Study On Preparation Of High Performance RO Composite Membranes And Synthesis Of Functional Monomers

Nowadays the percentage of indigenous reverse osmosis (RO) membrane applied in our country is low for the deficiency of RO membrane functional materials which lead to little species RO membranes. Investigation of functional materials and film formation mechanism is crucial for preparation of high performance RO composite membranes. In this study there are four main parts which were synthesis of monomers, preparation and characterization of functional membrane materials, preparation and characterization of RO composite membranes, as well as analysis of film formation process by interfacial polymerization.Four functional monomers were synthesized firstly including 5-chloroformloxy-isophthaloyl chloride(CFIC;the best yield was 29.3%, purity ≥ 99.1%), 5-isocyanate -isophthaloyl chloride(ICIC;the best yield was 64.4%, purity ≥ 99.2%), 1, 4-cylohexane diamine(HDA;the best yield was 55%, purity ≥ 99.5%) and 1,3,5-cyclohexane triacyl chloride(HT;the best yield was 99%, purity ≥ 99.5% for the first step, the best yield was 85% for the second step). The chemical structure of all monomers was proved by Infrared Spectroscopy (IR), Nuclear Magnetic Resonance Spectroscopy (NMR), Gas Chromatogram -Mass spectrum(GC-Ms) and Element Analysis (EA).CFIC and ICIC were prepared with triphosgene and oxalic chloride respectively to replace phosgene in traditional technics at room temperature and low pressure, high yield and good purity were obtained;HDA and HT were prepared according to related reference, similar yield and purity were obtained.Secondly, membrane barrier's materials were prepared with synthesized monomers and purchased monomers through interfacial polymerization technique and characterized by water vapor adsorption and active chloride consumption to decide preliminarily which monomers were suitable to prepare which kind RO composite membranes. Results revealed that the order of water vapor adsorption for polymer prepared with m-phenylenedi amine (MPD) (or HDA) and various multiacyl chloride is: HT>ICIC>TMC>CFIC;the order of water vapor adsorption for polymer prepared with different multiamines and the same multiacyl chloride is: HDA>MPD. So the structure of cyclohexane is helpful for improving the water flux. Although CFIC/MPD material had lowest weight gain, its time consumption of reaching to adsorption balance is much longer than others because of its compact structure which is potential to prepared RO composite membrane with high rejection for sodium chloride. The active chlorine consumption of polymer prepared with methyl-m-phenylenediamine (MMPD) is less than the others and the active chlorine consumption of polymers prepared with ICIC is more than others. So MMPD is suitable to prepared chlorine-resistant RO composite membrane and ICIC is not.Thirdly, some new reverse osmosis composite membranes were prepared with multiacylchloride (chloroformloxy or isocyanate) monomers and diamine monomers through interfacial polymerization technique on the polysulphone supporting film. It contains four kinds RO composite membranes: Chlorine-resistant RO composite membrane (CFIC/MMPD. HT/MMPD, TMC-HT/MMPD),Antifouling RO composite membrane (ICIC/MPD),High flux RO composite membrane (TMC/MPD- SMPD (5-sulfonic acid m-phenylenediamine) , ICIC-IPC/MPD, ICIC-HT/MPD) and High rejection RO composite membrane (CFIC/MPD).The membranes were characterized using permeation experiments with salt water, Attenuated total reflectance infrared (ATR-IR), X-ray photoelectronic spectrum(XPS), as well as imaging using atomic force microscopy (AFM) , scanning electronic microscopy (SEM) and so on. Results revealed that introducing a methyl on aromatic multiamine can improve chlorine-resistance property of RO composite membranes;the surface of antifouling RO composite membranes was smoother than the others and its absolute value of surface zeta potential was less than the others which lead to a good antifouling property;the flux can be enhanced more than 30% with little decrease of rejection for sodium chloride by changing the cross-linking degree of high flux RO composite membrane's barrier or introducing cyclohexane structure in its polymer chain;there were much hydroxyl in the high rejection RO composite membrane's barrier which lead to its rejection for sodium chloride decreasing much more slowly than the others.Lastly, hydrolysis of multiacyl chloride and interfacial polymerization of multiacyl chloride and multiamine were monitored by a pH measurement with continuous record. Result revealed that hydrolysis of multiacyl chloride is relatively so slow that can be ignored. The diffusion of multiamine from aqueous solution to oil solution was correlative to their partition coefficient in two solutions. A mathematic model for film formation by interfacial polymerization was set up based on diffusion of multimode from aqueous solution to oil solution and the increase of film thickness layer by layer. The equation of membrane thickness, time, monomer concentration et al is obtained. The effective membrane thickness was defined as the thickness of cross linking polymer membrane. When the average function degree of reactive zone is 2, the efficient membrane thickness is the maximum, just as follow:The mathematic model of membrane thickness, time, monomer concentration et al agreed with the experiment well. It described the process of interfacial polymerization quantificationally and was useful to control the process of interfacial polymerization.