Critical properties of some aliphatic symmetrical ethers

• Critical properties of simple aliphatic ethers were measured.
• The ethers decompose at near-critical temperatures.
• Pulse-heating method with short residence times was used.

The critical temperatures Tc and the critical pressures pc of dihexyl, dioctyl, and didecyl ethers have been measured. According to the measurements, the coordinates of the critical points are Tc = (665 ± 7) K, pc = (1.44 ± 0.04) MPa for dihexyl ether, Tc = (723 ± 7) K, pc = (1.19 ± 0.04) MPa for dioctyl ether, and Tc = (768 ± 8) K, pc = (1.03 ± 0.03) MPa for didecyl ether. All the ethers studied degrade chemically at near-critical temperatures. A pulse-heating method applicable to measuring the critical properties of thermally unstable compounds has been used. The times from the beginning of a heating pulse to the moment of reaching the critical temperature were from 0.06 to 0.46 ms. The short residence times provide little decomposition of the substances in the course of the experiments. The critical properties of the ethers investigated in this work have been discussed together with those of methyl to butyl ethers. The experimental critical constants of the ethers have been compared with those estimated by the group-contribution methods of Wilson and Jasperson and Marrero and Gani. The Wilson/Jasperson method provides a better estimation of the critical temperatures and pressures of simple aliphatic ethers in comparison with the Marrero/Gani method if reliable normal boiling temperatures are used in the method of Wilson and Jasperson.