COSMO-SAC 2013-ADFΒΆ

On the basis of the framework of COSMO-RS, Lin and Sandler [8] suggested a variation, the COSMO-SAC (where SAC denotes segment activity coefficient) model by invoking a necessary thermodynamic consistency criterion. Although there are differences, COSMO-RS and COSMO-SAC share some similarities. Later improvements of COSMO-SAC appeared, like in Refs. [6,7,9]. The COSMO-SAC 2013-ADF method used in ADF is the one developed by Xiong et al., which is described in detail in Ref. [9]. The COSMO-SAC 2013-ADF parameters in Ref. [9] were optimized for use with ADF COSMO result files. COSMO-SAC 2013-ADF is an improved COSMO-SAC method compatible to ADF and different than previous COSMO-SAC methods. The main difference compared to previous COSMO-SAC methods is that the COSMO-SAC 2013 model includes a dispersion contribution in the mixture interaction.

The ADF COSMO-RS program can calculate activity coefficients using the COSMO-SAC 2013-ADF model, based on Ref. [9]. Like in the COSMO-RS method, pure compound vapor pressures can be given as input, for example, if experimental values are available. If these values are not specified then the pure compound vapor pressure will be calculated according to the COSMO-SAC 2013-ADF model This part of the COSMO-SAC 2013-ADF has been implemented in ADF2016. It is also possible to use some earlier COSMO-SAC methods [6,7], but note that the parameters in those methods were not optimized for use with ADF COSMO result files.

The COSMO-SAC 2013 model includes a dispersion contribution in the mixture interaction. This dispersion contribution is a complicated expression which also depends on the liquid molar volume of the pure compounds and on the molar volume of the mixture. The molar volume of the mixture is calculated from the pure compound liquid molar volumes assuming ideal mixing. In the input for the ADF COSMO-RS program one include for each compound the experimental pure compound liquid density (kg/L), from which the program can calculated the pure compound liquid molar volumes. If this density is not given the pure compound liquid molar volume will be calculated from its COSMO volume. Note that in the calculations with the COSMO-SAC 2013-ADF model in Ref. [9] often experimental pure compound liquid molar volumes were used.