完全液相法制CuZnAl合成二甲醚浆状催化剂的催化性能

利用完全液相法制备了CuZnAl浆状催化剂,考察了反应温度、反应压力、搅拌速度、原料气组成等工艺条件, 以及催化剂中各组分配比对浆态床合成气一步法合成二甲醚反应过程的影响。结果表明, 利用完全液相法制备的催化剂在升温段和降温段活性保持稳定,随着反应时间的延长,催化剂活性呈现增长趋势,且其水煤气变换反应速率很快。Cu/Zn/Al摩尔比为1∶1∶2.09时催化剂的CO转化率与DME 选择性最好。     

A novel liquid-phase technology for the preparation of slurry catalysts

A novel catalyst preparation method aimed to a slurry reactor has been suggested. Its main innovative thought lies in preparing the slurry catalysts directly from solution. Activity tests indicate that the CuO–ZnO/Al₂O₃ catalyst prepared by the novel method can efficiently catalyze syngas to DME and the selectivity to DME reaches 93.08%. The catalyst shows a good stability during the reaction of 440 h.     

Liquid-phase preparation of catalysts used in slurry reactors to synthesize dimethyl ether from syngas: Effect of heat-treatment atmosphere

A CuZnAl slurry catalyst was prepared directly from a solution of metal salts by an entirely liquid-phase method. The influence of heat-treatment atmospheres with different proportions of CO₂ on the single-step synthesis of dimethyl ether (DME) from syngas was investigated and the catalysts were characterized by powder X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD), X-ray photoelectron spectrometry (XPS) and thermogravimetry-mass spectrometry (TG-MS). Results showed that the introduction of CO₂ into the heat-treatment atmosphere made it easier to reduce the catalyst. It also adjusted the Cu⁰/Cu⁺ ratio on the catalyst surface, the CO₂ reacting with the metallic carbide there to form CO, which then reduced part of the Cu₂O to Cu. Moreover, it was concluded that the final phase structure of the catalyst and the Cu/Zn ratio on its surface depended mainly on its composition and the reaction environment and less so on the heat-treatment atmosphere. In the DME synthesis reaction, it was found that the introduction of CO₂ into the heat-treatment atmosphere restrained the water–gas shift reaction and raised the DME selectivity. An optimal amount of CO₂ in the heat-treatment atmosphere favored the increase of the DME space–time yield. The catalysts performed best when the heat-treatment atmosphere contained 50% CO₂.     

不同加料方式对完全液相法制CuZnAl浆状催化剂结构和性能的影响

采用完全液相法,以拟薄水铝石为铝源,选择不同加料方式制备了CuZnAl浆状催化剂,并采用X射线粉末衍射、氮吸附、X射线光电子能谱和程序升温还原对其进行了表征,考察了CuZnAl浆状催化剂在合成气制取甲醇、二甲醚反应中的催化性能.结果表明,不同加料方式对催化剂性能有显著的影响,其中采用铜与锌同时加入的方式制备的催化剂相结构稳定,比表面积较大,催化剂表面元素铜含量高,可还原铜量多,且还原温度低,从而提高了催化剂的CO转化率和醇醚总选择性.     

Effect of pressure on direct synthesis of DME from syngas over metal-pillared ilerites and metal/metal-pillared ilerites

The effect of pressure on the direct synthesis of dimethyl ether (DME) from syngas over metal (Cu, Zn) pillared ilerites and metal (Cu, Zn) impregnated metal-pillared ilerites was explored. The prepared catalysts were characterized by XRD, BET, ICP-AES, SEM and FT-IR. The direct DME synthesis reaction was carried out in a differential fixed bed reactor with the prepared catalysts at various pressures (10, 20, 30 bar), 250°C and H₂/CO ratio of 2. The Cu/Zn-pillared ilerite catalyst showed the highest catalytic activity among the prepared catalysts at 20 bar, in which CO conversion was about 62% and DME selectivity was about 89%. CO conversion increased with pressure, and DME selectivity increased with pressure in the range of 10–20 bar, and above the pressure slightly decreased with pressure. The optimum pressure for this reaction was 20 bar.     

溶剂对完全液相法制CuZnAl浆状催化剂结构和性能的影响

采用完全液相法,以拟薄水铝石为铝源,选择不同溶剂溶解催化剂前体硝酸铜和硝酸锌制备了CuZnAl浆状催化剂,并采用X射线粉末衍射、氮吸附.X射线光电子能谱和程序升温还原对其进行了表征,考察了CuZnAI浆状催化剂在合成气一步法合成二甲醚反应中的催化性能.结果表明,不同的溶剂对催化剂性能有显著的影响,其中以乙二醇为溶剂制备的催化荆相结构稳定,孔径及孔体积最大,表面铜含量高,可还原铜量较多且还原温度偏低,从而在保证DME选择性不变的条件下显著提高了催化剂CO转化率.     

完全液相制备催化剂上合成二甲醚动力学研究

采用浆态床反应器,研究了用完全液相法制备的Cu-Zn-A l双功能催化剂上CO加氢直接合成二甲醚(DME)的反应动力学。按CO加氢先合成CH3OH,再由CH3OH脱水生成DME二步串联的反应机理,根据不同的中间产物及控制步骤分别建立了动力学模型,以反应物的平衡浓度代替逸度进行计算,最终选取的模型计算值和实验值吻合较好,说明采用L-H型动力学模型可以合理地描述催化剂表面的反应过程,模型参数计算结果表明,催化剂表面对CO2的弱吸附是该催化剂在浆态床中稳定性较好的主要原因之一。     

Effect of Preparation Method of Fe–based Fischer–Tropsch Catalyst on their Light Olefin Production

Fischer–Tropsch synthesis (FTS) for the production of light olefin from syngas was investigated on K–Fe–Cu–Al catalysts. The catalysts were prepared by different methods, such as K impregnated over co-precipitated Fe–Cu–Al, K impregnated over sol–gel (pechini) synthesized Fe–Cu–Al, Fe–Cu–K impregnated on alumina and K impregnated over co-precipitated Fe–Cu in a slurry phase of Al₂O₃. Among four catalysts, K impregnated over Fe–Cu–Al prepared by sol–gel method has shown the best activity. A favorable pore size distribution and pore volume, manifested in a facile reducibility of the iron oxide, is found to be responsible for high activity. The catalyst also exhibits high olefin selectivity compared with the others, due to the presence of moderate number of acid sites.     

Performance of Silicotungstic Acid Incorporated Mesoporous Catalyst in Direct Synthesis of Dimethyl Ether from Syngas in the Presence and Absence of CO2

Dimethyl ether (DME), which is an excellent green diesel fuel alternate, is synthesized following a direct synthesis route from synthesis gas, by using a bi-functional catalyst mixture, which was composed of a silicotungstic acid incorporated mesoporous catalyst [TRC-75(L)] and a commercial Cu–Zn based catalyst. Higher DME selectivity values were obtained by using TRC-75(L), than commercial γ-alumina at 50 bars. Presence of CO₂ in the feed stream caused significant enhancement in DME selectivity. Results showed that DME selectivity of about 0.85 was obtained in a temperature range 250–275 °C in the presence of 10 % CO₂. In fact, CO₂ was also used as a resource to produce DME at lower temperatures. Reverse dry reforming and ethanol formation reactions were observed as side reactions, especially at higher temperatures. Results also proved that direct synthesis of DME from syngas has major CO conversion and DME selectivity advantages over the two step process involving consecutive methanol synthesis and dehydration steps.     

Equilibrium calculations for direct synthesis of dimethyl ether from syngas

Thermodynamic analysis of single‐step synthesis of dimethyl ether (DME) from syngas over a bi‐functional catalyst (BFC) in a slurry bed reactor has been investigated as a function of temperature (200–240°C), pressure (20–50 bar), and composition feed ratio (H₂/CO: 1–2). The BFC was prepared by physical mixing of CuO/ZnO/Al₂O₃ as a methanol synthesis catalyst and H‐ZSM‐5 as a methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H₂, methanol dehydration to DME and water–gas shift reaction were chosen as the independent reactions. The equilibrium thermodynamic analysis includes a theoretical model predicting the behaviour and a comparison to experimental results. Theoretical model calculations of thermodynamic equilibrium constants of the reactions and equilibrium composition of all components at different reaction temperature, pressure, and H₂/CO ratio in feed are in good accordance with experimental values.     

Synthesis of AlOOH slurry catalyst and catalytic activity for methanol dehydration to dimethyl ether

AlOOH slurry catalysts were prepared by complete liquid-phase technology from aluminum iso-propoxide (AIP). Dehydration of methanol to dimethyl ether (DME) over these catalysts was investigated in slurry reactor. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, temperature-programmed desorption of ammonia (NH₃–TPD). The results showed that the slurry catalysts had high specific surface area and pore volume, and the specific surface area and the strength of weak acidic sites were influenced considerably by the molar ratio of H₂O/AIP and HNO₃/AIP. Activity tests indicated that AlOOH slurry catalysts had excellent catalytic activity and stability in slurry reactor for the dehydration of methanol to dimethyl ether, and the activity correlated well with the strength of weak acidic sites of catalysts, which can be controlled by changing the H₂O/AIP and HNO₃/AIP molar ratios. The average methanol conversion at even stage reaches nearly 80% and DME selectivity almost 100% over CAT-P1 catalyst. No deactivation was found during the reaction of 500 h. It is also expected that CAT-P1 becomes a promising methanol dehydration catalyst for the STD process based on CuZuAl methanol synthesis catalyst.     

改进共沉淀法制Cu基甲醇催化剂

采用传统共沉淀法和加表面活性剂改进共沉淀法制备了两种超细 Cu/ Zn O/ Al2 O3 催化剂 ,并应用 XRD,TEM对催化剂的结构和形貌进行了表征 ,同时用流动固定床微型反应器在3.0 MPa和体积空速 760 0 h-1下考察了其催化合成气合成甲醇的活性 .结果表明 ,改进共沉淀法制备的超细 Cu/ Zn O/ Al2 O3 催化剂具有比传统共沉淀法制备的催化剂更细的粒径和更高的催化活性 .同时从理论上对表面活性剂的作用机制进行了讨论 .     

固体酸对二氧化碳加氢合成二甲醚催化剂性能的影响

以Cu-ZnO-Al2O3催化剂作为甲醇合成组分,以不同固体酸作为脱水组分,制备了一系列CO2加氢合成二甲醚的复合催化剂。研究表明CO2的转化率与固体酸的酸性无关,而取决于Cu-ZnO-Al2O3催化剂上甲醇的合成速率;二甲醚的选择性取决于固体酸的酸量和酸强度,脱水速率与固体酸的中/强酸有关。HZSM-5分子筛作为复合催化剂脱水组分时,二甲醚的收率最高;硅铝比对CO2转化率无影响,但可显著地影响二甲醚选择性;低硅铝比的HZSM-5更适合作为CO2加氢合成二甲醚复合催化剂的脱水组分。     

Effect of Structural Promoters on Fe-Based Fischer–Tropsch Synthesis of Biomass Derived Syngas

Biomass gasification and subsequent conversion of this syngas to liquid hydrocarbons using Fischer–Tropsch (F–T) synthesis is a promising source of hydrocarbon fuels. However, biomass-derived syngas is different from syngas obtained from other sources such as steam reforming of methane. Specifically the H₂/CO ratio is less than 1/1 and the CO₂ concentrations are somewhat higher. Here, we report the use of Fe-based F–T catalysts for the conversion of syngas produced by the air-blown, atmospheric pressure gasification of southern pine wood chips. The syngas from the gasification step is compressed and cleaned in a series of sorbents to produce the following feed to the F–T step: 2.78 % CH₄, 11 % CO₂, 15.4 % H₂, 21.3 % CO, and balance N₂. The relatively high level of CO₂ suggests the need to use catalysts that are active for CO₂ hydrogenation as well is resistant to oxidation in presence of high levels of CO₂. The work reported here focuses on the effect of these different structural promoters on iron-based F–T catalysts with the general formulas 100Fe/5Cu/4K/15Si, 100Fe/5Cu/4K/15Al and 100Fe/5Cu/4K/15Zn. Although the effect of Si, Al or Zn on iron-based F–T catalysts has been examined previously for CO+CO₂ hydrogenation, we have found no direct comparison of these three structural promoters, nor any studies of these promoters for a syngas produced from biomass. Results show that catalysts promoted with Zn and Al have a higher extent of reduction and carburization in CO and higher amount of carbides and CO adsorption as compared to Fe/Cu/K/Si. This resulted in higher activity and selectivity to C₅+ hydrocarbons than the catalyst promoted with silica.     

ZSM-5 Supported Cobalt Catalyst for the Direct Production of Gasoline Range Hydrocarbons by Fischer–Tropsch Synthesis

Abstract  

Fischer–Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C₅–C₉) from syngas was investigated on cobalt-based FTS catalyst supported on the ZSM-5 possessing a four different Si/Al ratio. The FTS catalysts were prepared by impregnation method using cobalt nitrate precursor in a slurry of ZSM-5, and they were characterized by surface area, XRD, H₂-TPR and NH₃-TPD. Cobalt supported catalyst on ZSM-5 having a low Si/Al ratio of 15 was found to be superior to the other catalysts in terms of better C₅–C₉ selectivity due to the formation of small cobalt particle and the presence of larger number of weak acidic sites. It also exhibited the highest catalytic activity because of the higher reducibility and the small cobalt particle size.     

Simulation of DME synthesis from coal syngas by kinetics model

DME (Dimethyl Ether) has emerged as a clean alternative fuel for diesel. There are largely two methods for DME synthesis. A direct method of DME synthesis has been recently developed that has a more compact process than the indirect method. However, the direct method of DME synthesis has not yet been optimized at the face of its performance: yield and production rate of DME. In this study it is developed a simulation model through a kinetics model of the ASPEN plus simulator, performed to detect operating characteristics of DME direct synthesis. An overall DME synthesis process is referenced by experimental data of 3 ton/day (TPD) coal gasification pilot plant located at IAE in Korea. Supplying condition of DME synthesis model is equivalently set to 80 N/m³ of syngas which is derived from a coal gasification plant. In the simulation it is assumed that the overall DME synthesis process proceeds with steadystate, vapor-solid reaction with DME catalyst. The physical properties of reactants are governed by Soave-Redlich-Kwong (SRK) EOS in this model. A reaction model of DME synthesis is considered that is applied with the LHHW (Langmuir-Hinshelwood Hougen Watson) equation as an adsorption-desorption model on the surface of the DME catalyst. After adjusting the kinetics of the DME synthesis reaction among reactants with experimental data, the kinetics of the governing reactions inner DME reactor are modified and coupled with the entire DME synthesis reaction. For validating simulation results of the DME synthesis model, the obtained simulation results are compared with experimental results: conversion ratio, DME yield and DME production rate. Then, a sensitivity analysis is performed by effects of operating variables such as pressure, temperature of the reactor, void fraction of catalyst and H₂/CO ratio of supplied syngas with modified model. According to simulation results, optimum operating conditions of DME reactor are obtained in the range of 265–275 °C and 60 kg/cm². And DME production rate has a maximum value in the range of 1–1.5 of H₂/CO ratio in the syngas composition.     

Specifics of dimethyl ether synthesis from syngas over mixed catalysts

Dimethyl ether (DME) synthesis from syngas over a mixture of a methanol synthesis catalyst (ZnO, 25.10 wt %; AuO, 64.86 wt %; Al₂O₃, 10.04 wt %) and a methanol dehydration catalyst (γ-A1₂O₃) has been investigated for one-, two-, and three-layer catalyst beds. There is a common regularity for these three variants: with an increasing temperature, the total CO conversion decreases, the CO-to-methanol conversion decreases, and the CO-to-DME conversion increases. The largest values of DME selectivity and DME yield have been attained with the three-layer bed. The highest DME yield has been obtained at 250–285°C. Use of a mechanical mixture of the methanol synthesis catalyst and alumina makes it possible to efficiently obtain DME from syngas ballasted with nitrogen (20 vol %) at an H₂/CO ratio of 1, which is unfavorable for methanol synthesis. The DME yield on the syngas input basis in this case with the ballast gas (nitrogen or CO₂) taken into account can be about 10 wt %.     

Effect of H2O on Cu-based catalyst in one-step slurry phase dimethyl ether synthesis

One-step dimethyl ether (DME) synthesis in slurry phase was catalyzed by a hybrid catalyst composed of a Cu-based methanol synthesis catalyst and a γ-Al₂O₃ methanol dehydration catalyst under reaction conditions of 260 °C and 5.0 MPa. It was found that instability of the Cu-based catalyst led to rapid deactivation of the hybrid catalyst. The stability of the Cu-based catalyst under DME synthesis conditions was compared with that under methanol synthesis conditions. The results indicated that harmfulness of water, which formed in DME synthesis, caused the Cu-based catalyst to deactivate at a high rate. Surface physical analysis, elemental analysis, XRD and XPS were used to characterize the surface physical properties, components, crystal structures and surface morphologies of the Cu-based catalysts. It was found that Cu⁰ was the active component for methanol synthesis and Cu₂O might have less activity for the reaction. Compared with methanol synthesis process, crystallite size of Cu became bigger in DME synthesis process, but carbon deposition was less severe. It was also found that there was distinct metal loss of Zn and Al caused by hydrothermal leaching, impairing the stability of the catalyst. In slurry phase DME synthesis, a part of Cu transformed into Cu₂(OH)₂CO₃, causing a decrease in the number of active sites of the Cu-based catalyst. And some ZnO converted to Zn₅(OH)₆(CO₃)₂, which caused the synergistic effect between Cu and ZnO to become weaker. Crystallite size growth of Cu, carbon deposition, metal loss of Zn and Al, formation of Cu₂(OH)₂CO₃ and Zn₅(OH)₆(CO₃)₂ were important reasons for rapid deactivation of the Cu-based catalyst.     

Conversion of methane on catalysts obtained via self-propagating high-temperature synthesis

Monolith metalloceramic catalysts for the selective oxidation of methane are prepared via self-propagating high-temperature synthesis (SHS) from NiO, ZrO₂, MgO, Al, Ni and other powders. Catalytic tests of monolith samples are performed in a flow reactor at 800°C using a methane-air mixture (methane, 29.6 vol %). SHS catalysts are shown to attain the level of platinum and platinum/rhodium catalysts through the yield of syngas (CO + H₂) and to surpass them in the case of Ni 52.9 ZrO₂ 9.5 composition. The latter is used as a catalyst to develop a pilot autothermal syngas generator with a capacity of 30 m³/h. Syngas is generated via carbon dioxide methane conversion (CDMC) on SHS platinum-modified Ni₃Al powder catalysts. The samples are tested in a flow fixed-bed reactor at a catalyst volume of 1 cm³, a grain size of 600–1000 μm, temperatures of 600–900°C, and a volumetric flow rate of 100 cm³/min (CH₄ : CO₂ : He = 20 : 20 : 60 vol %). The catalysts developed for converting natural gas into syngas are shown to be highly active and stable in a high-temperature redox medium. This work is the first step in the synthesis of dimethyl ether, which could compete successfully with diesel fuel.     

A study on the catalytic performance of Pd/γ-Al2O3, prepared by microwave calcination, in the direct synthesis of dimethylether

A series of Pd/γ-Al₂O₃ hybrid catalysts were prepared by impregnation and subsequent calcination under microwave irradiation. The catalysts were used for direct synthesis of dimethylether (DME) from syngas. The results show that calcination under microwave irradiation improved both the activity and selectivity of the catalysts for DME synthesis. The optimum power of the microwave was determined to be 420 W. Under such optimum conditions, CO conversion, DME selectivity and time space yield of DME were 60.1%, 67.0%, and 21.5 mmol·mL⁻¹·h⁻¹, respectively. Based on various characterizations such as nitrogen physisorption, X-ray diffraction, CO-temperature- programmed desorption, and Fourier transform infrared spectral analysis, the promotional effect of the microwave irradiation on the catalytic property was mainly attributed to both the higher dispersion of Pd and the significant increase in the adsorption on the CO-bridge of Pd. Microwave irradiation with very high power led to the increase in CO-bridge adsorption and thereby decreased the catalytic activity, whereas the coverage by metallic Pd of the active sites on acidic γ-Al₂O₃ significantly occurred under microwave irradiation with very low power, resulting in a decrease in the selectivity to DME.