Modeling and simulation of hydrogen production from dimethyl ether steam reforming using exhaust gas

In this paper, hydrogen production from steam reforming of DME (dimethyl ether) has been modeled and simulated using a CFD (computational fluid dynamics) method. The reformation chemistry occurs in a porous catalytic bed where exhaust gas is supplied through the EGR (exhaust gas recycling) valve of the engine to drive the endothermic reaction system. The tightly coupled system of mass, energy, and momentum equations are used to describe the complex physical and chemical process of DME steam reforming. The global reaction kinetics for the reforming is adopted in the CFD model. The mathematical models are introduced into the commercial software Comsol, and then numerical simulations are also performed based on this model. The model predictions are quantitatively validated by experiment data. The simulation results indicate the temperature distribution, mass distribution, DME conversion, and hydrogen production from steam reforming of DME. In addition, the fuel to steam ratio and velocity of exhaust gas are manipulated as operating parameters. These simulation results will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor. Copyright © 2015 John Wiley & Sons, Ltd.     

Numerical and experimental study on hydrogen production via dimethyl ether steam reforming

This work presents the characteristics of catalytic dimethyl ether (DME)/steam reforming based on a Cu–Zn/γ-Al₂O₃ catalyst for hydrogen production. A kinetic model for a reformer that operates at low temperature (200 °C–500 °C) is simulated using COMSOL 5.2 software. Experimental verification is performed to examine the critical parameters for the reforming process. During the experiment, superior Cu–Zn/γ-Al₂O₃catalysts are manufactured using the sol-gel method, and ceramic honeycombs coated with this catalyst (1.77 g on each honeycomb, five honeycombs in the reactor) are utilized as catalyst bed in the reformer to enhance performance. The steam, DME mass ratio is stabilized at 3:1 using a mass flow controller (MFC) and a generator. The hydrogen production rate can be significantly affected depending on the reactant's mass flow rate and temperature. And the maximum hydrogen yield can reach 90% at 400 °C. Maximum 8% error for the hydrogen yield is achieved between modeling and experimental results. These experiments can be further explored for directly feeding hydrogen to proton exchange membrane fuel cell (PEMFC) under the load variations.     

Numerical simulation and experimental study of hydrogen production from dimethyl ether steam reforming in a micro-reactor

To enhance the heat and mass transfer during dimethyl ether (DME) steam reforming, a micro-reactor with catalyst coated on nickel foam support was designed and fabricated. A two-dimensional numerical model with SIMPLE algorithm and finite volume method was used to investigate 1) the fluid flow, 2) the heat transfer and 3) chemical reactions consist of DME hydrolysis, methanol steam reforming, methanol decomposition and water gas shift reactions. Both the numerical and the experimental results showed that the DME conversion in the micro-reactor is higher than that in the fixed bed reactor. The numerical study also showed that the velocity and the temperature distribution were more uniform in the micro-reactor. Wall temperature, porosity and steam/DME ratio have been investigated in order to optimize the process in the micro-reactor. The wall temperature of 270 °C and the steam/DME feed ratio of 5 were recommended. Meanwhile the results indicate that a larger porosity will give a higher DME conversion and CO concentration.     

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 evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.     

Thermodynamic analysis of steam reforming and oxidative steam reforming of propane and butane for hydrogen production

Thermodynamic analyses of cracking, partial oxidation (POX), steam reforming (SR) and oxidative steam reforming (OSR) of butane and propane (for comparison) were performed using the Gibbs free energy minimization method under the reaction conditions of T = 250–1000 °C, steam-to-carbon ratio (S/C) of 0.5–5 and O₂/HC (hydrocarbon) ratio of 0–2.4. The simulations for the cracking and POX processes showed that olefins and acetylene can be easily generated through the cracking reactions and can be removed by adding an appropriate amount of oxygen. For SR and OSR of propane and butane, predicted carbon formation only occurred at low S/C ratios (<2) with the maximum level of carbon formation at 550–650 °C. For the thermal-neutral conditions, the TN temperatures decrease with the increase of the S/C ratio (except for O/C = 0.6) and the decrease of the O/C ratio. The simulated results for SR or OSR of propane and butane are very close under the investigated conditions.     

Thermodynamic equilibrium analysis of combined carbon dioxide reforming with partial oxidation of methane to syngas

The chemical equilibrium analysis on combined CH₄-reforming with CO₂ and O₂ (combined CORM–POM) has been conducted by total Gibbs energy minimization using Lagrange's undetermined multiplier method. The equilibrium compositions of the combined CORM–POM process were considerably influenced by CH₄:CO₂:O₂ feed ratios and operating temperatures. Methane oxidation reaction occurred predominantly at low temperatures, while the CO₂ conversion was strongly influenced by the O₂/CH₄ feed ratio. The addition of O₂ to the CORM process improved the CH₄ conversion, H₂ and H₂O yields and also the H₂/CO product ratio at the expense of CO₂ conversion and CO yield. Accordingly, the optimal equilibrium conditions for the CH₄:CO₂:O₂ ratio were within the range of 1:0.8:0.2–1:1:0.2 and a minimum requirement temperature of 1000 K.     

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 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 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.     

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.     

Hydrogen production by steam reforming of dimethyl ether and CO-PrOx in a metal foam micro-reactor

A bi-function catalyst containing CuZnAlCr and HZSM-5 was used to generate hydrogen by stream reforming of dimethyl ether (SRD) in a metal foam micro-reactor and a fix-bed reactor. Dimethyl ether conversion of 99% and hydrogen yield of >95% was reached with HZSM-5/CuZnAlCr (mass ratio of 1:1) in the micro-reactor. A suitable balance between the dimethyl ether hydrolysis and methanol reforming steps requires the proper acidity and the metal sites. The CuZnAlCr/HZSM-5 properties, effect of CuZnAlCr to HZSM-5 mass ratio were investigated in the metal foam micro-reactor. Moreover, CO was removed from hydrogen-rich gas by preferential oxidation reaction (CO-PrOx) with PtFe/γ-Al₂O₃ catalyst in a similar metal foam micro-reactor follows the SRD stage. With the optimized O₂/CO ratio and reaction temperature, the CO concentration dropped to <10 ppm and hydrogen yield of ∼90% were achieved in the new-type SRD-COPrOx system. The SRD-COPrOx system provide a constant hydrogen production with CO concentration lower than 10 ppm during 20 h. The results indicate that metal foam micro-reactor has the great potential in the DME steam reforming to supply hydrogen for low-temperature fuel cells.     

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.     

Catalysts for hydrogen production in a multifuel processor by methanol,dimethyl ether and bioethanol steam reforming for fuel cell applications

Methanol, dimethyl ether and bioethanol steam reforming to hydrogen-rich gas were studied over CuO/CeO₂ and CuO–CeO₂/γ-Al₂O₃ catalysts. Both catalysts were found to provide complete conversion of methanol to hydrogen-rich gas at 300–350 °C. Complete conversion of dimethyl ether to hydrogen-rich gas occurred over CuO–CeO₂/γ-Al₂O₃ at 350–370 °C. Complete conversion of ethanol to hydrogen-rich gas occurred over CuO/CeO₂ at 350 °C. In both cases, the CO content in the obtained gas mixture was low (<2 vol.%). This hydrogen-rich gas can be used directly for fuelling high-temperature PEM FC. For fuelling low-temperature PEM FC, it is needed only to clean up the hydrogen-rich gas from CO to the level of 10 ppm. CuO/CeO₂ catalyst can be used for this purpose as well. Since no individual WGS stage, that is necessary in most other hydrogen production processes, is involved here, the miniaturization of the multifuel processor for hydrogen production by methanol, ethanol or DME SR is quite feasible.     

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.     

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.     

Evaluation of the thermodynamic equilibrium of the autothermal reforming of dimethyl ether

In the present study, a thermodynamic analysis of the autothermal reforming of dimethyl ether (DME) for the production of hydrogen was carried out. The results clearly indicated that the carbon formation behavior, the boundary conditions between coke-free and coking regions, and the equilibrium composition of the reformate were dependent on the steam/DME ratio, O₂/DME ratio, temperature, and pressure of the system. For instance, carbon formation was effectively suppressed as the steam/DME ratio increased from 0 to 5, the O₂/DME ratio increased from 0 to 3, or the temperature rose from 100 to 1000 °C. In contrast, carbon formation was enhanced as the pressure was increased from 0.5 to 10 atm. The boundary temperature of coke-free operation decreased with an increase in the steam/DME and O₂/DME ratios. More specifically, at a steam/DME ratio of 3-5 and an O₂/DME ratio of 0-3, the boundary temperature ranged from 50 to 280 °C (when CH₄ formation was promoted) and 380 to 670 °C (when CH₄ formation was suppressed), respectively. Furthermore, at elevated temperatures, H₂ and CO formations were enhanced, and CH₄ formation was inhibited. The addition of steam enhanced H₂ production while reducing CO formation. On the contrary, an increase in the O₂/DME ratio reduced H₂ production while enhancing CO formation. Interestingly, the desired temperature for thermo-neutral condition, in which energy consumption was zero, can be achieved by correctly controlling the O₂/DME and steam/DME ratios.     

Underwater vehicle hydrogen production from methanol steam reforming using hydrogen peroxide

Methanol steam reforming (MSR) can supply hydrogen (H₂) to underwater vehicles equipped with a fuel cell. Low reaction temperatures ensure the composition of the reformed gas suitable for the H₂ purification unit and increase the design freedom of a reforming plant. However, such temperatures decrease the catalyst activity and thereby the methanol (MeOH) conversion and H₂ production. Herein, hydrogen peroxide (H₂O₂) was supplied with MeOH and water (H₂O) to ensure sufficient MeOH conversion and H₂ production at low temperatures. A tube reactor loaded with a commercial Cu/Zn catalyst was installed in an electric furnace maintained at 200–250 °C, and MeOH and 0 wt%, 11.88 wt%, 22.51 wt%, and 32.07 wt% H₂O₂ were supplied. When the furnace temperature was 200 °C, the MeOH conversion was 49.3% at 0 wt% H₂O₂ but 93.5% at 32.07 wt% H₂O₂. The effect of adding H₂O₂ was greater under the temperature conditions where the MeOH conversion was 100% or less. To analyze the effect of H₂O₂ addition on catalyst durability, the furnace was maintained at 200 °C, and the reactor was continuously operated for 110 h with 0 wt% and 32.07 wt% H₂O₂. The addition of H₂O₂ did not significantly decrease the Cu/Zn catalyst durability.