Turning used cooking oil in a microwave into beneficial compounds

Researchers at Kyushu University have discovered that employing microwaves to enhance the chemical conversion of biomass into olefins—a precursor chemical used to create anything from plastics to pharmaceuticals—is possible with a zeolite material known as Na-ZSM-5. The team explains that microwave heating of Na-ZSM-5 could lead to a more sustainable and energy-efficient chemical industry in a paper published in the Chemical Engineering Journal.

Chemical precursors with simple structures are usually the first step in the synthesis of complex organic molecules, such as food additives, medicines, and polymers. It goes without saying that a great deal of study has been done in the area of efficiently and sustainably synthesizing precursor compounds.

One often employed technique for producing these necessary compounds is the reforming of naphtha. Nevertheless, this process emits carbon dioxide and uses a lot of energy. Microalgal oils and cooking oil waste have been proposed as low-cost alternatives for synthesizing these basic compounds.

Zeolite is a substance that can be used in a process known as “catalytic cracking” to convert these oils. Zeolite is a naturally occurring porous substance that is frequently employed as an absorbent or catalyst. Up to 500–600°C of heat is required for the materials to undergo catalytic cracking. Operating at such temperatures not only uses a lot of energy but also increases the risk of undesirable deposits building up, a process known as coking, which lowers the lifetime of the catalyst.

In the current work, Associate Professor Shuntaro Tsubaki of the Faculty of Agriculture at Kyushu University and his colleagues conducted microwave experiments to heat zeolite catalysts to the necessary temperature without causing side effects like coking.

“Microwaves interact directly with materials and can selectively deliver energy to them, enabling significant energy savings compared to conventional heat-convective processes,” says Tsubaki. Specifically, by going through the gas phase directly and heating the solid catalyst only, microwaves can speed up gas-solid catalysis. They do this by creating hot spots in certain locations throughout the catalyst bed.”

In order to identify the best zeolite catalysts for efficient microwave heating and successful catalysis, the researchers first examined a variety of zeolite catalysts. They identified Na-ZSM-5, a sodium ion substitution zeolite, by means of theoretical and experimental investigations.

The researchers then converted methyl oleate catalytically to demonstrate the benefits of microwave heating over traditional heating. Na-ZSM-5 performed better than other catalysts when microwave heating was applied, converting fatty acid esters into olefins with a high selectivity. Furthermore, just 1.3% of the reaction’s total output was created as carbon dioxide, and no carbon monoxide was formed at all.

Most notably, compared to conventional heating to 500°C, microwave heating of Na-ZSM-5 produced four times more olefin. This resulted in part from Na-ZSM-5’s increased selectivity for producing olefins rather than other chemicals. Furthermore, even at the elevated temperature of 600°C, no coke production was noted throughout the microwave heating process.

Finally, the researchers examined the local structural alterations in the zeolite upon exposure to microwaves in order to provide insight into why microwave heating enhanced certain parts of the catalytic process. It’s interesting to note that even though the bulk material’s temperature stayed at 500°C, they discovered that microwave absorption led to localized temperatures of over 1000°C in the zeolite’s crystal lattice.

Catalysts heated in a microwave could greatly increase catalytic biomass conversion and aid in the current chemical industry’s pursuit of sustainability.

Our research is anticipated to help the chemical sector become even more electrified. We can lessen the environmental impact of the synthesis of these basic compounds because microwaves may be produced using renewable energy sources like solar and wind,” emphasizes Tsubaki.

The goal of the researchers’ plans is to scale up the capacity of microwave-driven catalytic processes while simultaneously improving yield and energy efficiency. They believe that by working together, the production of sustainable chemicals may enter a new phase.

 

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