Strategies for multiphase reactor selection

Abstract

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 strategy levels. Decisions are made at each strategy level using the reactor "wish" list. Combination of the individual decisions yields the final, ideal, reactor configuration. The three strategy levels are: Strategy level I:"Catalyst"design strategy. At this strategy level the ideal catalyst particle size, shape, porous structure and distribution of active material are determined. For gas-liquid systems, the appropriate decision concerns the choice of gas-dispersed or liquid-dispersed systems, and the provision of the appropriate ratio between liquid-phase bulk volume and volume of liquid-phase diffusion layer. Strategy level II:Injection and dispersion strategies. (a) Reactant and energy injection strategy: injection strategies examined include one-shot (batch), continuous, pulsed injection, reversed flow operation, and staged injection (in time or space), and the use of dispersionless contacting by keeping the reactants separated by a barrie (membrane). (b) Choice of the optimum state of mixedness for concentration and temperature: the proper choice of state of mixedness can influence selectivity and product properties. (c) Separation of product or energy in situ: product removal in situ helps to increase conversion by driving the reaction to the right and preventing undesirable side reactions. Removal of energy in situ by use of evaporating solvents has the function of a thermal flywheel. (d) Contacting flow pattern: here there is a choice between co-, counter- and cross-current contacting of phases. Strategy level III:Choice of hydrodynamic flow regime. Here the choice between 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 characteristics, heat transfer, mixing, etc. Combination of the decisions reached at the three strategy levels will yield the most suitable reactor configuration. In this paper it is argued that a systematic approach to reactor selection may lead to novel and innovative reactor configurations with a potential edge over existing and conventional technologies.