Turning Cooking Oil Into Useful Chemicals Using Microwaves

Researchers at Kyushu University have demonstrated that a zeolite material, Na-ZSM-5, can enhance the chemical conversion of biomass into olefins—a key precursor in the production of plastics, pharmaceuticals, and other products—by using microwave heating. Their study, published in the Chemical Engineering Journal, suggests that this method could provide a more energy-efficient and sustainable approach to chemical manufacturing.

Current methods for synthesizing precursor chemicals, such as the reforming of naphtha, are energy-intensive and result in significant carbon dioxide emissions. In contrast, the use of waste oils, like cooking oil and microalgal oils, offers a more sustainable alternative. However, these oils require a process called catalytic cracking, typically using zeolite catalysts, to be converted into simpler chemicals. This conventional process requires temperatures of up to 500–600°C, which not only consumes a large amount of energy but also results in unwanted deposits, or “coking,” that reduce the catalyst’s lifespan.

The research team, led by Associate Professor Shuntaro Tsubaki of Kyushu University’s Faculty of Agriculture, explored the use of microwave heating as an alternative to conventional methods. Unlike traditional heating methods, microwaves directly interact with materials, providing targeted energy delivery. This approach can reduce energy consumption and enhance gas-solid catalytic reactions by selectively heating the catalyst material.

The researchers tested several zeolite catalysts to identify those that could be effectively heated by microwaves while maintaining high catalytic performance. Their analysis identified Na-ZSM-5, a sodium ion substituted zeolite, as a particularly effective catalyst for this purpose. In experiments comparing microwave heating with conventional heating, Na-ZSM-5 showed superior performance, achieving high conversion efficiency of fatty acid esters into olefins while minimizing carbon dioxide production.

Importantly, the study found that microwave heating resulted in four times higher olefin production than conventional heating, even at the same temperature of 500°C. Moreover, the microwave process did not lead to coke formation, even at temperatures as high as 600°C. This improvement was attributed to the creation of localized hot spots within the zeolite’s structure, with temperatures exceeding 1000°C, while the bulk material temperature remained at 500°C. These localized high temperatures likely contributed to the selective production of olefins.

The researchers suggest that microwave heating could play a significant role in making chemical processes more sustainable by reducing energy consumption and emissions. This method aligns with the broader goals of the chemical industry to reduce its environmental impact by relying more on renewable energy sources.

The team plans to continue refining microwave-driven catalytic processes to further improve efficiency and scalability, potentially ushering in new, more sustainable practices in chemical manufacturing.