Study On Synergetic Treatment Of Sodium Sulfate Wastewater From Coal Tar Processing By Ternary Solvent And Centrifugal Extractor

With the development of economy and society,the demand for cleaner production and resource recovery is more and more urgent.Sodium sulfate wastewater is a kind of coal tar processing effluent with high-concentrated phenol.Due to the high toxicity of phenol,it could pose a serious threat to the natural environment and human health.Solvent extraction is a preferred method for phenol wastewater for the advantages of high extraction eff-iciency and simple operation,but the common extraction agent often cannot meet the requirements of high extraction performance,low solubility,regeneration performance,economy and other industrial use.In this paper,on the basis of selection and comparison of a variety of extractants,a highly efficient,green and new ternary solvent(TBP/DEC/cyclohexane)was selected as the extractant to extract sodium sulfate wastewater,and then NaOH solution was used as the reverse extractant to complete the regeneration of extractant and recovery of phenol.In order to meet the requirements of continuous treatment in industry,the centrnfugal extractor,combining the ternary extractant was used as the equipment platform to realize the synergetic treatment of sodium sulfate wastewater on the basis of studying the hydraulic characteristics and internal flow characteristics of the equipment.The main research contents and innovative achievements of this paper are as follows:(1)The effects of composition were studied,resulting in that the optimum volume ratio of TBP/DEC/cyclohexane was 20%:20%:60%and the optimum concentration of NaOH solution was 1mol/L.The effects of extraction and back-extraction conditions were systemically studied,and the maximum efficiency were 99.79%and 96.29%under the optimal conditions,respectively.The FTIR analysis illustrated that the extraction of phenol was contributed by the intermolecular hydrogen bonds with TBP and DEC.The pH response analysis showed that the four stages for the stripping process.(2)The extraction and back-extraction conditions were optimized based on RSM response surface method,and four quadratic regression equation models were obtained to predict the efficiency.Under the principles of high efficiency and low phase ratio,the optimal extraction conditions for the extraction time were contact time of 299.4 s,extraction temperature of 33.43 ?,O/A of 0.45,the extraction efficiency was up to 98.40%.Under the principle of efficient recovery of phenol resources,the optimal back-extraction conditions were contact time of 213.4 s,temperature of 36.85 ?,A/O of 0.97,the extraction efficiency could reach 96.39%.(3)The centrifugal extraction platform was designed and built to study the hydraulic characteristics of the equipment,including phase separation characteristics,phase entrainment characteristics,maximum separation capacity and liquid storage capacity.It was found that the phase separation ability of the ternary extractant-wastewater system increased with the increase of salt concentration.With the increase of rotating speed,the phase entrainment decreases,and the maximum separation capacity increases linearly.When the flow ratio departs from 1,the phase entrainment will increase rapidly,leading to the maximum separation capacity,And the and liquid storage capacity remained basically unchanged with flow ratio.The appropriate flow ratio range is 0.25-4.(4)By PIV experiment and CFD calculation,the Taylor vortex state changes in the mixing region and the flow field distribution in the drum were obtained.The calculation of vorticity showed that the vortex mixing capacity increased with the increase of rotating speed.The calculation of drum suction capacity indicated that the suction capacity of the drum increases with the increase of rotating speed.The gas-liquid interface in the centrifugal extractor was regulated to obtain the gas-liquid regulation law of rotating speed both for the mixing region and the separation region.The liquid-liquid mixing in the mixing zone was calculated to show that the increase of rotational speed and the decrease of flow rate could result more uniform mixing of the two phases.(5)The synergistic treatment of sodium sulfate wastewater by ternary solvent and centrifugal extraction was studied.The effects of flow ratio,speed and flow rate on extraction efficiency,back-extraction efficiency and stage efficiency were investigated.When the flow ratio is far away from 1,the stage efficiency gradually declined.And the increase of speed contributed to the efficiency.The effect of flow rate on efficiency increases first and then decreases.The maximum extraction efficiency for single stage can reach 99.76%,and the stage efficiency is close to 100%.And the phenol content in the wastewater after secondary extraction was lower than 0.12mg/L,meeting the discharge requirements.