Study Of Novel Cloud Point Extraction Using Non-Ionic Surfactant

It was paid more and more attention to preconcentrate and separate trace-level pollutants in the water, represented by polycyclic aromatic hydrocarbons (PAHs), while the environment protection becomes more and more important. But the traditional separation methods usually showed a low performance, wasting too much energy and with a high cost in the treatment of such trace-level dangerous substances whose concentrations are commonly at ppm or even ppb level. Cloud point extraction (CPE), as a new separation method, offers many advantages including low cost, higher efficiency and environment-friendliness, and has been proved efficienct in the separation of many trace-level substances. Such advantages also determine that the application in water treatment was an important direction and trend of CPE. While it showed a very low performance when scaling the process up from a lab tube scale to an industrial scale.This thesis did a deep discovery focusing in the limitations occurred in the key processes of traditional CPE, including the high water content in the surfactant-rich phase aroused by the common used poor-performance nonionic surfactant, the phase separation process based on throughput-limited centrifugation operation, and the low efficient back extraction process. Through developing new processes, a high efficient application of CPE in the continuous water treatment was realized, and with a wider extracted species extension.First of all, after analyzing the relationship of surfactant structure and water content in surfactant-rich phase, a more suitable surfactant for CPE was selected. Through employing the polyether silicone surfactant with flexible main structure as the extractant of CPE, forming a more hydrophobic and compact micelle structure, the water content and volume of the resulting surfactant-rich phase was decreased even in a high surfactant concentration. Meanwhile an almost 100% recovery was obtained in the treatment of a PAHs pollutant solution with a wide concentration range, and based on the low surfactant-rich phase volume, a PAHs concentration as high as 700 mg/L to 800 mg/L in the surfactant-rich phase was obtained after the CPE process, resulting in the highest preconcentration factor of PAHs (30-40) that has ever been reported in the related research and a very high distribution coefficient (2.5-2.9 (Log(Kd))).Secondly, in order to enlarge the treatment capability of CPE process, two novel CPE processes, ultrasonic assisted CPE and stirring assisted CPE, were developed by substituting the traditional centrifugation operation by ultrasonic and stirring effects respectively, which make the processes able to be scaled up and operated continuously. Comparing with the traditional process based on centrifugation (C-CPE) with a same surfactant concentration, a lower surfactant-rich phase water content, a comparable or higher phase separation speed and a higher distribution coefficient of PAHs in the treatment of pollutant water were obtained in the two new CPE processes after selecting suitable surfactant. Then, the scaling up experiments of the two new processes were successfully performed in the continuous treatment of low concentration PAHs pollutant water with constant flow pump and purposed made extractant column. Both of the two continuous processes were able to achieve a stable status within a short time, and comparing with the corresponding batch experiment, an equal or even higher performance were obtained in most PAHs concentration range of actual PAHs pollutant waters (<20 mg/L), and the performance increased with the volume of extractant column. The results indicated that both of the new processes were able to offer an efficient continuous treatment to most actual PAHs pollutant water, and a higher performance was predictable in a treatment with a larger scale.Meanwhile, a new back extraction technology suitable for the continuous application of CPE was developed based on the reverse micelle phenomenon. Comparing with the traditional liquid-liquid extraction based back extraction process, the new one avoided the usage of high energy-cost assistant operation, i.e. ultrasonic or microwave, and almost 100% recoveries were obtained for both of the surfactant and extracted species at the same time.At last, the CPE process was successfully applied in the separation of hydrophilic organic acid, represented by acetic acid, from water by combined with complex extraction technology. The organic solvent diluent in the traditional complex extraction was substituted by micelle solution in the new combined CPE process, and acetic acid was separated by the phase separation operation of the followed CPE process. The new process offered a recovery of 71.4% and a distribution coefficient of 1.4 for acetic acid with a 0.1M concentration, which was comparable with the performance of traditional process; moreover, the combined CPE process is also with a lower cost and more environment-friendly. Thus, it is expected to be a high efficient treatment process for the acetic acid pollutant water in a low concentration.