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Thermodynamic properties of n-butanol Esplen, Robert William


Pressure-volume-temperature data for n-butanol have been determined from 117.5°C and 14.7 psi to 268°C. and 480 psi. The apparatus, designed to reach 1100 psi, was modeled after Kay⁴⁰ and used a dead weight gauge tester for pressure readings and a glass capillary tube as the sample container. Pressures were obtained to ± 0.1 per cent. Nitrogen manometers were also used for pressure measurement in some cases but much less successfully. Temperatures were maintained constant within a vacuum jacketed column, and measured by a copper-constantan thermocouple calibrated against a standard platinum resistance thermometer to ± 0.05°C. Trial runs were made on purified water and pure (research grade) n-hexane. The results for water checked with Keyes'⁵⁵ data within 0.5 per cent, and for n-hexane checked with Kay's²³ vapor pressure equation within 3 per cent. The latter deviation was possibly due to contamination while filling the capillary, and a modified filling procedure was introduced for the n-butanol. Vapor pressure results fell on smooth curves and checked within 0.5 per cent of Stull's critical collection of vapor pressure data at lower pressures, but at higher pressures (400 psi) deviations as much as 7 per cent were found. The saturated and superheated specific volume data also fell on smooth curves. Saturated values were shown to be accurate for heats of vaporization calculations. The superheated values compared favorably with values calculated from the reduced compressibility charts for hydrocarbons. Available thermodynamic data were compiled for n-butanol. A pressure-enthalpy diagram was constructed using only Cp data and heats of vaporization as calculated by the correlative methods of Othmer³⁰ and Thomas²⁹. Heats of vaporization were also calculated from the vapor-pressure and specific volume data using the Clausius-Clapeyron equation agreeing within 3 per cent of the Othmer and Thomas correlations.

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