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 φ (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 φ 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

Kinetics of lipase-mediated synthesis of butyl butyrate in n-hexane

This paper reports experimental and modeling work concerning alcoholysis reactions between butanol and ethyl butanoate, catalyzed by Lipozymee in n-hexane, using a batch stirred system at 608C. Description of the reaction kinetics was based on a postulated multisubstrate Ping Pong Bi Bi mechanism, and appropriate rate expressions were derived for all components in the reaction medium. Simplified models were fitted by nonlinear multiresponse regression analysis to data (experimental or calculated from mass balances, as appropriate) encompassing the concentrations of free butanol, ethyl butanoate, ethanol and butyl butanoate. Finally, incremental F-tests were performed to assess the simplest model form that was able to provide a statistically good fit throughout the entire reaction time frame

Lipase-catalyzed synthesis of butyl butyrate by alcoholysis in an integrated liquid-vapor system

This paper reports experimental work pertaining to alcoholysis between butanol and ethyl butanoate, catalyzed by an immobilized lipase in a liquid-vapor system where chemical reaction and physical separation are simultaneously carried out. The processing setup was tested for various compositions of the starting feedstock and operated under reduced pressure. Samples were withdrawn both from the boiler and the condenser, and they were chromatographically assayed for butyl butyrate. The integrated configuration tested is quite effective toward improvement of the final yield of the desired product

Cascading reactor-separator sets reduces total processing time for low yield Michaelis-Menten reactions: model predictions

Integration of reaction with separation has often been claimed to provide enhanced processing due to alleviation of processing constraints which, like equilibrium limitation or product inhibition, are common in enzyme-catalyzed reactions. In this paper, a mathematical model is developed to assess the effect of cascading sets of enzyme reactors and physical separators (which, when the number of sets tends to infinity, is equivalent to full integration of reaction and separation), when compared with the classical unit operation approach, in terms of total time required to effect reaction and separation for a given overall conversion. The analysis is laid out using several relevant reactional parameters [final conversion of substrate (χf), equilibrium constant (Keq) and dimensionless dissociation constants of substrate and product (K*m,S and K*m,P)] and separational parameters [extent of separation in a single step (ζ) and ratio of time scales for molecular transport and chemical reaction ((Ξ)]. Cascading provides a gain in processing time, up to an optimum at a finite degree of cascading, only for reaction-controlled processes (typified by low ζ, low Ξ, low Keq, low K*m,P, high χf and high K*m,S); hence, full integration is not necessarily the best processing solution. Lengthening of the cascade leads to a decrease in the maximum substrate conversion while permitting higher degrees of product recovery. Read More: http://informahealthcare.com/doi/abs/10.3109/1024242980900319