PRESS RELEASE (2024/09/09)

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Microwaving waste cooking oil into useful chemicals

Researchers develop a zeolite catalyst that can be heated up using microwaves to speed up
the conversion of fatty acid esters to olefins
Fukuoka, Japan—Researchers from Kyushu University have revealed that a zeolite material
called Na-ZSM-5 is effective in improving the chemical conversion of biomass into olefins—aprecursor chemical that makes everything from plastics to pharmaceuticals—usingmicrowaves. Publishing their work in Chemical Engineering Journal, the team explains thatmicrowave heating of Na-ZSM-5 could open doors to a more energy-efficient and sustainablechemical industry.
If you want to synthesize complex organic compounds, whether it be plastics,
pharmaceuticals, or food additives, you generally need to start with chemical precursors withsimple structures. Naturally, finding ways to efficiently and sustainably synthesize precursor
chemicals is an extensively researched field.
A commonly used method of synthesizing these essential chemicals is via a process calledreforming of naphtha. However, this process requires high amounts of energy and releases
carbon dioxide. Cooking oil waste and microalgal oils have been considered as alternative andinexpensive sources to synthesize said simple chemicals.
These oils can be converted using a method called ‘catalytic cracking’ with the help of amaterial called zeolite. Zeolite is a porous natural material, commonly used as a catalyst or as
an absorbent. In the catalytic cracking process, materials need to be heated up totemperatures as high as 500–600°C. In addition to being very energy intensive, operating at
such temperatures can cause a buildup of unwanted deposits, a phenomenon known as
coking, which reduces the lifetime of the catalyst.
In the present study, Associate Professor Shuntaro Tsubaki from Kyushu University’s Facultyof Agriculture and his team experimented with microwaves to heat zeolite catalysts to therequired temperature without the negative 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,”
explains Tsubaki. “In particular, microwaves can accelerate gas–solid catalysis by passing
straight through the gas phase and selectively heating the solid catalyst. They achieve this byforming spatial hot spots inside the catalyst bed.”
In their study, the researchers first compared various zeolite catalysts, looking for the ones
that could be effectively heated by microwaves and deliver good catalytic performance. Using
both theoretical and experimental analyses, they narrowed it down to Na-ZSM-5, a sodium
ion substituted zeolite.
Next, to showcase the advantages of microwave heating versus conventional heating, theresearchers performed a catalytic conversion of methyl oleate. When microwave heating wasused, Na-ZSM-5 outperformed other catalysts, achieving a high conversion efficiency of fatty

acid esters into olefins with high selectivity. Moreover, carbon dioxide production wassuppressed to only 1.3% of the total reaction output, and carbon monoxide was not produced
at all.
Most importantly, microwave heating of Na-ZSM-5 to 500°C resulted in four times higher
olefin production compared to conventional heating to 500°C. This was in part caused by ahigher selectivity of Na-ZSM-5 to produce olefins instead of other compounds. Moreover, coke
formation was not observed when microwave heating was used, even at the hightemperature of 600°C.
Finally, to shed light on why microwave heating improved upon various aspects of thecatalytic process, the researchers analyzed the local structural changes in the zeolite when
exposed by microwaves. Interestingly, they found that microwave absorption caused localizedtemperatures of over 1000°C in the zeolite’s crystal lattice, even as the temperature of thebulk material remained at 500°C. These extreme temperatures were likely responsible fordriving the selective production of olefins.
Microwave heating of catalysts could significantly improve catalytic biomass conversion andhelp in achieving the sustainability goals of the modern chemical industry.
“Our findings are expected to contribute to the further electrification of the chemical industry.
Since microwaves can be generated from renewable energy sources such as solar and wind,
we can reduce the environmental impact of the synthesis of these fundamental chemicals,”highlights Tsubaki.
The researchers are planning on further enhancing microwave-driven catalytic processes,
seeking to improve yield and energy efficiency while scaling up their capacity. They hope
their efforts could lead to a new era in sustainable chemical manufacturing.
###For more information about this research, see “Microwave-enhanced catalytic conversion offatty acid ester to olefins by Na-ZSM-5”, Shunsuke Ota, Jun Fukushima, Ken'ichi Kimijima,Masao Kimura, Noriyuki Igura, Noriyasu Tezuka, Takashi Sato, Hisahiro Einaga, and Shuntaro
Tsubaki, Chemical Engineering Journal, https://doi.org/10.1016/j.cej.2024.154737.
About Kyushu UniversityKyushu University is one of Japan's leading research-oriented institutes of higher education
since its founding in 1911. Home to around 19,000 students and 8,000 faculty and staff,
Kyushu U's world-class research centers cover a wide range of study areas and research
fields, from the humanities and arts to engineering and medical sciences. Its multiple
campuses—including one of the largest in Japan—are located around Fukuoka City, a coastal
metropolis on the southwestern Japanese island of Kyushu that is frequently ranked among
the world's most livable cities and historically known as Japan's gateway to Asia. Through its
Vision 2030, Kyushu U will 'Drive Social Change with Integrative Knowledge.' Its synergistic
application of knowledge will encompass all of academia and solve issues in society while
innovating new systems for a better future.

Fig. 1. Design and performance of the
proposed microwave-heatable catalyst.
Researchers from Kyushu University usedmicrowaves to heat up a sodium-substitutedzeolite catalyst, Na-ZSM-5, so that it could
more efficiently convert biomass to usefulindustrial precursor chemicals. without
harmful side effects. (KyushuUniversity/Shuntaro Tsubaki)[Contact]
Shuntaro Tsubaki, Associate Professor
Department of Bioscience and Biotechnology, Faculty of Agriculture
Tel: +81-92-802-4805
E-mail: stsubaki@agr.kyushu-u.ac.jp