By replacing heterogeneous catalyst with homogeneous catalysts in Continuous Stirred Tank Reactor (CSTR) slurry processes, catalyst cost can be reduced dramatically and a significant reduction in environmental footprint can be reached. The polymer powder morphology can be adjusted to meet the requirements given by the polymerisation technology.
From the start, metallocene catalysts have been well known for producing mPE with very good comonomer distribution and narrow Molecular Weight Distribution (MWD), and for limitations in Molecular Weight (Mw). The poor processing performance from the narrow MWD was for many years a roadblock for exploring the positive aspects with mPE, resulting in a slow market penetration. In the recent years however, new catalysts and bimodal polymerisation technology has enabled production of easy processing mPE grades with capabilities for higher Mw, also giving opportunities for more robust HDPE products at higher densities. The market for mPE is currently growing faster than ever and also in value added segments.
The majority of LLDPE and HDPE is produced using heterogeneous catalysts where SiO2 and MgCl2 are the most common catalyst supports. Metallocene catalysts are typically impregnated on SiO2 when used in gas phase and slurry processes. Although the SiO2 has high surface area and good pore structure, the activity of a heterogeneous metallocene catalyst will be significantly lower than the homogeneous counterpart.
Nevertheless, heterogeneous catalyst in gas phase and slurry processes is deeply embedded as a “must have” among the mPE producers to avoid fouling and to obtain the required powder morphology.
With Norner Advance M technology a range of metallocene complexes and co-catalysts can safely be used in slurry reactors and only minor modifications to the catalyst feeding system would be required to compensate for the lack of catalyst support.
» Figure 1: Advance M technology – more than double activity vs. conventional catalysts.
Heterogeneous metallocene catalysts are among the most expensive on the market, while many metallocene complexes and co-catalysts are readily available as commodities to a significantly lower price. With ref to Fig 1, the higher activity will in addition reduce the consumption of catalysts per kg PE significantly. Heterogenization of catalysts requires substantial amounts of energy and consumption of solvents and other chemicals, and the same is the case for production of the SiO2. All together this adds up to a considerable reduction in environmental footprint through reduced CO2 emission and waste when converting from traditional catalyst concept to Norner Advance M
As an example, this opens for a very attractive transformation for a 150kta CSTR 2-reactor plant which normally would be running a fairly traditional product mix where most grades are produced with heterogeneous ZN catalyst. Let us imagine such a plant would be converted only to produce MDPE and HDPE from metallocene catalysts only, utilizing Norner Advance M technology for all products. The product mix opportunities enabled with Norner Advance M technology have no practical limitations in higher Mw and higher densities, and without SiO2 the products are free from contaminants. This combination will open the door to a broad product mix covering advanced products for extrusion-, blow moulding-, injection moulding-, rotomoulding-, film and membrane applications which would meet or surpass the performance of leading grades in a variety of market areas. We foresee e.g. PE100RC with superior properties from excellent comonomer distribution in the UHMw polymer chains combined with the absence of contaminants from SiO2, and super clean products for HV W&C insulation and medical applications.
Savings on catalyst cost alone will be significant and we expect the improved purity will allow for a reduction in additive loading in the LLDPE and HDPE products, giving potentials for further cost reductions. Many mPE products sell already today at a higher price than ZN or Cr based grades and with new specialities on top, a substantially increase in average margin can be achieved.
Norner is already in discussion with potential licensees of the Advance M technology and look forward to welcome other companies to evaluate the benefits of revamping their CSTR plants.
Contact person: Lars H. Evensen, Director Business Development