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Biodiesel production can be accelerated with new type of catalyst

The more sustainable production of biodiesel has been widely studied on different research fronts. A study published in the journal ACS Applied Nano Materials brought promising results when applying carbon nitrides as catalysts for the reaction that transforms vegetable oils into biofuel.

Biodiesel is one of the alternatives to the use of fossil fuels and can be produced by different processes, such as transesterification, thermal cracking or pyrolysis and microemulsion. Transesterification is the most common, as it is efficient and more easily controllable. In this production method, the triglycerides in vegetable oil react with an alcohol in the presence of a catalyst.

In the work, seven different types of carbon nitride-based nanomaterials were tested, characterized by various techniques, to verify their structural and morphological properties. The catalytic tests verified the effectiveness of the transesterification of canola oil for the production of biodiesel – a reaction that can occur without a catalyst, but both the quality of the biodiesel produced and the reaction time are improved with the use of these agents.

“We modified a series of carbon nitrides and discovered a correlation between the number of basic sites and their activity for the transesterification reaction. We demonstrated that they act as basic catalysts, a mechanism that was still poorly understood for these materials”, details Ivo Freitas Teixeira, professor in the Department of Chemistry at the Federal University of São Carlos (UFSCar) and one of the authors of the article.

The study also involved the Federal University of Minas Gerais (UFMG) and the Max Planck Institut, in Germany, and was supported by FAPESP both for the acquisition of equipment and for supporting Teixeira as a Young Researcher. “Our group has been investigating these materials for a few years and we have developed methods to modulate their surface, in order to allow them to behave as acidic or basic catalysts. Acid and basic catalysts have a series of applications, including use in the reaction to produce biodiesel from vegetable oils”, explains Teixeira.

Tests and evaluations

Multiple reaction parameters were evaluated to determine the ideal conditions and the required amount of catalyst in order to obtain the highest possible biodiesel conversion. Finally, the use of LiK-PHI (carbon nitride with lithium and potassium cations) showed the best performance, with 94% yield in the transesterification of canola oil.

Teixeira points out that, in most cases, the reaction to convert vegetable oils into biodiesel uses sodium hydroxide as the basic catalyst, but, as it is homogeneous, it is not recovered at the end of the reaction and still requires a pH adjustment step. Replacing sodium hydroxide with a heterogeneous catalyst, that is, one that does not solubilize in the medium, avoids the pH adjustment phase, in addition to allowing it to be recovered so that it can be reused. This reduces the cost of producing biodiesel. Furthermore, these carbon nitride-based materials are essentially composed of carbon and nitrogen, which are also low-cost.

“Although still very preliminary, our work has shown that carbon nitrides have great potential to be applied as catalysts in the production of biodiesel. As these materials are solid and do not solubilize under the reaction conditions, by applying a simple centrifugation we were able to separate them at the end of the reaction and reuse them. Furthermore, the biodiesel obtained was within the required specifications, not requiring any post-treatment, such as, for example, pH adjustment. We believe that, in the future, replacing homogeneous catalysts with heterogeneous catalysts can simplify the biodiesel production process and reduce costs”, details Teixeira.

The work paves the way to explore the performance of different materials for more sustainable and efficient fuel production. However, one caveat is that, although there is no high cost associated with producing the catalyst in a laboratory environment, on an industrial scale there may be increased costs. Thus, the group recognizes the need for more work on technical and economic feasibility.


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