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84.
Lawrence K. Wang Richard P. Leonard Dennis W. Goupil Mu Hao Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1975,25(7):491-502
Industrial effluents usually include multicomponent organic solutes. The optimum pH for adsorption of a specific industrial effluent on activated carbon should be determined experimentally because, in general, more than one mechanism is involved. A series of experiments was conducted to establish the influence of the initial hydrogen ion concentration on carbon adsorption of organic solutes. For these studies, powdered activated carbon was used, and the water systems studied included both single component pure organic compounds as well as multicomponent organic wastes. Results indicate that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. In general, the degree of ionisation is the controlling factor for adsorption of ionic organic solutes on activated carbon. Adsorption reaches a maximum at the point of least ionisation of the adsorbate. As the organic compounds become more complex (i.e. longer hydrocarbon chains, higher molecular weights, increased branching), the electrical adsorption forces between activated carbon and ionic organic solutes will govern. Anionic surfactants meet with decreased electronegative repulsive forces at low pH levels, which increase the effectiveness of carbon adsorption. However, the adsorption of a cationic surfactant is increased by an increase in the electronegative carbon surface at high pH levels. When ionic organic solutes become much more complex, like a polymer, the effects of both ionisation and electrical adsorption forces become less important. Instead, the adsorption rate will be controlled by the extent of hydrolysis caused by the pH adjustment. For non-ionic organic solutes, chemical reaction(s) between the adsorbate and the added chemical (acid or base) for pH adjustment is an important controlling factor. Again, hydrolysis is responsible for the breakdown of larger size molecules to smaller sizes. Then an increase in adsorption rate with decreasing molecular weight of adsorbate is expected. 相似文献
85.
W. Dennis Pocklington 《Journal of the American Oil Chemists' Society》1992,69(8):789-793
The development, by collaborative study, of a standardized method for the determination of tetrachloroethylene in olive oils
is described. The results of the study, which was carried out in 1989 under the direction of the International Olive Oil Council
(IOOC), are presented and show that tetrachloroethylene can be readily determined, to an acceptable degree of precision, by
gas-liquid chromatography with electron capture detection. A limited number of results obtained for the determination of trichloroethylene
and chloroform by the same method indicate that a similar precision could be obtained with the method when determining these
solvents also. 相似文献
86.
Esmail O. Elakesh T. Richard Hull Dennis Price Graham J. Milnes Peter Carty 《乙烯基与添加剂工艺杂志》2005,11(1):21-27
Plasticized samples of chlorinated polyvinylchloride (CPVC) were investigated by using thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Three different plasticizers were studied, namely, dioctyl phthalate (DOP), alkyldiaryl phosphate ester (Santiciser 2148), and triaryl phosphate ester (Reofos 50). TG experiments in nitrogen showed one major decomposition stage, involving dehydrochlorination, and minor pyrolysis reaction of the hydrocarbon residue. In contrast to the three stages previously reported to occur in the nonplasticized‐stabilized CPVC, TG analyses in air showed two distinctive decomposition stages for the plasticized CPVC samples. The DOP system provided a suggestion of a third stage. The first decomposition stage was due not only to the loss of all the chlorine present, but also to loss of the plasticizer or its decomposition products. The second decomposition stage was mostly due to char oxidation, the char being formed almost exclusively from the DCE and VDC units in CPVC polymer. DSC results showed that in the presence of nitrogen, there was no significant plasticizer effect on the thermal decomposition behavior of CPVC up to about 330°C, while in air the DSC traces also show no significant differences below 400°C. The two phosphate plasticizers showed no significant differences in their effect on the thermal decomposition behavior of CPVC under the same experimental conditions. It is believed that P2O5 and polyphosphoric acid are among the main constituents of the residua. These would impart a protective glassy surface to the char. This will facilitate effective flame retardant action. This preliminary conclusion is based on the premise that the more stable the char layers are, the more resilient will be the protective layer, and consequently, the better the flame retardant effect. J. VINYL ADDIT. TECHNOL., 11:21–27, 2005. © 2005 Society of Plastics Engineers 相似文献
87.
Fatigue testing of polymers has revealed significant differences between the fatigue response of polymers and metals. Generally, fatigue failure in metals is a process of crack initiation, propagation, and failure. Also, fatigue damage in metals is cumulative and cycle dependent, but remains essentially independent of test frequency. Unlike that of metals, the fatigue behavior of polymers is influenced by viscoelastic effects. At high frequencies, softening and melting occur, and fatigue failure depends largely on the test frequency. At lower frequencies, fatigue failure becomes less sensitive to test frequency and results from crack initiation and propagation. These polymer characteristics arise from the production of hysteresis energy during fatigue. A portion of this energy is released as heat, some of which is dissipated, but most is absorbed in the sample, raising its temperature. This temperature rise leads to degradation of the material and a short fatigue life. Experiments were conducted to measure hysteresis energy and temperature rise for a talc-filled polypropylene. A mathematical model was developed to calculate the energy and temperature distribution during fatigue. Correlation of the temperature rise predicted by the model with that observed experimentally provided values for the various energy terms that quantitatively defined the thermomechanical fatigue response of this polymer. 相似文献
88.
Vapor pressures were determined for several polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at 75-275 °C, extending the available literature data to more relevant temperature regions and providing the first experimental data for 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-TriCD). A modification of the effusion technique, based upon controlling the diffusion of the target compound and subsequent high resolution gas chromatography/low resolution mass spectrometry (HRGC/LRMS) analysis, was proven comparable to other accepted methods for determining the vapor pressures of semi-volatile organic compounds (SVOCs). Vapor pressures for octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) were in excellent agreement with those reported in literature. The application of the current method for the vapor pressure determinations of eight polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/PCDFs) in the extended temperature range (up to 275 °C) is reported. The extension of the vapor pressures to such temperatures, unprecedented for the PCDDs/Fs, is important for vapor-particle partitioning modeling in regions relevant to PCDD/F formation and control. Estimates for the melting temperatures and enthalpies of sublimation and vaporization are also reported, the latter for which no experimentally determined values have been found in the literature. The use of the method to deliver reproducible, trace concentrations (ppt-ppb) of targets was applied to the calibration of the jet-REMPI/TOFMS as an online detector for low chlorinated PCDDs/Fs. 相似文献
89.
Ralph W. Howard C. A. McDaniel Dennis R. Nelson Gary J. Blomquist Leslie T. Gelbaum Leon H. Zalkow 《Journal of chemical ecology》1982,8(9):1227-1239
The cuticular hydrocarbon components of four castes ofReticulitermes virginicus (Banks) have been identified and quantitated. Components identified includen-alkanes; 2-, 3-, 11-, 13-, and 15-methyl-alkanes; 11,15-dimethylalkanes, (Z)-9-alkenes; (Z,Z)-7,9-dienes; and (E/Z)-6,9-dienes ranging in carbon number from C21 to C40. All caste forms ofR.virginicus contained the same components, but showed caste-specific proportions. Comparison of these hydrocarbons with those of the sympatric termiteR. flavipes (Kollar) suggest that cuticular hydrocarbons might serve as species- and caste-recognition cues. A bioassay was developed to test this species-recognition hypothesis, with the experimental results supporting the hypothesis.Isoptera: Rhinotermitidae. 相似文献
90.
消能锥形阀是一种用于中、高水头下的消能控流阀门,其内部结构设计的好坏直接影响着控流效果。为探究消能锥形阀在不同开度下,过流流量及内部流场的变化情况。进行了模型试验与CFD数值模拟计算,试验中发现开度从100%关至85%时出现了流量反而上升、进口压力下降的情况。利用CFD数值模拟的方法对内部流场进行了可视化研究。研究结果表明,在全开状态下锥形阀内部存在以下问题:过强的局部高速高压区域、低速流动死区范围过大、涡流区过度影响高速过流部分。并对锥形阀进行了一定的结构改进,优化了其内部流场情况。 相似文献