In-situ Study Of Ionic Liauid Synthesis Process With Low-field Nuclear Magnetic Resonance Technology

Ionic liquids(ILs),as a platform compound,have exhibited excellent performance in fields due to their outstanding and unique properties,and is one of the important research topics under the green technology revolution.However,the increasing market and industrial application of ionic liquids have boosted the production cost and quality of the ionic liquids.The development of three-dimensional visualization in-situ monitoring technology to study the kinetic characteristics and reaction transfer laws of the synthesis process of ionic liquids is the key to the optimization design of key equipment and precise control of the process.However,most of the current in-situ process analysis technologies cannot provide spatial information about the reaction system.This paper aims to provide a new,non-destructive,rapid and flexible process analysis technique to operando monitoring the synthesis process of ionic liquids.The main research contents are as follows:(1)The relaxation characteristics T1/T2 of imidazole,pyridine,halogenated alkanes and corresponding ionic liquids were systematically measured,and then the low-field nuclear magnetic resonance imaging technology was chosen as a process analysis tool to study operando the ionic liquid synthesis process.Taking the synthesis of[C4mim]Br as a model reaction,we established the methods for qualitative and quantitative analysis of the components of the reaction system and validated it with in-situ infrared spectroscopy.The results were consistent.(2)In-situ studies on[C4mim]Br using low-field nuclear magnetic resonance imaging have shown that the higher the initial molar ratio of imidazole to bromobutane,the higher the reaction temperature and the faster the stirring speed,resulting in faster synthesis speed.The calculated second order kinetic rate constant k(0.042 to 1.378 mol-1.L·h-1)and apparent activation energy EA(72 kJ/mol)were in accordance with the literatures.The phase behavior of the[C4mim]Br synthesis process was visualized based Ti-weighted images with LF-MRI,and it was found that the whole system underwent phase separation when the yield of ionic liquid was 40 mol%,coalescence and phase inversion,and finally the ionic liquid flowed from the upper layer to the bottom of the tower at 32?,1.2 mol ratio of BuBr/MIM(3)The effects of halogenated alkane chain length,halogen element type and tertiary amine basicity on alkylation of tertiary amine/halohydrocarbon synthetic ionic liquids were systematically studied using low-field MRI system.The results show that the longer the alkyl carbon chain,the slower the synthesis rate;the greater the electronegativity of the halogen element of the halogenated alkane,the faster the synthesis rate of the ionic liquid,such as BuI>BuBr>BuCl.In addition,the basicity of tertiary amine also has a great influence on the synthesis rate,for example,the synthesis rate of[C4py]Br is far less than[C4mim]Br,and the rate constants are 0.047 and 0.807(mol/L)-1·h-1,respectively.