| 6-APA(6- aminopenicillanic acid) is an important intermediate of semi-synthetic penicillin, and has broad market prospects. Separation and recovery of the 6-APA in pharmaceutical wastewater have significant economic and environmental benefits. At present, the 6-APA separation methods include: resin adsorption, nanofiltration, electrodialysis, reverse osmosis, etc., and all of them have obvious shortcomings. Hence, this paper constructed a new complexation extraction system to separate and recover 6-APA. On this basis, a small scale experiment using packed extration tower was carried out and its hydrodynamic and mass transfer performance were calculated and analyzed. Provided theoretical basis and data support for industrial application of recovery of 6-APA by packed extraction column.Firstly, based on the principle of complexation extraction and extraction equilibrium experiments, determined a complexation extraction system with aliquat 336 as complexing agent, chloroform as diluent. Studied the effects of various factors on the extraction and back-extraction, the results showed that: The optimum concentration of the complexing agent of 0.1175 mol / L, phase ratio of 0.4, p H of 6, then complexation extraction distribution coefficient of 3.31, a single-stage extraction rate of 56.96%; With the feed concentration range from 4g / L to 0.5g / L, distribution coefficient were not reduced and maintained at a high level; optimum back-extraction p H between 1 and 2, back-extraction phase ratio of 0.4, then the back-extraction partition coefficient of 2.65, a single-stage back-extraction rate of 51.42%. The co-extraction studies showed that a total extraction effect, the greater concentration of complexing agent and p H, and smaller phase ratio and feed concentration, decided lower complexation extraction selectivity and significant effect of co-extraction. Tertiary extraction rate and tertiary back-extraction rate was 98.62% and 96.28%, respectively, and after seven times regeneration and reusing of complexation extraction agent, partition coefficient were not significantly reduced.Secondly, based on the optimum operating conditions resulted from complexation extraction experiments; a process of recycling 6-APA by packed extraction tower was proposed and did small scale experiments. Effects of packing type?flow ratio and flowrates on the extraction ratio were researched. The results showed that in the tower with the inner diameter of 45 mm, the extraction efficiency of ? ring packing was better than regular gauze packing. The optimum operating conditions were as follows: the dispersed phase flow rate was 25L/h, the continuous phase flow rate was 10L/h and the flow ratio was 2.5. The extraction efficiency could reach 73.95%.Finally, calculated and analyzed the hydrodynamic and mass transfer performance. Studied the effects of different flow ratio and dispersed phase superficial velocity on the speed of the flooding, the dispersed phase holdup and mass transfer surface area and slip velocity.Inner-turbulence model was applied to calculate the mass transfer coefficient inside and outside droplet. The results showed that complexation extraction process controlled by the outside diffusion and mass transfer resistance concentrated in the stage of complex diffusion in the continuous phase. Examined the overall mass transfer coefficient ratio Kod, mass transfer unit height Hod and number of transfer units Nod under different flow ratios and dispersed superficial velocity, under optimum operating conditions, Kod of 4.1×10-5m/s, Hod of 0.3418 m, Nod of 2.048.Complexation extraction process could effectively separate and recover 6-APA in the pharmaceutical wastewater, and extraction column packing process had many advantages, such as large capacity, low energy consumption, simple operation. This study laid a good foundation for industrial application of recovery of 6-APA by packed extraction column. |
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