In TEA, when using CAPE-OPEN version 1.0, K-values are only available for phase "VaporLiquid". Composition derivatives are not supported.
For CAPE-OPEN version 1.1, K-values are a regular two-phase property.
The only internal routine calculates log(K-values) for phase 1 and phase 2 as log(fugacity coefficient,phase 2) minus log(fugacity coefficient,phase 1). So logFugacityCoefficient must be available for both phases.