Producing hexamethylenediamine from caprolactam via 6-aminocapronitrile: a green production technology of the monomer of nylon-66

Abstract

Hexamethylenediamine (HMDA), a crucial precursor of nylon-66, can be synthesized from caprolactam (CPL) via a two-step route involving CPL ammoniation and 6-aminocapronitrile (ACN) hydrogenation. Based on theoretical calculations and experimental screening, mesoporous alumina was selected which served as a highly active and cost-efficient catalyst for CPL ammoniation, catalysing the ring-opening of amides by C–N bond breakage and subsequent amide dehydration to nitrile. A 57.9% CPL conversion and 98.3% ACN selectivity were achieved at 320 °C with stability over 480 hours. The subsequent hydrogenation of ACN using the commercial RANEY® Ni catalyst yielded 100% HMDA, requiring milder conditions and half the hydrogen compared to adiponitrile processes. Overall, this research highlights a green HMDA production pathway, employing CPL as a feedstock.