Abstract
The use of residual oils as raw materials to produce fatty esters in the biodiesel industry is of great interest, as it may improve both the economic and environmental aspects of a process. The use of these residual materials in biofuel production can aggregate value to something that would otherwise be solely disposed of and, as they have lower costs related to the refined oil, its use could reduce operating costs in the industry. However, these resources usually present high free fatty acid (FFA) content. Therefore, considering the traditional biodiesel production process, these fatty acids must be removed before entering the transesterification reactor due to soap formation, which reduces the reaction yield. As a result, to remove these FFA, one of the most common procedures is through the inclusion of a previous step, the esterification reaction. In both esterification and transesterification, short-chain alcohols are generally used to promote FFA and triglycerides conversion into long-chain esters. Concerning the influence associated with the choice of different alcohols, there is a wide variety of process analyses presented in the literature focusing on using only one type of alcohol, usually methanol or ethanol, in both reactions. Nevertheless, the study of a biodiesel production process evaluating the possibility of using the two alcohols at distinct parts in the process is a significant gap to be filled. In this study, an in-depth analysis of the esterification and transesterification reaction kinetics using methanol and ethanol was carried out as a possible optimization variable. In addition, the process simulation concerning the use of different alcohols for each reaction was performed. Several conditions were tested in both reactors before the final alcohol selection, and the use of methanol in the esterification and ethanol in the transesterification reaction presented the most promising results, indicating that a hybrid process concerning alcohol use may bring significant advantages to the process. To validate this theory, a complete process and economic analysis were carried out, evaluating not only the results obtained from the reaction but also the purification steps. Another essential aspect considered in the project is the fatty acid content in the oil, which may vary according to storage conditions and prior use. Thus, the impact due to this fluctuation in the economic aspects was verified. With the simulated base project, different optimizations were made to reduce the entire process's equipment and operational costs. An energy analysis was also developed with the inclusion of energy-saving heat exchangers, which reduced utility costs. Finally, an economic evaluation of the final process was obtained to assess the main variables affecting the project and its payback time. It is essential to say that the kinetic study was based on the content present in the literature, and the simulation was performed on the software Aspen Plus® V10, including the energy and economic analyses. Considering the importance of optimizing the industrial process for biodiesel production and improving its economic aspects, the main target of this study is to demonstrate how the use of different alcohols for the esterification and transesterification reactions may enrich these previously reported vital aspects.
