Ethylene polymerization steady-state

According to Demin et al. (125, 126) the steady-state polymerization of ethylene occurs at 5-70°C in the presence of Cr(7r-C3H6)3 and Zr (tt-CsHs) 4. In Ballard et al. (123) the induction period at ethylene polymerization using Zr (7r-C3H6)4 was observed the introduction of hydrogen... 

The kinetics of ethylene polymerization at temperatures below 90°C (the slurry process) were studied in Bukatov el al. (157, 159). The steady-state polymerization rate was observed the first order in the polymerize tion rate with respect to ethylene and the catalyst concentration was found. The polymerization rate increased on increasing the polymerization temperature from 20° to 80°C (Eeu = 7.5 0.5 kcal/mole). 

Finally the ESR spectrum of Nb(7r-allyl)4/alumina was unaffected by the addition of ethylene gas to the ESR sample tube. It is assumed that polyethylene is produced in this process since polymer can be isolated from larger scale reactions under similar conditions. The accepted mechanism for the ethylene growth reaction postulates a steady-state concentration of a a-bonded transition metal-hydrocarbon species which would be expected to modify the ESR spectrum of the supported complex. A possible explanation for the failure to detect a change in the ESR spectrum may be that only a small number of the niobium sites are active for polymerization. Although further experiments are needed to verify this proposition, it is consistent with IR data and radiochemical studies of similar catalyst systems (41, 42, 43). 

The polymerization of ethylene is a highly exothermic reaction and when highly exothermic reactions occur in fluidized-bed reactors, unusual steady state and dynamic behavior may occur. 

Figure 9. (left) Steady state response to 31.5 mM glucose of the ferrocene-siloxane-ethylene oxide polymer/glucose oxidase/carbon paste electrodes at several applied potentials. The polymeric relay systems are indicated next to each curve. Each curve is the mean result for four electrodes. 

Figure 1. The average degree of polymerization of the product, n, is a function of the relative rates of ethylene consumption and transfer. By invoking the steady-state assumption, it can be shown that the average degree of polymerization is governed by the competitive rates of propagation and transfer.

Borstar is an industrial olefin polymerization plant/technology, which combines different polymerization processes and reactor units, utilizing an advanced catalytic system. In the present work, a detailed model for the dynamic and steady-state simulation of this industrial plant has been developed. A comprehensive kinetic model for the ethylene-1-butene copolymerization over a two-site catalyst was employed to predict the MWD and CCD in the Borstar process. The Sanchez-Lacombe equation of state (S-L EoS) was employed for the thermodynamic properties of the polymerization system and the phase equilibrium calculations in the process units. 

In a classic 1978 paper [5,6], L.L. Bohm reported on the experimental parameters needed to establish steady-state polymerization conditions in order to eliminate monomer transport phenomena from the experimental results. As pointed out by Bohm, suspension or slurry polymerization takes place if the polymerization temperature is lower than the polyethylene solubility temperature and, therefore, the semicrystalline polymer precipitates from the suspension medium as the polymerization proceeds. The important physical process is the mass transfer of ethylene, comonomer and hydrogen (chain transfer reagent used to control polymer molecular weight) from the gas phase through the suspension medium and into the growing polymer particle to the active site. In order to obtain correct kinetic results, concentration gradients and temperature gradients within the polymer particle need to be removed from the polymerization process to achieve the necessary steady-state polymerization conditions. 

Ethylene Homo- and Co- polymerization. Ethylene homopolymerization and copolymerization with 1-hexene as a comonomer were carried out at 70 "C using AlEt, as a cocatalyst. The rate profiles of homo- and co-polymerization were changed drastically as the Hg/Ti ratio of the catalyst was changed. In homopolymer-ization the time to reach maximum rates becomes short as Hg/Ti ratio of the catalyst increases (Fig. 6). At the low Hg/Ti ratios to less than 2.6 the polymerization rate increases slowly to reach a steady-state value, which remains unchanged for an experimental period. At high Mg/Ti ratios, ca., Mg/Ti 16.5, poly-... 

The commercial production of LDPE is by free-radical polymerization. Supercritical bulk ethylene is fed into a tubular reactor operated at steady state. The polymers experience both short-and long-chain branching. The short-chain branches are a consequence of backbiting and the long-chain branches are a consequence of chain transfer to polymers. The low density of the product is a consequence of short-chain branching. 

Anionic polymerization of cyclic compounds may also belong to the first category of the steady state, namely, with invariant concentration of the active species and sufficiently high rate of initiation. The polymerization of ethylene oxide has already been known for a long time, and similar approaches (and... 

In Section 3.02.11, steady-state living polymerization was discussed. Initiation has been assumed to be fast as compared with propagation. This is then a class of polymerizations where the number of propagating chains remains invariant throughout the course of reaction. Such a situation exists, for example, in anionic polymerization of ethylene oxide, described by Floty, who has shown that such a process leads to the Poisson distribution. ... 

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