Design And Application Research Of Liquid-Liquid Two-Phase Flow Mixer Used In The Treatment Of Acetic Acid Wastewater

With the production of acetic acid and related fine chemical products in China,a large amount of acetic acid wastewater has been produced inevitably.Nearly 100,000 tons of acetic acid wastewater is discharged every year in the furfural production industry alone.The acetic acid wastewater will not only cause serious pollution to the environment,but also cause a lot of waste of resources and economic losses.Existing treatment technologies such as rectification method and neutralization method are only suitable for the treatment of high-concentration acetic acid wastewater;the treatment of low-concentration acetic acid wastewater is still a difficult problem.The extraction method is a method for the treatment of low-concentration acetic acid wastewater.The traditional extraction device has weak mixing capacity and long solution residence time,which is not positive to the liquid-liquid mass transfer of the extraction process,and the separation time of oil and water after extraction is also long.These results in a not high extraction efficiency.Therefore,it has obvious research value and practical significance to develop continuous extraction enhancement technology to improve extraction efficiency and simplify extraction operations.The key to the continuous extraction enhancement process is continuous and efficient liquid-liquid two-phase mixing and subsequent separation.The point is mainly on the liquid-liquid two-phase mixing.The mixing process requires both uniform droplet distribution and rapid separation.In this paper,numerical simulation and experiment have been combined and static mixer has been taken as the research object,computational fluid dynamics software Fluent has been used to design and optimize static mixer’s structure.Through experiments and numerical simulation,the particle size of the oil droplets in the static mixer at different residence times has been obtained,the mixing performance could be evaluated by comparing the distribution of particle size.Then the static mixer has been applied to the intensification the process of extraction of low-concentration acetic acid wastewater.Therefore,the optimal extraction conditions could be screened,and the extraction and subsequent separation processes has been combined to design a continuous treatment for acetic acid wastewater.At the same time,this paper plans to start from the characteristics of two-phase flow mixer,research and design a micromixer structure which is conducive to the two-phase mixing of oil and water,and provide different options for the process enhancement and application of continuous extraction operations.According to the current research results,the following conclusions can be summarized:(1)Considering the energy consumption and the mixing index,when the feed oil-water ratio is 1:1,the structure of the SK static mixer which is conducive to two-phase mixing is: the torsion angle is 180°,the elements are arranged to cross in the same direction and L/D=2:1.(2)The simulation results of the oil diameter which using PBM model are relatively close to experimental results.The distribution range of the oil diameter narrows with the increasement of the flow rate.Finally,it distributes in the interval of 0～3 mm,mainly concentrating in 0～1 mm.It shows that the mixing capacity of the SK static mixer designed and optimized in this paper increases with the shortening of residence time.However,there is an upper limit of the mixing capacity.If the two-phase feed ratio is defined,the particle size of oil will not decrease all the time.For the SK static mixer in this paper,when the feed oil-water ratio is 1:1 and the residence time is less than 7.5 s,the oil droplet has a smaller particle size,which is suitable for preparing emulsions with a particle size less than 1.5 mm;when the residence time is between 10～15 s,the particle size of oil is moderate,mainly concentrated in1～2 mm,which is suitable for subsequent rapid extraction experiments.(3)At room temperature,when the residence time is 15 s and the oil-water flow ratio in the SK static mixer is 1:1,the maximum single extraction rate is 47.92%.When the number of extraction stages is 4,the extraction rate is 97.53%.Compared with the batch reactor,the processing capacity of the SK static mixer is 42 times,and the reaction time has shortened by 800 times.Using Na OH as a stripping agent,the SK static mixer and the T-type oil-water separator could be connected in series to treat the acetic acid wastewater continuously,the combination of the extraction process and the subsequent oil-water separation process could be realized.Finally,the acetic acid in the acetic acid wastewater can be converted into sodium acetate crystals whose purity is 95%.(4)The optimal working angle of the micromixer designed in this paper is θ=30°.When Re=52.5,the mixing index is 96.47% and the pressure drop is330.45 Pa in 4 cycles.The simulation and experimental results show that its high mixing efficiency,spatial fluidity,and good mixing index could satisfy the oil-water two-phase mixing in the extraction process.