Plantwide Control of a Biodiesel Process by Reactive Absorption

Integrated biodiesel processes based on reactive separations powered by solid acid/base catalysts are available nowadays, offering significant advantages such as minimal capital investment and operating costs, as well as no catalyst-related waste streams and no soap formation. However, the controllability of the process is just as important as the capital and operating savings. In such processes the small number of degrees of freedom is a drawback which makes it difficult to set the reactants feed ratio correctly and consequently to avoid impurities in the products. This work considers the process control of biodiesel production by reactive absorption, the main result being an efficient control structure that ensures the stoichiometric ratio of reactants. Moreover, the excess of methanol operating constraint that is necessary for the total conversion of the fatty acids and for prevention of the difficult separations is fulfilled. Rigorous simulations were performed using Aspen Plus and Aspen Dynamics as efficient computer aided process engineering tools.