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1.
Dry reforming of CH4 on a platinum-rhodium alumina catalyst is selected to numerically investigate biogas reforming process. Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expressions for dry reforming and reverse water-gas shift reactions are presented. Activation energies are estimated by combining microkinetics with the theory of unity bond index-quadratic exponential potential (UBI-QEP). Pre-exponential factors are initially obtained by using the transition state theory (TST) and optimised, later, by minimising errors between modelling and experimental data. Adsorption of CH4 on the catalyst surface is found to be the rate determining step in the range of relatively low temperature (600–770 °C), while at relatively high temperature (770–950 °C) the thermal cracking of adsorbed CH4 is the rate controlling step. Small effect of reverse water-gas shift reaction results in the ratio of H2 to CO produced less than unity for all operating conditions. The simulation shows that the dry reforming process proceeds with reaction rate far from equilibrium state. The presented mechanism is capable of predicting the dependence of biogas dry reforming activities (e.g., reactant conversions, product formations, H2 to CO ratio, and temperature profile inside the catalyst) on operating conditions (e.g., inlet temperature, heat supplied through the catalyst wall, and composition of biogas at inlet).  相似文献   

2.
Among the alternative pathways for hydrogen production, the use of biogas from organic waste via dry reforming of methane (DRM), water gas shift reaction and pressure swing adsorption (PSA) is often seen as an interesting option. In this work, the thermodynamic performance of this type of biohydrogen energy system –additionally including a combined-cycle scheme that satisfies the electricity and steam requirements of the process– is evaluated through exergy analysis. The main data needed for the analysis are acquired from a predictive simulation model implemented in Aspen Plus®. The system shows an exergetic efficiency of 55%, with the DRM and the power generation subsystems arising as the main sources of irreversibility. Furthermore, given the significant influence found for the PSA off-gas on the thermodynamic performance of the system, two alternative process configurations based on the use of this stream are evaluated. In this regard, full recirculation of the PSA off-gas to the DRM reactor is found to improve the system's exergetic performance.  相似文献   

3.
A Ni based catalyst supported on a cordierite monolithic substrate was applied to the autothermal reforming (ATR) of biogas to produce hydrogen. When the feed rates of oxygen and steam were constant, the Steam/CH4 (S/CH4) and O2/CH4 ratios changed because of an increase or decrease in the methane concentration of the biogas. The concentration of methane in the biogas fluctuates roughly between 35% and 65% according to factors such as the properties or amount of the waste. Therefore, the effect of S/CH4 and O2/CH4 ratios on catalyst durability was confirmed by using actual biogas, which was produced by anaerobic fermentation of biomass at the biogasification bench-scale plant in Kyoto. Reforming reactions were carried out at ratios of S/CH4 = 0–4, O2/CH4 = 0.5 and at S/CH4 = 2, O2/CH4 = 0.6. The S/CH4 range of 0–2.0 and the O2/CH4 range of 0.5–0.6 had no effect on the catalyst durability and a S/CH4 ratio of more than 3.0 led to decreased catalytic performance.  相似文献   

4.
The study evaluates the effect of forced periodic cycling between methane dry reforming and carbon regeneration using a gasifying agent, such as carbon dioxide. The activity of Ce-promoted Ni–CO/Al2O3 catalyst was evaluated in a methane dry reforming process using a fixed-bed reactor under steady-state and periodic operation. Forced cycling reactions (reforming and regeneration) were conducted by manipulating the reactor feed between methane dry reforming and catalyst gasification using CO2 at cycle periods of 10, 20, and 30 min, and cycle splits of 0.8, 0.6, and 0.4. The physicochemical properties of fresh and spent catalysts were evaluated using several characterization techniques, such as the BET surface area, H2-chemisorption, and XRD. The results confirmed that methane dry reforming under periodic cycling provides an opportunity to improve methane conversion and increase the catalyst activity and longevity because of the periodic interruption of coke deposition. In particular, methane conversion deteriorated from 68% to 37% under steady-state within five hours of reforming, whereas a modest decrease in methane conversion (from 68% to 63% for a cycle period of 10 min and cycle split 0.8) was observed under periodic operation conditions. The results of catalyst characterization also demonstrated that the on-line removal of carbon during CO2 regeneration did not lead to any structural effect on the catalyst properties, and it absolutely restored the catalyst properties up to the values measured for the fresh catalyst.  相似文献   

5.
This paper presents detailed study of biogas reforming. Model biogas with different levels of H2S is subjected to reforming reaction over supported Ni catalyst in a fixed bed reactor at 700 °C and 800 °C. In order to understand the poisoning effects of H2S the reactions have been initially carried out without H2S in the feed stream. Three different H2S concentrations (20, 50 and 100 ppm) have been considered in the study. The H2O to CH4 ratio is maintained in such as way that CO2 also participates in the reforming reaction. After performing the poisoning studies, regeneration of the catalyst has been studied using three different techniques i) removal of H2S from the feed stream ii) temperature enhancement and iii) steam treatment. Poisoning at low temperature is not recoverable just by removal of H2S from the feed stream. However, poisoning at high temperature is easily reversed just by removal of H2S from the feed stream. Unlike some previous reports by Li et al. (2010) and Rostrup-nielsen (1971) [1,2], catalyst regeneration is achieved in shorter time frames for all the regeneration techniques attempted.  相似文献   

6.
The catalytic efficiency and bench scale time on steam stability of Ni dispersed on three commercially available catalytic supports (ZrO2, La2O3–ZrO2 and CeO2–ZrO2) has been studied for the dry reforming of methane (DRM) in the temperature range of 500–800 °C and a CH4/CO2 ratio equal to 1.5, simulating typical biogas quality. Ni supported on LaZr and CeZr carriers that obeyed enhanced basicity and oxygen ion lability values than Zr, exhibited superior catalytic efficiency and stability. A variety of techniques, namely N2 physisorption-desorption (BET method), powder X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, potentiometric titration and inductively coupled plasma emission spectroscopy (ICP), were applied for the characterization of particles morphology, textural, structural and other physical properties of the materials, as well as the type of carbon deposited on the catalytic surface after exposure to DRM reaction conditions. Post-reaction analysis of the deposited carbon on the catalysts surfaces showed that the prominent trend of the carbon deposits on the Ni/Zr and Ni/LaZr samples was to have a filamentous tube like morphology (graphite-2H). In contrast, on the Ni/CeZr used catalyst, the formation of small amount of carbon tube-like architectures was detected. The enhanced basicity and Ni dispersion of the Ni/LaZr and Ni/CeZr samples as well as the high oxygen ion lability of the lattice oxygen in the latter, were considered to be the major factors involved in the superior efficiency and durability of these samples in comparison to Ni/Zr sample.  相似文献   

7.
Biogas is a renewable resource obtained mainly from the anaerobic fermentation of agro-industrial and anthropogenic residues. The production of hydrogen by dry reforming of methane represents a potential application for this renewable energy carrier. This could play a positive contribution towards meeting the challenge of providing a global supply of energetically sustainable and environmentally friendly energy. This work combines a catalytic reaction, a separation and the catalyst regeneration in a single reactor. To this end, a two zone fluidized bed reactor (TZFBR) with hydrogen selective membranes has been employed (TZFBR + MB). The operating conditions for the process of dry reforming of biogas have been optimized experimentally, both in TZFBR and TZFBR + MB. Several catalysts were prepared (Ni/Al2O3, NiCe/Al2O3, NiCo/Al2O3), characterized and tested in reactions in both TZFBR and in TZFBR + MB. Finally, the influence of using oxygen or carbon dioxide as regenerating gases in the process has been studied. Experimental results show the feasibility of using CO2 for in situ catalyst regeneration, avoiding the potential problems associated with the use of O2.  相似文献   

8.
The activity of Ni-containing hydrotalcite-derived catalysts was assayed in the excess-methane dry reforming of different CH4-CO2 mixtures, aiming to simulate biogas upgrading to hydrogen and/or syngas. These catalysts yielded methane conversions quite far away from the thermodynamically predicted values, pointing to the inhibition of important methane consuming reactions, such as direct methane decomposition (DMD). Adding oxygen to the gas mixture (12.5%) results in increased methane conversions. Almost constant H2/CO ratios, around 1.5, were measured at any temperature (600–850 °C). However, solid carbon formation was found to take place to a higher extent. The intrinsic properties of the hydrotalcite-derived catalysts tested results in favored reverse water gas shift reaction, leading to CO2 and H2 conversion.  相似文献   

9.
An experimental and theoretical study for the biogas steam reforming reaction over 5%Ru/Al2O3 catalyst have been performed. An apparatus was constructed for the conduction of the experiments, the core of which was a tube reactor, filled with the catalyst in form of pellets. The inlet gas mixture consisted of CH4 and CO2 in various composition ratios as a model biogas and steam. A theoretical model of the process was developed. The experimental reactor was modelled as an isothermal pseudo homogeneous fixed bed reactor. Internal and external transport phenomena were neglected and appropriate effectiveness factors were employed instead. A physical properties model was used for the calculation of the physicochemical properties of the real mixture. Five reactant species, CH4, CO2, H2O, CO and H2, were included in the model, whereas the feed consisted of the first three. Steam reforming and water gas shift were the main reactions. Experimental results and theoretical predictions match closely, stability of the catalyst was assured and an optimal operational window was identified, at GHSV = 10,000–20,000 h−1, T = 700–800 °C, CH4/CO2 = 1.0–1.5 and H2O/CH4 = 3.0–5.0.  相似文献   

10.
Mesoporous nanocrystalline Mg1-xNixAl2O4 (x = 0.10, 0.13, 0.17 and 0.20) with large surface area were synthesized via a simple one-step sol-gel method using nonprecious metals. The prepared Mg1-xNixAl2O4 catalysts exhibit good catalytic performance towards methane and carbon dioxide dry reforming reaction. The catalysts were evaluated by various techniques, including XRD, BET, TPR, TPO, EPR, Chemisorption, SEM and TEM. All the Ni incorporated MgAl2O4 samples possessed high BET area (296–305 m2 g?1) and pore volume (0.47–0.56 cm3 g?1) with small pore size (6.4–7.4 nm) in meso region after calcination at 700 °C. The TPR results suggested strong interaction effect in NiMg and the reducibility property of the catalysts improved with the increase of nickel doping. Mg0.8Ni0.2Al2O4 exhibited the highest activity for biogas dry reforming with 72.6% CH4 and 80.7% CO2 conversion at 700 °C. Electron paramagnetic resonance (EPR) results indicated that the incorporation of Ni in MgAl2O4 spinel lattice led to the lattice distortion and formed oxygen vacancies which are a benefit for the dry reforming reaction.  相似文献   

11.
The influence of operating parameters over dry reforming of methane reaction was evaluated using a Ni-based catalyst obtained after calcination of a hydrotalcite-like precursor. The studied variables were mass to flow ratio (W/F), reaction temperature and CO2/CH4 ratio. Maximum methane and carbon dioxide conversions were achieved at W/F ratios above 0.21 g h L−1. The higher the W/F ratio was, the lower amount of water was formed, which led to a higher H2/CO ratio. The increase in reaction temperature produced an increase in conversions. Water concentration in the outlet stream showed a maximum at 600 °C. At this temperature, reverse water–gas-shift reaction (RWGS) was favoured because it is endothermic. However, steam reforming and carbon gasification were also favoured and they consumed great part of the water produced. CO2/CH4 ratios above 1 led to a higher CH4 conversion but selectivity to hydrogen decreased because RWGS reaction was favoured. When CO2/CH4 was below unity, CH4 conversion decreased but less amount of water was produced so a higher H2 selectivity was achieved. The catalyst exhibited good stability over dry reforming of methane under all the tested conditions, which may be ascribed to its high basicity. This property improved CO2 adsorption and then RWGS reaction and carbon gasification.  相似文献   

12.
This study reports the influence of biogas poisoning on a Ni based catalyst working under steam reforming conditions (atmospheric pressure, T = 1073 K and H2O/CH4 = 2 mol/mol). A biogas stream composed by CH4 and CO2 with a ratio 55/45 vol.%, added with different chemical species (H2S, hydrocarbons mixture and D5) as contaminants, was used as inlet gas stream.First, effect of poisoning on Ni catalyst were separately evaluated and the boundary concentrations for each contaminants were revealed (0.4 ppm, 200 ppm and 0.5 ppm for H2S, hydrocarbons and D5 respectively) to assure Ni stable performances on time on stream (100 h at 50,000 h?1 of GHSV). Successively, a comparison between Ni catalytic behaviors in presence of two combined poisoning in the biogas (H2S + Hydrocarbons and Hydrocarbons + D5) was carried out.It was found that the effect of combined poisoning, even though it considered in moderate concentration, is harmful for Ni catalyst activity. Methane conversion on time on stream was reduced from 86% to 40% after 50 h, when the couple of poisoning Hydrocarbons + D5 was added to the inlet gas stream, while a lower deactivation pattern (about 73%) was leaded by couple H2S + Hydrocarbons. Both poisoning mixtures promoted coke deposition on Ni catalyst surface (about ≥0.5 mgC/gcat·h) independently by poisoning chemical characteristics probably due to adsorption/deposition of contaminants on catalytic sites.  相似文献   

13.
Direct feeding of biogas to SOFC, which is derived from municipal organic wastes, has been investigated as a carbon-neutral renewable energy system. CH4/CO2 ratio in the actual biogas fluctuated between 1.4 and 1.9 indicating biogas composition is strongly affected by the kinds of organic wastes and the operational conditions of methane fermentation. Using anode-supported button cells, stable operation of biogas-fueled SOFC was achieved with the internal reforming mode at 800 °C. Cell voltage above 0.8 V was recorded over 800 h at 200 mA cm−2. It has been revealed that air addition to actual biogas reduced the risk of carbon formation and led to more stable operation without compromising cell voltage due to the lowering of anodic overvoltage.  相似文献   

14.
The paper aims to investigate the steam reforming of biogas in an industrial-scale reformer for hydrogen production. A non-isothermal one dimensional reactor model has been constituted by using mass, momentum and energy balances. The model equations have been solved using MATLAB software. The developed model has been validated with the available modeling studies on industrial steam reforming of methane as well as with the those on lab-scale steam reforming of biogas. It demonstrates excellent agreement with them. Effect of change in biogas compositions on the performance of industrial steam reformer has been investigated in terms of methane conversion, yields of hydrogen and carbon monoxide, product gas compositions, reactor temperature and total pressure. For this, compositions of biogas (CH4/CO2 = 40/60 to 80/20), S/C ratio, reformer feed temperature and heat flux have been varied. Preferable feed conditions to the reformer are total molar feed rate of 21 kmol/h, steam to methane ratio of 4.0, temperature of 973 K and pressure of 25 bar. Under these conditions, industrial reformer fed with biogas, provides methane conversion (93.08–85.65%) and hydrogen yield (1.02–2.28), that are close to thermodynamic equilibrium condition.  相似文献   

15.
Mathematical modeling and simulation analysis of the dimethyl ether steam reforming reaction system were carried out in the study. The numerical results of simulation and experiment were consistent. The effects of reaction conditions on the conversion of dimethyl ether and hydrogen production were analyzed. The internal structure of the reforming reactor was adjusted to obtain higher hydrogen production efficiency. The study established the reforming hydrogen production industry system, and analyzed the thermal efficiency of the system. The results show that when the temperature of the conversion bed is 673 K, the inlet flow rate of the mixture gas is 0.5 ms?1 and the ratio of water to ether is 3, the dimethyl ether steam reforming reaction system could obtain the dimethyl ether conversion rate of 90%, the hydrogen production rate of 88% and system thermal efficiency of 74%.  相似文献   

16.
The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH4/CO2 volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m2 g?1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H2 temperature-programmed reaction shows that NiO particles were reduced to metallic Ni0 phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH4 decomposition reaction. Both CH4 and CO2 conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO2 and CH4 partial pressure of 20 kPa. CH4 conversion improved with increasing CO2 partial pressure, PCO2 and exhibited an optimum at PCO2 of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO2 conversion was observed with growing PCO2. Additionally, CH4 and CO2 conversions decreased significantly with rising CH4 partial pressure because of increasing carbon formation rate via CH4 cracking in CH4-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement.  相似文献   

17.
Bio-ethanol is a prosperous renewable energy carrier mainly produced from biomass fermentation. Reforming of bio-ethanol provides a promising method for hydrogen production from renewable resources. Besides operating conditions, the use of catalysts plays a crucial role in hydrogen production through ethanol reforming. Rh and Ni are so far the best and the most commonly used catalysts for ethanol steam reforming towards hydrogen production. The selection of proper support for catalyst and the methods of catalyst preparation significantly affect the activity of catalysts. In terms of hydrogen production and long-term stability, MgO, ZnO, CeO2CeO2, and La2O3La2O3 are suitable supports for Rh and Ni due to their basic characteristics, which favor ethanol dehydrogenation but inhibit dehydration. As Rh and Ni are inactive for water gas shift reaction (WGSR), the development of bimetallic catalysts, alloy catalysts, and double-bed reactors is promising to enhance hydrogen production and long-term catalyst stability. Autothermal reforming of bio-ethanol has the advantages of lesser external heat input and long-term stability. Its overall efficiency needs to be further enhanced, as part of the ethanol feedstock is used to provide low-grade thermal energy. Development of millisecond-contact time reactor provides a low-cost and effective way to reform bio-ethanol and hydrocarbons for fuel upgrading. Despite its early R&D stage, bio-ethanol reforming for hydrogen production shows promises for its future fuel cell applications.  相似文献   

18.
Dry reforming of methane with carbon dioxide was investigated using oil palm shell activated carbon (OPS-AC) supported cobalt catalyst. The cobalt loaded OPS-AC catalysts were prepared by wet-impregnation method and characterized using SEM, FESEM, BET, TPR and TPD. Surface morphology of OPS-AC supported cobalt catalysts exhibited higher porosity, surface area and micropore volume with different densities of cobalt particles and support. Furthermore, greater amount of H2 chemisorbed and acidity were observed with increasing cobalt contents. Response surface methodology (RSM) was employed to design the experiments based on factorial central composite design. Catalytic testing was performed using a micro reactor system by varying four variables: temperature, gauge pressure, CH4/ CO2 ratio and gas hourly specific velocity (GHSV). H2 and CO yields were analyzed and quantified by gas chromatography with thermal conductivity detector (TCD). Both responses (H2 and CO) yields were optimized simultaneously using desirability function analysis. Reaction temperature was the most influential variable with high desirability prevalent for both responses. The optimum response values of H2 and CO yields corresponded to 903 °C, 0.88 bar(g), CH4/ CO2 = 1.31 and GHSV = 4,488 mL/h.g-catalyst.  相似文献   

19.
Catalytic dry reforming of biogas for hydrogen enrichment was studied over cerium oxide promoted nickel catalysts supported on titanium dioxide and aluminium oxide. The catalysts were prepared by wet impregnation method and characterized by H2-TPR, XRD, BET and FESEM techniques. Their catalytic performance in the biogas dry reforming reaction was studied at temperature ranges from 650 to 850 °C, with a CH4/CO2 ratio of 1.5:1. The H2-TPR results revealed that 11 wt % Ni impregnation on TiO2 support makes the catalyst with strong metal-support interaction which moderates the metal sintering. Also, the addition of CeO2 effectively improved the CH4 and CO2 conversions as well as H2 enrichment. At 850 °C, 11 wt % Ni/TiO2 catalyst leads to 70.5% CH4 conversion with 32.0% H2 enrichment, whereas, Ni0·11/Ce0.20 (Al2O3TiO2) yielded high CH4 conversion (84.9%) with 40.6% of H2 enrichment. No significant change in the activity of the catalyst was observed with 8.8 wt % of carbon deposited on the Ni0·11/Ce0.20 (Al2O3TiO2) catalyst, after 7 h of continuous reforming. Moreover, under combined (dry and oxidative) reforming of biogas, the stoichiometric H2/CO ratio (1.2) was observed at 0.47 O2/CH4 ratios with negligible carbon deposition. Thus, Ni0·11/Ce0.20 (Al2O3TiO2) catalyst exhibited better activity and selectivity with high catalyst stability at 850 °C.  相似文献   

20.
The performance of a tubular Ni/YSZ anode supported SOFC directly fed by an anaerobic digestion simulated biogas, with an extra addition of carbon dioxide to operate in conservative operating conditions to avoid coking on the anode support, was investigated. The fuel cell has been tested at a fixed oven temperature of 800 °C and under biogas/CO2 mixtures with different volumetric ratios, fuel utilization (FU) and current densities. Polarization curves and performance maps were obtained to better understand the influence of the investigated operational parameters on the cell behavior. Furthermore, since the tubular geometry enables an easy separation of the anode and cathode exhaust gases, the anode off-gas has been collected and monitored through a gas-chromatograph under open circuit voltage to investigate on the catalytic behavior of a Ni-based state-of-the-art anode. For corresponding operative conditions, performances of the cell for biogas/CO2 1/1.5 (i.e. CH4/CO2 30/70) and 1/2 (i.e. CH4/CO2 24/76) were at least 2% and 4% lower than the case 1/1 (i.e. CH4/CO2 20/80), respectively. The highest efficiency of 43.4% was reached at 17.5 A and FU = 70%.  相似文献   

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