Making propylene directly from ethanol

Propylene is one of the most essential petrochemical feedstocks, used to make high-volume chemicals such as acrylonitrile, propylene oxide, and polypropylene. The three-carbon monomer is produced mostly through naphtha cracking at petrochemical plants and fluid catalytic cracking in petroleum refineries. In both cases, fossil fuels are the main raw material.

Sumitomo Chemical is developing a new technology to produce propylene directly from ethanol. Ethanol is now made mainly from crops such as sugarcane and corn, but Sumitomo points to methods emerging to make the alcohol from waste plastics, household waste, or carbon dioxide. Making propylene from such ethanol would fit with the Japanese firm’s goal to be carbon neutral by 2050.

With carbon neutrality in mind, Sumitomo installed a pilot facility at its Chiba, Japan, site in 2022 that produces ethylene, a two-carbon chemical, from ethanol using technology from the French engineering firm Axens. Now Sumitomo is developing its own technology to produce propylene from the alcohol.

The roots of the technology go back to 2008, when Sumitomo participated in a project funded by Japan’s New Energy and Industrial Technology Development Organization to foster use of biobased raw materials. Sumitomo’s focus was on catalysts that can drive the ethanol-to-propylene (ETP) conversion. During the 5-year project, company researchers discovered a metal catalyst that aided the conversion, and they verified the approach at the bench scale.

This project ended in 2013, and Sumitomo halted its R&D. But almost 10 years later, heeding its new mandate to decarbonize, the firm has resumed work. One sweetener to restart was that the program was selected in 2022 to receive funding from the $13.8 billion Green Innovation Fund established by Japan’s Ministry of Economy, Trade, and Industry. The fund will subsidize two-thirds of the firm’s R&D for the project and one-half its cost of building a pilot facility.

At present, Sumitomo says, propylene is produced from ethanol in a three-step process: ethanol is dehydrated to ethylene; ethylene is dimerized to 2-butene; and 2-butene is converted to propylene through a metathesis reaction with ethylene. In fact, Sumitomo already practices the second two steps at its Singapore-based subsidiary, Petrochemical Corporation of Singapore.

In contrast, the ETP technology that the firm is now developing is a single-step process “in which ethanol is converted to propylene through various catalytic reactions,” says Yohei Kashiwame, deputy manager of the firm’s Research Planning and Coordination Department. The process also yields by-product hydrogen.

Other research groups have hit on the same idea. Wei Xia of the China University of Petroleum and colleagues published a paper in 2022 about a zeolite catalyst that converts ethanol to propylene, but the yield was only 19% (Nanomaterials, DOI: 10.3390/nano12162746). Kashiwame says that Sumitomo’s catalysts are much more efficient. “Our metal catalysts are completely different,” he says, “and we have confirmed that the propylene yields of our method are well over 50%.”

Sumitomo researchers think they can push the yield even higher and are “making improvements centered on metal selection and blending technology,” Kashiwame says. The company is constructing a pilot facility at its R&D center in Sodegaura, Japan. It aims to establish the technology in the first half of 2025 and put it into practice in 2028 or later. The number of researchers and engineers involved has reached several dozen, he says.

Because the ETP technology produces propylene directly from ethanol, commercial plants will be more compact and less expensive than ones built to accommodate multiple intermediates, Kashiwame says. “Metathesis will be the main technology for converting ethanol to propylene for the next few years,” he says. “However, if our technological development can guarantee economic superiority, we can make our ETP technology a mainstream technology to be adopted in new plants after 2030.”

To secure ethanol, Sumitomo has teamed up with Sekisui Chemical, a Japanese firm that uses microorganisms to convert municipal waste into ethanol. Sekisui developed the technology with the US firm LanzaTech and is running a demonstration plant in cooperation with a Japanese government–affiliated investment company. Sumitomo is using the ethanol from Sekisui as a feedstock in its ethanol-to-ethylene demonstration plant and may use it in the ETP process as well.

Katsumori Matsuoka is a freelance writer based in Japan.