Recovery Of Caprolactam And Cyclohexanecarboxylic Acid From Wastewater

This paper aims to develop a new technology to recover Caprolactam and cyclohexanecarboxylic acid from wastewater. Influences of various parameters to the extraction were studied. Consequently, the new technology has significant benefits from economy and environment.Solvent extraction studies have been carried out for the recovery of caprolactam from simulated wastewater. The behavior of caprolactam extraction with chloroform as extractant was studied. Influences of various parameters including equilibration time, pH of the solution, extraction temperature and initial concentrations of caprolactam, etc.,were studied. The experimental results showed that the extraction process is a fast extraction process. The distribution ratio increases with the increase of pH of the aqueous solution and reaches its maximum when pH≥7. After three stage cross-flow extractions, more than 98% extraction efficiency was achieved at aqueous to organic phase ratio 1:1 when caprolactam concentration was lower than 38.4 g-L(-1). It was found that ammonium sulfate and 1-sulfonic acid-1-cyclohexanecarboxylic acid in the aqueous solution have the salting-out effect which can enhance the distribution ratio. The extraction temperature has only a little effect on the extraction process. The distribution equilibrium relation of caprolactam with chloroform in aqueous and organic solution with pH=7 was determined.Solvent extraction studies have been carried out for the recovery of cyclohexanecarboxylic acid from simulated wastewater. A mixture of toluene and 1-octanol (90:10, v/v) was found suitable for the extraction. Influences of various parameters including equilibration time, pH of the solution, and initial concentrations of cyclohexanecarboxylic acid, etc., were studied. The extraction was found quite rapidly. The results showed that solution pH had a great effect on the distribution ratio, and cyclohexanecarboxylic acid could be efficiently extracted when the pH was lower than 3.5.After three stage cross-flow extractions, more than 97% extraction efficiency was achieved at aqueous to organic phase ratio 2:1 when cyclohexanecarboxylic acid concentration was lower than 36.5 g-L(-1). The distribution ratio decreased as the initial concentration of cyclohexanecarboxylic acid increased. It was found that ammonium sulfate and 1-sulfonic acid-1-cyclohexanecarboxylic acid in the aqueous solution have the salting-out effect which can enhance the distribution ratio. The stripping efficiency increases with the increase of sodium hydroxide solution concentration, and decreases with the increase of cyclohexanecarboxylic acid concentration in the organic phase.After once back extraction, more than 98% stripping efficiency was achieved with 0.8 mol/L sodium hydroxide solution at aqueous to organic phase ratio 1:1 when cyclohexanecarboxylic acid concentration was lower than 32.1 g/L.The practical extraction process was carried out for the wastewater discharged in the production of caprolactam from toluene. The practical extraction efficiency of caprolactam reached 80% in one single stage with chloroform as extractant. After three stage cross-flow extractions, more than 98% extraction efficiency was achieved at aqueous to organic phase ratio 1:1 when caprolactam concentration was lower than 36.7 g·L(-1). The practical extraction efficiency of cyclohexanecarboxylic acid reached 85% in one single stage with the mixture of toluene and 1-octanol (90:10, v/v) as extractant. After four stage cross-flow extractions, more than 97% extraction efficiency was achieved at aqueous to organic phase ratio 2:1 when cyclohexanecarboxylic acid concentration was lower than 29.8 g·L(-1). After once back extraction, more than 980 0stripping efficiency was achieved with 0.8 mol/L sodium hydroxide solution at aqueous to organic phase ratio 1:1 when cyclohexanecarboxylic acid concentration was lower than 25.3g·L(-1).