Vapor pressure measurement of liquid dessicants at low temperatures by a novel technique.

Due to non-condensable gas under conditions of vacuum and low temperatures, it becomes difficult to obtain precise vapor pressures of typical liquid desiccants by an experiment. Usually, non-condensable gas is removed by a traditional degassing method (degassing after prepared solutions - DPS), in which prepared liquid desiccants are circularly frozen and non-condensable gas is pumped out. However, the solvent of liquid desiccants could greatly evaporate during traditional degassing processes. Concentrations of the prepared liquid desiccants could be greatly deviated from those of the prepared liquid desiccants. Accordingly, measured vapor pressures usually greatly deviate from those corresponding to the concentrations of the prepared liquid desiccants. Moreover, it becomes very difficult to determine new concentrations of the prepared liquid desiccants after degassing, precisely. To overcome the challenges for precise measurements of typical liquid desiccants, a novel technique is developed in this context. The new method is called DSSPS (degassing solvents and solutes before preparing solutions - DSSPS), in which degassed solvent and solute is weighted respectively, and then, is mixed as measured solutions. Thus, concentrations of the measured solutions could be determined easily and precisely. Vapor pressures of LiCl-H2O desiccants are measured by the new method at a range from 218K to 258K and with the mass fractions of solutions from 5% to 20%. Totally, 35 sets of vapor pressure are measured. Then, the data is correlated based on Antoine equation.The ARD% (Absolute Relative Deviation - ARD) of equation is from 0.04% to 3.21% and AARD% (Average Absolute Relative Deviation - AARD) is 1.73%. So, the new method could be used to measure vapor pressure of aqueous solutions at vacuum and low temperatures precisely. The average error between experimental data and the results calculated by EES (Engineering Equation Solver - EES) is within 15.2%, and its maximum error is 35.46%. Vapor pressure data in this context also provides important reference for development of a precise calculation model.