Study On Analysis And Extraction Of Sulfonated By-product In P608 Wastewater From Caprolactam Production

Caprolactam, as one of the most important petro-chemical products in synthetic fibre and plastic industy, is greatly in demand. Amidation is the key reaction of the SNIA process in caprolactam production, and there are many side reactions involved. The concentration of sulfonated by-product directly influences the yield of caprolactam. Currently, neutralizationtitration is applied to analyse the content of the sulfonated by-product, and this analytic technique is time-consuming and lack of accuracy and reproducibility. Because of large quantity of sulfonated by-product involved, the treatment of P608 wastewater, which is derived from extraction unit in the SNIA process, will not only lead to environmental pollution, but also cause resource waste, and seriously affect the market competitiveness of SNIA process. Therefore, the research on the recovery processing of P608 wastewater, as well as a novel technique development for qualitative and quantitative analysis of sulfonated by-product, become the most urgent difficult problems that need to resolve.In the first part of this thesis, a paired-ion reversed-phase HPLC method was developed for determination of sulfonated by-product in the amination system. The ion exchange resin adsorption method was applied in enrichment of the sulfonated by-product, and the qualitative and quantitative analysis of sulfonated by-product and other ingredients were made. The separation was performed by using methanol/water=37.5/62.5(v/v) as mobile phase,containing 10 mmol/L tetrabutyl ammonium bromide as ion-pair reagent and 25 mmol/L potassium dihydrogen phosphate as buffer salt, with the flow rate of 1.0mL/min,and a UV spectrophotometric detector at 230nm. The analysis can separate sulfonated by-product from other compotents well with appropriate response signals. The analysis conditions are not vigorous and can lead to accurate and reproducible results.In the second part, in order to study on the process of sulfonated by-product changing into higher value-added products, chemical precipitation and metathesis method was proposed to extract sulfonated by-product from the P608 wastewater: with BaCl2 as precipitant and sulfuric acid as displacer, the sulfonated by-product was separated from cyclohexanecarbonic acid and other acid by-products in P608 wastewater. By altering the precipitant, the reaction time, the ratio of Ba/SO4, effectiveness of these parameters were discussed. The research showed the favorable reaction conditions: the reaction time 60min, the molar ratio of Ba/SO4 1:1. The favorable conditions of activated carbon absorption were as follows: absorption temperature was 75～80℃, pH value 2～4, the contact time 1h. Under the conditions, the sulfonated by-product recovery can reach 45%.Then, a complexometric extraction method for recoverying sulfonated by-product and cyclohexane carboxylic acid from P608 wastewater was presented. Meanwhile, the influence of the ratio of extractants and diluents, pH of wastewater, extraction time and temperature were investigated. The experiment results indicated that high extraction efficiency can be obtained under the conditions of tributyl phosphate: kerosene=1:4 as the first complex extractant and tri-n-octylamine: octanol: kerosene =2:3:5 as the second complex extractant. The favorable results were: the recovery of sulfonated by-product can reach 39.6%; the recovery of cyclohexanecarbonic acid can reach 53%.