Modelagem e simulação CFD de reações de transesterificação em tanques com agitação mecânica

Abstract

Alcohol and triglycerides do not form a single phase mixture and thus there is a poor surface contact between them causing transesterification to proceed relatively slow. Introduction of stirring improves the surface contact and consequently the reaction rates and biodiesel yields. Thus, in industrial processes, transesterification is usually carried out in stirred tank reactors. Investigating how this type of reactor works is necessary for successful design, operation and optimization. Experimental methods for investigating flow-fields and chemical reactions are expensive and time demanding and cannot meet this challenge accurately. An alternate way is to model and simulate stirred tanks by computational fluid dynamics (CFD). Thus, in this work, CFD simulations of transesterification inside stirred tanks were performed, with source terms of generation and consumption of the mixture components being the reaction rates evaluated by solving a set of differential equations describing the transesterification process kinetics. The concentration-time profiles for the expected components were in accordance with the experimental data that originated the kinetic models, and the mass fraction patterns inside the tank showed efficient mixture. More accurate results would be achieved by using experimentally obtained reactions rates for each specific vegetable oil. Considerable influence of turbulence phenomena and impeller positioning on transesterification efficiency was verified. The impeller rotational speed, on the other hand, did not present significant influence on transesterification efficiency.