Experimental and Numerical Study of the Hydrodynamics of a Thin Film Reactor (TFR) for the Decarboxylation of Anacardic Acid

Abstract

A newly designed laboratory scale thin film reactor (TFR) was tested for the decarboxylation of anacardic acid in Cashew Nut Shell Liquid (CNSL) and to investigate the fluid flow behaviour under the influence of temperature since the fluid properties like viscosity and density have strong dependence on temperature. The CNSL containing 60-65 % anacardic acid was decarboxylated to produce cardanol and CO<inf>2</inf> at wall temperatures ranging between 393 K and 433 K, respectively. The characteristics of the CNSL, essentially a non-Newtonian fluid, was analysed at different temperatures and its rheological behaviour was studied using the well-known power law model. It was observed that CNSL follows a pseudoplastic behaviour and its viscosity, along with the liquid residence time, was found to decrease till 413 K, while a further increase in temperature resulted in product degradation due to charring, accompanied by an increase in viscosity and residence time. Using measured values for the viscosity, the film thickness was calculated for each wall temperature within the 393-433 K temperature range, showing an increase of the film thickness with temperature and viscosity. Computational Fluid Dynamics (CFD) studies were carried out for the first time for this reactor configuration, using the volume of fluid (VOF) model for the reactive flow. The results obtained from these simulations were in concurrence with the experimental outcomes: velocity profiles along the length of the reactor show its highest values at a wall temperature of 413 K, while lower velocity values were observed when the temperatures were lower or greater than 413 K. © 2018 Walter de Gruyter GmbH, Berlin/Boston 2018.