Molecular Design Of Highly-hydrophobic Fluorinated Neutral Extractants Along With Suitable Diluents And Assessments Of Their Extraction Performance

Solvent extraction is widely used in chemical industry such as mineral recovery,biopharmaceutical purification,and sewage treatment,etc.However,during the solvent extraction process,the loss of extractant often occurs.After careful investigation of relevant researches on the loss of extractants,we believe that improving the hydrophobicity of extractants is the key to solve the loss of extractants.Fluorinated organic solvents possess ultra-high hydrophobicity.In this paper,fluorinated neutral phosphate ester and alcohol were designed based on the prototypes of the commonly used neutral phosphate ester and alcohol extractants to manifest their high hydrophobicity during solvent extraction process by DFT calculations and experiments.Furthermore,fluorinated arene and hexane were designed as diluents and their synergistic effects on extraction capability of fluorinated extractants were investigated.The rational synergistic mechanisms were proposed,which provided the direction of the development of fluorinated extractants and diluents.Specific research results include the following aspects.The creation includes the following aspects:(1)Tri-n-amylphosphate(TAP)and tris(2,2,3,3,4,4,5,5-octafluoropentyl)phosphate(FTAP)were taken as exemplar to investigate the effect of fluorination on hydrobicity of neutral phosphate ester extractants both theoretically and experimentally.According to DFT calculations,solvation free energy of FTAP with-20.5 kJ·mol-1 was higher than that of TAP with-24.1 kJ·mol-1,which suggested that FTAP was more hydrophobic than TAP.The hydrophobicity of FTAP and TAP was estimated by water solubility and the residual amount in water during extraction.The FTAP residual in water was reduced 8 times compared with that of TAP,which proved that fluorination can significantly increase the hydrophobicity of the neutral phosphate ester extractant.(2)The extraction capability of fluorinated neutral phosphate was reduced due to the electron-withdrawing of fluorine atoms and its high hydrophobicity.In order to compensate this shortage,a binary fluorinated diluent-extractant system which contained one of four different fluorinated arenes(benzene,toluene)as diluents and tris(2,2,3,3,4,4,4-heptafluorobutyl)phosphate as extractant was designed for the first time.The extraction rate of the extracts was increased 200%through the addition of fluorinated arene.By analyzing the small-angle x-ray scattering(SAXS)data and the water content of the organic phase as well as molecular dynamics simulation calculations,a method for selecting fluorinated arene diluents was proposed.The synergistic mechanism of fluorinated arene improving the extraction performance of FTBP by promoting the formation of reverse micelle aggregates in the organic phase was discovered,which enriches the theoretical understanding of fluorinated extraction system.(3)To further explore the application of fluorinated neutral extractant for reducing extractant loss,n-octanol was chosen to investigate the feasibility of the application of fluorinated alcohol extractants both experimentally and theoretically.According to DFT calculations,when the number of substituted fluorine atoms is not less than 13,the values of solvation free energy of fluorinated octanol are positive,indicating that these species of fluorinated octanols should be superhydrophobic.Then,n-octanol and 1H,1H,2H,2H-perfluorooctan-1-ol(C8H5F13O)were used as a pair of model molecules for solvent extraction experiments under different conditions,and the residual amount of C8H5F13O in water was 250 times lower than that of n-octanol,indicating that C8H5F13O is more hydrophobic than n-octanol.(4)The extraction performance of fluorinated octanol decreases due to its high hydrophobicity and the electron-withdrawing of fluorine atoms.In order to improve the extraction behavior of fluorinated octanol,a binary fluorinated diluent-extractant system which contained one of three different fluorinated hexane as diluents and C8H5F13O as an extractant was designed.The effect of different fluorohexanes on the extraction capacity of C8H5F13O was analyzed using DFT calculations and extraction experiments.According to DFT calculation,supported by FT-IR and 1H NMR spectra,the hydrogen-bonding interactions between diluents and extraction complex were analyzed in detail,and the synergistic mechanism for improving the extraction performance of fluorinated alcohol by fluorinated hexane over hydrogen bonds were imovatively proposed,which offered theoretical guidance for the development of fluoroalkane diluents.