In December 2024, the Pacific Northwest National Laboratory (PNNL; Richland, Wash.; www.pnnl.gov) announced a three-year collaborative project with vehicle-tire manufacturer Bridgestone (Tokyo, Japan; www.bridgestone.com) to scale up a thermocatalytic process for converting renewably derived ethanol to n-butene.
Conventionally, n-butene is produced from petroleum-based feedstocks using energy-intensive cracking of large hydrocarbons. The PNNL process, using a catalyst PNNL researchers first conceived in 2018, could lower the energy requirements for n-butene production compared to the conventional process, and allow the use of renewably derived n-butene as a starting material for multiple commercial processes, including those for tires (styrene-butadiene), as well as other synthetic rubbers, plastics and diesel and jet fuels.
After advancing the catalyst over the past few years, PNNL partnered with Bridgestone to scale up and pilot the catalysis process using $10 million in funding from the U.S. Dept. of Energy’s Industrial Efficiency and Decarbonization Office. Bridgestone plans to build a pilot plant for the process in Akron, Ohio.
The PNNL catalytic process has shown the ability to convert ethanol to n-butene at high rates and with high yields. A highly active, multifunctional catalyst comprising silica as a support material, with silver nitrate powder and zirconium nitrate as the catalytic material, enables a single-step conversion process (diagram). The catalyst, together with the process, generates n-butene with greater than 90% ethanol conversion and greater than 60% selectivity (byproducts are predominantly other olefins), PNNL says.
The process works by removing hydrogen from ethanol molecules, creating acetaldehyde. Formation of carbon-carbon bonds follows to produce crotonaldehyde, which occurs in a variety of foods, like soybean oils. The crotonaldehyde is then converted to crotyl alcohol, which undergoes dehydration, resulting in butadiene. Butadiene then is selectively hydrogenated to n-butene. A more recent catalyst formulation produces n-butene through butyraldehyde instead of butadiene intermediate, PNNL says. This new catalyst formulation produces three times less coke, leading to significantly improved catalyst stability, PNNL says.
Catalyst regeneration has been demonstrated, the laboratory adds. The technology is available for licensing.