1 Department of Chemical and Biochemical Engineering, Technical University of Denmark
The analysis of multiphase systems at elevated pressure is of great interest both from an academic side and an industrial point of view. The literature contains limited data for such systems, and the measurement of the composition of the different phases of multiphase systems at elevated pressures has traditionally been considered very time consuming. This work aims at developing and operating an equipment which allows routine measurements of both VLE and VLLE, in the temperature range of 25-45°C and pressure range of 1-100 bar. This has been done by taking advantage of on-line sampling and pure component calibration. Samples from the different liquid phases in the high-pressure cell is taken using a moveable needle. The systems investigated have been a combination of the components: CO2, N2, di-methyl ether (DME), water, methanol, ethanol and 1-propanol. 41 isotherms have been measured and of these 18 were VLLE systems and 32 have not previously been published. Some of the experimental results have been modelled using an equation of state, SRK combined with the MHV1 mixing rule for the a-parameter and the NRTL model for the Gibbs excess energy. The Mathias-Copeman model was used in the expression for the pure-component a-parameter. For all the involved binary pairs the interaction parameters, τij, for the NRTL model were fitted to experimental data with the α- parameter fixed at 0.2. The obtained model has showed very good results when used to predict multi component VLE and VLLE systems containing CO2, while the model has some problems with systems containing N2.