Biodiesel is an alternative diesel fuel made from renewable biological sources such as vegetable oils and animal fats. Its conventional production processes are mainly based on the use of homogeneous alkaline catalysts, which drive the transesterification of triacylglycerides with short-chain alcohols. The characteristics of the oils and fats used as feedstocks for conventional biodiesel production are among the most important aspects to consider. Low free fatty acids (FFA) content is necessary. If there is an elevated content of FFA in the feedstocks, a higher amount of the alkaline homogeneous catalysts is required to carry out the process, being partly lost for FFA neutralization. This neutralization is also a drawback considering the soap formation, which makes the downstream processing more complex. There are several ways to decrease high FFA content in oils and fats. One of them is based on the esterification of the FFA with the same alcohol that is going to be used later in the biodiesel production. This method of deacidification produces the same biodiesel that is provided by the main reaction of the complete process (i.e. transesterification of the oils and fats). Solid acid catalysts for esterification of FFA were synthesized using different methods. This kind of catalysts can be easily separated from the reaction mixture and be reused or regenerated. Silica and diatomite (being the latter a sedimentary rock composed of amorphous silica) were used as catalytic supports. Typically, catalysts were prepared as follows: 1) catalytic support preparation, which includes silica synthesis using sol-gel methods or purification of the diatomite, 2) modification of the support using a direct reaction of (3-mercaptopropyl)trimethoxysilane (MPTMS) with superficial sylanols or co-condensation processes of tetraethyl orthosilicate and MPTMS over its surface, 3) oxidation of the thiol groups of the surface modifier (MPTMS) followed by their protonation, producing sulfonic acids. The catalysts obtained were characterized using SEM-EDX, FT-IR, XRD, contact angle measurements of the pelletized materials, and acidity determination using acid-base back titration. The catalytic performance of these materials was tested analyzing their influence on esterification reactions of different types of carboxylic acids in presence of methanol under different reaction conditions. These esterification reactions were followed using 1H-NMR, FT-IR and acid-base titration.

Modified silicas as solid acid catalysts for esterification reactions: Convenient materials for deacidification of biodiesel feedstocks

249th National Meeting (2015)

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