Hydrogen production via sorption enhanced steam reforming of butanol: Thermodynamic analysis

Thermodynamic equilibrium for sorption enhanced steam reforming of butanol (SESRB) to hydrogen was investigated using Gibbs free energy minimization method. The optimal operation conditions for SESRB are at 800 K, the steam-to-butanol molar ratio of 10, the calcium oxide-to-butanol molar ratio of 8 and atmospheric pressure. Under the optimal conditions, complete conversion of butanol, 97.07% concentration of H₂ and 0.05% concentration of CO₂, and efficiency of 86.60% could be achieved and at which no coke tends to form. Under the same conditions in SRB, 58.18% concentration of H₂, 21.62% concentration of CO₂, and energy efficiency of 81.51% could be achieved. Butanol steam reforming with CO₂ adsorption has the higher H₂ content and efficiency, and lower CO₂ content than that without adsorption under the same reaction conditions. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in butanol steam reforming with or without CO₂ separation.     

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 investigation on hydrogen production via self-sufficient chemical looping reforming of glycerol (CLRG) using metal oxide oxygen carriers

The self-sufficient chemical looping reforming of glycerol (CLRG) utilizes the same basic principles as chemical looping combustion (CLC), the main difference being that the desired product in CLRG is not heat but H₂. Therefore, in the CLR process the O/C ratio is kept low to prevent the complete oxidation of glycerol to H₂O. A systematic thermodynamic study of CLRG using metal oxide oxygen carriers (NiO, CuO, CoO, Co₃O₄, Mn₃O₄, Mn₂O₃ and Fe₂O₃) is performed to analyze the product yield, carbon deposition and energy requirements at different temperatures and pressures. The calculation results show higher temperatures promote, but higher pressures inhibit H₂ production. Favorable conditions (800 °C and 1 atm) are obtained for H₂ manufacture from CLRG process. CuO is the best performing oxygen carrier followed by Mn-based oxygen carriers, while Fe₂O₃ is the least preferred oxygen carrier for CLRG. These results obtained in this theoretical study can offer helpful information for CLRG experimental tests.     

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.     

Thermodynamic analysis of hydrogen production from glycerol autothermal reforming

In this work, thermodynamics was applied to investigate the glycerol autothermal reforming to generate hydrogen for fuel cell application. Equilibrium calculations employing the Gibbs free energy minimization were performed in a wide range of temperature (700–1000 K), steam to glycerol ratio (1–12) and oxygen to glycerol ratio (0.0–3.0). Results show that the most favorable conditions for hydrogen production are achieved with the temperatures, steam to glycerol ratios and oxygen to glycerol ratios of 900–1000 K, 9–12 and 0.0–0.4, respectively. Further, it is demonstrated that thermoneutral conditions (steam to glycerol ratio 9–12) can be obtained at oxygen to glycerol ratios of around 0.36 (at 900 K) and 0.38–0.39 (at 1000 K). Under these thermoneutral conditions, the maximum number of moles of hydrogen produced are 5.62 (900 K) and 5.43 (1000 K) with a steam to glycerol ratio of 12. Also, it should be noted that methane and carbon formation can be effectively eliminated.     

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.     

Comparative study of fuel gas production for SOFC from steam and supercritical-water reforming of bioethanol

Theoretical study of fuel gas (H₂ + CO) production for SOFC from bioethanol was carried out to compare performances between two reforming technologies, including steam reforming (SR) and supercritical-water reforming (SCWR). It demonstrates that the fuel gas productions are comparable among the two reforming systems; however, SCWR requires the operation at much higher temperature and pressure than SR. The maximum hydrogen yield can be obtained at 850 K, atmospheric pressure, ethanol to water molar feed ratio of 1:20 for SR system and at 1300 K, 22.1 MPa, and ethanol to water feed ratio of 1:20 for SCWR. The use of a distillation column to purify the bioethanol feed was proven to improve the fuel conversion efficiency of both systems. The analysis reveals that SCWR is a promising system for fuel production for SOFC when a gas turbine is incorporated to the system for energy recovery. Further, it is not necessary to distil bioethanol to obtain too high ethanol recovery (i.e. >90%) as higher energy consumption at the distillation column could lead to lower overall thermal efficiency.     

Thermodynamic analysis of glycerol-steam reforming in the presence of CO2 or H2 as carbon gasifying agent

This paper deals with the thermodynamic analysis of glycerol-steam reforming with H₂ or CO₂ co-fed as carbon gasifying agents in order to mitigate carbon deposition. Thermodynamic calculations were carried out at temperatures from 500 to 800 K and steam-to-glycerol ratios of 0:1–20:1 at atmospheric pressure. Carbon deposition was significant (1.0–1.7 mol C/mol C₃H₈O₃) at low steam-to-glycerol ratio (<4.0) within the reaction temperature range (500–800 K). Carbon-free regime can only be achieved at temperatures above 700 K at steam-to-glycerol ratio of 3:1. Beyond the steam-to-glycerol ratio of 4:1, carbon deposition is essentially zero. The addition of H₂ (as co-reactant) reduced the carbon deposition (down to 0.58 mol C/mol C₃H₈O₃ from 1.70 mol C/mol C₃H₈O₃) even at steam-to-glycerol ratio of 0:1 and reaction temperature of 500 K. Above 5 mol H₂/mol C₃H₈O₃, thermodynamic analysis showed undetectable carbon deposition. Significantly, this could be attributed to the H₂-gasification of carbon species to produce CH₄ and hence, the concomitant increase in the latter. The introduction of CO₂ into the glycerol-steam system, however, led to increased carbon deposition at all temperatures considered in this study due to the reaction between CO₂ and CH₄ in forming carbon deposits. Nevertheless, the carbon yield can be reduced through reforming at higher temperatures. It was further concluded from the current work that H₂ co-feeding linearly increased the exothermicity of reforming system.     

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.     

Effect of ZrO2 addition on Ni/Al2O3 catalyst to produce H2 from glycerol

In this work, ZrO₂ was employed as support and as Al₂O₃ modifier of Ni based catalysts due to its special interesting characteristics. The catalytic activity of these systems was studied in steam reforming of glycerol to produce H₂. As the activity results at 773 K and 873 K showed, the NiZ catalyst allowed low glycerol conversion and H₂ production when compared to the NiγA catalyst. Moreover, the NiZ catalyst was not able to reform intermediate liquid products into gaseous products.     

Thermodynamic analysis of steam reforming of ethanol for hydrogen generation

Thermodynamic equilibrium of ethanol steam reforming has been studied by Gibbs free energy minimization method for hydrogen production in the ranges of water‐to‐ethanol ratio from 0 to 20, reaction temperature from 400 to 2000 K, pressure from 1 to 60 atm, argon‐to‐ethanol ratio from 0 to 100. The optimal conditions suitable for the use in molten carbonate fuel cell and solid oxide fuel cell were obtained as follows: 900–1200 K, water‐to‐ethanol ratio of 3:6, and 1 atm. Under the optimal conditions, complete conversion of ethanol, 60.52–83.58% yield of hydrogen and 32.82–79.60% yield of carbon monoxide could be obtained and no coke forms. Higher pressures have a negative effect, but inert gases have a positive effect, on the hydrogen yield. Coke tends to form at lower temperatures and lower water‐to‐ethanol ratios. Copyright © 2008 John Wiley & Sons, Ltd.     

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 equilibrium analysis of combined carbon dioxide reforming with steam reforming of methane to synthesis gas

Thermodynamics equilibrium analysis of carbon dioxide reforming of methane combined with steam reforming to synthesis gas was studied by Gibbs free energy minimization method to understand the effects of process variables such as temperature, pressure and inlet CH₄/H₂O/CO₂ ratios on product distributions. For this purpose, the calculations were carried out at total pressures of 1 and 20 bar, and at ranges of temperature and steam-to-carbon ratios of 200–1200 °C and 0–0.50, respectively. The results revealed that carbon dioxide reforming of methane combined with steam reforming process was controlled by different reactions with regard to the operating temperature, pressure and varying feed compositions. The H₂/CO product ratio could be modified by changing the relative concentration of steam and CO₂ in the feed, temperature and pressure, depending on the downstream application.     

Optimization of bio-oil steam reforming process by thermodynamic analysis

A straightforward thermodynamic analysis of bio-oil steam reforming was carried out in the context of hydrogen and syngas production, employing Gibbs energy minimization method to determine equilibrium composition and global reaction heat. The bio-oil model compound was a mixture of acetic acid, phenol, and acetone. The effects of process variables, such as temperature and inlet S/C molar ratio, were investigated over a wide range of conditions. Thermodynamic analysis was performed using the software Aspen Plus v.11. It was identified the best operational conditions that could maximize syngas and further hydrogen production considering energy efficiency. The optimum production of hydrogen is 2.28 mol per carbon mole at S/C = 10 and 850 K, and syngas is 2.37 mol per carbon mole at S/C = 10 and 900 K. It has been demonstrated that the equilibrium calculations can be used to simulate these steam reforming reactions, given the catalyst's behavior.     

Hydrogen from glycerol steam reforming with a platinum catalyst supported on a SiO2-C composite

This work studies 2 wt% Pt catalysts. The support is a SiO₂-C composite whose main features are a high specific surface due to its mesoporosity, a higher thermal stability than the C support, and the absence of surface acid sites which could promote the dehydration reactions that produce coke precursors. The Pt/SiO₂-C catalyst has very small metallic particles (d_va = 1.37 nm) that favor the CC bond cleavage reactions which allow obtaining total gas conversion at 450 °C. With this catalyst, it is possible to obtain high yields to H₂, between 4 and 5, which indicates that the active sites promote the WGS reaction, even with glycerol concentrations of 30 and 50%. Pt/SiO₂-C is a very stable catalyst since it loses only 10% of its initial activity after 66 h on stream and is resistant to sintering and coke deposition.     

Selection of appropriate primary fuel for hydrogen production for different fuel cell types: Comparison between decomposition and steam reforming

In order to select a proper hydrogen production system being compatible with fuel cell, a variety of interesting primary fuels such as light hydrocarbons and alcohols were tested in the decomposition (D) and the steam reforming (SR) processes by thermodynamic approach. The reaction performances of the systems particularly under thermally self-sustained condition were focused on. To obtain self-sustained condition, two approaches, splitting feed and splitting gas product streams to the burner for heat supply to endothermic hydrogen processor, are investigated. Our results revealed that splitting gas product gave higher carbon capture than splitting feed but lower in hydrogen yield. As expected, steam reforming provides higher hydrogen production, however, lower in hydrogen purity and carbon capture comparing to decomposition process. By considering primary fuels, D-alcohols could be applied to MCFC and SOFC, among these, D-C₂H₅OH was preferable because it gives the highest ratio of H₂/CO. For D-light hydrocarbon systems, which is operated at 1100 K providing 97% hydrogen purity, is suitable to be connected to MCFC, SOFC and also PEMFC.     

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.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

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.