Kohichi Kashiwagi

Direct conversion of polyamides to ω-hydroxyalkanoic acid derivatives by using supercritical MeOH

We examined the decomposition of polyamides such as nylon-6 and nylon-12 by using supercritical MeOH as the reaction media. The treatment of waste nylon-6 with supercritical MeOH resulted in smooth depolymerization, forming caprolactam as the first product which was then converted to a mixture of methyl 6-hydroxycapronate and methyl 5-hexenoate in a ratio of approximately 1 : 1. The reaction progress was traced using gas chromatography (GC) analyses, and precise product distribution was estimated. During the decomposition of nylon-6, N-methylcaprolactam and methyl 6-(N,N-dimethylamino)capronate were detected as intermediates. The sum of the all detectable products and intermediates exceeded 80%. In addition, we examined the decomposition reaction initiating from caprolactam, N-methylcaprolactam, and methylN,N-dimethylcapronate under similar reaction conditions, and observed that the final two products were formed in similar yields and ratios. Kinetic analyses by using a simulation study based on the experimental data were performed, and kinetic parameters for each step were estimated. Nylon-12 underwent similar conversion to produce methyl 12-hydroxydodecanoate in good yield. Because methyl ω-hydroxyalkanoate is known to be an important intermediate in the chemical industry, the present method has the potential for producing valuable compounds from waste material. Thus, the first upgrade in the chemical recycling of plastics was accomplished.

Efficient Conversion of Polyamides to ω-Hydroxyalkanoic Acids: A New Method for Chemical Recycling of Waste Plastics

An efficient transformation of polyamides to ω-hydroxy alkanoic acids was achieved. Treatment of nylon-12 with supercritical MeOH in the presence of glycolic acid gave methyl ω-hydroxydodecanoate in 85% yield and the alcohol/alkene selectivity in the product was enhanced to up to 9.5:1. The use of (18)O-enriched acetic acid for the reaction successfully introduced an (18)O atom at the alcoholic OH group in the product. This strategy may provide a new and economical solution for the chemical recycling of waste plastics.