Alkanes systems

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

The substances H S, C02 and (C Hj-UO (diethyl ether) were treated as slightly active as there afen ndications that with these compounds cross-association occurs in liquid water. In the case of diethyl ether this conclusion is supported by the considerably higher mutual solubility for the H-O- -HgJgO system compared with water-alkane systems as shown Tn Table 5. To keep the number of parameters low, the following procedure was adopted in accounting for cross-association ... 

Treszczanowicz, A.J. and Benson, G.C., Excess volumes of alkanols + alkane systems in terms of an association model with a Flory contribution term, Fluid Phase EquUib., 23,117,1985. 

In Figure 2.2-8 the critical endpoint temperatures for the family 0f CO2 + n-alkanes systems are plotted as a function of the carbon number n. If in a particular binary system the three-phase curve hhg is followed to low temperature then at a certain temperature a solid phase is formed (solid n-alkane or solid C02 at low carbon numbers). This occurs at one unique temperature because we now have four phases in equilibrium in a binary system, so according to the phase rule F= 0. Below this so-called quadruple point temperature the hhg curve is metastable. 

As discussed for CO2 + n-alkane systems at carbon numbers n<24 the three-phase curve hhg ends a low temperature in a quadruple point s2l2lig. This is shown schematically in Figure 2.2-9a and b. In the quadrupel point three other three-phase curves terminate. The s2hh curve runs steeply to high pressure and ends in a critical endpoint where this curve intersects the critical curve. The s2l2g curve runs to the triple point of pure component B and the s/l/g curve runs to lower temperature and ends at low temperature in a second quadruple point s2silig (not shown). 

Sequential double Michael addition of cyclic dienolates, generated from (107) or (108), to fulvene (109) has been developed as a method for rapid access to the tricyclo[5.3.0. 2,5]alkane system (Scheme 24).90... 

If 1 1 complexes are formed (1) in the ground state, then two types of photoreactions will occur parallel to each other, that of the bare and that of the complexed solute, each in its own type of cage. Mixed alcohol/ alkane systems, for example, show an indication of preformed solute-solvent complexes as evidenced by the picosecond experiments of Wang and Eisenthal80 81 on DMABN. Planar model systems like the indolines 3 and 5 (Sec. II.A.l) indicate that an additional channel opens for the B state in alcoholic solvents which increases the nonradiative decay path. This can explain the observed reduction of the fluorescence quantum yield in jirotic solvents about 0.1 in the aprotic polar solvent n-butyl chloride, about 0.01 in 1,2-propanediol, and about 0.001 in water.228... 

Jensen, M.P., Chiarizia, R., Ferrato, J.R. et al. 2002. New insights in third phase formation in the U(VI)-HN03, TBP-alkane system. In Proc. ISEC 2002. Sole, K.C., Cole, P.M., Preston, J.S., Robinson, DJ. Eds. South African Institute of Mining and Metallurgy, Cape Town, South Africa, March 18-21, Chris van Rensburg, Melville, pp. 1137-1142. 

The trend for the different alcohols according to their ability to suppress the third phase in the DMDBTDMA-alkane system is consistent with the results reported by Dhamodaran and Srinivasan and summarized in the review of Rao et al. (4). Dhamodaran et al. showed that increasing the carbon chain length of the alcohol from C4 to C9 leads to a monotonous increase in LOC in the Th(IV)-TBP system. Srinivasan et al. showed a similar effect of alcohol between butanol and heptanol on the LOC of a Pu(IV)-TBP system. 

In the DMDBTDMA-alkane system (37, 140), the third phase is a gel when neodymium nitrate or thorium nitrate are extracted at high concentration, but... 

M. Borkowski, J. R. Ferraro, R. Chiarizia, andD. R. McAlister. Ft-ir study of third phase formation in the U(VI) or Th(IV)/HN03, TBP/alkane systems. Solvent Extr. Ion Exch., 20 313-330, 2002. 

Recently, the primary processes were investigated using pulse radiolysis with two extractant-alkane systems (182, 292). Transient optical absorption spectra proved that in the presence of ligands like TODGA, the excited species of -dodecane (singlet excited state and radical cation) disappeared immediately. Results showed that an energy transfer occurred from the excited alkane to the extractant molecule (TBP, TOPO, or amide), which constituted an additional decomposition route, as described in the following set of reactions ... 

The use of sc C02 instead of toluene as a solvent leads to some rate enhancement in these two systems, although it is clear that this activity is still not practical for most nonpolar, nonvolatile substrates. Significant improvements to the biphasic water/supercritical C02 system were accomplished by forming H20/C02 emulsions using newly developed surfactants (Jacobson et al., 1999). Three different surfactants were used that form water in C02 (w/c) or C02 in water (c/w) emulsions (1) anionic surfactant perfluoropolyether ammonium carboxylate, (2) cationic Lodyne 106A, and (3) nonionic poly(butylene oxide)-h-poly(ethylene oxide). The low interfacial tension, y, between water and C02 (17 mNm-1 at pressures above 70 bar), which is significantly lower than water/alkane systems (30-60 mNm-1),... 

Figure 5. Enhancement factor (E) vs. Carbon number ethane + n-alkane systems.

Bonsor, D. H. and Bloor, D. (1977). Phase transitions of n-alkane systems. 2. Melting and solid state transition of binary mixtures. J. Mater. Sci, 12,1559-1564. 

Pandey, G. and Devi Reddy, G. (1992) Stereoselectivity in the cyclisation of photoinduced electron transfer (PET) generated cyclic a-amino radicals first general stereoselective entry to 1-azabicyclo (m n o) alkane systems. Tetrahedron Letters, 33, 6533-6536. 

Johnson and Willson interpreted the main feature of the observations on solid polyethylene doped with aromatic solutes in terms of an ionic mechanism it was analogous to that proposed for irradiated frozen glassy-alkane-systems in which ionization occurred with G = 3 — 4 [96], The produced charged species, electron and positive hole, were both mobile as indicated by the radiation-induced conductivity. The production of excited states of aromatic solutes was caused mainly by ion-electron neutralization. The ion-ion recombination was relatively slow but it might contribute to the delayed fluorescence observed. On the basis of Debye-Simoluchovski equation, they evaluated the diffusion coefficients of the radical anion of naphthalene and pyrene as approximately 4 x 10 12 and 1 x 10 12 m2 s 1 respectively the values were about three orders of magnitude less than those found in typical liquid systems. 

We have been using the common nomenclature of ethers, which is sometimes called the alkyl alkyl ether system. The IUPAC system, generally used with more complicated ethers, is sometimes called the alkoxy alkane system. Common names are almost always used for simple ethers. 

A New Mixing Rule for Accurate Prediction of High Pressure Vapor-Liquid Equilibria of Gas/Large n-Alkane Systems... 

The original UNIFAC model(Fredenslund et al., 1975) was used in this work, as it is a widely applicable model with the most available parameters which are updated and extended regularly. For gas/n-alkane systems, temperature dependent interaction parameters were used, and the UNIFAC expression ... 

CO2 is an important industrial gas, consequently, the study of phase behavior of C02/n-alkane systems is necessary. Though they are nonpolar systems, the predictive accuracies of MHV2(Dahl and Michelsen, 1990) and PSRK(Holderbaum and Gmehling, 1991, using MHV1) are dramatically bad for large n-alkanes (Boukouvalas et al., 1994). So, it is necessary to do some modification to improve the predictive accuracy for them, which is the motive of this work. 

Fig. 3 AAD of vapor pressure versus carbon number for C2 II6/n-alkane systems...

A new mixing rule has been proposed and tested coupled with SRK EOS and UNIFAC in this work. The new mixing rule, which is obtained by introducing a correction parameter to the Ge from the original UNIFAC in MHV1, is accurate for both binary and ternary gas/large n-alkane systems. The correction parameters have been correlated as a simple function of carbon number for a certain kind of gas/n-alkane system, which is convenient for engineering purposes. 

Delmas, G. Saint-Romain, P., "Upper and Lower Critical Solution Temperatures in Polybuta-diene- Alkane Systems," Eur. Polym. J., 10, 1133 (1974). 

Hamada, F. Fujisawa, K. Nakajima, A., "Lower Critical Solution Temperature in Linear Polyethylene-n-Alkane Systems," Polym. J., 4, 316 (1973). 

Roth, M., "Thermodynamics of Poly(methyl(trifluoropropyl)siloxane]-Alkane Systems by Gas-Liquid Chromatography," Macromolecules, 23, 1696 (1990). 

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