Hexane-polyethylene system

HAR Haruki, M., Takakura, Y., Sugiura, H., Kihara, S., and Takishima, S., Phase behavior for the supercritical ethylene + hexane + polyethylene systems, J. Supercrit Fluids, 44, 284, 2008. 

Nies, E., Stroeks, A., Simha, R., and Jain, R. K., LCST [lower critical solution temperature] phase behavior according to the Simha-Somcynsky theory apphcation to the n-hexane/polyethylene system. Colloid Polym. Sci., 268, 731-743 (1990). 

In the irradiation of polyethylene Dole et al.71 have found that the initially present vinylidene unsaturation decreases markedly with dose and have suggested a free-radical migration mechanism. Charge transfer could equally well explain these results this would be a direct extension of the results from solid n-hexane to the polyethylene system. The close correspondence of these two systems in their response to high-energy radiation will be pointed out below. 

KEN Kennis, H.A.J., Loos, Th.W. de, DeSwaan Arons, J., Van der Haegen, R., and Kleintjens, L.A., The influence of nitrogen on the liquid-hquid phase behavioiu of the system n-hexane-polyethylene experimental results and predictions with the mean-field lattice-gas model, (experimental data by Th.W. de Loos), Chem. Eng. Sci., 45, 1875, 1990. 

This mode was subsequently used to predict excess properties (excess volume, excess enthalpy, AH ) of binary mixtures of -alkanes. For instance, the decrease of A// and the reversal of its sign with a change in the temperature, observed in several systems, are correctly predicted though the magnitude of the effect is underestimated. In addition, LCM behavior was predicted to occur in mixtures of poly(ethylene) and -alkanes, in agreement with experimental findings. Calculated LCST s, however, were only in qualitative agreement with the observed data, e.g., the location of the miscibility gap for ra-hexane/polyethylene was predicted to be about 60°C too low. 

The alternative is hexane, which because of the explosion hazard requires a more expensive type of extractor construction. After the extraction the product is dull gray. The continuos sheet is slit to the final width according to customer requirements, searched by fully automatic detectors for any pinholes, wound into rolls of about 1 m diameter (corresponding to a length of 900-1000 m), and packed for shipping. Such a continuous production process is excellently suited for supervision by modern quality assurance systems, such as statistical process control (SPC). Figures 7-9 give a schematic picture of the production process for microporous polyethylene separators. 

It is possible to synthesize cobalt complexes which are soluble in polyethylene glycols and not in. solvents like hexane, hexene, heptenal etc. Ritter et al. (1996) have reported the oxo reaction of 1-hexene in such a system. 

A massive explosion in Pasadena, Texas, on October 23,1989, resulted in 23 fatalities, 314 injuries, and capital losses of over 715 million. This explosion occurred in a high-density polyethylene plant after the accidental release of 85,000 pounds of a flammable mixture containing ethylene, isobutane, hexane, and hydrogen. The release formed a large gas cloud instantaneously because the system was under high pressure and temperature. The cloud was ignited about 2 minutes after the release by an unidentified ignition source. 

In 1989, the NDF Company opened a facility in Georgetown, South Carolina to produce low density polyethylene. Manufacturing of the polyethylene is done in two 50-ton reactors that are encased individually within their own 8-story-high process unit. The main raw materials for the manufacturing operations include ethylene, hexane, and hutene. The polymerization is completed in the presence of a catalyst. The hase chemicals for the catalyst are aluminum alkyl and isopentane. The reactor and catalyst preparation areas are on a distributed control system (DCS). A simplihed process flow diagram is attached. 

Diphasic liquid systems used in CCC may have a wide variety of polarities. The most polar systems are the ATPS made by two aqueous-liquid phases, one containing a polymer, for example, polyethylene glycol (PEG), the other one being a salt solution, for example, sodium hydrogen phosphate. The less polar systems do not contain water there can be two-solvent systems, such as heptane/acetonitrile or dimethylsulfoxide/hexane systems or mixtures of three or more solvents. Intermediate polarity systems are countless since any proportion of three or more solvents can be mixed. Ternary phase diagrams are used when three solvents are mixed together. 

Synthesis. The early PP plants used a slurry process adopted from polyethylene technology. An inert liquid hydrocarbon diluent, such as hexane, was stirred in an autoclave at temperatures and pressures sufficient to keep 10-20 percent of the propylene monomer concentrated in the liquid phase. The traditional catalyst system was the crystalline, violet form ofTiCl3 and A1C1(C2H5)2. Isotactic polymer particles that were formed remained in suspension and were removed as a 20-40 percent solid slurry while the atactic portion remained as a solution in the liquid hydrocarbon. The catalyst was deactivated and solubilized by adding HC1 and alcohol. The iPP was removed by centrifuging, filtration, or aqueous extraction, and the atactic portion was recovered by evaporation of the solvent. The first plants were inefficient because of low catalyst productivity and low crystalline yields. With some modifications to the catalyst system, basically the same process is in use today. 

The Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

Olah (17a) has also reported the alkylation reactions (at -10 with 1 1 HS03F-SbF5) of n-butane with ethylene to yield 38 weight percent of hexanes and of n utane with propylene to yield 29 weight percent of heptanes. The former reaction has also been reported by Parker (31) at 60 , but the product in this case more nearly resembles polyethylene degradation products. In our work with 10 1 HF-TaF5 at 40 , in a flow system, ethylene (14.1 wt.%) reacted with rv-butane to form 3-methyl-pentane as the initial product of 94% selectivity (Scheme 6, path a). The alternative, i.e., the direct reaction of ethylene with a secondary-butyl cation (path b), can be ruled out since butane does not ionize under these conditions (vide supra). 

Diluents must be inert toward the catalyst system and are usually saturated hydrocarbons such as propane, isobutane and hexane. Slurry processes typically operate at temperatures from about 80 to 110 °C and pressures of 200-500 psig. Polyethylene precipitates as formed resulting in a suspension of polymer in diluent. The catalysts most commonly used in slurry processes are chromium-on-silica or supported Ziegler-Natta catalysts. 

Optionally, in the case of Fe- and Co-containing nanoparticles, the mineral oil was substituted for a mineral oil-low density polyethylene (LDPE) solution-melt. The thermal destruction was carried out at vigorous stirring at a constant temperature in the argon flow. The MCC solution was introduced into the reaction system dropwise at a constant rate. The black material produced after the addition of all the MCC solution was stirred at the synthesis temperature for 0.5 h and cooled down to room temperature. The product was extracted via rinsing the mixture with hexane. The calculated concentrations of metal-containing nanoparticles in the product resulted varied from 1 to 50 wt.%. 

V(L)Cl2(TpMs )] (L = N Bu L = O) were in situ supported onto SiC>2 and onto MAO and trimethylaluminum. All catalyst systems were shown to be active in ethylene polymerization. The systems were stable at different [A1]/[V] molar ratios and polymerization temperatures.21 Branched polyethylene/high-density polyethylene blends were prepared using the combined [NiChfa-diimine)] and V(T(Tp-vls )(N Bu) catalysts. The polymerization reactions were performed in hexane or toluene at three different polymerization temperatures (CPC, 30°C and 50°C) and several nickel molar fractions, using MAO as cocatalyst.22 TpMs- and TpMs -imido vanadium (V) were immobilized onto a series of inorganic supports All the systems were shown to be active in ethylene polymerization in the presence of MAO or TiBA/MAO mixture.23... 

Microwave-assisted esterification by a heterogeneous acid catalyst has been studied in a low dielectric constant medium (see Scheme 35) [64]. A continuous-flow setup has been devised in the system and the heterogeneous acid catalyst (Amberlyst A15 sulphonic acid cation-exchange resin) 61 localized in a polyethylene active flow cell. Use of a low dielectric constant medium (hexane) ensured absorption of microwave radiation only to the reacting species. In this case, the findings suggest a comparable esterification reaction under both microwave and thermal conditions. Furthermore, the presence of water in the catalytic resin resulted in a reduction of the reaction rate irrespective of the type... 

NAG Nagy, I., Loos, Th.W.de, Krenz, R.A., and Heidemami, R.A., High pressure phase equilibria in the systems linear low density polyethylene -1- n-hexane and linear low density polyethylene + n-hexane + ethylene Experimental results and modelling with the Sanchez-Lacombe equation of state, J. Supercrit Fluids, 37,115,2006. 

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