Studies On Reactive Extraction Of Amino Acid Amino Acid-L-Valine?L-Alanine?Glycine

Reactive extraction,which is a new separation technique with high efficiency and selectivity,is a promising technique for the recovery of amino acids from aqueous solutions.Such technique overcomes the poor reversibility of chemical extraction,and absorbs the advantages of the physical extraction,such as the easy recovery of solvents,the simple operation and low cost.Recently,it has been used in the separation of diluent solution.Especially,the wastewater containing phenols from 10 factories in Wuxi?China?has been successfully treated,which exhibited great economic and social benefits.In this thesis,the reactive extraction of amino acids with di?2-ethylhexyl?phosphate acid?D2EHPA?has been studied.The factors which affect the reactive extraction were analyzed,and the reaction mechanism was confirmed by infrared spectra.Based on the experimental results,the model was established by using the mass action law,and the results were satisfactory.Moreover,the back extraction were investigated,which would supply the theoretical foundation for the industrial application.As neutral amino acids,L-Valine,L-Alanine,and Glycine contain–COOH and–NH₂,which make them exhibit Lewis acid-base characters and possess particular physical,chemical and biological properties.In this thesis,D2EHPA,tri-n-butyl phosphate?TBP?and tri-octyl tertiary amine?7301?were used to explore the best complexing agents.And it found that D2EHPA has best extraction ability.Then,the reactive extraction of L-Valine,L-Alanine and Glycine with D2EHPA in polar n-octanol,inert solvent oil and weak polar butyl acetate were investigated detail.The key factors that affect the extraction equilibrium distribution?D?,including the types of diluents,p H value,the concentrations of amino acids and extracting agents have been discussed.Results showed that,in a certain concentration range,the D value was increased with the increasing of D2EHPA in regardless of 1-octanol,solvent oil and n-Butyl acetate.The D increases sharply up to the highest with the increasing equilibrium pH(pH_eq),and then changed slightly.The hightest D value appeared in the pH region,where the neutral amino acid molecules dominated.D values in various diluents were in the order of 1-octanol>n-butyl acetate>solvent naphtha,which indicated D2EHPA in 1-octanol had the stronger extraction ability for amino acids than in solvent naphtha and in n-butyl acetate.The reactive extraction equilibrium model was established by using the mass action law,and the values of K and?were calculated.It was concluded D2EHPA mainly reacted with them to form 1:1complexe through ion exchange and proton transfer.By comparing the characteristic peaks in Fourier onfrared spectra of the solute?L-valine,L-alanine,glycine?,the original organic phase and the loading organic phase with the solute,the mechanisms for D2EHPA reacted with solute were further confirmed.Morover,aqueous pHshowed no influence on the structure of complex whether in 1-octanol or n-butyl acetate and solvent naphtha.Based on these results,the effects of electronic parameters of solutes(pK_a,pK_b and lg P)and the lipophilicity parameter?lg P?were preliminarily discussed.It showed that both the pK_a,pK_b and lgP had great influence on D.Back extraction is the reverse process of reactive extraction,which could achieve the solutes reverse back to aqueous phase by destroying the structure of complex in organic phase.To optimize the conditions for back extraction of L-valine,L-alanine and glycine,HCl,H₂SO₄,Na OH,Na₂CO₃ and water were selected as stripping agents.The best stripping agent was found to be HCl with optoimum conditions of25?of stripping temperature,20min of stripping time.Under the operation conditions,the concentration of stripping agent had negligible influence on stripping rate?E%?,The phase ratio?R?had significant influence on E%of L-valine,L-alanine and glycine.The highest E%were received when R=2.