Polymer Fractionation Processes

POLYMER FRACTIONATION PROCESSES Isothermal Decreasing Pressure Profiling 

In the figure, a heavy fraction leaving the primary contactor vessel is indicated this is the highest molecular weight fraction that has not been dissolved based upon the extraction pressure and temperature. If the extraction pressure or temperature or both are changed such that the dissolving power is greater, the entire feed could just as easily be dissolved, but to isolate the 

Although the density of the supercritical extractant is typically lower than that of the polymer, the column could as easily operate upside down, that is, if the density of the supercritical extractant was higher than that of the feed oil, the inlet positions of the respective streams shown in figure 9.2 would be reversed. Later in this chapter some phase and fractionation studies on an acrylate-ethylene copolymer with supercritical chlorodifluoromethane are presented. Over much of its active P-T range, supercritical chlorodifluoromethane is more dense than some of the polymers. Therefore, if that system were to be scaled to continuous operation at the commercial level, the liquid or melted polymer would be fed to the bottom of the extractor and chlorodifluoromethane to the top the subsequent fractions would be removed from the top of each separation vessel instead of from the bottom, as shown in the figure. In the polymers patent section of this book, we describe a process for polymer fractionation via stepwise pressure reduction exactly analogous to the process shown schematically in figure 9.2—the Hunter and Richards 1945 patent. 

In a simplistic description of the laboratory process, a low pressure is first used and the extraction continued until no more polymer is collected in the 

U-tube shown in the figure. The term no more is a relative one since the rate of extraction will slow down markedly, but not necessarily to zero, after the polymer fraction that is most soluble, or more precisely, after the fraction that exhibits the highest distribution coefficient in the gas, is dissolved and removed from the column. When the extraction rate drops markedly, indicating that the oligomers of extractable molecular weight have been removed at the specific pressure level, the pressure level is raised, the collection vessel changed, and a new polymer fraction is collected in the U-tube. The sequential pressure increase/collection sequence is continued until all the polymer is dissolved, or until some maximum pressure dictated by the system design is reached. 

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Montedison and Mitsui Petrochemical iatroduced MgCl2-supported high yield catalysts ia 1975 (7). These third-generation catalyst systems reduced the level of corrosive catalyst residues to the extent that neutralization or removal from the polymer was not required. Stereospecificity, however, was iasufficient to eliminate the requirement for removal of the atactic polymer fraction. These catalysts are used ia the Montedison high yield slurry process (Fig. 9), which demonstrates the process simplification achieved when the sections for polymer de-ashing and separation and purification of the hydrocarbon diluent and alcohol are eliminated (121). These catalysts have also been used ia retrofitted RexaH (El Paso) Hquid monomer processes, eliminating the de-ashing sections of the plant (Fig. 10) (129). 

A typical balance of processability and end use performance is the general requirement of polymeric resins. The studies on the different polymer fractions have provided a great support in tailoring the MW and MWD in order to achieve the required properties and eliminating the unwanted molecular species. The increase in low-... 

The calculations are applied to a polymer sample following a Schulz-Zimm distribution with Mw = 1.03 x 10s and Mw/N4n = 1.017. These values are representative for the polymer fractions used in most of the experiments in transient elongational flow [147, 155], To visualize the evolution of the degradation, it is convenient to make a distinction between the polymer fraction N from the starting material which remains intact and the fraction Nf newly formed following the degradation process... 

The resin composition was indeed found to influence the ageing processes in mastic, the polymer fraction was shown to reduce the oxidation of triterpenoids (Figure 5.8). This was found for both natural ageing [33, 36] and artificial ageing. Because the polymer, a polymyrcene, contains many double bonds that can easily be oxidised [42], it might act as a radical stabiliser. The mastic samples shown in Figure 5.8 were obtained from three aliquots of the same mastic solution, the polymer part of the first aliquot was removed and added to the third. 

Hydropol A process for co-hydrogenating u-butenes with olefinic gasoline fractions. Developed by the Institut Frangais du Petiole as part of its polymer gasoline process. Hydrocarbon Process., 1980, 59(9), 219. 

Moreover, we confirmed the results previously ascertained through radiochemical measurements. In fact, the comparison between such data and those obtained by IR measurements on the atactic polymer fraction (Table IV) shows that the ratio between the number of polymeric chains with a —C2H6 end group (corresponding to a chain transfer process depending on the catalyst concentration) and the number of polymeric chains with a vinylidenic end group of polymeric chains (corresponding to the chain transfer process with the monomer) is closely in accordance with the data reported in Fig. 33. 

It has to be noted that EpoA molecules bound to tubulin polymers do not contribute to the NMR signal because only ligands in the fast-exchange regime are observable in these NMR experiments. Besides, tubulin polymers precipitate out of solution in a few hours. Therefore, the structure derived by NMR reflects the complex of EpoA binding transiently to the fraction of tubulin that remains soluble, that is very likely the first species formed during the drug-induced polymer assembly process. 

The slurry bulk process is slightly more expensive than the slurry diluent process, the claimed advantage being low catalyst residues in the polypropylene produced [43,51]. The bulk process may be simplified by not removing the atactic polymer fraction (Figure 3.56) [51]. 

By contrast, when the product from crude oil is limited to only one or two specific hydrocarbons of fairly high purity, the fraction is called a petrochemical. Examples of petrochemicals are ethylene, propylene, benzene, toluene, and styrene. Refined products are defined by the fraction s boiling point and may be composed of various hydrocarbons. Multiple compounds compose refined-product fractions. In contrast, petrochemicals are single-compound fractions, which are required for feedstocks for other petrochemicals and polymers. More processing and separation (distillation, extraction, etc.) operations are used to extract petrochemical products from processing streams. Thus, more identifiable petrochemical products are processed than refined products. Many specific hydrocarbon compounds can be derived from crude oil. However, these hydrocarbons lose their individual identity when they are grouped together as a refined product. 

Pervaporation is a fractionation process which uses a polymer membrane between the liquid phase (upstream side) and the vapor phase (downstream side) of a mixture. 

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