Vapor-Liquid-Liquid Equilibrium (VLLE) systems are complicated systems; they involve both a two phase liquid and a two phase vapor.Obtaining equilibrium data on these systems is very difficult, Vapor-LiquidEquilibrium (VLE) recirculation stills can not be used to obtain accurate VLLE data due to incorrect composition of the recycled condensed vapor to the boiler, modifications are made to these stills to obtain accurate equilibrium data for partial and immiscible liquid systems.Another difficulty when collecting the vapor & liquid samples, a modification must be made in order to collect a sample with the correct composition.VLLE systems are non-ideal and polar systems, many Equations Of States (EOS) failed in correlating or predicting VLLE data. Activity coefficient models gave reasonable accuracy in correlating or predicting VLLE data such as T.K.Wilson and NRTL (Non-Random-Two-Liquid) and UNIQUAC (Universal-Quasi chemical-Activity-Coefficient) models while the UNIFAC (Uniquac-Functional group-Activity-Coefficient) model failed in predicting VLLE data especially for immiscible and some partial miscible liquid systems. In this study the following was accomplished:
1- A modified recirculation still was assembled to deal with partial and immiscible liquid systems. The still consisted of 55 mm diameter boiling section and a 40 mm diameter condensing section. The modification involved supplying the still with mixers in the two mentioned sections, the speed of mixing was 1400-1600 rpm. The mixers helped in keeping the two phase liquid mixtures in the boiler and the condenser in a kind of a homogenous state. This gave a correct composition of the recycled liquid in the condenser and a correct boiling temperature reading in the boiler.
2- Isobaric VLLE data for two binary systems; Ethyl-acetate\Water and Toluene\Water and one ternary system Toluene\Ethyl-acetate\Water have been measured at 101.325 kPa in the modified still. All the systems are two phase mixtures were the system Ethyl-acetate\Water is a partial miscible system and the systems Toluene\Water and Toluene\Ethyl-acetate\Water are immiscible systems. No equilibrium data are available on the ternary system measured in this study. The binary systems and the ternary system forms minimum boiling point Azotropes.
3- The VLLE data where correlated and predicted by using the PengRobinson Equation Of State (EOS) in both the vapor and liquid phases and one of the activity coefficient models T.K.Wilson, NRTL, UNIQUAC and UNIFAC in the liquid phase and the Peng-Robinson (EOS) in the vapor phase. The overall average absolute deviations in vapor mole fraction for the system Ethyl-acetate \ Water measured in the present study by the prediction and correlation methods was 37.98 and 0.12 respectively and for the system Toluene \ Water it was 1.62 and 0.08 respectively and for the system Toluene
\ Ethyl-acetate \ Water it was 0.16 and 0.06 respectively.
4- A modification was applied on the the UNIQUAC model by converting the coordination number ( Z / 2 ) which was considered as a constant = 5 into a third adjustable parameter, this helped in decreasing the average absolute deviation in vapor mole fraction from 20% to 65%.
5- liquid-liquid-Equilibrium (LLE) data of the binary system Ethylacetate\Water was measured in the Temperature range 20oC to 75
C by the same modified still and the overall average absolute deviation in predicted activity coefficient ratio of top and bottom layers ∆(γ1T/γ1B) were 0.0561,0.0112, 0.0361 and 0.1512 by using the activity coefficient models T.K.Wilson, NRTL, UNIQUAC and UNIFAC respectively.
