Synthesis Of2,6-Naphthalene Dicarboxylic Acid By Air Oxidation Of2-Methyl-6-Propionylnaphthalen In Liquid Phase

As an important industrial intermediate,2,6-Naphthalen dicarboxylic acid (2,6-NDA) is the main synthetic materials of various polyesters, polyurethanes, and liquid crystal materials. Polyethylene naphthalene-2,6-dicarboxylate (PEN) synthesized by2,6-NDA polymerizes and ethylene glycol (EG) is a widely used high quality polyester which has received global attention. However, due to synthesis difficulty of its raw materials, the development of PEN is limited.In order to improve the yield and purity of2,6-NDA,2-methyl-6-propionyl naphthalene(2,6-MPN) was oxidized by air in a semi-continuous stirred titanium autoclave under the catalysis of cobalt, manganese and bromine in an acetic acid solvent. The autoclave was self-designed while2,6-MPN was self-made. The main factors effecting catalytic oxidation reaction such as the amount of catalyst, the additive amount of Co and Fe were discussed. Experimental results show that this reaction needs less catalysts whose optimal composition ratio is m(Co):m(Mn):m(Br):m(HOAc)=1:2:5:1000. Since the concentration of cobalt in catalysts affects the reaction most and cobalt can catalyze the slow oxidation of acetic acid, the concentration of cobalt should be controlled at a low level, but not less than0.1%. Fe has little influence on the reaction and its concentration should not be more than0.2%. Besides, we designed an orthogonal experiment and analyze some factors such as temperature, pressure and time of the catalytic oxidation reaction. The orthogonal experiment results show that the optimal operating conditions is that the optimal composition ratio is m(HOAc):m(2,6-MPN)=15:1,m(Co):m(Mn):m(Br):m(HOAc)=1:2:5:1000with optimal temperature of200℃, optimal pressure of1.9MPa, optimal reaction time of2.5h, optimal air flow rate of3L/min, optimal stirring rotation number of900r/min. Under these optimal operating conditions, the yield of2,6-NDA can be up to91.44%.Another part of this thesis is to design and optimize the purification route of oxidation products. Although2,6-NDA has a high purity after the catalytic oxidation reaction, a small amount of impurities and metal ions contained in it can still have bad effect on subsequent operations. The crude2,6-NDA was dissolved in sodium hydroxide solutions, and then decolored with active carbons. Precipitations and activated carbons were removed by filtration and acetone was added in the process of filtration to get2,6-NDA disodium salt solids. The disodium salts were dissolved in deionized water, and then acidized by sulfuric acid to get purified2,6-NDA. After purification, most of the impurities and metal salt catalysts could be removed. The purity of the product2,6-NDA is close to100%with white color which will meet the requirements of subsequent steps.