Critical temperatures and pressures of straight-chain alkanediols (C3 to C12)

The critical pressures pc and the critical temperatures Tc of diols with straight alkylchains HO(CH2)nOH and n = 3, 4, 5, 6, 8, 9, 10, 12 have been measured. All the alkanediols studied decompose at near-critical temperatures. A pulse-heating method which allows measuring the critical properties of thermally unstable compounds has been used. The times of heating from the beginning of a pulse to the moment of reaching the critical temperature were from (0.03 to 0.46) ms. The short residence times provided little degradation of the substances in the course of the experiments. The uncertainties of the measurement of the critical properties of alkanediols are 0.04 pc and 0.015 Tc, where Tc is the absolute temperature. The critical properties obtained have been compared with the values measured earlier by various techniques. The experimental critical constants of alkanediols have also been compared with those calculated using the group-contribution methods of Lydersen, Wilson and Jasperson, and Marrero and Gani.