Computer Applications to Chemical Engineering - American Chemical

23 Computer Simulation of Heterogeneous Nitration of Toluene to Dinitrotoluene A. K. S. MURTHY Downloaded by UNIV OF NEW ENGLAND on February 8, 2017 | http://pubs.acs.org Publication Date: May 30, 1980 | doi: 10.1021/bk-1980-0124.ch023

Allied Chemical Corporation, Morristown, NJ 07960

Nitration of aromatic compounds, particularly that of benzene and toluene, has been extensively studied partly because of its industrial importance in the manufacture of explosives, solvents, pharmaceuticals and organic intermediates and partly because of its theoretical significance in studying electrophilic substitution (1,2). Most of the reported studies of toluene nitration are under conditions where only mononitration reactions take place. Studies on dinitration reactions have been carried out (3,4,5), but starting with mononitrotoluenes. In commercially important nitration of toluene for the manufacture of tolylene diisocyanate (TDI) and trinitrotoluene (TNT), dinitrotoluene (DNT) is the desired product and mononitration is simply an intermediate reaction. Optimum use of a DNT production facility can be achieved by integrating the mononitration and the dinitration steps. A computer simulation model, to be useful in such optimization studies, must be capable of representing the various physical and chemical phenomena over a wide range of operating variables where mono- and dinitration reactions take place. This paper describes a successful effort to synthesize such a model using information on the various phenomena available in the open literature, reported by different authors. A systems engineering approach was used to decompose the total phenomenon into subphenomena which have been separately studied. The original intention of developing the model was to form a basis for planning and designing a process development study in a pilot plant for optimizing an existing DNT production facility. However, when a computer simulation program for the plant based on the model was developed, it was found to be already adequate for

0-8412-0549-3/80/47-124-403$05.25/0 © 1980 American Chemical Society Squires and Reklaitis; Computer Applications to Chemical Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

COMPUTER

Downloaded by UNIV OF NEW ENGLAND on February 8, 2017 | http://pubs.acs.org Publication Date: May 30, 1980 | doi: 10.1021/bk-1980-0124.ch023

404

APPLICATIONS

TO

CHEMICAL

ENGINEERING

t r o u b l e s h o o t i n g and p r e l i m i n a r y o p t i m i z a t i o n o f plant operation. The n i t r a t i n g agent used in most i n d u s t r i a l n i t r a t i o n p r o c e s s e s is a m i x t u r e o f aqueous n i t r i c and s u l f u r i c a c i d s , commonly known as the mixed a c i d . The o r g a n i c s p e c i e s a r e o n l y s p a r i n g l y s o l u b l e in the a c i d and hence i n d u s t r i a l n i t r a t i o n is heterogenous i n v o l v i n g two liquid phases. The term " m a c r o k i n e t i c s " has been used (6) t o d e s c r i b e o v e r a l l k i n e t i c s o f n i t r a t i o n underHheterogenous c o n d i t i o n s . In micros c o p i c s c a l e , two phenomena, v i z . , c h e m i c a l r e a c t i o n o r " m i c r o k i n e t i c s and i n t e r p h a s e mass t r a n s f e r , simultaneously occur. E a r l y workers (7,IB,£) assumed t h a t mass t r a n s f e r e f f e c t s can be e l i m i n a t e d by s t r o n g a g i t a t i o n . Hanson and A l b r i g h t ( (37)

Χ

r

4

= k gX X

9

(38)

k

5

- k gX X

9

(39)

r

6 r

2

3

=

7

f

2

3

r

3 5 - k gX X 4

4

( 4 0

> (41)

9

H

where/ g = 10" R fi - 2 exp (-[B x

f

2

- 2 exp ( - [ E

f

3

- exp ( - [ E

2 6

and

(42)

0

- Ε ]/RT)

(43)

m

- E ]/RT)

(44)

- E ]/RT)

(45)

p

2 4

Squires and Reklaitis; Computer Applications to Chemical Engineering ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

23.

MURTHY

Heterogeneous

Nitration

419


S o l u t i o n o f Equations I t is n o t p o s s i b l e t o a n a l y t i c a l l y s o l v e t h e s e t o f e q u a t i o n s f o r m u l a t e d in t h e above s e c t i o n s . However, it is p o s s i b l e t o o b t a i n a n u m e r i c a l s o l u t i o n corresponding t o a s p e c i f i c set of r e a c t o r conditions. The model d e s c r i b e d here c a n be used t o s i m u l a t e any one s t a g e o f t h e n i t r a t i o n r e a c t o r s . A l l i e d Chemical's p r o c e s s f o r DNT p r o d u c t i o n c o n s i s t s o f s e v e r a l i n t e r c o n n e c t e d n i t r a t o r s and phase s e p a r a t o r s . The o v e r a l l p r o c e s s s i m u l t i o n was accomplished u s i n g the s o - c a l l e d " b u i l d i n g b l o c k " approach. T h i s approach c o n s i s t s o f d e v e l o p i n g subroutines f o r c a l c u l a t i n g the output o f process v e s s e l s , g i v e n t h e o p e r a t i n g c o n d i t i o n s and t h e i n p u t streams, and then d e v e l o p i n g a main program which c a l l s t h e s e subprograms in a c e r t a i n sequence d e t e r mined by t h e p r o c e s s t o p o l o g y (flow scheme) and converge on t h e r e c y c l e streams. A f t e r convergence/ an energy b a l a n c e is performed around each s t a g e t o permit quick e v a l u a t i o n o f t e m p e r a t u r e - c o n t r o l a b i l i t y . V e r i f i c a t i o n o f t h e Model A development p r o j e c t was undertaken t o v e r i f y the model d e v e l o p e d here and t o s t u d y t h e mass t r a n s f e r parameter k a as a f u n c t i o n o f phase r a t i o ( o r g a n i c / a c i d v o l u m e t r i c r a t i o ) in t h e r e a c t o r , agitation, i n t e r n a l configuration of the reactor, etc. R e s u l t s o f l a b o r a t o r y runs c o u l d be e x p l a i n e d by t h e model u s i n g k a as t h e o n l y a d j u s t a b l e p a r a meter. T a b l e 1 shows an example o f t h e e x c e l l e n t agreement between model p r e d i c t i o n s and l a b o r a t o r y data. I n each r u n , at a d i f f e r e n t a g i t a t o r speed, k a was determined by matching t o l u e n e c o n t e n t o f t h e reactor effluent. The c l o s e agreement between t h e m o n o n i t r o t o l u e n e and d i n i t r o t o l u e n e isomer c o n t e n t o f t h e a c t u a l r e a c t o r e f f l u e n t w i t h t h o s e p r e d i c t e d by the model v e r i f i e s t h e a c c u r a c y and t h e adequacy o f the model. A d m i t t e d l y , in t h e s t r i c t l y t h e o r e t i c a l sense, such a v e r i f i c a t i o n is a n e c e s s a r y b u t n o t s u f f i c i e n t requirement f o r t h e model t o be t h e t r u e model. I t s h o u l d be o b v i o u s t o r e a d e r s f a m i l i a r w i t h c u r r e n t r e s e a r c h work on t h e n i t r a t i o n o f a r o m a t i c compounds t h a t t h e assumptions and mechanisms on w h i c h this model is based a r e under debate, a l b e i t g e n e r a l l y accepted. E x h a u s t i v e t e s t i n g and v e r i f i c a t i o n o f a model is u s u a l l y n o t j u s t i f i a b l e in a b u s i n e s s



Toluene p-MNT o-MNT m-MNT 2,4-DNT 2,6-DNT O t h e r DNT

Compound 0.345 30.48 39.81 4.77 18.44 5.53 0.63

0.35 30.71 40.38 3.37 19.35 5.42 0.42

0.49 30.52 39.92 4.77 18.21 5.46 0.62

0.49 30.61 39.89 2.86 20.11 5.59 0.45

Calculated

Measured

Measured

1500 RPM

Calculated

=

Agitation

0.28 32.16 42.24 3.07 17.04 4.86 0.36

Measured

NITRATION

0.28 32.22 43.35 4.97 24.36 4.35 0.47

Calculated

= 2300 RPM

Basis)

Agitation

(Acid-Free

1900 RPM

Reactor E f f l u e n t

DATA FOR L A B C F S T R

=

P e r c e n t in

VS EXPERIMENTAL

I

Agitation

Weight

COMPARISON OF MODEL PREDICTIONS

Table


23.

MURTHY

Heterogeneous

Nitration

421

environment where t h e model is used p r i m a r i l y t o p r o v i d e d i r e c t i o n in o p t i m i z i n g a m u l t i v a r i a b l e process.


Remarks The s i m u l a t i o n program has been e x t e n s i v e l y used f o r p r o c e s s o p t i m i z a t i o n s t u d i e s as it p e r m i t s a c c u r a t e p r e d i c t i o n o f isomer d i s t r i b u t i o n and h e a t r e l e a s e . I t o f f e r s t h e o r e t i c a l e x p l a n a t i o n s f o r isomer c o n t r o l p r a c t i c e s a r r i v e d at t h r o u g h s e v e r a l y e a r s o f p l a n t o p e r a t i n g e x p e r i e n c e . The model was used in de s i g n i n g l a b o r a t o r y experiments t o study mass t r a n s f e r under v a r i o u s p r o c e s s c o n d i t i o n s and r e a c t o r con f i g u r a t i o n . S i n c e mass t r a n s f e r and c h e m i c a l k i n e t i c s a r e s i m u l t a n e o u s l y i m p o r t a n t in this p r o c e s s , a model is n e c e s s a r y t o " f i l t e r o u t " t h e k i n e t i c s e f f e c t s f o r mass t r a n s f e r c o r r e l a t i o n s . The r e s u l t s o f o u r l a b o r a t o r y s t u d i e s will be p r e s e n t e d in f u t u r e p a p e r s . NOMENCLATURE a = a c t i v i t y o r i n t e r f a c i a l a r e a as e x p l a i n e d in t e x t A = frequency f a c t o r c = concentration e = extent o f r e a c t i o n Ε = A c t i v a t i o n energy G = O r g a n i c molar f l o w r a t e H R = A c i d i t y f u n c t i o n , d e f i n e d by eqn (10) J i = I n t e r p h a s e mass t r a n s f e r r a t e f o r t h e i - t h species k = c h e m i c a l v e l o c i t y o r t r a n s p o r t parameter Κ = E q u i l i b r i u m constant P^ = r a t e o f p r o d u c t i o n o f i - t h s p e c i e s / u n i t volume o f a c i d phase Q = molar f l o w r a t e f o r i n o r g a n i c s p e c i e s r ^ = r a t e o f i - t h r e a c t i o n , l b mol/hr f t R = gas law c o n s t a n t Τ = absolute temperature A volume o f a c i d phase W = weight p e r c e n t s u l f u r i c on n i t r i c f r e e b a s i s X = m o l e f r a c t i o n in t h e a c i d phase y = m o l e f r a c t i o n in t h e o r g a n i c phase ( a c i d f r e e ) V

=

GREEK LETTERS r-

activity

coefficient


C O M P U T E R APPLICATIONS T O C H E M I C A L ENGINEERING

422

SUBSCRIPT FOR SPECIES 1 3 5

toluene o-Nitrotoluene 2,4 - Dinitrotoluene

2 4 6

7 9

Qrtho Dinitrotoluenes n i t r i c acid

8 10


Literature

p-Nitrotoluene m-Nitrotoluene 2,6 - Dinitrotoluene water sulfuric acid

Cited

1.

Norman, R.O.C., Taylor, R., "Electrophilic Substitution in Benzenoid Compounds", Elsevier Publishing Company, Amsterdam, 1965.

2.

De La Mare, P.B.D., Ridd, J.H., "Aromatic Substitution, Nitration and Halogenation", Academic Press, New York, 1959.

3.

Vinrik, M.I., Grabovskaya, Zh.E., Arzamaskova, L.N., Zh. Fiz. Khim., 1967, 41, 1102.

4.

Tillet,

5.

Kobe, K.A., Fortman, 1961, 53, 269.

6.

Hanson, C., Marsland, Ind., 1966, p 675.

7.

McKinley, C., White, 40, 143.

8.

Barduhn, A.J., Kobe, K.A., Ind. Eng. Chem., 1956, 48, 1305.

9.

Miller, R.C., Noyce, D.S., Vermeulen, Eng. Chem., 1964, 56, 43.

J.G., J. Chem. Soc., 1962, p 5142. J.T., Ind. Eng. Chem.,

J.G., Wilson,

R.R., Trans.

G., Chem.

AIChE, 1944,

T., Ind.

10.

Albright,

L.F., Ind. Eng. Chem., 1965, 57, 53.

11.

Giles, J., Hanson, C., Ismail, H.A.M., ACS Symposium Series, 1976, 22, 190.

12.

Cox, P.R., Strachan, 1972, 27, 457.

A.N., Chem. Eng. Sci.,

13.

Cox, P.R., Strachan, 4, 253.

A.N., Chem. Eng. J., 1972,


23. MURTHY

Nitration

423

14.

Aris, R., "Introduction to the Analysis of Chemical Reactors", Prentice-Hall, 1965.

15.

Ismail, H.A.M., Ph.D. Thesis, Bradford, U.K., 1973.

16.

Redlich, O., Kister, 1948, 40, 345.

17. Downloaded by UNIV OF NEW ENGLAND on February 8, 2017 | http://pubs.acs.org Publication Date: May 30, 1980 | doi: 10.1021/bk-1980-0124.ch023

Heterogeneous

Ellis,

University

of

A.T., Ind. Eng. Chem.,

S.R.M., J. Appl.

Chem., 1957, 7, 152.

18.

Renon, H., Prausnitz, 135.

19.

Cerfontain, 545.

20.

Grabovskaya, Ζ.Ε., Vinnik, 1966, 40, 1221.

21.

Bennett, G.M., Brand, J.S.D., James, D.M., Saunders, T.G., Williams, D., J. Chem. Soc., 1947, p 474.

22.

Deno, N.C., Jaruzelski, J.J., Schriesheim, J. Am. Chem. Soc., 1955, 77, 3044.

23.

Gold, V., Hawes, B.W.V., J. Chem. Soc., 1951, p 2102.

24.

Hammett, L.P., "Physical McGraw Hill, 1940.

25.

Arnett, E.M., Bushick, 1964, 86, 1564.

26.

Olah, G.A., Kuhn, S.J., Flood, S.H., Evans, J.C., J. Am. Chem. Soc., 1962, 84, 3687.

27.

Coombes, R.G., Moodie, R.B., Schofield, J. Chem. Soc. (Β), 1968 p 800.

RECEIVED

November

J.M., AIChE J, 1968, 14,

H., Telder,

5,

Α., Recueil,

1965, 84,

M.I., Zh. Fiz. Khim.,

Organic

Α.,

Chemistry",

R.D., J. Am. Chem. Soc.,

Κ.,

1979.


Computer Applications to Chemical Engineering - American Chemical

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