Production of polyolefins

Polyolefins represent one of the main types of synthetic polymeric materials. World production of polyolefins in 1980 amounted to 23 million tons, and since then the tendency to further growth has been prevailing [1]. The grave defect of polyolefins is low thermal and heat resistance, which is detrimental to the processing efficiency and limits their useability (Table 1). 

The total 1997 U.S. production of polyolefin fibers, including polypropylene fibers, was approximately 2.5 billion pounds. 

The metal catalyzed production of polyolefins such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and polypropylene (PP) has grown into an enormous industry. Heterogeneous transition metal catalysts are used for the vast majority of PE and all of the PP production. These catalysts fall generally within two broad classes. Most commercial PP is isotactic and is produced with a catalyst based on a combination of titanium chloride and alkylaluminum chlorides. HDPE and LLDPE are produced with either a titanium catalyst or one based on chromium supported on silica. Most commercial titanium-based PE catalysts are supported on MgCl2. 

Products Driving forces Threats Phenolic primary AOs, organophosphite secondary AOs Global production of polyolefins None... 

The Zr-FI catalyst selectively forms PE even in the presence of ethylene and 1-octene, while the Hf complex affords amorphous copolymers, resulting in the catalytic generation of PE- and poly(ethylene-c6>-l-octene)-based multiblock copolymers through a reversible chain transfer reaction mediated by R2Zn. The development of an FI catalyst with extremely high ethylene selectivity as well as a reversible chain transfer nature has made it possible to produce these unique polymers. Therefore, both Ti- and Zr-FI catalysts are at the forefront of the commercial production of polyolefinic block copolymers. 

Effective catalyst systems for the production of polyolefins with vinyl groups were developed by Weng et and by Ishii et It was found by Weng and co-workers that raf-[Me2Si(2-Me—4-Ph-l-Ind)2]ZrCl2... 

S. Kobayashi, T. Mizoe, and Y. Iwanami, Process for continuous production of polyolefin material, US Patent 5 200129, assigned to Nippon Oil Co., Ltd. (Tokyo, JP), April 6,1993. 

They are able to polymerize a large variety of vinyl monomers. The polymer microstructure can be controlled by the symmetry of the catalyst precursor. Prochiral alkenes such as propylene can be polymerized to give stereospecific polymers,554 572-574 allowing production of polyolefin elastomers. They can give polyolefins with regularly distributed short- and long-chain branches which are new materials for new applications. 

Phillips catalysts for linear polyethylene and polypropylene and the graft copolymerizations for impact polystyrene and ABS are even younger and have not yet spread into the less industrialized countries of world. The production of polyolefins, poly (vinyl chloride), and styrene resins on a worldwide basis as well as of all synthetic polymers is shown in Figure 3. A comparison of the U.S. production in Figure 1 and in Figure 3 demonstrates the effect of age and dissemination of technology. It shows that relatively more poly (vinyl chloride) but less polyolefins and styrene resins are produced worldwide than in this country. 

As films are used e.g. the polymerization product of ethylbenzene and divinylbenzene (33) the copolymer of styrene and butadiene (755) the copolymer of styrene and butadiene mixed with polyethylene (157) a vulcanized or cyclized copolymer of an aromatic vinylcompound and an aliphatic conjugated polyene (2). As a crack resisting matrix is mentioned the copolymer of styrene, divinylbenzene and butadiene with e.g. dioctylphthalate as a plasticizer (176). Other examples are the copolymers of unsaturated aromatic compounds and unsaturated aliphatic compounds (77) and the reaction products of polyolefines and partially polymerized styrene (174). Primary groups can be introduced also with the help of Friedel-Crafts catalyst. Ts. Kuwata and co-workers treated a film of a copolymer of styrene and butadiene with an aluminium-ether complex and ethylenedichloride (79). Afterwards they allowed the film to react with trimethylamine. Another technique is the grafting of e.g. a polyethylene film with styrene (28). 

Organoaluminum compounds are widely used in the production of polyolefines and stereoregular elastomers (as components of catalyst complex), as raw stock in the production of higher alcohols and carboxylic acids, as additives for reactive fuels, etc. 

The technologies that have been developed for the production of polyolefins, olefin homopolymers and copolymers are slurry, solution and gas-phase polymerisation bulk polymerisation of propylene in the liquid monomer as a special case of the slurry process has also emerged. The fundamental differences in the various olefin polymerisation processes reflect the different approaches that have been devised to remove the substantial heat of polymerisation. In addition, processes can be operated in a batch or a continuous mode. In the batch process the reagents are loaded into a polymerisation vessel, the polymer forms and the vessel is emptied before a new charge of reagents is introduced. In the continuous process, the catalyst precursor, activator and other necessary... 

The development of the gas-phase technology represents a major advance for the commercial production of polyolefins. A gas-phase process avoids the problem of the high cost remaining in the high-mileage slurry and solution processes (associated with recycling of diluent or solvent and drying of the polymer). 

Metallocenes are very versatile catalysts for the production of polyolefins, polystyrene and copolymers. Some polymers such as syndiotaetic polypropene, syndiotactic polystyrene, cycloolefin copolymers, optically active oligomers, and polymethylenecycloalkenes can be produced only by metallocene catalysts. It is possible to tailor the microstructure of polymers by changing the ligand structure of the metallocene. The effect and influence of the ligands can more and more be predicted and understood by molecular modeling and other calculations. 

Titanium-based solid-state catalysts for the industrial production of polyolefin materials were discovered in the early 1950 s and have been continually improved since then (see Section 7.3). Due to the high degree to which they have been perfected for the production of large-volume polyolefin commodities, they continue to dominate the processes presently used for polyolefin production. Despite (or because of) this product-oriented perfection, only limited degrees of variability with regard to some relevant polymer properties appear to be inherent in these solid-state catalysts. 

Access to polyolefins with a wider choice of properties has more recently been provided by various homogeneously soluble organometallic catalysts. Some of these catalysts, in particular those based on sandwich and half-sandwich complexes of zirconium and titanium and on nitrogen-containing complexes of group 4 and of some of the group 8-10 metals (see Section 7.4), are thus likely to be increasingly used for the production of polyolefins for special-purpose applications, which require properties not easily accessible otherwise. 

During the last five decades, industrial production of polyolefin materials has experienced strong increases in production volumes as well as changes in production procedures. Here we give an overview of the situation in 2005 (Boxes 1 and 2). 

The most important monomers for the production of polyolefins, in terms of industrial capacity, are ethylene, propylene and butene, followed by isobutene and 4-methyl-1-pentene. Higher a-olefins, such as 1-hexene, and cyclic monomers, such as norbornene, are used together with the monomers mentioned above, to produce copolymer materials. Another monomer with wide application in the polymer industry is styrene. The main sources presently used and conceivably usable for olefin monomer production are petroleum (see also Chapters 1 and 3), natural gas (largely methane plus some ethane, etc.), coal (a composite of polymerized and cross-linked hydrocarbons containing many impurities), biomass (organic wastes from plants or animals), and vegetable oils (see Chapter 3). 

Discussion Point DPI At present the production of polyolefin materials is based almost exclusively on petroleum. However further increases in crude-oil prices might make other potential sources competitive. Identify three alternative olefin sources, formulate the essential chemical reactions necessary for each production process and try to assess advantages, disadvantages and relative likelihoods of industrial implementation for such processes. 

In the particular case of transparent and sufficiently clean wastes, the production of polyolefin wax can be considered as described above. Such products have a higher commercial value than that of the new plastic material itself. 

The development of commercially useful polymers in the early 20th century ushered in an era where mass-produced, organo-polymeric materials have become a ubiquitous part of daily life. " Sixty years after the Nobel prize-winning discovery by Ziegler and Natta, " the scale of worldwide polyolefin production is massive. The current estimated aimual global production of polyolefins is over 150 million metric tons. However, the inherent chemical inertness of these substances causes them to persist in the environment centuries after they have been discarded. The detrimental environmental impact of a man-made waste problem of this scale has generated an interest in commercially viable, biodegradable alternatives. ... 

The content of aldehyde groups in the final product of polypropylene photodegradation is 7%. In the case of polyethylene degradation these groups are completely absent [6]. The relatively lower amount of aldehyde groups in the products of polyolefine photo-oxidation is due to the fact that they absorb radiation and subsequently react as above [278]. 

New markets are being created, and old ones expanded, at such rates that the exponential growth shown in Figure 7 seems likely to continue for some time. Stanford Research Institute has even predicted, on the basis of long-range extrapolations, that by the year 2000 U.S. production of polyolefins will reach the staggering total of almost 100 billion lb. It is predicted that polyolefins will then (as they do already) constitute well over half of all thermoplastics production. 

In the case of commodities, as fuels, plastics or fertilisers, the raw materials are intermediate chemicals produced fi om more basic raw materials, as oil, natural gas or minerals. For example, the production of polyolefin is integrated on a petrochemical platform with refining and other basic chemicals. The combination of several processes on a large industrial site is a typical feature of chemical industry that determines in large extent the profitability of a particular plant. 

The production of polyolefins such as polyethylene (PE) or polypropylene (PP) and their copolymers increases continuously due to their outstanding product properties and their environmental compatibility. They are commonly applied as packing material. foils, fibers, as well as components for the automotive and electrical industry. In 1996 the worldwide production of PE and PP counted 40 million and 20 million tons, respectively. On the basis of the global demand. the growth rate of PP production is predicted to rise up to 7% per year until 2002/ 2003. 

Breakthroughs in single-site catalysis have completely transformed our view of alpha-olefin polymerization catalysis. The conventional Ziegler—Natta catalysts used in industrial production of polyolefins... 

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