Download romanova2018

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