STRATEGIES FOR MULTIPHASE REACTOR SELECTION

The central theme addressed in this paper is: how do we arrive at the ''ideal'' reactor configuration meeting most closely with the process requirements? The problem of reactor selection is analyzed at three st rategy levels. Decisions are made at each strategy level using the rea ctor ''wish'' list. Combination of the individual decisions yields the final, ideal, reactor configuration. The three strategy levels are: S trategy level I: ''Catalyst'' design strategy. At this strategy level the ideal catalyst particle size, shape, porous structure and distribu tion of active material are determined. For gas-liquid systems, the ap propriate decision concerns the choice of gas-dispersed or liquid-disp ersed systems, and the provision of the appropriate ratio between liqu id-phase bulk volume and volume of liquid-phase diffusion layer. Strat egy level II: Injection and dispersion strategies. (a) Reactant and en ergy injection strategy: injection strategies examined include one-sho t (batch), continuous, pulsed injection, reversed flow operation, and staged injection (in time or space), and the use of dispersionless con tacting by keeping the reactants separated by a barrier (membrane). (b ) Choice of the optimum state of mixedness for concentration and tempe rature: the proper choice of state of mixedness can influence selectiv ity and product properties. (c) Separation of product or energy in sit u: product removal in situ helps to increase conversion by driving the reaction to the right and preventing undesirable side reactions. Remo val of energy in situ by use of evaporating solvents has the function of a thermal flywheel. (d) Contacting flow pattern: here there is a ch oice between co-, counter- and cross-current contacting of phases. Str ategy level III. Choice of hydrodynamic pow regime. Here the choice be tween the various ''fluidization'' regimes, e.g. dispersed bubbly flow , slug flow, churn-turbulent flow, dense-phase transport, dilute-phase transport, is made on the basis of the interphase mass transfer chara cteristics, heat transfer, mixing, etc. Combination of the decisions r eached at the three strategy levels will yield the most suitable react or configuration. In this paper it is argued that a systematic approac h to reactor selection may lead to novel and innovative reactor config urations with a potential edge over existing and conventional technolo gies.