Experimental and theoretical study of a tubular flow reactor: Homogeneous liquid-phase reaction.

Abstract

An experimental and theoretical study has been carried out for the evaluation of concentration and temperature profiles for non-isothermal liquid-phase reactions taking place in a vertical tubular reactor. Theoretically homogeneous, irreversible first- and second-orders reactions were investigated. Three different flow models were assumed: (1) plug flow, (2) laminar flow and (3) laminar flow accompanied by radial diffusion. In addition, two modes of reactor operations were considered: adiabatic and constant-wall-temperature (CWT) reactors with the hydrolysis of acetic anhydride being chosen as the reference reaction. The effects of flow model, reaction kinetics, reaction conditions and reactant concentrations on conversion and temperature rises were then investigated. Point concentration and temperature profiles were computed together with the corresponding flow average values. The results showed that under adiabatic reaction conditions, radial concentration and temperature profiles were greatly affected by both reaction conditions and flow model with the heat of reaction group, G4, having the most significant effect. It was also observed that large radial diffusion effects could significantly influence overall conversions. In the CWT reactor, curves were found to show a characteristic maximum which were again highly dependent on G4. It was found that in a CWT reactor, radial temperature variation could be expected even in plug flow and under laminar flow conditions, large G4 values increased conversions over those calculated for plug flow conditions. Inlet concentration effects were noted for both the adiabatic and the CWT reactors with reaction kinetics significantly affecting reactor performance. Experimental runs were carried out on a vertical reactor 250 cm. long and 1.865 cm. I.D. The inlet acetic anhydride concentration ranged from 0.291 to 1.470 mole/ℓ and the Reynolds number from 88 to 346. Temperatures varied from 25.57 to 38.91°C and the average velocity from 0.402 to 1.316 cm/sec. The reactor was operated under adiabatic and constant-wall-temperature conditions. Temperature rises were limited to 7°C in accordance with the assumptions formulated in theoretical models. Experimental results indicated that radial temperature profiles tended to be flat but showed some difference between the wall temperature and the centreline temperature compared to the value predicted by the plug flow model. The laminar flow model gave the closest agreement with experimental results. Six causes are possible for the observed difference between experimental and predicted results. However, the presence of acetic acid is considered to be the most influential.