Reactive separation processes applied to biodiesel production: phase equilibrium, design, optimization and techno-economic assessment

Abstract

Reactive separation processes (RSP) have been widely studied, since companies have looked for ways to reduce costs, environment impacts and loss of energy. As a result, the keyphrase has been “produce more with less being sustainable”, so that process intensification have received more attention. Among these processes, reactive distillation column (RDC) and catalytic distillation column (CDC) for homogeneous and heterogeneous catalyzed processes have been applied to develop more economical processes as well as increasing performance of equilibrium reactions as found in biodiesel production. For this reason, many studies from RDC and CDC applied to equilibrium-limited esterification and transesterification reactions have been developed. In addition, an alternative process of biodiesel production by free fatty acids (FFA) separation from residual oil and fats (ROF) showed to be more economical feasible than conventional processes. Despite this, there is no economic investigation of RDC in this alternative route. Moreover, few studies evaluated the possibility to produce biodiesel by both reactions simultaneuosly using a solid acid-catalyzed (SAC) route in a CDC. This SAC process can result in cheaper biodiesel since low-cost ROF can be used with less number of equipment and use of alcohol. On the other hand, other cheap feedstock as crude tall oil (CTO) can be used to produce biodiesel from esterification reaction by CDC. In addition, from RDC and CDC studies, absence of a phase equilibrium (PE) modeling for biodiesel reaction systems was detected. Furthermore, few simulation studies of RDC and CDC made comparisons with experiments to validate the results. For all these reasons, this work was proposed in order to investigate innovative RSP applied for biodiesel production from ROF and CTO and to develop a PE modeling for the components involved. Firstly, two processes based on optimized FFA separation from ROF were investigated including a set of reactor/distillation column and a RDC. Both processes presented similar economic results. Secondly, thermophysical properties for acylglycerols were estimated. PE databanks were built and a modeling involving components from biodiesel reactions was proposed using the Non-random two-liquid (NRTL) model. A validation based on simulation of experiments was also carried out. Thirdly, three SAC processes were investigated based on: simultaneous esterification and transterification reactions using a CDC and a catalytic absorption column (CAC); and a hydro-esterification process. CDC and CAC processes were more economical and enviromentally friendly. CDC was the optimal process. A global optimization and a final design for CDC process were proposed. Finally, a SAC process for biodiesel production from CTO was developed. A base case and an alternative process for CTO purification from three and four distillation columns, respectively, were investigated. The alternative process was the unique techno-economic feasible and was evaluated for biodiesel production by SAC process using a CDC and a catalytic divided-wall column. CDC process was the unique technically feasible. This was globally optimized and flexibilized. Therefore, RSP proved to be useful unit operations to obtain more economical and eco-friendly biodiesel production processes.