Intrinsic kinetics study of LPDME process from syngas over bi-functional catalyst

The intrinsic kinetics of the three-phase dimethyl ether (DME) synthesis from syngas over a bi-functional catalyst has been investigated in a agitated slurry reactor at 20–50 bar, 200–240 °C and H₂/CO feed ratio from 1 to 2. The bi-functional catalyst was prepared by physical mixing of CuO/ZnO/Al₂O₃ as methanol synthesis catalyst and H-ZSM-5 as methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H₂, methanol dehydration and water gas shift reaction were chosen as the independent reactions. A kinetic model for the combined methanol and DME synthesis based on a methanol synthesis model proposed by Graaf et al. [G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of low pressure methanol synthesis, Chem. Eng. Sci. 43 (12) (1988) 3185; G.H. Graaf, E.J. Stamhuis, A.A.C.M. Beenackers, Kinetics of the three-phase methanol synthesis, Chem. Eng. Sci. 43 (8) (1988) 2161] and a methanol dehydration model by Bercic and Levec [G. Bercic, J. Levec, Intrinsic and global reaction rate of methanol dehydration over γ-Al₂O₃ pellets, Ind. Eng. Chem. Res. 31 (1992) 399–434] has been fitted our experimental data. The obtained coefficients in equations follow the Arrhenius and the Van’t Hoff relations. The calculated apparent activation energy of methanol synthesis reaction and methanol dehydration reaction are 115 kJ/mol and 82 kJ/mol, respectively. Also, the effects of different parameters on the reactor performance have been investigated based on the presented kinetic model.     

一步法合成二甲醚反应器的研究进展

综述了合成气一步法合成二甲醚反应器的发展近况,着重介绍了固定床、浆态床及组合床的研究进展,并根据国内外的研究对几种反应器进行了工艺比较。     

生物质合成气一步法合成二甲醚的研究

用共沉淀沉积法制备了生物质合成气直接合成二甲醚(DME)的催化剂,考察了固定床中温度、压力、空速等工艺条件对二甲醚合成性能的影响,同时基于Gibbs自由能最小法对合成DIME反应的化学平衡进行模拟计算,并与实际测试结果相比较.结果表明,模拟结果与测试结果吻合较好.     

Intrinsic kinetics of the Fischer-Tropsch synthesis over an impregnated cobalt-potassium catalyst

The optimal amount of 15 wt%Co/10 wt%K/Al₂O₃ catalyst was prepared using the impregnation technique in order to study the kinetics of the Fischer-Tropsch synthesis. The rate of synthesis was measured in a fixed-bed micro reactor with H₂/CO feed ratio of 1–3 and space velocity in the range of 2,700–5,200 h⁻¹ under reactor pressure of 8 bar and a temperature range of 210–240 °C. The experimental data were best fitted by a Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach rate in the form of - r_CO = (k₂ K₁ P_CO P_H2 )/(1 + K₁ P_CO ) - r_{CO} = (k_2 K_1 P_{CO} P_{H_2 } )/(1 + K_1 P_{CO} ). Furthermore, the data were fitted fairly well by a power law equation in the form of - r_CO = kP_CO^1.32 P_H2 ^1.42 - r_{CO} = kP_{CO}^{1.32} P_{H_2 }^{1.42} . The activation energies for LHHW approach model and power law equation were obtained as 138.5 kJ/mol and 87.39 kJ/mol, respectively.     

Thermodynamic equilibrium in the synthesis of dimethyl ether from synthesis gas

Chemical equilibrium in dimethyl ether synthesis from synthesis gas was studied thermodynamically over wide ranges of gas compositions and process parameters.     

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.     

串联催化剂在二甲醚与合成气制备乙醇反应中的性能研究

通过水热合成法和共沉淀法分别制备了分子筛催化剂和Cu/ZnO催化剂,将分子筛与Cu/ZnO调控成双层串联催化剂,并用于二甲醚与合成气通过两段反应制备乙醇。研究了反应温度和反应气组成等因素对反应的影响,比较了分子筛类型、助剂种类和含量等对催化剂活性的影响。结果表明,随反应温度增加,DME转化率和乙醇选择性呈现先增加后减小趋势,随着DME含量减少和CO含量增加,DME转化率和乙醇选择性增加。H-MOR分子筛与Cu/ZnO串联催化剂显示了最佳的催化活性;金属助剂能提高催化剂活性,尤其是含5%Cu的Cu/H-MOR与Cu/ZnO串联催化剂显示了最佳的催化反应活性,于最佳反应温度493 K下以Ar/DME/CO/H_2(1.6/1.0/47.4/50.0)为原料进行反应,DME转化率达到33.6%,乙醇选择性达到了44.5%。     

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。     

合成气一步法制二甲醚的一种分离流程

针对合成气一步法制备二甲醚的工艺路线,在进行了二甲醚吸收和精馏的实验基础上,提出了用水吸收一步反应冷凝后气相产物中的二甲醚的分离工艺流程:反应冷凝液相与吸收后的液体混合后进入二甲醚精馏塔,二甲醚产品从精馏塔侧线引出,塔底甲醇和水去甲醇精馏塔。在实验数据的基础上,对二甲醚分离工艺流程进行了模拟计算。     

Nanocrystalline gamma-alumina: A highly active catalyst for dimethyl ether synthesis

In this article, mesoporous nanocrystalline γ-Al₂O₃ with high surface area is synthesized by a simple sol-gel method with cationic surfactant as template. This sample is used for vapor-phase dehydration of methanol to Dimethyl ether. The synthesized catalyst showed a high surface area of 375 m² g^− 1 and a crystallite size of about 3.9 nm. NH₃-TPD analysis revealed that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently the catalytic activity.     

Intrinsic reaction rate and the effects of operating conditions in dimethyl ether synthesis from methanol dehydration

The kinetic behavior of a commercial γ-Al₂O₃ catalyst for the methanol to dimethyl ether (DME) dehydration reaction has been investigated using a differential fixed bed reactor at the pressure range 1–16 barg within a temperature range of 260–380 °C. The experimental runs were performed in a wide range of feed to water ratios. The experiments were designed by general full factorial design (GEFD) and a novel rate equation has been developed which exhibited the best fitting with our experimental data. Based on the analysis of variance (ANOVA), the following order of importance for operating conditions was obtained when the objective function is the yield of DME: Temperature >Water % in feed >Pressure. In addition, the optimum operating conditions for the maximum yield of DME, were found at T= 380°C, P=16 barg and zero wt% of water in the feed.     

Kinetics studies of dimethyl carbonate synthesis from urea and methanol over ZnO catalyst

A kinetic experiment of dimethyl carbonate (DMC) synthesis by urea methanol over ZnO catalyst was carried out in an isothermal fixed-bed reactor. A kinetic model based on the mole fraction was proposed and the kinetic parameters were estimated from the experimental results. The model predictions were compared with the experimental data and fair agreements were found. The effects of the reaction temperature (443–473 K), space time (0–4.7 h mol⁻¹ kg _cat ) and urea mass percent (5–9%) in feed on DMC mole fraction were investigated. It was found that the reactions are mainly influenced by the reaction temperature and space time rather than urea mass percent in feed. The experimental and simulated results indicated that the reaction from MC to DMC was the rate-controlling step in the DMC synthesis process from urea and methanol. It is important to remove the DMC and byproduct ammonia to achieve a high selectivity of DMC. This implies that reactive distillation might be used in the DMC synthesis on an industrial scale to achieve a higher selectivity of DMC.     

Direct synthesis of dimethyl ether from carbon-monoxide-rich synthesis gas: Influence of dehydration catalysts and operating conditions

Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO/ZnO system) with catalysts for methanol dehydration based on γ-Al₂O₃ or zeolites and γ-Al₂O₃ was identified as the most favorable dehydration catalyst. Various reaction parameters such as temperature, H₂/CO ratio and space velocity were studied. The impact of water on Cu/ZnO/Al₂O₃-γ-Al₂O₃ catalysts was investigated and no deactivation could be observed at water contents below 10% during running times of several hours. A running time of several days and a water content of 10% led to a significant increase of CO conversion but the water gas shift reaction became dominating and CO₂ was the main product. After termination of water feeding significant deactivation of the catalyst system was observed but the system returned to high DME selectivity. Catalyst stability and the influence of CO₂ in the gas feed were studied in experiments lasting for about three weeks. The presence of 8% of CO₂ caused an approximately 10% lower CO conversion and an about 5% lower DME selectivity compared to the reaction system without CO₂.     

Direct synthesis of dimethyl carbonate over rare earth oxide supported catalyst

Solid base catalysts for the direct synthesis of dimethyl carbonate (DMC) from carbon dioxide, methanol, and propylene oxide were prepared by loading KCl and K₂CO₃ on the surface of La₂O₃, Y₂O₃, CeO₂ and Nd₂O₃. The catalysts were characterized by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. The catalytic activities were efficiently influenced by the preparation conditions. The optimal loading amount of K₂CO₃ is 17.6% (mass) for KCl-K₂CO₃/Y₂O₃ and 22.2% for other catalysts. Supports affected the activity of catalyst. KCl-K₂CO₃/Nd₂O₃ exhibited the highest activity. The activity of KCl-K₂CO₃/Y₂O₃ increased with the increase of calcination temperature in the range of 800°C–900°C. The formation of KYO₂, Y₃O₄Cl or YO_X species probably promoted the catalysts. Translated from Natural Gas Chemical Industry, 2006, 31(1): 39–43 [译自: 天然气化工]     

Modeling the low-temperature synthesis of dimethyl ether from methanol

The low-temperature catalytic dehydration of methanol to dimethyl ether (DME) has been analyzed. Efficient sulfocationic catalysts for the liquid-phase dehydration of methanol within a temperature range of 90–150°C and polyoxide catalysts for the gas-phase dehydration of methanol within a temperature range of 130–220°C have been selected. Kinetic models of these reactions are constructed, and their constants are determined from the results of kinetic experiments. The constructed models are shown to be adequate to experiment. The selected catalysts open additional opportunities for intensifying the processes of DME synthesis from methanol and syngas, abruptly reducing the primecost of the target product, dimethyl ether.     

The electro-oxidation of dimethyl ether on platinum-based catalyst

Cyclic voltammetry (CV) and stripping voltammetry were used to study the electro-oxidation of dimethyl ether (DME) on powder microelectrodes (PMEs) containing Pt black and Pt–Ru black. As evidenced by current–time curves of DME oxidation, Pt–Ru was better than Pt in catalytic oxidation of DME, which is due to the high concentration of OH_ads species on its surface. Results also showed that high temperature not only promotes the oxidation of DME, but also increases the concentration of OH_ads species formed by water decomposition. In addition, the performance of single direct DME fuel cell was investigated combined with gas chromatographic (GC) analyses of its anode outlet stream. Based on CV tests, a mechanism of DME electro-oxidation was tentatively proposed, indicating two kinds of DME adsorption modes, Pt–CO and Pt–COH existed on Pt surface.     

Liquid phase methanol and dimethyl ether synthesis from syngas

The Liquid Phase Methanol Synthesis (LPMeOH^TM) process has been investigated in our laboratories since 1982The reaction chemistry of liquid phase methanol synthesis over commercial Cu/ZnO/Al₂O₃ catalysts, established for diverse feed gas conditions including H₂-rich, CO-rich, CO₂-rich, and CO-free environments, is predominantly based on the CO₂ hydrogenation reaction and the forward water-gas shift reactionImportant aspects of the liquid phase methanol synthesis investigated in this in-depth study include global kinetic rate expressions, external mass transfer mechanisms and rates, correlation for the overall gas-to-liquid mass transfer rate coefficient, computation of the multicomponent phase equilibrium and prediction of the ultimate and isolated chemical equilibrium compositions, thermal stability analysis of the liquid phase methanol synthesis reactor, investigation of pore diffusion in the methanol catalyst, and elucidation of catalyst deactivation/regenerationThese studies were conducted in a mechanically agitated slurry reactor as well as in a liquid entrained reactorA novel liquid phase process for co-production of dimethyl ether (DME) and methanol has also been developedThe process is based on dual-catalytic synthesis in a single reactor stage, where the methanol synthesis and water gas shift reactions takes place over Cu/ZnO/Al₂O₃ catalysts and the in-situ methanol dehydration reaction takes place over -Al₂O₃ catalystCo-production of DME and methanol can increase the single-stage reactor productivity by as much as 80%. By varying the mass ratios of methanol synthesis catalyst to methanol dehydration catalyst, it is possible to co-produce DME and methanol in any fixed proportion, from 5% DME to 95% DMEAlso, dual catalysts exhibit higher activity, and more importantly these activities are sustained for a longer catalyst on-stream life by alleviating catalyst deactivation.     

NC306型铜基甲醇合成催化剂宏观动力学研究

采用磁力搅拌内循环无梯度反应器在５ＭＰａ、２３０～２７０Ｃ和气体组成（摩尔分率）ＣＯ０．０３９１～０．１７２３,ＣＯ２０．００５５～０．１２３８,Ｈ２０．５８４０～０．７３４９（余为Ｎ２和ＣＨ４）条件下,对国产ＮＣ３０６型铜基甲醇合成催化剂的低压宏观动力学特性进行了实验研究,基于ＣＯ、ＣＯ２竞争加氢双路线合成甲醇反应模式。以Ｓｉｍｐｌｅｘ－Ｐｏｗｅｌｌ复合法对实验数据进行搜索、寻优,建立了ＮＣ３０６催化剂的宏观动力学模型。统计检验结果表明,所建模型良好地吻合了实验结果,是适宜和可信的。     

NC306型铜基甲醇合成催化剂宏观动力学研究C

采用磁力搅拌内循环无梯度反应器在 5MPa、 2 30～ 2 70℃和气体组成 (摩尔分率 ) CO0 .0 391～ 0 .1 72 3,CO2 0 .0 0 55～ 0 .1 2 38,H2 0 .5840～ 0 .7349(余为 N2 和 CH4 )条件下 ,对国产 NC30 6型铜基甲醇合成催化剂的低压宏观动力学特性进行了实验研究。基于 CO、CO2 竞争加氢双路线合成甲醇反应模式 ,以 Simplex- Powell复合法对实验数据进行搜索、寻优 ,建立了 NC30 6催化剂的宏观动力学模型。统计检验结果表明 ,所建模型良好地吻合了实验结果 ,是适宜和可信的。