Ethylene at High Pressures

The maximum density of loosely packed xmdistorted ethylene molecules is at a density value of 0.28 g/cc, which is reached at only 300 atm. Beyond this point, density increases more slowly as the molecules are forced into a quasi-liquid state such that the ethylene density of 0.6 g/cc at 3,000 atm 

Some characteristics of the autoclave reactor and the tubular reactors are summarized in Table 5.13. 

Single peroxide injection point Multiple peroxide injection points 

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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). 

It is manufactured by high pressure process by polymerising ethylene at high pressure of 1000-3000 atmosphere and temperature of 80-300°C. The common initiators used for polymerising ethylene are traces of oxygen, azobisisobutyronitrile, and benzoyl peroxide. 

There is evidence that an unstable complex is formed when rhodium(III) chloride is treated with ethylene at high pressure (97). 

Because of its commercial importance, the polymerization of ethylene at high pressure has been extensively studied.204-209 Free-radical polymerization is characteristic of ethylene and vinyl compounds. Simple alkenes, such as 1-butene, however, do not give high-molecular-weight polymers, but they, as well as internal alkenes, can copolymerize with polymerizable monomers. 

Figure 17.14. Some unusual reactor configurations, (a) Flame reactor for making ethylene and acetylene from liquid hydrocarbons [Patton et al., Pet Refin 37(li) 180, (1958)]. (b) Shallow bed reactor for oxidation of ammonia, using Pt-Rh gauze [Gillespie and Kenson, Chemtech, 625 (Oct. 1971)]. (c) Sdioenherr furnace for fixation of atmospheric nitrogen, (d) Production of acetic acid anhydride from acetic acid and gaseous ketene in a mixing pump, (e) Phillips reactor for low pressure polymerization of ethylene (closed loop tubular reactor), (f) Polymerization of ethylene at high pressure.

Transfer to polymer, causing reactivation of a polymer molecule al some point along its length, leads to the growth of branches. The process can occur intermolecularly and also intramolecularly the latter process is particularly important in the free radical polymerization of ethylene at high pressure where it leads to the production of numerous short branches which considerably affect the properties of the polymer. 

It was reported also that bis(triphenylsilyl) chromate [(Ph3Si)2Cr04], which is closely related to the proposed active species of the Phillips catalyst, polymerises ethylene at high pressure [238]. When supported on silica, it forms a very active catalyst for low-pressure ethylene polymerisation [226]. 

These results, opposite to those observed for the cyclopentadienyl early transition metal systems, can be accounted for in terms of the known influence of the cocatalyst concentration on the possible eliminations, alkyl transfer pathways, and other deactivation processes [45,46]. Under similar conditions, the polymerization of ethylene at high pressure leads to a considerable increase in activity and produces polymers of higher molecular weight than at atmospheric pressure (entries 6 and 3). This effect is a consequence of the rate of insertion, which is proportional to the monomer concentration in solution. 

Polyethylene (PE), CAS 9002-88-4, is a common polymer with numerous practical utilizations. The polymer is available in several forms, two of them being the most common. One is the low-density or branched polyethylene (LDPE) [1], and the other is high-density or linear polyethylene (HOPE). Medium-density polyethylenes also are known, having a structure of the type [-(CH2CH2)x-(branched hydrocarbon)-(CH2CH2)y]-. Low-density polyethylene is typically obtained from ethylene at high pressure in the... 

An important application of this approach is the radical polymerization of ethylene at high pressure. In101 an attempt is made to model a process which takes place in an industrial mixing reactor. It appears that by solving an inverse kinetic problem, the researchers have verified the pre-exponential factors and the E values for a series of elementary stages, although what these stages are is not mentioned in the paper. 

Carbon tetrachloride reacts with ethylene at high pressure (15—20 MPa) to produce nylon 7 (n = 3) and nylon 9 (n = 4) ... 

LOO Loos, Th.W. de, Poot, W., and Diepen, G.A.M., Fluid phase equilibriums in the system polyethylene + ethylene. 1. Systems of linear polyethylene + ethylene at high pressure,... 

Schneider has reviewed this for non-polymer systems, Noguchi and Nose for polymer solutions using corresponding states theories (p. 304), and Bogdanovic et al. have critically reviewed the representation of thermodynamic data for polyethylene-ethylene at high pressure. For the same system, Harmony et have extended corresponding states models to calculate phase equilibria data over a wide pressure range. 

Using the well-known tables by Pltzer, it Is easily possible to construct a generalized solubility parameter diagram as shown in Figure 25. In this particular case the acentric factor 0.075 is close to that of ethylene because when this chart was prepared over ten years ago, application was directed at interpreting solubility data for naphthalene in ethylene at high pressure. Just to orient ourselves, when the temperature is around 20 C and the pressure is... 

The ethyl 6-(trifluoromethyl)-2-pyrone-3-carboxylate (61) was prepared by condensation of trifluoroacetone with diethyl ethoxymethylenemalonate, followed by cyclization of intermediate diethyl p-acylethylidenemalonate. This pyrone was used for the preparation of cage derivatives to explore their usefulness as antiviral agents. Reaction of 61 with ethylene at high pressure afforded ester 62. Hydrogenation of 62 yielded the corresponding alkyl bicyclo[2.2.2]octane-l-carboxylate, which was hydrolyzed to 63. The latter was converted into bicyclo[2.2.2]octan-l-amine hydrochloride 64 via the Schmidt reaction [29] (Scheme 21). 

GRE Gregorowicz, J., Solid-fluid phase behaviom of linear polyethylene solutions in propane, ethane and ethylene at high pressures, J. Supercrit Fluids, 43, 357, 2007. 

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