Industrial applications of aromatic/aliphatic separation require the separation of multi component mixtures. Mainly studies of binary systems with benzene or toluene as aromatic components can be found in the literature. It is questionable whether the results gained from binary systems can be transferred to multi component mixtures. In order to create more realistic conditions, multi component aromatic/aliphatic mixtures and a higher temperature up to 150 degrees C were used for pervaporation experiments. Ingredients of the feed were not only mononuclear but also di-and trinuclear aromatics (trimethylbenzene, naphthalene, phenanthrene, n-hexadecane and decalin). Additionally, we tested the effects of temperature variation and different pre-treatments of the membrane. For all the experiments, various crosslinked copolyimide membranes were applied. In the course of the measurements, we observed that permeation of di- and trinuclear aromatics is possible with almost no loss of selectivity, if a certain temperature is exceeded. But the permeability can also be influenced by other parameters i.e. the chain length of the crosslinker, the permeate pressure and pre-treatment of the membranes.