Vapor–liquid equilibrium experiment using a true heat flow reaction calorimeter

“The experiments were performed in a true heat flow reaction calorimeter (CPA 201 Chemical process Analyzer from ChemiSens AB). The reactor used had a volume of 250 cm3 and about 100 g of solvent mixture was added to reactor before the start of each experiment. The reactor was then evacuated for 10–12 s, using a vacuum pump, at 25 °C. The reactor temperature was then raised to the experimental temperature and the system was left to equilibrate before any CO2 was added to the reactor. All experiments were performed at constant temperature, controlled using the built-in water bath. The temperature sensors in the reactor and water bath had an accuracy of 2.7 K (at 100 °C). The vapor pressure of amine and organic solvent was assumed to be constant during the experiment, and thus equal to the equilibrium pressure at the experimental temperature before any addition of CO2. Pure CO2 was then injected into the reactor in a series of small doses, each lasting for about 10 s, and each causing an initial total pressure increase of about 0.5 bar. The injection of CO2 was performed using a Bronkhorst Hi–Tec mass flow controller (MFC), with an accuracy of 0.8%. After each injection, the system was allowed to reach equilibrium, which was assumed to be reached when the change in the total pressure and the true heat flow signals were less than 0.005 bar and 0.02 W for at least 25 and 33 min, respectively. The pressure in the reactor was measured using an Omega pressure transducer with an accuracy of 1.0%. The MFC signal, pressure and true heat flow were measured throughout the experiment, and continuously logged in a computer. A ProFind™ automation script was used to control the temperature and CO2 dosage, and to determine when equilibrium had been reached.

Two independent experimental runs were performed at each temperature and for each concentration in order to ensure repeatability. Each experiment consisted of 5–8 equilibrium points. The uncertainties in the amount of CO2 absorbed were determined to be 1.6% for the 10 wt% AMP/DMSO system and 1.3% for the 25 wt% AMP/DMSO system. The uncertainty in the heat of absorption was determined to be 4.0% for 10 wt% AMP/DMSO and 1.9% for 25 wt% AMP/DMSO.”

Leave a Comment