Separation Of Binary Homogeneous Azeotropic Mixtures By Pressure-swing Distillation

Methanol and acetonitrile are the important organic solvenst, which are widely used in chemical and pharmaceutical industry and so on. But the mixture of these two components can not be separated by conventional distillation, because they form azeotrope at atmospheric pressure.This paper discussed the batch pressure-swing distillation (BPSD) to separate the mixture, and put forward an empirical formula, to judge whether binary homogeneous azeotropic mixtures can be separated by pressure-swing distillation (PSD).The vapor - liquid equilibrium (VLE) data was measured with vapor - liquid equilibrium caldron at 101.30kPa. The experimental data were tested for thermodynamic consistency and correlated satisfactorily with the thermodynamic model Wilson activity coefficient equation. Then the small scale BPSD was done to separate the binary mixture. The result showed that the purity of both methanol and acetonitrile were up to 99.5%, verifying the feasibility of the method. In addition, this paper simulated this BPSD process. The simulated values were in agreement with the experimental data.VLE data at different pressures of alcohols– nitriles (the number of the carbons is below 5) binary systems were calculated by Wilson equations. The result showed that every azeotrope (if formed) was homogeneous and sensitive to pressure, which means a significant change in the azeotropic composition and allows the recovery of feed components without adding a separating agent. Then VLE data at different pressures of some other binary homogeneous systems were studied. It was showed that if the temperature deviation value accorded with the formula the azeotrope maybe pressure-sensitive and can be separated by PSD.