Study On The Mass Transfer Characteristics Of Hydrophobic Deep Eutectic Solvents For Selective Separation Of Organic Components From Microalga

Organic components of microalgae such as lipids,proteins and polysaccharides are potential raw materials for the production of biofuels,which is of great significance to solve the problems of energy shortage and environmental pollution.Volatile toxic organic solvents are widely used in the traditional separation process of microalgae organic components,which seriously endangers the environment and human health,and is difficult to use under high temperature and pressure conditions such as hydrothermal.Compared with novel solvents such as supercritical fluids and ionic liquids,hydrophobic deep eutectic solvents(HDES)have the advantages of simple preparation,high thermal stability,low toxicity and adjustable physical and chemical properties.Based on this,an innovative method to promote the separation of microalgae organic components under hydrothermal conditions by using the hydrophobic deep eutectic solvent is proposed in this thesis,and realizes the efficient selective separation of microalgae organic components.The mass transfer and diffusion characteristics of microalgae organic components under the action of hydrophobic deep eutectic solvent are revealed by quantum chemical calculation and molecular dynamics simulation.The hydrophobic deep eutectic solvent was used to quickly and accurately separated lipids under hydrothermal conditions to prevent the reaction of lipids with proteins and polysaccharides from causing quality degradation,and to avoid the use of toxic organic solvents.The efficient and selective separation of microalgae organic components was achieved.The lipids extraction rate of OCT-DEC synthesized from octanoic acid(OCT)and decanoic acid(DEC)could reach 95.42%,and the aqueous phase of OCT-DEC system contained 318.97 mg/g DW proteins and 39.92 mg/g DW polysaccharides content.Additionally,OCT-DEC significantly enhanced the thermal stability of unsaturated fatty acids during the hydrothermal process and prevented the reaction of unsaturated fatty acids from causing quality degradation.Particularly the content of eicosapentaenoic acid in the lipids which extracted by OCT-DEC was significantly increased from 26.85 mg/g DW to 38.09 mg/g DW.The microscopic mechanism of HDES as an extraction solvent to promote the separation of microalgae organic components under hydrothermal conditions was studied by quantum chemical density functional theory and molecular dynamics simulation in this thesis.OCT-DEC significantly weakened the intermolecular interaction between proteins,polysaccharides and lipids from-66.01 k J/mol and-67.49 k J/mol to-53.21 k J/mol and-54.90 k J/mol respectively,which promoted the separation of microalgae organic components.OCT-DEC showed stable solvent structure and strong affinity for lipids,then there were a large number of(0.20)and very short lifetime(1.38 ps)HDES-HDES hydrogen bonds at the liquid-liquid interface of OCT-DEC system,which could overcame the interface obstacles by quickly reconstructing hydrogen bonds and promoted the diffusion of lipids to the hydrophobic phase,therefore it could achieved noticeable lipid extraction effect.In addition,the weak affinity of OCT-DEC to proteins makes the proteins more retained in the aqueous phase,while the strong affinity to polysaccharides leads to the extraction of some polysaccharides to the hydrophobic phase,so the polysaccharide content in the aqueous phase decreases slightly.The mass transfer and diffusion characteristics of microalgae lipids,proteins and polysaccharides in ten kinds of hydrophobic deep eutectic solvent systems were studied by experimental and molecular simulation methods,and the action laws of selective separation of microalgae organic components by HDES was revealed in this thesis.HDES promotes the separation of proteins,polysaccharides and lipids by breaking the interaction between microalgae organic components,especially electrostatic interaction.When HDES maintains stable solvent structure and strong affinity for lipid,and there are a certain number of short-lived hydrogen bonds at the liquid-liquid interface of the solvent system,especially HDES-HDES hydrogen bonds,then the interface barrier can be broken by quickly and stably reconstructing hydrogen bonds,which promotes the diffusion of lipids from the aqueous phase to the hydrophobic phase.The weak affinity of HDES for proteins and polysaccharides can prevent proteins and polysaccharides from being extracted to the hydrophobic phase,which is conducive to the efficient and selective separation of microalgae organic components.