Chemists From St. Petersburg State University Create A Reusable Catalyst For Producing Biodiesel From Soybean Oil

Scientists from St. Petersburg State University have developed a new magnetic catalyst based on calcium oxide and proposed an optimal method for its recovery after the reaction. This research paves the way for more economical and environmentally friendly biofuel production technologies.

Biodiesel, produced from vegetable oils by transesterification, is one of the most promising types of renewable fuel. To increase the economic efficiency and environmental sustainability of production, it is essential to ensure the repeated use of substances that accelerate the reaction, thereby reducing costs and the volume of waste generated.

In practice, however, the regeneration and reuse of such materials remain challenging. In scientific research, different recovery methods are often applied to different compositions, which makes it difficult to assess the effectiveness of the methods themselves in an objective manner.

The experts from St. Petersburg State University created a new magnetic composition from industrial waste and, through experimentation, identified the most effective regeneration method for it. For the first time, the researchers conducted a direct comparison of the three main recovery methods—filtration, centrifugation and magnetic extraction—for the same sample under identical biofuel production conditions. This approach made it possible to identify the optimal method for preparing the material for industrial use.

We solved two key problems simultaneously: we created an inexpensive composition from production waste and, equally importantly, identified an optimal regeneration method for it. Our experiments demonstrated that, for such systems, vacuum filtration ensures maximum preservation of the active component and a high product yield, while magnetic extraction proved to be the least effective method. - Konstantin Rodygin, a co-author of the study, Associate Professor in the Department of Organic Chemistry at St. Petersburg State University

The scientists synthesised a new magnetic system based on calcium oxide (CaO) and magnetite (Fe_₃O_₄), using carbide slag—a cheap and readily available industrial waste product from acetylene production—as the raw material. They then conducted a series of experiments on biodiesel production from soybean oil. The same material was used in all experiments, but it was recovered using different methods: magnetic extraction, centrifugation, and vacuum filtration.

After each cycle, the researchers determined the yield of the final product as well as the mass of the active composition preserved for subsequent use.

Additional analysis showed that the active phase of the catalyst irreversibly transforms into less active compounds, such as calcium hydroxide and calcium diglyceroxide, during the reaction, regardless of the extraction method. This explains the overall decrease in activity; however, it is the method used to separate the catalyst from the mixture that determines the rate at which it is physically lost.

The experiments revealed significant differences between the recovery methods. Magnetic extraction was the least effective: after five cycles, the loss of the active component reached 72% and the biodiesel yield decreased to 84%.

Centrifugation demonstrated moderate effectiveness. By the fifth cycle, approximately 67% of the material was returned to the process, but its activity declined and the biofuel yield fell to 82%.

Vacuum filtration produced the best results, providing an optimal balance between preserving the active phase and maintaining process stability. By the fifth cycle, up to 81% of the working composition mass was preserved and the biodiesel yield remained high, at around 90%.

The study was conducted at the resource centres of the St. Petersburg State University Research Park.