Change in Vapor Concentrations Emitted from Multicomponent Organic Solvents

Introduction
Most organic solvents used in workplaces are mixtures of several components. When two or more kinds of solvents are mixed and left in a vessel, composition of vapor phase and liquid phase are usually different. In addition, because of the difference in the evaporation rates of solvents, the composition of the solvents in the liquid phase is continuously changing with time, and therefore, the vapor concentrations of each component also change with time. In this study, we investigated generation characteristics of multicomponent organic vapors that evaporated from a liquid mixture in a reservoir continuously, and a method of estimating the vapor concentration was presented.

Methods
Two to 4 kinds of organic solvents were put into a small reservoir made of glass (3 cm in diameter and 3 cm high) that was installed in a cylindrical glass vessel (10 cm in diameter and 15 cm high). Air was introduced into the glass vessel at a flow rate of 150 ml/min, and the generated vapor concentrations were intermittently monitored for up to 5 hours with a gas chromatograph equipped with a flame ionization detector. A prediction model on generated vapor concentration was developed based on the vapor- liquid equilibria using the UNIFAC equation and a mass transfer rate theory. Predicted vapor concentrations were compared with the experimental ones.

Results
The vapor concentration of the more volatile component was high at first, and then decreased with time. On the other hand, the concentration of the less volatile component was low at first, and then increased with time. The estimated vapor concentrations were relatively in good agreement with the experimental ones. 

Discussion
The results suggest that changes in concentrations of multicomponent organic vapors continuously evaporating from liquid reservoir can be estimated by the proposed model.