Reactive stripping in pilot scale monolith reactors—application to esterification

The principle and the feasibility of using monoliths for intensification in three-phase processes are demonstrated for reactive stripping application. The solid-acid BEA catalyzed esterification of hexanoic acid with 1-octanol is studied as model reaction. Water, besides the hexyl-octanoate one of the reaction products, strongly inhibits the activity of the catalyst and lowers the maximally obtainable conversion of this equilibrium-limited reaction. As a side reaction, di-octyl-ether is formed. In a monolithic reactor, the water formed by both reactions is stripped out of the liquid reactant stream by a co- or countercurrent nitrogen stream. This results in an improved reactor performance. Reactive and non-reactive stripping experiments in a pilot scale reactor (2 m column length, 43 mm column diameter) showed that the stripping is improved by lower pressures, higher strip gas flows or higher temperature. For the liquid to gas phase mass transfer, no significant differences between different monolith types (internally finned, square, rounded) were observed. Low selectivities can be increased by elevated acid concentrations. As the reaction is in first order to the acid, additionally the reaction rate is increased. However, higher acid concentrations cause higher water contents due to a shift of the VLE, thus limiting the enhancement of the reaction rate.