Polyamides have been decomposed to ω-hydroxyalkanoic acid derivatives – important intermediates in the chemical industry – using supercritical methanol. This is one of the first methods for economical upgrading of polymers through the depolymerisation process.
Akio Kamimura and colleagues from Yamaguchi University and UIbe Industries Ltd., Japan, have developed a method to convert polyamides to valuable chemicals. Currently, recycling of plastics commonly involves converting the polymers back to their monomers. However, these methods are not always economically viable because they are often more expensive than other ways of treating waste plastics. By converting polymers to valuable chemicals, this would make polymer recycling a more attractive route and solve some of the economic problems.
In this study, by using supercritical methanol, Kamimura converted nylon-6 selectively to two valuable compounds – methyl 6-hydroxycapronate and methyl 5-hexenoate. Given that the average price for these ω-hydroxyalkanoic acid derivatives is about 6-7 times higher (per kg, based on 2008 figures) than the monomer (caprolactam), Kamimura believes that this method will open up new avenues in the development of plastics recycling.
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Direct conversion of polyamides to ω-hydroxyalkanoic acid derivatives by using supercritical MeOH, Akio Kamimura, Kouji Kaiso, Shuzo Suzuki, Yusuke Oishi, Yuki Ohara, Tsunemi Sugimoto, Kohichi Kashiwagi and Makoto Yoshimoto, Green Chem., 2011, DOI: 10.1039/C1GC15172J