives of the major classes of components present in the aqueous fraction of bio-oil were used for the study. The equilibrium product compositions were investigated in a broad range of conditions like temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm). Any of the three model compounds can be fully reformed even at low temperatures producing hydrogen with maximum yield ranging from 80% to 90% at 900 K. Steam to fuel ratio positively affect the hydrogen content over the entire range of temperature studied. Conversely, higher pressure decreases the hydrogen yield. The formation of solid carbon (graphite) does not constitute a problem provided that reforming temperatures higher than 600 K and steam to fuel ratios higher than 4 for acetic acid and ethylene glycol and 6 for acetone are to be used. Thermal decomposition of the bio-oil components is thermodynamically feasible, forming a mixture containing _C(s)${\mathrm{C}}_{(\mathrm{s})}$, CH₄, H₂, CO, CO₂, and H₂O at various proportions depending on the specific nature of the compound and the temperature. Material and energy balances of complete reforming system demonstrated that the production of 1 kmol/s hydrogen from bio-oil steam reforming requires almost the same amount of energy as with natural gas reforming.     

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.     

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%.     

Adsorption-membrane hybrid system for ethanol steam reforming: Thermodynamic analysis

In this study, an adsorption-membrane hybrid system in which a carbon dioxide adsorbent is used to remove undesired carbon dioxide and a membrane is applied for hydrogen separation is theoretically investigated with the aim to improve the performance of an ethanol steam reforming. A thermodynamic analysis of such the system was performed and compared with a membrane reactor and an adsorptive reactor. It was found that the removal of hydrogen by membrane separation has higher impact on the reformer performance than the carbon dioxide capture by adsorption. The adsorption-membrane hybrid system for ethanol steam reforming gives the highest hydrogen yield. Considering a possibility for carbon formation, the simulation results showed that the use of membrane for pure hydrogen production increases the trend toward carbon formation. This is due to an increase in carbon monoxide concentration in the reaction zone that promotes the Boudouard reaction. In contrast, the use of carbon dioxide adsorbent reduces the formation of carbon as carbon monoxide is less generated in the system.     

Thermodynamic and kinetic model of reforming coke-oven gas with steam

The experiments of reforming the methane of coke-oven gas with steam were performed. The effects of the thermodynamic factors, such as the H₂O/CH₄ ratio, the conversion temperature (T) of methane and the reaction time (t), on the methane conversion rate have been investigated. The experimental results show that the H₂O/CH₄ ratio within the range of 1.1–1.3 and the temperature 1223–1273 K are the reasonable thermodynamic conditions for methane conversion. A methane conversion of more than 95% can be achieved when the H₂O/CH₄ ratio is 1.2, the conversion temperature is above 1223 K and the conversion time is up to 15 s respectively. In additional, kinetic data of different reaction conditions were measured, and a dynamic model of methane conversion was proposed and verified. All results demonstrated that the results of the dynamic models agree well with the experiments, of which the deviation is less than 1.5%.     

Oxidative steam reforming of vacuum residue for hydrogen production

A two-step process for production of hydrogen from vacuum residue has been developed. In the first step, which has already been communicated [18], the residue is reacted with ozone to get oxidized and cracked products. Next, the catalytic oxidative steam reforming of the product obtained after ozonation over a Pt catalyst supported on La₂O₃-CeO₂-γ-Al₂O₃ was carried out. Effects of the operating conditions: the temperature, the steam to carbon ratio and the oxygen to carbon ratio on oxidative steam reforming were investigated. The oxidative steam reforming was efficient at the molar ratio of O₂/C = 0.5, S/C = 4 at 1173 K. Pt catalyst deactivated with time due to coke formation. The catalyst could be regeneration by blowing oxygen through the catalytic bed. Catalysts were characterized by XRD, N₂ adsorption–desorption and thermo gravimetrically to understand the microstructures.     

Preparation and characterization of active Ni/MgO in oxidative steam reforming of n-C4H10

Oxidative steam reforming of n-C₄H₁₀ over MgO-supported Ni catalysts is described. The Ni/MgO catalysts were prepared by the impregnation method from aqueous Ni(NO₃)₂ precursor solutions at two pH values. Ni/MgO prepared at pH 7 exhibited considerably higher activity than Ni/MgO prepared from a conventional acidic aqueous precursor solution (pH 3.5). The H₂ formation rate for the modified Ni/MgO was up to 2.3 times that for conventional Ni/MgO under a high space velocity of 1660 L(h g)⁻¹. Furthermore, after reduction at high temperature (1273 K), the modified Ni/MgO showed a higher H₂ formation rate than did Rh/MgO. The superior performance of the modified Ni/MgO was ascribed to stronger resistance to oxidation of Ni⁰ due to the formation of relatively large Ni⁰ particles.     

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).