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2012, Vol. 21, No. 4　Online: 2012-07-27

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Hydrogen production by catalytic decomposition of methane using a Fe-based catalyst in a fluidized bed reactor D. Torres, S. de Llobet, J. L. Pinilla, M. J. Lázaro, I. Suelves*, R. Moliner 2012, 21(4): 367-373.  DOI: 10.1016/S1003-9953(11)60378-2 摘要 ( 8802 )   Catalytic decomposition of methane using a Fe-based catalyst for hydrogen production has been studied in this work. A Fe/Al2O3 catalyst previously developed by our research group has been tested in a fluidized bed reactor (FBR). A parametric study of the effects of some process variables, including reaction temperature and space velocity, is undertaken. The operating conditions strongly affect the catalyst performance. Methane conversion was increased by increasing the temperature and lowering the space velocity. Using temperatures between 700 and 900 ℃ and space velocities between 3 and 6 LN/(gcat·h), a methane conversion in the range of 25%—40% for the gas exiting the reactor could be obtained during a 6 h run. In addition, carbon was deposited in the form of nanofilaments (chain like nanofibers and multiwall nanotubes) with similar properties to those obtained in a fixed bed reactor.

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Experimental studies of biomass gasification with air Huili Liu, Jianhang Hu*, Hua Wang, Chao Wang, Juanqin Li 2012, 21(4): 374-380.  DOI: 10.1016/S1003-9953(11)60379-4 摘要 ( 8916 )   In this work, experimental studies of biomass gasification under different operating conditions were carried out in an updraft gasifier combined with a copper slag reformer. The influence of gasification temperature, equivalence ratio (ER) and copper slag catalyst addition on gas production and tar yield were investigated. The experimental results showed that the content of H2 and CO, gas yield and LHV increased, while the tar yield and the content of CO2, CH4 and C2Hx in the gas product decreased with the temperature. At 800 ℃, with the increase of ER, the LHV, the tar yield and the content of H2, CO, CH4 and C2Hx in gas products decreased, while the gas yield and the content of CO2 increased. Copper slag was introduced into the secondary reformer for tar decomposition. The Fe3O4 phase in the fresh copper slag was reduced to FeO (Fe2+) and metallic Fe by the gas product. Fe species (FeO and metallic Fe) acted as the active sites for tar catalytic decomposition. The catalytic temperature had a significant influence on tar conversion and the composition of the gas product. Typically, the tar conversion of about 17%—54% could be achieved when the catalytic temperature was varied from 750 to 950 ℃. Also, the content of H2 and CO increased with the catalytic temperature, while that of CO2, CH4 and C2Hx in the gas product decreased. It was demonstrated that copper slag was a good catalyst for upgrading the gas product from biomass gasification.

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Numerical studies of hydrate dissociation and gas production behavior in porous media during depressurization process Xuke Ruan, Mingjun Yang, Yongchen Song*, Haifeng Liang, Yanghui Li 2012, 21(4): 381-392.  DOI: 10.1016/S1003-9953(11)60380-0 摘要 ( 8333 )   The permeability of porous media with the presence of hydrate is one of the important information needed to reliably predict the feasibility of producing natural gas from hydrates. The characterization of how the permeability affects hydrate dissociation and gas production is of key interest for numerical reservoir engineering studies. In this study, a numerical model is developed to investigate the hydrate dissociation and gas production in porous media by depressurization. A series of simulation runs are conducted to study the impacts of permeability characteristics, including permeability reduction exponent, absolute permeability, hydrate accumulation habits and hydrate saturation, sand average grain size and irreducible water saturation. The effects of the distribution of hydrate in porous media are examined by adapting conceptual models of hydrate accumulation habits into simulations to govern the evolution of permeability with hydrate decomposition, which is also compared with the conventional reservoir permeability model, i.e. Corey model. The simulations show that the hydrate dissociation rate increases with the decrease of permeability reduction exponent, hydrate saturation and the sand average grain size. Compared with the conceptual models of hydrate accumulation habits, our simulations indicate that Corey model overpredicts the gas production and the performance of hydrate coating models is superior to that of hydrate filling models in gas production, which behavior does follow by the order of capillary coating>pore coating>pore filling>capillary filling. From the analysis of t1/2, some interesting results are suggested as follows: (1) there is a ``switch'' value (the ``switch'' absolute permeability) for laboratory-scale hydrate dissociation in porous media, the absolute permeability has almost no influence on the gas production behavior when the permeability exceeds the ``switch'' value. In this study, the ``switch'' value of absolute permeability can be estimated to be between 10 and 50 md. (2) An optimum value of initial effective water saturation Sw, e exists where hydrate dissociation rate reaches the maximum and the optimum value largely coincides with the value of irreducible water saturation Swr, e. For the case of Sw, e<Swr, e, or Sw, e>Swr, e, there are different control mechanisms dominating the process of hydrate dissociation and gas production.

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Pd catalysts supported on modified Zr0.5Al0.5O1.75 used for lean-burn natural gas vehicles exhaust purification Hongyan Shang, Yun Wang, Maochu Gong, Yaoqiang Chen* 2012, 21(4): 393-399.  DOI: 10.1016/S1003-9953(11)60381-2 摘要 ( 8381 )   Composite supports Zr0.5Al0.5O1.75 modified by metal oxides, such as La2O3, ZnO, Y2O3 or BaO, were prepared by co-precipitation method, and palladium catalysts supported on the modified composite supports were prepared by impregnation method. Their properties were characterized by X-ray diffraction (XRD), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), N2 adsorption/desorption, and CO-chemisorption. The catalytic activity and the resistance to water poisoning of the prepared Pd catalysts were tested in a simulated exhaust gas from lean-burn natural gas vehicles with and without water vapor. The results demonstrated that the modified supports had an apparent effect on the performance of Pd catalysts, compared with the Pd catalyst supported on the unmodified ZrAl. The addition of ZnO or Y2O3 promoted the conversion of CH4. In the absence of water vapor, Pd/ZnZrAl exhibited the best activity for CH4 conversion with the light-off temperature (T50) of 275 ℃ and the complete conversion temperature (T90) of 314 ℃, respectively. However, in the presence of water vapor, Pd/YZrAl was the best one over which the light-off temperature (T50) of methane was 339 ℃ and the complete conversion temperature (T90) was 371 ℃. These results indicated that Pd catalyst supported on the modified composite ZrAl support showed excellent catalytic activity at low temperature and high resistance to H2O poisoning for the exhaust purification of lean-burn natural gas vehicles.

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Particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen: Construction and performance for oxidative coupling of methane Wenhua Wang, Zhao Zhang, Shengfu Ji* 2012, 21(4): 400-406.  DOI: 10.1016/S1003-9953(11)60382-4 摘要 ( 7833 )   A novel particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen is constructed comprising of the upper-layer 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst and the under-layer 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst as well as a side tube in the interspaces of two layers for supplementing O2. The reaction performance of oxidative coupling of methane (OCM) in the dual-bed reactor system is evaluated. The effects of the reaction parameters such as feed CH4/O2 ratio, reaction temperature and side tube feed O2 flowrate on the catalytic performance are investigated. The results indicate that the suggested mode of dual-bed reactor exhibits an excellent performance for OCM. CH4 conversion of 33.2%, C2H4 selectivity of 46.5% and C2 yield of 22.5% could be obtained, which have been increased by 6.4%, 4.1% and 5.5%, respectively, as compared with 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst in a single-bed reactor and increased by 10.7%, 31.9% and 17.7%, respectively, as compared with 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst in a single-bed reactor. The effective promotion of OCM performance in the reactor would supply a valuable reference for the industrialization of OCM process.

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Dynamic modeling of a H2O-permselective membrane reactor to enhance methanol synthesis from syngas considering catalyst deactivation M. Farsi, A. Jahanmiri* 2012, 21(4): 407-414.  DOI: 10.1016/S1003-9953(11)60383-6 摘要 ( 6959 )   In this paper, the effect of water vapor removal on methanol synthesis capacity from syngas in a fixed-bed membrane reactor is studied considering long-term catalyst deactivation. A dynamic heterogeneous one-dimensional mathematical model that is composed of two sides is developed to predict the performance of this configuration. In this configuration, conventional methanol reactor is supported by an alumina-silica composite membrane layer for water vapor removal from reaction zone. To verify the accuracy of the considered model and assumptions, simulation results of the conventional methanol reactor is compared with the industrial plant data under the same process condition. The membrane reactor improves catalyst life time and enhances CO2 conversion to methanol by overcoming the limitation imposed by thermodynamic equilibrium. This configuration has enhanced the methanol production capacity about 4.06% compared with the industrial methanol reactor during the production time.

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Optimization of preparation conditions of Fe-Co nanoparticles in low-temperature CO oxidation reaction by taguchi design method Abolfazl Biabani, Mehran Rezaei*, Zohreh Fattah 2012, 21(4): 415-420.  DOI: 10.1016/S1003-9953(11)60384-8 摘要 ( 8245 )   Mixed iron-cobalt oxide (Co/Fe molar ratio = 1/5) are prepared using a simple co-precipitation procedure and studied for the catalytic oxidation of carbon monoxide. In particular, the effects of a range of preparation variables such as pH value when precipitation, aging temperature, precipitation agent type and aging time are investigated on the catalytic performance of synthesized Fe-Co oxides in CO oxidation reaction. In addition, the preparation factors were optimized by Taguchi design method. The optimized sample was characterized by XRD, N2 adsorption/desorption, TEM and TGA/DTA techniques. The results reveal that the optimized sample shows a mesoporous structure with a narrow pore size distribution centered in the range of 2-7 nm. The sample prepared under optimized conditions has high activity and stability toward removal of carbon monoxide at lower temperatures. It is shown that different preparation variables influence the catalytic performance of Fe-Co oxide in CO oxidation reaction.

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Effects of toluene on thiophene adsorption over NaY and Ce(IV)Y zeolites Yanchun Shi, Xiaojian Yang, Fuping Tian*, Cuiying Jia, Yongying Chen 2012, 21(4): 421-425.  DOI: 10.1016/S1003-9953(11)60385-X 摘要 ( 7963 )   Zeolites NaY and Ce(IV)Y were employed as adsorbents to remove organic sulfur compounds from model gasoline (MG) solutions with and without toluene in static adsorption experiments at room temperature (RT) and atmospheric pressure. The adsorbents were characterized by XRD, XRF and pyridine infrared spectrum (IR). The adsorption experiments show that the desulfurization performance of Ce(IV)Y is much better than that of NaY. The sulfur removal over both NaY and Ce(IV)Y decreases with the increase of toluene concentration in MG, however, the decline tendency on Ce(IV)Y is smooth, and it is steep on NaY. FT-IR spectra of thiophene adsorption indicate that thiophene molecules are mainly adsorbed on NaY via π electron interaction, but on Ce(IV)Y, in addition to the π electron interaction, both Ce4+-S direct interaction and protonation of thiophene also play important roles. Toluene molecules are adsorbed on NaY also via π electron interaction. Although the amount of Br\"{o}nsted acid sites is increased due to the introduction of Ce4+ ions into NaY zeolite, it is not found to influence the adsorption mode of toluene over Ce(IV)Y. Compared with NaY zeolite, the improved desulfurization performance over Ce(IV)Y for removing organic sulfur compounds from MG solution, especially those containing large amount of aromatics, may be ascribed to the direct Ce(IV)-S interaction, which is much resistant to the influence resulted from toluene adsorption.

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Effect of preparation method on halloysite supported cobalt catalysts for Fischer-Tropsch synthesis Sufang Chen, Jinlin Li*, Yuhua Zhang, Daohong Zhang, Junjiang Zhu 2012, 21(4): 426-430.  DOI: 10.1016/S1003-9953(11)60386-1 摘要 ( 8207 )   Novel cobalt Fischer-Tropsch synthesis (FTS) catalysts were prepared from natural halloysite nanotubes (HNT) by double-solvent and wet-impregnation methods, and characterized by TEM, XRD, TPR and N2 adsorption-desorption. Comparing with the catalyst prepared by wet-impregnation method, the catalyst prepared by double-solvent method reduces Co3O4 particle migration and agglomeration due to size-induced effect, thus showing higher catalytic activity for Fischer-Tropsch synthesis.

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An effective route to improve the catalytic performance of SAPO-34 in the methanol-to-olefin reaction Guangyu Liu, Peng Tian, Qinhua Xia, Zhongmin Liu* 2012, 21(4): 431-434.  DOI: 10.1016/S1003-9953(11)60387-3 摘要 ( 8297 )   An effective route to improve the catalytic performance of SAPO-34 in the methanol-to-olefin reaction by simple oxalic acid treatment was investigated. The samples were characterized by XRD, SEM, N2 adsorption-desorption, XRF, TG, 29Si MAS NMR and NH3-TPD techniques. The results indicated that the external surface acidity of SAPO-34 was finely tuned by oxalic acid treatment, and the selectivity to C2H4 on SAPO-34 and the catalyst lifetime in the methanol-to-olefin reaction were greatly improved.

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Conversion enhancement of tubular fixed-bed reactor for Fischer-Tropsch synthesis using static mixer Phavanee Narataruksa, Sabaithip Tungkamani, Karn Pana-Suppamassadu, Phongsak Kee 2012, 21(4): 435-444.  DOI: 10.1016/S1003-9953(11)60388-5 摘要 ( 9438 )   Recently, Fischer-Tropsch synthesis (FTS) has become an interesting technology because of its potential role in producing biofuels via Biomass-to-Liquids (BTL) processes. In Fischer-Tropsch (FT) section, biomass-derived syngas, mainly composed of a mixture of carbon monoxide (CO) and hydrogen (H2), is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure. Fixed-bed reactors are typically used for these processes as conventional FT reactors. The fixed-bed or packed-bed type reactor has its drawbacks, which are heat transfer limitation, i.e. a hot spot problem involved highly exothermic characteristics of FT reaction, and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface. This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved, and led to higher throughput and conversion. The main goal of the research is the enhancement of a fixed-bed reactor, focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor. Two FTS experiments were carried out using two reactors i.e., with and without static mixer insertion within catalytic beds. The modeled syngas used was a mixed gas composed of H2/CO in 2 : 1 molar ratio that was fed at the rate of 30 mL(STP)·min-1 (GHSV≈136 mL·gcat-1·h-1) into the fixed Ru supported aluminum catalyst bed of weight 13.3 g. The reaction was carried out at 180 ℃ and atmospheric pressure continuously for 36 h for both experiments. Both transient and steady-state conversions (in terms of time on stream) were reported. The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer. In both cases, the values of chain growth probability of hydrocarbon products (α) for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer, respectively.

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CO selective methanation in hydrogen-rich gas mixtures over carbon nanotube supported Ru-based catalysts Jun Xiong, Xinfa Dong*, Lingling Li 2012, 21(4): 445-451.  DOI: 10.1016/S1003-9953(11)60389-7 摘要 ( 8626 )   Series of carbon nanotube supported Ru-based catalysts were prepared by impregnation method and applied successfully for complete removal of CO by CO selective methanation from H2-rich gas stream conducted in a fixed-bed quartz tubular reactor at ambient pressure. It was found that the metal promoter, reduction temperature and metal loading affected the catalytic properties significantly. The most excellent performance was presented by 30 wt% Ru-Zr/CNTs catalyst reduced at 350 ℃. since it decreased CO concentration to below 10 ppm from 12000 ppm by CO selective methanation at the temperature range of 180-240 ℃, and kept CO selectivity higher than 85% at the temperature below 200 ℃. Characterization using XRD, TEM, H2-TPR and XPS suggests that Zr modification of Ru/CNTs results in the weakening of the interaction between Ru and CNTs, a higher Ru dispersion and the oxidization of surface Ru. Amorphous and high dispersed Ru particles with small size were obtained for 30 wt% Ru-Zr/CNTs catalyst reduced at 350 ℃, leading to excellent catalytic performance in CO selective methanation.

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Styrene epoxidation with hydrogen peroxide over calcium oxide catalysts prepared from various precursors Qingming Gu, Dan Han, Lei Shi, Qi Sun* 2012, 21(4): 452-458.  DOI: 10.1016/S1003-9953(11)60390-3 摘要 ( 8598 )   A series of CaO samples were prepared by calcination of commercially available and synthesis of calcium salt precursors such as calcium acetate, carbonate, hydroxide and oxalate etc. CaO samples were found to be effective for the epoxidation of styrene using hydrogen peroxide as an oxidant in the presence of acetonitrile. To determine the influence of the physicochemical properties and surface basicity on the catalytic activity, the prepared CaO samples were characterized using thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), N2-adsorption and temperature-programmed desorption of CO2 (CO2-TPD). The results indicate that the amounts of very strong basic sites and high basicity strength on CaO sample are key factors for its excellent catalytic performance. In contrast, the surface area, porosity and the surface structure of CaO sample have a relatively minor effect on the catalytic activity. CaO sample, obtained by the decomposition of Ca(OH)2, prepared by precipitating calcium nitrate with sodium hydroxide in ethylene glycol solution, exhibits the highest amount of very strong basic sites and stronger strength of basic sites, and therefore it catalyses the epoxidation of styrene with the highest rate among the tested CaO samples. Under the selected reaction conditions, the selectivity of 97.5% to styrene oxide at a conversion in excess of 99% could be obtained.

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Modeling phase equilibria of semiclathrate hydrates of CH4, CO2 and N2 in aqueous solution of tetra-n-butyl ammonium bromide Abhishek Joshi, Prathyusha Mekala, Jitendra S. Sangwai* 2012, 21(4): 459-465.  DOI: 10.1016/S1003-9953(11)60391-5 摘要 ( 8093 )   Semiclathrate hydrates of tetra-n-butyl ammonium bromide (TBAB) offer potential solution for gas storage, transportation, separation of flue gases and CO2 sequestration. Models for phase equilibria for these systems have not yet been developed in open literatures and thus require urgent attention. In this work, the first attempt has been made to model phase equilibria of semiclathrate hydrates of CH4, CO2 and N2 in aqueous solution of TBAB. A thermodynamic model for gas hydrate system as proposed by Chen and Guo has been extended for semiclathrate hydrates of gases in aqueous solution of TBAB. A correlation for the activity of water relating to the system temperature, concentration of TBAB in the system and the nature of guest gas molecule has been proposed. The model results have been validated against available experimental data on phase equilibria of semiclathrate hydrate systems of aqueous TBAB with different gases as guest molecule. The extended Chen and Guo's model is found to be suitable to explain the promotion effect of TBAB for the studied gaseous system such as, methane, carbon dioxide and nitrogen as a guest molecule. Additionally, a correlation for the increase in equilibrium formation temperature (hydrate promotion temperature, ΔTp) of semiclathrate hydrate system with respect to pure gas hydrate system has been developed and applied to semiclathrate hydrate of TBAB with several gases as guest molecules. The developed correlation is found to predict the promotion effect satisfactorily for the system studied.

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Comparison of dry reforming of methane in low temperature hybrid plasma-catalytic corona with thermal catalytic reactor over Ni/γ-Al2O3 Amin Aziznia, Hamid Reza Bozorgzadeh*, Naser Seyed-Matin, Morteza Baghalha 2012, 21(4): 466-475.  DOI: 10.1016/S1003-9953(11)60392-7 摘要 ( 9047 )   In the current study, the hybrid effect of a corona discharge and γ-alumina supported Ni catalysts in CO2 reforming of methane is investigated. The study includes both purely catalytic operation in the temperature range of 923-1023 K, and hybrid catalytic-plasma operation of DC corona discharge reactor at room temperature and ambient pressure. The effect of feed flow rate, discharge power and Ni/γ-Al2O3 catalysts are studied. When CH4/CO2 ratio in the feed is 1/2, the syngas of low H2/CO ratio at about 0.56 is obtained, which is a potential feedstock for synthesis of liquid hydrocarbons. Although Ni catalyst is only active above 573 K, presence of Ni catalysts in the cold corona plasma reactor (T≤523 K) shows promising increase in the conversions of methane and carbon dioxide. When Ni catalysts are used in the plasma reaction, H2/CO ratios in the products are slightly modified, selectivity to CO increases whereas fewer by-products such as hydrocarbons and oxygenates are formed.

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Ionic liquid mediated CO2 activation for DMC synthesis Jun Du*, Jing Shi, Zhengfei Li, Zuohua Liu, Xing Fan, Changyuan Tao 2012, 21(4): 476-479.  DOI: 10.1016/S1003-9953(11)60393-9 摘要 ( 10383 )   Promoted catalytic reaction between methanol and CO2 for dimethyl carbonate (DMC) synthesis is conducted over K2CO3/CH3I catalyst in the presence of ionic liquid under microwave irradiation. The effect of ionic liquids incorporated with microwave irradiation on the yield of DMC is investigated. DMC was found to form at lower temperature in a relative short time, which indicated an enhanced catalytic process by ionic liquid. Among the ionic liquids used, 1-butyl-3-methylimidazolium chloride is the most effective promoter. Density functional theory calculations indicate that CO2 bond lengths and angles changed due to the molecular interaction of ionic liquid and CO2, resulting in the activation of CO2 molecules and consequently the acceleration of reaction rate.