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排序方式: 共有214条查询结果,搜索用时 203 毫秒
21.
制备了表面修饰多壁碳纳米管负载TiO2的催化剂,并将其应用于碳酸二甲酯与苯酚的酯交换反应. 采用X射线电子能谱、透射电子显微镜、低温N2吸附-脱附和X射线衍射等对催化剂进行了表征. 结果表明,以低浓度的氨水(0.4%)代替去离子水作为沉淀剂时,制备的催化剂显示出更好的催化活性、分离性与重复使用性. 考察了TiO2负载量、催化剂用量及反应时间对反应性能的影响. 在最佳反应条件下,苯酚转化率为42.5%,碳酸甲苯酯与碳酸二苯酯的总选择性达到99.9%以上. 经过4次重复使用后,催化剂的活性略有下降. 相似文献
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Esters containing tertiary amine functionalities were successfully synthesized under mild conditions and in good yields, using a three-step process involving the activation of acids into their corresponding cyanomethyl esters, followed by transesterification with the alcohol counterparts, and subsequent scavenging of the excess of alcohol to facilitate purification. 相似文献
25.
Maria-Beatrice Coltelli Claudio ToncelliFrancesco Ciardelli Simona Bronco 《Polymer Degradation and Stability》2011,96(5):982-990
The transesterification during the melt blending of polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) was investigated in presence of Ti(OBu)4 as a catalyst. Both the effect of catalyst concentration and reaction duration was considered. The process was studied by analyzing the molecular weight of the polyesters by size exclusion chromatography (SEC). The rheological, thermal and morphological properties of the blends were investigated by melt flow rate, DSC and SEM analyses, respectively. Evidences about the formation of PBAT-PLA copolymers were obtained and discussed. The tensile properties of compression moulded films were also determined and correlated to the structure and phase morphology development of the blends. In particular, the use of Ti(OBu)4 resulted in the improvement of compatibility. Moreover, the decrease in stiffness and the increase in elongation at break with the increase of mixing time was observed, in good agreement with the improved compatibility of the modified blend. 相似文献
26.
Shiue-Shien Weng Chih-Shueh KeFong-Kuang Chen You-Fu LyuGuan-Ying Lin 《Tetrahedron》2011,67(9):1640-1648
A practical and clean protocol for transesterification catalyzed by a 5 mol % cheap, non-toxic and moisture stable Fe(acac)3 or other iron(III) β-diketonate species in solvent, such as heptane under azeotropic condition is developed. A remarkable rate enhancement was observed upon the addition of 5 mol % of an inorganic base, such as Na2CO3, which suggests that faster formation of a dimeric μ-alkoxy-bridged iron(III) species under alkaline conditions facilitates catalytic turnover. This system provides smooth transesterification over a wide range of structurally diverse esters and alcohols without disturbing functional groups. In addition, the use of iron β-diketonate complexes as catalysts is more environmentally friendly, safer, and economical than other transition-metal catalysts. Preliminary mechanistic studies indicate that the active catalyst is likely a dimeric μ-alkoxy-bridged iron(III) species, as determined by X-ray crystallography of [Fe(dbm)2(O-n-Bu)]2 derived from the alcoholysis of Fe(dbm)3 under alkaline conditions. 相似文献
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Ternary blends consisting of thermoplastic and thermotropic immiscible polymers were studied. Both thermodynamic and kinetic considerations were found to affect their multiphase structure. Thermodynamics is expressed by means of spreading coefficients, whereas the kinetic effect is driven by the dispersed phase viscosity ratio. Some morphologies could be predicted, when both effects acted cooperatively. However, in cases where the effects were opposing, kinetics hindered the development of the expected structure; interpenetration between the two minor phases, rather than engulfing or separately dispersed morphology, took place. In cases where two relatively polar phases were dispersed in a nonpolar matrix (e.g., nylon and polycarbonate in polypropylene), the interaction between the two dispersed minor phases always existed due to their low interfacial tension. Spreading of one minor phase over another, rather than penetration, is the dominating mechanism of encapsulation in polymer blends, contrary to low molecular weight liquids where both spreading and penetration play an important role in the structurization. 相似文献
28.
《Arabian Journal of Chemistry》2022,15(7):103915
There is a growing attention to the bio and renewable energies due to fast depletion of fossil fuels as well as the global warming problem. Here, we developed a modeling and simulation method by means of artificial intelligence (AI) for prediction of the bioenergy production from vegetable bean oil. AI methods are well known for prediction of complex and nonlinear process. Three distinct Adaptive Boosted models including Huber regression, LASSO, and Support Vector Regression (SVR) as well as artificial neural network (ANN) were applied in this study to predict actual yield of Fatty acid methyl esters (FAME) production. All boosted utilizing the Adaptive boosting algorithm. The important influencing parameters on the biodiesel production such as the catalyst loading (CAO/Ag, wt%) and methanol to oil (Soybean oil) molar ratio were selected as the input variables of models while the yield of FAME production was selected as output. Model hyper-parameters were tuned to maintain generality while improving prediction accuracy. The models were evaluated using three distinct metrics Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and R2. Error rates of 8.16780E-01, 4.43895E-01, 2.06692E + 00, and 3.92713 E-01 were obtained with the MAE metric for boosted Huber, SVR, LASSO and ANN models. On the other hand, the RMSE error of these models were about 1.092E-02, 1.015E-02, 2.669E-02, and 1.01174E-02, respectively. Finally, the R-square score were calculated for boosted Huber, boosted SVR, and boosted LASSO as 0.976, 0.990, 0.872, and 0.99702, respectively. Therefore, it can be concluded that although the boosted SVR and ANN models were better models for prediction of process efficiency in terms of error, but all algorithms had high accuracy. The optimum yield of 83.77% and 81.60% for biodiesel production were observed at optimum operating values from boosted SVR and ANN models, respectively. 相似文献
29.
《中国化学会会志》2018,65(6):696-705
Magnetic porous polymeric microspheres containing epoxy groups were prepared by suspension polymerization (denoted as magnetic Fe3O4@GEM microspheres). Fe3O4@GEM with a specific surface area of 30.41 m2/g, average pore diameter of 17.13 nm, and pore volume of 0.13 cm3/g exhibited superparamagnetic behavior with the saturation magnetization of 7.1 emu/g. The content of epoxy groups on Fe3O4@GEM was 0.22 mmol/g. Pseudomonas sp. lipase (PSL) was covalently immobilized onto the Fe3O4@GEM microspheres through the reaction between the amino groups of the enzyme and the epoxy groups on the microspheres. PSL/Fe3O4@GEM exhibited enhanced enantioselectivity for the resolution of allylic alcohol to the corresponding optically active (S)‐allylic alcohol and (R)‐allylic alcohol acetate compared to free PSL. The enantiomeric excess of (S)‐l‐pheny‐2‐propen‐1‐ol for the former (98.1%) was 81.7 times that of the latter (1.2%) when the immobilized PSL was used for transesterification resolution of (R,S)‐l‐pheny‐2‐propen‐1‐ol. Furthermore, the ees and eep values were still retained at 95.2% and 95.4% after PSL/Fe3O4@GEM was recycled 10 times, indicating that PSL/Fe3O4@GEM had very good reusability. In addition, the transesterification resolution of (R,S)‐1‐(4‐methylphenyl)‐2‐propen‐1‐ol and (R,S)‐1‐(4‐bromophenyl)‐2‐propen‐1‐ol was catalyzed by PSL/Fe3O4@GEM, affording ideal ees and eep values of 99.3%, 97.4% and 99.6%, 98.2%, respectively. Therefore, PSL/Fe3O4@GEM demonstrated its potential as a highly efficient enzymatic reactor and Fe3O4@GEM would be very promising carriers for immobilizing enzymes in industrial application. 相似文献
30.
Shekhar Putta Annem Mallikarjun Reddy Gurrala Sheelu B.V. Subba Reddy Thenkrishnan Kumaraguru 《Tetrahedron》2018,74(46):6673-6679
Photooxidation of cyclopentadiene has been carried out in methanol using white light of LED lamp, rose bengal as photo initiator, and compressed air at 0?°C. Under conditions of [thiourea] ? [cyclopentadiene], the consumption of thiourea follows a pseudo-first-order reaction kinetics with half life of 75?±?10?min; corr. coeff. r?=?0.989. Slow addition of the monomer and maintaining excess thiourea concentration in reaction mass improves the yield. cis-3,5-Dihydroxy-1-cyclopentene is acetylated without isolation to obtain cis-3,5-Diacetoxy-1-cyclopentene of high purity (>99%) with overall isolated yield of 30%. Desymmetrization of the diacetate to (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate has been carried out via enzymatic transesterification with methanol in methyl tert-butyl ether (MTBE) at 5?°C using Novozym-435®. The enantiomerically pure monoacetate (e.e. >99%) was obtained in 95% isolated yield. The recovered enzyme was reused for more than 10 times without loss in yield and selectivity. The entire protocol does not require purification of final product by chromatography. 相似文献