Melt index potential

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.

As noted in Section III,E the hydroxyl population on the catalyst seems to exert a powerful influence on the activity and melt index potential, which are... 

Table IX shows the effect of dehydration by chemical means. Silica samples were calcined at 870°C in various gases, impregnated anhydrously with 0.5% Cr, and finally calcined in air at 650°C, producing Cr(VI). Only the silica (not the chromium) was exposed to the reducing treatment. Even so, CO more than doubled the melt index potential and COS improved it by a factor of 60. Activity was also increased.

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).

Results indicate that, far from being a necessary part of the active center as has sometimes been proposed, these hydroxyls may actually interfeiewith the active site. Hydroxyls could be removed by chemical as well as by thermal means to improve activity and melt index potential, such as by treating the catalyst in carbon monoxide, sulfur, or halides. 

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. 

Melt index potential means the maximum MI that can be obtained with a catalyst activated at maximum temperature (871 °C), and making homopolymer at maximum reaction temperature (110 °C). Catalystshaving a high-MI potential need not be used to make high MI resins, but they have the capability. Low-MI polymers are typically manufactured more easily with catalysts having a high-MI potential. 

FIGURE 123 Melt index potentials of Cr/silica-titania catalysts that were activated in various gases by the R R process. Catalysts were reduced 3 h in the gas shown at the temperature shown, then reoxidized 2 h in air at the same temperature. Reduction in CS2 produced polymers of the highest melt index. 

FIGURE 125 Melt index potentials of two series of R R-activated catalysts. Amorphous Cr(lIl)/silica—titania was heated to 870 °C in N2. Crystalline Cr(lll)/silica—titania was heated to 650 °C in air, then to 870 °C in N2 to form a-Cr203. Both catalysts were then treated in CO at 870 °C for 3 h, followed by 2 h in dry air at the temperature shown. The crystalline catalyst was more difficult to reoxidize, and therefore it produced polymers of lower melt index. 

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.

By using the simulation model developed in Samsung Total we applied the ideas of pFoductivily enhancement successfiiUy to LDPE plant and accomplished considerable productivity incn e. The MWD as well as the melt index and density calculated by the simulation model convinced us of applying the ideas to commercial plant. The end user property prediction capabilities of the model will be refined further by integration of phj icxjchemical and statistical approaches and be one of the next potential research items. 

The melt index (MI) is also shown in Figure 18. MI is a measure of the viscosity of the molten polymer under standard extrusion conditions. Because it has an inverse relationship with MW, it declines during the course of the run. Both MI and Mw eventually level out to time-independent values as all potentially active sites are functioning. This MW dependence on reaction time is different from what is observed with Ziegler catalysts, which display no dependence, or from metallocene catalysts, which exhibit the opposite behavior because of H2 generation. 

Exxon LL5202.09 LLDPE, a barefoot 12 melt index, 0.924 density polyethylene was used as the carrier resin for preparation of all concentrate formulations. Exxon LL1001.09 LLDPE, a barefoot 1.0 melt index, 0.918 density film resin was selected as the matrix material for the preparation of all letdown compounds. Additive-lree resins were used throughout this trial to minimize potential interactions with additive packages and to simplify the analysis task. 

When a molecule takes part in a reaction, it is properties at the molecular level which determine its chemical behaviour. Such intrinsic properties cannot be measured directly, however. What can be measured are macroscopic molecular properties which are likely to be manifestations of the intrinsic properties. It is therefore reasonable to assume that we can use macroscopic properties as probes on intrinsic properties. Through physical chemical models it is sometimes possible to relate macroscopic properties to intrinsic properties. For instance 13C NMR shifts can be used to estimate electron densities on different carbon atoms in a molecule. It is reasonable to expect that macroscopic observable properties which depend on the same intrinsic property will be more or less correlated to each other. It is also likely that observed properties which depend on different intrinsic properties will not be strongly correlated. A few examples illustrate this In a homologous series of compounds, the melting points and the boiling points are correlated. They depend on the strengths of intermolecular forces. To some extent such forces are due to van der Waals interactions, and hence, it is reasonable to assume a correlation also to the molar mass. Another example is furnished by the rather fuzzy concept nucleophilicity . What is usually meant by this term is the ability to donate electron density to an electron-deficient site. A number of measurable properties are related to this intrinsic property, e.g. refractive index, basicity as measured by pK, ionization potential, HOMO-LUMO energies, n — n ... 

Ethyl lactate has a boiling point of 154 °C and melting point of —26 °C. It has the potential to replace many toxic halogenated solvents. A study of its physical properties neat and mixed with water was recently performed at room temperature it has a polarity (E x) of 0.64, refractive index 1.41 and density 1.02 gcm . ... 

A number of phosphate and thiophosphate esters are of limited thermal stability and undergo highly exothemiic self-accelerating decomposition reactions which may be further catalysed by impurities. The potential hazards can be reduced by appropriate thermal control measures. An example is the substitution of hot water at 60 C for pressurised steam to melt a solid phosphate ester, which on adiabatic calorimetric examination was found to have a time to maximum decomposition rate of 6 h at 110° but 11 h at lOO C [2]. The combined use of vapour phase pyrolysis to decompose various phosphoms esters, and of GLC and mass spectrometry to analyse the pyrolysis products, allowed a thermal degradation scheme to be developed for phosphorus esters [3]. Individually indexed compounds are ... 

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