Separation Of 3-Picoline And 4-Picoline

3-picoline and 4-picoline are close boiling point isomers with similar properties. They are difficult to be separated with traditional methods. It's of significant economical value to divide them and take the single product with higher purity to fill the urgent demand at home and abroad. Dissociation extraction is a form of chemical exchange process in which the difference in the dissociation constants of the components in a mixture is exploited in order to effect a separation. It is particularly useful for the separation of close related compounds or isomers. The method is very practical for the separation, while seldom studied at home.According to the basic extraction theory, the separation factors of dissociation extraction are put forward and the experiment conditions are identified. The results show that the volume ratio of 3-picoline and 4-picoline in organic phase is the highest when 24 mL picolines(volume percent of 3-picoline is 68.47% and 4-picoline 26.52%) are separated at 0°C by 2.0 mol/L p-toluenesulfonic and n-heptane whose dosages are 40 mL and 48 mL, respectively. The results are proved by the repeatability test. The effect of the single stage separation is so good that the volume ratio of 3-picoline and 4-picoline in organic phase is improved once to the oringinal value. On the basis of the experiment data, the effect of the extractant and organic solvent are thoroughly discussed. Rules for the selection of the extractant and organic solvent in dissociation extraction are also pointed out.The two phases and mutlicomponents system after the addition of the extractant is analyzed in detail. Moreover, deduced by the dissociation equilibrium equation and the competing reaction equation, a procedure is established by which the number of equilibrium stages required for a given separation may be determined by stage-stage calculation method. To the 2 mol/L HNO3～benzene system, the concentration of the single picoline in two phases are determined and the related calculation equations between the distribution coefficient of undissociated base and the concentration in organic phase are established as follows:By the using of these two equations and the established model, the required separation stages and the concentration on each stage of 2 mol/L HNO₃～benzene system through multistage dissociation extraction are calculated. Both the experimental and calculated stages are 6. Also the experimental and calculated results on each stage are compared and found to give decent agreement. The procedure accurately describes the concentration distribution of each component.Aimed at the minimum value of RMSD within the limit of the concentration of multistage operation, the distribution coefficients of two undissociated bases in 2 mol/L p-toluenesulfonic acid～n-heptane system are calculated by Nelder-Mead simplex method. They are: the top section D_A=14.00 ,D_B=14.80;the bottom section D_A=13.13,D_B=12.02. Along with these four values and the model, the essential stages of 2 mol/L p-toluenesulfonic acid～n-heptane system by multistage dissociation extraction are calculated and the result is 9.Finally the technique parameters are adjusted by the results of the orthogonal test as follows: the volume ration of the feed mixture is 2.58:1, the volume ratio of the organic solvent to the mixture is 2:1 and the mole ration of the extractant to 4-picoline is 1.2:1. Toward the mixture which the content of 3-picoline is higher than that of 4-picoline(yAf=0.68), the designed results show the required stages to obtain the products with purity≥80% are 3, to obtain the products with purity≥90% are 6 and≥99% are 14.