Production of Commercial Naphthalene by Coal-Tar Processing

The derivation of commercial naphthalene by rectification is a possible approach in coal-tar processing. Naphthalene is widely used in chemical synthesis for the production of phthalic anhydride, superplasticizers, and intermediate products such as Cleve’s acids in dye production. The quality of the naphthalene derived from petroleum is markedly higher than that of coal-tar naphthalene, primarily in terms of the thionaphthene content, since the thionaphthene content in the initial petroleum fractions is much less than in the naphthalene fraction of coal tar. Simulation of the vapor–liquid equilibrium of binary and ternary mixtures of the components in coal tar by means of the NRTL activity model, at different pressures, indicates that 2,3-xylenol–naphthalene, naphthalene–thionaphthene, and 3-xylenol–naphthalene–thionaphthene mixtures are characterized by positive homogeneous azeotropes. The composition and boiling points of the azeotropes are determined. The presence of the azeotropes significantly complicates the derivation of naphthalene from the naphthalene fraction of coal tar, in which the naphthalene content exceeds 97%. Analysis of the composition of the initial mixture and the azeotropes suggests a design for a three-column system for the distillation of commercial naphthalene, with the preliminary separation of water without the need for special separating agents or chemical extraction of impurities. Optimization of the proposed equipment by means of HYSYS software indicates high technological flexibility of the process and the production of naphthalene from coal tar that matches the quality of the naphthalene derived from petroleum. The naphthalene content in the commercial product derived from coal tar by the proposed method is 99.99 wt %. The yield of naphthalene is 90.5 wt %. The energy consumption in the basic three-column system is 0.92 Gcal/t of commercial naphthalene (of purity 99.99 wt %). If heat is recycled in the three-column system, the energy consumption is reduced to 0.6 Gkal/t of product (with the same degree of purity). That is comparable with the energy consumption in a two-column system, and the commercial naphthalene produced is characterized by greater yield and purity.