Producing ethylene oxide releases millions of tons of carbon dioxide every year. Researchers at CEBC are working to clean up this chemical’s big carbon footprint.
Ethylene oxide, or EO, is an industrially important chemical intermediate. Most EO is used to make ethylene glycol, or anti-freeze, for cars. EO is also used to make plastic soda bottles. Eighteen million tons of EO are manufactured every year, with that number rising by 4 to 6 percent annually. Methods for producing EO have improved significantly over the years. But the process of making it stills puts out more carbon dioxide than most other manufactured chemicals.
EO is currently made at high temperatures with a silver catalyst. It gets so hot that some of the ethylene and ethylene oxide burn, releasing about 4 million tons of carbon dioxide into the atmosphere each year worldwide. That is about what 900,000 cars release each year.
CEBC researchers have developed a new way to produce EO without making carbon dioxide. The approach is called “Pressure Intensified Light Olefin Epoxidation.” It was first developed at CEBC for the conversion of propylene to propylene oxide. The reaction operates at moderate temperatures and pressures (40°C, ~50 bars). This forces gaseous ethylene to dissolve in a methanol solution. Aqueous hydrogen peroxide and a Lewis acid catalyst are also present. The catalyst transfers an oxygen atom from hydrogen peroxide to ethylene. The result: ethylene oxide. There’s no heating or burning, so there’s no carbon dioxide waste.
Oxygen gas is the usual oxidant to make EO. Although cheaper, combining it with ethylene oxide can be explosive. The use of hydrogen peroxide eliminates contact between ethylene, EO and oxygen gas and makes the process "inherently safer". Using it means avoiding accidents instead of managing them.
More research will be needed to find out if this “greener” technology is economically attractive to the chemical industry. The Center is giving this process high priority because of the potential for eliminating ethylene oxide’s “Bigfoot-sized” carbon footprint.
More technical information may be found in recent publications shown below:
1. Lee, H-J.; Shi, T-P.; Busch, D.H.; Subramaniam, B. "A Greener, Pressure Intensified Propylene Epoxidation Process with Facile Product Separation," Chemical Engineering Science 2007 62 7282-7289.
2. Lee, H-J.; Ghanta, M.; Busch, D.H.; Subramaniam, B. "Towards a CO2-Free Ethylene Epoxidation Process: Homogeneous Ethylene Epoxidation in Gas-Expanded Liquids," Chemical Engineering Science 2009 in press.