Basic Research On Bipolar Membrane Based Applications For Acid And Base Production At High Current Density

The realization of the circular economy is crucial for sustainable development as civilization continues to advance.However,the current chemical industry has difficulties including resource waste,high energy consumption,and environmental pollution.Therefore,it is necessary to improve and optimize the current manufacturing processes or create new chemical processes.Today,a number of ion exchange membrane technologies have demonstrated promising application potential.Among them,bipolar membrane electrodialysis(BMED)is a new electro-membrane technology that makes use of the property that water molecules can be split into H+ and OH-in the middle layer of bipolar membranes(BPM).BMED has been widely utilized in the chemical sector for the production of acids and bases,desalination,resource recycling,environmental protection,etc.The major use of bipolar membrane technology to date is the generation of inorganic acids and bases.Though the primary causes are the massive consumption of BPMs,the restriction of low current density operation,and the depletion of salt chamber ions,the development of bipolar membrane technology still faces challenges with high costs and low concentrations of acid and basic products.Based on this,this dissertation proposes an optimization improvement of the process of acid and base production based on BPMs.This dissertation comprises five chapters,which are presented as follows.An overview of ion exchange membrane technology is given at the beginning of Chapter one,and this is followed by a study of the historical development of BPMs,the mechanism of water dissociation,and associated application processes,which highlights the broad range of applications for bipolar membrane technology.Then,a dialectical discussion is held on the present inorganic acid and base manufacturing methods based on electro-membranes,such as the chlor-alkali industry,direct electrosynthesis(DE),and BMED.Finally,the research concepts and the research content of this dissertation are presented.In Chapter two,we suggested an innovative method for producing acid and bases called asymmetric bipolar membrane electrodialysis(ABMED).The design of the standard BMED membrane assembly has been improved.The findings demonstrate that ABMED is capable of controlling orientational ion migration in electrodialysis(ED)and water splitting in the BPM.When the monopolar membrane’s effective area was half that of the BPM,ABMED’s performance in the generation of acids and bases was equivalent to that of standard BMED.The overall cost of the ABMED process was 0.78 $/kg NaOH,which was 21%less expensive than the standard BMED method.Additionally,it was discovered that the asymmetric membrane design prevented the concentration polarization phenomena in ED.In Chapter three,an online integrated process:ED-BMED system was presented to create acid and base.Brine,which is commonly produced by various industrial wastewater treatment plants,is a viable resource.Previous attempts by BMED have been made to convert brine into the more beneficial caustic soda.However,the comparatively low concentration of recovered base,typically less than 4.0 mol/L,severely restricts the spread of BMED technology.ED and BMED are effectively relating in an online integrated system in this chapter to boost the concentration of the produced base.The concentration function in ED can supply enough feedstock for BMED,allowing for effective water splitting in BPMs at extremely high current densities.This combined ED-BMED system was capable of produce 6.20 mol/L NaOH,a high concentration that has not been reported.The ED-BMED system was thoroughly tested with a single BMED process and a normal industrial BMED+ED process(acid/base generation by BMED followed by concentration using ED)to further assess this online integrated system.The ED-BMED system was discovered to use less energy than the other two.As a result,the ED-BMED system converts low concentration brine to high concentration base in a single step with minimal energy consumption and has considerable potential for industrial applications.Based on the previous study,ion-injection bipolar membrane electrodialysis(IJBMED)was proposed in Chapter four.An overflow feed mechanism was designed to provide continuous feedstock supply for BMED.This BMED design was able to enhance the water splitting of BPMs with ultra-high current density while avoiding anion and cation exchange membrane concentration polarization.BMED enabled one-step conversion of NaCI-containing brine to 8.4 mol/L NaOH with specific energy consumption of 870 kWh/t NaOH(24 wt.%→26 wt.%)and 2740 kWh/t NaOH(0→26 wt.%).This bench-scale experiment demonstrated that IJBMED is a potential caustic base manufacturing technology that might augment or possibly compete with the chloralkali method.Chapter five primarily covers the whole dissertation and provides an outlook on the industrialization of the BMED process.