Phase equilibria of linear saturated high molecular mass acids in supercritical ethane

• Phase equilibria measurements of ethane/long chain fatty acid homologous series.
• No three-phase regions and increase in pressure with temperature.
• Linear increase in pressure with increase in hydrocarbon backbone length.
• Phase transition pressure higher than n-alkane, ethyl ester and methyl ester.
• Phase transition pressure of acid lower than in CO2 and higher than in propane.

High-pressure phase equilibria of the ethane/acid homologous series for linear saturated acids with between 10 and 22 carbon atoms are investigated. Measurements for ethane with decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic, octadecanoic and docosanoic acid were conducted between 308 and 353 K in the acid mass fraction range of 0.016–0.68. Higher phase transition pressures were measured at higher temperatures and no three-phase regions, or indications thereof, were observed. The measurements revealed that as the number of carbon atoms increased, so the phase transition pressure increased linearly, prompting the compilation of a set of linear pressure–carbon number plots. The observed phase transition pressures for the ethane/acid systems are also lower than that of the CO2/acids systems, suggesting that ethane is an alternative supercritical solvent to or co-solvent with CO2 for processes involving high molecular mass acids.

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