Study On Extraction Kinetics Of Acetic Acid From Its Dilute Aqueous Solution

Recycling acetic acid from the dilute aqueous solution of acetic acid is a difficult problem to chemical plant at present. Statistic data show that a considerable amount of acetic acid which is produced or consumed in industries is discharged with wastewater. For example, in the production of furfural, about 10,000 tons of acetic acid is discharged each year, which is not only losing a great deal of useful resources, but also polluting the environment. Therefore, recovering the acetic acid from the dilute aqueous solution of acetic acid can be beneficial to the economy and the environment.So the extraction of acetic acid from its dilute aqueous solution was studied in this paper. On the basis of the discussion of the complex extraction technology in the treatment of organic carboxylic acid, the extractive kinetics on acetic acid extraction from its dilute aqueous solution has been studied. The chelators are TBP and three alkyl amines (7301 and N235), the diluents are n-caprylic alcohol and hydrogenating kerosene. The efficient complex extractant was successfully examined. The complex extraction factors, the equilibrium time, extractant volume, the initial concentration of acetic acid, temperature, pH value, stirring rate and contacting area were considered by the Lews cell method. In the meantime, the kinetic order of the extraction process and the mechanism of the complex extraction process were analyzed, with which the extraction efficiency of such process can be improved.The results showed that the better effect of extraction of acetic acid were obtained with trialkylamines (7301), and the extraction capacity could be increased significantly after adding amount of n-caprylic alcohol. According to the orthogonal experiments, the better extraction system is trialkylamines +n-caprylic alcohol+ hydrogenating kerosene with the ratio of 3:6:1. The higher equilibrium distribution coefficient was obtained with the lower pH value. With increasing the pH value, the equilibrium distribution coefficient decreased significantly and the lowest distribution coefficient was measured, when pH value increased to a certain level. With the temperature of 27℃and the concentration of 0.346 mol/l, the form of the complex was likely 1:1. The distribution coefficient decreased with increasing the initial concentration of acetic acid solution, the ratio of the aqueous phase to the oil phase and the temperature. The distribution coefficient increased with the increasing the concentration of trialkylamines (7301 N235), two-phase contact area and stirring rate.With the data analysis, the kinetic order of the extraction process is nearly 1. There are three steps in the acetic acid complex extraction process, which are the transfer of trialkylamines into the aqueous phase or the interface of it, the formation of the complex of trialkylamines and acetic acid, and the transfer of the complex into the organic phase. A distribution coefficient mathematical model of the extraction process based on the above analysis was presented in the paper.