Design of periodic adsorptive reactors for the optimal integration of reaction, separation and heat exchange

Abstract

Optimisation techniques are used for the design of novel forced-periodic reactors in which there is the integration of catalytic reaction, adsorptive separation and direct fluid to solid heat exchange within a single unit operation. For such configurations, dynamic operation is utilised to generate favourable temperature (catalyst activity) profiles, and, through in situ separation, to provide reaction enhancement and the enriched recovery of the primary product(s). The work thus involves aspects of thermal and concentration swing adsorption, reverse (or bidirectional) flow reactor operation, and thermal regeneration. The design methodology is based on fully discretised mathematical models, upon which periodic constraints are imposed to yield direct cyclic steady state solutions. The models are then formulated as non-linear programming problems to yield optimal operating schedules and conditions. Models are developed for general endothermic and equilibrium limited reaction schemes; as a case study, specific consideration is given to the dehydrogenation of methylcyclohexane to toluene over and admixture of Pt–Al 2O 3 catalyst and zeolite 5A adsorbent. When compared to an equivalent and optimally operated adiabatic plug flow reactor, design and operating conditions are calculated for both single and multistage configurations in which there are significant improvements in reactant conversion, with the additional benefit of the bulk separation of the product species. These qualities of the hybrid reactors are attained for energy inputs (i.e. feed pre-heat requirements) which do not exceed that of the equivalent steady flow reactor. The results also predict larger improvements in reactor performance when there is greater flexibility in the way in which heat and material are introduced into the reactor systems. For example, for a five-stage configuration involving mixed series–parallel connections of the stages, and the disproportional splitting of feed streams to each stage, a conversion of 59% is calculated for the production of 0.02 mol/m 2 s toluene (cf. 23% for an equivalent reactor), with 72% recovery of the toluene in a near pure form (inert-free basis).