Study Of Salting Out And Aqueous Two-phase Extraction In The Separation Of Nicotine From Aqueous Solution

Nicotine has many uses in the agricultural and pharmaceutical industries,and it is of great commercial value to study the separation and extraction of nicotine from aqueous solutions.However,the liquid-liquid extraction method used to separate and extract nicotine from an aqueous solution has the problems that organic solvents are toxic and flammable and explosive.Therefore,this thesis adopts the salting-out method and the aqueous two-phase extraction method,which have the characteristics of low cost,environmental friendliness,high selectivity and high yield of separating biomolecules,to study the separation of nicotine aqueous solution.The main research contents are as follows:（1）Six different inorganic salts（Na Cl、KCl、Na Br、KBr、Na₂CO₃、Na₂SO₄）were used as salting-out medium to systematically evaluate the effect of salt types on the separation of nicotine by salting-out.The complete phase diagrams were drawn experimentally at 298.15K and atmospheric pressure,and the correlations between binodal curves and tie-lines were measured by empirical equation.The latter is used to calculate the partition coefficient and recovery of nicotine.The partition coefficients ranged from 5.79 to 1325.82,and the recoveries ranged from 75.81%to 99.70%.The salting out ability of anions:CO₃^2–>SO₄^2–>Cl^–>Br^–,which follows the Hofmeister sequence,valence and hydration free energy theory.However,the cations（K⁺>Na⁺）exhibited the opposite order to the Hofmeister sequence,which was attributed to the strong interaction of Na⁺with nicotine nitrogen.EEV is used to evaluate the salting-out capacity,which is consistent with the size of the two-phase region.The increase of temperature and p H enhanced the salting-out effect of nicotine―Na₂SO₄system.The calculation of thermodynamic function shows that entropy increase is the driving force of nicotine separation process.（2）Three biodegradable organic salts（C₆H₅Na₃O₇、C₄H₄Na₂O₄、HCOONa）were used to replace inorganic salts to study the feasibility of salting-out to separate nicotine.The phase diagram of the（nicotine+salt+water）ternary solution was experimentally obtained at298.15 K and atmospheric pressure,and the correlation between the cloud point curve and the equilibrium line in the phase diagram was determined.The partition coefficients and recoveries of nicotine were calculated according to the equilibrium line,the partition coefficients ranged from 3.45 to 124.24,and the recoveries ranged from 79.57%to 98.61%.The ability of anions to promote phase separation is explained by valence and the Gibbs hydration free energy theory:C₆H₅O₇^3->C₄H₄O₄^2->HCOO^-.The EEV of salt is consistent with the size of the two-phase region,which can accurately evaluate the phase separation ability.The increase of temperature and alkaline environment are conducive to the phase separation of nicotine―C₆H₅Na₃O₇ system.Computational thermodynamic functions indicate that the entropy increase promotes the desolvation of nicotine in aqueous solutions.（3）The ATPS composed of Na₂SO₄/C₆H₅Na₃O₇+ethanol/1-propanol/2-propanol+water was established to study its separation performance for nicotine.The phase diagram of ternary solution（alcohol+salt+water）was obtained by experiment at 298.15 K and atmospheric pressure,the correlation was determined.The cloud point data in the phase diagram showed good similarity compared with the data in the literature.The effects of salt and alcohol on the phase separation process were analyzed:The ability of salt anion to promote the formation of two phases is C₆H₅O₇^3->SO₄^2-,which follows the theory of valence and hydration free energy;the phase formation ability of alcohol is 1-propanol>2-propanol>ethanol,which can be clearly explained by the interfacial tension of alcohol aqueous solution and the boiling point of alcohol.The EEV value of the system can evaluate the phase separation ability,which is consistent with the size of the two-phase region.The effects of alcohol/salt type,phase composition,temperature and p H on the separation process of nicotine were studied.The optimum condition is that ATPS composed of 30 wt%1-propanol+15 wt%C₆H₅Na₃O₇+55 wt%water is used to separate nicotine at 298.15 K and p H=10.The partition coefficient of nicotine is 73.18 and the recovery is 98.69%.Under these conditions,nicotine preferentially migrated to the 1-propanol enrichment phase through an endothermic and spontaneous process controlled by entropy increase.In this thesis,the salting-out characteristics and mechanism of inorganic salts were studied in depth.And the use of biodegradable organic salts instead of inorganic salts optimizes the performance of salting-out method in terms of toxicity and environmental problems.Then the alcohol-salt ATPS is constructed by using the salt with excellent effect in the salting-out method,and the best conditions for separating nicotine are obtained,avoiding the extensive use of salt and its environmental impact.The experimental data in this thesis will be helpful for large-scale industrial liquid-liquid extraction and separation of nicotine.