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Deactivation of nitrile hydrogenation catalysts: New mechanistic insight from a nylon recycle process

Paper ID Volume ID Publish Year Pages File Format Full-Text
44082 46002 2007 9 PDF Available
Title
Deactivation of nitrile hydrogenation catalysts: New mechanistic insight from a nylon recycle process
Abstract

In the recycling of nylon-6 and nylon-6,6, high temperature ammonolysis leads to reversion of the polymers to monomer units and dehydration of amide monomers to nitrile molecules. The resulting product is a mixture of 6-aminocapronitrile, caprolactam, adiponitrile, hexamethylenediamine and other species. To complete the recycle loop the nitrile molecule can be hydrogenated to hexamethylenediamine. This liquid phase hydrogenation has been studied over Raney® Ni and Raney® Co catalysts at less than 100 °C and 3.5 MPa in semi-batch mode. Raney® Ni exhibited rapid deactivation in the absence of sodium hydroxide, while Raney® Co provided long catalyst life. In comparison studies, Raney® Ni also deactivated during hydrogenation of pure adiponitrile, in the absence of sodium hydroxide. While sodium hydroxide inhibits Raney® Ni deactivation, it presents an economic and environmental challenge for waste handling. Analysis of recovered catalyst samples by ESCA showed an increase in nitrogen and carbon on the surface of deactivated Raney® Ni samples compared to recovered Raney® Co and control samples. The observed overlayer was consistent with the formation of oligomeric secondary amines, which covered the catalyst surface and prevented further reaction. Amine coupling reactions were favored for Raney® Ni compared to Raney® Co.

Graphical abstractIn the recycling of nylon polymer, ammonolysis and subsequent nitrile hydrogenation leads to reversion of polymers to monomer units. The use of certain Raney® catalysts in the hydrogenation step results in deactivation by a different mechanism than that previously reported for acetonitrile hydrogenation. The process and catalysts are characterized and improved reactivity for Raney® Co over Raney® Ni is documented. Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Deactivation; Raney; Nitrile hydrogenation; Nylon; Recycle; Polyamine; Hexamethylenediamine; Adiponitrile; Caprolactam; Ammonolysis
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Deactivation of nitrile hydrogenation catalysts: New mechanistic insight from a nylon recycle process
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 318, 20 February 2007, Pages 190–198
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us