Integrated vs. sequential reaction and separation: contributions for a global analysis

Integration of reaction and separation in one single step has often been claimed to provide enhanced processing and economic results when compared with the traditional configuration where a reaction unit is followed by a downstream separation unit, due to alleviation of kinetic and thermodynamic constraints. This paper quantitatively addresses the kinetic and thermodynamic improvements which can be brought about by performing reaction and separation simultaneously instead of sequentially, in the case of a unisubstrate/uniproduct reversible reaction following first-order kinetics and that takes place in a system behaving as an ideal solution. Kinetic enhancement was ascertained via theoretical evolution of the molar fraction of product in both streams coming from either the separator (in series with the reactor) or from the integrated unit, whereas thermodynamic enhancement was ascertained via theoretical evolution of the overall Gibbs’ free energy in either configuration. The time required to achieve a predefined degree of conversion and separation is always lower for simultaneous than for sequential reaction and separation. The molar fraction of product in the product-rich stream is always higher for the integrated unit except for high values of parameter / (defined as the ratio of the time scale associated with chemical reaction to the time scale associated with mass transfer of reactant) and of the chemical equilibrium constant. Comparison of the thermodynamic behaviour of both systems also leads to the conclusion that high values of / yield worse results when the integrated unit is used instead of the sequential reactor/separator system because reactant is removed from the reacting system at a rate that is higher than the reaction rate itself.