Title: “Dynamic modelling of crossflow ultrafiltration processes in the case of the separation of macromolecules” Abstract In this Doctoral Thesis, the application of theoretical and semi-empirical dynamic models was analyzed to predict permeate flux decline with time due to fouling in crossflow ultrafiltration of macromolecules. Fouling is present in every ultrafiltration process and it is the main limiting factor in the application of membrane technology. Pilot plant tests were performed with two different ceramic ultrafiltration membranes using a polyethylene glycol aqueous solution as feed. Crossflow velocity, transmembrane pressure, feed concentration and temperature were varied. Experimental data and model predictions were compared. The results demonstrated that it was impossible to theoretically predict permeate flux decline with time under different experimental conditions. One of the reasons is the difficulty to theoretically estimate all the model parameters. However, for the experimental conditions tested, and using Hermia Models adapted to crossflow filtration, it was possible to predict reasonably well permeate flux decline with time from steady state and initial permeate flux data, while the rest of model parameters were theoretically calculated.