The present invention relates to a process for handling product fluid streams which are obtained in the catalytic hydrogenation of liquid feeds in laboratory catalysis apparatuses. The liquid feeds are preferably hydrocarbons comprising sulfur- and nitrogen-comprising compounds as impurities. The hydrogenation serves to convert the impurities into hydrogen sulfide and ammonia which in this form can be readily separated off from the other constituents of the liquid feed. The product fluid streams are contacted with an inert gas stream, with the flow rate of the inert gas being a multiple of the flow rate of the product fluid stream. The formation of deposits in lines of the region on the outlet side of the reaction space can be effectively prevented by means of the process of the invention.