This thesis demonstrates the recyclability of superbase-based ionic liquids in the scope of developing a sustainable Lyocell process for the man-made cellulose fiber industry. Ioncell is a Lyocell-based technology that utilizes ionic liquids in the direct dissolution of cellulose and the production of textile-grade fibers via a dry-jet wet spinning process. In order to commercialize this technology, there are several important criteria to be met: The selection of a solvent with a strong cellulose dissolution power, a stable spinning process, good mechanical properties of the regenerated fibers, and above of all, the quantitative recovery of the solvent from the coagulation bath without impairing its solvation power. The work presented herein aspires to cover all the mentioned challenges. We chose a thermal recovery path to recycle the ionic liquids while identifying potential solvent alterations taking place. Such alterations include the consumption of the ionic liquid in nucleophilic hydrolysis reactions, the selective vaporization of the base during recovery, and the residual water in the recovered solvent. The combination of these alterations can interfere with the dissolution process. Initially, we investigated the potential of guanidine- and amidine-based ionic liquids, in comparison to N-methylmorpholine N-oxide, as solvents capable of producing textile-grade fibers. We also presented the recyclability of the guanidine-based ionic liquid, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate, and the amidine-based ionic liquid, 1,5-diaza-bicyclo[4.3.0]non-5-enium acetate, in the Ioncell process, while we quantitively analyzed the changes in solvent composition (= alterations) occurring during the thermal recovery stages. The results revealed that the 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate is hydrothermally more stable, implying that the alterations in the solvent did not affect its dissolution capabilities. Contrarily, a relatively large fraction of the 1,5-diaza-bicyclo[4.3.0]non-5-enium acetate was consumed in undesired hydrolysis reactions and in the vaporization of the neutral base, which inhibited the dissolution power of the recovered solvent. Additionally, we simulated the solvent alterations in both ionic liquids to explore the thresholds for cellulose dissolution and the impact of the alterations on the rheological properties of the solution and the spinnability of the fibers. The outcome confirmed the tolerance of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate to substantially more alterations in its composition, while the fibers produced from it exhibited superior properties. These findings favor 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate as a promising solvent in the Lyocell process and can be regarded as an important milestone in the scaling up of the Ioncell process.
|Translated title of the contribution||Recycling and Spinning of Superbase-Based Ionic Liquid Solutions in the Lyocell Process: Potential and Limitations|
|Publication status||Published - 2021|
|MoE publication type||G5 Doctoral dissertation (article)|
- ionic liquid
- regenerated fiber
- solvent recycling
- cellulose dissolution