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481.
Lyubomir T.?VlaevEmail author Maria M.?Nikolova Georgy G.?Gospodinov 《Monatshefte für Chemie / Chemical Monthly》2005,136(9):1553-1566
Summary. The dehydration kinetics of crystallohydrates of beryllium, magnesium and calcium selenites were studied under non-isothermal conditions. The values of the activation energy of dehydration, the pre-exponential factor in Arrhenius equation and the change of entropy for the formation of the activated complex were calculated using the calculation procedure of Coats and Redfern. Thermal stability and activation energy of dehydration of the crystallohydrates were found to increase by the same order. The relationships observed were interpreted using Klopman’s generalized perturbation theory of chemical reactivity. The same theory was applied to explain the differences in the IR spectra of the selenite crystallohydrates studied. 相似文献
482.
483.
K. I. Kuchkova A. N. Aricu I. P. Dragalin P. F. Vlad 《Russian Chemical Bulletin》2004,53(12):2862-2865
A convenient synthesis of drimenol by treatment of readily available drimane-8, 11-diol 11-monoacetate with sulfuric acid in ethanol under mild conditions was developed. Oxidation of drimenol with selenium dioxide gives known drim-7-ene-9, 11-diol and drim-7-ene-11,12-diol as the major products.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2745–2748, December, 2004. 相似文献
484.
M. Sourbaji K. Pintye-Hódi C. S. Novák P. Szabó-Révész P. Kása Jr. I. Erõs 《Journal of inclusion phenomena and macrocyclic chemistry》2000,37(1-4):299-307
A physical mixture and a kneadedproduct containing sulfadimidine and-cyclodextrin were prepared. The morphology ofthese products and of the sulfadimidine bulk substancewere studied by scanning electron microscopy (SEM).The thermoanalytical behaviour of the samples wasinvestigated. The existence of an inclusion complex inthe products could not be proved. However an increasein dissolution rate was observed. The reason in thecase of the physical mixture lies in the regulardistribution of the active agent crystals and the-cyclodextrin crystals, and in the case of thekneaded product in the formation of new recrystallizedparticles. 相似文献
485.
Kazunori Kadota Atsuko Shimosaka Yoshiyuki Shirakawa Jusuke Hidaka 《Journal of nanoparticle research》2007,9(3):377-387
Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD)
simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100)
and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated
as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the
interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore,
the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the
crystal growth was discussed. As the electric field increased, it was observed that the Na+ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure
is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl.
If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing
the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends
on the electric field or crystal surface structure. 相似文献
486.
在HZSM-5分子筛催化乙醇脱水反应中观察到了停料效应:即当停止乙醇-水进料一定时间,恢复进料后乙烯选择性明显提高。通过考察不同反应条件下的停料效应,发现乙醇质量分数控制在55%附近、延长停料时间、升高反应温度和降低乙醇进料空速会提高停料效应强度,并较长时间维持高乙烯选择性。500 h的催化剂稳定性测试表明,停料效应可有效延长催化剂的使用寿命。结合含水乙醇脱水反应机理和实验结果,推测HZSM-5催化乙醇脱水停料效应产生的原因是停料时乙氧基中间体的积累和催化活性空位的再生。 相似文献
487.
488.
489.
A facile route for fabricating novel polyelectrolyte complex membrane with high pervaporation performance in isopropanol dehydration 总被引:1,自引:1,他引:0
Qiang Zhao Jin-Wen Qian Quan-Fu An Qian Yang Peng Zhang 《Journal of membrane science》2008,320(1-2):8-12
Polyelectrolyte complexes (PECs) of sodium carboxymethyl cellulose (CMCNa) and poly(diallyldimethylammonium chloride) (PDDA) were prepared in dilute hydrochloric acid (HCl) aqueous solution and obtained in its solid form. Element analysis and FT-IR showed that the composition of PECs could effectively be tuned by the concentration of HCl in parent polyelectrolyte solution. The PECs were then dissolved in 0.1 mol/L aqueous NaOH and subsequently cast onto polysulfone ultra-filtration membrane. This composite membrane, which has a unique homogeneous PECs separation layer, was subjected to pervaporation test for the first time and gave a performance of J = 3.0 kg/m2 h, α = 960 for 10 wt% water–isopropanol feed at 75 °C. Meanwhile, performance of the PECs membrane displays good stability and unique dependence on feed temperature. These findings, together with its ultra-high performance, are primarily explained by the structure characteristic of PECs. 相似文献
490.
用氟硅酸铵对HMCM-22分子筛进行了改性处理,并采用氨程序升温脱附和吡啶吸附红外光谱法测定了其酸性.结果表明,随着氟硅酸铵处理温度的提高,HMCM-22分子筛的B酸和L酸中心的酸量均逐渐减少.以氟硅酸铵改性的HMCM-22分子筛为甲醇脱水活性组分与铜基甲醇合成活性组分(CuO-ZnO-Al2O3)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,对HMCM-22分子筛在适当温度(45℃)下进行氟硅酸铵改性,可使反应产物中烃类和CO2副产物的选择性下降,使目的产物二甲醚的选择性显著升高.当氟硅酸铵处理温度过高(85℃)时,CO的转化率和二甲醚的选择性均大幅度降低。 相似文献