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PL-5MULTIPHASE CATALYTIC REACTIONS IN REACTORSSTRUCTURED AT THE MESO-SCALEHugh Stitt 1, *, Dan Enache 1 , Steve Pollington 1 , Mike Winterbottom 21 Johnson Matthey plc, Billingham, Cleveland, TS23 1LB, UK* hugh.stitt@matthey.com2 School of Chem. Eng., University of Birmingham, Edgbaston B15 2TT, UKMultiphase reactions are very common in the chemical industry. Many industrialreactions, such as hydrogenation, oxidation, carbonylation and hydroformylation takeplace in two or even three phase conditions 1 . Such processes have to deal withdiffusion (or mass transport) limitations. The workhorse of the fine chemicals industryis the stirred batch reactor. This is a versatile reactor and can be used for more thanone reaction and more than one product. This multi-reaction and multi-productcapability offers huge advantages for batch plant scheduling. But despite advances inthe design of the impeller and of the gas sparge pipe, this reactor still presents somedisadvantages. They can be inadequately mixed and frequently mixing, masstransfer or heat transfer steps govern the reaction rate. The net result of this is thatreaction times tend to increase significantly with increasing scale, leading to reducedoperating and thus capital efficiency. Commonly reaction selectivity will alsodecrease on scaling from batch to plant operation as a direct result of the transportlimitations. They are difficult to scale-up as the critical dimensions associated with amultiphase reaction (reactor dimensions, bubbles size, micro-mixing scale andkinetic-related distances) do not scale in proportion; increasing reactor sizecommonly increases the limitations due to mass and heat transport 2 .There has recently been significant attention to the potential of structuredreactors and catalysts to achieve increases in volumetric productivity andcontrollability 3,4 . This is exemplified by the micro-channel and monolith reactorconcepts. In this case, each channel is nominally an independent plug flow reactorand scaling-up simply becomes an issue of increasing the number of channels(scaling-out) as long as flow is equally distributed over all channels 5 .Significant work has been done to demonstrate the process benefits of monolithbased catalysts for multi-phase reactions since the pioneering work of Andersson’sgroup at Chalmers University 6 . The preferred operating regime of Taylor flow hasbeen shown to generate high gas-liquid mass transfer coefficients and volumetricrate benefits over conventional reactors (notably stirred tanks) in the order of 10-100times have been widely reported. The dominant mass transfer mechanism is via thebubble wake (not the thin film between the bubble and catalysed wall as originallybelieved) 7,8 . The monolith reactor is substantially adiabatic, but recycle processconfigurations have been proposed to overcome this 9 .16