Catalytic dehydration of methanol to dimethyl ether over mordenite catalysts

The conversion of methanol to dimethyl ether was carried out over various commercial mordenite and ion-exchanged catalysts to evaluate the catalytic performance of mordenite catalysts with different pore structures and acidities. These catalysts were compared for their catalytic properties in a fixed-bed reactor at 1 atm, 573 K and LHSV of 2.84 h^− 1. The catalysts were characterized by BET, ICP, NH₃-TPD, XRD, TGA and FT-IR techniques. The ion-exchanged mordenite showed higher activity, selectivity and good stability in dehydration of methanol due to the addition of medium acid sites. Also, the effect of water on catalyst deactivation was investigated over two selected catalysts in order to develop a suitable catalyst for synthesis of dimethyl ether. It was found that the H-mordenite catalyst supplied by Süd-chemie Co., (MCDH-1) was more active and less deactivated than another one in a feed containing 20 wt.% water.     

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.     

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.     

Dimethyl ether synthesis via methanol and syngas over rare earth metals modified zeolite Y and dual Cu–Mn–Zn catalysts

A series of zeolite Y modified with La, Ce, Pr, Nd, Sm and Eu were prepared via ion-exchange, and characterized by XRD, FT-IR and NH₃-TPD. It was found that these rare earth metals were encapsulated in the supercage of zeolite Y and resulted in its enhanced acidity. Among them, La-, Ce-, Pr- and Nd-modified zeolite Y exhibited higher activity and stability (than pure HY) for methanol dehydration to dimethyl ether (DME). For DME synthesis directly from CO hydrogenation using the dual Cu–Mn–Zn/modified-Y catalysts, it was found that Cu–Mn–Zn/La–Y and Cu–Mn–Zn/Ce–Y were more active than Cu–Mn–Zn/pure-HY. The conversion of CO on Cu–Mn–Zn/Ce–HY achieved 77.1% in an isothermal fixed bed reactor at 245 °C, 2.0 MPa, H₂/CO = 3/2 and 1500 h⁻¹.     

工艺条件对甲醇脱水制二甲醚反应的影响

以La改性氧化铝为催化剂,在模拟绝热固定床反应器中考察工艺条件对甲醇气相脱水制二甲醚反应的影响。结果表明,甲醇进料温度210℃时,甲醇脱水反应剧烈,绝热温升约130℃。催化剂床层热点温度低于380℃时,二甲醚选择性大于98%,过高温度产生大量副产物甲烷。反应压力对反应影响甚微。在甲醇进料温度240℃(热点温度370℃)、甲醇进料空速1.5 h-1和反应系统压力为50 k Pa条件下,甲醇转化率大于84%,二甲醚选择性大于98.5%,连续运转2 000 h,催化剂无明显失活迹象。     

甲醇气相脱水制二甲醚催化剂研究进展

甲醇气相脱水制二甲醚反应为固体酸催化反应,常用的固体酸催化剂有γ-Al₂O₃和分子筛类。γ-Al₂O₃表面存在弱酸中心或中等强度酸中心,催化剂有较好的初始催化活性,但活化所需的反应温度较高,耐水稳定性差;分子筛类催化剂表面有许多强酸性位,低温下催化活性较高,但在高温反应条件下易产生烃类副产物和积炭,热稳定性差。为改善这两类催化剂的催化性能,对催化剂进行了各种改性研究,改性后催化剂的活性、选择性和稳定性均有一定程度提高。综述了近年来在γ-Al₂O₃和分子筛催化剂上进行的改性研究,总结并展望了甲醇脱水催化剂的发展方向。     

Catalytic and kinetic study of methanol dehydration to dimethyl ether

Dimethyl ether (DME), as a solution to environmental pollution and diminishing energy supplies, can be synthesized more efficiently, compared to conventional methods, using a catalytic distillation column for methanol dehydration to DME over an active and selective catalyst. In this work, using an autoclave batch reactor, a variety of commercial catalysts are investigated to find a proper catalyst for this reaction at moderate temperature and pressure (110–135 °C and 900 kPa). Among the γ-alumina, zeolites (HY, HZSM-5 and HM) and ion exchange resins (Amberlyst 15, Amberlyst 35, Amberlyst 36 and Amberlyst 70), Amberlysts 35 and 36 demonstrate good activity for the studied reaction at the desired temperature and pressure. Then, the kinetics of the reaction over Amberlyst 35 is determined. The experimental data are described well by Langmuir–Hinshelwood kinetic expression, for which the surface reaction is the rate determining step. The calculated apparent activation energy for this study is 98 kJ/mol.     

Synthesis of alumina nanofibers: Role of calcination temperature on dimethyl ether production

In this work, we present the aluminum oxide (Al₂O₃) ceramic nanofiber synthesis by means of thermal calcination of polyvinylpyrrolidone–aluminum nitrate (PVP–Al(NO₃)₃) composite nanofibers previously prepared by electrospinning; the studied calcination temperatures were: 500, 650, and 800 °C. These nanofibers were evaluated for their catalytic conversion of methanol to dimethyl ether (DME) by dehydration reaction. Thermal properties were evaluated via thermal gravimetric analysis (TGA). The results showed full calcination of the PVP polymer support and complete transformation of Al(NO₃)₃ to Al₂O₃. The chemical composition was elucidated through Fourier-transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX). Structural characteristics were obtained by X-ray diffraction (XRD) and selected-area electron diffraction (SAED), which demonstrated an amorphous-to-crystalline evolution as the calcination temperature is increased, obtaining the cubic gamma-alumina (γ-Al₂O₃) structure with a crystallite size of 6 nm at 800 °C. Scanning and transmission electron microscopies (SEM and TEM, respectively) showed a decrease of the diameter fiber from 254 to 160 nm and an increase in surface roughness as the calcination temperature is increased. The Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) methods were employed to study the texture properties, and the results indicated an increase in pore volume (from 0.008022 to 0.04 cm³ g^–1), as well as surface area (from 10.22 to 37.46 g/m²) with increasing the calcination temperature. Finally, the synthesized Al₂O₃ ceramic nanofibers presented a catalytic conversion of methanol to DME of around 70% and a selectivity of 100% at 350 °C and 1 atm of pressure.     

甲醇催化脱水制二甲醚

研究了甲醇在ZSM-5沸石分子筛上催化脱水制二甲醚反应条件的影响。并在等温积分反应器中进行了本征动力学测试,对动力学模型进行筛选和参数估值,获得反应速率方程。     

甲醇制二甲醚用铝基催化剂的制备及其性能研究

研制出以氧化铝为载体的催化剂Ａ以及添加第ＩＶ副族元素的催化剂Ａ＋Ｂ,并与ＨＺＳＭ－５催化剂进行了活性对比。催化剂Ａ经１０００ｈ原粒度测试,结果表明：在反应温度３００℃,空速４．２５～４．５０ｈ－１,压力为常压的条件下,二甲醚选择性＞９９％,甲醇转化率≥８０％。     

甲醇气相脱水制二甲醚的催化剂

采用硝酸铝和氨水中和方法得到拟薄水铝石为原料,制备了甲醇制二甲醚催化剂。考察拟薄水铝石制备过程中的中和pH值、中和温度以及催化剂制备过程中的煅烧温度对甲醇气相脱水制二甲醚性能的影响。结果表明,当中和pH值在8.0±0.2、中和温度为50～60 ℃以及煅烧温度在550～600 ℃时得到的甲醇制二甲醚催化剂活性最高。通过在催化剂上添加SiO2、SO42?、PO43?等对甲醇脱水催化剂进行改性表明,改性后甲醇脱水催化剂活性有明显的提高。     

甲醇及二甲醚的生产现状和发展前景

介绍了甲醇及二甲醚的生产现状和发展前景,叙述了二甲醚的制备方法及用途。     

Methanol dehydration to dimethyl ether over highly porous xerogel alumina catalyst: Flow rate effect

Template-free sol-gel synthesis in the absence of an acid catalyst resulted in mesoporous nanocrystalline γ-alumina, meso-γ-Al₂O₃, possessing high surface areas, 400-460 m²/g, and high porosity, 1.4-1.9 cm³/g. The prepared alumina was characterized by powder XRD, SEM, and N₂ adsorption for BET surface area and porosity measurements. FTIR spectroscopy was employed to study the catalytic activity of meso-γ-Al₂O₃ and commercial γ-alumina, com-γ-Al₂O₃, in the dehydration reaction of methanol to dimethyl ether, DME. The prepared meso-γ-Al₂O₃ showed higher catalytic activity than the commercial catalyst with a conversion around 86% and DME selectivity around 99%. The products' selectivity showed a significant dependence on the flow rate of the feed gas stream. As the flow rate increased, the selectivity to DME increased on the account of the minor products, CO₂ and CH₄. However, as the flow rate decreased, more CO₂ formed and the DME selectivity decreased.     

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。     

Role of acidity on the hydrolysis of dimethyl ether (DME) to methanol

The activity of dimethyl ether (DME) hydrolysis was investigated over a series of solid acid and non-acid catalysts, zeolite Y [Si/Al = 2.5 and 15: denoted Y(Si/Al)], zeolite ZSM-5 [Si/Al = 15, 25, 40, and 140: denoted Z(Si/Al)], silica, zirconia, γ-alumina, and BASF K3-110 (commercial Cu/ZnO/Al₂O₃ catalyst). Dimethyl ether hydrolysis was carried out in an isothermal packed-bed reactor at ambient pressure.

Acid catalyzed dimethyl ether hydrolysis is equilibrium limited. All solid acid catalysts, with the exception of ZrO₂, attained equilibrium-limited conversions in the temperature range of interest (125–400 °C). Z(15), Z(25), and Z(40) reached equilibrium conversions at 200 °C, while Z(140), Y(15), and Y(2.5) reached equilibrium at 275 °C. γ-Alumina, the most active non-zeolite solid acid, attained equilibrium at 350 °C. Silica and BASF K3-110 were both ineffective in converting dimethyl ether to methanol. The observed activity trend for DME hydrolysis to methanol as a function of Si–Al ratio and catalyst type was:

     

甲醇制二甲醚用全氟磺酸树脂催化剂的研究

采用溶胶-凝胶法制备了用于甲醇气相脱水制二甲醚的新型催化剂全氟磺酸树脂/二氧化硅,应用X射线衍射、红外光谱、热重-差示扫描量热、低温氮物理吸附和氨程序升温脱附法对所得催化剂进行了表征。考察了反应温度、甲醇液空速、全氟磺酸树脂含量对甲醇气相催化脱水制二甲醚反应性能和催化剂稳定性的影响。结果表明,催化剂比表面积达820m2/g,在全氟磺酸树脂负载量10.0%、甲醇液空速1h?1、反应温度184℃时,甲醇转化率92.0%,二甲醚选择性99.9%,经350h实验测试,活性和稳定性没有明显变化。     

三相床中合成气一步法制二甲醚

在反应温度 2 30～ 2 70℃、压力 2～ 5MPa下 ,以医药用石蜡油为惰性液相介质 ,使用C30 2铜基催化剂和CM - 3- 1改性分子筛组成的复合催化剂 ,在三相搅拌釜中研究了合成气 (CO、CO2 、H2 )一步法合成二甲醚的反应。结果表明随着温度的升高 ,碳的转化率增加 ,二甲醚的选择性提高 ,甲醇的选择性降低 ;随着压力的增加 ,碳的转化率升高 ,二甲醚的选择性提高 ,甲醇的选择性降低     

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.     

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.