KINETICS MODELING OF FATTY ACID ESTERIFICATION USING ION EXCHANGE RESIN CATALYST IN THE BIODIESEL PRODUCTION

Fossil-fuels is being depleted to date. Therefore, a global movement toward the generation of renewable energy is in progress to meet energy needs. Among the various alternative energy resources, biodiesel has been receiving increasing attention due to its advantages. Conventionally, biodiesel is produced by transesterification of triglycerides by homogeneous alkaline catalysts. However, such process is not suitable for the feedstocks that contain high amount of free fatty acids (FFAs). FFAs will react with the alkaline catalysts, forming soap by-products and deactivating the catalyst. It accordingly causes problems of product separation and lower the biodiesel yield. To overcome this problem, a 2-steps process involving fatty acid esterification and subsequent alkaline-catalyzed transesterification have been applied.

Esterification by acid catalyzing is a common method of producing biodiesel from high FFA oil. Homogeneous acidic catalysts usually gives high conversion. However, it has drawbacks in terms of selectivity, equipment corrosion, and difficult separation of catalyst from the products. Hence, heterogeneous acid catalysts have been studied as substitutes since it is easy to recover and reuse, and compatible with environmental considerations. One of the solid catalysts is ion-exchange resin, which has good properties and high esterification efficiency. Considering the significance of this esterification step in the biodiesel production process, the kinetics modeling of the heterogeneous esterification of fatty acid over an acidic ion-exchange resin was investigated in this work. The experimental data of the esterification reaction of lactic acid with ethanol was used for validation.

Different kinetics models taking into account both the ideal and the non-ideal solution assumption have been developed to represent the kinetic behaviors of heterogeneous esterification. The models studied in this work were Eley-Rideal (non-ideal-solution assumption), Modified Langmuir-Hinshelwood (ideal and non-ideal-solution assumption), Langmuir-Hinshelwood-Hougen-Watson (ideal and non–ideal-solution assumption) and Quasi-Homogeneous (ideal and non-ideal-solution assumption) Models. For the non-ideal approach, the activity coefficients were obtained based on the UNIFAC model. It was found the Modified Langmuir-Hinshelwood Model taking into account the non-ideal-solution assumption gives the best representation for the kinetic behavior of the lactic acid esterification over acid ion-exchange catalyst. A good agreement between the experimental data and the model has been obtained.