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ISSN 1068-364X, Coke and Chemistry, 2018, Vol. 61, No. 11, pp. 453–456. © Allerton Press, Inc., 2018. Original Russian Text © N.A. Romanova, V.S. Leont’ev, A.S. Khrekin, 2018, published in Koks i Khimiya, 2018, No. 11, pp. 36–40. CHEMISTRY Production of Commercial Naphthalene by Coal-Tar Processing N. A. Romanovaa, *, V. S. Leont’eva, **, and A. S. Khrekina, *** a Saint-Petersburg Mining University, St. Petersburg, Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] Received October 19, 2018; revised October 19, 2018; accepted November 12, 2018 Abstract—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. Keywords: naphthalene production, phase equilibria, naphthalene azeotropes, coal-tar processing, rectification, energy conservation, design optimization DOI: 10.3103/S1068364X18110078 Coal tar may be processed by rectification so as to obtain several fractions: light, phenolic, naphthalene, anthracene, absorbing, and so on. Each fraction is subsequently distilled to obtain valuable individual products, which are mainly aromatic compounds. Globally, industry processes coal tar at a rate of ~7 million t/yr [1]. The naphthalene content of the initial tar may be 10–11%. Given the high market value of commercial naphthalene, we may regard this hydrocarbon as a promising product. Details regarding the first stage of tar processing— its separation into broad fractions—may be found in [2]. The technology for producing commercial naphthalene of different grades from the naphthalene fraction was considered in [2]. Naphthalene is an aromatic compound that is widely used for the production of phthalic anhydride, superplasticizers, and intermediate products such as Cleve’s acids in dye production. Considerable quantities of naphthalene are required for large-scale phthalic-anhydride production. The quantity of Cleve’s acids produced is much smaller, but the quality of the naphthalene must be higher. Purified naphthalene may be derived not only from coal tar but from petroleum tar. Table 1 compares the quality of naphthalene samples from coal tar and petroleum [3]. We see that the quality of the naphthalene derived from petroleum is markedly higher than that of coal-tar naphthalene, primarily in terms of the thionaphthene content. In fact, the naphthalene derived from petroleum is produced from residues of reforming catalyzates, as a rule, and the solid catalysts employed in that process are sensitive to the sulfur 453 454 ROMANOVA et al. Table 1. Characteristics of pitch from petroleum (A) and coal tar (B) Parameter Melting point, °C Content, wt %: naphthalene tetrahydronaphthalene methyl naphthalenes thionaphthene A B 80.0 79.8 99.73 0.23 0.04 0.00004 99.1 – 0.05–0.10 0.7–0.8 content of the materials being processed. Accordingly, the content of organosulfur products is minimized. Many authors have discussed the possibility of removing impurities from naphthalene by rectification. For example, experiments on the separation of naphthalene and thionaphthene were described in [15]. It is difficult to remove thionaphthene and other impurities from naphthalene, because it tends to form binary and ternary azeotropic mixtures, for which rectification is ineffective. Instead, it is necessary to use azeotropic agents or chemical extraction of the impurities, or else special methods such as the purification of naphthalene by sulfuric acid. In the latter method, regeneration of the sulfuric acid is expensive. Detailed analysis of the quality of spent sulfuric acid may be found in [16]. One of the four different compositions of the naphthalene fractions in coal tar here considered (differing in the impurities present and their proportions) is as follows (mass fractions) [4]: Water o-Xylene Indan Indene Phenol Xylenol-2,3 Naphthalene Thionaphthene Quinoline 1-Methylnaphthalene 2-Methylnaphthalene Diphenyl Fluoranthene 0.00500 0.00790 0.02391 0.00600 0.00350 0.01800 0.72004 0.03200 0.02500 0.03422 0.10111 0.00050 0.02064 We do not have clear information regarding the presence or absence of specific azeotropic pairs in the naphthalene fraction, as noted in [5, 6]. In particular, the existence of the 3,4-xylenol–naphthalene azeotrope was mentioned in [7–14]. It was also concluded that the naphthalene–thionaphthene mixture consists of components with close boiling points but is not azeotropic. Difficulty in separating the 2,3-xylenol– naphthalene pair and the ternary xylenol–naphthalene–thionaphthene azeotrope was noted in [7–14]. In the present work, we simulate the vapor–liquid equilibrium of binary and ternary mixtures of the components in coal tar at different pressures. The composition of the liquid phase and the vapor in equilibrium with that phase is calculated with variation in the content of the low-boiling component in increments of 0.1 wt % close to a possible azeotrope. Table 2 presents the results. In Fig. 1, we show an example of the equilibrium curve for the 2,3-xylenol–naphthalene pair at a residual pressure of 100 mm Hg, plotted by means of the NRTL activity model (Ideal pair calculation model), in the coordinates t and x, y. (The upper curve corresponds to the vapor phase and the lower curve to the concentration y of the low-boiling component x in the liquid phase.) In the production of chemically pure naphthalene (>97%), the main difficulty is the removal of 2,3-xylenol and thionaphthene, which form azeotropic mixtures with naphthalene. The possibility of producing naphthalene of purity no less than 97% and 99%1 was considered in [6]. Naphthalene is extracted in two rectification columns, the first of which operates under vacuum, while the second is at normal pressure. The costs in producing naphthalene of different quality are compared. We find that the costs in supplying heat to the second column are 3.7 times greater in producing 99% naphthalene than for 97% naphthalene, with constant energetics of the first (vacuum) column. After calculating the phase equilibria by means of the NRTL model and determining the uniform binary coefficients between the components in Table 1 by the UNIFAC method, with information regarding the type, composition, and boiling point of the azeotropic mixtures, we may propose a three-column system for the distillation of commercial naphthalene, with the preliminary separation of water (Fig. 2). In the proposed system, light hydrocarbons that boil sooner than the ternary azeotropic mixture are removed in the first column, which operates at a residual pressure of 70 mm Hg (9.3 kPa), on 15 theoretical plates. Some of the naphthalene is lost with the vapor components removed at the top of this column; in particular, around 3% of the available naphthalene is lost with the water–naphthalene azeotrope. The bottoms from column 1 are sent to column 2, with a residual pressure of 100 mm Hg (13.3 kPa). The distillate obtained is a ternary positive azeotrope from which other impurities have been removed. The distillate is sent to column 3, which operates under excess pressure. In the 2,3-xylenol–naphthalene–thionaphthene azeotropic mixture, 2,3-xylenol has the lowest boiling 1 We use wt % throughout. COKE AND CHEMISTRY Vol. 61 No. 11 2018 PRODUCTION OF COMMERCIAL NAPHTHALENE BY COAL-TAR PROCESSING 455 Table 2. Results of simulating the vapor–liquid equilibrium Content of component (1), mass fraction Material Tbo (1), °C 2,3-Xylenol (1)–naphthalene (2) 0.410 (760 mm Hg) 0.27 (100 mm Hg) Naphthalene (1)–thionaphthene (2) 0.793 (760 mm Hg) 2,3-Xylenol (1)–thionaphthene (1) 2,3-Xylenol (1)–naphthalene (2)– Xylenol—0.43 thionaphthene (3) Naphthalene—0.05 Thionaphthene—0.52 (760 mm Hg) Table 3. Operational parameters of columns Characteristic Number of theoretical plates Supply plates (counting from the top) Reflux ratio Sampling ratio (Distillate stream/Inlet stream) Pressure at the top, mm Hg (kPa) Still temperature, °C Temperature at the top, °C Energy consumption, Gcal/t Total energy consumption, Gcal/t Tbo (2), °C 216.9 – 217.9 Nonazeotropic – – – Tbo (azeo), °C 217.9 – 219.9 210.5 141.5 (100) 217.7 – – – 201 Column 1 Column 2 Column 3 15 2 3.2 0.075 159 (21.2) 159 43 0.12 30 22 2.5 0.790 100 (13.3) 169 144 0.33 0.92 40 40 42 0.100 2000 (266.0) 265 249 0.47 point (217°C), closely followed by naphthalene (218°C). As we know, increasing the pressure in positive azeotropes shifts the vapor–liquid equilibrium to higher content of the heavier component. Hence, the thionaphthene content of the mixture increases, with decrease in the naphthalene content. The bottoms contain 99.99% naphthalene and traces of thionaphthene and 2,3-xylenol. The operational parameters of the columns are summarized in Table 3. tionating section of column 3 is sufficient to supply heat to column 2. The temperature at the top of column 3 is 249°C, while the still temperature of column 2 is 169°C. On that basis, the heat of condensation of the distillate vapor in column 3 may be used to generate the vapor flux in column 2. In the proposed system, the total heat consumption in the three column is 0.6 Gcal/t (taking account of recycling), and the purity of the naphthalene produced is at least 99.99%. Analysis of the heat fluxes shows that heat liberated in the condensation of the vapor flux within the frac- Temperature, qC 2 1 218 217 216 215 214 213 212 211 210 C-1 3 6 C-2 4 C-3 5 0 20 40 60 80 100 x, y Fig. 1. Equilibrium curves for the 2,3-xylenol–naphthalene pair at normal pressure. COKE AND CHEMISTRY Vol. 61 No. 11 2018 7 Fig. 2. Three-column system for the distillation of commercial naphthalene: column 1 (C-1) separates the light products (phenol, indan, indene, xylenols); column 2 (C-2) separates the heavy products (quinoline, 1-methylnaphthalene, 2-methylnaphthalene, fluoranthene, diphenyl); column 3 (C-3) separates the commercial naphthalene fraction; (1) initial coal-tar fraction; (2, 6) light hydrocarbons; (3, 5) heavy hydrocarbons; (4) partially rectified naphthalene; (7) commercial naphthalene fraction. 456 ROMANOVA et al. In selecting the operating conditions in the columns that separate the components with high melting points, attention must be paid to the temperature at the top of the column, especially when operating under vacuum. Note that the temperature at the top of column 1 exceeds the melting points of all the distillate components. That reduces the probability of a solid residue to zero. The melting points (°C) of all the distillate components in column 1 are as follows: Water Phenol Indan Indene o-Xylene 0 40.5 –51.0 1.8 –25.2 The yield of commercial naphthalene in the threecolumn system is at least 90.5%. Thus, we have shown that rectification in a threecolumn system permits the production of coal-tar naphthalene matching the quality of naphthalene derived from petroleum (purity at least 99.99%), with a yield no lower than 90.5% and ensures the removal of thionaphthene and other contaminants. CONCLUSIONS (1) We have simulated 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. We find that 2,3-xylenol– naphthalene, naphthalene– thionaphthene, and 3-xylenol– naphthalene– thionaphthene mixtures are characterized by positive homogeneous azeotropes. The 2,3-xylenol-thionaphthene mixture is nonazeotropic. (2) We have proposed a three-column system for the distillation of commercial naphthalene, with the preliminary separation of water. This system ensures the removal of thionaphthene and other contaminants. The naphthalene content in the commercial product derived from coal tar in this system is 99.99 wt %., while the yield of naphthalene is at least 90.5 wt %. (3) In the basic three-column system, the total heat consumption is 0.92 Gcal/t of commercial naphthalene (of purity 99.99 wt %). (4) If heat is recycled in the three-column system, the energy consumption is reduced from 0.92 to 0.60 Gkal/t of product (with 99.99% purity). That is comparable with the energy consumption in a twocolumn system, and the commercial naphthalene produced is characterized by greater yield and purity. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFERENCES 1. Pavlovich, O.N., Sostav, svoistva i perspektivy pererabotki kamennougol’snoi smoly: uchebnoe posobie (Composition, Properties, and Prospective Processing of Coal Tar: Manual), Yekaterinburg: Ural. Gos. Tekh. Univ.–Ural. Politekh. Inst., 2006. Oshchepkov, I.A. and Chenchenko, I.M., Formation and processing of coal tar, Vestn. Kuzbass. Gos. Tekh. Univ., 2009, no. 2, pp. 78–82. Ballard, H.D., Jr., Naphthalene from petroleum, in Advances in Petroleum Chemistry and Refining, New York: Wiley, 1965, vol. 10, pp. 219–273. Spravochnik koksokhimika. Tom 3. Ulavlivanie i pererabotka khimicheskikh produktov koksovaniya (Handbook of Coke Chemist, Vol. 3: Trapping and Recycling of Side Chemical Products of Coking), Kovalev, E.T., Ed., Kharkov: INZhEK, 2009. Romanova, N.A., Khrekin, A.S., and Leont’ev, V.S., Naphthalene separation from residues of coal tar by superfractionating method, Mezhd. Nauchno-Issled. Zh., 2017, no. 3-4 (57), pp. 80–85. Romanova, N.A., Leont’ev, V.S., and Khrekin, A.S., Structural optimization of naphthalene separation scheme based on analysis of phase equilibria, Neftegaz. Delo, 2018, no. 3, pp. 43–61. Sidorov, O.F., Thermal oxidation of coal tar pitches, Koks Khim., 2002, no. 9, pp. 35–43. Bron, A.Ya., Pererabotka kamennougol’noi smoly (Coal Tar Processing), Moscow: Metallurgiya, 1963. Leibovich, R.E., Yakovleva, E.I., and Filatov, A.B., Tekhnologiya koksokhimicheskogo proizvodstva: uchebnik dlya tekhnikumov (Technology of Coke Chemical Industry: Manual for Technical Colleges), Moscow: Metallurgiya, 1982, 3rd ed. Kharlampovich, G.D. and Kaufman, A.A., Tekhnologiya koksokhimicheskogo proizvodstva: uchebnik dlya vuzov (Technology of Coke Chemical Industry: Manual for Higher Education Institutions), Moscow: Metallurgiya, 1995. Sulimov, A.D., Prizvodstvo aromaticheskikh uglevodorodov iz neftyanogo syr’ya (Production of Aromatic Hydrocarbons for Petroleum Products), Moscow: Khimiya, 1975. Kryukov, A.S., Gabrielova, I.S., Markhovskaya, Zh.V., and Kiva, V.N., Liquid–vapor equilibrium in the systems of benzaldehyde, phenols, and naphthalene at pressures below 13.3 kPa (100 mm Hg), in Osnovnoi organicheskii sintez i neftekhimiya (General Organic Synthesis and Petroleum Chemistry), Yaroslavl: Yarosl. Politekh. Inst., 1986, pp. 52–55. Sokolov, V.Z. and Kharlampovich, G.D., Proizvodstvo i ispol’zovanie aromaticheskikh uglevodorodov (Production and Use of Aromatic Hydrocarbons), Moscow: Khimiya, 1980, pp. 281–293. Spravochnik neftekhimika (Handbook of Petroleum Chemist), Ogorodnikov, S.K., Ed., Leningrad: Khimiya, 1978, vol. 1. Markus, G.A., Terent’ev, V.Kh., and Kirsanova, V.K., The separation of naphthalene and thionaphthene by rectification, Koks Khim., 1977, no. 1, pp. 27–33. Yakusheva, E.A., Zvonarev, V.V., and Zverev, I.V., Processing the spent acid from the sulfuric-acid washing of naphthalene in coke production at OAO EVRAZ NTMK, Coke Chem., 2015, vol. 58, no. 6, pp. 220–223. Translated by Bernard Gilbert COKE AND CHEMISTRY Vol. 61 No. 11 2018