Study On Mechanism Of Microwave Assisted Ionic Liquids Treatment Followed By Hydro-Distillation Efficient Extraction Of Essential Oils From Traditional Chinese Medicine

Research objectiveAt present,the conventional hydrodistillation method is widely used to extract essential oils(EOs)of traditional Chinese medicine(TCM).But this method has long extraction time,low extraction rate and high energy consumption,which is difficult to meet the growing clinical application needs.Microwave assisted ionic liquids treatment followed by hydro-distillation(MILT-HD)can significantly improve the EOs extraction rate and shorten the extraction time.And it has been used to efficiently extract the TCM EOs.However,there are obvious differences in the extraction performance of this method when extracting EOs of various TCM.The reasons for the differences in the extraction performance of MILT-HD have not been explored,and the mechanism of this method for improving the EOs extraction efficiency is still unclear.The purpose of this study is to elucidate the mechanism for efficiently extracting TCM EOs by MILT-HD at molecular level.And the anther purpose is to analyze the extraction rules of MILT-HD for extracting EOs from various TCM.It provides a technical basis for the wide application of MILT-HD.Research method(1)The extraction performance of four imidazole-based ionic liquids(ILs)is screened by single factor test.And the ILs with the best performance is selected as the research object.The Box-Behnken experimental design is used to make three-factor and three-level experimental arrangements for three key extraction process parameters.The mathematical relationships among extraction process parameters ILs ratio,microwave time,microwave power and EOs extraction yield and mass transfer rate are established by multivariate modeling technique.The extraction process parameters are optimized based on the multi-objective optimization,and the optimal process conditions are verified by three batches of experiments.GC-MS is used to detect the chemical constituents of TCM EOs extracted by MILT-HD.The EO extracted by hydrodistillation is used as a control to evaluate the changes in the composition of EOs extracted by MILT-HD.By calculating the extraction efficiency,energy consumption and CO2 emission of the extraction process,the advantages and disadvantages of MILT-HD for extracting EOs are evaluated.(2)The interaction between ILs and cellulose is calculated based on the density functional theory(DFT),and energy change is computed during the cellulose cleavage reaction.It is used to evaluate the difficulty of the cleavage reaction.The structural changes of cellulose bundles in different extraction solvents are simulated based on molecular dynamics(MD)simulation.And the damage degree of ionic liquids on cell wall was evaluated by counting the number of hydrogen bonds.The interaction between ILs and water solvent,water solvent and EOs was further calculated by DFT to explore the salting-out effect of ILs.And the temperature distribution curve is used to characterize the microwave thermal effect of ILs.Based on the above methods the extraction mechanism of MILT-HD is comprehensively explored.Through infrared spectroscopy(IR)and scanning electron microscopy(SEM)characterization of the samples of TCM before and after extraction,the mechanism of MILT-HD improving the TCM EOs is verified based on experiments.(2)By characterizing the porous media structure,cell wall structure thickness and cellulose content of different Chinese herbal medicines,the mathematical relationship between the properties of herbs,extraction process parameters and MILT-HD extraction performance is established by multi-block partial least squares(MBPLS).By further calculating the BIP value of the statistical model,the key blocks affecting the extraction performance are identified.And the VIP value of the MBPLS model is calculated to identify the important factors affecting the extraction performance of EOs.A multiple linear model(MLR)for predicting the extraction performance of MILT-HD is established by stepwise regression.And a design space for efficient extraction of EOs from TCM is established based on the MLR.Finally,the design space is verified by experiments.Research results(1)The single factor experiment shows that the extraction time of[C4mim]Cl is short and the extraction rate is high.Therefore,the subsequent study uses ionic liquid[C4mim]Cl as the best ionic liquids(ILs)to study the extraction of TCM EOs.Based on the design of experiment,the mathematical models of extraction process parameters and EOs yield,mass transfer rate are established by multivariate modeling technique.The multi-objective optimization method is used to determine the optimal process of MILT-HD for extracting TCM EOs.The ILs ratio is 74.00%.The microwave time is 4.24 min,and the microwave power is 233.10 W.After the EOs is extracted by the optimal process,the actual extraction yield and extraction rate were 3.750%±0.119 and 0.188(%min-1)±0.0045,respectively.The relative errors between actual values and the model predicted values are 3.71 and-3.19,respectively,and the errors are small.Twelve main chemical constituents are identified by GC-MS.Compared with conventional hydrodistillation,the MILT-HD has no obvious effect on the chemical constituents of EOs.After calculating the extraction efficiency and energy consumption of different extraction methods,it is found that MILT-HD produces 584.0 g CO2 emission,which was only one-third of that of hydrodistillation,but the extraction efficiency was 4 times that of steam distillation.(2)By comparing the electrostatic potential(ESP)distribution and the general interaction property function(GIPF),it is found that the interaction between ILs and cellulose is stronger.The non-covalent bond analysis proves that ILs can generate halogen bond,hydrogen bonds and van der walls forces with cellulose.Based on MD simulations,it is proved that ILs can reduce the number of hydrogen bonds in cellulose bundles.It can destroy the network hydrogen bond structure,and gradually disintegrate the structure of cellulose.By calculating the energy change of the cellulose cleavage reaction,it is found that ILs can act as a catalyst to promote the cleavage of cellulose chains,further destroying the structural integrity of cellulose.Through the temperature distribution curve,it is found that ILs can quickly convert microwave energy into heat energy,which is conducive to the damage of cell wall,and exerts the thermal effect of microwave to promote the extraction of EOs.Based on IR and SEM,it is proved that MILT-HD can destroy the structure of cellulose in the cell wall of medicinal materials.It can destroy the integrity of the cell wall and increase the mass transfer rate of EOs.Based on the above analysis,ILs can improve the extraction efficiency of EOs.Besides,after theoretical calculations,it is found that ILs and water can form stronger hydrogen bonds,resulting in the competitive binding of ILs and water.It can reduce the interaction of water with EOs components,reducing the solubility of EOs.IILs can exert the salting-out effect to promote EOs extraction.The experiment proves that ILs can play salting-out effect to improve the extraction rate of EOs.(3)By characterizing the relevant properties of medicinal materials,a MBPLS model is established to predict the extraction performance of MILT-HD.The R2Y(cum)of the established model is 0.780,and the Q2Y(cum)is 0.541,indicating that the model has good performance.Based on the VIP value,it is identified that the tortuosity of the pores of the medicinal materials,the fractal dimension,the thickness of the cell wall structure of the medicinal materials,the microwave time,and the microwave power are important variables that affect the extraction performance of MILT-HD.A simplified MLR model is established based on stepwise regression.It is identified that the thickness of medicinal material cell wall,microwave time and microwave power are the key factors affecting MILT-HD.A design space for adjusting the extraction performance of MILT-HD is established based on the MLR model.The experimental verification of the space is carried out.The error is small,which proves that the established design space has high reliability.Research conclusionBased on the results of multi-objective optimization,it can be seen that the three batches of experimental repeatability are high and the fluctuations are small,which proves that the optimized process has high repeatability and stable extraction process.Through comprehensive comparison of various aspects,it is proved that MILT-HD is an efficient and energy-saving extraction method of EOs,and it is a potentially effective solution to replace steam distillation.The theoretical calculation of DFT,MD and the characterization results of IR and SEM shows that in the process of MILT-HD extraction of EOs,ILs destroy the cellulose structure in the cell wall through a variety of synergistic effects.And then the integrity of call wall was destroyed.It can reduce the resistance of EOs diffusion,and improve the extraction efficiency of EOs.In addition,ILs form stronger hydrogen bonds with water,resulting in the competitive binding of ILs and water,reducing the interaction of water with volatile oil components.It can reduce the solubility of EOs in water.The extraction yield of EOs can be increased by the salting-out effect of ILs.Based on theoretical calculations,the interaction mode of ILs with cellulose and aqueous solution in the cell wall is explored from the molecular level.And the mechanism of MILT-HD for efficient extraction of TCM EOs is explored from multiple perspectives.Based on the established statistical model,it can be seen that the cell wall structure thickness of different medicinal materials,microwave power and microwave time have a significant impact on the efficient extraction of MILT-HD.The reason for the significant difference in the extraction performance of HD in the extraction of EOs of various TCMs.Through the verification of the design space,it is proved that the established design space has high reliability.According to the cell wall properties of medicinal materials,reasonable adjustment of the extraction process parameters can achieve the efficient extraction of EOs from different TCMs by MILT-HD.It provides a new research idea and strategy for the efficient extraction of TCM EOs...