SCALE EFFECTS IN LABORATORY AND PILOT-PLANT REACTORS FOR TRICKLE-FLOW PROCESSES

Research and development studies in a laboratory are necessarily conducted on a scale which is orders of magnitude smaller than that in commercial practice. In the case of the development and commercialization of an unprecedented novel process technology, available laboratory results have to be translated into envisaged technology on a commercial scale, i.e. the problem is that of scaling-up. However, in many circumstances the commercial technology is more or less defined as far as type of reactor is concerned and laboratory studies are concerned with the generation of predictive information on the behaviour of new catalysts, alternative feedstocks, etc., in such a reactor. In many cases the complexity of feed composition and reaction kinetics preclude the prediction to be made on the basis of a combination of fundamental kinetic data and computer models, so that there is no other option than to simulate the commercial reactor on a laboratory scale, i.e. the problem is that of scaling-down. From the point of view of R & D Defficiency, the scale of the laboratory experiments should be as small as possible without detracting from the meaningfulness of the results. In the present paper some problems in the scaling-down of a trickle-flow reactor as applied in hydrotreating processes to kinetically equivalent laboratory reactors of different sizes will be discussed. Two main aspects relating to inequalities in fluid dynamics resulting from the differences in scale will be treated in more detail, viz. deviations from ideal plug flow and non-ideal wetting or irrigation of the catalyst particles. Although a laboratory reactor can never be a true small-scale replica of a commercial trickle-flow reactor in all respects, it can nevertheless be made to provide representative data as far as the catalytic conversion aspects are concerned. By ressorting to measures such as catalyst bed dilution with fine catalytically inert material it proves possible to carry out meaningful process research on hydrotreating processes on the scale of micro-reactors.