Melt index potential relative

This is also apparent from the relative melt index potential (RMIP) of the catalyst, which is plotted in Fig. 9. Melt index increases with calcining temperature up to 925°C, indicating that the rate of termination relative to propagation varies in the same manner. 

Fig. 16. The relative melt index potential (RMIP) of a series of cogelled Cr/silica titania catalysts rises and then falls with calcining temperature, indicating first dehydroxylation then sintering. However, the more titania in the catalyst, the more easily it sinters and therefore the lower the temperature at which peak RMIP develops.

Fig. 19. The termination rate, plotted here as relative melt index potential (RMIP), reflects the extent of surface dehydroxylation in two series of Cr/silica-titania catalysts, calcined in (Y) air or ( ) CO and then air to reoxidize the chromium, both at the temperatures shown. The third series ( ) shows the additional benefit of low-temperature attachment. It was calcined in CO at the temperatures shown, then air at a lower temperature (760°C).

Relative Melt Index Potential. Melt indices were obtained from polymer samples by the standard test (ASTM D 1238-73) at 190 C using a weight of 2160 grams. However, melt index values are not just affected by activation parameters, but also by reactor conditions, such as the temperature, monomer concentration, and residence time. Therefore for clarity in this report we have normalized melt index values against those of a reference catalyst run under the same reactor conditions. We call the normalized value the relative melt index potential (RMIP) because it is... 

Figure 2 also plots the melt index (RMIP = relative melt index potential) of these same polymers. Since a high RMIP indicates a high termination rate, it also (like the activity) increased with increasing activation temperature up to the point of sintering. Other measures of the termination rate, such as the vinyl content of the polymer, also displayed this same pattern. 

R/R Activation. Figure 5 shows that the enhanced dehydroxyl-ation by carbon monoxide also had a pronounced effect on the termination rate during polymerization. In these experiments, two series of Cr/silica catalyst samples were activated and allowed to polymerize ethylene to a yield of about 5000g PE/g. In one series the catalyst samples were simply calcined five hours in air as usual at the temperatures shown. The relative melt index potential (RMIP) has been plotted against activation temperature and the expected increase up to the point of sintering was observed. 

Figure 3.12 Relative Melt Index potential (RMIP) vs secondary catalyst activation temperature. RMIP is the melt index of the polyethylene sample normalized by the Melt Index of the standard Phillips catalyst containing 1 wt% Cr and activated with one thermal treatment in air at 870°C. Melt Index is inversely proportional to polymer MW. Reprinted from [12] with permission from Elsevier Publishing.

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