Dioctyl phthalate (DOP) is used in substantial quantities in industry, primarily as a plasticiser for PVC and other polymers. One route to its production is via the esterification of 2-ethylhexanol (2EH) with phthalic anhydride (PA) using a homogeneous catalyst. The process can be carried out in batch reactors. A detailed dynamic model describing both the physics and chemistry of the plant, and its operating procedures has been constructed using the gPROMS process modelling system. It is shown that, by incorporating a sufficient degree of detail and eliminating unnecessary assumptions, the model is able to predict accurately the observed dynamic behaviour of an existing industrial plant. Following validation, the model has been used to derive optimal operating policies for the plant. This corresponds to a dynamic optimisation problem incorporating an economic objective function, several time-dependent decision variables ("controls"), the equipment design characteristics and other time-invariant parameters, and all important constraints. This is then solved using the dynamic optimisation facilities in gPROMS.