The greening of nylon

Because of their high melting points and excellent resistance to wear, the various forms of nylon, or polyamides, have more uses than we might expect, establishing nylon's image as a clean, versatile polymer. This impression changes quickly when we look at the production of the monomer on which the nylon 6 polymer is based-- epsilon -caprolactam. The conventional synthesis route to this monomer uses toxic hydroxylamine (NH sub 2 OY, as its sulfate) and, in the last two steps, concentrated sulfuric acid. Every metric ton of epsilon -caprolactam produces up to 4.5 t of ammonium sulfate byproduct. This salt, which is sometimes used as a fertilizer, causes increased economic and ecological concern for manufacturers. Because epsilon -caprolactam is a major intermediate chemical produced worldwide (4.4 million t/year), companies such as BASF, DuPont, and DSM have conducted research for alternative routes that avoid the use of toxic and corrosive ingredients and do not produce (NH sub 4 ) sub 2 SO sub 4 . The challenge was also taken up by some universities to demonstrate their competitiveness in developing alternative "green" processes. The Department of Technical Chemistry and Heterogeneous Catalysis at the University of Technology (RWTH), Aachen, Germany, became involved when one of the authors (WFH) switched from industry to academia.