Study On Reactive Extraction Of Long-Chain Ester Formation Intensified By Bifunctional Ionic Liquid

As an important raw material,the demand of long-chain esters in food,spices,additives,pharmaceuticals and other industries is growing rapidly,and its green and efficient synthesis has also attracted widespread attention.However,the synthesis of long-chain esters generally uses the traditional Fisher esterification with concentrated sulfuric acid as an acid catalyst,which suffers from a series of problems.On the one hand,due to the strong oxidation and dehydration of sulfuric acid,side reactions such as etherification and carbonization often occur along with esterification,which results in low purity and grade of ester product.On the other hand,the dissolution of sulfuric acid in the ester and its sever corrosion do not benefit the recycling of catalyst,and post-treatment of the product ester,which finally leads to a large amount of acidic waste,increasing equipment investment and the unsafe production.As a new green solvent,ionic liquid can be used as both a catalyst and an extractant.With the aid of ionic liquid,the reactive extraction as a typical process intensification can improve the conversion and simultaneously achieve the further separation and purification of the target product.Therefore,the research on reactive extraction of long-chain ester formation intensified by bifunctional ionic liquid is of great significance.Since it is time-consuming,labor-intensive and inefficient to select a suitable catalyst to meet the requirement of esterification through massvie experimental synthesis,an ionic liquid screening method for long-chain ester formation system is proposed.Considering the advantages of ionic liquids as catalysts and extractants,this method takes into the thermodynamic indexes for esterification system(overall selectivity Smix,solvent loss and ionic liquid capacity),knowledge base(regarding on acidic functional group for catalysis,sustainability concerns,and side-recation),physical properties(melting point and viscosity),and availability(experimental or commercial).In the case study for the system of butyl hexanoate and isobutyl isobutyrate formation,ionic liquid candidantes with good separation performance,acid catalysis,and practical availability are screened out,which verifies the feasibility of the screening method.During the step-by-step screening,ionic liquids that lead to side-reactions,fail to meet the requiments of physical properties for esterification,and have difficulty in obtainning are excluded.Then,the roles of extractant and acid catalysis for the screened ionic liquid[BMIm][HSO4]are investigated and verified by liquid-liquid phase equilibrium(LLE)and kinetic experiments.In the system of butyl hexanoate formation,the LLE experiments prove that[BMIm][HSO4]can form two phase with ester,and play as an extractant to extract carboxylic acid and alochol.And the comparison of esterification with different ionic liquid dosage proves that[BMIm][HSO4]is a promsing catalyst alternative.Based on these facts,conditions for the formation of butyl hexanoate are optimized and then the possible mechanism of intensification of ionic liquid for the synthesis of butyl hexanoate is discussed.Similarly in the system of isobutyl isobutyrate formation,ternary and quinary LLE experiments are carried out to verify the role of ionic liquid as extractant and catalyst.Besides,LLE data of the system of isobutyl isobutyrate formation are fitted to obtain the NRTL model parameters,which can help the thermodynamic analysis for the esterification system.Since esterification is limited by chemical equilibrium,to shift the equilibrium,a conceptual design of the reactive extraction for synthesis of long-chain ester intensified by ionic liquid is proposed,which removes ester and isolates ester from the reaction system.With the guidance of the conceptual design of the reactive extraction,thermodynamic analysis and kinetic study of the reaction of isobutanol and isobutyric acid are carried out to identify the intensification of ionic liquid.Thermodynamic analysis shows that in most cases the system before the reaction({[BMIm][HSO4]+isobutyric acid+isobutanol})is homogeneous.And after reaction,hydrophilicity of[BMIm][HSO4]and immiscibility of[BMIm][HSO4]and ester play a key role to isolate ester from the reaction system and maintain the phase-splitting,thus shifting chemical equilibrium and intensifying esterification.The experimental kinetics of the esterification is well fitted using the activity-based kinetic model,which suggests the good catalytic performance of[BMIm][HSO4].Combining the NRTL model and activity-based kinetic model,the whole reactive extraction process for the formation of isobutyl isobutyrate intensified by ionic liquid is designed and simulated.Simulation resuls show that overall esterification runs at stoichiometric ratio of 1:1 with a high conversion(99.3%),high purity of isobutyl isobutyrate(mass fraction,99.03%).Finally,the corrosion of ionic liquid[BMIm][HSO4]in the system of formation of isobutyl isobutyrate is studied.The corrosion kinetics of 304 and 316L stainless steels in pure ionic liquid and esterification system,measured by weight loss,show two stainless steel have good corrosion resistance and their corrosion rates are within the acceptable range.For a long corrosion time up to 18 days in esterification system,the 316L stainless steel still maintains a relatively complete surface morphology,which is a good choice of corrosion-resistant material for esterification system.