| With the rapid progress of the economy and society,the social demand for machinery,electronics,new materials,and new energy,continues to increase.The global chemical industry is growing rapidly,and its production capacity and output value have been greatly improved.The rapid and remarkable development of the chemical industry and resulted in abundant production materials and daily necessities,however,it has caused environmental pollution problems.Therefore,the development of a kind of environmental protection and energy-saving technology has been an urgent problem,it can recover wastes produced in chemical production,recycle treated wastes,and reduce environmental pollution,duo to chemical production process.Electrodialysis technology is an important branch of chemical engineering based on an ion exchange membrane.It is a novel separation technology developed in the middle and late 20th century.Under the action of an electric field force,electrodialysis can realize the wastewater desalination,chemical refining purification and abraum salt resource utilization because of the special selective permeability of ion exchange membranes.Electrodialysis technology has emerged as one of the important clean production technologies.It has been widely used in chemical industry production,environmental protection,biological food,and other fields,because of its efficiency and environmentally friendliness.Electrodialysis can be divided into common electrodialysis and bipolar membrane electrodialysis according to the different ion exchange membranes used.Common electrodialysis is composed of anion and cation exchange membranes,which are mainly used to perform desalination and obtain the desired concentration of the saline solutions.Bipolar membrane electrodialysis combines the advantages of ion directional transport and water dissociation in a common electrodialysis process.In this way,slat can be recovered,and its resources can be utilized in solutions.It has the characteristics of advanced technology,economic energy saving and environmental friendliness.According to the technical characteristics of common electrodialysis and bipolar membrane electrodialysis,this manuscript carried out the application research of electrodialysis technology in chemical separation and purification to expand the application range and application model of electrodialysis technology in the chemical industry.The contents are as follows:In chapter 1,the development status of the chemical industry and electrodialysis technology is introduced briefly.Then,the structure of electrodialysis and the classification of ion exchange membrane are introduced in detail.the development and application of common electrodialysis and bipolar membrane electrodialysis are described.In chapter 2,the feasibility of the desalting and purification of Methyl Sulfonyl Methane(MSM)from saline mixtures is studied in terms of common electrodialysis.The effects of operating voltage difference,feed concentration and electrolyte salt concentration on desalination and recovery rate were investigated,and the effects on the energy consumption and current efficiency of electrodialysis are analyzed.The cost and process economy of electrodialysis in the demineralization and purification of dimethyl sulfone are evaluated by process cost accounting.Results show that the recovery rate increased slightly as the operating voltage increases,furthermore,molecular penetration is the main reason for the loss of the MSM in the electrodialysis experiment.The recovery rate decreased as the MSM concentration increase the MSM concentration gradient between a desalination chamber and a concentration chamber increase as the feed MSM concentration increases.Common electrodiaiysis can be operated at low feed dimethyl sulfoxide concentration,which is advantageous to obtain a high recovery.The recovery rate is not significantly affected by the concentration of electrolyte salt,but the current efficiency decreased as the electrolyte salt concentration increase.In electrodialysis,the current efficiency and energy consumption reach 74.0%and 12.3 Wh/L,respectively.In terms of the recovery and desalination rate,the highest recovery is 97.4%,and the desalination ratios was both higher than 98,5%.According to the calculation of process energy consumption,the total cost of the whole process is only 2.34 $/t.Therefore,the separation and purification of dimethyl sulfone by common electrodialysis can have high efficiency and economic benefits.In chapter 3,the recycling and utilization of waste salt containing neopentyl glycol was studied by using bipolar membrane electrodialysis.High-value formic acid and sodium hydroxide has been transmuted directly by sodium formate,which is the by-product of neopentyl glycol,and then,they will be used as raw materials in the upstream process of neopentyl glycol synthesis,to realize the sustainable closed-loop production of neopentyl glycol.By changing the current density and salt concentration in the process,the effects on the potential difference,salt conversion and acid-base concentration in the electrodialysis process of bipolar membrane were investigated,and the effects on the energy consumption and current efficiency of the process were analyzed.Through the calculation of capital cost and operating cost,the total process cost of the by-product sodium formate of neopentyl glycol for the recovery of bipolar membrane electrodialysis is calculated,and compared with the traditional sodium formate waste salt treatment method for comparison and reference.The results show that the current density has a significant effect on the electrodialysis performance of the bipolar membrane.High current density helps to reduce capital cost,but leads to high energy consumption.When the current density is 10 mA/cm2,the minimum energy consumption is 6.1 kWh/kg.By tradeoff between capital and operating costs,an optimal current density of 30 mA/cm2 is recommended.When the feed salt concentration increased from 0.1 mol/L to 0.4 mol/L,the electrodialysis performance of the bipolar membrane was improved,but when the feed salt concentration further increased to 0.5 mol/L,the bipolar membrane electrodialysis performance decreases.This may be due to the migration of more formate ions from the salt chamber to adjacent chambers and a concentration gradient at higher feed salt concentrations.The recovered formic acid and NaOH obtained satisfactory purity by electrodialysis with bipolar membrane,and there was almost no neopentyl glycol.The total process cost of bipolar membrane electrodialysis is estimated to be 1.304 $/kg HCOOH.Compared with conventional treatment methods,bipolar membrane electrodialysis is more competitive in the treatment of neopentyl glycol wastewater.However,in the industrial application of bipolar membrane electrodialysis to clean production of neopentyl glycol,a great deal of effort is still needed to focus on the treatment of membrane fouling.In chapter 4,the bipolar membrane electrodialysis process has been used to replace the traditional production process of vanadium pentoxide to avoid the high ammonia nitrogen and high salt wastewater generated by using a large number of ammonias,so as to realize the green production of vanadium pentoxide.The effects of initial pH of salt chamber and initial concentration of vanadium solution in acid chamber on the experimental process of electrodialysis of bipolar membrane were investigated.The influence on the concentration and yield of vanadium pentoxide in acid chamber was investigated by changing the current density,salt chamber concentration,acid chamber volume ratio and other conditions.The results show that compared to the salt concentration,the current density and the acid chamber volume ratio have great effects on the experimental performance.When the current density is 30 mA/cm2,the salt concentration is 0.3 mol/L,and the acid chamber volume ratio is 1:2,the acid chamber vanadium concentration can reach the highest value,the highest vanadium concentration is 0.168 mol/L,and the corresponding conversion rate is 17.3%.Compared with the conventional vanadium precipitation process,although the final vanadium concentration and the amount of red cake production is not high,but its advantages are simple operation,low impurity content,and its cost is much lower than the traditional route of complex process.The fifth chapter mainly summarizes the whole paper and prospects the application of electrodialysis technology in chemical production. |
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