Reactors, Reactions and Structures in Olefin Polymerisation: A novel investigation of the world's most important polymers – REACT-OP

1. Scientific background and objectives Polyolefins polymers based on polyethylene (PE) and polypropylene (PP) represent the largest family of polymers in the world in terms of volume, with annual production over 100 million tonnes - 80% of which is made on supported catalysts. Advances in R&D over the course of the last few years help polyolefins to steadily replace other, more expensive, less environmentally-benign engineering thermoplastics and traditional materials. This progress in the control of the microstructure of macromolecules has allowed producers to offer a wider range of properties to their customers than previously. However, part of the attractiveness of polyolefins comes from the fact that they are outwardly simple molecules composed only of carbon and hydrogen. While this confers environmental and cost benefits, it makes it difficult to propose an ever-wider range of properties. One of the ways this can be done is by the manipulation of the structure of the catalyst and its support during the preparation stage, or by correctly growing the polymer in the reactor environment. This requires us to have total mastery of the complex issues that govern polymer production on supported catalysts, and dedicated reactors and tools. The catalysts used for this type of polymerisation are chemically and physically complex structures. The active site upon which the polymer chains grow is usually obtained from a metal chloride (e.g. TiCl4) in the case of Ziegler-Natta catalysts, a metal oxide (CrOx) in the case of Phillips catalysts, or a metallocene catalyst (metal linked to one or two cyclopentadienal rings). The precursors are deposited on a highly porous solid support (typically MgCl2 for ZN catalysts, or silica for the others), and the supported catalyst is often activated by the addition of a cocatalyst (e.g. alkyl alumina). The challenges currently faced by polymer and catalyst producers include: Ø Complex interactions between the support and the precursors that lead to different active polymerization sites. Ø Modification of the chemical structure in situ. E.g. exposure to monomer alters the behaviour of the active sites. Such changes are less well established in other catalytic systems. Also, local overheating can cause the catalyst to deactivate in unforeseen ways. Ø Rapid morphological changes of the particle structure. It appears that the morphology of the particle is fixed within the first seconds of the reaction. Ø Highly non-linear , dynamic kinetics. It is not feasible to extrapolate the behaviour of the reaction at one bar to more realistic conditions (10-30 bars). We need to have reactors that run under such conditions, and that allow us to recover the particles. 2. Description of project, methodology The project is centred on the design, implementation, and exploitation of specialised reactors for the study of the nascent (time < 5 sec) and short term polymerisation. It is crucial to develop such tools and the associated knowledge. To do this we have formed a well-focused group of experienced researchers in an attempt to create a new set of knowledge. This will be done by dividing the work into three workpackages (WP), each of which is associated with a well-defined activity in the process. WP 1. Elaboration of specially adapted reactors for the study of nascent polymerisation. The starting point is a unique reactor build by the two partners that allows to polymerise for times on the order of 40 ms. Current limitations in the use of this slurry phase reactor will be overcome, and more importantly, we will design flexible alternatives for the study of more environmentally benign gas phase processes. WP2. Control of particle morphology and its impact on long term reaction behaviour. Preliminary studies have shown that the way in which catalysts are treated during the initial instants of the reaction influences how they behave at longer times. Well-defined series of experi...