SIMULATIVE PROGRAMMING OF A HYBRID WASHING OIL

SEPARATION SCHEME FOR PURE CHEMICALS

Lining Zhang

1,2

, Duo Zhao

, Peng Wu

, Jinsheng Sun

*, Lili Liu

, Yulan Ji

and Shuo Jiang

School of Chemical Engineering and Technology, Tianjin University, No. 92 Wei Jin Road, 300072, Tianjin, P.R. China

CNOOC Shandong Chemical Engineering Co., Ltd, No. 80 Lishan Road, Jinan, 250013, Shandong Province, P.R. China

Henan Shenma Nylon Chemical Co. Ltd, No.711 Jianshe Road, Pingdingshan, 467000, Henan Province, P.R. China

Keywords: Washing oil, Coupling separation technology, Distillation, Crystallization, Process simulation.

Abstract: Washing oil, one of the important distillation cut of coal tar, consists of a series of high value-added

components which can form azetropic and eutectic system, making it impossible to separate certain

components completely by normal distillation. In this work, a scheme coupling distillation with

crystallization to deal with this cut for pure chemicals is simulatively investigated before an industrial

design. By the aid of this research, a 25Kt/a pilot scale unit was successfully designed which is now running

with α-methyl-naphthalene, β-methyl-naphthalene, fluorene, dibenzofuran and acenaphthylene in high

purity as main products and naphthalene fraction, medium washing oil (dimethylnaphthalene) and heavy

washing oil as by-products.

1 INTRODUCTION

Washing oil is the distillation cut of coal tar between

230~300ºC, which consists of many organic

chemical materials, such as naphthalene, methyl-

naphthalene, dimethyl naphthalene, fluorene,

dibenzofuran, acenaphthylene etc (Wang, 2004).

Basically, there are two ways to produce these

substances of high purity, synthesis and separation.

The cost of the former is undoubtedly high, while

the physical separating way from washing oil is

simple and proved to be economical (Liang and Xue,

2008). Therefore, deep processing of this cut

through physical separative method becomes

practically significant (Song and Schobert, 1993).

On the other hand, washing oil was widely

available in coal based coking industry which is

usually applied in washing benzene from coal gas,

making this cut missed the opportunities for further

deep utilization for more value-added fine chemicals,

with the residue still remaining the above mentioned

bulk features, or becomes even better. The good

news is that the concern to separation options has

been given rise to with the increasing demanding for

fine chemicals, which can be extensively used in

pesticides, pharmaceuticals, dyes, synthetic

materials (Yang and Duan, 2006; González and

Gutierrez, 2008), as well as the increasing large-

scale of coal tar plant to offer more and more

resource of washing oil .

In the present work, a novel scheme coupling

distillation with crystallization for comprehensively

deep processing of washing oil is reported, and

subsequently simulatively researched and

programmed from the angle of industrial design,

with the recommended scheme then manifested to be

feasible through successfully running over 12

months of a 25Kt/a pilot scale unit. By the aid of this

research, this unit was designed with α-

methylnaphthalene, β-methylnaphthalene, fluorene,

dibenzofuran, and acenaphthylene as main product,

and the naphthalene, medium washing oil, and heavy

washing oil as byproducts.

2 MODELLA SCHEDULE

2.1 Crude Washing Oil Feedstock

The components of washing oil are listed in Table 1,

some of which with low content cannot be defined

by instrument analyses. One possibility for this

situation is to select substitutes for the undefined

components in the simulation calculation process,

through assigning corresponding selected substances

of different normal boiling points in accordance with

chromatograph peak sequence.

425

Zhang L., Zhao D., Wu P., Sun J., Liu L., Ji Y. and Jiang S..

SIMULATIVE PROGRAMMING OF A HYBRID WASHING OIL SEPARATION SCHEME FOR PURE CHEMICALS.

DOI: 10.5220/0003619404250428

In Proceedings of 1st International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SIMULTECH-2011), pages

425-428

ISBN: 978-989-8425-78-2

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

Table1: Components of original materials (washing oil)

and their characteristics.

No. Name

Boiling

Point

(ºC)

Molecular

Weight

kg/kmol

Mass

Fraction

(wt%)

1 Naphthalene 217.96 128.175 3.849

2 Quinoline 237.69 129.161 3.023

3 X-01 239.73 144.210 0.817

4 X-02 239.73 150.220 1.732

5 X-03 240.75 149.236 0.285

6 β-methylnaphthalene 241.05 142.202 21.153

7 α-methylnaphthalene 244.69 142.202 10.020

8 X-04 246.50 134.134 0.108

9 X-05 247.80 143.188 0.165

10 X-06 247.96 143.188 0.278

11 X-07 248.11 172.310 0.136

12 X-08 249.85 122.124 0.099

13 Biphenyl 255.00 154.211 4.589

14 X-09 258.05 170.211 1.497

15 2,6-

dimethylnaphthalene

262.00 156.227 3.244

16 X-10 264.85 220.354 0.093

1,3-

Dimethylnaphthalene/

1,4-

Dimethylnaphthalene

263.00 156.227 4.697

18 X-11 267.00 198.349 1.320

19 X-12 268.39 105.138 0.319

20 indole 253.00 117.15 1.396

21 Acenaphthylene 277.39 154.21 18.88

22 X-13 282.05 204.356 1.380

23 Dibenzofuran 284.71 168.195 9.491

24 X-14 284.85 152.15 0.336

25 X-15 286.00 196.29 0.337

26 X-16 293.15 183.252 0.508

27 X-17 293.85 166.177 0.277

28 Fluorene 297.29 166.222 7.624

29 X-18 300.78 143.188 0.341

30 X-19 306.09 143.188 0.972

31 X-20 336.85 192.26 0.443

32 X-21 346.00 179.221 0.594

As shown in Table 1, the boiling points of the

components in the mixture are so close. This implies

high challenges for distillation requiring high

purities of the distillates. Besides, many binary

azeotropics, e.g. indole-acenaphthylene, indole-

dimethylnaphthalene, together with some eutectics

which summarized in Table 2 are formed in washing

oil, which further increase the difficulty for

completely the separation of single component.

Table 2: The main eutectics of washing oil.

Eutectic

Melting Point (

℃)

Naphthalene/β-methylnaphthalene 26

Naphthalene/α-methylnaphthalene -34.6

Naphthalene/acenaphthylene 51

Naphthalene/fluorene 57

Naphthalene/indole 41.8

β-methylnaphthalene/α-

methylnaphthalene

-41

2.2 Flowsheet Description for Current

Deep Processing of Washing Oil

Currently, washing oil was only rough finished or

selectively separated for several components in

China. A number of processing technics have

already been reported, such as narrow fractions

separating method, azeotropic distillation, extractive

distillation, and combination of distillation and

washing (Wang, 2004). However, all of these

methods have extremely complex process with

limited product species. Reportedly, the most

recommended method was from the Chemical Co.,

Nippon Steel Corporation in Japan (Zhang and Yan,

2002). Their processing flowsheet is shown in

Figure 1.

Figure 1: The washing oil processing flowsheet of The

Chemical Co., Nippon Steel Corporation.

1- alkaline tower; 2-washed material distillation tower ; 3-

acenaphthylene tower; 4-naphthalene tower; 5-acid tower;

6-neutralizing tower; 7-methyl naphthalene tower; 8-β-

methylnaphthalene tower.

Washing oil is added to the alkaline tower after

mixed with naphthalene oil, and NaOH solution is

used as detergent to remove phenol. Then the

washed material is heated and pumped to the

distillation towers to separate low naphthalene oil,

medium oil, and residual oil in sequence. Low

naphthalene oil is used to recover benzene, residual

oil to obtain industrial acenaphthylene in the next

column, and medium oil is heated and then pumped

to naphthalene tower to distill industrial naphthalene,

methyl naphthalene, and residual oil. After that, the

methyl naphthalene is pumped to the acid tower to

remove pyridine and quinoline, and then neutralized

using NaOH in neutralizing tower. Afterwards,

industrial methyl naphthalene is obtained in methyl

naphthalene tower, and further it also can be refined

to β-methylnaphthalene. At the end, it can not only

obtain β-methylnaphthalene of high purity, but also

industrial naphthalene, industrial methyl naphthalene,

industrial fluorene and medium washing oil.

This technic can not only use to separate washing

oil, but also treat naphthalene oil and

methylnaphthalene oil, with large capacity. In the

SIMULTECH 2011 - 1st International Conference on Simulation and Modeling Methodologies, Technologies and

Applications

426

process, methylnaphthalene oil was drawn in gas

phase to avoid emulsification. As the five distillation

columns are packed with high efficient packing, all

the products are distilled to high purity, among

which the purity of β-methylnaphthalene reached

98wt%. With all the packed columns operated in

decompression, bottom temperatures are lowered

and demands of heating medium of high temperature

resisted. Besides, this process can take advantage of

self-produced steam and warm water to reduce the

energy consumption.

2.3 Novel Separation Process for

Washing Oil

To make full use of the washing oil resource, a novel

separation process was encouraged to present, as

shown in Figure 2. Crude washing oil is first fed into

naphthalene tower to obtain naphthalene cut. The

residual oil is pumped into methyl naphthalene

tower, where industrial methyl naphthalene can be

recovered as top product which is then driven to the

β-methylnaphthalene tower to produce β-

methylnaphthalene and α-methylnaphthalene

simultaneously. Moreover, the bottom α-

methylnaphthalene stream can exchange heat with

methylnaphthalene stream for sake of energy saving.

Residual methylnaphthalene oil is pumped into

acenaphthylene tower after mixed with crystalline

raffinate from acenaphthylene crystallizer to

distillate medium washing oil, crude acenaphthylene

and residual acenaphthylene oil. And then the crude

acenaphthylene is further refined by crystallization

to obtain industrial acenaphthalene. Residual

acenaphthalene oil is pumped into dibenzofuran

tower for dibenzofuran with the bottom residual

dibenzofuran oil driven into fluorene tower after

mixed with fluorene crystallizer raffinate. The side

product pumped to crystallization unit for industrial

fluorene.

In the original flowsheet, fluorene is reclaimed

from the top of T6, after crystallization, fluorene of

industrial grade is obtained, and the residual liquid

with a series of light components returns to the feed

stream of T6. Consequently, the light components

accumulated in the reflux and increased

continuously, resulting in decrease of fluorene

quality. As an improved process, the fluorene

fraction is drawn out as a side-product, the light

components is removed from the top of the column.

This is just the starting point of the coupled scheme

between ordinary distillation and crystallization. So

in this scheme, α-methyl-naphthalene, β-methyl-

naphthalene, fluorene, dibenzofuran, and

acenaphthylene are simultaneously obtained in high

purity, and the naphthalene fraction, medium

washing oil (dimethyl naphthalene), and heavy

washing oil can also be attained as by-product.

Figure 2: Flowsheet of distillation coupled with

crystallization and its on-site counterparts

T1-naphthalene tower; T2-methylnaphthalene tower; T3-

β-methylnaphthalene tower; T4- acenaphthylene tower;

T5- dibenzofuran tower; T6-fluorene tower; 7-

acenaphthylene crystallizer; 8-fluorene crystallizer

2.4 Simulative Design of Distillation

Coupled with Crystallization

Process

This novel process was simulatively analyzed with

SRK-modified Panag-Reid equation of state

(SRKM) and Grayson-Streed generalized

correlations (GS), which were empirically confirmed

by the co-authors in similar industrial practices to

describe the basic thermodynamic behavior of the

system appropriately.

SRKM equation is an

improvement for SRK equation to provide better

predictions of properties for multicomponent

systems:

{

}

jiijiijijjiij

xxxkkkααα ))+/()((+)1()(=

2/1

(1)

And GS correlation is a modification of the Chao-

Seader correlation, which can be expressed as:

)(==

(2)

)ln(+)ln(=)ln(

(3)

Besides, the purity of acenaphthylene and

fluorene separated by crystallization was both set to

be 97%, and their yield were 75% and 60%

respectively according to the designers of the

crystallizers. So in the process simulation, the above

parameters are specified in the input procedures and

the quantity of circumfluence from the crystallizers

is calculated automatically.

In order to obtain simulative parameters that

agree as well as possible with the on-site

counterparts, hydraulic calculations of packings, and

the pressure drops of the distributers are taken into

account. That is, process simulation and structure

design rise alternately, with the results of process

SIMULATIVE PROGRAMMING OF A HYBRID WASHING OIL SEPARATION SCHEME FOR PURE CHEMICALS

427

calculation guiding the structure parameter design

and structure design, in return, amending the process

simulation. The operating parameters and the results

of process simulation are listed in Table 3 and 4.

Table 3: The operating data of six columns in simulation.

T1 T2 T3

Top Bottom Top Bottom Top Bottom

100 100 120

R 28 9 22

Mr 134 152 141 159

℃)

85 266 85 280 110 251

P (kpa) 105 114 105 114 80 115

T4 T5 T6

Top Bottom Top Bottom Top Bottom

100 100 104

R 18 30 19

Mr 158 166 168 164 169 154

T (

℃)

85 295 85 304 85 320

P (kpa) 105 114 105 114 105 114

As shown, the purity of methylnaphthalene, β-

methylnaphthalene, fluorene, and acenaphthylene all

reach industrial grade. And actually the field date of

this 25Kt/a pilot scale unit indicated that the purity

of the 5 main products all go beyond 95wt%, which

fully accommodated the requirements of fine

chemicals.

Table 4: The components of main production in simulation.

No.

Methylnapht

halene

Acenaphthyle

Fluorene

β-

methylnaphthale

1 6.28E-10 0.0000 0.0000 9.25E-10

2 5.95E-03 9.15E-11 0.0000 8.7E-03

3 1.76E-04 3.14E-13 0.0000 2.59E-04

4 9.67E-03 1.57E-09 0.0000 0.0142

5 1.64E-03 3.52E-10 0.0000 2.42E-03

6 0.637 9.16E-07 0.0000 0.9201

7 0.306 8.18E-06 0.0000 0.0417

8 3.18E-03 1.26E-11 0.000 9.22E-05

9 2.64E-03 6.34E-06 0.0000 3.70E-03

10 5.71E-03 7.16E-06 0.0000 8.18E-03

11 7.77E-09 1.81E-17 0.0000 1.15E-08

12 2.95E-03 3.47E-12 0.0000 5.85E-04

13 3.31E-07 7.33E-04 0.0000 1.00E-16

14 1.27E-09 3.35E-04 0.0000 0.0000

15 4.89E-08 1.16E-03 0.0000 0.0000

16 9.24E-10 1.96E-03 0.0000 0.0000

17 7.21E-07 9.27E-13 0.0000 3.23E-16

18 3.29E-05 4.66E-04 0.0000 6.43E-20

19 0.0000 5.51E-05 0.0000 0.0000

20 0.0260 7.33E-11 0.0000 9.41E-08

21 0.0000 0.9695 4.07E-12 0.0000

22 9.75E-15 0.0182 0.0000 0.0000

23 1.46E-20 1.58E-03 1.68E-07 0.0000

24 2.02E-20 5.71E-03 1.36E-08 0.0000

25 0.0000 3.05E-05 0.0000 0.0000

26 0.0000 9.03E-08 1.15E-03 0.0000

27 0.0000 8.72E-09 1.47E-04 0.0000

28 0.0000 1.22E-04 0.9706 0.0000

29 0.0000 5.23E-06 0.0278 0.0000

30 0.0000 1.19E-07 2.77E-04 0.0000

31 0.0000 4.54E-05 1.44E-18 0.0000

32 0.0000 0.0000 2.44E-20 0.0000

3 CONCLUSIONS

A novel process based on distillation coupled with

crystallization for the separation washing oil to

reclaim high grade fine chemicals is presented in

this work, from first step simulative research to the

successful field fulfillment. It demonstrates that this

process can utilize washing oil more

comprehensively with up to 5 fine chemicals,

namely, α-methyl-naphthalene, β-methyl-

naphthalene, fluorene, dibenzofuran and

acenaphthylene as principal products, and

naphthalene fraction, medium washing oil (dimethyl

naphthalene), as well as heavy washing oil of

improved quality as byproducts. In addition, results

from a converged simulation revealed these main

products were in high purity, suggesting the

feasibility of this hybrid scheme, which was then

verified by field running data.

On this foundation, by the aid of high efficient

packing technology, a 25Kt/a pilot scale unit was

designed, and has already successfully run over 12

months.

REFERENCES

González, A. M. D., Gutierrez, B. C., Casal, B. M. D.,

2008. The use of solvents for purifying industrial

naphthalene from coal tar distilled oils. Fuel

Processing Technology.

Liang, X., Xue, Y., 2008. The abstraction of fluorene and

dibenzofuran from fas absorber oil. Thesis.

Song C., Schobert H. H., 1993. Opportunities for

developing specialty chemicals and advanced

materials from coals. Fuel Processing Technology.

Wang, F., 2004. Extraction of washing oil distillate from

tar and its application in fine chemistry industry. Coal

Chemical Industry.

Yang, R., Duan, R., 2006. Extraction, application and

prospect of the components of wash oil. Coal

Chemical Industry.

Zhang, X., Yan, H., 2002. Brief introduction to wash oil

processing technology of the Chemical Co., Nippon

Steel Corporation. Fuel & Chemical Processes.

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Applications

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