Kinetic study of isopropanol dehydration over silicoaluminophosphate catalyst

The catalytic dehydration of isopropanol has been studied over a solid acid silicoaluminophosphate type SAPO-5. The reaction was processed varying the temperature and weight hourly space velocity, using a fixed bed continous flow reactor. The isopropanol undergoes inter- and intramolecular dehydration, forming propylene and isopropyl ether, respectively. Nevertheless, the catalyst was selective to the olefin, with an activation energy of the order of 46.1 kJ/mol.     

Kinetics of Non-Isothermal Behaviour of Synthetic Cationites with Low Acidity

An investigation was made of the thermal behaviour under non-isothermal conditions of a series of low-acidity synthetic cationites having a methacrylic-divinylbenzene (DVB) matrix, such as Amberlite IRC 120, Ionenaustauscher IV Merck, Vionit CC1, and Purolite C104, C105 and C106. The macroporous, macroreticular and gel cationites were in acidic or sodium form, with various granulations and degrees of cross-linking. The apparent kinetic parameters (reaction order, n, activation energy, E, and pre-exponential factor A) were evaluated for two dehydration processes and the effects of the experimental conditions on these parameters were investigated. This revised version was published online in July 2006 with corrections to the Cover Date.     

A synthetic iron phosphate mineral, spheniscidite, [NH4]+[Fe2(OH)(H2O)(PO4)2]?H2O, exhibiting reversible dehydration

Spheniscidite, a synthetic iron phosphate mineral has been synthesized by hydrothermal methods. The material is isotypic with another iron phosphate mineral, leucophosphite. Spheniscidite crystallizes in the monoclinic spacegroupP2₁/n. (a=9·845(1),b=9·771(3),c=9·897(1),β=102·9°,V=928·5(1),Z=4,M=372·2,d _calc=2·02 g cm⁻³ andR=0·02). The structure consists of a network of FeO₆ octahedra vertex-linked with PO₄ tetrahedra forming 8-membered one-dimensional channels in which the NH₄ ⁺ ions and H₂O molecules are located. The material exhibits reversible dehydration and good adsorption behaviour. Magnetic susceptibility measurements indicate that the solid orders antiferromagnetically.     

掺C_(60)二氧化钛微晶特性和光催化活性研究

通过热分析、X射线衍射以及光活性测试 ,分析了不同掺杂量、不同煅烧温度下掺杂 C60 二氧化钛微晶样品 ,研究了掺杂对二氧化钛光活性的改善情况 . C60 掺杂二氧化钛体系中 C60 的热解温度明显提前 ,二氧化钛的晶化温度延迟、相变受到抑制且光活性得到一定程度的提高 ,其微晶参数也有一定规律变化 .     

TMA and SEM characterization of the thermal dehydration of australian sedimentary opal

The dehydration of samples of a Coober Pedy, South Australian sedimentary white opal, displaying play of colour, was investigated using TMA by heating the samples of the specimen to a range of temperatures between room temperature and 1000 at 200°C intervals followed by cooling to room temperature. Etched fracture surfaces of the samples were then examined using SEM. The samples showed the typical expansion at low temperature up to 210°C before contraction was observed. The contraction of the opals was ascribed to both sintering, supported by morphological change observed in the SEM micrographs, and dehydroxylation of the silanol groups producing silicon-oxygen-silicon bridges resulting in a more dense silica network.     

Triphenylphosphine-iodine: an efficient reagent for the regioselective dehydration of tertiary alcohols

Tertiary alcohols react under mild conditions with triphenylphosphine and iodine to give the most stable alkene in good yield.     

Oral Breathing Increases Pth and Vocal Effort by Superficial Drying of Vocal Fold Mucosa

Oral breathing superficially dehydrates the airway lumen by decreasing the depth of the sol layer in humans and animals. Conversely, nasal breathing can increase the humidity of inspired air. We compared the effects of short-term oral and nasal breathing on P_th and perceived vocal effort in 20 female subjects randomly assigned to two groups: oral breathing (N = 10, age 21–32 years); nasal breathing (N = 10, age 20–36 years). We hypothesized that short-term oral breathing, but not nasal breathing, would increase P_th, and that subjects would perceive this change as an increase in vocal effort. Following 15 minutes of oral breathing, P_th increased at comfortable and low pitch (p < 0.01) with 6 of 10 subjects reporting increased vocal effort. Nasal breathing reduced P_th at all three pitches (p < 0.01), and 7 of 10 subjects reported decreased vocal effort. Over all subjects, 49% of the variance in treatment-induced change in P_th was accounted for by change in vocal effort (R = 0.70). We posit that obligatory oral breathing places healthy subjects at risk for symptoms of increased vocal effort. The facilitatory role of superficial hydration on vocal fold oscillation should be considered in biomechanical models of phonation and in the clinical prevention of laryngeal dryness.     

Decomposition Reactions of Methanol and Ethanol Catalyzed by Tungsten Oxide Supported on Activated Carbon

Activity of the catalysts to obtain the dehydration products linearly increases with their total surface acidity. Results obtained seem to point out that the surface basicity of the support influences the acid strength of the tungsten oxide particles, especially at low tungsten loading.     

Doped Sol-Gel Materials as Heterogeneous Reagents for Organic Synthesis

We advance the use of reactive doped sol-gel materials as heterogeneous reagents for organic-chemistry synthesis. Three approaches were demonstrated with SiO₂-based materials: Direct physical entrapment of the organic reagent; in-situ generation of an inorganic reagent within the matrix; and covalent attachment of the reagent to the matrix. With the first, entrapped p-toluenesulfonic acid facilitated the 100% yield esterification of benzoic acid with 1-pentanol, and the 100% dehydration of 1-tetralol to 1,2-dihydronaphthalene; with the second approach, a sol-gel oxidant, SiO₂/MnO₂ was used to convert benzyl alcohol to benzaldehyde and 1-tetralol to 1-tetralone; and with the third, anchored propylamine facilitated dehydrobromination reactions resulting in double-bond formation. Several other reactions with these reagents are described, and their reactivities analyzed.     

镁改性HZSM-5对Cu-ZnO-Al2O3/HZSM-5催化合成气直接制二甲醚反应的影响

 采用浸渍法制备了一系列MgO改性的HZSM-5分子筛,并以MgO/HZSM-5为甲醇脱水催化剂与Cu-ZnO-Al2O3甲醇合成催化剂组成双功能催化剂,在连续流动加压固定床反应器上考察了其对合成气直接制二甲醚反应的催化性能. 结果表明,以适量MgO改性的HZSM-5分子筛组成的双功能催化剂上,二甲醚选择性可高达64.8%,CO2和烃类副产物的选择性分别为30.2%和0.4%; 由未改性的HZSM-5分子筛组成的双功能催化剂上,二甲醚选择性仅为49.1%,CO2和烃类副产物的选择性则分别高达37.1%和9.3%. 当MgO含量过高时,则CO转化率和二甲醚选择性均降低. 根据实验结果,提出了甲醇在MgO/HZSM-5上脱水的反应机理.