Recovery of protic ionic liquid by short path distillation

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Kemian tekniikan korkeakoulu | Master's thesis
Chemical and Process Engineering
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
110 + 25
Ionic liquids (IL) have been recognized as great alternatives to existing organic solvents in a wide array of chemical processes. Their physical and chemical properties which can be customized allows to improve and produce ILs that are of particular importance to cellulose dissolution for fiber production. 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate, [mTBDH][OAc] is a suitable alternative to replace existing solvents for this application in the IONCELL® process. However, mTBD is an expensive base and the presence of different impurities in a closed loop process such as inorganics, xylan, lignin and other impurities present a challenge in scaling up the process using this IL. Improving recovery fractions and understanding the interaction of the IL with the different impurities is essential in increasing the amount of the recovered base for a high-value IL like [mTBDH][OAc]. This thesis focuses on the recovery of [mTBDH][OAc] in the presence of different impurities and to find suitable operating conditions for removing the impurities using a short path distillation unit. KCl, NaCl, CaCl2, lactic acid, xylan and hydrolysis products were the impurities used in understanding their interaction with the ionic liquid. The operating pressures and temperatures were kept constant at approximately 9 mbar and 200°C while varying the flowrate to investigate the recovery of the IL at different fractions. The collected samples from the experiments were analyzed by proton nuclear magnetic resonance to obtain mass balance compositions of the different components. The load needed to scale up the units and the yield of the major components in the IL are also presented in this thesis. It was possible to successfully separate all the tested impurities using the short path distillation technique even though there was slight entrainment in some of the runs. The final experimental run was carried out at 220°C to test the formation of the amide, A-mTBD but did not result in its formation. The final experiment was simulated using Aspen models which presented challenges to replicating experimental conditions as the use of pure component vapor pressures of lactic acid and mTBD alone are not sufficient for the simulation of this system due to the lack of literature data available with respect to the lactic acid-mTBD complex. The thermodynamic model also needs to be developed further to account for TBD in the simulations which is an impurity with respect to the IL. A-mTBD formation took place in the feed when CaCl2 was mixed with [mTBDH][OAc] at 200°C and 9.2 mbar. Highest recovery fractions of the IL were obtained in the SPD unit at a flowrate of 0.378 kg/h. The ratios of mTBD and HOAc remained the same in the distillate and residue for most of the tested experimental conditions. More than 80% of the base mTBD can be recovered using this process in the presence of the mentioned impurities. The distillate to feed ratios from the simulations are compared with the experimental ratios which gave results that indicate the need for further model development in Aspen.
Alopaeus, Ville
Thesis advisor
Uusi-Kyyny, Petri
[mTBDH][OAc], protic ionic liquid, short path distillation, hydrolysis product, Ioncell®, recovery
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