A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and N-methylmorpholine-N-oxide

Cellulose, Apr 2017

N-Methylmorpholine-N-oxide (NMMO) cannot be completely separated by extraction from mixtures with common 1,3-dialkylimidazolium ionic liquids (ILs) due to strong ionic interactions between the two components. At elevated temperatures, above approx. 90 °C, especially under dry conditions and in the presence of acid, alkylating or acylating agents, remaining NMMO in ILs tends to undergo autocatalytic degradation. This is a highly exothermic, unstoppable process that results in explosions, flames, and complete charring of the reaction mixtures. Thus, caution must be exercised when drying or heating ILs that were in previous contact with NMMO, and the absence of amine oxide must be confirmed to avoid potential danger.

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A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and N-methylmorpholine-N-oxide

A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and N-methylmorpholine-N-oxide Stefan B?hmdorfer . Takashi Hosoya . Thomas R?der . Antje Potthast . Thomas Rosenau 0 1 2 3 0 T. Ro ?der Lenzing AG , Werkstr. 2, 4860 Lenzing , Austria 1 Present Address: T. Hosoya Graduate School of Life and Environmental Sciences, Kyoto Prefectural University , Shimogamo-hangi-cho 11-5, Sakyo-ku, Kyoto-shi, Kyoto , Japan 2 S. Bo ?hmdorfer ? T. Hosoya ? A. Potthast ? T. Rosenau (&) Department of Chemistry, University of Natural Resources and Life Sciences Vienna (BOKU) , Muthgasse 18, 1190 Vienna , Austria 3 T. Rosenau Johan Gadolin Process Chemistry Centre, A ? bo Akademi University , Porthansgatan 3, 20500 A ? bo/Turku , Finland N-Methylmorpholine-N-oxide (NMMO) cannot be completely separated by extraction from mixtures with common 1,3-dialkylimidazolium ionic liquids (ILs) due to strong ionic interactions between the two components. At elevated temperatures, above approx. 90 ?C, especially under dry conditions and in the presence of acid, alkylating or acylating agents, remaining NMMO in ILs tends to undergo autocatalytic degradation. This is a highly exothermic, unstoppable process that results in explosions, flames, and complete charring of the reaction mixtures. Thus, caution must be exercised when drying or heating ILs that were in previous contact with NMMO, and the absence of amine oxide must be confirmed to avoid potential danger. Cellulose; Ionic liquids; NMMO; Binary mixtures; Extractability; Decomposition; Degradation; Exothermicity; Work safety - N-Methylmorpholine-N-oxide (NMMO), as the monohydrate, is well-known as a cellulose solvent and is used industrially in the production of Lyocell. 1-Alkyl3-methylimidazolium ionic liquids (ILs)?with 1-butyl-3-methylimidazolium and 1-ethyl-3methylimidazolium being the most prominent representatives?are much newer, and can be seen as a first generation of ionic liquid-based cellulose solvents. NMMO, apart from its beneficial properties regarding interaction with cellulose, is a strong oxidant and tends to undergo side reactions (Rosenau et al. 2001; Bernier et al. 2009). These might manifest themselves by degradation of the solvent, oxidation of dissolved cellulose (Potthast et al. 2006), discoloration during processing, and yellowing of spun fibers (Rosenau et al. 2005a). There are efficient stabilizers for lyocell dopes available that reliably counteract those effects (Wendler et al. 2008; Rosenau et al. 2005b). Most severe and dangerous, however, is the tendency of NMMO to undergo autocatalytic degradation, with carbenium-iminium ions as the central, catalytically active intermediate in this cycle (Rosenau et al. 1999). Once this reaction has started there is no way to stop it again, because of its high exothermicity. Eventually, it will result in complete charring of the mixture, possibly accompanied by explosive degradation, flames, and strong smoke development. Literature accounts describing these effects often use the terms ?thermal runaway reaction? or ?exothermicity?, which are euphemisms for explosive events that in the best case damage lab equipment or production sites or?much worse?might harm health and wellbeing of workers. The degradation mechanisms of NMMO have been comprehensively reviewed (Rosenau et al. 2001); some of them have even been turned into procedures useful in organic synthesis (Rosenau et al. 2004). 1-Butyl-3-methylimidazolium (BMIm) and 1-ethyl-3-methylimidazolium (EMIm), mostly as acetate and chloride, were among the first ionic liquids to be described as cellulose solvents (Swatloski et al. 2002). Most 1,3-dialkylimidazolium ILs are of the 1-alkyl-3-methyl type, so in the following the general term XMIm will be used to described these ILs. Initial optimistic claims of seemingly unlimited applications of these solvents in lignocellulose research have given way to a more realistic view of their advantages and drawbacks. In particular, problems with recycling and byproduct accumulation have cast doubts on their general usefulness in biomass fractionation or pulping, as have literature accounts showing that these solvents undergo reactions with cellulose (Ko?hler et al. 2007; Liebert et al. 2009; Ebner et al. 2008; Zweckmair et al. 2015) and thus lack the inertness that is often claimed as one of benefits of ILs. Also thermal stress causes slow byproduct formation in XMim ionic liquids, mainly imidazole derivatives (Wendler et al. 2012; Liebner et al. 2010; Dorn et al. 2008). NMMO has been used in combination with amines or polar organic solvents to achieve cellulose dissolution. Also, ILs have been used as the second component in binary NMMO solvent mixtures, and in turn NMMO has been added to ILs in attempts to further boost their dissolution power (Ingildeev et al. 2013). Most frequently, ILs and NMMO were combined in biorefinery approaches, attempting to pretreat or dissolve bi (...truncated)


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Stefan Böhmdorfer, Takashi Hosoya, Thomas Röder, Antje Potthast, Thomas Rosenau. A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and N-methylmorpholine-N-oxide, Cellulose, 2017, pp. 1927-1932, Volume 24, Issue 5, DOI: 10.1007/s10570-017-1257-2