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1.
Overall chemical kinetics model for partial oxidation of methane in inert porous media 总被引:1,自引:0,他引:1
K.V. Dobrego N.N. Gnesdilov S.H. Lee H.K. Choi 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,144(1):79-87
An overall three-step six-component chemical kinetics model which includes CH4 + O2 → CO + H2O + H2 and reversible 2CO + O2 ←→ 2CO2 and CH4 + H2O ←→ CO + 3H2 reactions is elaborated for the simulation of partial oxidation of methane in inert porous media. Procedure of the model adjusting to the experimental data is described. Kinetic parameters of the model are derived on the basis of temperature–flow rate, H2 and CO output concentration–flow rate and temperature–pressure experimental correlations. It is found that extremely slow solid body temperature growth with flow rate Ts,max(G) reported in the works on partial oxidation of methane (and other hydrocarbons) in inert porous media may be reproduced by the model. The model is designed for optimization, scale up and design assistance of the reactors of partial oxidation of methane.It is demonstrated that the overall chemical kinetics model can be combined with detailed gas-phase kinetics model for the investigation of detailed composition of syngas and intermediary components. 相似文献
2.
S. Barama C. Dupeyrat-Batiot M. Capron E. Bordes-Richard O. Bakhti-Mohammedi 《Catalysis Today》2009,141(3-4):385
A natural Maghnia clay was pillared by Al13 and impregnated by 3–10 wt.% Me (Me = Rh, Ni, Pd, Ce) to be used as catalysts in the reforming of methane with carbon dioxide to synthesis gas. The structural and textural properties of materials calcined at 450 °C were determined by several techniques (XRD, FT-IR, 27Al magic angle spinning (MAS) NMR, X-ray photoelectron spectroscopy (XPS), BET, thermogravimetric analysis (TGA)–DSC, H2-temperature programmed reduction (TPR) and NH3-TPR). Although impurities are present in the Al-pillared layered clay (PILC) support, most properties are close to those of pure Al-pillared Na-montmorillonite. Impregnation and calcination leads to the plugging of most micropores by clusters or microparticles of oxides. The NMR resonances of AlVI and AlIV specie are not modified after impregnation, and AlVI/AlIV ratio only varies on loading when compared to Al-PILC. Catalytic experiments show that the most active catalyst is 3% Rh/Al-PILC on which 88 mol.% of methane is converted at 650 °C with a minimum amount of carbon deposit. The conversions decrease along the 3% Rh ≈ 10% Ni > 3% Pd > 3% Ni > 3% Ce series. The H2/CO ratio amounts to 1.1 with Rh and to 0.85 with Pd which are metallic at the temperature of reaction, but it has a lower value with Ni and Ce due to the RWGS reaction known to proceed in the presence of oxides. 相似文献
3.
Qing Miao Guoxing Xiong Xinsheng Li Shishan Sheng Xiexian Guo 《Catalysis Letters》1996,36(3-4):165-169
The reactions of dry (CO2) reforming and partial oxidation of methane have been investigated in a membrane reactor. The membrane is composed of a dense thin silica (SiO2) film supported on porous Vycor tubes and was synthesized by chemical vapor deposition. The hydrogen permeance of the membrane was 0.2–0.3 cm3/(cm2 min atm) at 600°C combined with a H2/N2 selectivity of 200–300. Significant increases in methane conversion were attained in both reactions at 500–750°C, albeit at very low space velocities. The membrane permeance declined by 50% after exposure to feeds containing H2O, but otherwise exhibited excellent stability under reaction conditions. 相似文献
4.
The oxy-CO2 methane reforming reaction (OCRM) has been investigated over CoOx supported on a MgO precoated highly macroporous silica–alumina catalyst carrier (SA-5205) at different reaction temperatures (700–900 °C), O2/CH4 ratios (0.3–0.45) and space velocites (20,000–100,000 cc/g/h). The reaction temperature had a profound influence on the OCRM performance over the CoO/MgO/SA-5205 catalyst; the methane conversion, CO2 conversion and H2 selectivity increased while the H2/CO ratio decreased markedly with increasing reaction temperature. While the O2/CH4 ratio did not strongly affect the CH4 and CO2 conversion and H2 selectivity, it had an intense influence on the H2/CO ratio. The CH4 and CO2 conversion and the H2 selectivity decreased while the H2/CO increased with increasing space velocity. The O2/CH4 ratio and the reaction temperature could be used to manipulate the heat of the reaction for the OCRM process. Depending on the O2/CH4 ratio and temperature the OCRM process could be operated in a mildly exothermic, thermal neutral or mildly endothermic mode. The OCRM reaction became almost thermoneutral at an OCRM reaction temperature of 850 °C, O2/CH4 ratio of 0.45 and space velocity of 46,000 cc/g/h. The CH4 conversion and H2 selectivity over the CoO/MgO/SA-5205 catalyst corresponding to thermoneutral conditions were excellent: 95% and 97%, respectively with a H2/CO ratio of 1.8. 相似文献
5.
Manfred Nacken Lina Ma Steffen Heidenreich Gino V. Baron 《Applied catalysis. B, Environmental》2009,88(3-4):292-298
Silicon carbide-based filter elements were catalytically activated to provide filter elements for catalytic tar removal from biomass-derived syngas. The filter element support was coated with CeO2, CaO–Al2O3 and MgO with a specific surface of 7.4, 15.9 and 21.9 m2/g synthesized by exo-templating with activated carbon. Doping of a MgO coated filter element with 60 wt% NiO has led to an increase of the specific surface from 0.15 to 0.21 m2/g, whereas in case of a MgO–Al2O3 coated filter element a decrease from 1.18 to 0.91 m2/g was found. An increase of the NiO loading from 6 to 60 wt% on a MgO coated filter element resulted in an increase of the naphthalene conversion from 91 to 100% at 800 °C and a face velocity of 2.5 cm/s at a naphthalene concentration of 5 g/Nm3 in model biomass gasification gas. In case of a MgO–Al2O3 coated filter element with 60 wt% NiO in addition to complete naphthalene conversion in the absence of H2S, a higher conversion of 66% was found in the presence of 100 ppmv H2S compared to 49% of the MgO–NiO coated filter element. After scaling up of the catalytic activation procedure to a 1520 mm long filter candle, which shows an acceptable differential pressure of 54.9 mbar, 58 and 97% naphthalene conversion was achieved in the presence and absence of H2S, respectively. The calculated WHSV value of 209.6 Nm3 h−1 kg−1 indicates the technical feasibility of a further increase of the catalytic performance by an increase of the NiO loading. 相似文献
6.
Khampol Sirichaiprasert Sangobtip Pongstabodee Apanee Luengnaruemitchai 《Journal of the Chinese Institute of Chemical Engineers》2008,39(6):597-607
Single- and double-stage catalytic preferential CO oxidation (CO-PrOx) over-Fe2O3-promoted CuO–CeO2 in a H2-rich stream has been investigated in this work. The catalyst was prepared by the urea-nitrate combustion method and was characterized by X-ray diffractometer (XRD), X-ray fluorescence (XRF), Brunauer–Emmet–Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM). The catalytic activity tests were carried out in the temperature range of 50–225 °C under atmospheric pressure. The results of the single-stage reaction indicated that complete CO oxidation was obtained when operating at a O2/CO ratio of 1.5, W/F ratio of 0.36 g s/cm3, and at a reaction temperature of 175 °C. At these conditions, H2 consumption in the oxidation was estimated at 58.4%. Applying the same conditions to the double-stage reaction, complete CO oxidation was found and H2 consumption in the oxidation was reduced about 4.9%. When decreasing the double-stage reaction temperature to 150 °C, the results elucidated that CO could be converted to CO2 completely while H2 consumption in the oxidation was further reduced to 33.5%. A temperature blocking 22 factorial design has been used to describe the importance of the factors influencing the catalytic activity. The factorial design was according to the experimental results. When adding CO2 and H2O in feed, reduction of CO conversion for single- and double-stage reaction is obtained due to a blocking of CO2 and H2O at a catalytic active site. Comparing CO conversion obtained when operating with/without CO2 and H2O in feed for single- and double-stage reaction, less reduction is achieved when operating in double-stage reaction. 相似文献
7.
Selective methanation of CO over supported Ru catalysts 总被引:1,自引:0,他引:1
Paraskevi Panagiotopoulou Dimitris I. Kondarides Xenophon. E. Verykios 《Applied catalysis. B, Environmental》2009,88(3-4):470-478
The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO2 has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al2O3, TiO2, YSZ, CeO2 and SiO2). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H2 15% CO2 and 0–30% H2O (balance He). It has been found that, for all catalysts investigated, conversion of CO2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO2 methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO2 hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO2 catalysts, TOFs of both CO (at 215 °C) and CO2 (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al2O3. Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO2, compared to YSZ or SiO2, whereas CeO2- and Al2O3-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO2 catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO2 conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO2 catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications. 相似文献
8.
Ta-Jen Huang Meng-Chin Huang 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2009,155(1-2):333-338
A solid oxide fuel cell (SOFC) with a Ni-yttria-stabilized zirconia anode of 1 cm2 area was set up with a porous disk of gadolinia-doped ceria-impregnated FeCr as a gas diffusion layer (GDL) under direct-methane feeding. In this setup of SOFC plus GDL, the tests at 800 °C and ambient pressure show that the current density, the methane conversion rate, the product formation rates, and the CO2 selectivity increased with increasing methane concentration. The major reaction in the GDL is CO2 reforming of methane to produce the syngas (CO plus H2). The anodic electrochemical oxidation of CO from GDL results in an overall rate of CO2 formation being much larger than that of CO formation. There is a synergy between the rate of reaction in the GDL and that over the anode. 相似文献
9.
Plasma catalytic methane conversion was carried out in the presence of sol–gel derived Ru/TiO2 catalysts within a dielectric-barrier discharge (DBD) reactor. Plasma-assisted reduction (PAR) was applied to reduce the prepared Ru/TiO2 catalysts in DBD reactor, and most of the catalysts were successively reduced by PAR within 15 min. The highest methane conversion was obtained when 5 wt% Ru/TiO2 catalysts were used after calcination at 400 °C. The selectivities of light alkanes (C2H6, C3H8, C4H10) were highly increased when Ru/TiO2 catalysts were used in DBD reactor. 相似文献
10.
The rate of Fischer–Tropsch synthesis over an industrial well-characterized Co–Ru/γ-Al2O3 catalyst was studied in a laboratory well mixed, continuous flow, slurry reactor under the conditions relevant to industrial operations as follows: temperature of 200–240 °C, pressure of 20–35 bar, H2/CO feed ratio of 1.0–2.5, gas hourly space velocity of 500–1500 N cm3 gcat− 1 h− 1 and conversions of 10–84% of carbon monoxide and 13–89% of hydrogen. The ranges of partial pressures of CO and H2 have been chosen as 5–15 and 10–25 bar respectively. Five kinetic models are considered: one empirical power law model and four variations of the Langmuir–Hinshelwood–Hougen–Watson representation. All models considered incorporate a strong inhibition due to CO adsorption. The data of this study are fitted fairly well by a simple LHHW form − RH2 + CO = apH20.988pCO0.508 / (1 + bpCO0.508)2 in comparison to fits of the same data by several other representative LHHW rate forms proposed in other works. The apparent activation energy was 94–103 kJ/mol. Kinetic parameters are determined using the genetic algorithm approach (GA), followed by the Levenberg–Marquardt (LM) method to make refined optimization, and are validated by means of statistical analysis. Also, the performance of the catalyst for Fischer–Tropsch synthesis and the hydrocarbon product distributions were investigated under different reaction conditions. 相似文献
11.
A microchannel catalytic reactor with improved heat and mass transport has been used for Fischer–Tropsch synthesis. It was demonstrated that this microchannel reactor based process can be carried out at gas hourly space velocity (GHSV) as high as 60,000 h−1 to achieve greater than 60% of single-pass CO conversion while maintaining relatively low methane selectivity (<10%) and high chain growth probability (>0.9). In this study, performance data were obtained over a wide range of pressure (10–35 atm) and hydrogen-to-carbon monoxide ratio (1–2.5). The catalytic materials were characterized using BET, scanning electron microcopy (SEM), transmission electron microcopy (TEM), and H2 chemisorption. A three-dimensional pseudo-homogeneous model was used to simulate temperature profiles in the exothermic reaction system in order to optimize the reactor design. Intraparticle non-isothermal characteristics are also analyzed for the FT synthesis catalyst. 相似文献
12.
Jesús lvarez-Rodríguez Inmaculada Rodríguez-Ramos Antonio Guerrero-Ruiz Adolfo Arcoya 《Applied Catalysis A: General》2009,366(1):114-121
Several 2 wt.% Ru/KL supported catalysts were prepared by various methods with different ruthenium precursors and characterized by CO and H2 chemisorption, N2 adsorption, TPD of NH3, TEM and XPS. Furthermore, CO chemisorbed species have been studied by FT-IR and microcalorimetry. Characterization measurements of catalyst IWI-Ru, prepared by incipient wetness impregnation from ruthenium acetylacetonate, evidence metal nanoparticles of 1 nm placed inside the zeolite channels, thus blocking the accessibility to part of ruthenium loading inside the micropores. Catalyst prepared by treating the KL zeolite with RuCl3·xH2O aqueous solution (I-Ru) exhibits nanoparticles in the range 6–8 nm at the external surface and clusters smaller that 1 nm, inside the micropores. These latter do not significantly affect the diffusion of probe molecules through the channels. Catalytic performances in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa, show that IWI-Ru is less active than I-Ru, but more selective towards unsaturated alcohols. Furthermore, for IWI-Ru, selectivity increases with the increasing conversion. On the other hand, removal of acid sites of the I-Ru catalyst enhances the hydrogenation activity and increases the selectivity towards citronellal. All these results are analyzed and discussed in terms of the size, shape and location of ruthenium particles in the catalysts, as well as of the metal–support interaction. 相似文献
13.
《Carbon》2014
A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500 m2/g) and pore volumes (0.80–1.56 cm3/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9 nm, but some have a second set of micropores (1.3–1.4 nm pore size), further broadened to 1.9–2.1 nm as a result of increasing either the activation temperature to 750 °C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H2 uptake of up to 2.4 wt% at 1 bar and −196 °C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35 bar), the saturated H2 uptake reaches 4.2–4.7 wt% at −196 °C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H2 on-board storage media. 相似文献
14.
Pedro Castao Ana G. Gayubo Barbara Pawelec Jos Luis G. Fierro Jos Maria Arandes 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,140(1-3):287-295
A kinetic model is proposed in order to quantify product distribution in the ring-opening (using high hydrogen concentration in the reaction medium) of methylcyclohexane (MCH) over a catalyst based on HZSM-5 zeolite. The model is based on a reaction scheme proposed by Cerqueira et al. for methylcyclohexane cracking at atmospheric pressure, which has been modified in order to include the effect of hydrogen over the individual reaction steps. The experimental results used for estimating the kinetic constant were obtained in a fixed bed isothermal reactor in a wide range of conditions, i.e. 250–450 °C; WHSV = 0.5–10.5 h−1 (τ = 0.095–2 gcat h gMCH−1); pressure = 5–80 bar; H2/MCH molar flow ratio = 4–79; conversion = 0–100%. The kinetic model proposed can be regarded as a basis for the proposal of models for ring-opening reactions of more complex naphthenic feedstock from a prior hydrogenation step involving aromatic refinery streams of secondary interest. 相似文献
15.
Valerio Choque Narcís Homs Renata Cicha-Szot Pilar Ramírez de la Piscina 《Catalysis Today》2009,142(3-4):308
Ru-based catalysts supported on Ta2O5–ZrO2 and Nb2O5–ZrO2 are studied in the partial oxidation of methane at 673–873 K. Supports with different Ta2O5 or Nb2O5 content were prepared by a sol–gel method, and RuCl3 and RuNO(NO3)3 were used as precursors to prepare the catalysts (ca. 2 wt.% Ru). At 673 K high selectivity to CO2 was found. An increase of temperature up to 773 K produced an increase in the selectivity to syngas (H2/CO = 2.2–3.1), and this is related with the transformation of RuO2 to metallic Ru as was determined from XRD and XPS results. At 873 K and with co-fed CO2 an increase of the catalytic activity and CO selectivity was found. A TOF value of 5.7 s−1 and H2/CO ratio ca. 1 was achieved over Ru(Cl)/6TaZr. Catalytic results are discussed as a function of the support composition and characteristics of Ru-based phases. 相似文献
16.
Yihang Guo Kexin Li Xiaodan Yu James H. Clark 《Applied catalysis. B, Environmental》2008,81(3-4):182-191
Mesoporous H3PW12O40-silica composite catalysts with controllable H3PW12O40 loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H3PW12O40 loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0 m2 g−1), larger and well-distributed pore size (6.1–8.6 nm), larger pore volume (0.75–1.2 cm3 g−1), and highly dispersed Keggin unit throughout the materials. Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites. As a novel kind of reusable solid acid catalyst, as-prepared H3PW12O40-silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed. 相似文献
17.
Results from a single grain activated carbon adsorption study indicate that the effective diffusion coefficient was from 0.65×10−6 to 7.4×10−6 cm2/s for H2S in the concentration range of 20–300 ppmv at 23 °C for both virgin activated carbon (FAC) and impregnated-regenerative activated carbon (IRAC). The effective diffusivity of the IRAC was nearly two times the FAC for H2S adsorption. The surface reaction of H2S-impregnated regenerative activated carbon was faster than that of H2S and virgin activated carbon. The single grain activated carbon kinetic curve and a time scale conversion method were used to predict the breakthrough curve and the adsorption capacity of the column adsorption system. The single grain activated carbon adsorption system measured the breakthrough curve more efficiently than column adsorption. The prediction error was between 10 and 30%. Improvement can be further achieved by enhanced experimental approaches. It has a great potential for scale-up. 相似文献
18.
Pt–W and Pt–Mo based catalysts were evaluated for methane combustion using a sandwich-type microreactor. Alumina washcoated microchannels were impregnated with platinum in combination with and promoted with tungsten and molybdenum and compared with commercially available Pt/Al2O3 catalysts. Catalysts were tested in the range of 300–700 °C with flow rates adjusted to GHSV of 74,000 h−1 and WHSV of 316 L h−1 g−1. Catalysts containing tungsten were found to be the most active and the most stable possibly due to a metal interaction effect. A Pt–W/γ-Al2O3 containing 4.6 wt% Pt and 9 wt% W displayed the highest activity with full conversion at 600 °C and a selectivity to CO2 of 99%. 相似文献
19.
Feifei Zhang Hua Shang Bolun Zhai Xiaomin Li Yingying Zhang Xiaoqing Wang Jinping Li Jiangfeng Yang 《American Institute of Chemical Engineers》2023,69(6):e18079
A robust aluminum-based metal–organic framework (Al-MOF) MIL-120Al with 1D rhombic ultra-microporous was reported. The nonpolar porous walls composed of para-benzene rings with a comparable pore size to the kinetic diameter of methane allow it to exhibit a novel thermodynamic-kinetic synergistic separation of CH4/N2 mixtures. The CH4 adsorption capacity was as high as 33.7 cm3/g (298 K, 1 bar), which is the highest uptake value among the Al-MOFs reported to date. The diffusion rates of CH4 were faster than N2 in this structure as confirmed by time-dependent kinetic adsorption profiles. Breakthrough experiments confirm that this MOF can completely separate the CH4/N2 mixture and the separation performance is not affected in the presence of H2O. Theoretical calculations reveal that pore centers with more energetically-favorable binding sites for CH4 than N2. The results of pressure swing adsorption (PSA) simulations indicate that MIL-120Al is a potential candidate for selective capture coal-mine methane. 相似文献
20.
“Pd nanopore” composite membranes are a novel class of H2 permselective membranes in which a thin layer of Pd is grown within the pores of a supported nanoporous layer. In this work, Pd nanopore membranes and conventional Pd top-layer membranes were used in the generation of high-purity H2 from the catalytic decomposition of anhydrous NH3. An effective 4 μm thick Pd nanopore membrane and 13 μm thick Pd top-layer membrane were synthesized on 2 mm O.D. α-Al2O3 hollow fibers. The permeation features of the membranes were determined and the membranes were then employed in a single fiber packed-bed membrane reactor in which Ni-catalyzed NH3 decomposition served as the test reaction, with conditions spanning a range of conditions (500–600 °C; 3–5 bar total retentate pressure; 60–1200 scc/h g cat space velocity). The NH3 conversions in both the PBMRs were approximately 10% higher than in a packed-bed reactor (PBR) under similar conditions. The increase in conversion with the PBMR was attributed to the removal of H2, which has an inhibitory effect on the forward kinetics of the reaction as per the Temkin-Pyzhev type rate mechanism. Reactor productivities in the range of 2 mol/s m3 (at 85% H2 utilization) to 7 mol/s m3 (at 50% H2 utilization) were obtained. The permeate stream purity exceeded 99.2% H2. A two-dimensional pseudo-homogeneous model was successfully used to simulate the experimental results and to interpret the findings. Permeation and kinetic parameters were estimated in permeation and PBR experiments, respectively. Without any data fitting the PBMR model predictions demonstrated very good agreement with experimental trends. Together with an analysis of the characteristic times, the model determined that transverse transport of hydrogen in the catalyst bed limited PBMR performance. The model was used to determine the rate limiting step and to suggest ways in which the reactor productivities could be further improved. 相似文献