Manufacture of Polyethylene

About 35% of total U.S. LPG consumption is as chemical feedstock for petrochemicals and polymer iatermediates. The manufacture of polyethylene, polypropylene, and poly(vinyl chloride) requires huge volumes of ethylene (qv) and propylene which, ia the United States, are produced by thermal cracking/dehydrogenation of propane, butane, and ethane (see Olefin polymers Vinyl polymers). 

Chemical Hazards. Chemical manufacturers and employees contend with various ha2ards inherent ia productioa of evea commonplace materials. For example, some catalysts used ia the manufacture of polyethylene (see Olefin polymers) ignite when exposed to air or explode if allowed to become too warm the basic ingredient ia fluorocarboa polymers, eg, Tefloa (see Fluorine compounds, organic), can become violently self-reactive if overheated or contaminated with caustic substances (45,46) one of the raw materials for the manufacture of acryflc fibers (see Fibers, acrylic) is the highly toxic hydrogen cyanide (see Cyanides). 

Figure 24.3 Two-step polymerization process for the manufacture of polyethylene terephthalate ...

In addition to the desired polymerization reaction, the dialcohol reactants can participate in deleterious side reactions. Ethylene glycol, used in the manufacture of polyethylene terephthalate, can react with itself to form a dialcohol ether and water as shown in Fig. 24.4a). This dialcohol ether can incorporate into the growing polymer chain because it contains terminal alcohol units. Unfortunately, this incorporation lowers the crystallinity of the polyester on cooling which alters the polymer s physical properties. 1,4 butanediol, the dialcohol used to manufacture polybutylene terephthalate, can form tetrahydrofuran and water as shown in Fig. 24.4b). Both the tetrahydrofuran and water can be easily removed from the melt but this reaction reduces the efficiency of the process since reactants are lost. 

The manufacture of polyethylene naphthalate) (PEN) is carried out using dimethyl 2,6-naphthalene dicarboxylate (NDC) and EG and is similar to the manufacture of PET from DMT. The IV after the melt is typically in the range of 0.5... 

Uses. Chemical intermediate in the manufacture of polyethylene, ethylene oxide, ethylene dichloride, and ethyl benzene used as a fruit and vegetable ripening agent... 

Glycols can be used in the manufacture of polyethylene glycol) (PEG). Ethylene glycol, ethylene oxide, and a base catalyst react to form a family of z CH u q ... 

Hydrocarbons with double bonds are called alkenes. Ethene, CH2=CH2, is the simplest example of an alkene. It used to be (and still widely is) called ethylene it is used in the manufacture of polyethylene. Benzene is a hydrocarbon with double bonds that has such distinct properties that it is regarded as the parent hydrocarbon of a whole new class of compounds called—for historical reasons—aromatic compounds. The benzene ring is exceptionally stable and can be found in many important compounds. 

The solution process has been developed mainly for the manufacture of polyethylene. The term solution should not be taken literally since the polymer formed is often present in a molten state owing to maintenance of a high polymerisation temperature. In the solution process, a solvent such as... 

Farnell Packaging has been in business for over forty years as a custom manufacturer of polyethylene and co-polyester films, bags, sheets and pressure-sensitive labels. Farnell Packaging products are sold throughout the North American market and all of its quality systems are registered under IS09001 2000. 

This chapter introduces basic features of polyethylene, a product that touches everyday life in countless ways. However, polyethylene is not monolithic. The various types, their nomenclatures, and how they differ will be discussed. Key characteristics and classification methods will be briefly surveyed. An overview of transition metal catalysts has been included in this introductory chapter (see section 1.5) because these are the most important types of catalysts currently used in the manufacture of polyethylene. Additional details on transition metal catalysts will be addressed in subsequent chapters. 

Using a variety of approaches (3), hydrocarbon-soluble R Mg were discovered, including the so-called "unsymmetrical" dialkylmagnesium compounds (RMgR, where R and R are to n-C alkyl groups). In fact, RMgR compounds are today the most important of the commercially available dialkylmagnesiums used in manufacture of polyethylene ... 

Modified methylaluminoxanes exhibit much improved storage stability and several are highly soluble in aliphatic hydrocarbons. (Manufacturers of polyethylene prefer to avoid toluene because of toxicity concerns, especially if resins are destined for food contact.) Most importantly, because yields are higher, modified methylaluminoxane formulations are less costly than MAO. However, since modified methylaluminoxanes contain other types of alkylaluminoxanes, they do not match the performance of conventional methylaluminoxane in some single site catalyst systems. Consequently, modified methylaluminoxanes should be considered niche cocatalysts for single site catalysts. 

Principal process technologies employed in the manufacture of polyethylene are ... 

The largest global manufacturer of polyethylene in 2006 was The Dow Chemical Company followed by ExxonMobil. The top 10 industrial producers for 2006 are shown in Table 8.2, using the total of the three major types of polyethylene. In recent years such listings have been dynamic because of acquisitions, mergers and shifting trends in markets. For example, LyondellBasell (created by... 

Chapter 1 is used to review the history of polyethylene, to survey quintessential features and nomenclatures for this versatile polymer and to introduce transition metal catalysts (the most important catalysts for industrial polyethylene). Free radical polymerization of ethylene and organic peroxide initiators are discussed in Chapter 2. Also in Chapter 2, hazards of organic peroxides and high pressure processes are briefly addressed. Transition metal catalysts are essential to production of nearly three quarters of all polyethylene manufactured and are described in Chapters 3, 5 and 6. Metal alkyl cocatalysts used with transition metal catalysts and their potentially hazardous reactivity with air and water are reviewed in Chapter 4. Chapter 7 gives an overview of processes used in manufacture of polyethylene and contrasts the wide range of operating conditions characteristic of each process. Chapter 8 surveys downstream aspects of polyethylene (additives, rheology, environmental issues, etc.). However, topics in Chapter 8 are complex and extensive subjects unto themselves and detailed discussions are beyond the scope of an introductory text. 

Use Polymerization initiator for vinyl monomers, manufacture of polyethylene and polystyrene. 

Use Manufacture of polyethylene, polypropylene, ethylene oxide, ethylene dichloride, ethylene glycols, aluminum alkyls, vinyl chloride, vinyl acetate, ethyl chloride, ethylene chlorohydrin, acetaldehyde, ethyl alcohol, polystyrene, styrene, polyvinyl chloride, SBR, polyester resins, trichloroethylene, etc. as a refrigerant, in welding and cutting of metals, an anesthetic, and in orchard sprays to accelerate fruit ripening. 

An important use of ethylene, C2H4, is in the manufacture of polyethylene, a nonbreakable, nonreactive plastic. 

The company is a leading manufacturer of polyethylene, the world s most widely used plastics, for films, bags, bottles, and electrical insulation. Not surprisingly, it is a technology leader in polyethylene and polypropylene. 

Reaction temperature seems to have little effect on the LCB levels in the polymer, which is convenient because reaction temperature is a primary variable used to control MW in the manufacture of polyethylene. Figure 78 shows another Arnett plot representing polymers made from Cr/silica-titania activated at four different temperatures [407]. Each catalyst was tested at a series of reaction temperatures, ranging from 98 up to 110 °C, in order to vary the polymer MW. The polymers were analyzed by rheology, and when plotted on an Arnett graph, the points representing each activation temperature formed a unique line. That is, the variation of reactor temperature resulted in points distributed along a line, and each activation temperature produced a different line. 

Most commercial manufacture of polyethylene with the Phillips catalyst is carried out with Cr(VI)/silica as the catalyst. Cr(VI) is reduced by ethylene in the reactor to form the active precursor, probably Cr(II). However, in some cases, it is desirable to reduce the Cr(VI) to Cr(II) before the catalyst goes into the reactor. Treatment in CO at about 350 °C reduces the hexavalent chromium almost quantitatively to a divalent species. In practice, one must be careful to fully flush out the CO with an inert gas like N2 before the catalyst is allowed to cool. Otherwise, CO is chemisorbed and poisons the catalyst. Actually, CO begins to react with Cr(VI) / silica even at room temperature, although that reaction is slow. Over a period of hours, the Cr(VI) can become highly reduced at 25 °C. However, purging with N2 at higher temperatures is still needed to remove the adsorbed CO. Otherwise, the catalyst will be inactive. 

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