Dehydration of ethyl alcohol on alumina-coated silica

Catalysts were prepared by precipitation of aluminium hydroxide on a wet silica gel. The dehydration of ethyl alcohol on catalysts varying in alumina content was studied at 307° using a flow system. The products of dehydration were ethylene, ether and water. The kinetics of the formation of ethylene followed the Langmuir-Hinshelwood mechanism, while the formation of ether occurred according to the Langmuir-Hinshelwood mechanism and the Rideal-Eley mechanism simultaneously. The catalytic activity was controlled by the amount of aluminium on the surface. The rate constants were correlated with the surface nature of the catalysts.     

Modeling the low-temperature synthesis of dimethyl ether from methanol

The low-temperature catalytic dehydration of methanol to dimethyl ether (DME) has been analyzed. Efficient sulfocationic catalysts for the liquid-phase dehydration of methanol within a temperature range of 90–150°C and polyoxide catalysts for the gas-phase dehydration of methanol within a temperature range of 130–220°C have been selected. Kinetic models of these reactions are constructed, and their constants are determined from the results of kinetic experiments. The constructed models are shown to be adequate to experiment. The selected catalysts open additional opportunities for intensifying the processes of DME synthesis from methanol and syngas, abruptly reducing the primecost of the target product, dimethyl ether.     

不同制备方法对AlOOH结构和甲醇脱水性能的影响

采用完全液相、水热和沉淀法制备了4种不同的AlOOH催化剂, 选用工业AlOOH(SB粉)作为对照催化剂, 分别用XRD、NH₃-TPD-MS、FT-IR、氮物理吸附和热重分析等方法对催化剂进行了表征并将其用于固定床甲醇脱水制二甲醚反应。活性评价结果显示, 不同方法制备的AlOOH催化剂的甲醇脱水能力存在明显差异, 完全液相法制备的催化剂经焙烧除炭后活性高, 稳定性好, 特别是有良好的低温催化活性, 而沉淀法制备的催化剂活性低且稳定性差。表征结果发现, 与γ-Al₂O₃不同, AlOOH表面拥有强、弱两种酸性中心, 弱酸量相对较高的AlOOH催化剂具有强的甲醇脱水能力, 较多晶格缺陷和晶粒度适中的催化剂有利于甲醇脱水能力的提高。     

醇类在Pt-TiO2纳米管上的光催化制氢

采用溶胶-凝胶法(sol-gel)、水热法和光沉积法制备了铂(Pt)负载量为0.5%的二氧化钛纳米管催化剂(TNT),并利用甲醇等醇类制氢。结果表明,所制备的催化剂具有良好的管状形貌;甲醇(CH₃OH)和水在同等数量级上共同吸附在催化剂表面9 h后制氢效率最高,核磁共振氢谱(¹H NMR)分析表明甲醇裂解制氢过程在催化剂表面进行,因氢键束缚产生的过渡产物无法脱附直至形成CO₂;醇类碳链长度、支链数目、羟基数目以及苯环基团等都对醇类制氢有着不同的影响,制氢过程中醇分子与催化剂的吸附作用强弱和醇分子被羟基植入的难易程度是制氢效果差异的主要原因。     

Analysis of microporosity and specific vapour sorption by zirconia gel

The surface properties of zirconia gel and its thermal dehydration products obtained in the temperature range 300–1000°C (573–1273 K) were investigated through the adsorption of water, methanol and carbon tetrachloride vapours at 35°C (308 K). The non specific character of carbon tetrachloride makes it a good probe for detecting microporosity in the gel. Hydrophilic centres on the zirconia surface appear to function as favourable adsorption sites for polar water and methanol adsorbate molecule. The high values of the areas obtained from water adsorption for highly hydroxylated samples may be explained by the fact that the smaller polar water molecules can penetrate into narrow pores and interact with the hydroxyl groups located there. The presence of a high concentration of hydroxyl groups in the micropores is evident from the sharp decrease in the methanol uptake by zirconia gel, since methanol is known to interact specifically with hydroxyl groups existing in mesopores or on plane surfaces through hydrogen bonding.     

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。     

CO2和甲醇直接合成碳酸二甲酯耦合脱水体系研究进展

二氧化碳和甲醇直接合成碳酸二甲酯反应受热力学平衡限制,导致反应物转化率和产物收率较低,极大地阻碍了其工业化应用。耦合脱水体系能够将反应过程中产生的水及时脱除,促进反应正向进行,进而提高产物碳酸二甲酯收率。根据耦合脱水的原理不同,主要可分为物理耦合脱水和化学耦合脱水。本文综合分析了近年来应用于该反应不同物理脱水工艺和化学脱水剂的研究进展,详细论述了不同脱水体系的脱水原理和对反应的促进作用,并对不同脱水体系的优点及局限进行了归纳和分析,提出通过优化反应工艺或设计新的反应工艺大幅降低反应体系的能耗,同时探索更加廉价、低毒且易循环利用的化学脱水剂是耦合脱水体系今后的主要发展趋势。     

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.     

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。     

乙基叔戊基醚的合成及反应动力学研究

用国产NKC－29型强酸性阳离子交换树脂为催化剂，在常液相条件下用乙醇和叔戊醇为原料合成了乙基叔戊基醚。讨论了温度，催化剂浓度，反应物初始摩尔比等参数对反应速度以及反应选择性的影响。结果表明：反应温度升高，将加快反应速度，但是当温度过高将加速叔戊醇的分解，使反应的选择性降低，催化剂浓度与产物的初始生成速率成线性关系，表明反应为动力学控制步骤：增加乙醇与叔戊醇的初始摩尔比，可有效控制叔戊醇分解为水与异戊烯的副反应。与另一种国产S－54型树脂催化剂比较的结果显示：NKC－29的催化活性及选择性优于S－54。根据实验结果并考虑水对催化剂的阻碍效应，建立了该反应的动力学模型，并得到了相应的模型参数，即反应速度常数和水的阻碍系数。实验结果与模型计算值吻合得较好。     

Influence of high-pressure on cononsolvency of poly(N-isopropylacrylamide) nanogels in water/methanol mixtures

We show that the temperature-induced collapse of poly(N-isopropylacrylamide) (PNiPAm) nanogels in water/methanol mixtures can be reversed by excess hydrostatic pressure. Small angle X-ray scattering (SAXS) results reveal that first a swollen surface layer is established and then the particles swell homogeneously. A threshold pressure needed for rewelling fully collapsed nanogels indicates that hydrophobic interactions inside the nanogel have to be compensated to form a swollen surface layer. The size change is related to a change in polymer solvation detected by infrared (IR) spectroscopy. Pressure favours polymer/water hydrogen bonds to the cost of methanol/polymer bonds so that water is enriched inside the nanogel.     

Dehydration of water‐plasticized poly(vinyl alcohol) systems: particular behavior of isothermal mass transfer

BACKGROUND: Water‐plasticized poly(vinyl alcohol) has been obtained by thermal processing. Dehydration is the key process for controlling the structure and performance of the water‐soluble polymer, and mass transfer is an important part of dehydration. RESULTS: A simple new model of a hyperbolic‐type function was developed to understand the mass transfer process of water‐plasticized poly(vinyl alcohol) systems during isothermal dehydration. The model was verified by statistical tests. The physical parameters in the model were defined as the maximum weight loss fraction and characteristic time. The dehydration rate, the key physical parameter in mass transfer, was obtained from the differential equation of the model. By use of the model, the characteristics of dehydration of poly(vinyl alcohol) were determined: the complete mass transfer process can be divided into a fast mass transfer before a characteristic time (τ) and a slow mass transfer after τ, and dehydration temperatures can also be divided into two intervals by different activation energies. In addition, the dehydration rate is inversely proportional to the degree of crystallinity. CONCLUSION: The results of the new model agree reasonably well with experimental results obtained by thermogravimetry and weighing. Poly(vinyl alcohol), as a water‐soluble semicrystalline polymer, exhibits a particular mass transfer behavior during dehydration. Copyright © 2008 Society of Chemical Industry     

The influence of dehydration on the interfacial bonding,microstructure and mechanical properties of poly(vinyl alcohol)/graphene oxide nanocomposites

The relationship between the interfacial bonding, microstructure and mechanical properties of the poly(vinyl alcohol)/graphene oxide nanocomposites (PVA/GO) has been investigated by controlling the water content through a dehydration process. The interfacial bonding in PVA/GO was predominantly by hydrogen bonds which were strongly affected by the dehydration process. Micro-voids in the microstructure formed after dehydration due to the shrinkage of the fibrils. A variety of hydrogen bonds including water–water, water–GO and water–PVA can be replaced with the strong PVA–GO interfacial bond resulting in a transition from ductile to brittle fracture. The tensile modulus and strength properties of the PVA and PVA/GO increased as the amount of residual water reduced, while the fracture strain was decreased. The surface mechanical properties of PVA/GO measured by nanoindentation showed broadly similar trends with water content as the bulk mechanical properties. However, there was a threshold value of approximately 3 wt.% water below which the surface mechanical properties decrease slightly. The indentation modulus was higher than the tensile modulus by a factor of at least three. The combined influence of the microstructure and the distribution of water in the nanocomposite is considered to be responsible for this.     

Poly(vinyl alcohol)/poly(vinyl pyrrolidone) interpenetrating polymer network: Synthesis and pervaporation properties

Novel interpenetrating polymer network membranes were made from poly(vinyl alcohol)/poly(vinyl pyrrolidone) blends of different compositions. The two polymer components were independently crosslinked chemically with glutaraldehyde and photochemically with 4,4′‐diazostilbene‐2,2′‐disulfonic acid disodium salt. The membrane performances were studied in pervaporation of tetrahydrofuran (THF)/water and THF/methanol mixtures. It was found that the membranes were excellent in THF dehydration, but much less efficient for the separation of THF/methanol mixtures. The pervaporation results were consistent with the membrane swelling data. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2808–2814, 2003     

Dehydration of Methanol to Dimethyl Ether by Catalytic Distillation

The kinetics of liquid catalytic dehydration of methanol over an ion exchange resin (Amberlyst 35) has been determined for the temperature range 343 to 403 K using a batch reactor. The experimental data are described well by an Eley‐Rideal type kinetic expression, for which the surface reaction is the rate‐determining step. A catalytic distillation process for methanol dehydration to dimethyl ether (DME) has been modeled using the experimentally determined kinetic data. The results were incorporated into the rate‐controlled reaction mode for RadFrac, a part of the commercial simulation program Aspen Plus. It was shown that synthesis of high purity DME can be achieved using a single catalytic distillation column. Thus there is significant potential for reduction of overall capital cost for a plant for methanol dehydration to DME when compared to conventional production facilities that involve separate reaction and distillation processes.     

叔丁醇脱水反应动力学研究

以国产NKC-9型强酸性阳离子交换树脂为催化剂,在常压液相下进行了叔丁醇脱水的反应动力学研究,为由叔丁醇脱水生产异丁烯工艺的开发提供了基本理论依据。在消除内外扩散影响下,讨论了反应温度、反应物初始浓度和催化剂用量等条件对反应速率的影响。结果表明：反应温度升高,将加快反应速率：水的存在对此反应过程产生阻碍效应,随着反应物初始浓度中水含量的增加,反应速率减小。考虑异丁烯在液相中含量很低以及产物水对反应的阻碍效应,建立了该反应的动力学模型,并得到了相应的模型参数。在实验温度范围内,速率模型计算结果与实验结果吻合较好。     

PEA-NaA /α-Al2OPEA-NaA /α-Al2O3复合支撑分子筛膜的微波水热合成

采用微波水热合成法在聚醚酰亚胺(PEI)-NaA分子筛/α-Al2O3复合载体表面合成了具有高选择性的致密NaA型分子筛膜,重点考察了微波辐射时间对成膜的影响。采用X射线衍射图谱(XRD)和扫描电子显微镜(SEM)对NaA型分子筛膜进行了表征。XRD结果表明,复合载体表面生成的膜中只有NaA分子筛的晶相;SEM结果表明,复合载体基膜表面覆盖了一层致密连续的NaA型分子筛膜。合成的NaA型分子筛膜在不同质量分数乙醇中的渗透汽化性能结果表明,渗透通量随乙醇质量分数增大而减小,分离因子则反之,当乙醇质量分数为95%时,渗透通量仅0.05 kg/(m2.h),而分离因子高达13 000。     

Cation Effects in the Conversion of Methanol on Calcium, Strontium, Barium and Lead Hydroxyapatites

The effect of the nature of the cation on the surface and catalytic properties of calcium, strontium, barium and lead hydroxyapatites and dicationic analogs containing lead and strontium or barium has been studied with methanol and deuterated methanol. XRD, XPS and ³¹P MAS NMR have been used to characterize the samples, and temperature programmed desorption of deuterated methanol has been employed to provide ancillary information. The dehydration/dehydrogenation of methanol is found to depend strongly on the nature of the divalent cation and is related to the binding strengths of methanol on the hydroxyapatites.     

From laboratory experiments to simulation studies of methanol dehydration to produce dimethyl ether—Part I: Reaction kinetic study

Most of the reaction rate equations for methanol dehydration are derived from the experiments conducted for crude methanol as feed and laboratory prepared catalysts, which are not exactly the same as industrial reactors conditions. In the present contribution, it is attempted to find suitable rate of reactions for pure methanol with no water as feed and commercial catalysts of HZSM-5 and γ-alumina at industrial conditions in methanol dehydration process. In addition, a comparison between the performances of the catalysts is performed. It is found that HZSM-5 has superior performances compared to the γ-alumina in terms of conversion. Modeling results are also indicated that the proposed rate of reaction predicts the behavior of the process, properly.     

氯乙酸氨解法甘氨酸合成工艺的研究

研究了氯乙酸氨解法制备甘氨酸的工艺条件,讨论了反应温度、催化剂用量和氨水浓度对氨解过程中氯乙酸转化率和甘氨酸产率的影响;研究了甲醇加入量和醇析温度对醇析过程中甘氨酸得率和纯度的影响。结果表明,氨解反应适宜温度为70～80℃,催化剂适宜用量为氯乙酸添加量的15%左右,氨水质量分数高有利于反应,在此工艺条件下氯乙酸的转化率达99.0%以上,反应液中甘氨酸的产率达98.0%以上;醇析过程中甲醇适宜加入量为氨解反应液体积的4.0～4.5倍,醇析温度选择在70～75℃之间,醇析过程中甘氨酸的得率大于79.0%,析出甘氨酸的纯度大于90.0%。