Study On The Separation Of TFP-H₂O Azeotropic System By Extraction With DESs

As an important fluorinated alcohol,2,2,3,3-Tetrafluoro-1-propanol(TFP)is one of the fine fluorochemicals,which has many benign properties such as good solubility,non-corrosive,non-toxic,good lubricity,high surface activity and good biological activity and can be applied as intermediate for preparation of pesticides,surfactants and detergents.A large number of TFP and TFP-H2O are used as cleaning agents for electronic equipment worldwide.So,a lot of wastewater solutions containing TFP has been produced in the cleaning industry.In order to realize the sustainable utilization of TFP resources,the more environmentally friendly and economical deep eutectic solvents(DESs)were selected as extractants to separate TFP-H2O azeotrope,and studied on the mechanism.The main research contents are as follows:(1)Based on the COSMO-SAC model,the structure parameter database of 22 kinds of hydrogen bond acceptors(HBAs)and 46 kinds of hydrogen bond donors(HBDs)were calculated.The selection method of DESs extractants was established on this basis.Comparing the ?-profiles of different HBAs and HBDs,the correspondence between molecular polarities and functional groups and the peak position in the ?-profiles is analyzed.Then,the ?-profile features of DESs,which can be used to extract TFP,should be:In the polar region(?>0.0084e/A2),it has a wider coverage than water,and there is a peak near ?=+0.016 e/A2,and it don't have too many overlapping peaks with the ?-profile of H2O.100 DESs were matched by the representative HBAs and HBDs.By comparing the distribution coefficiency(D),selectivity(S),extractant loss(SL)and solvent solubility(SP)parameters of the above DESs,the DESs which have the ?-profile features have high extraction capacity.(2)The three selected DESs were synthesized as extractants,which were MTMAC/Decanol(1:1),MTMAC/Decanol(1:2)and TBAC/Decanol(1:2),and characterized by 1H NMR.First,stirring for 3 hours and standing for 12 hours were determined by examining the effect of stirring time and standing time on the extraction efficiency.After that,the liquid-liquid phase equilibrium data of the ternary system MTMAC/Decanol(1:1),MTMAC/Decanol(1:2),TBAC/Decanol(1:2)-TFP-H2O were measured at T=303K,and the distribution coefficient D and selectivity S were caculated to show the extraction ability of different DESs.The experimental data were verified by Othmer-Tobias,Bachman and Hand equations,and the minimum correlation coefficient R2 was 0.9699.The revised "Lydersen-Joback-Reid"(LJR)method was used to estimate the critical temperature(Tc)critical pressure(Pc),critical molar volume(Vc),boiling point(Tb)and asymmetry factor(?)of different DESs,and filled into the Aspen plus database in a user-defined form.The measured liquid-liquid equilibrium data of the ternary system were correlated with NRTL model,and the calculated RMSD values are 0.0577,0.0668 and 0.0495,which indicated that the experimental values and the regression results of the NRTL model can be better fitted.The model parameters obtained by NRTL model have passed the consistency test of GUI-MATLAB software in order to ensure the validity of the model parameters obtained by correlation.(3)The interaction between DESs and TFP-H2O azeotropic system was discussed by quantum calculations and molecular dynamics simulations.First,the bond length,bond energy,and deformation charge density between the molecules in the systems are obtained.The results show that the bond length of MTMAC/Decanol(1:1)-TFP,MTMAC/Decanol(1:2)-TFP and TBAC/Decanol(1:2)-TFP are 2.080A,2.123 A and 2.105A,respectively.The interaction energies are-52.166,-51.722,-46.213 kJ·mol-1,and the intermolecular interaction belongs to the hydrogen bonding.In charge density analysis,the hydrogen bond formed between DESs and TFP is obvious with isovalue=0.2,and the charge density between MTMAC/Decanol(1:1)and TFP is the largest.Through the scatter diagram and color-filled RDG isosurface map,it is found that there is a blue isosurface between TFP and Cl-1,which is a hydrogen bonding area.Second,the interaction of MTMAC/Decanol(1:1)(DES1)/TBAC/Decanol(1:2)(DES2)-H2O-TFP system are calculated by the molecular dynamics simulation.Taking Cl-1 as the central atom,the number of instantaneous molecules of TFP is calculated in the spherical shell at a distance r.There is a sharp and high peak at r=0.318,and the intensity is above 17,which indicats hydrogen bond formed between Cl-1 and TFP.The RDF for DES2-TFP has a peak at r=0.318,and the indensity is about 16,so the interaction between DES1 and TFP is stronger than DES2.The RDF of the cation N+with TFP has a strength of 2.5,which belongs to van der Waals force.Finally,the molecular self-assembly calculation results show that Cl-1 is the effective active site of DESs.(4)The separation process of TFP-H2O azeotrope system by MTMAC/Decanol(1:1),MTMAC/Decanol(1:2),TBAC/Decanol(1:2)have been designed.With the annual total cost(TAC)as the target,the optimal process parameters were determined by the sequential iterative search method.The heat duty and CO2 emissions were calculated at the same time.The calculation results show that the three DESs can realize the separation of TFP-H2O azeotropic system,in which the product purity of water is 0.999 mol%,and TFP is 0.995 mol%.Comparing TAC,heat duty and CO2 emissions of the processes,optimal process flow with DES1 as extraction agent is the most economical and environmentally friendly process.