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.     

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 %.     

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。     

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.     

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.     

不同硅铝比HZSM-5分子筛对合成气一步法制二甲醚的影响

采用固定床高压反应装置,以工业用（CuO／ZnO／Al2O3）作为甲醇合成催化剂,四种不同硅铝比（硅铝比为25、38、50和150）的HZSM-5作为甲醇脱水催化剂,二者机械混合制备出一步法合成二甲醚双功能催化剂。考察了催化剂中脱水组分（HZSM-5分子筛）的硅铝比对二甲醚合成反应的影响,并通过BET、XRD和NH,-TPD等手段对催化剂进行表征。结果表明,一步法合成二甲醚催化剂中脱水组分HZSM-5的最佳的硅铝比为50。     

Investigation of different precipitating agents effects on performance of γ-Al2O3 nanocatalysts for methanol dehydration to dimethyl ether

This research includes synthesis of nano-sized γ-Al₂O₃ catalyst for methanol dehydration reaction to produce DME. A co-precipitation method with four precipitants including sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate was used for this purpose. The catalysts were characterized by XRD, FTIR, NH₃-TPD, SEM, TEM and N₂ adsorption–desorption techniques. In order to investigate the catalyst activity, they were used in the fixed bed micro reactor for methanol dehydration reaction at different operating conditions. Also, a commercial γ-Al₂O₃ nanocatalyst was utilized for comparison purposes. The catalyst prepared by ammonium carbonate showed the highest yield of DME in comparison with other ones.     

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.     

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.     

不同硅铝比ZSM-5分子筛催化剂一步法甲醇制汽油

分别使用硅铝比为26、38、60和90的ZSM-5分子筛原粉制备4种催化剂ZSM-5-26、ZSM-5-38、ZSM-5-60和ZSM-5-90,用于一步法甲醇制汽油实验,并对催化剂进行XRD、IR、BET和NH3-TPD表征。利用100 m L微反固定床实验装置,在反应温度380℃、系统压力2.0 MPa和空速1.0 h-1条件下,考察4种催化剂一步法合成汽油过程的甲醇转化率、产物分布和产品组成等性质。结果表明,ZSM-5-60分子筛催化剂性能相对较好,拥有32.2%较为理想的汽油收率和产物组成。     

Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al-Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol-gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N₂ adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350-410 m²/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al-Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ?220 °C and as the temperature was raised to 300 °C, some CH₄ and CO₂ formed on the account of DME.     

Experimental study of improved two step synthesis for DME production

Dimethyl ether (DME) has received growing attention due to its potential use as a multi-purpose fuel. A new technical route of improved two step synthesis is proposed for DME production, which is composed of methanol synthesis and methanol dehydration in a fixed-bed reactor. The influences of the operating conditions including reaction pressure, temperature, H₂/CO mole ratio in the syngas and space velocity on CO conversion, selectivity and yield of DME are investigated. CO conversion and DME yield both increase monotonically with the pressure increase. The optimal reaction temperatures for the synthesis and dehydration of methanol are different. CO conversion increases at first and keeps constant when the H₂/CO mole ratio is above 2. DME yield increases obviously and then decreases gradually with the space velocity increase. The optimal conditions are obtained to maximize the CO conversion and DME selectivity. The reaction temperatures of the top and bottom stage are in the range of 270-280 °C and 235-245 °C, respectively. The optimal ratio of H₂/CO is above 2, and the space velocity is in the range of 1000-1300 h^− 1.     

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.     

二甲醚水蒸气重整制氢CuO-ZnO-Al2O3-ZrO2/固体酸复合催化剂

Steam reforming(SR) of dimethyl ether(DME) was investigated for the production of hydrogen for fuel cells.The activity of a series of solid acids for DME hydrolysis was investigated.The solid acid catalysts were ZSM-5 [Si/Al=25,38 and 50:denoted Z(Si/Al)] and acidic alumina(γ-Al₂O₃) with an acid strength order that was Z(25)>Z(38)>Z(50)>γ-Al₂O₃.Stronger acidity gave higher DME hydrolysis conversion.Physical mixtures containing a CuO-ZnO-Al₂O₃-ZrO₂ catalyst and solid acid catalyst to couple DME hydrolysis and methanol SR were used to examine the acidity effects on DME SR.DME SR activity strongly depended on the activity for DME hydrolysis.Z(25) was the best solid acid catalyst for DME SR and gave a DME conversion>90% [T=24℃,n(H₂O)/n(DME)=3.5,space velocity=1179 ml·(g cat)^-1·h^-1,and P=0.1MPa].The influences of the reaction temperature,space velocity and feed molar ratio were studied.Hydrogen production significantly depended on temperature and space velocity.A bifunctional catalyst of CuO-ZnO-Al₂O₃-ZrO₂ catalyst and ZSM-5 gave a high H₂ production rate and CO₂ selectivity.     

Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein

The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h^?1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H_xNa_1–xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol.     

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.     

Transformation of methanol to gasoline range hydrocarbons using HZSM-5 catalysts impregnated with copper oxide

Various CuO/HZSM-5 catalysts were studied in a fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. The catalysts were prepared by wet impregnation technique. Copper oxide loading over HZSM-5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, BET surface area, metal oxide content, scanning electron microscopy (SEM) and thermogravimetric (TGA) techniques were used to characterize the catalysts. Higher yield of gasoline range hydrocarbons (C₅-C₁₂) was obtained with increased weight % of CuO over HZSM. Effect of run time on the hydrocarbon yields and methanol conversion was also investigated. The activity of the catalyst decreased progressively with time on-stream. Hydrocarbon products’ yield also decreased with the increase in wt% of CuO. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst.     

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.     

Ammonolysis of ethanol on pure and zinc oxide modified HZSM-5 zeolites

Reaction between ethanol and ammonia have been studied on various zinc oxide modified HZSM-5 (Si/Al=225) catalysts under various conditions of temperature, C/N ratio of the reactants and their WHSV. Two pure zinc oxides were taken for the study. One was a highly active acidic form Z₁ and the other was a stoichiometric non acidic zinc oxide Z₂. The activity of the catalysts for ammonolysis reaction followed the order Z₂⪡Z₁⪡HZSM-5. However, for composite catalysts containing 10–40% Z₁ on HZSM-5, the activity increased synergistically and became maximum (∼81% conversion of alcohol) for the catalyst 40% Z₁/HZSM-5 and about 50% conversion for the catalyst 40% Z₂/HZSM-5. The products formed were mainly N-heterocycles. Some novel high molar mass N-heterocycles were also detected. The catalytic activity and product selectivity was crucially affected by the reaction conditions, particularly the effect of temperature; the optimum yield of the products was obtained at the catalyst temperature of 723 K, C/N ratio 0.3892 and WHSV of 2.5 h⁻¹.     

Selective Oxidation of Propylene to Propylene Oxide by Molecular Oxygen over Ti-Al-HMS Catalysts

Ti- and Al-containing hexagonal mesoporous silicas (HMS) were synthesized at ambient temperature using dodecylamine as surfactant, and the resultant compounds were used as catalysts for the oxidation of propylene by molecular oxygen. Ti-Al-HMS, which was prepared by reaction of Ti(iso-OC₃H₇)₄, Al(iso-OC₃H₇)₃ and SiOC₂H₅)₄ in an alcohol-aqueous solution in the presence of dodecylamine, showed 47.8 of conversion and 30.6 of selectivity for propylene oxide (PO) at 523K. The yield of PO over Ti-Al-HMS (14.6) was much higher than those over Ti-HMS (1.3) and Al-HMS (0.9) at the same reaction conditions. Ti-Al-HMS was also found to be more effective for PO formation than the supported catalysts (Ti/Al-HMS and Al/Ti-HMS) prepared by impregnation method. These results indicated that the simultaneous existence of Ti and Al in HMS was very important for improving the yield of PO from the oxidation of propylene, and the synthesis method influenced the catalytic activity of the Ti- and Al-containing HMS catalysts.