Hexanes, isomerization equilibria

Equilibria. The equilibrium distributions of butane, pentane, and hexane isomers have been experimentally determined (5, 16) and are diagrammed in Figure 2. In each case, lower temperatures favor the more highly branched structures. At the approximately 200° F. temperature usually employed for isomerization, the butane equilibrium mixture contains about 75% isobutane. That for pentane contains about 85% isopentane.. In the case of hexane, the equilibrium product contains about 50% neohexane and has a Motor octane rating of about 82. In all cases, of course, the yield of the desired isomers can be increased by fractionation and recycle. 

Catalyst Testing. The hexane isomerization activity was measured for several catalysts containing about 0.2 wt % Pt. Appreciable differences in activity were evident which depended upon the method of preparation (Table VI). None of the catalysts is particularly active (c/. equilibrium values in Table VI). The surface areas of the catalysts (Table VI) are somewhat less than expected, and thus one can speculate that better activation procedures will lead to some improvement in performance. 

The data given for a reaction temperature of 300°C clearly showed the mordenite catalyst to be the more active for isomerization of both the C5 and Ce fractions. Conversions quoted were precious-metal-H-mordenite C5 —65 wt %, Cq >— 15 wt % precious metal-H-Y C5 — 40 wt %, Ce 4 wt %. These data suggest that the pentane fraction may be slightly easier to isomerize over mordenite than the hexane. The equilibrium conversions to isopentane and 2,2-DMB at 300°C are in the vicinity of 65 and 18 wt %, respectively. A possible explanation is that impurities present—e.g., cyclohexane and/or benzene—aifect the rate of 2,2-DMB formation more than that of the isopentane. 

The objective of this paper is to demonstrate the importance of phase and reaction equilibria considerations in the rational development of SCF reaction schemes. Theoretical analysis of phase and reaction equilibria are presented for two relatively simple reactions, viz., the isomerizations of n-hexane and 1-hexene. Our simulated conversion and yield plots compare well with experimental results reported in the literature for n-hexane isomerization (4) and obtained by us for 1-hexene isomerization. Based on our analysis, the choice of an appropriate SCF reaction medium for each of these reactions is discussed. Properties such as viscosity, surface tension and polarity can affect transport and kinetic behavior and hence should also be considered for complete evaluation of SCF solvents. These rate effects are not considered in our equilibrium study. 

Skeletal isomerization of n-Cs, Cs paraffins to corresponding isoparaffins is important for improving the octane number as they are mixed in gasoline. Since low temperature is favored for the equilibrium of this reaction, catalysts active at low temperatures are desirable. Noble metals loaded on zeolites such as Pt —Y zeolite with low Na content are effective and used at about 520 Fig 4.3 shows the effect of Na content of zeolite on the catalydc activity for hexane isomerization. As the acidity increases with decreasing Na content the optimum temperature of operadon b gready suppressed. 

Effect of Butyllithium Concentration on the Rate of Isomerization and Equilibrium Constant of 2-Methylphenyl-di-/m-butylcarbinol (74) in Hexane at 25°C... 

Let us exemplify the effectiveness of the idea of tree in equilibrium thermodynamic modeling again by isomerization, using the calculations of transformations of three hexane isomers h-hexane (ay), 2-methylpen-tane (x2), and 3-methylpentane (x3) at T = 600 K and P = 0.1 MPa. Graphical interpretation of the analysis is presented in Figure 6a and b. 

The temperature of isomerization controls equilibrium isomer composition, and thereby product octane. Figure 4.8 is a plot of isopentane in the C5 product as a function of temperature. The data are from pilot plant runs with three types of commercial UOP isomerization catalysts. The feedstock was a 50/50 mixture of normal pentane and normal hexane, containing about 6% cyclics. The 1-8 and I-80 catalysts are very active at a low temperature, where equilibrium isopentane content is highest. The acid functions in 1-8 and 1-80 are chlorided aluminas. The zeolitic catalyst, HS-10 , requires relatively high temperatures of operation. The LPI-100 catalyst contains sulfated zirconia as the acid function and falls in the middle of the temperature range (12). Due to the equilibrium constraints, a lower temperature operation yields a higher octane product. The 1-8 and 1-80 catalysts yielded Research Octane Numbers of 82-84, as compared to 80-82 for LPI-100 catalyst and 78-80 for HS-10. 

Ono and Ware"" have measured the absorption, emission, and excitation spectra, the fluorescence decay times, and the quantum yields of a series of substituted diphenylmethylenes in rigid matrices at low temperatures. Acean-thrylene shows S2- So emission in hexane with a yield of 0.017 and lifetime of 4.3 ns. The low-temperature fluorescence spectra of bis-2-naphthyl-alkanes and their derivatives have been studied. Excimer formation is an activated process. The fluorescence and absorption spectra of 1,1-diphenyl-ethylenes have been analysed in some detail by Gustav and Bolke. " The S — Si transitions in trans isomers of phenylnaphthylethylenes have been assigned by picosecond absorption spectroscopy. Effects of solvent viscosity and the role of conformers in the mechanism of isomerization are elucidated. The production of non-equilibrium conformer concentrations in glassy solutions of diarylethylenes at 77 K due to restrictions imposed by the solid matrix has also been reported. Free jet excitation and emission spectra of diphenyl-butadiene show clearly the lowest excited Ag state and give a lifetime of 52.8 ns for 0-0 excitation.Electric field-induced charges in the optical... 

A simple naphtha isomerization process has a feed of 10,000 barrels per day (bpd) of a 50 wt% mixture of n-hexane and methyl pentane. The feed is heated and sent to a reactor, where it is brought to equilibrium at 1300 kPa and 250°C. The reactor products are cooled to the dew point and fed to a distillation column operated at 300 kPa. The bottoms product of the distillation is rich in n-hexane and is recycled to the reactor feed. An overall conversion of n-hexane of 95% is achieved. 

Paraffin isomerization over dual function catalysts based on zeolite Y and mordenite has been reviewedand a reaction mechanism was proposed in which olefin-paraffin equilibrium is established and carbonium ions are formed from both paraffins and olefins. The isomerization of n-hexane and hydrocrack-... 

The equilibria for isomerization reactions are much less temperature sensitive than those for dehydrogenation reactions, since the heats of reaction are relatively small. The equilibrium between methylcyclopentane and cyclohexane favors the former, indicating that the five-membered ring structure is more stable than the six-membered ring. In the equilibria between n-hexane and the methylpentanes, 2-methylpentane is the favored isomer over 3-methylpentane. This is reasonable from the simple statistical consideration that the substituent methyl group can occupy either of two equivalent positions in the former molecule, compared to one in the latter. 

The reaction behavior of the more flexible allyl-substituted cyclopropenes strongly depends on the substitution pattern of the substrate766, and competing rearrangement or internal [2 4- 2] cycloaddition either yields isomeric allylcyclopropenes or tricyclohexane derivatives. Thus, thermolysis of 3-methyl-3-(l,2,3-triphenyl-2-cyclopropenyl)-l -butene (7) at 175 °C in benzene/pyridine affords 2-methyl-4-(1.2,3-triphenyl-2-cyclopropenyl)-l-butene (8) irreversibly679,960, 961. On the other hand, cyclopropane 9 is partially converted to [2.2.0.02,6]hexane 10 on heating at 175°C. Thermolysis of 11 at 150°C for 48 hours results in the formation of an equilibrium mixture of 11, 12, and tricyclohexane 13. 

The influence of the solvent will not, however, be restricted to that on the equilibrium solvation may also lead to a partial displacement of bond polarity. This may be regarded as an intermediate state between the two extremes involved in bond isomerism. The effects of different solvents on the same reaction may be considered from this point of view. It is understandable that radical reactions take place more quickly in nonpolar than in polar solvents. The photochemical oxidation of iodoform, for example, occurs more than 50 times more rapidly in carbon tetrachloride than in the polar solvent acetone (14 ). On the other hand, reaction between N(C2H6)3 and C2H5I to give [N(C2H6)4]I is more than 100 times faster in nitrobenzene than in the nonpolar hexane (56). 

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