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71.
M. E. A. P. Jaspers F. F. van Leeuwen H. J. W. Nieuwenhuis G. M. Vianen 《Journal of the American Oil Chemists' Society》1987,64(7):1020-1025
The synthesis of sucrose fatty acid esters always results in complex mixtures. Two procedures for quantitative analysis of
sucrose monoesters, respectively sucrose diesters, by means of high performance liquid chromatography on reversed-phase columns,
are described. A mixture of methanol and water (85:15, v/v) was used for the separation of the monoesters, while methanol,
ethyl acetate and water (65:25:10, v/v/v) was used for the separation of diesters. These methods gave information about the
amount of monoesters and diesters in the product; the ratio between sucrose monopalmitate and sucrose monostearate, and the
number of the most important structure isomers. A complete separation of all the possible diester products seemed to be impossible,
due to the presence of more complex structure isomers. The described procedures can give important support during preparative
work on sucrose fatty acid esters and also in the evaluation of these products for application purposes. 相似文献
72.
Quantum chemical studies of zeolite proton catalyzed reactions 总被引:1,自引:0,他引:1
Theoretical chemistry applied to zeolite acid catalysis is becoming an important tool in the understanding of the adsorption and interaction of guest molecules with the zeolitic lattice. Especially the understanding of the mechanisms by which zeolite catalyzed chemical reactions proceed becomes possible. It is shown here that the old interpretation of carbonium and carbenium ions as intermediates for zeolite catalyzed reactions has to be replaced by a new approach in terms of positively charged transition states that are strongly stabilized by the zeolitic lattice. The large deprotonation energy of the acidic zeolite is overcome by stabilization of the intermediate or transition state positive charge by the negative charge left in the lattice. The zeolitic sites responsible for the adsorption and/or reaction of guest molecules are the Brønsted-acid and Lewis-base sites. We also show that different transition states are responsible for different kinds of reactions, such as cracking, dehydrogenation, etc. 相似文献
73.
74.
In observation-cage experiments some new contact kairomones for the egg parasiteTrichogramma evanescens Westwood are demonstrated.T. evanescens females search significantly longer on cabbage leaves treated with the wing scales of two hosts,Pieris brassicae L. andP. rapae L. Further, egg washes ofP. brassicae containing an oviposition deterrent pheromone for the butterflies, were found to have a contact-kairomonal effect on the parasite.T. evanescens females search significantly longer on cabbage leaves sprayed with a methanol or water wash ofP. brassicae eggs than on leaves treated with the solvent only.Hymenoptera: Trichogrammatidae.Lepidoptera: Pieridae. 相似文献
75.
具有高含量3,4-结构的IR能特别有效地提高高性能轮胎的湿抓着力。因此,可以通过调整炭黑和BR用量来提高轮胎的磨耗和滚动阻力性能,同时保持优异的湿抓着性能。 相似文献
76.
F. W. J. L. Maase R. van Tilburg 《Journal of the American Oil Chemists' Society》1983,60(9):1672-1675
The influence of two commercial proteolytic enzymes, Maxatase® and PB-92, were studied viz á viz changing phosphate content and washing conditions. (Maxatase® is a registered trademark of Gist-Brocades N.V.; PB-92 will be sold under the trademark MaxacalTM.) In the USA and Western Europe, detergent phosphate content is decreasing because of environmental considerations/legislation. Washing conditions are changing towards lower temperatures be-cause of the increased use of synthetic fibers and the need to con-serve energy. Both Maxatase and PB-92 are shown to improve sig-nificantly the performance of US detergents, even at temperatures as low as 70 F. This conclusion is based on Terg-O-Tometer tests on EMPA 116 cloth using US detergents and presoak products. 相似文献
77.
The phase behaviour and morphology of injection moulded specimens of polysulphone (PSF) and poly(phenylene sulphide) (PPS) blends were studied by differential scanning calorimetry (d.s.c.), dynamical mechanical thermal analysis (d.m.t.a.) and transmission electron microscopy (TEM). The blends are phase separated regardless of the blend composition as revealed by d.s.c., d.m.t.a. and TEM. Upon annealing at 160°C for 2 h, d.m.t.a. results indicate that the PPS phase remains in the amorphous state at compositions <10%. At compositions between 20 and 35%, the PPS appears to be dispersed in a mixed mode of amorphous and crystalline domains. Above 35% the PPS phase appears to become fully crystallized upon annealing of the blends. At 10% PPS, TEM results showed 35–200 nm size dispersion both in the as-moulded and in the annealed specimens. At 20% the PPS phase varied widely in size, from 35 nm to tens of micrometres but remained as an included phase. TEM also revealed a compound morphology of the included phase at a composition of 50 wt% of each component. 相似文献
78.
Conventional gasification processes use coal not only as feedstock to be gasified but also for supply of energy for reaction heat, steam production, and other purposes. With a nuclear high temperature reactor (HTR) as a source for process heat, it is possible to transform the whole of the coal feed into gas. This concept offers advantages over existing gasification processes: saving of coal, as more gas can be produced from coal; less emission of pollutants, as the HTR is used for the production of steam and electricity instead of a coal-fired boiler; and a lower production cost for the gas. However, the process has the disadvantage that the temperature is limited to the outlet temperature (950 °C max) of the helium cooling gas of the HTR. Therefore the possibility of catalytic steam gasification was examined. Model calculations based on experimental results show that use of 3–4 wt% relative to coal of K2CO3 catalyst increases the throughput of a large scale nuclear gasification plant by ≈65%, while gas production costs decrease by ≈15%. Corrosion by catalysts is not significant at low concentration (< 5 wt%) and low temperature (< 900 °C). 相似文献
79.
The composition of the lipids of two samples of krill and one of “red crab” was determined by thin layer, column and gas chromatographic
procedures. A large number of unusual fatty acids were present. 相似文献
80.
M. J. Kappers M. Vaarkamp J. T. Miller F. S. Modica M. K. Barr J. H. van der Maas D. C. Koningsberger 《Catalysis Letters》1993,21(3-4):235-244
The adsorption of carbon monoxide on a non-acidic Pt/K-LTL catalyst has been studied by diffuse reflectance and transmission IR spectroscopy. The CO spectrum is strongly dependent on the experimental conditions. Adsorption on the small Pt clusters in the presence of water gives linear-CO bands between 2060 and 1990 cm–1 and a bridging-CO band around 1800 cm–1. In the absence of water, the linear bands are red shifted to about 1940 and 1720 cm–1, respectively. The frequency shift is attributed to an ion-dipole interaction between adsorbed CO and support cations. The ion-dipole interaction is screened by the adsorbed water leading to a smaller red shift in the CO stretching frequency. 相似文献