Study On Synthesis And Properties Of Organic-Inorganic PTFE-Based Composite Membranes For Electrosynthesis Of N₂O₅

As a green nitrating agent, N₂O₅has great application prospect in nitrationreaction. Among the methods to synthesize N₂O₅, the method of electrochemicaloxidation of N₂O₄is the most promising one to be industrialized. And in the processof electrochemical oxidation to synthesize N₂O₅, separator is one of the mostimportant key materials, which is crucial to the yield of N₂O₅and the consumptionlevel of energy.PTFE membrane has good chemical resistance while it has a lot of defects too,such as high membrane resistance, high N₂O₄and H₂O permeability and serious NO⁺and NO2⁺electro migration from anode to cathode. In this paper, PTFE membrane,the basal lamina, is prepared to be the organic-inorganic composite membrane throughorganic-inorganic doping method in order to decrease the membrane resistance,promote N₂O₄-resistance and H₂O-resistance ability, restrain NO⁺and NO2⁺electromigration, finally achieving the goal of increasing the yield of N₂O₅and decreasingthe consumption level of energy.PTFE/SiO₂modified membrane, with SiO₂mass fraction up to3.7%, can beobtained through direct immersion method using TEOS as the impregnation liquid.The experimental results show that the ability of preventing water and N₂O₄frompermeating and the membrane resistance both decrease significantly with the massfraction of SiO₂increasing. And also, with the mass fraction of SiO₂increasing, thecurrent efficiency increases and the specific energy decreases.PTFE/Nafion membrane is obtained through Nafion solution modificationmethod. Then symmetric and asymmetric PTFE/Nafion-SiO₂membrane can beobtained through adding SiO₂.The experimental results show that the membraneresistance can be significantly reduced through the addition of Nafion, but beincreased with excessive amount of SiO₂. When SiO₂layer is on the anode side, N₂O₄permeating from anode to cathode can be restrained effectively. When SiO₂layer is onthe cathode side, the current efficiency can be increased and the specific energy canbe decreased.PTFE/Nafion/SiO₂–TiO₂membrane can be obtained through the directimmersion method using PTFE/Nafion membrane as the basal lamina. Theexperimental results show that the addition of TiO₂can significantly enhance theH₂O-resistance ability so as to increase the current efficiency. At last, composite membranes contained-NH₂、-NH-are prepared through thedirect immersion method using3-APTES and DAMO. The experimental results showthat these membrane have excellent performance because of the existing of-NH₂、-NH-which can restrain NO⁺and NO2⁺electro migration. PNSDA has a betterperformance during electrolysis: N₂O₅: N₂O₄（molar ratio） is1.74, current efficiencyis96.5%, and specific energy is0.9kWhr/kg N₂O₅.