Metallocene polyethylene Company

The highest global consumption of any plastic coupled with the many distinct types of commercially available polyethylenes are testament to the rich history of major innovations in products, processes and breadth of applications of polyethylene. This chapter will give a historical perspective of these innovations in polyethylene including a breadth of product applications of polyethylene and the impact of metallocene polyethylenes commercialized in last 15 years. A very recent innovation of olefin block copolymers by The Dow Chemical Company will be described and some remarks will be made on future product innovations and trends. 

FIGURE 2.10 Downgauging of polyethylene film in plastie garbage bag applications. Source Exxon Mobil Corporation. Life Cycle Assessment of Metallocene Polyethylene in Heavy Duty Sacks. ExxonMobil Chemieal Company May 2011. 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

Exxpol [Exxon polymerization] A gas-phase process for making polyethylene from ethylene. The process uses single-site catalysis (SSC), based on a zirconium metallocene catalyst. Developed by Exxon Chemical Company in 1990 with plans to be commercialized in 1994. 

UNIPOL [Union Carbide Polymerization] A process for polymerizing ethylene to polyethylene, and propylene to polypropylene. It is a low-pressure, gas-phase, fluidized-bed process, in contrast to the Ziegler-Natta process, which is conducted in the liquid phase. The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn. A co-monomer such as 1-butene is normally used. The polyethylene process was developed by F. J. Karol and his colleagues at Union Carbide Corporation the polypropylene process was developed jointly with the Shell Chemical Company. The development of the ethylene process started in the mid 1960s, the propylene process was first commercialized in 1983. It is currently used under license by 75 producers in 26 countries, in a total of 96 reactors with a combined capacity of over 12 million tonnes/y. It is now available through Univation, the joint licensing subsidiary of Union Carbide and Exxon Chemical. A supported metallocene catalyst is used today. 

In recent years metallocene catalysts have been introduced into low-pressure gas-phase-, solution-, and slurry-processes to manufacture polyethylene and polypropylene. The new technology extends not only the range of conventional materials but generates new speciality polymers. Some companies have also retro-fitted high-pressure reactors to make use of the advantages of metallocene catalysts. 

Evolue Also written Evolue. A gas-phase process for making linear low-density polyethylene using higher a-olelin co-monomers and a metallocene catalyst. Developed by Mitsui Chemicals and Idemitsu Kosan, and now manufactured in Japan by Prime Polymer, a joint venture of these two companies. 

New types of LLDPEs based on the metallocene catalyst technology have been introduced recently in the market place. Such LLDPEs are characterized by narrower molecular weight and homogeneous short-chain branching distribution. Some of the metallocene catalyst based octene-1 LLDPE copolymers made by the Dow Chemical Company are known to have LCB. For the properties of metallocene LLDPE see the entry Polyethylene, metallocene linear low density, in this handbook. 

Metallocene catalysts have been successfully adapted to all commercial polyethylene processes. Recently, companies have begun to join forces to avoid patent disputes as well as to accelerate the pace of commercialization. Joint ventures between Exxon and Union Carbide (Univation Technologies) and between Dow and BP were formed to leverage popular process technologies (variants of fluidized-bed gas-phase reactor systems) to expand the market for metallocene catalysts and products. The Dow-Union Carbide merger of 2001 could greatly influence the rate of technology dissemination. 

Cycloolefin (CO)Polymers. Many metallocenes can incorporate bulky cycloolefins into polyethylene, but only a few companies, notably Hoechst and its successor Ticona, have attempted to sell the resulting materials. These glassy, amorphous copol5miers have high rigidity, chemical resistance, and clarity, which predisposes them to be useful in optical applications and in pharmaceutical containers. 

While metallocenes have been known to polymerize olefins since the 1950s, only in the last 10 years have they been introduced commercially. Exxon introduced its first generation metallocene in 1989 for the limited production of polyethylene. This was a homogeneous catalyst used in solution. Other companies have followed with their own metallocene catalyst technologies, which are supported and are used in solution, gas phase, and supercondensed phases and processes. 

Dr. Sehanobish has authored a series of publications and holds more than 25 patents in the areas of polyethylene pipes, blown and cast films, speciality fibers and films, and TPOs. His research is the basis for the INSITETM technology platform and new resin families such as ENGAGE , AERNITY , NORDEL ip and ELHE . The INSITE technology received the R D 100 Award in 1994 from R D Magazine, and the ELITE enhanced polyethylenes received the R D 100 Award in 1999. These efforts also resulted in currently more than one billion pounds per year of sales of metallocene-catalyzed polyethylene resins by The Dow Chemical Company. 

Many companies are involved in the commercialization of polyolefin technology based on metallocene catalysts (Figs. 21-24) using solution, slurry and gas phase processes. Exxon Chemical developed the Exxpol process to produce a wide range of polyethylene with different densities. Dow Plastics has focussed... 

Borealis has started up its metallocene-based slurry loop polyethylene (PE) plant at Ruenningen, Norway. Borealis will produce 30,000 t/yr of metallocene-based products at the plant in 1997. Borealis has agreed a licensing deal with Exxon Chemical which should avoid future patent conflicts over the companies respective metallocene technologies. In 1996... 

It should also be noted that recently a new high-pressure autoclave process has been developed by Exxon Chemical Company to produce linear low-density polyethylene using metallocene catalyst technology. Because the metallocene catalyst is a single-site catalyst, the molecular-weight distribution of the resulting polyethylene is very low (M /M = 2.0). The polymerization is carried out in a staged autoclave reactor at 1000-2000 atm and 150-250°C with 30-120 sec of reactor residence time [13]. 

---