Preparation Of Recycling Aqueous Two-Phase Systems Composed Of Two PH-response Polymers And Liquid-Liquid Extraction Of Some Bioproducts

Compared with traditional extraction technology like organic solvent extraction or ion exchange resin, aqueous two-phase systems (ATPS) have been widely used for purification of bioproducts due to the simple manipulation, mild operation condition, and low pollution. However, the key problem was the recovery difficulty of polymers phase-forming ATPS, increasing the cost. In this paper, two pH-response polymers PADB and PADBA were synthesized and used to construct the pH-response aqueous two-phase systems. PADB was synthesized by acrylic acid (AA), dimethylamino-ethyl methacrylate (DMAEMA), butyl methacrylate (BMA) and PADBA was synthesized by AA, DMAEMA, BMA, allyl alcohol (Aal). The structures of these two polymers were confirmed by IR and H NMR. The viscosities of polymers were measured by ubbelohde viscometer and the average molecular weights of two polymers were calculated using Fuoss equation where molecular weight of PADBA is3.37×105and PADB is2.93×106. The recoveries of polymers at different pH were tested and the maximal recovery of PADBA is97.18%and PADB is98.87%. The isoelectric points were tested by measuring Zeta potential of polymers at different pH where pI of PADBA is4.01and PADB is2.79.The cloud point method was used to calculate the binodal curve of PADB/PADBA aqueous two-phase systems and the tie lines were determined by measurement of each polymer concentration in each phase. The effect of pH on the binodal curve and tie lines of PADB/PADBA aqueous two-phase systems was investigated. The results shows that the two-phase region becomes higher in the phase diagram as pH increases which means that to form ATPS at higher pH, higher concentration of PADB is needed with the same concentration of PADBA.The tie lines becomes shorter as pH increases which means that the difference between two phases becomes smaller after phase separation at the same initial concentrations. The NRTL model and Flory-Huggins model were used to fit the liquid-liquid equilibrium of PADB/PADBA aqueous two-phase systems. The minimal RMSD in Flory-Huggins model is0.8777at pH6.05, and in NRTL model is1.0092at pH6.05. Flory-Huggins model shows better correlation than NRTL model for PADB/PADBA aqueous two-phase systems.PADB/PADBA aqueous two-phase systems were used to partition some bioproducts, including Spiramycin, Erythromycin, Lincomycin, Stevioside and Demeclocycline. The influence of the polymer concentration, pH, salts, salts concentration on the partition in PADB/PADBA aqueous two-phase systems were investigated. The results shows that the polymer concentration and pH have limited effect on the partition of Spiramycin, Erythromycin and Lincomycin in PADB/PADBA aqueous two-phase systems. The partition coefficient of Demeclocycline in PADB/PADBA aqueous two-phase systems is at the range of0.4to0.8at different pH and reaches minimum (0.467) when pH is5.28. In all the addition of salts, the partition coefficient of Spiramycin in PADB/PADBA aqueous two-phase systems increases with the salt concentration and reaches maximum at90mmol/l (1.99). The partition coefficient of Erythromycin in PADB/PADBA aqueous two-phase systems reaches maximum at high concentration1200mmol/l (5.296).The partition coefficient of Demeclocycline in PADB/PADBA aqueous two-phase systems is at the range of0.1～0.2at the salt range of10mmol/1～90mmol/l and reaches minimum (0.084) at60mmol/l. This result shows extensive application prospect in purification of Demeclocycline. In the investigation of the sequence of adding salts, the partition coefficient of Stevioside in PADB/PADBA aqueous two-phase systems reachs maximum (9.0) when Stevioside is mixed with MgSO4(100mmol/l～200mmol/l) firstly then mixed with polymers solution.A modified Gibbs Ensemble Monte Carlo method was used to simulate the liquid-liquid equilibrium of aqueous two-phase systems composed of two model polymers. The results show that one polymer is enriched in one phase and the other polymer is enriched in the other phase which is the same with the real system. The effect of molecular weight (using the number of monomers to express the molecular weight) and the polymer concentration (using the number of initial polymer chains to express the polymer concentration) on the phase forming were investigated. Results show that ATPS can’t form ATPS at low molecular weight and at low polymer concentration which is also same with real system. And the simulated tie lines are parallel and the tie line length decreases as the concentration decreases, fitting the real system. The program was also used to simulate the experiment data of DEXT40/PEG4000ATPS at20"C, and the results show the same tendency of phase forming with real system.