The condensation/polymerisation of dimethyl siloxane fluids in a three-phase trickle flow monolith reactor

For the production of siloxane fluids, the viability of using a multi-chann el monolith as a catalyst support system in a three-phase reactor has been studied. The catalyst was tripotassium phosphate (K3PO4). Experiments were perfonned in a single-channel flow reactor (15 mm i.d. and 500 mm catalyst coated length). The rate of reaction was followed by monitoring the disappe arance of the hydroxyl group (-OH). Reaction experiments were performed at a hydroxyl group concentration T = 373-413 K and P = 7.9 kPa with a nitroge n purge. The maximum temperature of ran-e from 150 to 170 mol m(-3) operati on was restricted to 413 K to avoid the formation of undesirable by-product s. In the regime controlled by chemical kinetics, reaction was of an appare nt first order with respect to -OH concentration, and in the apparent rate constant, the pre-exponential factor was 4.19 x 10(-4) m s(-1), and the app arent activation energy was 16.1 U mol(-1). These are only valid for the op erating pressure and purge gas flowrate used, as both of these are shown to affect water removal from the liquid phase and, hence, reaction rates. Mas s transfer coefficients from the liquid to the catalyst surface were estima ted and these increased rapidly with flowrate and were higher than expected for a falling liquid film. (C) 2001 Elsevier Science BN. All rights reserv ed.