Modeling of butadiene polymerization using cobalt octoate/DEAC/water catalyst

Abstract

SynopsisTwo-level fractional factorial designs were employed to study the solution polymerization of butadiene in a batch reactor using cobalt octoate/DEAC/water as catalyst. Conversion and molecular weight data obtained as functions of time were used to develop a kinetic model, and the estimated kinetic parameters were correlated empirically with four operating variables: temperature and concentrations of cobalt octoate, DEAC, and water. The experimental data indicate that a t high water concentration a significant amount of oligomers is formed during early stages of polymerization, and the molecular weight of polymer increases with time. Analysis of the data suggests instantaneous initiation, first order propagation with cobalt and monomer, and transfer to monomer. Models which do not take account of the branching are shown to be incapable of fitting data for both a,, and Mu. The catalyst decay seems to follow a first-order mechanism, but the evidence is somewhat inconclusive. INTRODUCTIONCis-polybutadiene can be prepared using Ziegler-Natta catalysts of titanium or cobalt compounds with aluminum alkyls. A cobalt catalyst usually has the advantage of high solubility in organic solvents and as a result is more efficient in terms of polymer yield per unit mass of catalyst used.Several different cobalt salts have been reported to be effective for the 1,4-cis addition polymerization of butadiene, and cobalt salts of fatty acids have been used successfully in the commercial production of polybutadiene. The most common of these is cobalt octoate with diethyl aluminum chloride (DEAC) and water as cocatalysts. Despite its practical significance, however, the kinetics of this catalyst system have not been studied extensively.Among the few publications on this subject appearing in the open literature is Gippin's' investigation of the kinetic behavior of cobalt octoate and the effects of water and its substitutes, such as cumene hydroperoxide, elemental bromine, and tert-butyl alcohol, on the activity of the catalyst and the quality of polymer produced after 19 h of reaction at 5°C. Gippin believed that part of the DEAC reacts with water or its substitutes to produce higher acid derivatives. A possible reaction of DEAC with those compounds is the dialkylation of DEAC by the substitution of a reactive electronegative group for one ethyl group.Recently Honig et a1.2.S reported kinetic data on butadiene polymerization with a cobalt octoate-DEAC catalyst. The results and the proposed mechanism formed the basis for a kinetic model developed by Hamielec and co-worker~,~ who used an empirical factor to take account of the efficiency of In this work a batch reactor was used for polymerization. Under preselected operating conditions experiments were carried out according to two-level fractional factorial designs. The rate and average molecular weights were measured as functions of time to develop a kinetic model and estimate its kinetic parameters. The effects of temperature and concentration of DEAC, and of water, on those parame...

Replacement of benzene with regulators for the catalyzed polymerization of 1,3‐butadiene to high cis‐1,4‐polybutadiene

“…This is of little consequence in this investigation. There is instantaneous formation of catalyst sites. This is common with many Ziegler–Natta catalysts 12–17. A first‐order rate plot of −ln(1 − x ) (where x = fractional conversion) versus time, intercepting the origin, indicates instantaneous initiation of polymerization.…”

Replacement of benzene with regulators for the catalyzed polymerization of 1,3‐butadiene to high cis‐1,4‐polybutadiene

“…This is common with many Ziegler-Natta catalysts. 12 This method of calculating the concentration of active centers is more appropriate than tritiated methanol determination 7,8 or assuming that the fixed percentage activity 18,19 as a real value is obtained corresponding to the actual number of polymer chains related to the rate of propagation.…”