关键词: 膜污染, 清洗度, 对氨基酚, 电还原合成

Abstract: The electroreduction process of nitrobenzene, which consists of a series of elementary processes, is a complicated reaction system. Besides p-aminophenol, some by-products, such as azoxybenzene, azobenzene and diaminodiphenyl ether can also be produced in the process. These by-products which hardly dissolve in H₂SO₄ aqueous solution will adsorb and deposit on the surface of membrane material gradually and thus pollute the membrane material, which causes increases in bath voltages and decreases in current efficiency. In the paper, from the viewpoint of engineering application the fouling and cleaning processes of Nafion membrane in the direct electrochemical synthesis of p-aminophenol were investigated.In the process of direct electroreduction of nitrobenzene, the bath voltages and the current efficiency at different service times of Nafion membrane were measured, respectively.The fouling ratio of membrane and the cleaning degree of fouled membrane, characterized with bath voltage, were defined in this paper. Further, the fouling rate equation of Nafion membrane was presented.With the equation, the fouling rates and the fouling ratios of Nafion membrane at different service times could be calculated easily. Meanwhile, the bath voltages and the current efficiency at the different service times of Nafion membrane could be calculated easily as well. A kind of membrane cleaning agent consisting of anionic surfactants(AES,ABS and R-3), nonionic surfactants(JFC,APG-10 and Tween-60), isopropanol and water, was presented.When the fouled Nafion membrane was cleaned by the cleaning agent online for 2 h in the condition of pH≈13, 60 ℃ and 4 L•min^-1 circulation velocity, the bath voltage,SEM morphologies of membrane and membrane resistances could be restored to those of the initial membrane basically.The cleaning degree of fouled membranes was still close to 1 after the cleaning agent was used for 5 times repeatedly, and the strength of rinsed membranes was still the same as that of the initial membrane.

Key words: 膜污染, 清洗度, 对氨基酚, 电还原合成