Polyethylene patent, Phillips catalyst

The Cr/Si02 Phillips catalysts, patented in 1958 by Hogan and Banks [2], are nowadays responsible for the commercial production of more than one third of all the polyethylene sold world-wide [7,16]. 

Other kinds of coordination catalytic systems developed few years before the Ziegler-Natta catalysts were based on chromium and molybdenum oxides supported on SiOj AI2O3 and other supports. The catalysts were patented by Phillips Petroleum and Standard Oil companies of Indiana for the synthesis of polyolefins. Although Phillips catalysts were the first to produce a fraction of crystalline polypropylene, these systems were more useful for the production of polyethylene. In fact, the Phillips and the Ziegler-Natta catalysts are currently the two commercial systems that dominate the production of HDPE [2]. 

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). 

As discussed previously, the contents of the original Phillips patent was remarkable in the broad range of polymer compositions that were described in the patent. The details of the various types of polyethylene that were made with the Phillips catalyst were described by Hogan in a 1964 publication [10]. Unlike low-density polyethylene (LDPE) that was... 

Although little is known about the actual mechanism of action of these catalysts, they are industrially utilized to produce high-density polyethylene (HOPE) in significant quantity. Phillips catalysts (so called because they were patented by Phillips Petroleum Cy) consisted of chromium oxide (CrOa) deposited onto a silica support the system is activated by air-drying and by a progressive heating... 

The early Phillips catalysts only needed to be activated and reduced to generate active centers, but several patents since have described the use of co-catalysts to promote the production of LLDPE. For example, a typical catalyst that had been modified with titanium, activated in air and reduced in caibon monoxide was then further activated by addition of triethylboron prior to operation." This procedure led to the production of linear low density polyethylene, LLDPE, which had a density of 0.9726 g cm, directly, without the need for the addition of an a-olefin to the pure ethylene feed. Olefins were produced in situ and these were incorporated into the polyethylene. A second catdyst was made using silica with a very high pore volume, modified with titanium, activated in air, and finally reduced with caibon monoxide at 350°C. This catalyst was then treated with triethylboron before use. LLDPE polymers with densities in the range 0.890 to 0.915 were obtained from a feedstock of ethylene and hexene-1, but the addition of some hydrogen to the gas stream was required to limit the length of the polymer chain. 

Linear polyethylenes are produced in solution, slurry, and increasingly, gas-phase low-pressure processes. The Phillips process developed during the mid 1950s used supported chromium trioxide catalysts in a continuous slurry process (or particle-form process) carried out in loop reactors. Earlier, Standard Oil of Indiana patented a process using a supported molybdenum oxide catalyst. The polyethylenes made by both these processes are HDPE with densities of 0.950-0.965 g/cm and they are linear with very few side-chain branches and have a high degree of crystallinity. 

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]. 

Consequently, the Phillips Petroleum scientists isolated crystalline polypropylene between October 9,1951 and April 16,1952. Although, initially, the United States Patent and Trademark Office awarded the composition of matter patent for isotactic polypropylene (prepared with a Ti-based catalyst composition) to Montecatini on February 6, 1973 (U.S. Patent 3,715,344), the Federal District Court of Delaware reversed the United States Patent and Trademark Office decision on January 11, 1980, and awarded the composition of matter patent to Phillips Petroleum based on the earlier research carried out by Hogan and Banks (See Chapter 3 of this book for additional details on the historical origins of polyethylene and polypropylene.)... 

Although Phillips Petroleum did not commercialize a gas-phase process for the manufacture of polyethylene. Sailors and Hogan pointed out that the first commercial gas-phase process came on stream in 1964, with BASF using the licensed Phillips chromium-based catalyst [21]. BASF received U.S. Patent 3,300,457 on January 24, 1967 (filed on May 9, 1963), for a gas-phase process [37]. 

Paul Hogan and Robert L. Banks (ConocoPhillips, Bartlesville, Oklahoma) had observed the formation of crystalline polypropylene as well as linear polyethylene in 1951 using their own metal oxide catalyst system. In fact, about half a dozen companies filed patent applications in 1953 covering crystalline polypropylene. The consequent, technically complex legal battles for priority extended over a period of three decades. Finally, in 1983, the US patent on crystalline polypropylene was issued to Phillips. Hogan and Banks received the Perkin Medal in 1987 in recognition of their achievement. 

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