U develops new chemical manufacturing technique

by Andy Skemp

What do plastic, polyester and antifreeze all have in common? Winter car maintenance in the ’70s is a possible answer, but a chemical engineer might feel that “ethylene” is a better reply.
Today’s issue of Science magazine reported on a new ethylene manufacturing technique developed at the University. The method, called partial oxidation, was co-authored by University chemical engineering and material sciences professor Lanny Schmidt, who also acted as an adviser for students working on the project.
Ethylene, made from ethane gas, is one of the most heavily produced chemical compounds in the world. Annual U.S. production of ethylene is approximately 50 billion pounds, worth more than $10 billion.
Large chemical manufacturing companies have already shown serious interest in the new technique.
Schmidt said that the capabilities of the new method “look promising,” and a patent has been requested.
The new method would lessen production costs and the size of facilities that produce ethylene.
The new partial oxidation technique is about 1,000 times faster than the steam cracking method currently used by most producers.
Partial oxidation does its job in a catalytic reactor tube less than 1-inch long, rather than 300-foot reactor tubes presently used by the industry.
Another advantage of partial oxidation is the lack of environmentally unfriendly by-products brought about by the ethylene-producing reaction.
Steam cracking by-products include oxides of nitrogen, a precursor to acid rain, and carbon dioxide, element that is believed to be a contributor to the greenhouse effect.
A major hindrance to the industry’s immediate implementation of the partial oxidation method is cost.
“The main barrier to using this process is the capital involved in building an ethylene manufacturing facility,” said David Olschki, a third-year chemical engineering doctoral candidate who authored a computer simulation of the reaction that creates ethylene in the new process.
“Steam cracking facilities are extremely expensive to construct, so companies won’t want to stop using the ones they have,” said Ashish Bodke, who graduated last spring with a University doctorate in chemical engineering.
Bodke was the third doctoral candidate to take over the project.
By the time he started in 1997, seven years after the study had begun, the platinum-tin catalyst was already in use. It was Bodke’s idea to add hydrogen to the oxygen and ethane already being used in the reaction.
Bodke said many of his colleagues thought this explosive combination was too dangerous. “They were really worried. They told me not to do it,” he said.
In the new method, the gases are heated to about 950 degrees Celsius, 150 degrees hotter than steam cracking. This temperature causes an explosion when hydrogen and oxygen are mixed.
Bodke hypothesized that he would be able to add hydrogen to the oxygen and ethane because the tin in the platinum-tin catalyst would absorb enough heat to eliminate any danger of explosion.
After cautiously testing his hypothesis, Bodke found he could safely convert ethane to ethylene at a rate as good as and better than steam cracking.
“It’s really beautiful,” Bodke said after explaining his discovery on Wednesday.
Bodke now lives in California, doing research to improve computer chips at Applied Materials in Santa Clara.