Study On The Continuous Process Of "Pressure-Concentration" Double Driven Diffusion Dialysis And The Preparation Of Related Ion Exchange Membranes

With the mushroom growth of modern industry,the amount of industrial pollution discharges is increasing seriously.For example,a large amount of acidic wastewater is generated in metallurgy,metal processing,electroplating and other industries,and a large amount of alkali wastewater is generated in paper making,oil refining,petrochemical and other industries.If the acid/alkali wastewater was directly discharged without any treatment,on the one hand,the environment would be threatened,such as the acidity and alkalinity of water would be changed and the aquatic resources would be destroyed.On the other hand,it would waste a lot of recyclable resources.The existing methods to treat the acid/alkali wastewater includes the neutralization method,evaporation method,etc.However,these methods have some shortcomings.For example,the neutralization method cannot effectively recover acid/alkali resources and is easy to give rise to secondary pollution,and the evaporation method requires quite high energy consumption,resulting in a high process cost.Diffusion dialysis（DD）is a membrane separation process driven by concentration difference.With the advantages of convenient operation,low energy consumption and“zero pollution”,DD can avoid the defects of the traditional treatment methods and conforms to the concept of“green chemical industry”,and also has taken a place in the field of industrial wastewater treatment.However,with further application,the shortcomings of diffusion dialysis appear gradually,such as small treatment capacity,serious water osmosis,etc.Our group proposed a“pressure-concentration”double driven diffusion dialysis process.On the basis of the original concentration difference as the main mass transfer driving force,the pressure difference is added as the auxiliary mass transfer driving force to realize the diffusion dialysis mass transfer under the synergistic action of pressure field and concentration field.It not only increases the amount of wastewater treatment,but also inhibits the serious water osmosis phenomenon.On the basis of existing research,this thesis carried out two studies on“pressure-concentration”double driven diffusion dialysis.Firstly,the application of“pressure-concentration”double driven diffusion dialysis for continuous alkali recovery and the establishment of mass transfer model were studied.Secondly,a series of quaternary aminated polyphenylene ether-quaternary aminated graphene oxide（QPPO-QGO）porous anion exchange membranes were prepared for the application of“pressure-concentration”double driven diffusion dialysis.The membranes were successfully used to recover H₂SO₄from the simulated titanium dioxide waste acid（Fe SO₄/H₂SO₄）,showing good separation effect.This paper consists of four chapters,each of which is as follows:The first chapter is the Introduction.Firstly,the membrane separation technologies and ion exchange membrane varieties,preparation technologies and main performance indexes were straightforward introduced.Secondly,the principle,membrane modules and application of diffusion dialysis were introduced.Finally,it straightforward represented the starting point,significance and main content of this thesis.In the second chapter,the continuous alkali recovery and the establishment of mass transfer model of“pressure-concentration”double driven diffusion dialysis were discussed.The effects of pressure difference intensity and the initial concentration of NaOH and Na₂WO₄in the feed on the treatment performance were investigated.The results show that as the initial NaOH concentration in the feed increased,the alkali recovery ratio increased significantly,and the salt leakage ratio only slightly increased,suggesting the good separation effect can be obtained.At the same time,the water osmosis was effectively suppressed,and the alkali recovery capacity was extremely enhanced along with the increasing pressure difference intensity.With the increment of the initial NaOH concentration in the feed,the concentration of the recovered NaOH and the alkali recovery ratio increased.With the increment of the initial Na₂WO₄concentration in the feed,the recovered NaOH concentration increased,and the alkali recovery and salt leakage ratio increased due to the“salt effect”.In addition,based on non-equilibrium thermodynamics,we built a mathematical model for the continuous“pressure-concentration”double driven diffusion dialysis,and result shows that the experimental and calculated values fit well.The third chapter is the preparation and characterization of QPPO-QGO porous anion exchange membranes,which were used for the acid recovery through“pressure-concentration”double driven diffusion dialysis.BPPO and QGO were mixed in 1-methyl-2-pyrrolidone（NMP）,and then cross-linked and quaternized by triethylene tetramine（TETA）and tetramethylenediamine（TEMED）respectively,to obtain a series of QPPO-QGO porous anion exchange membrane.The results show that the sponge-like porous structure and the addition of QGO could significantly improve the DD properties of the membranes,including the dialysis coefficient（U_H⁺）and the separation factor（S）.When applied in the“pressure-concentration”double driven diffusion dialysis to recover H₂SO₄from Fe SO₄/H₂SO₄,U_H+increased obviously and S slightly decreased,but a good separation effect was obtained.It is expected to be used in the treatment of various waste acidic wastewater in the future.The fourth chapter is the Summary.This chapter is a summary of the above chapters.Based on the experimental results of Chapter 2 and Chapter 3,on one hand,the application of“pressure-concentration”double driven diffusion dialysis to recover alkali continuously has achieved the goal of inhibiting the water osmosis and improving the treatment capacity.On the other hand,the resulting high-performance QPPO-QGO anion exchange membranes could be applied to the field of“pressure-concentration”double driven diffusion dialysis.In conclusion,the“pressure-concentration”double driven diffusion dialysis and the QPPO-QGO anion exchange membranes put forward in this paper have obtained satisfactory experimental results in laboratory research,and have broad application prospects.