The application of renewable feedstocks, derived from biomass or biological sources, and their efficient processing are crucial in the development of novel technologies for biofuels production. Among the various bio-based,... [ view full abstract ]
The application of renewable feedstocks, derived from biomass or biological sources, and their efficient processing are crucial in the development of novel technologies for biofuels production. Among the various bio-based, renewable fuel options, biodiesel is fast emerging as the most popular and sustainable option for replacing oil based energy and other fossil fuels. Biodiesel, apart from being non-toxic and biodegradable, offers several environmental benefits such: i) a drastic reduction of CO2 emissions compared to fossil fuel, that is the main cause of global warming, ii) lower sulfur and aromatic content, and iii) safety (higher flash point 150°C). Furthermore, their combustion properties are similar to petroleum based diesel and the integration into the existing infrastructure of fossil fuels is easy. Chemically, biodiesel in a mixture of fatty acids alkyl esters (FAAEs), which are formed via esterification of vegetable oils having high free fatty acids; water is produced as a side product in this reaction.
In this work, the esterification of oleic acid with methanol is studied in a stirred tank chemical reactor (CSTR). Since H2SO4 shows high reaction rates and good economics, it is chosen to represent the homogeneous catalyst in this study. In order to develop a realistic design of the reaction unit it is essential to analyze an equation of state (EOS) able to correlate and predict the phase equilibria of several systems of interest in this field. Therefore, the design is based on a molecular model that considers the computation of thermodynamic properties of the ternary phase diagrams. Alongside established tools such as thermodynamic analysis, rigorous simulations of the CSTR were performed using a well-known process simulator, ASPEN PLUS. Methyl oleate as a model compound representing the biodiesel and a simple kinetic expression, were assumed as part of the design specifications. Additionally, the PC-SAFT EOS is used to calculate the phase equilibrium in order to thoroughly understand the esterification reaction pathway for biodiesel production
From preliminary results, we found that the conversion of the free fatty acid depends strongly of the molar methanol to oleic acid ratio. Besides, the reaction time has a direct effect on the conversion of the free fatty acid, i.e., the conversion decreased due the reaction temperature rise. The CSTR was able to handle more than 1% wt of fatty acid contents in the vegetable oil. However, the results showed that the amount of fatty acids in the vegetable oil feed plays an important role on the performance (mainly methanol flowrate) of the esterification process. As a conclusion, in order to obtain more reliable simulation results (even with the molecular thermodynamic model, i.e., PC-SAFT EOS), it is necessary to overcome the uncertainties about the thermodynamic properties predicted by molecular simulation.
