Biodiesel production through non-conventional supercritical routes: Process simulation and technical evaluation

Abstract

The conventional chemical route for biodiesel production is transesterification, which is carried out on industry via homogeneous alkaline catalysis. Although several alternative technologies have been studied to make transesterification more competitive, none of them, so far, has been interesting at commercial level. One of the drawbacks of transesterification is the generation of glycerol, which must be removed and whose excess demand makes it less profitable. Therefore, a possible solution would be to explore industrial processes that generate by-products other than glycerol, which could add value to the process. In this article, simulations of three “non-conventional” supercritical routes for industrial biodiesel production were carried out: interesterification with methyl acetate (Route 1); reaction with acetic acid followed by esterification with methanol (Route 2); and reaction with dimethyl carbonate (Route 3). As the main reactions occur at supercritical state, catalysts are not required and the purification steps are simpler than for the conventional technology. Routes 1 and 3 proved to be technically feasible. The first one consumes only 7.1–8.5% of the energy that will be produced as biofuel, while the second one consumes 8.8–10.4%. The incorporation of the by-products - triacetin and glycerol dicarbonate - in the final fuel was also evaluated and proved to be a possible alternative. Route 2, however, was not able to provide biodiesel meeting the specifications (high acidity), and demands three to four times more energy than the other routes. So, it cannot be considered technically feasible at this level and will require further development.