Thermodynamic Properties of Paraffins and Olefins

Abstract

By extrapolation of experimental data on the entropies and heats of formation of the lower hydrocarbons, a set of rules is deduced for estimating the entropy and heat of formation of any paraffin or olefin hydrocarbon at 25°C. These properties are tabulated for all paraffins through the octanes and for all olefins through the hexenes.These values can be used to calculate the approximate state of equilibrium in any hydrocarbon reaction. The equilibrium proportions of 2,3-dimethyl-l-butene, 3,3dimethyl-l-butene, and 2,3-dimethyl-2-butene at 300°C. are calculated to be 25.4:2.2:72.4, compared to Whitmore's experimental ratio of 31:3:61. Equilibrium calculations for the paraffins show that in the temperature range 150°to 175°C. all the isomers in any group of isomers have approximately the same free energy. The more highly branched isomers are more stable below this temperature range, and the straight-chain and less highly branched ones are more stable above this temperature range.

Free Energies of Formation of Gaseous Hydrocarbons and Related Substances

“…In all our derivations the heats of formation determined by Rossini were used when available. In cases where the heats of formation had not been determined directly, we used the extrapolations of Ewell (7). These extrapolated or approximation values were based on the known heats of formation of related hydrocarbons as determined by Rossini and co-workers.…”

“…The entropies of hydrocarbons at 298.1°K. were taken from Ewell (7). Examination of the various entropy values that had been published as a result of their direct determina-…”

Chemical Analysis of Refinery C5 Hydrocarbon Fractions

“…Thermodynamic equilibrium data indicate, however, that these hydrocarbons and neopentane are not likely to be found together in any significant concentration in refinery samples from a given operation. For the same reason, 3,3-dimethyl-l-butene, boiling at 41.2°, and 2,2-dimethylbutane, 49.7°, are of very unusual occurrence (7).…”

“…The intensity of color increases with heating REDUCING agents in the presence of phosphates, silicates, or certain other acid radicals react with molybdates to produce the familiar substance known as molybdenum blue (8). Several observers have noted that reducing sugars react with ammonium molybdate to develop a blue color when heated and have utilized this reaction for qualitative and approximate quantitative tests for sugars (7). The conditions for a more sensitive colorimetric determination for reducing sugars based upon the molybdenum blue reaction have been established by Gilbert and Neapass (3) with ammonium molybdate and potassium dihydrogen phosphate.…”

“…The molybdenum blue reaction has been used in the sugar industry to detect traces of sucrose by its reducing effect on molybdates in acid solution. Pinoff and Gude (7) found that fructose reacted much more quickly than aldoses, and that larger amounts of glucose or lactose were required to give the test than is the case with fructose. Dorfmiiller (2) stated that ammonium molybdate may be substituted for a-naphthol to detect sugar in factory condensates and sweet waters.…”