| In wrought iron, metallurgy, electroplating, textile printing and other modernindustrial production process, a lot of inorganic acids or alkali are often used,producing a large amount of waste acidic or alkali liquor. In order to avoid theenvironmental pollution of rivers and to recycle the useful resources, the liquorshould be treated before they are discharged. A lot of researches have been doneon industrial acids or alkali treatment, such as acid-base neutralization,extraction and crystallization. etc. However, these methods have theirdrawbacks, including consumiption of large amount of acids or alkali, strictrequirements of equipment or high operating and handling costs. Diffusiondialysis (DD) as a novel separation process, and has the advantages of lowoperation cost, clean nature and easiness for operation. Hence application of DDnot only can solve the problem of recovering waste acids or alkali pollution, butalso can be simple, effective, economic and eco-friendly.As for alkali recovery, the DD membranes should have the following featuresin order to achieve high alkali recovery efficiency: high OH-permeability andsalt rejection, low water permeability and good thermal and chemical stability.At present, commercially used membranes are mostly organic polymer cationexchange membranes, which have limitations in stability and alkali flux.Besides, the stability and selectivity are likely to decrease after long time ofruning. Therefore, the development of new membranes with outstandingstability and alkali permeability, and the application of such membranes for DDtreatment of waste alkaline liquor, is highly desirable.The ions transport process in organism can be taken as references to achievethe above goal. For instance, the cell membrane has ion channels, and thewater-soluble substances such as various sugars and ion enter and leave the cellmainly through the ion channels in the process of metabolism. Ion channels inhuman body allows selectively transmission of different ions at a relatively highrate.(about107ions per second). Accordingly, we tried to prepare a kind ofartificial ion channel membrane to enhance the membrane separation efficiency.The urea silane and carbon nanotubes are chosen as raw materials, which havethe ability for self-assembly, and PVA or SPPO are used as the membranematrix, so that a series of organic-inorganic hybrid ion channels membrane are prepared. The membrane structure and physicochemical properties arecharacterized and their performances in DD are explored.This dissertation consists of five chapters. The first chapter gives a briefintroduction of the membrane separation. Then characteristics and preparationmethods of the organic-inorganic hybrid ionic membranes as well as ion channelmembranes with the bionic structure and their applications are introduced indetails. Finally, the main contents of this dissertation are proposed.The rigid aromatic rings and urea ribbons in3-(4-methoxy phenyl urea base-)propyl triethoxy silane(UPTS) can assist the assembly of different UPTSmolecules to form ion channels. Therefore in the second chapter UPTS is chosenas the raw material, PVA or SPPO as the matrix to prepare hybrid membranes.The membranes show significantly improved DD performance. The dialysiscoefficients of OH-(UOH) values are in the range of0.013–0.022m/h,2–5timeshigher than those of PVA and SPPO bland membranes. The S values are in therange of26–32, also higher than PVA and SPPO blank membranes (thecorresponding values for the blank membranes are0.004-0.007m/h,8–11).Hence, the ‘‘trade-off’’ effect between ion fluxes and selectivity is broken andUHPS can be regarded as alkali transport promoter. The phenyl-groups and thehydrophilic ion conducting pathways from self-organized–OCH3groups canpromote the transport of Na+ions, while the urea groups and Si–OH groups canassist the transport of OH-ions through the hydrogen bonding.Chapter3is a development and extension of chapter2. In chapter1, we foundthe water swelling behavior of PVA blank membrane is significantly differentwhen different solvents are used for membrane preparation. Accordingly, the3rd chapter further studieds the influence of solvents on membraneperformances. Two series of membranes, PVA membrane and SPPO membraneare prepared. For PVA membrane, water and DMSO with different ratioanechosen. For SPPO membranes, N,N-dimethyl formamide (DMF) or dimethylsulfoxide DMSO is used as the solvent. Investigation of the membranes thecharacterizations reveals that solvent variety can influence the physical andchemical stability, ion exchange and ion transport ability of the membrane.Moreover, the effect of one certain solvent can be quite different for membraneswith different polymer matrix.In the4th, SPPO or PVA is blended with multiwalled carbon nanotubes (MWCNTs) to prepare two series of homogeneous DD membranes. Scanningelectron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR),alkali resistance, water uptake,65oC swelling and other tests are conducted tocharacterize the basic structure, morphology, physico-chemical properties of themembranes and the application for alkaline DD. The stability of the blendmembranes, for instance, the swelling degree at room temperature and65oC isbeen improved effectively, which may be because MWCNTs in the membranescan act as the reinforced material. Moreover, after addition of MWCNTs, themechanical strength and flexibility are also increased, which is important for themembrane practical application. When applied for NaOH/Na2WO4DD process,the UOHvalues of the blend membranes are improved as compared with PVAand SPPO blank membranes indicating that the addition of MWCNTs canpromote ion transport. Therefore, the blend membranes can be used in DD torecycle alkali.Chapter5is the summary of the dissertation. Meaningful conclusions aboutthe preparation and applications of the organic-inorganic hybrid ion channelsmembrane are drawn through summary of the experimental and theoreticalanalyses. |
PDF Full Text Request