Monitoring the formation of N-nitrosamines in lyocell plants-pitfalls and solutions

Abstract

In the lyocell process N-methylmorpholine N-oxide (NMMO) is used as a solvent to produce cellulosic fibers. During the process, NMMO degrades to a very low extent into amines, such as morpholine, which may be subject to N-nitrosation to generate traces of N-nitrosomorpholine (NMOR), if conditions prevail favoring this reaction. In addition to NMOR, trace amounts of N-nitroso-N-methylethanolamine (NNMEA) were identified in the ambient air around the spinning site using commercially available air sampling cartridges, analysis by gas chromatography coupled to mass spectrometry (GC–MS), and quantitation by a stable isotope dilution assay (SIDA). N-Nitrosamines present in ambient air are trapped on the cartridge’s adsorption material containing sulfamic acid to prevent de novo N-nitrosation reactions during trapping. Notwithstanding the presence of a nitrosation inhibitor, on-cartridge formation of NNMEA may occur during sampling at elevated nitrogen oxide (NO_x) concentrations in the sampling atmosphere. This as yet unrecognized problem of artifact formation was solved by insertion of a glass fiber filter impregnated with phosphoric acid in front of the air sampling cartridge. The additional filter warrants artifact-free sampling by trapping the most likely precursor 2,3-dehydro-N-methylmorpholine (DNMM) quantitatively on the glass fiber filter. A plausible mechanism of the reaction sequence leading to the formation of NNMEA is proposed.