Study On The Process Of Crystallization Of 2-Methyl-1,4-naphthoquinone

The gas-solid catalytic oxidation of 2-methylnaphthaene to 2-methyl-1,4-naphthoquinone is a complex process, with phthalic anhydride, and other by-products producing. In order to effectively separate target product 2-methyl-1,4-naphthoquinone, the crystallization separation method was adopted. It is critical to determine the solubility of 2-methylnaphthelene and 4-methylphthalic anhydride, which is important to improve the yield of target product 2-MNQ. This paper mainly focus on crystallization technique optimization for the separation of 2-methyl-1,4-naphthoquinone and 2-naphthaldehyde, and crystallization dynamics for 2-methyl-1,4-naphthoquinone purification. The study offers theoretical basis and data foundation for 2-methyl-1,4-naphthoquinone separation purification technique design and industrialized production.The solubility of 2-methylnaphthelene and byproduct 4-methylphthalic anhydride in different pure solvents were determined experimentally by the equilibrium methods at different temperatures. The temperature dependence of solubility of 2-methylnaphthelene and 4-methylphthalic anhydride were correlated by the Van’t Hoff equation, the modified Apelblat equation and λh equation.Base on the solubility data we determined, hexane is selected as the appropriate solvent to realize rough separation of raw material 2-methylnaphthelene and other products. Then, hot water is used to separate phthalic anhydride, 4-methylphthalic anhydride and 2-methyl-1,4-naphthoquinone, 2-naphthaldehyde. The effect on temperature, water volume, and stirring time is examined. When solid compound quality is 1.7096 g, the better separation technique condition is: heat temperature 30℃, stirring time 110 min, solvent water adding volume 30 mL. Under better separation conditions, purification of 2-methyl-1,4-naphthoquinone and 2-naphthaldehyde can reach 98.66%.With respect to the process of seperation, the conversion of 2-MN and the yield of 2-MNQ were considered as testing goaTake the high purification and yield of 2-methyl-1,4-naphthoquinone as target, the cooling crystallization and dilution crystallization process of 2-methyl-1,4-naphthoquinone were systematically studied, impact of the various operation conditions of cooling crystallization and dilution crystallization process on product purification is studied. And it is determined that the best operation condition for cooling crystallization is: ethanol and water ratio of 1: 1.5, cooling crystallization temperature of 13℃, cooling rate of 1℃/ min, crystallization time of 240 min. The best operation condition for dilution crystallization is: crystallization temperature of 25℃, stirring intensity of 360 rpm/min, dilution agent flow acceleration rate of 2.1 mLmin. Results show, compared with cooling crystallization dilution, crystallization can obtain product with higher purification and yield, and the operation process is easier to control.Based on quality balance principle and population balance equation, the paper established 2-methyl-1,4-naphthoquinone crystallization process dynamic model. And through model fitting, nucleation rate equation and growth rate equation are obtained. On basis of this, the impact of over-saturation, stirring velocity, density of the suspension on crystallization process are analyzed. For 2-methyl-1,4-naphthoquinone the solventing out crystallization process, from the dynamic equation can be seen, high suspension density, moderate stirring rate and higher over saturation is more conducive to get high quality 2-methyl-1,4-naphthoquinone crystal products.