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2010, Vol. 19, No. 3　Online: 2010-05-30

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Reviews

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Intensification of methane and hydrogen storage in clathrate hydrate and future prospect Xuemei Lang*;Shuanshi Fan;Yanhong Wang 2010, 19(3): 203-209.  DOI: 摘要 ( 8422 )   PDF   Gas hydrate is a new technology for energy gas (methane/hydrogen) storage due to its large capacity of gas storage and safe. But industrial application of hydrate storage process was hindered by some problems. For methane, the main problems are low formation rate and storage capacity, which can be solved by strengthening mass and heat transfer, such as adding additives, stirring, bubbling, etc. One kind of additives can change the equilibrium curve to reduce the formation pressure of methane hydrate, and the other kind of additives is surfactant, which can form micelle with water and increase the interface of water-gas. Dry water has the similar effects on the methane hydrate as surfactant. Additionally, stirring, bubbling, and spraying can increase formation rate and storage capacity due to mass transfer strengthened. Inserting internal or external heat exchange also can improve formation rate because of good heat transfer. For hydrogen, the main difficulties are very high pressure for hydrate formed. Tetrahydrofuran (THF), tetrabutylammonium bromide (TBAB) and tetrabutylammonium fluoride (TBAF) have been proved to be able to decrease the hydrogen hydrate formation pressure significantly.

Articles

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Experimental investigation of methane hydrate decomposition by depressurizing in porous media with 3-Dimension device Kehua Su;Changyu Sun*;Xin Yang;Guangjin Chen;Shuanshi Fan 2010, 19(3): 210-216.  DOI: 摘要 ( 7725 )   PDF   In order to simulate the behavior of gas hydrate formation and decomposition, a 3-Dimension experimental device was built, consisting of a high-pressure reactor with an inner diameter of 300 mm, effective height of 100 mm, and operation pressure of 16 MPa. Eight thermal resistances were mounted in the porous media at different depthes and radiuses to detect the temperature distribution during the hydrate formation/decomposition. To collect the pressure, temperature, and flux of gas production data, the Monitor and Control Generated System (MCGS) was used. Using this device, the formation and decomposition behavior of methane hydrate in the 20\sim40 mesh natural sand with salinity of 3.35 wt% was examined. It was found that the front of formation or decomposition of hydrate can be judged by the temperature distribution. The amount of hydrate formation can also be evaluated by the temperature change. During the hydrate decomposition process, the temperature curves indicated that the hydrate in the top and bottom of reactor dissociated earlier than in the inner. The hydrate decomposition front gradually moved from porous media surface to inner and kept a shape of column form, with different moving speed at different surface position. The proper decomposition pressure was also determined.

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Experimental studies of the formation and dissociation of methane hydrate in loess Guanli Jiang;Qingbai Wu*;Jing Zhan 2010, 19(3): 217-223.  DOI: 摘要 ( 7933 )   PDF   In order to study the nature of gas hydrate in porous media, the formation and dissociation processes of methane hydrate in loess were investigated. Five cooling rates were applied to form methane hydrate. The nucleation times of methane hydrate formation at each cooling rate were measured for comparison. The experimental results show that cooling rate is a significant factor affecting the nucleation of methane hydrate and gas conversion. Under the same initial conditions, the faster the cooling rate, the shorter the nucleation time, and the lower the methane gas conversion. Five dissociating temperatures were applied to conduct the dissociation experiment of methane hydrate formed in loess. The experimental results indicated that the temperature evidently controlled the dissociation of methane hydrate in loess and the higher the dissociating temperature, the faster the dissociating rates of methane hydrate.

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The detection of tetrahydrofuran hydrate formation and saturation using magnetic resonance imaging technique Yu Liu;Yongchen Song*;Yongjun Chen;Lei Yao;Qingping Li 2010, 19(3): 224-228.  DOI: 摘要 ( 6953 )   PDF   Tetrahydrofuran (THF) hydrate was formed in bulk as well as in glass beads pack with a mean diameter of 3.0 mm by controlling the temperature under ambient pressure. Images of THF hydrate formation procedure were obtained using the magnetic resonance imaging (MRI) technique. The experiment results showed that MRI is an effective method for the detection of hydrate formation. Saturation of hydrate formed both in bulk and glass beads can be confirmed by intensity integration of MRI images.

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Estimation of ultra-stability of methane hydrate at 1 atm by thermal conductivity measurement Dongliang Li;;Deqing Liang;*;Shuanshi Fan;Hao Peng; 2010, 19(3): 229-233.  DOI: 摘要 ( 10212 )   PDF   Thermal conductivity of methane hydrate was measured in hydrate dissociation self-preservation zone by means of the transient plane source (TPS) technique developed by Gustafsson. The sample was formed from 99.9% (volume ratio) methane gas with 280 ppm sodium dodecyl sulfate (SDS) solution under 6.6 MPa and 273.15 K. The methane hydrate sample was taken out of the cell and moved into a low temperature chamber when the conversion ratio of water was more than 90%. In order to measure the thermal conductivity, the sample was compacted into two columnar parts by compact tool at 268.15 K. The measurements are carried out in the temperature ranging from 263.15 K to 271.15 K at atmospheric pressure. Additionally, the relationship between thermal conductivity and time is also investigated at 263.15 K and 268.15 K, respectively. In 24 h, thermal conductivity increases only 5.45% at 268.15 K, but thermal conductivity increases 196.29% at 263.15 K. Methane hydrates exhibit only minimal decomposition at 1 atm and the temperature ranging from 263.15 K to 271.15 K. At 1 atm and 268.15 K, the total gas that evolved after 24 h was amounted to less than 0.71% of the originally stored gas, and this ultra-stability was maintained if the test was lasted for more than two hundreds hours before terminating.

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Gas-hydrate formation, agglomeration and inhibition in oil-based drilling fluids for deep-water drilling Fulong Ning;Ling Zhang;Yunzhong Tu;Guosheng Jiang*;Maoyong Shi 2010, 19(3): 234-240.  DOI: 摘要 ( 11062 )   PDF   One of the main challenges in deep-water drilling is gas-hydrate plugs, which make the drilling unsafe. Some oil-based drilling fluids (OBDF) that would be used for deep-water drilling in the South China Sea were tested to investigate the characteristics of gas-hydrate formation, agglomeration and inhibition by an experimental system under the temperature of 4 ℃ and pressure of 20 MPa, which would be similar to the case of 2000 m water depth. The results validate the hydrate shell formation model and show that the water cut can greatly influence hydrate formation and agglomeration behaviors in the OBDF. The oleophobic effect enhanced by hydrate shell formation which weakens or destroys the interfacial films effect and the hydrophilic effect are the dominant agglomeration mechanism of hydrate particles. The formation of gas hydrates in OBDF is easier and quicker than in water-based drilling fluids in deep-water conditions of low temperature and high pressure because the former is a W/O dispersive emulsion which means much more gas-water interfaces and nucleation sites than the later. Higher ethylene glycol concentrations can inhibit the formation of gas hydrates and to some extent also act as an anti-agglomerant to inhibit hydrates agglomeration in the OBDF.

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An improved model for predicting hydrate phase equilibrium in marine sediment environment Yongchen Song;Mingjun Yang*;Yongjun Chen;Qingping Li 2010, 19(3): 241-245.  DOI: 摘要 ( 7531 )   PDF   Based on the models of hydrate phase equilibrium in bulk water and porous media, an improved model was proposed to predict the methane hydrate equilibrium in marine sediment environment. In the suggested model, mechanical equilibrium of force between the interfaces in hydrate-liquid-vapor system was considered. When electrolyte was present in pore water, interfacial energy between hydrate and liquid was corrected by an equation that is expressed as the function of temperature and electrolyte concentration. The activity of water is calculated based on the Pitzer model and the interfacial energy between liquid and gas is solved using the Li method. The prediction results show good agreement with the experimental data. By comparison with other models, it is proved that this model can improve the accuracy for predicting hydrate phase equilibrium in marine sediment environment.

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Mechanical property of artificial methane hydrate under triaxial compression Yongchen Song*;Feng Yu;Yanghui Li;Weiguo Liu;Jiafei Zhao 2010, 19(3): 246-250.  DOI: 摘要 ( 7768 )   PDF   Methane production from hydrate reservoir may induce seabed slide and deformation of the hydrate-bearing strata. The research on mechanical properties of methane hydrate is considered to be important for developing an efficient methane exploitation technology. In this paper, a triaxial test system containing a pressure crystal device was developed with the conditions to stabilize the hydrate. A series of triaxial shear tests were carried out on artificial methane hydrate specimen. In addition, mechanical characteristics of methane hydrate were studied with the strain rates of 0.1 and 1.0 mm/min, respectively, under the conditions of different temperatures (T = -5, -10, and -20 ℃) and confining pressures (P = 0, 5, 10, 15, and 20 MPa). The preliminary results show that when the confining pressure was less than 10 MPa, the increase of confining pressure leaded to the enhancement of shear strength. Furthermore, the decreasing temperature and the increasing strain rate both caused the increase in shear strength.

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Promoting effect of super absorbent polymer on hydrate formation Fei Long;Shuanshi Fan;Yanhong Wang;Xuemei Lang* 2010, 19(3): 251-254.  DOI: 摘要 ( 7906 )   PDF   The effect of super absorbent polymer (SAP) on the formation of tetrahydrofuran (THF) hydrate was studied by the successional cooling method. It was found that THF solution samples with 0.004 wt% and 0.03 wt% of SAP formed THF hydrate completely during the same cooling process. The corresponding induction time was 16--29 min, 14--31 min, respectively, which was obviously shorter than that of THF solution samples without SAP (25--62 min). It indicated that SAP accelerated the formation of THF hydrate. At the same time, the pictures of hydrate formation with and without SAP had been compared. It was found that SAP did not change the morphology of the hydrate. Finally, the mechanism of SAP promoting effect on the formation of THF hydrate was suggested.

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Study of the permeability characteristics of porous media with methane hydrate by pore network model Haifeng Liang;Yongchen Song*;Yu Liu;Mingjun Yang;Xing Huang 2010, 19(3): 255-260.  DOI: 摘要 ( 7757 )   PDF   The permeability in the methane hydrate reservoir is one of the key parameters in estimating the gas production performance and the flow behavior of gas and water during dissociation. In this paper, a three-dimensional cubic pore-network model based on invasion percolation is developed to study the effect of hydrate particle formation and growth habit on the permeability. The variation of permeability in porous media with different hydrate saturation is studied by solving the network problem. The simulation results are well consistent with the experimental data. The proposed model predicts that the permeability will reduce exponentially with the increase of hydrate saturation, which is crucial in developing a deeper understanding of the mechanism of hydrate formation and dissociation in porous media.

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Natural gas hydrate shell model in gas-slurry pipeline flow Jing Gong*;Bohui Shi;Jiankui Zhao 2010, 19(3): 261-266.  DOI: 摘要 ( 7853 )   PDF   A hydrate shell model coupled with one-dimensional two-fluid pipe flow model was established to study the flow characteristics of gas-hydrate slurry flow system. The hydrate shell model was developed with kinetic limitations and mass transfer limitations, and it was solved by Euler method. The analysis of influence factors was performed. It was found that the diffusion coefficient was a key parameter in hydrate forming process. Considering the hydrate kinetics model and the contacting area between gas and water, the hydrate shell model was more close to its practical situations.

Reviews

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Textural characteristics, surface chemistry and oxidation of activated carbon Wan Mohd Ashri Wan Daud;Amir Hossein Houshamnd* 2010, 19(3): 267-279.  DOI: 摘要 ( 7963 )   PDF   Numerous researches were reviewed and interpreted to depict a comprehensive illustration of activated carbon and its behavior towards oxidation. Activated carbon as one of the most important adsorbents is tried to be described in this review paper by terms of its ``Textural Characteristics" and ``Surface Chemistry". These two terms, coupled with each other, are responsible for behavior of activated carbon in adsorption processes and in catalytic applications. Although as-prepared activated carbons are usually non-selective and their surfaces suffer from lack of enough reactive groups, their different aspects may be improved and developed by diverse types of modifications. Oxidation is one of the most conventional modifications used for activated carbons. It may be used as a final modification or as a pre-modification followed by further treatment. In this paper, methods of oxidation of activated carbon and other graphene-layer carbon materials are introduced and wet oxidation as an extensively-used category of oxidation is discussed in more detail.

Communctions

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Performance of a tubular oxygen-permeable membrane reactor for partial oxidation of CH4 in coke oven gas to syngas Yuwen Zhang*;Hongwei Cheng;Jiao Liu;Weizhong Ding 2010, 19(3): 280-283.  DOI: 摘要 ( 8182 )   PDF   A gas-tight BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) tubular membrane was fabricated by hot pressure casting. And a membrane reactor with BCFNO tubular membrane and Ag-based sealant was readily constructed and applied to partial oxidation of CH4 in coke oven gas. At 875 ℃, 95% of methane conversion, 91% of H2 and as high as 10 ml·cm-2·min-1 of oxygen permeation flux were obtained. There was a good match in the coefficient of thermal expansion between Ag-based alloy and BCFNO membrane materials. The tubular BCFNO membrane reactor packed with Ni-based catalysts exhibited not only high activity but also good stability in hydrogen-enriched coke oven gas (COG) atmosphere.

Articles

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Fischer-Tropsch synthesis by nano-structured iron catalyst Ali Nakhaei Pour;*;Mohammad Reza Housaindokht;Sayyed Faramarz Tayyari;Jamshid Zarkesh 2010, 19(3): 284-292.  DOI: 摘要 ( 9332 )   PDF   Effects of nanoscale iron oxide particles on textural structure, reduction, carburization and catalytic behavior of precipitated iron catalyst in Fischer-Tropsch synthesis (FTS) are investigated. Nanostructured iron catalysts were prepared by microemulsion method in two series. Firstly, Fe2O3, CuO and La2O3 nanoparticles were prepared separately and were mixed to attain Fe/Cu/La nanostructured catalyst (sep-nano catalyst); Secondly nanostructured catalyst was prepared by co-precipitation in a water-in-oil microemulsion method (mix-nano catalyst). Also, conventional iron catalyst was prepared with common co-precipitation method. Structural characterizations of the catalysts were performed by TEM, XRD, H2 and CO-TPR tests. Particle size of iron oxides for sep-nano and mix-nano catalysts, which were determined by XRD pattern (Scherrer equation) and TEM images was about 20 and 21.6 nm, respectively. Catalyst evaluation was conducted in a fixed-bed stainless steel reactor and compared with conventional iron catalyst. The results revealed that FTS reaction increased while WGS reaction and olefin/paraffin ratio decreased in nanostructured iron catalysts.

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Comparative study of kinetic modeling for the oxidative coupling of methane by genetic and marquardt algorithms Shahrnaz Mokhtari*;Ali Vatani;Nastaran Razmi Farooji 2010, 19(3): 293-299.  DOI: 摘要 ( 8165 )   PDF   Overall kinetic studies on the oxidative coupling of methane, OCM, have been conducted in a tubular fixed bed reactor, using perovskite titanate as the reaction catalyst. The appropriate operating conditions were found to be: temperature 750-775 ℃, total feed flow rate of 160 ml/min, CH4/O2 ratio of 2 and GHSV of 100 min-1. Under these conditions, C2 yield of 28% was achieved. Correlations of the kinetic data have been performed with lumped rate equations for C2 and COx formation as functions of temperature, O2 and CH4 partial pressures. Six models have been selected among the common lumped kinetic models. The selected models have been regressed with the experimental data which were obtained from the Catatest system by genetic algorithm in order to obtain optimized parameters. The kinetic coefficients in the overall reactions were optimized by different numerical optimization methods such as: the Levenberg-Marquardt and genetic algorithms and the results were compared with one another. It has been found that the Santamaria model is in good agreement with the experimental data. The Arrhenius parameters of this model have been obtained by linear regression. It should be noted that the Marquardt algorithm is sensitive to the first guesses and there is possibility to trap in the relative minimum.

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Density functional theory study of CO catalytic oxidation on Co2B2/TiO2 (110) surface Qingsong Zeng;Wenkai Chen*;Yongfan Zhang*;Wenxin Dai;Xin Guo 2010, 19(3): 300-306.  DOI: 摘要 ( 9846 )   PDF   Titanium dioxide with CoB amorphous alloys nanoparticles deposited on the surface is known to exhibit higher catalytic activity than the CoB amorphous. A study of the structure of such system is necessary to understand this effect. A quantum chemical study of Co2B2 on the TiO2 (110) surface was studied using periodic slab model within the framework of density functional theory (DFT). The results of geometry optimization indicated that the most stable model of adsorption was Co2B2 cluster adsorbed on the hollow site of TiO2. The adsorption energy calculated for Co2B2 on the hollow site was 439.3 kJ/mol. The adsorption of CO and O2 was further studied and the results indicated that CO and O2 are preferred to adsorb on the Co2 site. Co-adsorption of CO and O2 shows that Co2B2/TiO2 is a good catalyst for the oxidation of CO to carbon dioxide in the presence of oxygen.

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Study on Au/Al2O3 catalysts for low-temperature CO oxidation in situ FT-IR Xuhua Zou*;Shixue Qi;Jinguang Xu;Zhanghuai Suo;Lidun An;Feng Li 2010, 19(3): 307-312.  DOI: 摘要 ( 8478 )   PDF   Au/Al2O3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation. The activity changes of the catalyst were examined after separate treatment in CO+O2 or CO2+O2. Furthermore, in situ FT-IR studies were performed to investigate the species on the surface when CO or CO+O2 or CO2+O2 was selected separately as adsorption gas. The results showed that Au/Al2O3 catalyst exhibited very high initial activity, but the catalytic activity was found to decrease gradually during CO oxidation with time on stream. And also, the activity of the catalyst declined after treatment in CO+O2 or CO2+O2. The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO+O2 or CO2+O2 might be mainly responsible for the activity decrease, which was reversible.

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Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance for the preferential oxidation of CO in excess hydrogen Zhigang Liu;Shuren Yang;Renxian Zhou*;Xiaoming Zheng 2010, 19(3): 313-317.  DOI: 摘要 ( 8415 )   PDF   CuO-CeO2 catalyst prepared with co-precipitation showed high catalytic performance for the preferential oxidation of CO in excess hydrogen (PROX). Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance was investigated in this work. The CuO-CeO2 catalyst prepared at pH = 13.03 had the smallest particle size (5.4 nm), the largest surface areas (138 m2/g) and the highest activity with CO conversion of 99.6% at 130 ℃. The CuO-CeO2 catalyst was characterized using BET, XRD and TPR techniques. The results showed that when the pH value of the mixed solution containing Cu and Ce species was properly adjusted, both the adsorption layers and diffusion layers of the formed colloidal particles in hydroxide precursor of CuO-CeO2 were modified, resulting in the better catalytic performance for PROX on the final CuO-CeO2 catalyst.

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Experimental study on flow characteristics of tetrahydrofuran hydrate slurry in pipelines Wuchang Wang*;Shuanshi Fan;Deqing Liang;Yuxing Li 2010, 19(3): 318-322.  DOI: 摘要 ( 7157 )   PDF   Tetrahydrofuran (THF) was selected as the substitute to study the flow behaviors and the mechanism of the hydrates blockage in pipelines. The slurrylike hydrates and slushlike hydrates are observed with the formation of hydrates in pipeline. There is a critical hydrate volume concentration of 50.6% for THF slurries and pipeline will be free of hydrate blockage while the hydrate volume concentration is lower than the critical volume concentration; otherwise, pipeline will be easy to be blocked. Fully turbulent flow occurs and friction factors tend to be constant when the velocity reaches 1.5 m/s. And then, constant values of friction factors that depend on the volume concentrations in the slurry were regressed to estimate the pressure drops of THF hydrate slurry at large mean velocity. Finally, a safe region, defined according to the critical hydrate volume concentration, was proposed for THF hydrate slurry, which may provide some insight for further studying the natural gas hydrate slurries and judge whether the pipeline can be run safely or not.

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A new high performance gas hydrate inhibitor Ehsan Heidaryan*;Amir Salarabadi;Jamshid Moghadasi;Alireza Dourbash; 2010, 19(3): 323-326.  DOI: 摘要 ( 8442 )   PDF   In petroleum exploration and production operations, gas hydrates pose serious flow assurance, economic and safety concerns. Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation. In the present study, systematic laboratory work was undertaken to determine synergistic effects between methanol and a Poly Vinyl Methyl Ether as Low Dosage Hydrate Inhibitors (LDHIs). A valuable effect was discovered at a certain ratio of methanol to the low dosage hydrate inhibitor.

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Reactive adsorption of thiophene on Ni/ZnO adsorbent: Effect of ZnO textural structure on the desulfurization activity Jingcheng Zhang;Yunqi Liu*;Shuang Tian;Yongming Chai;Chenguang Liu 2010, 19(3): 327-332.  DOI: 摘要 ( 8654 )   PDF   To better understand the nature of reactive adsorption of thiophene on Ni/ZnO adsorbent, the effect of ZnO textural structure on the desulfurization activity was investigated. ZnO materials were synthesized by low-temperature solid-state reaction and the corresponding Ni/ZnO adsorbents were prepared by incipient impregnation method. The analysis results showed that the crystalline sizes of ZnO as-synthesized as well as the BET surface areas varied obviously with the calcination temperature. The activity evaluations indicated that the Ni/ZnO adsorbents prepared with ZnO possessed a favorable textural structure as active component exhibited good activity of removing thiophene. The evolutions of the main crystalline phases of Ni/ZnO adsorbents before and after reaction confirmed that ZnO played a crucial role in taking up S element and converting it into ZnS in the reactive adsorption process. It was concluded that ZnO with larger surface area and smaller crystal particles resulted in better desulfurization activity, which may be the main reason for the different activities of the Ni/ZnO adsorbents prepared with ZnO calcined at different temperatures.

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Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis Ali Nakhaei Pour;*;Mohammad Reza Housaindokht;Sayyed Faramarz Tayyari;Jamshid Zarkesh 2010, 19(3): 333-340.  DOI: 摘要 ( 8574 )   PDF   A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis (FTS) was prepared by micro-emulsion method. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2), and XRD techniques. Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst. The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite, and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.

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Effects of preparation and operation conditions on precipitated iron nickel catalysts for Fischer-Tropsch synthesis Mostafa Feyzi;Ali Akbar Mirzaei*;Hamid Reza Bozorgzadeh 2010, 19(3): 341-353.  DOI: 摘要 ( 8179 )   PDF   Iron nickel oxide catalysts were prepared using co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effects of a range of preparation variables such as [Fe]/[Ni] molar ratios of the precipitation solution, precipitate aging times, calcination conditions, different supports and loading of optimum support on the structure of catalysts and their catalytic performance for the tested reaction were investigated. It was found that the catalyst containing 40%Fe/60%Ni/40wt%Al2O3, which was aged for 180 min and calcined at 600 ℃ for 6 h was the optimum modified catalyst. The catalytic performance of optimal catalyst has been studied in different operation conditions such as reaction temperatures, H2/CO molar feed ratios and reaction total pressure. Characterization of both precursors and calcined catalysts was carried out by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area measurements, thermal analysis methods such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).