Ethene/polyethylene

The scope of this method is by far too broad to be presented in detail. The on-line NIR technique is especially valuable for studies under unusual or extreme conditions. The fluid phase equilibrium in the ethene-polyethylene system has been studied by Nees (1978) up to 300 °C and 3000 bar the solubility of adamantane, of octacosane, and of squalane in fluid CO2 up to 1000 bar has been determined NIR-spectroscopically by Swaid et al. (1985). 

Application of high-pressure vibrational spectroscopy in order to study and to monitor technically relevant fluid phase processes under extreme conditions is exemplified by high-pressure ethene polymerization. Several vibrational bands in the IR and the NIR may be used to detect concentrations directly in the ethene/polyethylene system (Buback, 1984). Some of these are plotted in Fig. 6.7-20. The conversion of unsaturated (ethylenic)... 

Poly(ethene) (polyethylene, polythene, PE) Ethene CH2=CH2 Tough, durable Plastic bags, bowls, bottles, packaging... 

Fig. 14 Phase equilibrium in the system ethene/polyethylene (LDPE = 43,000 g/mol, Af = 118,000 g/mol, = 231,000 g/mol). Symbols represent experimental data [55]. Lines show calculations using the SAFT model. Dashed lines show monodisperse calculations using M, and M, respectively. Solid line shows a calculation using two pseudocomponents as given in Table 4...

Ethene is used to make a host of organic compounds it is also the starting material for the preparation of polyethylene (Chapter 23). Since it is a plant hormone, ethene finds application in agriculture. It is used to ripen fruit that has been picked green to avoid spoilage in shipping. Exposure to ethene at very low concentrations produces the colors we associate with ripe bananas and oranges. 

In 1954, Ziegler and coworkers observed that the course of the reaction of ethene with trialkylalanes was drastically altered by the presence of traces of nickel salts [25]. Instead of low molecular weight polyethylene, the only product was 1-butene. Obviously, the transition metal strongly supports the displacement reaction of the alkyl group bonded to the aluminum by ethylene, a reaction which can be formally described as transfer of a hydridoalane. 

Ethene is used as a starting material for the synthesis of many industrial compounds, including ethanol, ethylene oxide, ethanal (acetaldehyde), and polyethylene (PE). 

SCFs will find applications in high cost areas such as fine chemical production. Having said that, marketing can also be an issue. For example, whilst decaffeina-tion of coffee with dichloromethane is possible, the use of scCC>2 can be said to be natural Industrial applications of SCFs have been around for a long time. Decaffeination of coffee is perhaps the use that is best known [16], but of course the Born-Haber process for ammonia synthesis operates under supercritical conditions as does low density polyethylene (LDPE) synthesis which is carried out in supercritical ethene [17]. 

Before we turn to "mechanisms" let us repeat how a catalyst works. We can reflux carboxylic acids and alcohols and nothing happens until we add traces of mineral acid that catalyse esterification. We can store ethene in cylinders for ages (until the cylinders have rusted away) without the formation of polyethylene, although the formation of the latter is exothermic by more than 80 kjoule/mol. We can heat methanol and carbon monoxide at 250 °C and 600 bar without acetic acid being formed. After we have added the catalyst the desired products are obtained at a high rate. 

Triazacyclohexane also gives rise to very active catalysts with the use of chromium [13] as do ligands of the type RS(CH2)2NH(CH2)2SR [14], The latter coordinate in a meridional fashion, while the former can only coordinate in a facial fashion. Recently examples using cyclopentadienyl titanium complexes [15] and tantalum have been reported [16], The diversity of the chromium systems and the new metal systems show that very likely more catalysts will be discovered that are useful for this reaction, including 1-octene producing catalysts (1-octene is in high demand as a comonomer for ethene polymerisation for certain grades of polyethylene). 

The name of a polymer is usually written with the prefix poly-(meaning many ) before the name of the monomer. Often the common name of the monomer is used, rather than the lUPAC name. For example, the common name of ethene is ethylene. Polyethene, the polymer that is made from ethene, is often called polyethylene. Similarly, the polymer that is made from chloroethene (common name vinyl chloride) is named polyvinylchloride (PVC). The polymer that is made from propene monomers (common name propylene) is commonly called polypropylene, instead of polypropene. 

At 24 °C and 15-60 bar ethylene, [Rh(Me)(0H)(H20)Cn] catalyzed the slow polymerization of ethylene [4], Propylene, methyl acrylate and methyl methacrylate did not react. After 90 days under 60 bar CH2=CH2 (the pressure was held constant throughout) the product was low molecular weight polyethylene with Mw =5100 and a polydispersity index of 1.6. This is certainly not a practical catalyst for ethylene polymerization (TOP 1 in a day), nevertheless the formation and further reactions of the various intermediates can be followed conveniently which may provide ideas for further catalyst design. For example, during such investigations it was established, that only the monohydroxo-monoaqua complex was a catalyst for this reaction, both [Rh(Me)3Cn] and [Rh(Me)(H20)2Cn] were found completely ineffective. The lack of catalytic activity of [Rh(Me)3Cn] is understandable since there is no free coordination site for ethylene. Such a coordination site can be provided by water dissociation from [Rh(Me)(OH)(H20)Cn] and [Rh(Me)(H20)2Cn] and the rate of this exchange is probably the lowest step of the overall reaction.The hydroxy ligand facilitates the dissociation of H2O and this leads to a slow catalysis of ethene polymerization. 

Enormous commerical applications flowed from the revolution initiated by Ziegler and Natta. These include high-density and linear low-density polyethylenes (HDPE, LLDE), polypropene, ethene-propene co- and terpolymers, and polymers from 1,3-dienes (Sec. 8-10). The annual United States production of these polymers exceeded 40 billion pounds in 2000 the global production was about 3-3.5 times the U.S. production. Ziegler-Natta chemistry accounts for the production of one-third of all polymers. 

It is of interest to note that under normal conditions methane, ethane, and ethene are all gases, and hexane, octane, and nonane are all liquids, whereas polyethylene is a waxy solid. This trend is primarily due to both an increase in mass per molecule and an increase in the London forces per molecule as the chain length increases. 

Acetic acid is used to produce the plastic polyethylene terephthalate (PET) (see Ethene [Ethylene]). Acetic acid is used to produce pharmaceuticals (see Acetylsalicylic Acid). 

Butene is used in the plastics industry to make both homopolymers and copolymers. Polybutylene (1-polybutene), polymerized from 1-butene, is a plastic with high tensile strength and other mechanical properties that makes it a tough, strong plastic. High-density polyethylenes and linear low-density polyethylenes are produced through co-polymerization by incorporating butene as a comonomer with ethene. Similarly, butene is used with propene to produce different types of polypropylenes. 

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. 

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