A Low-Temperature Process for TNT Manufacture Part 2. Pilot Plant

18 A Low-Temperature Process for T N T Manufacture Part 2. Pilot Plant Development

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 13, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0022.ch018

W. R. HAAS, E. G. FOCHTMAN, and L. CICIORA IIT Research Institute, 10 West 35th Street, Chicago,Ill.06016 D. YEE Picatinny Arsenal, Dover, N.J. 07801 The disposal of red water and of pink water from the manufacture of TNT has been a problem for several decades. The current emphasis on the minimizing of the environmental impact from government operations made it necessary to re-examine the entire process with a view to reducing this very difficult water pollution problem. With this goal in mind, Picatinny Arsenal contracted with the Stanford Research Institute (SRI) to investigate new processes for the manufacture of TNT. The SRI work resulted in the successful laboratory demonstration of a process which minimizes the formation of the meta isomer of toluene, the prime cause of pollution. This process was partially demonstrated in a 2 lb TNT/hr mini pilot plant. The scale of this plant was such that a number of difficulties were encountered; however, there was no indication that their laboratory work would not be substantiated if a larger plant were constructed. The basic feature of the SRI process involves low-temperature (-10°C) nitration, to the dinitrate of toluene, followed by a higher temperature (90°C) trinitration. The nitrobody concentration is maintained below the solubility limit in the nitration acid which results in the process being conducted in a single phase mixture. Process Description The low-temperature TNT process was developed at SRI for Picatinny Arsenal. Modifications to the standard process include: co-current flow of single phase anhydrous acid and the nitrobodies low-temperature (-10°C) dinitration crystallization and filtration of the product TNT from the anhydrous acid

272

In Industrial and Laboratory Nitrations; Albright, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

18.

HAAS ET AL.

TNT

Manufacture:

Pilot

273

Vlant

The p r o c e s s f l o w d i a g r a m f o r t h e p i l o t p l a n t i s shown i n F i g u r e 1. The d e s i g n i n c o r p o r a t e s t h e p r o c e s s a s d e f i n e d b y S R I and s y s t e m c h a n g e s t h a t w e r e recommended b y P i c a t i n n y A r s e n a l p e r sonnel . D i n i t r a t i o n , the f i r s t major step i n t h e p r o c e s s , takes p l a c e by m i x i n g t h e t o l u e n e w i t h r e c y c l e a c i d a t - 8 C . A f t e r r e a c t i n g , t h i s m i x t u r e flows through a f l o w s p l i t t e r t h a t d i v i d e s t h e stream i n t o two e q u a l p a r t s . One p o r t i o n i s s e n t d i r e c t l y t o t h e t r i n i t r a t i o n r e a c t o r s and t h e o t h e r t o a w a t e r d i l u t i o n t a n k where t h e n i t r o b o d i e s s e p a r a t e f r o m t h e a c i d p h a s e and a r e s e n t t o t h e trinitrators. The a c i d p h a s e i s p u r g e d f r o m t h e s y s t e m . A m i x t u r e o f 60% o l e u m and n i t r i c a c i d i s u s e d f o r t h e t r i nitration. The t e m p e r a t u r e o f t h i s e x o t h e r m i c t r i n i t r a t i o n r e a c t i o n i s c o n t r o l l e d a t o r below 90 C t o prevent e x c e s s i v e o x i d a tion. The r e a c t i o n r e q u i r e s a p p r o x i m a t e l y one h o u r . The m i x t u r e o f TNT d i s s o l v e d i n n i t r a t i o n a c i d l e a v i n g t h e t r i n i t r a t o r s i s f e d t o a c r y s t a l l i z e r s y s t e m where t h e t e m p e r a t u r e i s lowered by removing t h e heat through t h e v e s s e l w a l l s . This system c o n s i s t s o f f i v e s t i r r e d tank c r y s t a l l i z e r s i n s e r i e s w i t h each o p e r a t i n g a t s u c c e s s i v e l y lower temperatures. The c r y s t a l l i z e r e f f l u e n t c o n t a i n s a b o u t 1 6 . 5 w t % t o t a l TNT a t - 5 ° C .


Q

e

Dinitration The i n i t i a l r e a c t i o n s t e p i n t h e l o w - t e m p e r a t u r e TNT p r o c e s s r e s u l t s i n t h e c o n v e r s i o n o f t o l u e n e t o d i n i t r o t o l u e n e (DNT). The m a j o r c h a n g e s f r o m t h e e x i s t i n g p r o c e s s o c c u r i n t h i s p o r t i o n of t h e o p e r a t i o n ; t h e r e f o r e , e x t e n s i v e p i l o t p l a n t d a t a w i l l be needed. The d i n i t r a t i o n r e a c t i o n i s c o n d u c t e d i n a n a n h y d r o u s l ^ S O i * medium n e a r t h e f r e e z i n g p o i n t o f t h e e n t i r e m i x t u r e ( i . e . , V 1 0 ° C ) . The o v e r - a l l r e a c t i o n c a n b e w r i t t e n : H S0i> 2

CH -C H 3

6

5

+ 2N02HS0i*

CH -C H 3

6

3

(N0 ) 2 + 2

2Η 80ι* 2

-10°C

N i t r o n i u m b i s u l f a t e , N02HS0if, i s t h e n i t r a t i n g a g e n t w h i c h r e s u l t s from r e a c t i n g n i t r i c a c i d w i t h t h e s u l f u r t r i o x i d e i n oleum. I t i s d e l i v e r e d as the f u n c t i o n a l part of the r e c y c l e a c i d . The d i n i t r a t i o n c h e m i c a l r e a c t i o n h a s b e e n shown t o b e n e a r l y i n s t a n t a n e o u s and r e l a t i v e l y i n d e p e n d e n t o f n i t r i c a c i d c o n c e n t r a t i o n i n t h e SRI l a b o r a t o r y w o r k . T o l u e n e h a s a v e r y l o w s o l u b i l i t y i n t h e n i t r a t i n g a c i d and t h e r e f o r e t h e m o n o n i t r a t i o n r e a c t i o n i s h i g h l y d e p e n d e n t o n mass t r a n s f e r o f t h e r e a c t a n t s . T h i s f a c t was t a k e n i n t o a c c o u n t i n t h e p i l o t p l a n t d e s i g n b y u s i n g a r e c y c l e r e a c t o r s y s t e m w i t h t h e t o l u e n e added j u s t a h e a d o f t h e c e n t r i f u g a l c i r c u l a t i n g pump. T h i s s y s t e m w i l l a t o m i z e t h e t o l u e n e i n t h e n i t r a t i o n a c i d s t r e a m t o f a c i l i t a t e mass transfer.



Toluene

Dinitration section

Recycle acid storage an4 a c i d fortification

2

H 0

Figure 1.

Waste acid

I

Phase separator

Dilution tank

Flow splitter

nitrobodies

7ΓΓ

Trinitration section Crystallizers

N i t r i c acid storage

Diagram of low temperature TNT process

60% o l e u m storage


Filter

—^FNT J product


18.

HAAS E T A L .

TNT

Manufacture:

Pilot

Plant

275

The d i n i t r a t o r r e c y c l e r e a c t o r i s shown s c h e m a t i c a l l y i n F i g u r e 2. The SRI l a b o r a t o r y w o r k showed t h a t l o w e r i n g t h e t e m p e r a t u r e f r o m 33°C t o -8°C i n t h e d i n i t r a t i o n s t e p r e s u l t e d i n r e d u c i n g meta i s o m e r c o n c e n t r a t i o n i n t h e p r o d u c t f r o m 2.4% t o 1.8%. The r e c y c l e r e a c t o r c o n c e p t was i n c o r p o r a t e d i n t h e d i n i t r a t o r d e s i g n t o i n s u r e t h a t t h e d e s i g n t e m p e r a t u r e was m a i n t a i n e d . The h e a t o f r e a c t i o n was c a l c u l a t e d t o b e -1819.5 B t u / l b t o l u e n e b y S R I and measured a t -1410 B t u / l b t o l u e n e a t P i c a t i n n y . B a s e d on t h e S R I l a b o r a t o r y y i e l d i n f o r m a t i o n , 22 l b / h r o f t o l u e n e f e e d w i l l p r o d u c e t h e p r o c e s s d e s i g n c a p a c i t y , 50 l b TNT/hr. The d i n i t r a t o r s e c t i o n o f t h e p i l o t p l a n t c o n t a i n s f o u r ( 4 ) recycle reactors. The a c i d f l o w s t h r o u g h t h e r e a c t o r s i n a s e r i e s f a s h i o n a n d o n e - t h i r d o f t h e t o l u e n e i s added t o e a c h o f the f i r s t t h r e e r e a c t o r s w i t h t h e f o u r t h as an a d d i t i o n a l s a f e t y f a c t o r t o assure complete r e a c t i o n . The s e n s i b l e h e a t c a p a c i t y o f t h e r e a c t i o n m i x t u r e w i t h a 0.5°C t e m p e r a t u r e r i s e w i l l a b s o r b t h e h e a t o f r e a c t i o n a t a r e c y c l e f l o w r a t e o f l e s s t h a n 100 gpm. T h i s h e a t i s removed i n a 60 f t h e a t e x c h a n g e r w i t h a 7°C d r i v i n g f o r c e . 2

D i n i t r a t o r D e s i g n Summary The designed reactors three. The

d i n i t r a t i o n o f toluene i s conducted i n f o u r s p e c i a l l y recycle reactors. The a c i d s t r e a m moves t h r o u g h t h e i n s e r i e s a n d t o l u e n e i s added t o e a c h o f t h e f i r s t

basic reasons f o r t h i s p i l o t reactor design a r e : to insure c l o s e c o n t r o l of t h e exothermic r e a c t i o n to determine t h e e f f e c t o f decreasing a c i d concent r a t i o n on t h e r e a c t i o n The t e m p e r a t u r e r a n g e o f t h e r e a c t i o n m i x t u r e i n t h i s s y s t e m i s c o n t r o l l e d b y t h e r e c y c l e f l o w r a t e . These r e c y c l e r e a c t o r s w i l l a s s u r e a d e q u a t e c o n t a c t o f t h e two-phase r e a c t i o n m i x t u r e s w i t h a n i n s i g n i f i c a n t t e m p e r a t u r e r i s e o f l e s s t h a n 0.5°C when t h e r e c y c l e r a t e i s 100 gpm o r g r e a t e r . The t e m p e r a t u r e o f t h e p r o c e s s f l u i d a t t h e h e a t e x c h a n g e r o u t l e t c a n b e c o n t r o l l e d by automatically adjusting thecoolant flow rate. The d i n i t r a t i o n r e a c t o r s y s t e m i s d e s i g n e d t o d e p l e t e t h e n i t r a t i o n c a p a b i l i t y o f t h e a c i d phase. E x p e r i m e n t a l work has shown t h a t a c o l o r e d c o m p l e x f o r m s i f i n s u f f i c i e n t n i t r i c a c i d i s present. Some p i l o t p l a n t d a t a s h o u l d b e d e v e l o p e d t o d e t e r m i n e i f t h e e f f e c t w i l l b e i m p o r t a n t i n t h i s s y s t e m and i f t h e r e a c t i o n r a t e w i l l be a f f e c t e d by t h e l o w n i t r a t i o n c a p a c i t y o f the a c i d . S i n c e t o l u e n e i s added a t t h r e e d i s c r e t e p o i n t s i n t h e r e a c t o r system and t h e stream c a n be sampled a f t e r each a d d i t i o n , the e x t e n t o f r e a c t i o n and t h e n a t u r e o f t h e p r o d u c t c a n be


276

INDUSTRIAL A N D L A B O R A T O R Y NITRATIONS


TR FR FRC S

-

Temperature Recorder Flow Recorder Flow Recorder C o n t r o l l e r Sample P o i n t Vent -7.5°C

Gravity overflow fcp n e x t d i n i t r a t o r

Process A c i d Stream

(çRj)~"

Circulating pump

25°C Toluene metering pump

-8°C

N2 P u r g e Gas V For Shutdown

Figure 2. Dinitrator recycle reactor


18.

HAAS ET AL.

TNT

Manufacture:

Pilot

Plant

277


d e t e r m i n e d a t e a c h p o i n t . A f o u r t h r e a c t o r w i t h no t o l u e n e f e e d i s i n c l u d e d t o assure adequate h o l d i n g time i f the r e a c t i o n r a t e i s r e d u c e d and t o i n c r e a s e t h e c a p a c i t y o f t h i s p o r t i o n o f t h e p i l o t p l a n t i f i t i s n e c e s s a r y when o p e r a t i n g t h e s u b s e q u e n t units. Flow S p l i t t e r . The d i n i t r a t o r e f f l u e n t i s a s o l u t i o n o f TNT, DNT, and o x i d a t i o n p r o d u c t s d i s s o l v e d i n b y - p r o d u c t s u l furic acid. The e f f l u e n t s t r e a m i s h e a t e d f r o m -8°C t o 35°C and d i v i d e d a t t h i s p o i n t i n t h e p r o c e s s by f l o w i n g i n t o a t a n k f r o m w h i c h a p r e d e t e r m i n e d f l o w o f t h e p r o d u c t i s pumped t o t h e t r i n i t r a t o r w h i l e the remainder overflows to the n i t r o b o d y ( n i t r a t e d o r g a n i c s ) r e c o v e r y s y s t e m . A p p r o x i m a t e l y 220 B t u / l b TNT p r o d u c e d must be added t o t h e f l o w s p l i t t e r . I n the n i t r o body r e c o v e r y s y s t e m , t h e TNT and DNT a r e r e c o v e r e d and t h e s u l f u r i c a c i d i s exhausted from the process. The f r a c t i o n o f a c i d d i r e c t e d t o t h e n i t r o b o d y r e c o v e r y s y s t e m u n d e r s t e a d y o p e r a t i o n i s d e t e r m i n e d by t h e c o n c e n t r a t i o n o f S 0 and HN0 i n t h e a c i d f e e d s y s t e m . When 60% o l e u m and 100% HN0 a r e f e d t o t h e p r o c e s s , t h e f l o w s p l i t t e r s h o u l d o p e r a t e w i t h 50% o f t h e d i n i t r a t o r e f f l u e n t f l o w i n g t o t h e t r i n i t r a t o r s w h i l e the remainder i s exhausted through the n i t r o b o d y recovery system. 3

3

3

N i t r o b o d y R e c o v e r y . A p p r o x i m a t e l y 50% o f t h e n i t r o b o d i e s i n the d i n i t r a t o r e f f l u e n t l e a v e the f l o w s p l i t t e r w i t h the waste a c i d . SRI u s e d a l i q u i d - l i q u i d e x t r a c t i o n u n i t w i t h m e t h y l e n e c h l o r i d e as a s o l v e n t f o l l o w e d by d i s t i l l a t i o n t o r e c l a i m t h e s e o r g a n i c s . Due t o t h e c o r r o s i v e n a t u r e o f t h e a c i d p h a s e a f t e r i t had c o n t a c t e d t h e m e t h y l e n e c h l o r i d e , a d i f f e r e n t s e p a r a t i o n method has b e e n d e v i s e d w i t h a s s i s t a n c e f r o m P i c a t i n n y Arsenal. The w a s t e a c i d s t r e a m f r o m t h e f l o w s p l i t t e r f l o w s t o a d i l u t i o n t a n k where i t i s d i l u t e d t o 70% a c i d w i t h w a t e r . A p p r o x i m a t e l y 520 B t u / l b TNT p r o d u c e d must be removed f r o m t h i s operation. The n i t r o b o d y s o l u b i l i t y i s l o w e r e d t o 1 wt%. T w e n t y - n i n e l b / h r o f n i t r o b o d i e s w i l l s e p a r a t e a t t h i s p o i n t and be s e n t t o t h e t r i n i t r a t o r . When w a t e r i s added t o t h e d i n i t r a t i o n a c i d e f f l u e n t , n i t r o s y l s u l f u r i c a c i d (NOHSOi*), an o x i d a t i o n product, begins to decompose i n t o I^SOi* and NO gas. T h i s g a s e o u s e f f l u e n t must be t r a p p e d and s c r u b b e d t o m i n i m i z e a i r p o l l u t i o n . DNT R e a c t o r P r o d u c t . The DNT r e a c t o r i s d e s i g n e d t o o p e r a t e a t -8 C w i t h a n h y d r o u s r e c y c l e a c i d . Laboratory data obtained a t SRI i n d i c a t e s t h a t a t s t e a d y s t a t e c o n d i t i o n s t h e d i n i t r a t o r p r o d u c t w i l l c o n t a i n some TNT and NOHSOi* t h a t e n t e r s t h e d i n i t r a t o r i n the r e c y c l e a c i d . The d i n i t r a t o r e f f l u e n t c o m p o s i t i o n e x p e c t e d f r o m t h i s p i l o t d e s i g n i s shown i n T a b l e 1.


278

INDUSTRIAL AND

Table

LABORATORY NITRATIONS

I

COMPOSITION AND AMOUNT OF DINITRATOR EFFLUENT FOR 50 l b / h r TNT PRODUCTION Compound

Rate,

DNT TNT HN0 H S(K NOHSOv HN0


3

2

2

lb/hr

Wt

%

46.70 20.40 0.61 256.56 47.66 0.37

12.5 5.5 0.2 68.9 12.8 0.1

372.30

100.0

A c i d F o r t i f i c a t i o n S y s t e m . The n i t r i c a c i d and o l e u m needed t o t r i n i t r a t e t o l u e n e i s m i x e d w i t h s u l f u r i c a c i d i n an i n d e p e n d e n t l o o p . The TNT y i e l d and q u a l i t y i s d e p e n d e n t on t h e amount o f and t h e r a t i o o f t h e s e m a t e r i a l s ; t h u s , t h i s f e e d s y s t e m must be well controlled. I n t h e p r o p o s e d SRI p r o c e s s , s u l f u r t r i o x i d e , s u l f u r i c a c i d , and n i t r i c a c i d w e r e added t o t h e p o r t i o n o f t h e d i n i t r a t o r e f f l u e n t that flows to the t r i n i t r a t o r . T h i s c o n c e p t has b e e n changed t o a v o i d some o f t h e s a f e t y h a z a r d s t h e y e n c o u n t e r e d w i t h TNT p r e c i p i t a t i o n i n t h e f o r t i f i c a t i o n t a n k and t o u t i l i z e 60% o l e u m i n p l a c e o f p u r e SO3 w h i c h s h o u l d i m p r o v e t h e p r o c e s s e c o n o m i c s by r e d u c i n g e x i s t i n g p l a n t a u x i l i a r y e q u i p m e n t c h a n g e s . The 60% o l e u m and n i t r i c a c i d a r e f e d t o a r e c y c l e d l o o p t h a t c o n t a i n s a c e n t r i f u g a l pump and a h e a t e x c h a n g e r t o c o n t r o l the temperature. The w e i g h t r a t i o o f H N O 3 t o 60% o l e u m w i l l be c o n t r o l l e d a t 1 t o 2.48 and t h a t m i x t u r e w i l l be added t o t h e f i r s t t r i n i t r a t o r a t a w e i g h t r a t i o o f 9.35 t o 1 b a s e d on t o l u e n e f e e d . A p p r o x i m a t e l y 4.12 l b o f m i x e d a c i d / l b TNT p r o d u c e d i s needed f o r t h e r e a c t i o n . M i x i n g o f SO3 and H N O 3 i n a s u l f u r i c a c i d s o l v e n t i s exothermic. The f o l l o w i n g r e a c t i o n o c c u r s : SO3

+

HNO3

+

NO2HSO4

p r o d u c e s h e a t a t t h e r a t e o f 743.4 B t u / l b H N O 3 . The r e a c t i o n i s n e a r l y i n s t a n t a n e o u s s o , t o a v o i d h o t s p o t s and p r o m o t e m i x i n g , t h e f e e d s e n t e r a s t r e a m o f m i x e d a c i d r e c y c l i n g a t a l a r g e enough r a t e so t h e s e n s i b l e h e a t o f a 5°C r i s e i n t e m p e r a t u r e (60-65°C) w i l l a b s o r b t h e h e a t o f r e a c t i o n . T h i s e n e r g y i s removed w i t h a w a t e r c o o l e d h e a t e x c h a n g e r i n t h e recycled loop. The r e a c t o r f e e d a c i d i s removed f r o m t h e l o o p a t 4.09 l b / l b TNT p r o d u c e d ; t h e c o m p o s i t i o n i s g i v e n i n T a b l e I I . T h i s f e e d i s added t o t h e f i r s t t r i n i t r a t o r . and


18.

HAAS E T AL.

TNT

Manufacture:

Pilot

279

Plant

Table I I COMPOSITION AND FLOW RATE OF TRINITRATOR MIXED ACID FEEDS Material

R a t e , l b / l b TNT p r o d u c e d

Wt %

H S(K

1.173

28.7

S0

1.76

43.0

1.16

28.4

2

3


HN0

3

4.093

100.1

T r i n i t r a t i o n R e a c t o r System The

r e a c t i o n between d i n i t r o t o l u e n e and n i t r o n i u m

bisulfate

is CH -C H (N02)2 + N02HS0Î* 3

6

3

90°C -> C H - C H (N0 ) 3

6

2

2

3 + H2SO4

H2S0I*

and

proceeds r a t h e r slowly. SRI h a s shown t h a t l i t t l e o r no p r o d u c t change o c c u r s when t h e n i t r o b o d y c o n c e n t r a t i o n i s l o w enough t o m a i n t a i n a s i n g l e p h a s e i n t h e r e a c t o r s a s compared t o t h e p r e s e n t s y s t e m where a two-phase m i x t u r e e x i s t s . The r e a c t o r c o n c e p t i s s i m p l i f i e d a n d made s a f e r u s i n g t h i s a p p r o a c h b e c a u s e t h e s e p a r a t o r s b e t w e e n v e s s e l s a r e e l i m i n a t e d a n d t h e m i x i n g power r e q u i r e m e n t needed to m a i n t a i n the pure n i t r o b o d y phase d i s p e r s e d i s reduced. The f o l l o w i n g f e e d m a t e r i a l i s added a t a c o n t i n u o u s r a t e t o t h e t r i n i t r a t o r s y s t e m t o p r o d u c e 50 l b / h r o f TNT: 205

l b / h r o f mixed a c i d

189

lb/hr of dinitrator effluent

29 l b / h r o f d i n i t r a t o r e f f l u e n t n i t r o b o d i e s The t r i n i t r a t i o n r e a c t i o n r a t e showed a DNT c o n c e n t r a t i o n d e p e n d ency i n b a t c h r e a c t i o n run by SRI w i t h s i m i l a r m i x t u r e s . At 90°C, c o m p l e t e r e a c t i o n o f DNT was o b s e r v e d i n a b o u t 1 h o u r . The h e a t o f r e a c t i o n was m e a s u r e d a t 455.4 B t u / l b DNT i n t h e s e e x p e r i m e n t s . T h e r e f o r e , 394.3 B t u / l b TNT p r o d u c e d w i l l be g e n e r a t e d i n the p i l o t t r i n i t r a t o r s . The e x p e r i m e n t a l w o r k done a t S R I showed t h a t t h e t r i n i t r a t i o n r e a c t i o n r a t e i s i n s i g n i f i c a n t a t t e m p e r a t u r e s b e l o w 60°C and when t h e t e m p e r a t u r e i s g r e a t e r t h a n 90°C e x c e s s o x i d a t i o n occurs. The o x i d a t i o n r e a c t i o n s d i d n o t a p p e a r t o s e l e c t i v e l y d e s t r o y u n s y m m e t r i c a l TNT i s o m e r s u s i n g t h e c o n d i t i o n s t e s t e d . The p i l o t p l a n t was d e s i g n e d t o u s e t h r e e 3 0 - g a l j a c k e t e d s t i r r e d t a n k s i n s e r i e s w i t h 21 f t o f h e a t e x c h a n g e f o r e a c h p r o v i d e d by a c o m b i n a t i o n o f t h e j a c k e t and i n t e r n a l c o i l s . This 2


INDUSTRIAL

280

A N D LABORATORY

NITRATIONS

s y s t e m o p e r a t i n g a t 90°C s h o u l d p r o v i d e f o r a d e q u a t e t i m e t o c o m p l e t e l y c o n v e r t t h e n i t r o b o d i e s t o TNT. The e x p e c t e d p r o d u c t s o l u t i o n i s shown i n T a b l e I I I . Table I I I COMPOSITION AND FLOW RATE OF TRINITRATOR EFFLUENT


Compound TNT HN0 S0

Flow, l b / l b

TNT p r o d u c e d

1.397 0.649

3

Wt % 16-52 7

-63

0.799

9.45

HzSOi»

4.593

54.32

NOHSOi*

1.016

12.02

8.454

99.99

3

Crystallization The p r e - p i l o t p l a n t c r y s t a l l i z e r u s e d by SRI c o n s i s t e d o f an i n c l i n e d , j a c k e t e d , u p f l o w , s c r a p e d - p i p e c r y s t a l l i z e r . That s e c t i o n was f o l l o w e d by a c y l i n d r i c a l , p o r o u s , s t a i n l e s s s t e e l filter. A h o l l o w , Teflon-coated screw extended through the ent i r e l e n g t h and was u s e d t o move t h e TNT s o l i d s o u t t h e t o p o f t h e d e v i c e . The SRI r e s e a r c h e r s e n c o u n t e r e d p r o b l e m s due t o f i l t e r and f e e d l i n e b l o c k a g e s . They i m p r o v e d t h e o p e r a t i n g c o n d i t i o n s by d i l u t i n g t h e f e e d w i t h f i l t r a t e . This d i dnot appear t o l e n d i t s e l f t o e i t h e r t h e p i l o t f a c i l i t y o r p r o d u c t i o n e q u i p m e n t b e c a u s e i t s h i f t s t h e h e a t l o a d t o w a r d t h e c o o l e d end o f t h e c r y s t a l l i z e r e q u i p m e n t . The d r i v i n g f o r c e f o r h e a t t r a n s f e r has t o remain s m a l l t h e r e t o a v o i d f r e e z i n g t h e a c i d s o l v e n t on t h e e x c h a n g e r s u r f a c e ; t h e r e f o r e , t h e s u r f a c e a r e a w i l l h a v e t o be u n e c o n o m i c a l l y l a r g e . A d d i t i o n a l l a b o r a t o r y data were o b t a i n e d a t P i c a t i n n y A r s e n a l and u s e d t o d e v e l o p t h e f o l l o w i n g s p e c i f i c a t i o n s f o r a s t i r r e d t a n k s i n s e r i e s c r y s t a l l i z e r s y s t e m . The f o l l o w i n g c r i t e r i a were developed from t h a t d a t a . A s t r e a m c o n t a i n i n g a p p r o x i m a t e l y 16.5 w t % TNT c a n be u s e d a s c r y s t a l l i z e r f e e d w i t h o u t b e c o m i n g t o o v i s c o u s t o f l o w a t c r y s t a l l i z e r o p e r a t i n g temperatures. A f i n a l c r y s t a l l i z e r t e m p e r a t u r e o f -5°C i s s u f f i c i e n t t o r e c o v e r t h e p r o d u c t TNT c r y s t a l s .



18.

HAAS ET AL.

TNT

Manufacture:

Pilot

Plant

281

*

A minimum c o o l a n t t e m p e r a t u r e o f -15°C c a n be u s e d to cool the l a s t c r y s t a l l i z e r without f r e e z i n g t h e process stream.

•

F i v e c r y s t a l l i z e r s c a n be i n c o r p o r a t e d t o h e l p c o o l the product stream. (This gives a gradual temperature p r o g r e s s i o n r e s u l t i n g i n l a r g e r TNT c r y s t a l s ) . A p h a s e s e p a r a t o r may b e needed a f t e r a t r i n i t r a t i o n h o l d i n g t a n k (80°C) t o c o l l e c t a n y o r g a n i c t h a t may not be i n s o l u t i o n . R e p o r t e d l y , c r y s t a l l i z a t i o n o f a t w o - p h a s e s y s t e m r e s u l t s i n s o l i d TNT lumps and small crystal size.

E f f e c t o f Temperature on C r y s t a l l i z a t i o n . The s o l u b i l i t y o f TNT i n a s y n t h e t i c t r i n i t r a t o r a c i d a t d i f f e r e n t t e m p e r a t u r e s was d e t e r m i n e d b y P i c a t i n n y A r s e n a l . The d a t a a r e g i v e n i n Table IV. The i n f o r m a t i o n p r e s e n t e d i n t h e S R I r e p o r t i n d i c a t e d a h i g h degree o f s u p e r s a t u r a t i o n e x i s t e d i n t h e c r y s t a l l i z e r used i n t h e i r s t u d i e s . T h i s o c c u r s when t h e c r y s t a l l i z a t i o n r a t e i s s l o w compared t o t h e t e m p e r a t u r e c h a n g e . The s t i r r e d t a n k s i n s e r i e s c r y s t a l l i z a t i o n process suggested f o r the p i l o t p l a n t i s l e s s a f f e c t e d by t h e slow r a t e o f c r y s t a l l i z a t i o n because l a r g e h o l d i n g times are a v a i l a b l e a t each s p e c i f i e d temperature i n the system. The m a j o r h e a t t r a n s f e r b e t w e e n t h e warm s t r e a m e n t e r i n g a c r y s t a l l i z e r v e s s e l i n t h i s s y s t e m and t h e b u l k f l u i d w i l l be due t o i n t i m a t e m i x i n g . T h i s m i x i n g w i l l make t h e c r y s t a l l i z e r v o l u m e more homogeneous and e l i m i n a t e l o c a l v o l u m e s c o n t a i n i n g h i g h l y s u p e r s a t u r a t e d f l u i d w h i c h p r o m o t e s TNT c r y s t a l n u c l e a t i o n and t h u s s m a l l c r y s t a l s . Pilot

Crystallizer

The p i l o t p l a n t c r y s t a l l i z a t i o n s y s t e m d e s i g n i s shown i n F i g u r e 3. D i r e c t f e e d o f t h e t r i n i t r a t i o n e f f l u e n t i n t o t h e c r y s t a l l i z e r s w i t h no r e c y c l e o f c o l d d i l u t e f i l t r a t e i s b e l i e v e d a s a t i s f a c t o r y method o f o p e r a t i o n . The t o t a l h e a t l o a d c a n b e more e q u a l l y d i s t r i b u t e d o v e r t h e f i v e c r y s t a l l i z e r s and e l i m i n a t e s t h e need f o r t h e h i g h h e a t f l u x i n t h e l a s t v e s s e l w h i c h r e s u l t s when f i l t r a t e r e c y c l e i s u s e d a s a d i l u e n t . Table V g i v e s data on each o f t h e c r y s t a l l i z e r s . The t e m p e r a t u r e o f t h e c o o l a n t i n each heat exchanger i s c r i t i c a l . I f the heat t r a n s f e r surfaces a r e t o o c o l d , primary c r y s t a l 1

A

A s m a l l stream o f m a t e r i a l from the l a s t c r y s t a l l i z e r i s r e c y c l e d t o f u r n i s h seed c r y s t a l s i n t h e f i r s t v e s s e l .


INDUSTRIAL AND LABORATORY

NITRATIONS

Table IV TNT SOLUBILITY I N SYNTHETIC TRINITRATOR ACID

Synthetic Acid

Composition

Compound

Wt %

R S0n

75.8

S0

13.4


2

3

HNO3

10.6

TNT S o l u b i l i t y i n A c i d Temperature, °C

Mixture

Dissolved wt%

70

17.1

60

14.7

45

10.8

25

Concentration,

7.75

0

5.8

-10

5.3

-30

3.65


HAAS E T AL.

TNT

Manufacture:

Pilot Plant


18.


283


inside film coefficient,

A

n A

0

,

2

o v e r - a l l heat t r a n s f e r Btu/(hr)(ft )(°F)

T h e o r e t i c a l a r e a needed, f t

U

Coolant

2

2

Btu/(hr)(ft )(°F)

2

Btu/(hr)(ft )(°F)

coefficient,

h , coolant f i l m coefficient,

±

h ,

5.1

55.5

6. 84

41. 3

47.1 4.5

8. 2

25 w t % N a N 0

160

34. 3

2

H 0

H 0

H 0 2

61

77

2

3

84. 5

97. 2

90

168

5

3.4

41.5

25 w t % N a N 0

145

61.5

-15

-5

10

30

71.3

2541

3812

5083

50

Mean c o o l a n t t e m p e r a t u r e , °C

Btu/hr

5083

Q - heat l o a d ,

5083

200

57

125

50

10

V i s c o s i t y o f p r o c e s s f l u i d , cp

-5

5

20

40

60

O p e r a t i n g t e m p e r a t u r e , °C

4

3

2

1

Crystallizer

f o r 50 l b / h r TNT P r o d u c t i o n

CRYSTALLIZER DATA

Table V


3

18.

HAAS E T A L .

TNT

Manufacture:

Pilot

285

Plant

n u c l e a t i o n o c c u r s and r e s u l t s i n s m a l l c r y s t a l s w h i c h c o u l d b l o c k the l i n e s c o n n e c t i n g the v e s s e l s . Therefore, a driving force of 10°C was c h o s e n f o r e a c h c r y s t a l l i z e r .


Filtration A continuous f i l t e r i s incorporated i n t o t h e low-temperat u r e TNT p i l o t p l a n t t o s e p a r a t e t h e c r y s t a l l i n e TNT p r o d u c t f r o m t h e a c i d . The e q u i p m e n t must b e c a p a b l e o f r e m o v i n g 50 l b o f 100-ym n e e d l e - s h a p e d TNT c r y s t a l s p e r h o u r f r o m f i l t r a t e w i t h t h e c h a r a c t e r i s t i c s shown i n T a b l e V I . Table V I RECYCLE ACID CHARACTERISTICS Temperature

-10°C

Viscosity

250 - 300 c p

Flow r a t e

0.472 g a l / l b TNT p r o d u c e d Composition

Material

Wt %

TNT ( d i s s o l v e d )

0.378

5.3

HN0

0.616

9.7

3

H2S01»

4.397

62.0

S0

0.76

10.7

0.953

13.4

3

N0HS0»,

ing

lb/TNT p r o d u c e d

The c o n t i n u o u s f i l t r a t i o n c y c l e i s composed o f t h e f o l l o w operations: cake f o r m a t i o n •

deliquoring or drying

•

washing deliquor


INDUSTRIAL AND LABORATORY NITRATIONS


286

Cake f o r m a t i o n t i m e i s d e f i n e d as t h e p e r i o d o f t i m e b e t w e e n a p p l i c a t i o n o f t h e s l u r r y t o t h e f i l t e r and when t h e c a k e s u r f a c e i s d r y . The d e l i q u o r i n g t i m e i s t h e p e r i o d t h a t f o l l o w s when gas i s drawn t h r o u g h t h e c a k e t o remove o c c l u d e d f i l t r a t e . This p e r i o d i s n o t w e l l d e f i n e d , b u t s h o u l d end b e f o r e t h e c a k e c r a c k s . Time must be a l l o w e d f o r a s e r i e s o f w a s h i n g and d r y i n g o p e r a t i o n s w i t h d i f f e r e n t c o m p o s i t i o n wash l i q u o r s . The P i c a t i n n y A r s e n a l s t a f f c o n d u c t e d f i l t r a t i o n e x p e r i ments t o o b t a i n t h e d a t a n e e d e d t o d e s i g n a c o n t i n u o u s b e l t f i l ter. The f o l l o w i n g f i l t r a t i o n c y c l e was d e v e l o p e d f o r t h e p i l o t process: cake f o r m a t i o n deliquor 70% HaSO^wash deliquor H2O wash dewater The

d a t a a r e shown i n T a b l e V I I . The d a t a u s e d t o d e s i g n a f i l t e r b e l t w e r e : form time

(F.T.) = 25.0

f o r m r a t e (F.R.) = 2.3

s e c = 0.42 l b TNT/ft

min min

p r o d u c t r a t e (P.R.) = 50 l b TNT/hr = 0 . 8 3 belt width

lb/min

(B.W.) = 1 f t

The b e l t s p e e d , S, needed t o o b t a i n t h e p r e s c r i b e d c a k e ness i s : S =

P.R. (F.T.)(F.R.)(B.W.)

ft/min

0.83 (0.42)(2.3)(1) The

0.85

ft/min

times f o r i n d i v i d u a l operations are:


thick-


Filter

2

Drain time, min TNT l o s s , % Dry cake d e n s i t y

W a t e r wash

Form t i m e , s e c Drain time, min TNT l o s s , %

70% a c i d w a s h

Form t i m e , s e c Form r a t e , l b / f t / m i n Cake t h i c k n e s s , cm Drain time, min g a c i d / g TNT i n c a k e Dry cake weight, g Vacuum, i n Hg

Initial

0.508

0.5

8 1 -

35 2.32 1,3 3 1.35 10

1A

0.5 0.6 0.530

3 0.5 7.6

17 2.68 0.7 1.5 0.76

IB

2

TEST LEAF

0.474

-

6 7.2

23 3.54 1.4 2 1.24 1.36 20

2A

Experiment

PILOT PROCESS FILTRATION CYCLE USING A 0 . 1 - f t

Table V I I

0.392

-

9.0

18 2.4 0.9 2 1.24 0.72

2B


-

0.530

0.5

6 2 6.1

83 1.57 2.0 5 1.02 2.18 20

288

INDUSTRIAL

form

0.42

deliquor 70%

H2S01*

wash

min

0.10

wash 0.50 4.02


NITRATIONS

1.00

dewater

The

LABORATORY

2.00

deliquor H2O

AND

min

minimum a c t i v e b e l t l e n g t h i s 0.86(4.0) = 3.44

ft

A continuous b e l t f i l t e r should serve t h i s purpose w e l l . The s t a n d a r d d e s i g n w i l l h a v e t o be a l t e r e d t o o p e r a t e i n t h e e x p l o s i v e a t m o s p h e r e and t h e f i l t e r u n i t w i l l h a v e t o be e n c l o s e d i n an e n v i r o n m e n t a l chamber t h a t w i l l c o n t r o l t h e t e m p e r a t u r e a t -10°C and c o n t a i n any a c i d fumes t h a t may be e x h a u s t e d . A l l pumps s h o u l d be mounted o u t s i d e t h e chamber t o r e d u c e t h e heat load. Recycle

Acid

The f i l t r a t e removed f r o m t h e c a k e c o n t a i n s a p p r o x i m a t e l y 2/3 o f t h e n i t r i c a c i d and s u l f u r t r i o x i d e t h a t was f e d t o t h e trinitrators. T h i s s t r e a m i s r e c y c l e d b a c k t o t a n k s where t h e a c i d c o n c e n t r a t i o n s a r e a d j u s t e d and t h e n i t i s u s e d as f e e d for the d i n i t r a t o r s . Product The washed c r y s t a l l i z e d TNT c a k e t h a t i s removed f r o m t h e b e l t goes t o a m e l t t a n k w h e r e i t i s h e a t e d w i t h w a t e r t o remove occluded a c i d . The two-phase l i q u i d s t r e a m i s s e p a r a t e d w i t h t h e h e a v i e r o i l b e i n g t h e TNT p r o d u c t and t h e l i g h t e r w a t e r / a c i d s o l u t i o n being a waste stream. Instrumentation

System

An e l e c t r o n i c i n s t r u m e n t a t i o n s y s t e m w i t h c o m p u t e r comp a t i b i l i t y was i n c o r p o r a t e d i n t h e d e s i g n t o c o n t r o l t h e TNT p i l o t p l a n t . A l l components must be U n d e r w r i t e r s L a b o r a t o r y l i s t e d i n t r i n s i c a l l y s a f e o r s u i t a b l e f o r C l a s s I , Group D, Division 2 operation.



HAAS E T AL.

TNT

Manufacture:

Pilot

Plant

289

An i n s t r u m e n t a t i o n p a n e l - b o a r d i s l o c a t e d i n t h e r e m o t e c o n t r o l b u i l d i n g . I t w i l l b e l a i d o u t i n a manner t o f o l l o w t h e p r o c e s s w i t h r e c o r d e r s , c o n t r o l l e r s , i n d i c a t o r s and m a n u a l loaders i n convenient systematic use-oriented p o s i t i o n s . The c o n t r o l e q u i p m e n t w i l l p e r m i t o p e r a t i o n o f t h e p i l o t p l a n t f r o m t h e r e m o t e c o n t r o l b u i l d i n g . The e l e c t r i c a l s i g n a l s l e a v i n g the c o n t r o l b u i l d i n g w i l l be d i r e c t e d t h r o u g h zener d i o d e b a r r i e r s t h a t e s s e n t i a l l y s h o r t t h e f i e l d c i r c u i t when an o v e r - v o l t a g e i s d e t e c t e d . This w i l l p r o t e c t the process a r e a f r o m r e c e i v i n g e n e r g y f r o m c o n t r o l s y s t e m components t h a t c o u l d r e s u l t i n a h a z a r d o u s c o n d i t i o n . The c o n t r o l s y s t e m power i n t h e p r o c e s s a r e a w i l l n e v e r e x c e e d t h e 24 V, 20 ma level. The c o n t r o l e q u i p m e n t l o c a t e d i n p r o c e s s a r e a w i l l o p e r a t e on t h e power s p e c i f i e d a b o v e . The s e n s i n g e l e m e n t s w i l l m o n i t o r p r e s s u r e and t e m p e r a t u r e and l i n e a r l y c o n v e r t t h e p r o c e s s v a r i a b l e i n t o a l e v e l o f t h e c o n t r o l power. The p r o c e s s s t r e a m c o n t r o l e l e m e n t s w i l l f u n c t i o n o n 3-15 p s i a i r signals. These a i r s i g n a l s w i l l o r i g i n a t e i n t h e p r o c e s s b u i l d ing by c o n t r o l l i n g the instrument a i r supply p r e s s u r e w i t h an e l e c t r i c a l s i g n a l t h a t o r i g i n a t e s from a c o n t r o l l e r o r manual l o a d e r i n the c o n t r o l b u i l d i n g . A l l p r o c e s s w e t t e d c o n t r o l p a r t s w i l l b e made o f 3 1 6 L o r 304L s t a i n l e s s s t e e l o r a l l o y 20. A l l external f i e l d c a s i n g s w i l l be s u i t a b l e f o r m o u n t i n g i n a h i g h l y c o r r o s i v e a t m o s p h e r e a s d e s c r i b e d b e l o w . The e q u i p m e n t t h a t w i l l b e i n t h e p r o c e s s s t r e a m s o r v e s s e l s w i l l be f a b r i c a t e d f r o m m a t e r i a l impervious t o the c o r r o s i v e e f f e c t s o f s u l f u r i c a c i d , n i t r i c a c i d , a n d o l e u m . A l l o f t h e a b o v e a c i d s and a c i d m i x t u r e s may be p r e s e n t i n w a t e r s o l u t i o n s v a r y i n g i n c o n c e n t r a t i o n f r o m 0-100%. Summary A TNT p i l o t p l a n t d e s i g n b a s e d on l a b o r a t o r y i n f o r m a t i o n has b e e n d e s c r i b e d . The p r o c e s s i n c l u d e s two new m a n u f a c t u r i n g t e c h n o l o g y s t e p s , a l o w t e m p e r a t u r e (-8°C) d i n i t r a t i o n r e a c t o r and a TNT c r y s t a l l i z a t i o n u n i t . T h i s new s i n g l e p h a s e r e a c t i o n t e c h n i q u e f o r m a n u f a c t u r i n g TNT h a s p o s s i b i l i t i e s o f r e d u c i n g a i r a n d w a t e r p o l l u t i o n a n d improving the o p e r a t i o n a l s a f e t y o f munition p l a n t s . C o n s t r u c t i o n of the p i l o t p l a n t o r a m o d i f i c a t i o n o f t h e d e s i g n i s now u n d e r c o n s i d e r a t i o n b y t h e Army. Acknowledgement T h i s w o r k was s u p p o r t e d b y P i c a t i n n y A r s e n a l u n d e r Cont r a c t No. D A A A 2 1 - 7 3 - C — 7 4 3 , The a u t h o r s g r a t e f u l l y a c k n o w l e d g e t h e i r f i n a n c i a l s u p p o r t and g u i d a n c e f u r n i s h e d d u r i n g t h e d u r ation of the contract.


A Low-Temperature Process for TNT Manufacture Part 2. Pilot Plant

Recommend Documents