The impact of induced condensing agents in the gas phase polymerization of ethylene

The rate of polymer production in a commercial-scale fluidized bed reactor for making polyethylene is limited by the rate at which the heat of the polymerization can be removed from the reactor. In the condensed mode operation, one or more induced condensing agents (ICA) like pentane or hexane is added to the recycle stream, condensed in an external heat exchanger, and fed back into the reactor near the distributor plate. The original goal of this technology was to rely on the vaporization of the liquefied portion of feed stream in the reactorto remove heat from the reaction environment. However it is well-known that the liquid portion of the feed stream is vaporized within one to two meters above the distributor plate, meaning that most of the reactor (up to 20 m or more in height) contains little to no liquid. We were therefore interested in learning what other impact the ICA in vapor form might have on the reactor behavior. We used a lab-scale gas phase reactor; the effect of presence of different ICAs (isomers of pentane or hexane in the current study) in the gas phase composition during ethylene polymerization on heterogeneous catalyst is investigated. The catalyst used is conventional Ziegler-Natta supported on MgCl2. The presence of ICA in the gas phase composition is believed to induce a cosolubility effect that depends on the size and nature of the alkane in question. The enhanced ethylene solubility and diffusivity in the polymer phase in the presence of ICA results in higher rate of polymerization thanks to higher availability of monomer at the active sites