Phillips polyethylene catalysts discovery

Ziegler Catalysts. For his work in the discovery of a new class of highly active catalysts for polymerization of ethylene, propylene, and dienes, Karl Ziegler shared the 1963 Nobel Prize in Chemistry with Guilio Natta whose contributions were predominantly related to polypropylene. Today, these catalysts together with the Phillips catalyst are responsible for the majority of the world s polyethylene production. Loosely defined, Ziegler catalysts are polyethylene catalysts derived from transition-metal halides and main group metal alkyls (46,50-53). In modem... 

Commercial linear polyethylene, the most commonly used type of plastic, was bom more than half a century ago with the accidental discovery at Phillips Petroleum Company that chromium oxide supported on silica can polymerize a-olefins.1 The same catalyst system, modified and evolved, is used even today by dozens of companies throughout the world, and it accounts for a large share of the world s high-density polyethylene (HDPE) supply, as well as some low-density polymers. The catalyst is now more active and has been tailored in numerous ways for many specialized modem applications. This chapter provides a review of our understanding of the complex chemistry associated with this catalyst system, and it also provides examples of how the chemistry has been exploited commercially. It is written from an industrial perspective, drawing especially on the commercial experience and the research of numerous scientists working at Phillips Petroleum... 

The Phillips catalyst has now been used commercially for more than half a century. It has been adapted and improved and tailored for new markets and new reactors. Research, which is still ongoing, continues to lead to new ways to modify the catalyst and to new grades of polyethylene to make with it. These facts are contrary to the impression often taken from trade magazines, which sometimes describe the Phillips and Ziegler catalysts as "mature," in contrast to the many exciting discoveries of metallocenes that are being made. Indeed, some writers even predicted that metallocenes would replace Phillips and Ziegler catalysts. 

As we saw previously, polypropylene was first made in June 1951, unintentionally as a solid polymer, by Phillips Petroleum, who were at that time seeking to convert excess refinery gases, ethylene and propylene, to high-octane fuel. Phillips developed their chromium olefin polymerization catalyst for linear polyethylene, but in fact, Phillips never entered the polypropylene manufacturing business. Paul Hogan and Robert Banks recorded the invention of the process by which they produced crystalline polypropylene about an hour after their discovery. As we shall see in more detail below, their January 1953 patent application was issued in March 1983 (32 years after their discovery) [11]. 

Other Early Developments. In addition to the breakthrough by Ziegler, two other discoveries of ethylene polymerization catalysts were made in the early 1950s. A patent by Standard Oil of Indiana, filed in 1951, disclosed reduced molybdenum oxide or cobalt molybdate on alumina (13). At the same time, Phillips discovered supported chromium oxide catalysts, prepared by impregnation of a silica-alumina support with Cr03 (14 16). Both the Phillips catalyst and titanium chloride based Ziegler catalysts are widely used in the production of high density polyethylene (HDPE). 

For example, prior to the discovery of this new single-site catalyst type, commercial grades of polyethylene were primarily manufactured over the compositional range of 0-4 mol% of comonomer (1-butene, 1-hexene or 1 -octene) that provided ethylene copolymers over the density range of 0.915-0.970 g/cc. Commercial catalysts were primarily the Cr-based Phillips-type of catalyst or a Ti-based Ziegler catalyst with the xmderstand-ing that both types of catalyst consisted of many different types of active sites. Each type of active site produced a different composition of polyethylene (different molecular weight and branching content) which resulted in a final polyethylene material with a complex molecular structure. These multi-site catalysts limited the composition of the polyethylene that was commercially available due to both process and product constraints imposed by such catalysts. 

Although ethylene/1-olefin copolymers were well documented in the late 1950s with the discovery of the chromium-based Phillips catalyst and the titanimn-based Ziegler catalyst, it was the discovery of metallocene-based single-site catalysts and the constrained geometry catalyst system that significantly increased the various types of new ethylene-based copolymers that are available for commercial applications. These new catalysts created new products, applications and markets for the polyethylene industry. 

In the 1950s, almost two decades after the launch of LDPE, transition metal catalysts proved capable of producing unbranched linear low density polyethylene (LLDPE) and linear high-density polyethylene (HOPE), both of which had significantly different properties from LDPE. Remarkably, the discovery occuued nearly simultaneously in three different research groups using three different catalyst systems. First was Standard of Indiana s reduced molybdate on alumina catalyst in 1951, followed by Phillips with chromium oxide on silica ( chromox ) catalysts, and Ziegler s titanium chloride/ alkylaluminum halide systems in 1953 (only the latter two were widely commercialized). At about the same time, crystalline polypropylene (PP) was produced in the Phillips labs... 

At about the same time that news of the Ziegler discovery was released, the Phillips Petroleum Company in the United States atmounced that it had developed a medium-pressure, catalytic process (500 psig) to produce a high-density, crystalline polyethylene. The process was discovered when traces of ethylene in a flue gas had polymerized over conventional cracking catalysts. The Phillips catalyst contained chromic oxide supported on silica. The Standard Oil Company of Indiana (later Amoco) also introduced a medium pressure process using a catalyst comprising molybdenum oxide supported on carbon or alumina, but it did not enjoy the success of the Ziegler or Phillips processes and was only operated in three full-scale plants. ... 

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