Vapor–liquid equilibrium test

“In this study, a customized gas–liquid double-circulation device made of glass was adopted to determine the VLE data of the HEPZ aqueous solution. The working principle is gas–liquid dual circulation. The two circulating pumps are used to forcefully circulate the gas and liquid parts at the same time so that the gas and liquid phases are fully contacted and the time to balance is shortened. The equilibrium temperature can be accurately measured, and partial condensation is very small. The construction of the gas–liquid double-circulation device is shown in Figure 2.”


“The device is made of glass. The solution is pumped into the boiling chamber from the reagent inlet at the bottom of the equipment and heated to boiling using the heating rod. The outer-side air of the boiling chamber is evacuated using a vacuum pump to vacuum for heat preservation. The boiling solution is flushed to the liquid sampling port by bubbles, and the thermometer put in the temperature-measuring cell candetermine the temperature of the boiling liquid phase in order to obtain the boiling point, which is stable after reaching boiling. The vapor enters the condensing tube and flows back to the gas sampling port after condensing; we closed the cock to hold the condensate, which is a sample of the gas phase. After opening the cock, the condensate and reagent are stirred using a magnet and continued to be heated to boil. The entire equipment is connected to an external pressure control device, which is brought to a certain negative pressure using a vacuum pump, achieving the control of the equipment pressure. Therefore, the equipment can obtain VLE data at different pressures. After the solution is boiled, the liquid and vapor phase samples are collected, and the concentration of each phase solution is measured using an Abbe refractometer. This equipment used in this study can measure the boiling point of a certain concentration of the solution and the vapor–liquid composition after boiling at a certain negative pressure or atmospheric pressure. The construction and the operation principle of the Abbe refractometer are provided in the Supplementary Material.

The main sources of error of the device are as follows: the sampling time after boiling is difficult to determine, and the accuracy of the pressure control device is limited; the fluctuation is about ±±0.2 kPa. The uncertainty of the thermometer used in this study is ±0.2°C. The color of some solutions turns yellow at high temperature. There will be a certain error in the analysis of the refractometer.”

Leave a Comment