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.     

Hydrogen production from methanol steam reforming over Al2O3- and ZrO2-modified CuOZnOGa2O3 catalysts

New CuOZnOxGa₂O₃–Al₂O₃ and CuOZnOxGa₂O₃–ZrO₂ (CuZnxGaAl, CuZnxGaZr) catalysts with different Ga contents were prepared and tested in the methanol steam reforming reaction (MSR) under stoichiometric methanol/water = 1 mol ratio (S/C = 1) at 523 K and 548 K. Addition of Al₂O₃ or ZrO₂ components increases the surface area and modifies the reducibility of CuOZnOGa₂O₃ catalysts; the CuZnxGaZr systems showed the highest reducibility. The performance of CuOZnOGa₂O₃-based catalysts for MSR is improved by the presence of ZrO₂ promoter. CuZn3GaZr catalyst showed a high performance for MSR at 523 K and 548 K under stoichiometric conditions (S/C = 1). The catalyst resulted highly stable and selective for H₂ production, with formation of less than 0.3% mol of CO at 523 K. CO is produced as a secondary by-product through the reverse water gas shift reaction. The new catalysts show high resistance to carbon formation at the temperatures analyzed under stoichiometric conditions (S/C = 1).     

Methane OSR over Pt-Ni/δ-Al2O3: Performance and power law type kinetics

Methane oxidative steam reforming (OSR) performance of two bimetallic Pt-Ni/δ-Al₂O₃ catalysts, having Pt:Ni loadings, 0.2:10 and 0.3:10, were tested first. In the tests, residence time (W/F), carbon-to-oxygen (C/O₂) feed ratio, and temperature were used as the experimental parameters. Increase in temperature resulted in direct and indirect - through enhanced TOX yielding higher energy - increase in SR rate. As Pt:Ni metal loading ratio did not lead to significant changes in activity, the preliminary kinetic tests to determine merely kinetically controlled region were conducted over 0.2Pt-10Ni catalyst. Considering the outcomes of the preliminary tests, the kinetic experiments were performed for practical reaction conditions extending up to 20% methane conversion with feed ratio intervals of 4.0 < C/O₂ < 7.34 and 2.03 < S/C < 3.08 at two different residence time (W/F) values to obtain a power-law type rate equation. Reaction orders were estimated as 0.81, 1.60 and 0.44 for methane, oxygen and steam, respectively, by using multivariable non-linear optimization function of MATLAB?. The apparent activation energy of methane OSR was calculated as 24.61 kJ mol^?1 and pre-exponential factor as 0.110 μmol mgcat^?1 s^?1 kPa^?2.85 for the 375–450 °C temperature interval. The same analysis performed for a narrower temperature range, 375–425 °C, gave k₀ and E_A values as 0.251 μmol mgcat^?1 s^?1 kPa^?2.85 and 29.17 kJ mol^?1, respectively, confirming the high sensitivity of OSR pathway to temperature.     

Kinetic study of the catalytic reforming of biomass pyrolysis volatiles over a commercial Ni/Al2O3 catalyst

An original kinetic model has been proposed for the reforming of the volatiles derived from biomass fast pyrolysis over a commercial Ni/Al₂O₃ catalyst. The pyrolysis-reforming strategy consists of two in-line steps. The pyrolysis step is performed in a conical spouted bed reactor (CSBR) at 500 °C, and the catalytic steam reforming of the volatiles has been carried out in-line in a fluidized bed reactor. The reforming conditions are as follows: 600, 650 and 700 °C; catalyst mass, 0, 1.6, 3.1, 6.3, 9.4 and 12.5 g; steam/biomass ratio, 4, and; time on stream, up to 120 min. The integration of the kinetic equations has been carried out using a code developed in Matlab. The reaction scheme takes into account the individual steps of steam reforming of bio-oil oxygenated compounds, CH₄ and C₂-C₄ hydrocarbons, and the WGS reaction. Moreover, a kinetic equation for deactivation has been derived, in which the bio-oil oxygenated compounds have been considered as the main coke precursors. The kinetic model allows quantifying the effect reforming conditions (temperature, catalyst mass and time on stream) have on product distribution.     

Effect of La2O3 replacement on γ-Al2O3 supported nickel catalysts for acetic acid steam reforming

The effect of replacement of γ-Al₂O₃ by La₂O₃ was studied on Ni catalysts for hydrogen production via acetic acid steam reforming. The La/(La + Al) weight ratio ranged from 0 to 1 in the catalyst support prepared by co-precipitation method. Over the Ni/La-3Al catalyst (the La/(La + Al) weight ratio at 0.25), the carbon conversion and hydrogen yield reached 100% and 72.72%, respectively, which was obviously higher than other catalysts at 700 °C, S/C = 1 and LHSV = 10 h^?1. The effect of S/C, LHSV and stability test were studied in detail over Ni/La-3Al catalyst, whose high activity maintained for more than 30 h.     

Cu supported on ZnAl-LDHs precursor prepared by in-situ synthesis method on γ-Al2O3 as catalytic material with high catalytic activity for methanol steam reforming

A novel catalyst precursor ZnAl-LDHs/γ-Al₂O₃ was prepared by in-situ synthesis method, and the copper was supported on calcined hydrotalcite catalyst precursor by wet impregnation. The correlation between the structure and the catalytic activity for methanol steam reforming was studied by XRD, SEM, TPR, chemisorption N₂O, IR and N₂ adsorption techniques. The results showed that the ZnAl-LDHs was successfully synthesized by in-situ synthesis method on γ-Al₂O₃ and the copper mass fraction had a great effect on the interactions between support and copper species. Furthermore, the catalyst reducibility and copper surface area evidently influenced catalytic activity for methanol steam reforming. The 10% Cu/γ-Al@MMO exhibited the best catalytic activity, that was, the methanol conversion was 99.98% and the CO concentration was only 0.92% at 300 °C in hydrogen production by methanol steam reforming.     

Kinetic investigation on butanol steam reforming over Ru/Al2O3 catalyst

Steam reforming of biomass-derived oxygenates is an attractive technique for the renewable production of hydrogen (H₂). In this work, steam reforming of n-butanol – a representative of bio-oxygenates – was studied over commercial 5% Ru/Al₂O₃ catalyst in a fixed-bed reactor. Kinetics of butanol reforming was investigated between temperatures 623 and 773 K at steam/carbon (S/C) ratio equal to 33.3 mol/mol. The W/F_A0 ratio (W: mass of catalyst, F_A0: molar flow rate of butanol in feed) was varied between 3.3 and 16.7 g h/mol. At T = 773 K, butanol conversion and H₂ yield were 93.4% and 0.61 mol/mol. Evaluation of the kinetic data showed that reaction order with respect to butanol was unity. The activation energy for the investigated reaction was 78 kJ/mol. Finally, a Langmuir-Hinshelwood model that assumed the surface reaction between the adsorbed reactants as rate-determining was used to describe the kinetic data.     

A thermodynamic analysis of biogas partial oxidation to synthesis gas with emphasis on soot formation

A thermodynamic analysis of synthesis gas production via partial oxidation (POX) of biogas is performed in the present article. Chemical equilibrium calculations are conducted for partial oxidation of (CH₄+CO₂) mixtures based on Gibbs free energy minimization method emphasizing soot formation. Regarding precise evaluation of carbon dioxide effects on the reforming characteristics, the obtained results are compared with the experimental data. Furthermore, the effects of steam injection at the inlet of the reformer on the coking behavior and syngas production yield are studied. To investigate the effects of the equivalence ratio (?), temperature and pressure, a broad parametric study is performed. The results reveal that the process temperature plays a pivotal role in enhancing the syngas production and soot abatement. It is also found that the pressure has an impractical effect on the syngas production yield, leading to the soot formation and decrease in both hydrogen and carbon monoxide yields. Furthermore, increasing the inlet CO₂/CH₄ makes the thermal reforming efficiency to rise at an equivalence ratio lower than 3. Meanwhile, increasing the steam to methane (S/C) ratio reduces carbon formation and enhances hydrogen production. Nonetheless, when the S/C ratio is larger than 2 at ? = 2.5 and 1 at ? = 3, the enhancement of hydrogen generation is minimized and even tends to become impractical. Therefore, near adiabatic and atmospheric condition at ? = 2.5–3 with S/C < 1 are recommended as the optimum operating routes for partial oxidation of biogas.     

Hydrogen production and thermal behavior of methanol autothermal reforming and steam reforming triggered by microwave heating

Hydrogen production and thermal behavior of methanol autothermal reforming (ATR) triggered by microwave heating are studied. Methanol steam reforming (MSR) is also investigated for comparison. A commercial Cu–Zn-based catalyst is used. The gas hourly space velocity (GHSV) is fixed at 72,000 h⁻¹, and the reaction temperature and the oxygen/methanol molar ratio (i.e. O₂/C ratio) are in the ranges of 250–300 °C and 0–0.5, respectively. The results suggest that an increase in O₂/C ratio or reaction temperature diminishes the supplied energy for microwave irradiation, as a result of more oxidative reactions involved. However, the performance of methanol ATR at 300 °C is lower than that at 250 °C. The methanol conversion of ATR is beyond 90% at O₂/C = 0.125 and 0.5, whereas it is relatively low (56–67%) at O₂/C = 0.25, presumably due to the weakened microwave irradiation and insufficient heat release. The spectrum analysis of supplied power using the fast Fourier transform (FFT) algorithm indicates that the supplied power characteristics of endothermic reactions are different from those of exothermic reactions.     

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

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

Numerical analysis of performance enhancement and non-isothermal reactant transport of a cylindrical methanol reformer wrapped with a porous sheath under steam reforming

This paper accomplished a three-dimensional computational analysis of the methanol reformer with steam reforming by the Arrhenius form of reaction model and SIMPLE-C algorithm. The performance enhancement and non-isothermal reactant transport of the cylindrical reformer wrapped with a porous sheath were investigated. The parameters, including temperature of internal heater (T_H), porosity (ε), and thickness of porous sheath (R_P), on methanol conversion, hydrogen, carbon monoxide, carbon dioxide productions, temperature and velocity fields with the same inlet conditions have been investigated. The results present that higher methanol conversion and richer hydrogen production occur as temperature of heater, porosity, and porous sheath thickness increase. As temperature of internal heater is equal to 250 °C, employing a porous sheath with ε = 0.9 and R_P = 10 mm to wrap a reformer results in the maximum enhancements of 35.71% in methanol conversion and 21.18% in hydrogen production. Besides, a porous sheath with ε = 0.5 and R_P = 10 mm leads to the maximum reduction of 2.23% in carbon monoxide produced from the reformer at T_H = 300 °C.     

Enhanced hydrogen production in catalytic pyrolysis of sewage sludge by red mud: Thermogravimetric kinetic analysis and pyrolysis characteristics

The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe₂O₃, Al₂O₃, SiO₂) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe₂O₃ and Al₂O₃ in the RM. Adding Fe₂O₃ or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol^?1, respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al₂O₃, Fe₂O₃ or the RM could produce more gas than the addition of SiO₂, especially at high temperatures. Fe₂O₃ and Al₂O₃ acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of CC and CH bonds to produce more gases. Especially, Fe₂O₃ and Al₂O₃ increased the H₂ yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.     

Texture/phase evolution during microwave fabrication of nanocrystalline multicomponent (Cu/Zn/Al)O metal oxides with varying diethylene glycol content applied in hydrogen production

A series of Cu/Zn/Al mixed oxides, as steam methanol reforming catalysts, were synthesized via the microwave assisted combustion synthesis method using diethylene glycol as the organic fuel. The nanocatalysts were analyzed by XRD, FESEM, EDX, BET, H₂-TPR and FTIR techniques to ensure authenticity of the synthesis steps and pursuing the effect of the fuel/nitrate ratio on their physicochemical properties. The results proved the necessity of defining an optimum fuel/nitrate ratio for the combustion synthesis method. Fuel/nitrate ratio affects significantly on crystal growth and crystalline facets size. Proper crystallography of CuO/ZnO/Al₂O₃ (DEG/Nitrate = 3) nanocatalyst along with higher specific surface area and distributed particle size, made it predictable that it could result in higher methanol conversion in the steam methanol reforming process. The catalytic performance studies justified assumptions, since the CZA (DEG/N = 3) presented higher methanol conversion and selectivity toward desired products as well as its high stability.     

Tailoring Cu/Al2O3 catalysts for the catalytic pyrolysis of tomato waste

In this study, pyrolysis of tomato waste has been performed in fixed bed tubular reactor at 500 °C, both in absence and presence of Cu/Al₂O₃ catalyst. The influences of heating rate, catalyst preparation method and catalyst loading on bio-oil yields and properties were examined. According to pyrolysis experiments, the highest bio-oil yield was obtained as 30.31% with a heating rate of 100 °C/min, 5% Cu/Al₂O₃ catalyst loading ratio and co-precipitation method. Results showed that the catalysts have strong positive effect on bio-oil yields. Bio-oil quality obtained from fast catalytic pyrolysis was more favorable than that obtained from non-catalytic and slow catalytic pyrolysis.     

Preparation and characterization of CuOAl2O3 catalyst for dimethyl ether production via methanol dehydration

In the present study, a CuOAl₂O₃ catalyst with CuAl₂O₄ spinel structure was prepared by a co-precipitation method and used for dimethyl ether (DME) production via methanol dehydration at 50 bar and different reaction temperatures (150, 250, and 350 °C). Upon XPS analysis of the copper and aluminum species in the fresh and used CuOAl₂O₃ catalyst, CuAl₂O₄ was found to be the dominant species with more than 50% of total composition. Three reductive reactions and temperatures for the formation of CuH (102.3 °C), the interaction between Cu²⁺ and Al atoms (356.6 °C), and the reduction of CuO (520.1 °C) were analyzed by H₂-TPR. Furthermore, the copper oxidation state in the fresh and used catalyst was Cu(II), as determined by the XANES spectra. The fine structural parameters revealed that the coordination number of Cu changed from 2.75 to 2.44 during the catalytic reaction, and that the CuO bond distance increased from 1.94 to 1.98 Å due to strengthened Cu²⁺Al interactions. On-line FTIR spectra revealed that the optimum temperature for the formations of HCOOH (by-product) and DME (product) were 150 and 250 °C, respectively. The catalytic reactions in the duration of DME synthesis were found that included methanol decomposition, methanol/formic acid formations, and methanol dehydration occurring at CuO, Cu, and Al₂O₃/CuAl₂O₄ active sites, respectively. The highest methanol conversion (67.3%) and DME yield (40.6%) were obtained at 250 °C and 50 bar, as demonstrated by the catalyst performance. In addition, optimum DME formation (equilibrium constant 1.76 × 10^?2 L mol^?1 h^?1 and activation energy 5.14 kJ mol^?1) occurred at 250 °C, as determined from the linear regression of the second order model with a high R² value (0.98). The exothermal and non-spontaneous nature of DME formation at high temperature was evaluated through thermodynamic calculations of the reaction enthalpy, entropy, and Gibbs energy.     

High specific surface area supports for highly active Rh catalysts: Syngas production from methane at high space velocity

A series of high specific surface area mesoporous supports (CeO₂, CeO₂-Al₂O₃, and Al₂O₃) were synthesized by the surfactant-assisted precipitation method using cetyltrimethylammonium bromide (CTAB) as template. Highly dispersed Rh-based catalysts were prepared by the wetness impregnation technique. The physico-chemical properties of the as-prepared supports and catalysts were investigated by N₂-physisorption, CO-chemisorption, XRD, and H₂-TPR measurements. Catalytic performance was evaluated towards the methane steam reforming (MSR) reaction up to 300 h of time-on-stream varying temperature (700–800 °C), steam-to-carbon (S/C = 2–3), and space velocity (88–200 SL·g_cat^?1·h^?1); turnover frequencies were calculated at each reaction condition. All catalysts exhibited high activity strictly connected with high specific surface area (105–325 m² g^?1) and metal dispersion (34.3–84.0%). Significant enhanced stability was observed for Al₂O₃-containing catalysts towards the MSR reaction at high space velocity.     

Production of hydrogen from steam reforming of methanol carried out by self-combusted CuCr1-xFexO2 (x = 0–1) nanopowders catalyst

In this present work, the delafossite type CuCr_1-xFe_xO₂ (x = 0–1) nanopowder was prepared by a self-combusted glycine nitrate process used for the steam reforming of methanol (SRM). The effectiveness of hydrogen production was upgraded by the preparation of CuCr_1-xFe_xO₂ (x = 0–1). The prepared Cu based materials were characterized by field emission scanning electron microscope studies, X-ray diffraction studies, energy dispersive X-ray studies, and Brunauer-Emmett-Teller studies. The CuCr_1-xFe_xO₂ (x = 0–1) nanopowders were studies by the hydrogen production by methanol steam reforming reaction. The Cu based catalyst exhibited high catalytic activity and hydrogen production rate as 1740 ml/min g-cat at 360 °C. Furthermore, the catalyst nanopowder was stable up to 1200 min without any considerable changes in steam reforming methanol and product selectivity in the SRM process. The production rate of CuCr_1-xFe_xO₂ was improved by the adequate amount of iron incorporation (60%) and adjusted the feeding rate of methanol. These conditions obtain the best performance could reach the hydrogen production of 301.45 (μmol (min g-cat)⁻¹) at 350° over CuCr_0.4Fe_0.6O₂ with a flow rate of 60 sccm.     

Hydrogen production with a low carbon monoxide content via methanol steam reforming over CuxCeyMgz/Al2O3 catalysts: Optimization and stability

Catalytic activities of Ce–Mg promoted Cu/Al₂O₃ catalysts via methanol steam reforming was investigated in terms of the methanol conversion level, carbon monoxide selectivity and hydrogen yield. The factors chosen were the reaction temperature, copper content, Mg/(Ce + Mg) weight-percentage and steam to carbon ratios. The catalysts were prepared by co-precipitation and characterized by means of XRD, BET, H₂-TPR, and FESEM. The Ce–Mg bi-promoter catalysts gave higher performance due to magnesium penetration into the cerium structure causing oxygen vacancy defects on the ceria. A response-surface-model was then designed to optimize the condition at a 95% confidence interval for complete methanol conversion to a high H₂ yield with a low CO content, and revealed an optimal copper level of 46–50 wt%, Mg/(Ce + Mg) of 16.2–18.0%, temperature of 245–250 °C and S/C ratio of 1.74–1.80. No deactivation of the Cu_0.5Ce_0.25Mg_0.05/Al catalyst was observed during a 72-h stability test.     

Ni/MgAl2O4 catalyst for low-temperature oxidative dry methane reforming with CO2

Oxidative dry reforming of methane has been performed for 100 h on stream using Ni supported on MgAl₂O₄ spinel at different loadings at 500–700 °C, CO₂/CH₄ molar ratio of 0.76, and variable O₂/CH₄ molar ratio (0.12–0.47). Syngas with an H₂/CO ratio of 1.5–2.1 has been produced by manipulating reforming feed composition and temperature. The developed oxidative dry reforming process allowed high CH₄ conversion at all conditions, while CO₂ conversion decreased significantly with the lowering of the reforming temperature and increasing O₂ concentration. When considering both greenhouse gas conversions and H₂/CO ratio enhancement, the optimal reforming condition should be assigned to 550 °C and O₂/CH₄ molar ratio of 0.47, which delivered syngas with H₂/CO ratio of 1.5. Coke-free operation was also achieved, due to the combustion of surface carbon species by oxygen. The 3.4 wt% Ni/MgAl₂O₄ catalyst with a mean Ni nanoparticle diameter of 9.8 nm showed stable performance during oxidative dry reforming for 100 h on stream without deactivation by sintering or coke deposition. The superior activity and stability of MgAl₂O₄ supported Ni catalyst shown during reaction trials is consistent with characterization results from XRD, TPR, STEM, HR-STEM, XPS, and CHNS analysis.     

Selective substitution of Ni by Ti in LaNiO3 perovskites: A parameter governing the oxy-carbon dioxide reforming of methane

A series of LaNi_1?xTi_xO₃ perovskite catalysts varying titanium (x = 0.0, 0.2, 0.4, 0.5, 0.6 and 1.0) are synthesized and investigated using BET, XRD, TPR, TEM, FT-IR and XPS. The catalysts were evaluated for oxy-carbon dioxide reforming of methane at 800 °C under atmospheric pressure maintaining CO₂/CH₄/O₂ ratio 0.8/1.0/0.2. LaNi_0.5Ti_0.5O₃ is showing typical stability with gradual H₂ consumption in TPR. The stability of these catalysts is supported by O 1s binding energies wherein it is clearly evident that incorporation of Ti stabilized LaNiO₃ generating suitable catalysts in the range of x = 0.4–0.6 with high performance.