完全液相法催化剂上甲醇脱水合成二甲醚的动力学及DFT研究

采用完全液相法制备AlOOH催化剂并进行了浆态床反应器中甲醇脱水制备二甲醚的反应动力学和DFT的研究。在3种甲醇脱水制备二甲醚的反应机理中,以表面反应即两个同时吸附的甲醇反应生成二甲醚作为速控步骤,所建立动力学模型的计算值和实验值吻合较好。采用DFT计算了液体石蜡环境中AlOOH(100)面的脱水反应,其反应过程和活化能结果与动力学模型结果基本一致,进一步表明采用该模型可以合理描述完全液相法制备的AlOOH催化剂表面甲醇脱水反应过程。     

Catalytic dehydration of methanol to dimethyl ether (DME) over Al-HMS catalysts

A series of Al-HMS with different Si/Al ratio was used as a solid acid catalyst for methanol dehydration to dimethyl ether (DME). The effect of temperature, feed composition, space velocity, and the catalyst Si/Al ratio on the catalytic dehydration of methanol was investigated. By decreasing Si/Al, the temperature required to reach equilibrium conversion of methanol decreased due to the increased number of acidic sites. Compared to commercial γ-Al₂O₃, Al-HMS-5 and Al-HMS-10, catalysts exhibited a high yield of DME. Among all Al-HMS catalysts, Al-HMS-10 exhibited an optimum yield of 89% with 100% selectivity and excellent stability for methanol dehydration to DME.     

Effect of the hybrid catalysts preparation method upon direct synthesis of dimethyl ether from synthesis gas

Direct synthesis of DME from synthesis gas attains more attention recently due to higher conversion and lower cost in comparison to dehydration of the methanol. In this work Synthesis gas To Dimethylether (STD) conversion was examined on various hybrid catalysts prepared by seven different methods. These catalysts had the same general form as CuO/ZnO/Al₂O₃ with theoretical weight ratio 31/16/53, respectively. A novel preparation method for hybrid catalyst namely sol–gel impregnation has also been developed which showed better performance in comparison with the other methods. Also, in order to find out the effect of various alumina contents at a fixed CuO/ZnO ratio on the performance of the hybrid catalyst, a series of catalysts with different contents of alumina have been prepared by sol–gel impregnation method. The optimum weight ratio for CuO/ZnO/Al₂O₃ catalyst has been found to be about 2:1:5, respectively. These catalysts characterized by TPR, XRD, XRF, BET, TGA, N₂O absorption. The catalysts performance were tested at 240 °C, 40 bar and space velocity 1000 ml/g_cat.h, with the inlet gas composition H₂/CO/N₂ = 64/32/4 in a micro slurry reactor.     

Sunflower oil hydrogenation on Pd in supercritical solvents: Kinetics and selectivities

The partial hydrogenation of sunflower oil on a few supported Pd catalysts in supercritical (SC) dimethyl ether (DME) as reaction solvent was studied to obtain hydrogenates with low trans C 18:1 and stearic contents.The kinetics was determined on eggshell 0.5% Pd/Al₂O₃ and uniform 2% Pd/C catalysts using a sequential experimental design in a continuous, radial-flow, internal recycle reactor. The operating variables were temperature (456–513 K), pressure (18–23 MPa) and the space-velocity (WHSV = 41–975 h⁻¹). The rotation frequency and the molar feed concentration (oil:H₂:DME) were held constant at 157 rad/s and 1:4:95 mol%, respectively. Kinetic scheme was based on that published before. Some reactor runs were simulated using mixed-flow assumption and the kinetics data for both systems with good results. A comparison was established between the eggshell 0.5% Pd/Al₂O₃ in DME and the data for 2% Pd/C in propane with respect to trans production and stearic formation. trans seems to be lower using 2% Pd/C in propane, while the undesired stearic formation is less on the eggshell 0.5% Pd/Al₂O₃ catalyst in DME. An overview is presented on the merits of the catalysts available for the SCF process in terms of linoleic selectivity and trans yield on a few vegetable fats.     

Effect of the P/Al ratio on the performance of modified HZSM-5 for methanol dehydration reaction

The precipitation method was used to modify HZSM-5 by coating it with aluminophosphate at P/Al molar ratios of 0.3, 0.8, 1.2 and 1.5. These catalysts were characterized by XRD, NH₃-TPD, BET, FT-IR, ICP-TEOS and SEM and evaluated as catalysts for the methanol dehydration reaction. The ZALPO0.8 catalyst achieved 86% conversion which was the highest conversion till 315 °C. It was found that primary benefits of AlPO modification were that it tended to retard the activity of the highly active acid sites which promote dimethyl ether decomposition and led to decrease in the apparent activation energy.     

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.     

Process modelling of dimethyl ether production from Victorian brown coal—Integrating coal drying,gasification and synthesis processes

Power plants using Victorian brown coal operate at low efficiency. Being reactive and spontaneously combustible, dried brown coals cannot be exported either. Synthesis of dimethyl ether (DME) is one option for the production of liquid fuel, an exportable product for power generation and transportation. This paper presents a steady-state process model for DME production using brown coal including drying, gasification and DME synthesis. The yield of the DME was a maximum for H₂ to CO molar ratio of 1.41 and 0.81 at the gasifier outlet and the DME reactor inlet respectively. A process efficiency of 32% and CO₂ emission of 2.91 kg/kg of DME was obtained. Improved yield of DME is achieved when CO₂ is removed from the fuel gas prior to feeding to the synthesis reactor. Integration of waste heat and design of appropriate catalyst for gasification and DME synthesis can result in further improvements in the process.     

The Structure Properties of CuZnAl Slurry Catalysts Prepared by a Complete Liquid-Phase Method and its Catalytic Performance for DME Synthesis from Syngas

Four CuZnAl slurry catalysts with different contents of Al were directly prepared from the solution of these metal salts to catalyst slurry by a complete liquid-phase method. The structure properties of the catalysts were characterized by XRD, BET, XPS, FTIR, and their catalytic performances for the single-step synthesis of Dimethyl ether (DME) from syngas were evaluated in a slurry reactor of 250 mL with a mechanical magnetic agitator. The results indicate the main phase existed in the catalysts are Cu, Cu₂O, ZnO and boehmite (AlOOH) and the structures of pore and surface are comparable with those of the commercial methanol synthesis catalysts. Activity tests show that the slurry catalysts are quite effective for the single-step synthesis of DME from syngas. Among them, the catalyst with 2.09 mol% Al is best, whose DME selectivity reaches 93.08%. All of the catalysts prepared by the novel method exhibit good stability during the reaction time investigated for 18 days.     

Effects of temperature and feed composition on catalytic dehydration of methanol to dimethyl ether over γ-alumina

Catalytic dehydration of methanol to dimethyl ether (DME) is performed in an adiabatic fixed bed heterogeneous reactor by using acidic γ-alumina. By changing the mean average temperature of the catalyst bed (or operating temperature of the reactor) from 233 up to 303 °C, changes in methanol conversion were monitored. The results showed that the conversion of methanol strongly depended on the reactor operating temperature. Also, conversion of pure methanol and mixture of methanol and water versus time were studied and the effect of water on deactivation of the catalyst was investigated. The results revealed that when pure methanol was used as the process feed, the catalyst deactivation occurred very slowly. But, by adding water to the feed methanol, the deactivation of the γ-alumina was increased very rapidly; so much that, by increasing water content to 20 weight percent by weight, the catalyst lost its activity by about 12.5 folds more than in the process with pure methanol. Finally, a temperature dependent model developed to predict pure methanol conversion to DME correlates reasonably well with experimental data.     

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 and characterization of Ce–La oxides for the formation of dimethyl carbonate by transesterification of propylene carbonate

A series of cerium–lanthanum catalysts prepared using the co-precipitation method were investigated for transesterification of propylene carbonate (PC) with methanol to produce dimethyl carbonate (DMC). Synthesized catalysts were characterized by XRD, CO₂- and NH₃-TPD, N₂ adsorption/desorption and SEM–EDX techniques. Studies were carried out to study the effect of reaction conditions such as methanol/PC molar ratio (4–12), catalyst dose (2–10 wt.% of PC), reaction time (2–10 h) and temperature (140–180 °C) on the DMC yield. Highest PC conversion and DMC yield of 72% and 74%, respectively, were observed with catalysts having a 1:4 Ce/La molar ratio.     

Direct conversion of syngas to DME as a green fuel in a high pressure microreactor: Influence of slurry solid content on characteristics and reactivity of washcoated CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

Microchannels of a stainless steel microreactor were successfully washcoated with slurry of Cu–ZnO–Al₂O₃/HZSM-5 (CZAZ) nanocatalyst with different concentrations (10, 20 and 30 wt.%). The properties of nanocatalyst and the washcoated microchannels were investigated by XRD, FESEM, N₂ physisorption, FTIR, EDX-Dot mapping and EDX-Line mapping analysis. The best adherence was observed for 20 wt.% catalyst which has a uniform coating, almost no cracks and homogenous dispersion of copper and zinc. Trend of weight gain during 10 soaks in catalyst slurry was very slow for 10 wt.% but faster for 20 and 30 wt.%. Low amount of weight gain was observed for the last soaks of catalyst slurry in the case of 30 wt.% washcoating. The performance of microreactor with different slurry concentrations were evaluated in direct synthesis of DME at 200–300 °C, 60–150 cm³/min and 40 bar. Regardless of slurry concentration, the microreactor exhibited a better reactivity in comparison to fixed-bed reactor performance. Among three different slurry concentrations, 20 wt.% catalyst slurry revealed the best reactivity in direct DME synthesis. The reduction in reactor performance at higher flow rates was significant in the fixed-bed reactor while microreactor, particularly 20 wt.% washcoated channels, revealed less drastic reduction.     

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。     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

A novel monolith catalyst of plate-type anodic alumina for the hydrolysis of dimethyl ether

A novel monolith catalyst of plate-type anodic alumina was applied in the dimethyl ether (DME) hydrolysis reaction system. The reactivity of the anodic alumina with hydration treatments in DME hydrolysis reaction was investigated. The preferred hydration-treated temperature was found to be 80 °C and the anodic Al₂O₃/Al monolith exhibited higher activity than the commercial Al₂O₃ in DME hydrolysis reaction. Meanwhile, the anodic Al₂O₃/Al monolith was proven to have higher MeOH effluent mole percentage with less unfavorable side reactions than the ZSM-5 catalyst. The anodic γ-Al₂O₃/Al monolith had just 0.85% coking while the ZSM-5 catalyst had 8.81% after 100 h of continuous experiments.     

Surface Properties and Catalytic Activity of TiO2–ZrO2 Mixed Oxides in Dehydration of Methanol to Dimethyl Ether

A series of TiO₂–ZrO₂ mixed oxides with varying molar ratio of TiO₂ to ZrO₂ were prepared by the co-precipitation method. The crystalline phases of the oxides were characterized by XRD and their acid–base properties by TPD of NH₃ and CO₂ and IR of adsorbed pyridine. The catalytic activities were investigated for the vapor phase dehydration of methanol to dimethyl ether (DME) in a fixed-bed reactor under atmospheric pressure. The mixed oxides are highly amorphous in nature. The acid–base properties and CH₃OH conversion activity are increasing with TiO₂ content and an optimum value is achieved for a molar ratio of Ti/Zr in the vicinity of 1/1. At lower reaction temperature (<300 °C), the selectivity for DME is nearly 100%. A good correlation is observed between dehydration activity and the acid–base properties of the TiO₂–ZrO₂ catalysts. It is significant to note that TiO₂–ZrO₂ catalysts show high stability against water during dehydration reaction. Based on our results, a surface mechanism involving both acid–base sites has been proposed for DME formation.     

Performance of modified H-ZSM-5 zeolite for dehydration of methanol to dimethyl ether

The conversion of methanol to dimethyl ether was carried out over various commercial zeolites and modified H-ZSM-5 catalysts to evaluate their catalytic performance. A series of commercially available zeolite samples were used for vapor-phase dehydration of methanol to DME. Catalyst screening tests were performed in a fixed-bed reactor under the same operating conditions (T = 300 °С, P = 16 barg, WHSV = 3.8 h⁻¹). It was found that all the H-form zeolite catalysts in this study were active and selective for DME synthesis. According to the experimental results MDHC-1 catalyst exhibited the highest activity in dehydration of methanol.After finding the most active catalyst, the H-MFI90 zeolite was modified with Na content varying from 0 to 120 mol%, via wet-impregnation method to further improve its selectivity. All of catalysts were characterized by BET, XRD, NH₃-TPD, ICP, TGA, SEM, FT-IR and TPH techniques. It was found that these materials affected activity of MDHC-1 zeolite by changing its acidity. Ultimately, among all the catalysts studied, Na₁₀₀-modified H-MFI90 zeolite exhibited optimum activity, selectivity and stability at methanol dehydration reaction.     

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。     

Synthesis of dimethyl ether from syngas obtained by coal gasification

The characteristics of a tubular fixed-bed reactor for the direct synthesis of dimethyl ether (DME) from syngas obtained by coal gasification have been developed. DME synthesis test was conducted with a hybrid DME synthesis catalyst (CuO/ZnO/Al₂O₃ for methanol forming, γ-alumina for methanol dehydration) to understand the performance under the conditions of 6.0MPa, 260°C and GHSV=3,000 l/kg-cat·h. The H₂ conversion and CO conversion were 85-92%, 37-45%, respectively. About 68-80% of DME selectivity was observed. DME synthesis reactor also operated at the productivity of 4.6-4.9 mol/kg-cat·h, which is slightly higher than that in the Peng’s prediction results in case of H₂ : CO=0.5.     

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.