Purification of Ionic Liquid [mTBDH][OAc] Utilizing the Short-Path Distillation Technique

The Ioncell process is an innovative approach to producing sustainable textiles using an ionic liquid (IL) as a solvent, but this process generates side products and impurities that have negative effects on its solvent dissolution capability. Therefore, the purification of the IL is of utmost importance. 7-Methyl-1,5,7-triazabicyclo[4.4.0]-dec-5-enium acetate, [mTBDH]-[OAc], is a suitable alternative to replace existing solvents for the application of cellulose dissolution in the Ioncell process. 7-Methyl-1,5,7-triazabicyclo(4.4.0)-dec-5-ene (mTBD) is an expensive base, and consequently, a closed loop operation, without any losses, is desirable. Additionally, high recovery of the base and effective removal of the impurities from the IL are necessary for making the process sustainable. Understanding the interaction of the IL with impurities is essential to purify mTBD and, thereby, the IL. This study focuses on the purification of [mTBDH]-[OAc] in the presence of different impurities. KCl, NaCl, CaCl₂, lactic acid, xylan, and the hydrolysis products, 1-[3-(methylammonio)-propyl]-1,3-diazinan-2-onemium acetate (H-mTBD-1) and 1-(3-ammoniopropyl)-3-methyl-1,3-diazinan-2-onemium acetate (H-mTBD-2), were the impurities utilized to understand the IL-impurity interactions. Suitable conditions for purification were determined using a short path distillation (SPD) unit while varying the feed flow rate to investigate the recovery of the base mTBD at different mass fractions. SPD results indicated that the highest recovery fractions (0.97-1.00) were observed at the lowest flow rates-(0.378 kg/h). Experimental results also confirmed that approximately 75-100% of the base mTBD can be recovered in most cases. Overall, the results of the experiments confirm that the impurities K, Na, Ca, xylan, and lactic acid can be removed from the feed using an SPD unit.