Methodology for the experimental measurement of vapor–liquid equilibrium distillation curves using a modified ASTM D86 setup

Abstract

A method has been developed to determine experimental equilibrium distillation curves using a modified ASTM D86 distillation apparatus.The method determines accurate equilibrium initial boiling points and accounts for the dynamic holdup inherent in distillation curves measured in accordance with the ASTM D86 standard.In this work, the ASTM D86 distillation setup has been modified to simultaneously measure liquid and vapor temperature using two resistance temperature detectors (RTDs) and a data acquisition system has been employed to record temperature data at one-second time intervals for the duration of each distillation.Additionally, the time for each volume recovery point is recorded.The method presented here uses the time-resolved liquid temperature data to identify the true initial boiling point (IBP) of four fuel mixtures of known composition; the IBPs are within 2°C of the calculated equilibrium values.The time-resolved volume recovery information and the identified initial boiling point time are used to construct a volume evaporated versus time curve.The measured temperatures determined at the corresponding volume evaporated increments provide an experimental equilibrium distillation curve (EEDC). The EEDCs for the four fuel mixtures of known composition match the calculated equilibrium curves within a few degrees Celsius; a maximum mean absolute error of 2.2±1.4°C was observed.The dynamic holdup (volume difference between volume evaporated and volume recovered) associated with a distillation is found to correlate with the initial boiling point of the fuel being distilled and the temperature of the condenser bath used in the experiment.The method was also applied to measure EEDCs for a gasoline fuel and a diesel fuel, where the compositions were unknown, to investigate the differences between the EEDCs and the ASTM D86 distillation curves.The results highlight the large errors incurred when using ASTM D86 results to approximate equilibrium distillation curves.