Supercritical fluid ethylene

Table 9.27 Molecular Weight Distribution in Parent Poly(phenylmethyl)siloxane and in Fractions Separated by Supercritical Fluid Ethylene...

Gases at high pressures have been used in the chemical, oil and polymer industries for a long time. The production of low-density polyethylene is a good example of a reaction in a supercritical fluid. Ethylene (critical temperature 9 C) is used as both reactant and supercritical solvent... 

In a subsequent study, they used ethylene for a dual purpose, as a substrate as well as a supercritical fluid solvent. This notoriously unreactive olefin to PKR served nicely to give 2-substituted cyclopentenones. Reaction efficiency of each alkyne substrate can be tuned by changing catalyst precursors. Not only Co2(CO)8 but also the two cobalt clusters [Co4(CO)i2] and [Co4(GO)n P(OPh)3 ] work well for some substrates (Equation (8)). The comparison with Rautenstrauch s result clearly shows the beneficial effect of this approach. 

Among potentially interesting solvents for enzymatic catalysis, carbon dioxide is the most widely nsed snpercritical fluid. However, there is a growing interest in using other supercritical fluids (e.g., ethylene, fluoroform, ethane, sulfur hexafluoride, and near-critical propane) (Kamat et al., 1995b). 

Enzymes can express activity in supercritical and near-supercritical fluids, such as carbon dioxide, freons (CHF3), hydrocarbons (ethane, ethylene, propane) or inorganic compounds (SFe, N2O). The choice of supercritical fluids is often... 

Paprika can be extracted to recover carotenoids, not only with CO2 but also with other gases. For example, by using ethane or ethylene, better results were obtained for the yield, extraction time, and quality of product. The solubilities of carotenoids are better in these gases, which is why the consumption of solvent and the extraction time were reduced. Practically water-free dye-concentrate was recovered by supercritical fluid ethane (under the conditions extraction 250 bar, 45°C separation 46 bar, 45 °C). The separation of pungent substances (capsaicinoids, free fatty acids) from the pigments can be carried out effectively in a continuous, counter-current extraction column with a large number of theoretical plates. 

In the patent of the Krupp company [60], ground paprika and oleoresin may be used as the raw material in the SFE process. The solvent can be supercritical fluid carbon dioxide, ethane, ethylene, or a mixture of the last two. As modifiers ethanol, acetone, water, and mixtures of these solvents were proposed. 

Another important aspect of supercritical fluids application is in polymer fractionation, in order to obtain mono-dispersed molecular weights. The simulation of the fractionation of polyethylene from ethylene and hexane solutions into fractions of different molecular weights was proposed by Chen et al. [7]. 

The interfacial tension is a key property for describing the formation of emulsions and microemulsions (Aveyard et al., 1990), including those in supercritical fluids (da Rocha et al., 1999), as shown in Figure 8.3, where the v-axis represents a variety of formulation variables. A minimum in y is observed at the phase inversion point where the system is balanced with respect to the partitioning of the surfactant between the phases. Here, a middle-phase emulsion is present in equilibrium with excess C02-rich (top) and aqueous-rich (bottom) phases. Upon changing any of the formulation variables away from this point—for example, the hydrophilie/C02-philic balance (HCB) in the surfactant structure—the surfactant will migrate toward one of the phases. This phase usually becomes the external phase, according to the Bancroft rule. For example, a surfactant with a low HCB, such as PFPE COO NH4+ (2500 g/mol), favors the upper C02 phase and forms w/c microemulsions with an excess water phase. Likewise, a shift in formulation variable to the left would drive the surfactant toward water to form a c/w emulsion. Studies of y versus HCB for block copolymers of propylene oxide, and ethylene oxide, and polydimethylsiloxane (PDMS) and ethylene oxide, have been used to understand microemulsion and emulsion formation, curvature, and stability (da Rocha et al., 1999). 

Lopes JA, Gourgouillon D, Pereira PJ et al (2000) On the effect of polymer fractionation on phase equilibrium in C02 + poly(ethylene glycol)s systems. J Supercrit Fluids 16(3) 261-267... 

Daneshvar M, Gulari E (1992) Supercritical-fluid fractionation of poly(ethylene glycols). J Supercrit Fluids 5(2) 143-150... 

General overview of several studies of transport and intermolecular interactions in compressed supercritical fluids is presented. The unique aspects of the instrumentation used in these studies are emphasized. First, the results of NMR studies of self-diffusion in supercritical ethylene and toluene are discussed. These experiments used the fixed field gradient NMR spin-echo technique. Second, the novel NMR technique for the determination of solubility of solids in supercritical fluids is described. 

The physical picture that underlies this behavior, as pointed out first by Elgin and Weinstock (1), is the salting out effect by a supercritical fluid on an aqueous solution of an organic compound. As pressure is increased, the tendency of the supercritical fluid to solubilize in the organic liquid results in a phase split in the aqueous phase at a lower critical solution pressure (which varies with temperature). As pressure is further increased, the second liquid phase and the supercritical phase become more and more similar to each other and merge at an upper critical solution pressure. Above this pressure only two phases can coexist at equilibrium. This pattern of behavior was also observed by Elgin and Weinstock for the system ethylene - acetone - water at 288 K. In addition, the same type of... 

BTT and BTN, butane-1,2,4-triol-trinitrate DNT, dinitrotoluene EGDN, ethylene glycol dinitrate HPLC, high-performance liquid chromatography LOD, limits of detection MDQ, minimum detectable quantities NB, nitrobenzene NG, nitroglycerine NN, nitronaphthalene NT, nitrotoluene PETN, pentaerythritol tetranitrate RDX, cyclotrimethylene trinitramine SFE, supercritical fluid extraction SGC, solvating gas chromatography TDM, thermal desorption modulator TNB, trinitrobenzene and TNT, trinitrotoluene. 

Phase behavior studies with poly(ethylene-co-methyl acrylate), poly (ethylene-co-butyl acrylate), poly(ethylene-co-acrylic add), and poly(ethylene-co-methacrylic acid) were performed in the normal alkanes, their olefinic analogs, dimethyl ether, chlorodifluoromethane, and carbon dioxide up to 250 °C and 2,700 bar. The backbone architecture of the copolymers as well as the solvent quality greatly influences the solution behavior in supercritical fluids. The effect of cosolvent was also studied using dimethyl ether and ethanol as cosolvent in butane at varying concentrations of cosolvent, exhibiting that the cosolvent effect diminishes with increasing cosolvent concentrations. 

Abstract Alkylation of benzene with ethylene over Y-type zeolite has been carried out under supercritical conditions. Two aspects of the reaction have been paid attention to slowing down the deactivation rate and decreasing the by product selectivity. Experiments have revealed the existence of some coke precursors that are partly removed from the catalyst surface. By product xylenes are decreased and are explained due to high diffiisivity in the supercritical fluid. 

Supercritical fluids, another class of alternative reaction medium, have been used as solvents in catalysis for many years. Ipatiev reported the isomerisation of cyclohexane to methylcyclopentane under supercritical conditions using A1203 as the catalyst1151 and shortly afterwards communicated the oligomerisation of supercritical ethylene catalysed by AICI3.1161 However, it took another 60 years before supercritical fluids were used as solvents for... 

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