(388c) Effect of Cavitation Intensity on Thermal Efficiency and Reactive Performance of a Hydrodynamic Cavitation Reactor

The production of specialty chemicals is to-date conducted almost exclusively in large-volume batch reactors. However, emerging challenges, including supply chain limitations, stricter environmental regulations, and safety concerns, are driving an on-going transition to much smaller, compact, and modular continuous processing units. While this transition itself constitutes a “process intensification” step, the use of novel reactor concepts for continuous processing promises to further enhance the benefits of process intensification for specialty chemicals production terms of energy efficiency, product quality, process safety, and reduced physical footprint of the plant.

In this context, hydrodynamic cavitation reactors (CavR) are promising but to-date rarely utilized. CavR rely on the physical phenomenon of cavitation that involves the rapid formation, growth, and subsequent collapse of vapor micro-bubbles within a liquid which occurs on a very short time-scale (milliseconds) and releases large amounts of localized energy. It hence seems particularly well-suited to the processing of viscous reactive flows, as typical for dispersants production. The onset of cavitation can be predicted using the cavitation number equation (Cv = (P – P_v) / (0.5 ρ v²)), where P is the downstream system pressure, P_v and ρ the vapor pressure and density of the liquid, respectively, and v is the (local) flow velocity of the fluid. Cavitation occurs when Cv is unity and cavitation intensity increases with decreasing Cv.

Here we present an investigation into the effect of cavitation intensity on the thermal efficiency and reactive performance of a rotational CavR in the production of succinimide dispersants. By varying the cavitation number via changes in key experimental parameters, including viscosity and density of the working fluid, downstream system pressure, and rotational velocity, we evaluate the effect of Cv on (average) fluid temperature and reactive conversion. Our results suggest that the observed increase in bulk fluid temperature is mainly due to frictional heating between the rotating cylinder and the fluid, rather than due to cavitation. However, cavitation strongly enhances the observed reaction rates in comparison to a conventional tubular reactor at similar operating conditions. This suggests that either the very high, if short-lived, local temperature maxima during cavitation or the intense local mixing of the poorly miscible reactants result in this strong enhancement beyond reaction rates observed even in a (macroscopically) well-mixed conventional tubular reactor. We complement these studies by a detailed analysis of parameters affecting the cavitation intensity (tangential velocity and fluid viscosity) using stroboscopic videography in order to develop an improved fundamental understanding of cavitation in a rotational hydrodynamic cavitation reactor.

Overall, our results suggest that cavitation reactors constitute a promising, strongly intensified reactor configuration for the processing of viscous mixtures for the specialty chemicals industry.