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.     

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。     

以联醇气为原料合成二甲醚的工业侧流试验

介绍了以联醇气为原料合成二甲醚的工业侧流试验,考察了联醇气制二甲醚用催化剂的性能。试验结果表明,该二甲醚合成催化剂的转化率、选择性、稳定性等性能达到了国内同类催化剂的先进水平。     

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.     

A comparative study of n-heptane, methyl decanoate, and dimethyl ether combustion characteristics under homogeneous-charge compression-ignition engine conditions

Combustion characteristics of n-heptane, a surrogate for hydrocarbon diesel, methyl decanoate, a surrogate for biodiesel, and dimethyl ether, a fuel that can be derived from bio-feedstocks, are investigated with a homogeneous constant-pressure reactor model and a homogeneous-charge compression-ignition engine thermodynamic simulation model, with focus on two variables: ignition delay and NO formation, under conditions of varying oxygen concentration. Negative temperature coefficient (NTC) behavior is observed for the three fuels. Reducing oxygen concentration increases ignition delay for all fuels. The results and conclusions with the two models differ because it is necessary to vary initial conditions in the engine model to optimize combustion phasing and maximize indicated efficiency.     

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.     

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.     

Design and operation of integrated pilot-scale dimethyl ether synthesis system via pyrolysis/gasification of corncob

The integrated pilot-scale dimethyl ether (DME) synthesis system from corncob was demonstrated for modernizing utilization of biomass residues. The raw bio-syngas was obtained by the pyrolyzer/gasifier at the yield rate of 40-45 Nm³/h. The content of tar in the raw bio-syngas was decreased to less than 20 mg/Nm³ by high temperature gasification of the pyrolysates under O₂-rich air. More than 70% CO₂ in the raw bio-syngas was removed by pressure-swing adsorption unit (PSA). The bio-syngas (H₂/CO ≈ 1) was catalytically converted to DME in the fixed-bed tubular reactor directly over Cu/Zn/Al/HZSM-5 catalysts. CO conversion and space-time yield of DME were in the range of 82.0-73.6% and 124.3-203.8 kg/m_cat³/h, respectively, with a similar DME selectivity when gas hourly space velocity (GHSV, volumetric flow rate of syngas at STP divided by the volume of catalyst) increased from 650 h⁻¹ to 1500 h⁻¹ at 260 °C and 4.3 MPa. And the selectivity to methanol and products was less than 0.65% under typical synthesis condition. The thermal energy conversion efficiency was ca. 32.0% and about 16.4% carbon in dried corncob was essentially converted to DME with the production cost of ca. ¥ 3737/ton DME. Cu (1 1 1) was assumed to be the active phase for DME synthesis, confirmed by X-ray diffraction (XRD) characterization.     

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.     

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。     

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.     

CO_2加氢合成二甲醚的适宜工艺条件

采用甲醇合成催化剂C207和分子筛HZSM-5混合制得CO2加氢合成二甲醚双功能催化剂,并在微型固定床反应装置上进行了活性评价。考察了反应温度、压力、氢碳摩尔比、空速等工艺条件对催化反应的影响。结果表明,温度对催化剂活性影响显著,适当提高温度有利于提高反应速率,适宜的温度操作范围260～270℃,增加压力,提高氢碳摩尔比有利于提高CO2转化率、二甲醚收率;适宜的空速范围1500～3000h-1。     

Deactivation and regeneration of hybrid catalysts in the single-step synthesis of dimethyl ether from syngas and CO2

Synthesis of dimethyl ether (DME) has been studied in a single reaction step, from H₂ + CO and H₂ + CO₂, in a fixed bed reactor on CuO-ZnO-Al₂O₃/γ-Al₂O₃ and CuO-ZnO-Al₂O₃/NaHZSM-5 hybrid catalysts. It has been proven that water content in the reaction medium (which is higher when CO₂ is fed) contributes to efficiently decreasing deactivation by coke in both catalysts and, consequently, when water is in the feed deactivation is insignificant for 30 h reaction. Nevertheless, water also decreases the activity of γ-Al₂O₃ acid function, due to its high adsorption capacity on the acid sites. Due to its importance in the viability of the industrial process, a study has been carried on the regeneration of both catalysts by coke combustion under controlled conditions (in order to avoid CuO sintering). For this study, the catalysts have been used under severe deactivation conditions. It has been proven that γ-Al₂O₃ does not have a suitable hydrothermal stability and that CuO-ZnO-Al₂O₃/NaHZSM-5 catalyst has an excellent performance and is suitable for using it in uninterrupted reaction–regeneration cycles.     

ZSM-5分子筛的合成与应用

总结分析了ZSM-5分子筛合成方面的研究进展,主要包括ZSM-5分子筛的合成,ZSM-5复合分子筛以及含有杂原子的ZSM-5分子筛的合成.在介绍各具体合成方法原理的同时,还讨论了各合成方法的优势与缺陷,这为今后ZSM-5分子筛在合成方面的研究提供了一定的借鉴.其次,还介绍了ZSM-5分子筛在炼油工业、精细化工及环境保护...     

Pathways for steam reforming of dimethyl ether under cold plasma conditions: A DFT study

Density functional theory has been used to study the thermodynamics associated with the steam reforming of dimethyl ether (DME) under cold plasma conditions. The calculation showed that the only thermodynamic obstacle of the production of hydrogen, CO, dimethoxymethane (DMMT) and 1,2-dimethoxyethane (DMET) was the dissociation of DME and steam molecules, which was easy to be overcome under cold plasma conditions. The formation of hydrogen and CO was through a multi-step pathway via the methoxy radical conversion and dissociation of formaldehyde, while the recombination of H generated extra hydrogen. The syntheses of DMMT and DMET are from the recombination of and CH₃O, which could be primarily generated through DME dissociation or the reactions: H + CH₃OCH₃, OH + CH₃OCH₃, . The structure and electronic properties of DME anion were also studied in this work. Theoretical calculation showed that the DME anion was less stable than the neutral molecule. The route for the formation of and CH₃O from DME anion is thermodynamically favorable.     

Optimization of rubber seed oil extraction using liquefied dimethyl ether

The objective of this study was to find the optimal condition for the extraction of rubber seed oil (RSO), using liquefied dimethyl ether (DME). Response surface methodology with a spherical central composite design model was employed to determine the optimal extraction condition, consisting of a seed moisture content (%wt), a solvent to solid ratio (g/g), and an extraction temperature (°C). A quadratic regression equation suggested the optimal extraction condition was a moisture content of 56.4%wt, a solvent to solid ratio of 6.7 (g/g), and a temperature of 33.3?°C. At this condition, the RSO yield predicted by the model gave a slight deviation of 0.68% from the experimentally validated results (41.48 versus 41.20%). RSO has a kinematic viscosity of 36.8 cSt, an acid value of 10.7 KOH/g oil, a fatty acid content of 5.1% and an unsaturated fatty acid content of 80%, resulting in the potential production of biodiesel, biolubricants, and biodegradable plastics.     

浆态床合成气合成二甲醚的工艺研究

考察了反应温度、反应压力、进料空速对浆态床合成二甲醚反应过程的影响,结果表明,在245～300℃范围内,随着反应温度的升高,一氧化碳转化率、二甲醚选择性和时空收率逐渐增加,在265℃时达到最大值后开始下降;在3.0～5.0MPa范围内,随压力的升高,一氧化碳转化率、二甲醚选择性和时空收率逐渐增加;在700～2500h-1范围内,一氧化碳转化率、二甲醚选择性随空速的增加而逐渐减小,空速以1200h-1为宜。     

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.     

复合固体酸催化剂在合成气制二甲醚中的应用研究

对镁碱沸石(FER)进行Zn、Mn金属改性,对γ-Al2O3进行S2O2-3、Ni2+改性,将改性后的FER和γ-Al2O3复合用于合成气直接制二甲醚催化剂中,作为甲醇脱水催化剂组分,制备出了Cu-Zn-Al/ASN/FZM双功能催化剂.在连续固定床高压反应器中,研究了改性条件、复合比及反应温度对催化剂性能的影响.在2...