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1.
The oxidative coupling of methane to higher hydrocarbons (C2+) was studied in a bubbling fluidized bed reactor between 700°C and 820°C, and with partial pressures of methane from 40 to 70 kPa and of oxygen from 2 to 20 kPa; the total pressure was ca 100 kPa. CaO, Na2CO3/CaO and PbO/γ-Al2O3 were used as catalytic materials. C2+ selectivity depends markedly on temperature and oxygen partial pressure. The optimum temperature for maximizing C2+ selectivity varies between 720 and 800°C depending on the catalyst. Maximum C2+ selectivities were achieved at low oxygen and high methane partial pressures and amounted to 46% for CaO (T = 780°C; PCH4 = 70 kPa; PO2 = 5 kPa), 53% for Na2CO3/CaO (T = 760°C; PCH4 = 60 kPa; PO2 = 6 kPa) and 70% for PbO/γ-Al2O3 (T = 720°C; PCH4 = 60 kPa; PO2 = 5 kPa). Maximum yields were obtained at low methane-to-oxygen ratios; they amounted to 4.5% for CaO (T = 800°C; PCH4 = 70 kPa; PO2 = 12 kPa), 8.8% for Na2CO3/CaO (T = 820°C; PCH4 = 60 kPa; PO2 = 20 kPa) and 11.3% for PbO/γ-Al2O3 (T 2= 800°C; PCH4 = 60 kPa; PO2 = 20 kPa). 相似文献
2.
Thermodynamic analyses of the reforming of coke oven gas with gasification gas for syngas were investigated as a function of coke oven gas‐to‐gasification gas ratio (1–3), oxygen‐to‐methane ratio (0–1.56), pressure (25–35 bar) and temperature (700–1100 °C). Thermodynamic equilibrium results indicate that the operating temperature should be approximately 1100 °C and the oxygen‐to‐methane ratio should be approximately 0.39, where about 80 % CH4 and CO2 can be converted at 30 bar. Increasing the operating pressure shifts the equilibrium toward the reactants (CH4 and CO2); increasing the pressure from 25 to 35 bar decreases the conversion of CO2 from 73.7 % to 67.8 %. The conversion ratio of CO2 is less than that in the absence of O2. For a constant feed gas composition (7 % O2, 31 % gasification gas, and 62 % coke oven gas), a H2/CO ratio of about 2 occurs at temperatures of 950 °C and above. Pressure effects on the H2/CO ratio are negligible for temperatures greater than 750 °C. The steam produced has an effect on the hydrogen selectivity, but its mole fraction decreases with temperature; trace amounts of other secondary products are observed. 相似文献
3.
Alfred A Susu Emmanuel O Ogogo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(4):694-705
A platinum/alumina catalyst was sintered in oxygen and hydrogen atmospheres using two metal loadings of the catalyst: 0.3% Pt and 0.6% Pt. After sintering, the aromatization selectivity was investigated with the reforming of n‐heptane as the model reaction at a temperature of 500 °C and a pressure of 391.8 kPa. The primary products of n‐heptane reforming on the fresh platinum catalysts were methane and toluene, with subsequent conversion of benzene from toluene demethylation. To induce sintering, the catalysts were treated with oxygen at a flow rate of 60 mL min?1, pressure of 195.9 kPa and temperatures between 500 and 800 °C. The 0.3% Pt/Al2O3 catalyst exhibited enhanced aromatization selectivity at various sintering temperatures while the 0.6% Pt/Al2O3 catalyst was inherently hydrogenolytic. The fact that aromatization was absent on the 0.6% Pt/Al2O3 catalyst was attributed to the presence of surface structures with dimensionality between two and three as opposed to essentially 2‐D structures on the 0.3% Pt/Al2O3 catalyst surface. On the 0.3% Pt/Al2O3 catalyst, the reaction product ranged from only toluene at a 500 °C sintering temperature to predominantly cracked product at a sintering temperature of 650 °C and no reaction at 800 °C. For sintering at about 650 °C, subsequent conversion of n‐heptane was complete and dropped thereafter. The turnover number was observed to change from 0.07 to 2.26 s?1 as the dispersion changed from 0.33 to 0.09. The Koros–Nowark (K–N) test was used to check for the presence of internal diffusional incursions and Boudart's criterion was used for structural sensitivity determination. The K–N test indicated the absence of diffusional resistances while n‐heptane reforming was found to be structure sensitive on the Pt/Al2O3 catalyst. Copyright © 2006 Society of Chemical Industry 相似文献
4.
In this study, La0.6Sr0.4Co0.8Ga0.2O3‐δ (LSCG) hollow fiber membrane reactor was integrated with Ni/LaAlO3‐Al2O3 catalyst for the catalytic partial oxidation of methane (POM) reaction. The process was successfully carried out in the medium temperature range (600–800°C) for reaction of blank POM with bare membrane, catalytic POM reaction and swept with H2:CO gas mixture. For the catalytic POM reaction, enhancement in selectivity to H2 and CO is obtained between 650–750°C when O2:CH4 <1. High CH4 conversion of 97% is achieved at 750°C with corresponding H2 and CO selectivity of about 74 and 91%. The oxygen flux of the membranes also increased with the increase in oxygen partial pressure gradient across the membrane. The postreacted membranes were tested via XRD and FESEM‐EDX for their crystallinity and surface morphology. XPS analysis was further used to investigate the O1s, Co 2p and Sr 3d binding energies of the segregated elements from the reducing reaction environment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3874–3885, 2013 相似文献
5.
The oxidation of sintered aluminium nitride samples having porosity of 12–16% has been studied at temperatures of 900–1100°C and 98.66 kPa oxygen pressure. It has been established that the reaction of AIN with oxygen obeys the parabolic law. The main products of AIN oxidation are α-Al2O3 and nitrogen with nitrogen oxides traces. The corresponding rate constants and apparent activation energy (61 kcal/mol) were calculated from the experimental data. It has been demonstrated that sintered aluminium nitride is resistant enough to high-temperature oxidation and can be used as a refractory material up to 1100°C. 相似文献
6.
《Journal of the European Ceramic Society》2002,22(4):579-583
Impedance spectroscopy is used to deconvolute the dc conductivity (σ) of undoped BaTiO3 ceramics (∼95% of the theoretical X-ray density) into bulk (σb) and grain boundary (σgb) components at two oxygen partial pressures, PO2 ∼10 Pa (N2) and ∼0.21 MPa (air). At 900°C, σ∼σb in both atmospheres, however, at lower temperatures Z1 plots are dominated by the grain boundary component and σ∼σgb. The temperature of the switch from σ∼σb to σ∼σgb is different in the two atmospheres and occurs at ∼850°C in air and ∼650°C in N2. Isothermal plots of log σb vs log PO2 in the temperature range 450–900°C show the expected oxygen partial pressure dependence with a gradient of +1/4. In contrast, σgb is relatively insensitive to PO2 and log σgb vs log PO2 plots have gradients < +1/4 with values as low as ∼+1/14.0. In general, isothermal log σ vs log pO2 plots have gradients <+1/4 as σ is dominated by the grain boundary component. This may explain the wide range of gradients (∼1/4–1/9) reported in the literature for isothermal dc conductivity measurements on polycrystalline BaTiO3 in the p-type regime. 相似文献
7.
The reaction rates for the hydrolysis of CS2 on either alumina (Kaiser 201) or titania (CRS 31) were measured at 150 kPa and from 270 to 330°C using a laboratory Berty reactor over ranges of water concentration (2–12 mol%) and CS2 concentration (0.5–2 mol%). Four mechanism-related model functions were tested in the search for the best-fitting rate function by using non-linear regression techniques. The results show that the Eley-Rideal rate function best-fitted the kinetics using either Kaiser 201 or CRS 31 with different parameters. The kinetic parameters obtained confirm that CRS 31 appears to have the higher activity of the two catalysts for CS2 hydrolysis. The strong adsorption of water vapor on each of the two catalysts studied inhibits the hydrolysis rate and affords an effective reaction order close to zero for H2O, possibly by saturating the catalysis surface and reducing the fraction of catalyst surface available for CS2 and COS adsorption. 相似文献
8.
Dendrimer encapsulated Pt nanoparticles were prepared by using hydroxyl terminated generation four (G4OH) PAMAM dendrimers (DEN) as the templating agents. The encapsulated Pt nanoparticles were dispersed on γ-Al2O3 at room temperature by impregnation. Pt/Al2O3 (DEN) catalysts were then subjected to thermal treatments in oxidizing and reducing atmospheres at different temperatures. These catalysts were characterized by Transmission Electron microscopy (TEM) and In situ Fourier-Transform Infrared (FTIR) spectroscopy. The TEM analysis of the as synthesized catalysts revealed that the Pt nanoparticles were found to be 2–4 nm in size. It is observed that the Pt particle size in 0.5% Pt/Al2O3 (DEN) catalyst increased upon thermal decomposition of the dendrimer. The in situ FTIR results suggested that the presence of oxygen and the Pt nanoparticles in the Pt-dendrimer nanocomposite accelerate the dendrimer decomposition at low temperatures. All the catalysts were tested for the reduction of NO x with CH4 in the temperature range of 250–500 °C. NO x reduction efficiency of Pt/Al2O3 (DEN) catalysts were compared with the Pt/Al2O3 (CON; conventional) catalyst. The conversion of NO x was started from the low temperatures over Pt/Al2O3 (DEN) catalysts. The high selectivity of NO x to N2 of 74% was obtained over 0.5% Pt/Al2O3 (DEN) catalyst at low temperatures around 350 °C. 相似文献
9.
The catalytic rate of decomposition of pure nitric oxide on platinum (2NO → N2 + O2) was measured employing the batch, hot-wire technique at wire temperatures in the range 900–1200°C and at total pressures from 400–2260 torr. Chemisorbed oxygen is known to inhibit the rate of this reaction but very little surface oxygen is present at these elevated temperatures and thus an effectively clean platinum surface was realized. Also the experiments were limited to low conversions and thus low oxygen partial pressures (PO2 → O2), again minimizing the likelihood of oxygen inhibition. A Rideal—Eley type rate expression: ?r (moles NO reached/cm2 . sec) = k2P2NO/(1 + K1PO2 + K2PNO) describes quite well the dependence of the measured rate of the NO partial pressure on PNO. In contrast the data are not fit well by a Langmuir—Hinshelwood type rate-expression, similar to that above except for a unimolecular term PNO in the numerator. Owing to the large values of PNO and low conversions used in the present study with PO2 → O, the study focused on the kinetics with respect to NO itself. For the above Rideal—Eley mechanism: k2 ? 4·63 × 10?4 exp (?8,600/RT) mol/cm2 . atm2 . sec and K2 ? 3 · 5 × 10?2 exp (11,300/RT) atm?1. 相似文献
10.
Mathieu Q. Brisebourg Francis Rebillat Francis Teyssandier 《Journal of the European Ceramic Society》2018,38(13):4309-4319
The kinetics of silica growth during passive oxidation of SiC was studied using an original interferometric method carried out in a reactor specifically designed for that purpose. The influence of various oxidant species, O2, H2O, CO2 as well as their mixtures was investigated in a high temperature domain ranging from 1550 °C to 1850 °C at atmospheric pressure. This method is an efficient way to measure the various oxidation regimes usually described by the Deal-Grove model. Both the linear and parabolic rate constants are found to be independent of gas phase composition above 1700 °C, and to increase with oxygen partial pressure below 1700?°C for PO2?>?20?kPa. In the parabolic growth regime, we observed a transition from a low temperature interstitial-dominant to a high temperature network-dominant oxygen transport in the silica scale. The present results suggest the existence of a similar transition in the linear growth regime. 相似文献
11.
《Carbon》2014
Relevant carbon-based materials, home-made carbon–silica hybrids, commercial activated carbon, and nanostructured multi-walled carbon nanotubes (MWCNT) were tested in the oxidative dehydrogenation of ethylbenzene (EB). Special attention was given to the reaction conditions, using a relatively concentrated EB feed (10 vol.% EB), and limited excess of O2 (O2:EB = 0.6) in order to work at full oxygen conversion and consequently avoid O2 in the downstream processing and recycle streams. The temperature was varied between 425 and 475 °C, that is about 150–200 °C lower than that of the commercial steam dehydrogenation process. The stability was evaluated from runs of 60 h time on stream. Under the applied reactions conditions, all the carbon-based materials are apparently stable in the first 15 h time on stream. The effect of the gasification/burning was significantly visible only after this period where most of them fully decomposes. The carbon of the hybrids decomposes completely rendering the silica matrix and the activated carbon bed is fully consumed. Nano structured MWCNT is the most stable; the structure resists the demanding reaction conditions showing an EB conversion of ∼30% (but deactivating) with a steady selectivity of ∼80%. The catalyst stability under the ODH reaction conditions is predicted from the combustion apparent activation energies. 相似文献
12.
Jun He Guan-Qun Xie Ji-Qing Lu Lin Qian Xue-Liang Zhang Ping Fang Zhi-Ying Pu Meng-Fei Luo 《Journal of Catalysis》2008,253(1):1-10
A series of CrOx–Y2O3 catalysts were prepared by a deposition–precipitation method and tested for the fluorination of 2-chloro-1,1,1-trifluoroethane (CF3CH2Cl) to synthesize 1,1,1,2-tetrafluoroethane (CF3CH2F). The highest activity was obtained on a pre-fluorinated catalyst calcined at 400 °C, with 19% of CF3CH2Cl conversion at 320 °C. The effect of the calcination temperature on the CrOx species was investigated. X-ray diffraction and Raman results indicated that the CrOx species (Cr(VI)) were well dispersed on the catalyst surface when the catalyst was calcined at 400 °C. With increasing calcination temperature, most of the CrOx species changed from high oxidation state Cr(VI) to low oxidation state Cr(V) or Cr(III) species, which resulted in difficulty in pre-fluorination of the catalyst. It was also found that the CrFx, CrOxFy or Cr(OH)xFy phases originated from high oxidation state Cr(VI) species were the active sites for the fluorination reaction. 相似文献
13.
The partial oxidation of CH3OH to CO2 and H2 over a Cu/ZnO/Al2O3 catalyst has been studied by temperature-programmed oxidation (TPO) using N2O and O2 as the oxidant. Post-reaction analysis of the adsorbate composition of the surface of the catalyst was determined by temperature-programmed desorption (TPD). The temperature dependence of the composition of the mixture of products formed by TPO was shown to depend critically on the partial pressure of the oxidant, with the highest partial pressure of oxygen used (10% O2 in He, 101 kPa—the CH3OH partial pressure was 17% throughout), producing marked non-Arrhenius fluctuations on temperature programming. Unsurprisingly, therefore, the adsorbate composition of the catalyst revealed by post-reaction TPD was also found to be determined by the partial pressure of the oxidant. Using high partial pressures of oxidant (5% and 10% O2 in He, 101 kPa), the only adsorbate detected was the bidentate formate species adsorbed on Cu. Lowering the oxygen partial pressure to 2% in He (101 kPa) revealed a catalyst surface on which the bidentate formate on Cu was the dominant intermediate with the formate on Al2O3 also being present. A further lowering of the partial pressure of the oxidant, obtained by using N2O as the oxidant (2% N2O in He, 101 kPa), resulted in a surface on which the formate adsorbed on ZnO was the dominant adsorbate with only a small coverage of the Cu by the bidentate formate. 相似文献
14.
《Fuel》2006,85(5-6):736-747
The feasibility of using NiO as an oxygen carrier during chemical-looping combustion has been investigated. A thermodynamic analysis with CH4 as fuel showed that the yield of CH4 to CO2 and H2O was between 97.7 and 99.8% in the temperature range 700–1200 °C, with the yield decreasing as the temperature increases. Carbon deposition is not expected as long as sufficient metal oxide is supplied to the fuel reactor. Hydrogen sulfide, H2S, in the fuel gas will be converted partially to SO2 in the gas phase, with the degree of conversion increasing with temperature, but decreasing as a function of pressure. There is the possibility of sulfide formation as Ni3S2 at higher partial pressures of H2S+SO2 in the reactor. The reactivity of freeze granulated particles of NiO with NiAl2O4, MgAl2O4, TiO2 and ZrO2 sintered at different temperatures was investigated in a small fluidized bed reactor by exposing them cyclically to 50% CH4/50% H2O and 5% O2 at 950 °C. During the reducing period, the NiO initially reacted with the CH4 to form CO2 and H2O. However, there were always minor amounts of CO from the outlet of the reactor even at high concentrations of CO2, which was due to the thermodynamic limitations. Here, the ratio CO/(CO2+CO+CH4) was between 1.5 and 2.5% at 950 °C for the oxygen carriers with alumina based inert. A small amount of CH4 was released from the reactor at high degrees of oxidation of the NiAl2O4 and MgAl2O4-based carriers. As the time under reducing conditions increased, steam reforming of CH4 to CO and H2 became considerable, with Ni catalyzing this reaction. Whereas the ZrO2 particles showed similar behavior as the alumina-based carriers, the TiO2-based particles showed a markedly different reaction behavior, likely due to the complex interaction between NiO and TiO2. 相似文献
15.
Meng Shi Jihong Kim James A. Sawada Jade Lam Somayeh Sarabadan Tetyana M. Kuznicki Steven M. Kuznicki 《American Institute of Chemical Engineers》2013,59(3):982-987
The purification of different components of air, such as oxygen, nitrogen, and argon, is an important industrial process. Pressure swing adsorption (PSA) is surpassing the traditional cryogenic distillation for many air separation applications, because of its lower energy consumption. Unfortunately, the oxygen product purity in an industrial PSA process is typically limited to 95% due to the presence of argon which always shows the same adsorption equilibrium properties as oxygen on most molecular sieves. Recent work investigating the adsorption of nitrogen, oxygen and argon on the surface of silver‐exchanged Engelhard Titanosilicate‐10 (ETS‐10), indicates that this molecular sieve is promising as an adsorbent capable of producing high‐purity oxygen. High‐purity oxygen (99.7+%) was generated using a bed of Ag‐ETS‐10 granules to separate air (78% N2, 21% O2, 1% Ar) at 25°C and 100 kPa, with an O2 recovery rate greater than 30%. © 2012 American Institute of Chemical Engineers AIChE J, 59: 982–987, 2013 相似文献
16.
《Journal of Catalysis》2006,237(1):79-93
We examined the role of silver and alumina in Ag–alumina catalysts for the selective catalytic reduction (SCR) of NOx by methane in gas streams containing excess oxygen. A cogelation technique was used to prepare Ag–alumina materials with high dispersion of silver even at high metal loadings (>10 wt%) and after air calcination at 650 °C. Typically, a part of silver is present as fine nanoparticles on the alumina, whereas another part is ionic, bound with the alumina as [AgOAl] species. Dilute nitric acid leaching was used to remove the silver particles and all weakly bound silver from the surface of these materials. Complementary structural characterization was performed by HRTEM, XPS, XRD, and UV–vis DRS. We found that the higher the initial silver content, the higher the amount of the residual [AgOAl] species after leaching. NO–O2-TPD tests identified that silver does not modify the surface properties of the alumina. The SCR reaction-relevant NOx adsorption takes place on alumina. Temperature-programmed surface reaction (TPSR) and kinetic measurements at steady state were used to check the reactivity of the adsorbed NOx species with methane and oxygen to form dinitrogen. Only the alumina-adsorbed nitrates react with CH4 to produce N2 in the presence of oxygen, beginning at ∼300 °C as found by TPSR. Moreover, the SCR reaction rates and apparent activation energies are the same for the leached and parent Ag–alumina catalysts. Thus, metallic silver nanoparticles are spectator species in CH4-SCR of NOx. These catalyze the direct oxidation of methane at temperatures as low as 300 °C, which explains the lower methane selectivity for the SCR reaction measured over the parent samples. 相似文献
17.
《Journal of the European Ceramic Society》2007,27(13-15):3765-3768
Ferroelectric intergrowth-structured Bi4Ti3O12-based thin films have been fabricated by chemical solution deposition. Bi4Ti3O12–SrBi4Ti4O15 (BiT–SBTi) and SrBi2Nb2O9–Bi4Ti3O12 (SBN–BiT) precursor films crystallized in the desired intergrown BiT–SBTi and SBN–BiT structures on Pt/TiOx/SiO2/Si substrates by optimizing the processing conditions. Synthesized BiT–SBTi and SBN–BiT thin films exhibited ferroelectric P–E hysteresis loops. The BiT–SBTi thin films crystallized at 750 °C showed a 2Pr value approximately 20 μC/cm2. Although a little smaller Pr value was observed for the SBN–BiT thin films, the squareness of a P–E hysteresis loop was superior to that of BiT–SBTi thin films. Also, the SBN–BiT thin films had a smoother surface morphology compared with BiT–SBTi thin films. 相似文献
18.
A new perovskite material, BaCe0.1Co0.4Fe0.5O3?δ used as dense oxygen permeable membrane for partial oxidation of methane (POM) reaction was investigated. In order to improve the synergetic effects between membrane and catalyst, LiLaNiO/γ-Al2O3 catalyst was directly packed onto the surface of the membrane to carry out POM. In BaCe0.1Co0.4Fe0.5O3?δ membrane reactor, high oxygen permeation flux, high CH4 conversion and CO selectivity were obtained. At 950 °C, oxygen flux of 9.5 ml cm?2 min?1, CH4 conversion of 99% and CO selectivity of 93% were achieved with a membrane thickness of 1.0 mm. There was an induction process at the initial stage of POM, which was related to the reduction of NiO to Ni0 in LiLaNiO/γ-Al2O3 catalyst. Experiments illustrated that higher reaction temperature would shorten the induction time. During continuously operating for 1000 h at 875 °C, no degradation of performance of the membrane reaction was observed. SEM characterization also demonstrated that the membrane disc maintained an integral structure without any cracks after long-term operation. 相似文献
19.
Magnus Rydén Erik Cleverstam Marcus Johansson Anders Lyngfelt Tobias Mattisson 《American Institute of Chemical Engineers》2010,56(8):2211-2220
Oxygen‐carrier particles for chemical‐looping combustion have been manufactured by freeze granulation. The particles consisted of 60 wt % Fe2O3 as active phase and 40 wt % stabilized ZrO2 as support material. Ce, Ca, or Mg was used to stabilize the ZrO2. The hardness and porosity of the particles were altered by varying the sintering temperature. The oxygen carriers were examined by redox experiments in a batch fluidized‐bed reactor at 800–950°C, using CH4 as fuel. The experiments showed good reactivity between the particles and CH4. NiO was used as an additive and was found to reduce the fraction of unconverted CH4 with up to 80%. The combustion efficiency was 95.9% at best and was achieved using 57 kg oxygen carrier per MW fuel. Most produced oxygen carriers appear to have been decently stable, but using Ca as stabilizer resulting in uneven results. Further, particles sintered at high temperatures had a tendency to defluidize. © 2010 American Institute of Chemical Engineers AIChE J, 2010 相似文献
20.
《Diamond and Related Materials》2006,15(1):133-137
Dielectric materials with lower permittivity (low k) are required for isolation to reduce the interconnect RC delay in deep submicron integrated circuit. In this work, carbon doped silicon oxide [SiO(C–H)] films are investigated as a potential low k material. The films were prepared by the radio frequency plasma enhanced chemical vapor deposition (PECVD) technique from trimethylsilane (C3H10Si or 3MS) in an oxygen (O2) environment. SiO(C–H) films deposited with O2 and 3MS flow rates of 100 sccm and 600 sccm, respectively have been previously found to produce dielectric constant as low as 2.9. This is attributed to the incorporation of carbon in the form of Si–CH3 bond, which has lower polarizability compared to the Si–O bonds that were replaced. In this work, these low k films were annealed at 400, 500, 600 and 700 °C in a N2 atmosphere for 30 min to determine the thermal stability of their properties. The films were characterized in terms of their thickness shrinkage, refractive indices, dielectric constants, infrared absorption, surface morphology and stress upon annealing. For annealing temperatures up to 500 °C, which is beyond the current highest processing temperature for back end of the line structure of around 450 °C, a slight decrease in the refractive indices and dielectric constants of the films are observed. The SiO(C–H) films also remain smooth and exhibit tensile stress with stress level that is within practical acceptable range. The results suggest that the SiO(C–H) films are thermally stable to be applied as low dielectric constant materials for deep submicron integrated circuit. 相似文献