Synthesis of dimethyl ether from CO and H<Subscript>2</Subscript>

Thermodynamic conditions for synthesizing dimethyl ether from synthesis gas are determined. The optimum conditions of the process are as follow: T ∼ 300°C at p = 3 MPa for two catalysts loaded into the reactor: methanol synthesis catalyst (Katalco-58) and catalyst of methanol dehydration to dimethyl ether (γ-Al₂O₃). The changes that occur with the catalysts during this process are demonstrated by electron scanning microscopy.     

Dehydration of methanol to dimethyl ether over modified vermiculites

Vermiculite materials pillared with alumina and modified with titanium were tested as catalysts for methanol dehydration to dimethyl ether. The different samples were characterized by powder XRD, TG, nitrogen adsorption, and pyridine adsorption followed by FTIR. Catalytic activity was evaluated in the temperature range 250–450 °C using different hourly space velocities, in the absence and in the presence of water in the feed. Modified vermiculites were shown to be active and selective in methanol dehydration. Al pillaring was found to result in more active catalysts than in the case of the modification with TiO₂. The influence of methanol hourly space velocity did not have a significant effect on methanol conversion, but it changed drastically selectivity to dimethyl ether at the beginning of the reaction. The addition of water had a negative effect on the catalysts’ activity and led to a faster catalyst deactivation.     

Phenol methylation over CrPO4 and CrPO4?AlPO4 catalysts

The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on a series of differently prepared CrPO₄ (Cr/P=1) and CrPO₄-AlPO₄ (CrAIP) catalysts, has been studied at different temperatures (473–673 K). The reaction is first order in phenol, giving a mixture of O- and C-alkylated products (C-alkylation taking place preferentially at theortho-position). Moreover, dimethyl carbonate is a better methylating agent than methanol.     

Synthesis of dimethyl carbonate from methanol and supercritical carbon dioxide

The synthesis of dimethyl carbonate (DMC) from methanol and supercritical carbon dioxide over various base catalysts has been studied. Compounds of group-I elements (Li, Na and K) were used as base catalysts. The promoter and the dehydrating agent were also used to enhance the yield of DMC. The effects of the catalysts, promoter and dehydrating agent on the yield of DMC were investigated. By-products such as dimethyl ether (DME) and C₁–C₂ hydrocarbons were formed with the DMC as a main product. The yield of DMC with different alkali metal catalysts ranked in the following order: K > Na > Li. The catalysts of the metal-CO₃ compounds were more effective than the metal-OH compounds in DMC synthesis. The maximum DMC yield reached up to about 12 mol% in the presence of K₂CO₃ (catalyst), CH₃I (promoter) and 2,2-dimethoxypropane (dehydrating agent) at 130–140°C and 200 bar. The reaction mechanism of DMC synthesis from methanol and supercritical carbon dioxide was proposed.     

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h^?1 and T = 560 K, while the inlet temperature (T_inlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al₂O₃ heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and ?102.1 kJ/mol, respectively.     

The mechanism of phenol methylation on acid and basic zeolite catalysts

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by ¹³C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.     

Cu-Fe-MgO/AlPO_4-5对甲醇水蒸气重整制氢的催化性能研究

以AlPO_4-5分子筛为载体,采用浸渍法制备Cu-Fe-MgO/AlPO_4-5催化剂,用于催化甲醇和水蒸气重整反应制氢气。采用XRD、N2吸附-脱附、H2-TPR、CO2-TPD和NH3-TPD等对催化剂进行表征。结果表明,加入Fe可以明显提高甲醇的转化率,但副产物二甲醚的选择性也增加,添加MgO对降低二甲醚具有明显的作用,但不能提高甲醇的转化率。AlPO_4-5负载Cu、Fe和MgO的质量分数分别为15%、6%和1%时具有较高的催化活性,在反应温度300℃、水醇物质的量比为1.1∶1和质量空速2.51 h~(-1)的条件下,对甲醇的转化率为93.08%,二氧化碳和氢气的选择性分别为95.80%和96.93%,对副产物一氧化碳和二甲醚的选择性分别为1.70%和2.51%。表征结果表明,Cu-Fe-MgO/AlPO_4-5同时含有弱酸弱碱和强酸强碱中心,适量的MgO增加了强碱中心的量,降低弱酸中心的强度,但对强酸中心影响不大。     

Influence of activated carbon modifications on their catalytic activity in methanol and ethanol conversion reactions

Activated carbons containing different surface functionalities have been investigated as catalysts in conversion reactions of ethanol and methanol. These carbon materials were prepared from Polish brown coal by chemical activation with potassium hydroxide and modified by the oxidation or reaction with ammonia or chlorine. The main process upon ethanol decomposition was its dehydrogenation, while in the process of methanol decomposition only a few samples were catalytically active, and the only product was dimethyl ether (a product of dehydration).      

Reaction Mechanism of Methanol to Formaldehyde over Fe‐ and FeO‐Modified Graphene

We employed periodic DFT calculations (PBE‐D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O?H cleavage. As a result, a methoxo‐containing intermediate is formed. Subsequently, H‐transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H₂O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol^?1.     

Hydration of dimethyl ether to methanol over solid acids

The hydration of dimethyl ether (DME) to methanol over various solid acids was studied. The acidity of the catalysts is determined by FTIR spectroscopy. The hydration is found to occur predominantly on the Br?nsted acid sites. Among the catalysts studied, WO_x/ZrO₂ and H-ZSM-5 appeared to be most active and selective.     

Synthesis of dimethyl carbonate (dmc) from co2, ethylene oxide and methanol using heterogeneous anion exchange resins as catalysts

Summary A two-step synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), carbon dioxide and methanol using heterogeneous anion exchange resins as catalysts is reported. The first step is the reaction of EO with CO₂ to form ethylene carbonate (EC), and the second one the transesterification of EC with methanol to yield DMC. Effect of various reaction parameters on the activity and selectivity of the catalysts used was investigated. After the first step, the crude mixture containing EC was directly reacted with methanol in the presence of a heterogeneous anion exchange resin catalyst to produce DMC in high yield and selectivity. Our process is highly economic.     

甲醇缩合生成二甲醚的质谱和量子化学研究

利用质谱分析结果结合量子化学abinitio方法,研究甲醇缩合脱水的反应过程.研究表明,在气相中,甲醇分子主要以二聚体和多聚体的形式存在,据此提出甲醇脱水反应的原始反应物是甲醇二聚体,而不是单个甲醇分子.研究了气相甲醇二聚体、过渡态的能量和结构、甲醇脱水生成二甲醚反应的可能反应途径和反应势垒,对甲醇缩合脱水生成二甲醚的反应性及其影响因素作了讨论.     

表面助剂改性对Cu/ZnO/Al2O3甲醇合成催化剂性能的影响

采用共沉淀-后浸渍方法制备了表面助剂改性的Cu/ZnO/Al₂O₃ (CZA)甲醇合成催化剂, 在固定床反应器上以合成气为原料分别考察了三种助剂(Zr、Ba和Mn)对CZA催化剂性能的影响; 以Zr为助剂时反应温度的影响; 并进行了催化稳定性试验. 利用粉末X射线衍射(XRD)、低温氮气吸脱附(N₂-sorption)、氧化亚氮(N₂O)反应吸附技术、X射线光电子能谱(XPS)、氢气程序升温吸脱附(H₂-TPD)、扫描电子显微镜(SEM)和高分辨透射电子显微镜(HR-TEM)技术对催化剂进行了表征.结果显示: 以Zr或Ba作为助剂能够明显提高CZA催化剂耐热前后的甲醇时空收率(STY); Mn的引入降低了CZA催化剂的耐热前活性; Zr的引入降低了CZA催化剂最高活性温度点, 增强了CZA催化剂的催化稳定性; 还原态CZA催化剂表面Cu⁰和ZnO都能吸附活化氢气, Cu⁰与ZnO的强相互作用有利于提高催化剂的性能, 耐热后催化剂性能的降低归因于Cu晶粒的长大. 在实验和表征结果基础上,提出了CZA催化剂上合成气制甲醇的“双向同步催化反应历程”.     

Features of Preparation of the Methanol Synthesis Component of a Bifunctional Dimethyl Ether Synthesis Catalyst

Kinetics and Catalysis - The production of dimethyl ether from synthesis gas involves the use of bifunctional catalysts, which mediate the synthesis and dehydration of methanol. The effect is...     

Preparation of ferric tungstate and its catalytic behavior toward methanol

Pure ferric tungstate, Fe₂(WO₄)₃, has been prepared and characterized for the first time. Ferric tungstate has a structure very similar to that of ferric molybdate with a unit cell volume about 1.5% larger. Decomposition to Fe₂WO₆ and WO₃ occurs at about 600°C. Ferric tungstate was tested as a catalyst for the selective oxidation of methanol and shown to have very different properties from ferric molybdate for this reaction. Whereas over the molybdate the predominant reaction is oxidation of methanol to formaldehyde, over the tungstate it is dehydration to dimethyl ether.     

Ethanol conversion and coke formation on TiO2 supported molybdovanadophosphoric acids

The catalytic conversion of ethanol on H_3+xPMo_12–xV_xO₄₀/TiO₂ catalysts (x=0,1,2) yielding both the products of alcohol dehydration (ethylene, diethyl ether) and dehydrogenation (acetaldehyde) but also ethane as secondary product is accompanied by the formation of coke. The amount and composition of coke was estimated on the basis of mass balance. The fact that the hydrogen/carbon atom ratio was low (0.6) supports the conclusion that coke is involved in the hydrogenation of primary ethylene.     

Catalytic Performances of Binder-free ZSM-5 Catalysts for Dehydration of Crude Methanol to Dimethyl Ether

A series of binder‐free ZSM‐5 catalysts and a binder‐containing catalyst were prepared and characterized with X‐ray diffraction (XRD), X‐ray fluorescence (XRF), ²⁷Al magic‐angle spinning (MAS) nuclear magnetic resonance (NMR), N₂ sorption and ammonia temperature‐programmed deposition (TPD) methods. The catalytic activity and selectivity in the dehydration of crude methanol to dimethyl ether (DME) were evaluated in a fixed‐bed reactor for the catalysts. The outstanding structural characters such as high zeolite contents, sufficiently open channels and richness in mesopores have been proved on these binder‐free catalysts. The influence of the solid‐acidity, which is closely related to the framework silica alumina ratio (SAR) of the catalysts, on the catalytic properties has been discussed. A binder‐free catalyst with a better potential in application has been selected for its high activity and selectivity, long life‐time and non‐sensitivity to water contents in the feed. The reason for its excellent performance of the catalyst was discussed.     

Direct synthesis of dimethyl carbonate ?from CH3OH AND CO2 by H3PW12O40/CexTi1-xO2 catalyst

Summary Ce_xTi_1-xO₂ and H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts were prepared using a sol-gel method, and applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ showed a better catalytic performance than the corresponding Ce_xTi_1-xO₂, due to the bifunctional catalysis of Br?nsted acid sites (provided by H₃PW₁₂O₄₀) and base sites (provided by Ce_xTi_1-xO₂). H₃PW₁₂O₄₀/Ce_0.1Ti_0.9O₂ showed the highest catalytic performance among the H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts.     

Review of Acetic Acid Synthesis from Various Feedstocks Through Different Catalytic Processes

Acetic acid (AA) has been largely used with a wide range of applications such as a raw material for a synthesis of vinyl acetate monomer, cellulose acetate or acetate anhydrate, acetate ester and a solvent for a synthesis of terephthalic acid and so on. The present paper briefly summarizes the commercialized chemical processes with their Rh or Ir-based catalytic systems in a liquid-phase carbonylation reaction such as Monsanto, Cativa and Acetica processes. In addition, some alternative catalytic systems such as heterogeneous catalysts to produce AA by direct oxidation or indirect carbonylation of dimethyl ether through BP-SaaBre process in a gas-phase reaction to solve some problems such as a difficult separation of homogeneous catalysts in a corrosive reaction medium. Some home-made heterogeneous catalysts such as a rhodium incorporated graphitic carbon nitride (Rh-g-C₃N₄) and some heterogenized homogeneous catalysts using the supports of tungsten carbide, iron oxide or graphitic carbon nitride containing rhodium complexes were also introduced for the synthesis of AA through a liquid-phase methanol carbonylation reaction to effectively solve the leaching problem of active rhodium metal as well as to mitigate the separation problem of homogeneous catalysts.     

Alkylation of phenol with dimethyl carbonate over AlPO4, Al2O3 and AlPO4-Al2O3 catalysts

The vapor-phase catalytic alkylation of phenol with dimethyl carbonate over different AlPO₄ (Al/P=1), Al₂O₃ and AlPO₄-Al₂O₃ (5–25 wt.% Al₂O₃) catalysts produces anisole (O-alkylation) as the major reaction product althougho-cresol (C-alkylation) and methylanisoles were also found. The reaction is first order in phenol while O-and C-alkylation follow parallel processes. As compared with methanol, DMC is far more effective as a methylating agent, and the methylation proceeds at a lower temperature and with higher O-alkylation selectivity.