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101.
Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and
molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers
are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that
the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition.
The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence
of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be
adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement
overlap.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
102.
In spite of its industrial importance, the detailed reaction mechanism of cyclohexane autoxidation by O2 is still insufficiently known. Based on quantum chemical potential energy surfaces, rate coefficients of the primary and secondary chain propagation steps involving the cyclohexylperoxyl (CyOO) radical were evaluated using multiconformer transition-state theory. Including tunneling and hindered-internal-rotation effects, the rate coefficient for hydrogen-atom abstraction from cyclohexane (CyH) by CyOO was calculated to be k(T)= 1.46 x 10(-11) x exp(-17.8 kcal mol(-1)/ RT) cm3s(-1) (300-600K), close to the experimental data. A "Franck-Rabinowitch cage" reaction between the nascent cyclohexylhydroperoxide (CyOOH) and cyclohexyl radical, products from CyOO + CyH, is put forward as an initially important cyclohexanol (CyOH) formation channel. alphaH abstraction by CyOO. from cyclohexanone was calculated to be only about five times faster than that from CyH, too slow to explain all the observed side products. The a-hydrogen (alphaH) abstractions from CyOH and CyOOH by CyOO. are predicted to be about 10 and 40 times faster, respectively, than the CyOO. +CyH reaction. The very fast CyOO.+CyOOH reaction proceeds through the unstable Cy-alphaH .OOH radical that decomposes spontaneously into the ketone (Q=O) plus the OH radical; the "hot" .OH is found to produce the bulk of the alcohol via a second, "activated cage" reaction analogous to that above. It is thus shown how the very reactive CyOOH intermediate is the predominant source of ketone and alcohol, while it also leads to some side products. The alpha-hydroxycyclohexylperoxyl radical formed during the moderately fast oxidation of CyOH is shown to decompose fast into HO2 + cyclohexanone in a rapidly equilibrated reaction, which constitutes a smaller, second ketone source. These two fast cyclohexanone forming routes avoid the need for unfavorable molecular routes hitherto invoked as ketone sources. The theoretical predictions are supported and complemented by experimental findings. The newly proposed scheme is also largely applicable to the oxidation of other hydrocarbons, such as toluene, xylene, and ethylbenzene. 相似文献
103.
YUAN Song-Yue ZHAO ZhenChangchun Institute of Applied Chemistry. Academia Sinica Changchun Jilin CYU Zuo-LongChengdu Institute of Organic Chemistry. Academia Sinica Chengdu. Sichuan To whom correspondence should be addressed 《天然气化学杂志》1995,(3)
The surface basicity of Ti-La-Li multicoinponent oxides has been investigated by means of CO2-TPD. The experiment results show that C2 (C2H6 C2H4) selectivity is related to surface basic strength. The surface active oxygen species have also been characterized by means of XPS, O2-TPD and so on. It has been indicated that C2 selectivity and CH4 conversion are correlated with lattice oxygen and the adsorbed oxygen on the surface of the catalyst respectively In the O2-TPD experiments, it has also been found that there are three kinds of oxygen species on the surface of the series catalvsts, which are a (100℃ 750℃) Among them α-oxvgen causes deep oxidation whileβand γ oxygen species are related to oxidalive coupling of methane (OCM). 相似文献
104.
[reaction: see text] A novel reaction between 1,3-dienes and selenium dioxide to give syn 1,2- and 1,4-diol cyclic selenites was studied in detail. This study indicates that an initial concerted [4 + 2] cycloaddition followed by a stereospecific carbon-selenium bond oxidation is involved in this unprecedented syn dihydroxy addition reaction mediated by selenium dioxide. 相似文献
105.
A rapid, selective, and sensitive method is described for the purification and analysis of fluoxetine and norfluoxetine using a solid-phase extraction column and gas chromatography-electron-capture detection. Linear quantitative response curves for fluoxetine and norfluoxetine are generated over a concentration range of 20-200 ng/ml. Overall extraction efficiency of the extraction procedure is found to be greater than 90% and greater than 75% with correlation coefficients of 0.997 and 0.993 for fluoxetine and norfluoxetine, respectively. 相似文献
106.
Zeta-potentials of self-assembled surface micelles of ionic surfactants adsorbed at hydrophobic graphite surfaces 总被引:1,自引:0,他引:1
Vamsi K. Paruchuri Anh V. Nguyen Jan D. Miller 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):519-526
The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate—SDS and hexadecyltrimethyl ammonium bromide—CTAB) on graphite surfaces were determined both from streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite–liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear, parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite surface were about −75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature. 相似文献
107.
Nguyen Huyen Rao A. Madhusudhan Phillips J. B. John Vijay T. Reed Wayne F. 《Applied biochemistry and biotechnology》1991,(1):843-853
We describe a technique to modify protein solubility and optimize enzyme activity in reversed micellar solutions. The technique
is based on the ability of hydrates of natural gas to form in the micro-aqueous phase. Clathrate hydrates are crystalline
inclusions of water and gas, and their formation in bulk water has traditionally been studied with relevance to natural gas
recovery. We have found that hydrates can form in the environment of the microaqueous pools of reversed micelles, and that
their extent of formation can be well controlled through the thermodynamic variables of temperature and pressure. Additionally,
formation of hydrates affects the size and aggregation number of the micelles, and thus influences the solubility and conformation
of encapsulated proteins. We demonstrate how the concept can be used in two applications: (i) protein extraction into reversed
micelles and subsequent recovery, and (ii) optimization of enzyme activity in reversed micelles. 相似文献
108.
XU Long-Ya WANG Qing-Xia XU Yi-De HUANG Jia-ShengDalian Institute of Chemical Physics Academia SinicaDalian Liaoning State Key Laboratory of CatalysisDalian Institute of Chemical Physics. Academia SinicaDalian Liaoning To whom correspondence should be addressed. 《天然气化学杂志》1995,(3)
The activity and the selectivity to light alkenes of silicalite-2 (Si-2) zeolite supported F'e catalyst tor CO hydrogenation can he improved obviously with the addition of K2O and MnO promoters. The results of CO hydrogenation, CO-TPD, CO/H2-TPSR, C2H4/H2-TPSR and C2H4/H2 pulse reaction over K-Fe-MnO/Si-2 catalysts clearly show that the K2O additive into Fe-MnO/Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO ad-species that will produce much more |Cad| via their disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins, and a decrease in CH4 formation. Moreover, K2O can suppress the disproportionate of C2H4 that occurs during the reaction as a side-reaction Meanwhile, the MnO promoter mainly prohibits the hydrogenation of C2H4 and C3H6, which is favorable to enhancing the selectivity to C2H4 and C3H6 and decreasing the formation of C2H6, and C3H8. It is also of interest that MnO has har 相似文献
109.
LIU Xing-Quan WU Yu-Tang JIA Zhao-XiaChengdu Institute uf Organic ChemistryAcademia SinicaChengdu Sichuan To whom correspondence should be addressed. 《天然气化学杂志》1995,(1)
1 , 5-diazabicyclo['1, 3, 0]non-5-ene(DBN) has been synthesized in our laboratory, and its catalytic activity and selectivity for methanol carbonylation to methyl formate (MF) have been studied. The experimental results have demonstrated that the synthetic processes of DBN used for the present work are reasonable and feasible. The total yield of three steps of DBN synthsis is approximate to 80%. The activity evaluation has shown that DBN can effectively catalyze the carbonylation reaction of methanol in the presence of propylene oxide (PO) promoter. PO-promoted DBN is a novel catalytic system superior to sodium methoxide. 相似文献
110.
A method of determination of adsorbed and absorbed hydrogen on palladium catalysts with carbon carriers is suggested and verified. The method allows Had and Hab to be determined with an accuracy of about 10% using catalysts containing at least 5% Pd.
- . . . 10% , , - , 5% Pd.相似文献