OP-II-3

PL-5Reactor designs with intensified heat transfer have been available for a numberof years, based in many cases on the concepts of compact heat exchangers 10,11 . Useof this type of reactor, generally featuring narrow flow channels and large heattransfer areas, has previously been proposed for single phase liquid reactions 12,13 , forliquid–liquid reactions 14 , for gas–liquid reactions 15,16 and for heterogeneouslycatalysed gas liquid reactions with the catalyst either adhered to the channel walls 17 ,or packed within the flow channels 18 .Trickle bed reactors are used commonly in the refinery and petrochemicalindustry for hydrogenation-based reactions. This reactor type is continuous inoperation and is regarded as a plug flow reactor (Haure et al, 1989, Boelhouwer etal., 2001) and essentially un-structured. Recent work to elicudate the mechanism offlow regime transition (from trickle to pulse) has however highlighted that thehydrodynamics, and thus reaction performance of a trickle bed are dominated bylocal bed packing structures 19,20 . The trickle bed should therefore be considered asstructured, albeit that the structure is random rather than orthogonalIt has of course been proposed variously to “structure” [systematically] tricklebeds 21 , and indeed the internals of reactive distillation columns (which are after all amultiphase catalytic reaction environment) 22,23,24Reticulated foams have received attention in recent years also as substrates forcatalysis in multiphase reactions 25 . These may ostensibly be considered as a“negative image” trickle bed, and have the same benefit of high substrate surfaceareas but the notable benefit of very high packing voidage (>90% rather than ca.40% in a trickle bed). Studies of these supports appear to indicate that thehydrodynamics here are also dominated by local structures and flow constrictions.The foam based catalyst reactor is therefore also essentially structured, but in arandom rather than orthogonal fashion.From the above it is apparent thatonly reactors with a void interior spaceand slurry, homogeneous or no catalystare truly unstructured: stirred tanks,slurry bubble columns. Considering theclassification of reactors according to thislogic highlights that the main part of theliterature largely misses one importantclass of reactors: namely a slurry reactorin a structured environment 26 . Studies on this embodiment, either as an adiabatic oras a heat exchange reactor, show that this design also offer significant rate benefits,and changes in selectivity for some chemistries 27,28 .17