| Cumene process is the predominant technology for phenol and acetone production,which discharges large volume of high-concentration phenolic wastewater.The wastewater contains high concentration of phenol,and is mainly treated with cumene extraction process at present.The composition of the wastewater is very complicated and contains many kinds of organics besides phenol.However,there is little knowledge on the extraction performance of these organics except phenol as well as on their interactions.The accumulation of organics in the extractant and their effects on ectraction performance are unclear.Therefore,the process optimization is lack of theoretical guidance.In this study,the organic composition of the wastewater was investigated.The interaction of different organics in the extraction process was investigated with both liquid-liquid phase-equilibrium test and simulation methods.The phase-equilibrium parameters were obtained.The extraction process model was established and then the model was used to investigate the influnces of different conditions.The optimal process parameters were obtained.Pilot-scale experiment of wastewater extraction was carried out to verify the model simulation results.The main conclusions are as follows:(1)There are many wastewater-discharging sites in phenol-acetone plant of cumene process.The wastewater compostions were complicated and distinguished with each other.Seperation tank of sodium phenolate after acidification,top separation tank of cumene tower and alkaline washing tower of oxidation unit feed were the predominant sources of phenol in the plant wastewater.Their phenolic concentrations were high and phenol recovery was necessary.Besides high-conctration phenol,the wastewater also contained acetone,acetophenone,2-phenyl-2-propanol and isobutyric acid.(2)Phase-equilibrium data were determined for five ternary systems,including cumene-phenol-water,cumene-acetone-water,cumene-acetophenone-water,cumene-2-phenyl-2-propanol-water,cumene-isobutyric-acid–water,and four quaternary systems,including cumene-phenol-acetone-water,cumene-phenol-acetophenone-water,cumene-phenol-2-phenyl-2-propanol-water,cumene-phenol-isobutyric-acid-water.Binary interaction parameters were regressed with NRTL model for all the above systems.On this basis,a process model for extraction of phenol-acetone wastewater with cumene was established.When suitable theoretical plate number of the extraction tower was 4selected,the simulated data was very close to the determined data.(3)Both pilot experiment and simulated optimization indicated that performance of pollutant removal was remarkable in the extraction of phenol-acetone wastewater by cumene.The performance was influenced siginificantly by oil-water ratio(OWR).There were critical values for OWR,below which the extraction efficiencies increased with OWR increase,and beyond which the extraction efficiency inproved little with OWR increase.The critical OWR of phenol was smaller than those of acetone,acetophenone,2-phenyl-2-propanol and isobutyric-acid.OWR should be more than 6:1 to aquire good extraction performance for all the organics.(4)Acetophenone,2-phenyl-2-propanol and isobutyric-acid,at the concentration levels in phenol-acetone wastewater,showed little influence on liquid-liquid phase-equilibrium of phenol.On the other hand,phenol of 2 g/L showed significant influence on liquid-liquid phase-equilibriums of acetophenone and 2-phenyl-2-propanol.(5)When the regeneration of the extractant was poor,high-concentration of organics would accumulate in the extractant,which deteriorated the extraction performance seriously.The extraction performances of phenol,acetone,acetophenone,2-phenyl-2-propanol and isobutyric-acid would be influenced significantly by themselves in the extractant.Acetone,acetophenone,2-phenyl-2-propanol and isobutyric-acid of 100mg/L,6g/L,8g/L,200mg/L in the extractant had little influence on the extraction performances of phenol,which deteriorated the extraction performances of themselves seriously. |
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