New Route To Adipic Acid Avoids Nitrous Oxide Production
 | December 22, 2014 Issue - Vol. 92 Issue 51 | Chemical & Engineering News
Volume 92 Issue 51 | p. 6 | News of The Week
Issue Date: December 22, 2014 | Web Date: December 18, 2014

New Route To Adipic Acid Avoids Nitrous Oxide Production

Synthesis: Process provides another option for making nylon precursor without production of potent greenhouse gas
Department: Science & Technology
Keywords: adipic acid, nitrous oxide, oxidation, ozone, green chemistry

A new route to adipic acid that uses ozone and ultraviolet light to eliminate the problematic nitrous oxide by-product has researchers intrigued. But once again, issues of scale-up and safety with a greener route to this chemical intermediate—used to make nylon, polyurethane, and plasticizers—temper the good news.

Right now, 95% of the world’s adipic acid production uses nitric acid as an oxidant, which releases N2O as a by-product. The gas eats away at Earth’s protective ozone layer and ranks behind only carbon dioxide and methane when it comes to greenhouse gas emissions. Some producers trap and destroy N2O, and emissions have been cut in half since 1990. But significant emissions remain.

Chemists have been exploring N2O-free routes to adipic acid for years by using O2 or H2O2 or employing enzymes. These methods tend to be more energy efficient, have better yields, and avoid corrosion problems from using nitric acid, but none has yet proven to be economical on a large scale.

Kuo Chu Hwang and Arunachalam Sagadevan of Taiwan’s National Tsing Hua University have developed an approach that uses ozone and UV light at room temperature and pressure (Science 2014, DOI: 10.1126/science.1259684).

Ozone and UV light may be more economical than other routes. But using them as “reagents” is potentially problematic from a commodity-scale perspective, says Thomas Boussie, cofounder of Rennovia. His company is developing a commercial process to make N2O-free adipic acid from glucose using an O2 (air) oxidation process coupled with a hydrogenation step.

Using ozone in organic oxidations can potentially form explosive organic peroxides, Boussie notes. Technical issues of efficient light penetration into large reactors also raise a red flag, he adds. “This paper reports an intriguing laboratory synthetic method,” Boussie says, “but it is one that would encounter significant hurdles scaling to an industrial process.”

Hwang doesn’t view those challenges as insurmountable. Any organic peroxides formed are short-lived, he says, and the engineering of photochemical reactors is improving with LED lighting. “We are optimistic,” Hwang says.

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Paul Eckler (December 22, 2014 1:42 PM)
What about Monsanto's electrodimerization of acrylonitrile, invented abt 1980. This produces Nylon 66 raw materials from natural gas rather than from oil. And what about Dupont's process for addition of HCN to 1,3-butadiene? It's surprising that cylohexane is the raw material for adipic acid in these times.
Steve Ritter (December 31, 2014 10:18 AM)
Thanks for your comment Paul. True, the Monsanto and DuPont nylon processes do not involve adipic acid. Most of the concern for nitrous oxide emissions seems to be nitric acid production and use, such as producing adipic acid. Much (maybe most, I can't confirm) nylon 6,6 is made from hexamethylenediamine and adipic acid. Nitric acid oxidation of cyclohexane accounts for about 95% of the worldwide adipic acid production and as a result is also responsible for as much as 8% of the annual worldwide emissions of nitrous oxide, according to references in the Science paper. Also, it's not clear that the Monsanto and Dupont processes don't also give off nitrous oxide emissions as well.

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