STRUCTURAL OPTIMIZATION OF THE NAPHTHALINE DISTILLATION SCHEME BASED ON PHASE EQUILIBRIUM ANALYSIS

Abstract

The research main aim is to analyze the presence, composition and naphthalene azeotropes type with impurities in the naphthalene fractions obtained by the distillation of coal tar. The presence of mentioned impurities significantly complicates the process of obtaining a pure product – naphthalene. The most difficult problem is the separation of naphthalene-thionaphthene mixture.Based on the simulations of the vapor-liquid equilibrium of the these mixtures components at different pressures, which were carried out in the HYSYS simulation environment using the UNIFAC method and the NRTL activity model, it has been shown that there are positive homogeneous azeotropes of 2,3-xylenol – naphthalene and naphthalene – thionaphthene. Azeotrope of xylenol – naphthalene – thionaphthene existence in the mixture was predicted. At atmospheric pressure, the azeotrope composition is presented: xylenol - 43 mass %, naphthalene - 5 mass % and thionaphthenes - 52 mass %. The boiling point is 201°C.Based on the analysis of phase equilibria, a unified energy efficient naphthalene separation method was proposed. Scheme consist of two columns, which operate under different pressures: the first column at a residual pressure of 100 mm Hg, the second at atmospheric pressure. The required regimes and efficiency of the columns were determined, ensuring the production of a commercial product with a main substance content of more than 99 % from naphthalene fractions with different composition with minimal loss of naphthalene.The conditions for the formation of the power-energy unit were determined in order to use the upper product condensation heat in the second column to heat the column operating under vacuum. This principal reduces the energy costs of obtaining the pure naphthalene (99 mass %) by 35 % in comparison with the design scheme without linking the heat fluxes.