Gas-Phase Synthesis of Ethyl tert-Butyl Ether (ETBE) on H-ZSM-5 Catalyst in Continuous Fixed-Bed and Fluidized-Bed Reactors

The gas-phase synthesis of ETBE from ethanol and isobutene has been carried out over a H-ZSM-5 catalyst in two types of continuous-flow catalytic reactors, fixed-bed and fluidized-bed. We have studied the influence of temperature, molar ratio ethanol/isobutene and weight hourly space velocity on the yield of ETBE.     

Heteropolyacid–silica mediated [3+2] cycloaddition of azomethine ylides—a facile multicomponent one-pot synthesis of novel dispiroheterocycles

An efficient synthesis of dispiroindenoquinoxaline pyrrolizidine derivatives has been expediently accomplished by a one-pot four component 1,3-dipolar cycloaddition reaction. High regioselectivity was achieved using heteropolyacid H₄[Si(W₃O₁₀)₃]–silica as a catalyst. X-ray diffraction studies of one of the cycloadducts proved the structure and regiochemistry of the cycloadduct.     

HZSM-5分子筛上乙基叔丁基醚合成反应的理论研究

采用ONIOM (B3LYP/6-31G(d,p):UFF)分层计算的方法, 研究了HZSM-5 分子筛上乙醇和异丁烯合成乙基叔丁基醚(ETBE)的反应机理. 通过反应物在HZSM-5 分子筛上吸附性质的研究发现, 乙醇与分子筛酸性位相互作用形成氢键, 而异丁烯则作用在Brönsted 酸位上形成π配位吸附. 确定反应物吸附位置后, 进一步探索反应机理, 结果表明: HZSM-5分子筛上乙醇和异丁烯合成乙基叔丁基醚的反应为协同反应, 并且, 反应物吸附顺序的不同对反应过程存在一定的影响. ETBE合成反应的最优途径以反应物同时吸附形成的复合物作为起点. 在反应过程中, 形成π配位的H原子向异丁烯分子中不饱和双键的端位C原子靠近, 被吸附的乙醇分子中的O原子向异丁烯双键中的另一个C原子靠近, 直到形成C－O键, 生成ETBE. 这一过程中, 原有的质子H加成到异丁烯的端基C上形成C－H键, 而原醇羟基中的H和B酸位附近的O原子作用形成新的酸性位. 相应的协同反应的最低的反应势垒为25.14 kJ·mol^-1.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

碱处理丝光沸石的表征及其催化合成乙基叔丁基醚的性能

 研究了碱处理对丝光沸石物相、酸性质和催化合成乙基叔丁基醚(ETBE)性能的影响,并采用XRD,NH3-TPD,吡啶吸附的IR,SEM和N2吸附等方法对其进行了表征. 结果表明,碱处理含有模板剂的丝光沸石的相对结晶度、酸量、比表面积和孔容都增大. 碱处理已脱除模板剂的丝光沸石的相对结晶度、酸量、比表面积和孔容都减小. 碱处理含有模板剂的丝光沸石催化合成ETBE的活性明显高于碱处理已脱除模板剂的丝光沸石,在80 ℃左右即可达到最高活性点,其催化异丁烯的最高转化率为58%,比未经碱处理样品上异丁烯的最高转化率高约13%.     

Kinetics of liquid phase synthesis of ethyl tert‐butyl ether from tert‐butyl alcohol and ethanol catalyzed by β‐zeolite supported on monolith

This paper compared the performance of β‐zeolite and Amberlyst‐15 catalysts on a liquid phase synthesis of ethyl tert‐butyl ether (ETBE) from ethanol (EtOH) and tert‐butyl alcohol (TBA) β‐Zeolite was synthesized and deposited on monolith support. Its structure was confirmed by an XRD measurement and its composition was analyzed by an XRF measurement. It was found that even though the catalytic activity of β‐zeolite was lower than that of Amberlyst‐15, the selectivity of ETBE was much higher than that of Amberlyst‐15, resulting in almost the same level of ETBE yield. The dehydration of TBA to isobutene (IB) was the major side reaction. The kinetic study of the reaction catalyzed by β‐zeolite supported on monolith was carried out by using a semibatch reactor. The effect of external mass transfer was investigated by varying stirring speeds. The activity‐based rate expressions were developed taking into account of water inhibition. Three temperature levels of 323, 333, and 343 K were performed in the study to obtain the parameters in the Arrhenius's equation and the Van't Hoff's equation. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 292–299, 2002     

Silicotungstic acid/organically modified silane proton-conducting membranes

Proton-conducting gels and membranes were made from an organically modified silane incorporating a heteropoly acid, i.e. silicotungstic acid. The ORMOSIL host was generated from a bis end-capped triethoxysilane chemically bonded via the urea bridges to (1) a long poly(propylene glycol) chain or (2) a long poly(dimethylsiloxane) chain. The heteropolyacid acted simultaneously as a source of mobile protons and as a catalyst, initiating the hydrolysis/condensation reactions of the sol–gel composite. In addition to the bis end-capped triethoxysilane network former, different alkoxysilanes were tested as network modifiers to optimize the gelation time, mechanical properties, ionic conductivity and the retention of the heteropolyacid during soaking of the membranes in water. Among alkoxysilane modifiers the most promising results were given by perfluorooctyltriethoxysilane and phenyltriethoxysilane. The conductivity of the membranes was up to 10^–2–10^–1 S cm^–1 at elevated temperatures and saturated humidity conditions. Fourier transform IR attenuated total reflection spectroscopy was used to follow the gelation of the samples and, in parallel to thermogravimetric/differential scanning calorimetry measurements, also the thermal stability of the membranes.     

Vapor–liquid equilibria and excess properties for methyl tert-butyl ether (MTBE) containing binary systems

Methyl tert-butyl ether (MTBE) is recently widely used in the chemical and petrochemical industry as a non-polluting octane booster for gasoline and as an organic solvent. The isobaric or isothermal vapor–liquid equilibria (VLE) were determined directly for MTBE+C₁–C₄ alcohols. The excess enthalpy (H^E) for butane+MTBE or isobutene+MTBE and excess volume (V^E) for MTBE+C₃–C₄ alcohols were also determined. Besides, the infinite dilute activity coefficient, partial molar excess enthalpies and volumes at infinite dilution (γ^∞, H^E,∞, V^E,∞) were calculated from measured data. Each experimental data were correlated with various g^E models or empirical polynomial.     

Esterification of phthalic anhydride with 1-butanol and 2-ethylhexanol catalyzed by heteropolyacids

Esterification of phthalic anhydride with 2-ethylhexanol and 1-butanol and ester decomposition of dioctyl phthalate (DOP) in presence of Keggin; H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₄SiMo₁₂O₄₀, Wells–Dawson; H₆P₂W₁₈O₆₂, H₆P₂W₁₇MoO₆₂ and Preyssler; H₁₄[NaP₅W₂₉MoO₁₁₀], H₁₄[NaP₅W₃₀O₁₁₀], type heteropolyacids have been investigated. The heteropolyacids with Preyssler and Wells–Dawson structures and their molybdenum substituted derivatives show higher activity in esterification and ester decomposition reactions than Keggin type heteropolyacids. A complete conversion of phthalic anhydride to dioctyl phthalate and dibutyl phthalate are achieved in 2 h in presence of molybdenum substituted Preyssler heteropolyacid. In the decomposition of dioctyl phthalate in the presence of Preyssler heteropolyacid, 2-ethylhexene is formed in quantitative yield.     

Catalysis by hetropoly compounds. Part XXVI. Gas phase synthesis of methyl tert-butyl ether over heteropolyacids

Gas phase synthesis of methyl tert-butyl ether (MTBE) from methanol and isobutylene has been studied with several heteropolyacids at 303–383 K. It was found that a Dawson-type heteropolyacid, H₆P₂W₁₈O₆₂, was much active than Keggin-type heteropolyacids, H_nXW₁₂O₄₀ (X = P, Si, Ge, B, and Co), and other solid acids such as SO²⁻₄/ZrO₂, SiO---Al₂O₃ and H-ZSM-5 at 323 K. Since the acid strength of H₆P₂W₁₈O₆₂ was weaker than H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀, factors other than the acid strength are important for the catalytic activity. Pseudoliquid phase behavior was demonstrated for H₆P₂W₁₈O₆₂ and H₃PW₁₂O₄₀ by the measurements of the absorption of methanol during the reaction and by the unique pressure dependencies of the rate of synthesis. From the absorption data (the amount and rate), it is concluded that the high catalytic activity of H₆P₂W₁₈O₆₂ is brought about by a high-activity state of the pseudoliquid phase in which controlled amounts of molecule are absorbed and the absorption-desorption is rapid. On the other hand, the pseudoliquid phase of H₃PW₁₂O₄₀ is in a low-activity state absorbing excessive amounts of molecule.     

NiO/Al_2O_3催化剂上二氧化碳气氛下异丁烷耦合脱氢制异丁烯

研究了二氧化碳气氛下NiO/Al2O3催化剂上异丁烷脱氢制异丁烯的反应性能,考察了助剂K2O对NiO/Al2O3催化性能的影响。结果表明,与在惰性气氛下的反应相比,在二氧化碳气氛下异丁烷脱氢与逆水煤气变换反应耦合,促进了异丁烷脱氢反应,异丁烯的收率得到提高。助剂K2O的加入,能降低催化剂的酸性,减缓反应过程中催化活性物种NiO的过度还原,并抑制异丁烷裂解及积炭生成等副反应,从而提高了异丁烯的收率以及催化剂的稳定性。     

Synthesis, characterization and solid-phase C NMR of naphtho-9-crown-3

The synthesis and characterization of naptho-9-crown-3, N9C3, as a novel 9-membered ring crown ether with greater lipophilicity than that of benzo-9-crown-3, B9C3, is reported. The solution AA′BB′ pattern of –CH₂O– protons in N9C3 is close to that of B9C3. The solid-phase ¹³C CPMAS NMR, as a tool for conformation prediction, reveals that the solid-phase conformation of the 9-membered ring crown cavity in N9C3 is different from B9C3, the two key C2O2CH₂ and C3O1CH₂ units are predicted to be out of naphthalene plane, and the two C1C2O2CH₂ and C4C3O1CH₂ torsion angles are close to each other.     

氧化铝载体对Pt-Sn-K/γ-Al2O3催化剂上异丁烷脱氢性能的影响

采用盐酸回流法和氨水沉淀法合成了氧化铝载体,并通过络合真空浸渍法制备了不同来源氧化铝负载的Pt-Sn-K/γ-Al₂O₃催化剂。利用N₂物理吸附、CO脉冲吸附、H₂程序升温还原、NH₃程序升温脱附、热重等手段对Pt-Sn-K/γ-Al₂O₃催化剂进行了表征,以异丁烷脱氢为探针反应研究了氧化铝载体对该催化剂脱氢性能的影响。结果表明,与由盐酸回流法合成的载体制备的催化剂相比,采用氨水沉淀法合成的氧化铝载体制备的Pt-Sn-K/γ-Al₂O₃催化剂表面具有较小的Pt颗粒和较弱的酸性分布,其脱氢活性及异丁烯选择性更优。14 d的连续运行数据显示,由氨水沉淀合成的载体制备的催化剂,其抗积炭能力更强,反应后催化剂的积炭石墨化程度更低,因而具有更好的稳定性;在该催化剂上,异丁烷初始转化率为56.67%,14 d后仍能达到34.71%,异丁烯初始选择性为80%,7 d后维持在94%左右。     

杂多酸引发四氢呋喃聚合反应Ⅴ.生长链浓度与链生长速率常数的测定

采用改进的酚钠法及端羟基测定法对环氧乙烷促进的低浓度磷钨杂多酸引发的四氢呋喃聚合反应过程中生长链浓度的测定表明 ,杂多酸分子中的三个质子均参与了引发反应 ,各引发一个聚合链 .采用醋酸酐为促进剂时杂多酸引发四氢呋喃聚合反应生长链浓度测定的结果也证明了这一点 .由此测得在 0℃和 2 0℃时四氢呋喃聚合反应链增长表观速率常数分别为 3 78× 10 -3 和 1 98× 10 -2 L·mol-1·s-1,这与四氢呋喃按离子型生长链增长时的反应速率常数相近 .说明PW12 引发的THF聚合反应是通过氧离子活性中心增长的     

Trimerization of isobutene over cation exchange resins: Effect of physical properties of the resins and reaction conditions

Oligomerization of isobutene has been investigated using several cation exchange resins in order to produce triisobutenes that are useful feedstock for heavy alkylates and neo-acids. Trimers selectivity increases with increasing isobutene conversion. High isobutene conversion is obtained at high temperature and low space velocity by using macroporous cation exchange resins that have high concentration of sulfonic acid groups. Under selected conditions (viz., isobutene WHSV: 10 h⁻¹; temperature: 70 °C; catalyst: Amberlyst-35), the isobutene is quantitatively oligomerized with higher than or equal to 70% selectivity for trimers. The wet resin catalysts containing water or ethanol are very stable for the oligomerization up to about 70 h contrary to the gradual decrease in the conversion with dehydrated catalysts.     

A new approach to the determination of the heat of phenolic resol synthesis

A new method has been developed for the determination of the heat of phenolic resol synthesis carried out in an aqueous solution. This heat is determined as the difference in the heats of syntheses of the resitol from the mixture of raw materials and from the resol studied. Heats of resitol syntheses were determined by DSC at constant heating rate using high-pressure crucibles, i.e. under isochoric conditions for the liquid–vapour sample.

The heat of synthesis of resols, obtained at formaldehyde-to-phenol molar ratio equal to 3.0 and using NaOH as catalyst, were determined. The relevant values were calculated on the basis of the chemical composition of the resols and the molar enthalpies of the aromatic ring substitution and methylene bridge formation reactions. The experimentally determined heats were consistent with the calculated ones, not when free formaldehyde (CH₂O) but its monohydrate, CH₂O·H₂O (methylene glycol, HO–CH₂–OH) was assumed to be the reactive form of formaldehyde in an aqueous medium (formalin).     

Behaviors of sodium glycochenodeoxycholate and sodium glycoursodeoxycholate in binary mixed micelles of bile salt and nonionic surfactant

The behavior of sodium glycochenodeoxycholate (NaGCDC) and sodium glycoursodeoxycholate (NaGUDC) in binary mixed micelles consisting of bile salt and octaoxyethylene glycol mono n-decyl ether (C₁₀E₈) has been studied on the basis of micellar compositions, polarities of the interior of intramicelles, mean aggregation numbers and ¹H NMR measurements. Micellar compositions for both NaGCDC---C₁₀E₈ and NaGUDC---C₁₀E₈ systems showed a tendency to change from C₁₀E₈-rich micelles to bile-salt-rich micelles with an increase on the mole fraction of bile salts from the results of both theoretical calculations using the critical micelle concentration and the micellar polarity. The microenvironment of intramicelles for the NaGCDC---C₁₀E₈ system was found to be more hydrophobic than that for the NaGUDC---C₁₀E₈ system. Mean aggregation numbers of mixed micelles for both systems decreased abruptly with an increase in the mole fraction of bile salts in the range of low mole fraction, but those for NaGCDC were larger than those for NaGUDC. Furthermore, from the results of ¹H NMR measurements, the motions of the methyl group protons in the 18 position of the molecular structure of NaGCDC were slightly restricted with an increase in the mole fraction of NaGCDC. In contrast, the methyl group protons in the 18 and 19 positions of the molecular structure of NaGUDC became freer with an increase in the mole fraction of NaGUDC.     

Modified poly(phenylene oxide) membranes for the separation of carbon dioxide from methane

Two types of poly(phenylene oxide) (PPO) membranes were prepared: one by chemical modification through sulfonation using chlorosulfonic acid and another by physical incorporation with a heteropolyacid (HPA), viz., phosphotungstic acid. These membranes were tested for the separation of CO₂/CH₄ mixtures. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction techniques were used to confirm the modified structure of PPO as well as to understand its interactions with gaseous molecules. Scanning electron microscopy (SEM) was used to investigate the membrane morphology. Thermal stability of the modified polymers was assessed by differential scanning calorimetry (DSC), while the tensile strength was measured to evaluate their mechanical stability. Both chemical and physical modifications did not adversely affect the thermally and mechanical stabilities. Experiments with pure CO₂ and CH₄ gases showed that CO₂ selectivity (27.2) for SPPO increased by a factor of 2.2, while the PPO–HPA membrane exhibited 1.7 times increase in selectivity with a reasonable permeability of 28.2 Barrer. An increase in flux was observed for the binary CO₂/CH₄ mixture permeation with an increasing feed concentration (5–40 mol%) of CO₂. An enhancement in feed pressure from 5 to 40 kg/cm² resulted in reduced CO₂ permeability and selectivity due to the competitive sorption of methane. Both the modified PPO membranes were found to be promising for enrichment of methane despite exhibiting lower permeability values than the pristine PPO membrane.     

Hydroformylation of alkyl alkenes catalyzed by rhodium supported on MCM-41: The effect of H3PW12O40 on the catalytic activity and recycling

Heteropolyacids impregnated with rhodium(I) or (III) complexes were prepared and used as supported catalysts in the hydroformylation of alkyl alkenes. Two general types of catalysts were prepared and tested: rhodium(I) or (III) in the presence and in the absence of the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (adopted as HPW₁₂) supported on MCM-41 (30 Å). 1-Octene was chosen as a model substrate. Different types of supported catalysts were tested in the hydroformylation of 1-octene and other alkyl alkenes. The effects of the temperature and the type of solvent on the reaction were studied. The results showed that the supported catalysts containing the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (HPW₁₂) along with rhodium(I) or (III) gave higher catalytic activity. In addition, the recycling of the supported catalysts was studied and the results showed again the important effect of the presence of HPW₁₂ on the recycling of the rhodium catalysts.     

Isobutene homo- and isobutene-isoprene copolymerization initiated by protic initiators associated with a series of novel, weakly coordinating counteranions

The highly electrophilic borane B(C₆F₅)₃ reacts with a variety of carboxylic acids RCO₂H to form 1:1 and 1:2 adducts [RCO₂H][B(C₆F₅)₃] and [RCO₂H][B(C₆F₅)₃]₂. These adducts exhibit enhanced acidities, and the 1:2 adduct of n-decanoic (stearic) acid in particular is an excellent initiator for the carbocationic polymerization of isobutene and copolymerization of isobutene with isoprene in methylene chloride and methyl chloride. High conversions to high molecular weight polyisobutene and isobutene-isoprene copolymers are obtained at unusually high temperatures, consistent with the anion [n-C₁₇H₃₅CO₂ BC₆F₅)_{3 2}]⁻ being very weakly coordinating. Interestingly, the system also exhibits a surprising, as yet not understood, dependence of polymer molecular weights on the nature of R in methyl chloride.