Chemistry of the Cellulose-N2O4-DMF Solution: Recovery and

5 Chemistry of the

Cellulose-N2O4-DMF

Solution:

Recovery and Recycle of Raw Materials NORMAN A. PORTNOY and DAVID P. ANDERSON

Downloaded by PURDUE UNIV on September 26, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0058.ch005

ITT Rayonier, Inc., Eastern Research Div., Whippany,N.J.07981

The purpose of the work presented in this paper is t o establish a foundation f o r a technically viable recovery and recycle system based on spinning rayon fibers from the cellulose/ N O /DMF s o l u t i o n . Other papers in this symposium d i s c u s s e d solution makeup, s p i n n i n g , and fiber p r o p e r t i e s . The paper presented h e r e , which is d i v i d e d into two parts, attempts t o e x p l a i n some o f the chemistry of dissolution and r e g e n e r a t i o n as well as our efforts in developing a technically f e a s i b l e recovery and recycle system. 2

A.

4

The Chemistry o f The

Cellulose/N O /DMF 2

4

Solution

Introduction When t h e i n v e s t i g a t i o n of this system was initiated, t h e importance of d e l i n e a t i n g t h e exact mode of dissolution o f t h e cellulose in DMF/N O was r e c o g n i z e d . To understand t h e dissolution step and t o p r o p e r l y formulate a recovery and r e c y c l e system, a thorough study o f the chemistry of cellulose in DMF/N O had t o be undertaken. From a theoretical viewpoint, s e v e r a l possibilities as t o the mechanism of cellulose d i s s o l u t i o n in DMF/N O a r e e v i d e n t . The s i m p l e s t would be a r e a c t i o n between the h y d r o x y l groups of cellulose and N O t o form a cellulose nitrite e s t e r and HNO as shown in equation 1 (mechanism 1). This c e l l u l o s e nitrite e s t e r may then be s o l u b l e in DMF. DMF DMF 1 . ) CellOH + N 0 OCellONO + HNO3 >solution. The components o f such a s o l u t i o n would be c e l l u l o s e n i t r i t e , n i t r i c a c i d (HNO3), unreacted N2O4, and DMF. T h i s k i n d of r e a c t i o n between a l c o h o l s and N2O4 i s w e l l known and has been ext e n s i v e l y documented i n the l i t e r a t u r e f o r a wide range of 2

4

2

2

2

4

4

3

2

4

52

Turbak; Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4

5.

PORTNOY AND ANDERSON

Cellulose-N0 -DMF Solution t

4

53

a l c o h o l s . Since c e l l u l o s e i s an a l c o h o l i t should r e a c t i n t h e same manner, A second p o s s i b i l i t y i s t h a t a complex, probably of the donor-acceptor type, between c e l l u l o s e and N2O4 forms and t h a t DMF acts as a s o l v e n t f o r t h i s complex as i n equation 2 (mechanism 2) · DMF 2 · ) CellOH + N 0 > CellOH : N 0 > solution


2

4

2

4

In t h i s case the s p i n n i n g s o l u t i o n would c o n t a i n t h e c e l l u l o s e : N2O4 complex, uncomplexed N2O4 and DMF. A t h i r d p o s s i b i l i t y i s t h a t DMF and N2O4 form a donor-acceptor complex i n which c e l l u l o s e i s s o l u b l e as i n equations 3 a and 3b (mechanism 3 ) · eq. 3 a . )

DMF + N2O4

eq. 3 b . )

DMF : N C>4 2

>DMF : N 0 2

+

4

C e l l O H — > solution

This s o l u t i o n would c o n t a i n unchanged c e l l u l o s e , DMF 1 ^ 0 4 complex and uncomplexed DMF as t h e s o l v e n t . An a d d i t i o n a l p o s s i b i l i t y would be t h a t d i s s o l u t i o n may occur v i a some combination of the above mechanisms. I t f o l l o w s t h a t the mechanism of d i s s o l u t i o n and thus the chemistry of the c e l l u l o s e 1^04:DMF i n t e r a c t i o n s i s v e r y important s i n c e t h i s w i l l determine not only the composition of the s p i n n i n g s o l u t i o n , s p i n n i n g procedures, and f i b e r p r o p e r t i e s , but a l s o the recovery and r e c y c l e process. Since some o f the above mechanisms r e q u i r e complexation between the c e l l u l o s e and N2O4 or between the DMF and N2O4, i t appeared t h a t during s p i n n i n g the c e l l u l o s i c f i b e r s (rayon) might not r e q u i r e a chemical regenerat i n g r e a c t i o n but might be p r e c i p i t a t e d o r coagulated by a nons o l v e n t system. T h i s could be e s p e c i a l l y t r u e f o r mechanism 3 s i n c e i t r e q u i r e s t h a t c e l l u l o s e remain unchanged and be simply s o l v a t e d by a DMF 1 ^ 0 4 complex. However, i f mechanism 1 were o p e r a t i v e , then a t r a n s n i t r o s a t i o n r e a c t i o n such as h y d r o l y s i s or a l c o h o l y s i s would be necessary t o o b t a i n regenerated c e l l u l o s e . One c o n c e i v a b l e advantage of such a system i s the poss i b i l i t y o f c o n t r o l of molecular o r i e n t a t i o n d u r i n g r e g e n e r a t i o n and s p i n n i n g by c o n t r o l of t h e removal of the n i t r i t e groups. Such i n c r e a s e d c o n t r o l would r e s u l t from the p l a s t i c i t y of t h e c e l l u l o s e n i t r i t e d e r i v a t i v e p e r m i t t i n g o r i e n t a t i o n and i s r e s p o n s i b l e f o r t h e l a r g e v a r i e t y of s t r o n g rayon f i b e r s a v a i l a b l e from the v i s c o s e process, i n which case the i n t e r m e d i a t e i s c e l l u l o s e xanthate. By c o n t r a s t , i f c e l l u l o s e i s merely p r e c i p i t a ted or coagulated from a s o l v e n t the p o s s i b i l i t y of t h i s c o n t r o l i s severely l i m i t e d . As a f u r t h e r consequence, the nature of the u l t i m a t e s p i n ning system i s r e l a t e d t o t h e d i s s o l u t i o n mechanism by the a c t u a l composition of t h e cellulose/N204/DMF s o l u t i o n . I f t h e s p i n n i n g s o l u t i o n contained unreacted c e l l u l o s e as i n mechanism 3 ,



54

S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FIBERS

then a dry s p i n n i n g system might be developed i n which the c e l l u lose/N204/DMF s o l u t i o n i s spun i n t o an evacuated chamber t o r e move the s o l v e n t s and p r e c i p i t a t e the f i l a m e n t s . This would be s i m i l a r t o the process f o r s p i n n i n g c e l l u l o s e d i a c e t a t e from acetone s o l u t i o n . Advantages t o t h i s are the h i g h speeds o f s p i n ning which are p o s s i b l e and the r e l a t i v e s i m p l i c i t y of the r e covery system which would have only t o r e c y c l e the DMF : N 2 O 4 complex. However, i f c e l l u l o s e had t o be regenerated from a c e l l u l o s e d e r i v a t i v e , i n t h i s case a n i t r i t e e s t e r , more complexity would be i n v o l v e d i n recovery and r e c y c l e . As p r e v i o u s l y e x p l a i n e d , r e g e n e r a t i n g c e l l u l o s e during s p i n n i n g from a t r u e c e l l u l o s e n i t r i t e e s t e r would r e q u i r e a t r a n s n i t r o s a t i o n r e a c t i o n by some agent t o remove the n i t r i t e and p r o v i d e a hydrogen i o n t o c e l l u l o s e . These requirements are met by p r o t o n i c n u c l e o p h i l i c s p e c i e s such as water, a l c o h o l , o r o t h e r s . I f the regenerant-coagulant were water o r a l c o h o l , then the spent s p i n bath would c o n t a i n n i t r o u s a c i d , H N O 2 , o r the a l k y l n i t r i t e , RONO, i n a d d i t i o n t o the DMF and H N O 3 from the s p i n n i n g s o l u t i o n , eq, 4 . Any unreacted N 2 O 4 i n the s p i n n i n g s o l u t i o n would make a d d i t i o n a l H N O 2 (or RONO) and H N O 3 i n the s p i n bath, eq. 5 . 4. )

5.

CellONO + H 0 (or ROH) regeneration

C e l l OH + HONO (or RONO)

2

) HOH (or ROH)

+ excess N 04-*HONO (or RONO) + 2

HNO3

T o t a l recovery and r e c y c l e , i n t h i s case, would i n v o l v e s p l i t t i n g the s p i n bath i n t o a t l e a s t 4 components and r e c y c l i n g DMF and H 0 ( o r ROH) w h i l e changing RONO (or HONO) and H N O 3 i n t o a form from which N 2 O 4 could be r e a d i l y obtained. Thus, one of the f i r s t questions t o be answered was whether the s p i n n i n g s o l u t i o n contained c e l l u l o s e n i t r i t e . 2

R e s u l t s and D i s c u s s i o n T h i s q u e s t i o n was answered by chemical and s p e c t r a l s t u d i e s . Because o f the h i g h l y complex nature of the s o l u t i o n , simple s t u d i e s using reagents to measure n i t r i t e composition were not p o s s i b l e . The accuracy o f any method using d i a z o t i z i n g reagents or o x i d a t i o n - r e d u c t i o n r e a c t i o n s to measure the c o n c e n t r a t i o n o f H N O 3 o r CellONO would be hampered by the strong o x i d i z i n g a b i l i t y of the excess N 2 O 4 . Studies i n which the s p i n n i n g s o l u t i o n was p r e c i p i t a t e d w i t h water i n a Waring Blender and the r e s u l t a n t c e l l u l o s i c m a t e r i a l then analyzed f o r n i t r o g e n and c a r b o x y l r e s i dues showed t h a t there was no i n c r e a s e i n these over s t a r t i n g p u l p , but there was a s l i g h t l o s s i n D.P. Thus any n i t r i t e d e r i v a t i v e which was being formed d u r i n g d i s s o l u t i o n was not s t a b l e t o c o a g u l a t i o n w i t h water. T h i s s u b s t a n t i a t e d the claims


5.

Cellulose-N O -DM F Solution

PORTNOY A N D ANDERSON

of e a r l i e r workers. I n f r a r e d s t u d i e s were not p e r t i n e n t s i n c e the n i t r i t e (N«0) a b s o r p t i o n occurs a t r*u 6 . Ou which i s i n d i r e c t c o n f l i c t w i t h the amide c a r b o n y l a b s o r p t i o n of DMF so any spect r a l i d e n t i f i c a t i o n on an i n f r a r e d b a s i s would be considered tenuous · Schweiger (1) had reported that a t r u e c e l l u l o s e n i t r i t e e s t e r could be i s o l a t e d from the c e l l u l o s e / N 0 / D M F s o l u t i o n by f i r s t s t a b i l i z i n g the s o l u t i o n w i t h an a c i d scavenger such as p y r i d i n e and then p r e c i p i t a t i n g the n i t r i t e e s t e r by water coagu l a t i o n . These experiments were repeated. P y r i d i n e was added t o the 8/15/77 c e l l u l o s e / N 0 / D M F s o l u t i o n a t a l e v e l of 20% by weight o f the s o l u t i o n and t h i s was spread on a g l a s s p l a t e . The p l a t e was then immersed i n 20% p y r i d i n e / 8 0 % water a t 5°C and an opaque f i l m ( c e l l u l o s e always formed a c l e a r f i l m ) was c o a g u l a t e d This f i l m was s o l u b l e i n DMF, DMSO, CH3CN and other organic s o l vents so i t was o b v i o u s l y not c e l l u l o s e . The UV-VIS. spectrum i n the 300 - 450 my r e g i o n of a DMF s o l u t i o n of the r e - d i s s o l v e d f i l m was n e a r l y i d e n t i c a l t o t h a t of i s o p r o p y l - , 1-pentyl- o r c y c l o h e x y l - n i t r i t e which were prepared as model compounds by adding N 0 t o a DMF s o l u t i o n of t h e corresponding a l c o h o l . When s e v e r a l drops o f aqueous H S 0 were added t o the UV c e l l and the s p e c t r a were rescanned, a l l of t h e above, the model a l k y l n i t r i t e s and the r e d i s s o l v e d f i l m , gave e x a c t l y the same spectrum. This new spectrum was i d e n t i c a l t o that o f an a c i d i f i e d DMF s o l u t i o n o f sodium n i t r i t e i n d i c a t i n g t h a t a l l of these compounds, the a l k y l n i t r i t e s and " c e l l u l o s e n i t r i t e " , were r e l e a s i n g n i t r o u s a c i d thus confirming t h a t the new m a t e r i a l d i d c o n t a i n the n i t r i t e moiety. Table I shows the UV-VIS. p o s i t i o n s and i n t e n s i t i e s o f v a r i o u s n i t r i t e m o i e t i e s used f o r comparison purposes i n t h i s s t r u c t u r e p r o o f . Figures 1 and 2 show the UV-VIS. s p e c t r a of DMF s o l u t i o n s of amyl n i t r i t e , " c e l l u l o s e n i t r i t e " , sodium n i t r i t e and sodium n i t r a t e b e f o r e and a f t e r a c i d i f i c a t i o n . When the " c e l l u l o s e n i t r i t e " f i l m was d r i e d , brown gas evolved from the f i l m and i t then became i n s o l u b l e i n those s o l v e n t s i n which i t had p r e v i o u s l y d i s s o l v e d . The i n f r a r e d spectrum of t h i s i n s o l u b l e d r i e d f i l m was i d e n t i c a l t o t h a t of c e l l u l o s e . This s p e c t r a l study r e p r e sents the f i r s t d e f i n i t i v e p r o o f t h a t the m a t e r i a l i s o l a t e d by c o a g u l a t i o n of t h e p y r i d i n e - s t a b i l i z e d c e l l u l o s e / N 2 0 / D M F s o l u t i o n was indeed c e l l u l o s e n i t r i t e . I t was d e s i r a b l e t o have chemical as w e l l as s p e c t r a l i d e n t i f i c a t i o n of the s t r u c t u r e of t h i s new m a t e r i a l . I n t h i s r e gard, a method was developed f o r i s o l a t i n g a s o l i d from the p y r i d i n e - s t a b i l i z e d s o l u t i o n s under anhydrous c o n d i t i o n s . This was accomplished by t h e a d d i t i o n of d i e t h y l ether t o the p y r i dine s t a b i l i z e d c e l l u l o s e / N 0 / D M F s o l u t i o n s causing p r e c i p i t a t i o n of a s o l i d . A d d i t i o n of 1-pentyl a l c o h o l t o the DMF s o l u t i o n of t h i s s o l i d caused p r e c i p i t a t i o n of a w h i t e f i b r o u s m a t e r i a l which was l a t e r i d e n t i f i e d as c e l l u l o s e . D i s t i l l a t i o n 2

2


55

4

t

4

4

2

4

2

4

2

4


4


56

TABLE I Positions and Intensities of N i t r i t e Ultraviolet Absorption Peaks Sample No.

Compound

Major Peaks max (my) 370 67.2 357 78.9 345 67.2 333 46.8


a

Minor Peaks or Shoulders max (my) a 385 32.2 323 30.2

1.

Amyl N i t r i t e

2.

Isopropyl N i t r i t e

373 358 348

55.4 67.2 67.2

385 338 328

31.2 56.4 (-)

3.

Cyclohexyl N i t r i t e

372 360

58.4 57.8

390 348 338

32.4 44.5 29.7

4.

"Cellulose N i t r i t e "

366 353 341

380 331 320

5.

Sodium N i t r i t e

359

25.5

6.

Sodium Nitrate

310

44

7.

Sodium Nitrate with acid added

270

69

389 375 361 349 338

49.0 80.8 72.0 47.6 37.5

8.

1, 3, 4 or 5 with acid added b

a.) b.)

€

β

molar extinction coefficient.

The values for € are from the experiment i n which H2SO4 was added to the sodium n i t r i t e solution.




5.

57

Cellulose-N O DMF Solution t

r

a. NaN02, DMF

Figure 2. Uv-vis spectra of aqueous acidified DMF solu tions of cellONO or AmylONO as well as NaNO and NaNO before and after aque' ous acidification t

400

Λου WAVELENGTH

(mp)

450

s

, Ί . Γ

. !


S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FD3ERS


58

of the supernatant gave a 60% y i e l d of 1-pentyl n i t r i t e which was i d e n t i c a l to commercial m a t e r i a l i n p h y s i c a l and s p e c t r a l properties. Therefore i t was a c e r t a i n t y t h a t the p y r i d i n e - m o d i f i e d cellulose/N^O^/DMF s o l u t i o n contained c e l l u l o s e n i t r i t e . I t could be argued however, t h a t the p y r i d i n e not only s t a b i l i z e d the c e l l u l o s e n i t r i t e but a l s o c a t a l y z e d the f o r m a t i o n of t h i s s p e c i e s as p y r i d i n e i s w i d e l y used i n s y n t h e t i c chemistry f o r c a t a l y s i s i n d e r i v a t i z i n g a l c o h o l s ( c e l l u l o s e i s an a l c o h o l ) w i t h anhydrides (N2O4 i s an a n h y d r i d e ) . S p e c t r o s c o p i c s t u d i e s on the cellulose/N204/DMF s o l u t i o n d i d not show t h a t the n i t r i t e was p r e s e n t , i n f a c t UV-VIS. s p e c t r a of the s o l u t i o n are almost the same as those of n i t r o u s a c i d . T h i s i s the r e s u l t of the excess N2O4 which has b a s i c a l l y the same UV-VIS. spectrum as n i t r o u s a c i d probably because of the s t r o n g l y absorbing n i t r o s y l (N«0) group. However, s y n t h e t i c experiments i n d i c a t e d t h a t model a l c o h o l s , such as c y c l o h e x a n o l or i s o p r o p a n o l r e a c t immediately w i t h DMF s o l u t i o n s of N2O4 a t 5°C i n the absence of p y r i d i n e and s i n c e c e l l u l o s e i s an a l c o h o l , i t i s expected t o r e a c t s i m i l a r l y .

B.

Recovery and Recycle of Raw M a t e r i a l s

Introduction The e n t i r e area of research and development a s s o c i a t e d w i t h the recovery and r e c y c l i n g of process chemicals i s c e n t r a l t o the t e c h n i c a l and commercial success of s p i n n i n g f i b e r s from o r ganic s o l v e n t s . With the chemistry background presented e a r l i e r i t appeared necessary to develop the recovery system based on p r o c e s s i n g the f o l l o w i n g : a. ) Dimethylformamide (DMF) b. ) Coagulant ( e i t h e r an a l c o h o l o r water) c. ) N i t r o g e n T e t r o x i d e (N2O4) 1.

When the coagulant i s water, then n i t r o u s a c i d (HNO2) and n i t r i c a c i d (HNO3) are the p r e c u r s o r s to N2O4 recovery.

2.

When the coagulant i s an a l c o h o l , then the a l c o h o l n i t r i t e (RONO) and HNO3 a r e the p r e c u r s o r s to N2O4 recovery.

An i n i t i a l c o n c e p t u a l i z a t i o n of the recovery and r e c y c l e system i s shown i n F i g u r e 3 which served as a p r e l i m i n a r y s k e t c h of the requirements of recovery and r e c y c l e f o r s p i n n i n g rayon f i b e r s from the cellulose/N2O4/DMF system. T h i s f i g u r e shows that the crude spent s p i n bath, c o n t a i n i n g DMF, HNO3, the coagu-



SPIN B A T H DMF i-PrOH HNO3 i-PrONO

i-PrOH

4

2

HN0 ,HN03

HNO3

HN02

HNO2

HYDROLYSIS

μρΓΟΝΟ

HNO3

S Ε Ρ A R A Τ I Ο Ν

2

N 0

Η

RAYON FIBER

NOf NO? SALTS

NEUTRALIZATION H ^ J P Y R O L Y S I S

t

k

Figure 3. Initial conceptualization of the total recycle and recovery system for spinning rayonfibersfrom CeUOH-N O -DMF solutions

N2O4 HNO3

Solu. M A K E U P l CallONO DMF

DMF


60


l e n t ( e i t h e r HOH o r ROH) and the n l t r o s a t e d coagulant ( e i t h e r HONO o r R0N0) must be separated i n t o f r a c t i o n s o f pure DMF, pure coagulant and the HN0 -HN0 (R0N0) f r a c t i o n s . The DMF must be returned t o the s o l u t i o n makeup, the coagulant t o the s p i n b a t h and the H N O 3 - H N O 2 (R0N0) p o r t i o n of the spent bath must be comb i n e d i n some way f o r c o n v e r s i o n t o N 2 O 4 . I f t h i s i s the o v e r a l l p l a n , then two major areas of r e s e a r c h would be necessary t o answer the f o l l o w i n g two q u e s t i o n s : a.) which methods o f separat i o n would be most e f f e c t i v e f o r the i n i t i a l s e p a r a t i o n o f t h e crude s p i n bath and b.) how can the n i t r i c and n i t r o u s a c i d f r a c t i o n s r e s u l t i n g from c e l l u l o s e d i s s o l u t i o n and r e g e n e r a t i o n be recombined t o form N 2 O 4 . I n a d d i t i o n , i f the n i t r o u s p o r t i o n of the o r i g i n a l N 0 ^ i s i n the a l k y l n i t r i t e form, i . e . because o f an a l c o h o l coagulant-régénérant, then a method f o r c o n v e r t i n g HNO3 and R0N0 to N 2 O 4 would have t o be found.


3

2

2

R e s u l t s and D i s c u s s i o n The recovery and r e c y c l e of N2O4 was s t u d i e d f i r s t . An ext e n s i v e l i t e r a t u r e survey on N 2 O 4 - H N O 3 chemistry uncovered seve r a l commercial processes which i n c l u d e d a step f o r p y r o l y z i n g a metal n i t r a t e s a l t to produce N 2 O 4 i n h i g h y i e l d s . Most of these processes i n v o l v e d decomposing c a l c i u m n i t r a t e i n a CO2 atmosphere (2) o r sodium n i t r a t e i n a CO atmosphere.(3) None of these r e p o r t s mentioned the recovery of N2O4 by p y r o l y z i n g a n i t r i t e s a l t o r a potassium s a l t as an i n d u s t r i a l p r o c e s s . S e v e r a l methods were considered r e l a t i v e t o the conversion of the HNO3 and HNO2 p o r t i o n o f the spent s p i n bath t o a s a l t and r e c o v e r y of t h i s s a l t f o r p y r o l y t i c p r o c e s s i n g . These methods i n c l u d e d : a.) P r e c i p i t a t i o n o f the s a l t - i f the coagulant were aqueous, then the spent s p i n bath c o n t a i n i n g HNO2 and HNO3 c o u l d be n e u t r a l i z e d t o form s a l t s . F o l l o w i n g t h i s , a d d i t i o n of a s u i t a b l e non-solvent such as a l c o h o l c o u l d p r e c i p i t a t e the s a l t s . T h i s presented unique problems s i n c e the s o l u b i l i t y of K N O 3 i s r e l a t i v e l y s m a l l (1.5%) i n M F , but t h a t o f Ca(N0 )2 or NaN03 i s /•^15-20%. I f the s p i n bath contained a l c o h o l as the coagulant then a h y d r o l y s i s s t e p , t o convert R0N0 to HONO, would precede the a c i d n e u t r a l i z a t i o n . However, i n such a non-aqueous b a t h , the p o s s i b i l i t i e s o f u s i n g other water i m m i s c i b l e précipitants such as methylene c h l o r i d e o r ether were r e c o g n i z e d . When s t u d i e s were done, e f f e c t i v e methods o f p r e c i p i t a t i n g K N O 3 and NaNOo but not C a ( N 0 o ) were found as can be seen i n Table I I . 3

2


5.


61

Cellulose-NODMF Solution t r

TABLE I I S o l u b i l i t i e s of N i t r a t e S a l t s i n D M F ^ P r e c i p i t a t i n g Solvent Mixtures ' Salt Left Precipitating % P r e c i p i t a t i n g Solvent* / D i s s o l v e d i n M i x t u r e Pb(N0 ) NaN0 KN0 Solvent Ca(N03) 0

1

3

3

3

2

0/1.1

0/14.2

0/18.0

0/130

None ( L i t . ) ( 4 ) 0/1.5

0/15.4

N. A.

N. A.

50/18.0

49/3.3

None (Exp·)


e

N

15.7/

2°4

0.5

47.5/

1

MeOH

63.4/1.1

41.5/12.2

53.5/18.0

75/42.4

EtOH

N. D.

59.7/4.3

N. D.

N. D.

i-PrOH

61.5/

0.5

60.3/

1

56.5/18.0

64/

Ether

59.4/

0.5

39.7/

1

61.3/18.0

N. D.

N. D.

N. D.

CH2C1 a) b) c)

2

73/

67/1.2

1

N. A. - not a v a i l a b l e N.D. •» no data obtained N 0 ^ « d i n i t r o g e n t e t r o x i d e , MeOH = methyl a l c o h o l , EtOH = e t h y l a l c o h o l , i-PrOH = i s o p r o p y l a l c o h o l , CH C1 » methylene c h l o r i d e , ether = d i e t h y l e t h e r % P r e c i p i t a t i n g s o l v e n t based on t o t a l mixture g. s a l t / 1 0 0 g DMF 2

2

d) e)

0.5

2

2

b.) D i s t i l l a t i o n of a l l l i q u i d t o leave a s a l t r e s i d u e - i f the coagulant were aqueous, then n e u t r a l i z a t i o n of the a c i d s f o l lowed by d i s t i l l a t i o n t o a s o l i d s a l t r e s i d u e (the p o t e n t i a l f o r d e t o n a t i o n a t t h i s p o i n t due t o the nitrate-DMF mixture was recogn i z e d e a r l y i n our work) would appear t o be v i a b l e . I f the coagul a n t were a l c o h o l , then as s t a t e d above, the h y d r o l y s i s step would precede the n e u t r a l i z a t i o n s t e p . A l t e r n a t e l y , the HNO3 port i o n o f the s p i n bath could be n e u t r a l i z e d p r i o r t o d i s t i l l a t i o n , the s p i n bath d i s t i l l e d t o a s a l t r e s i d u e and the a l c o h o l n i t r i t e p o r t i o n recovered from the d i s t i l l a t i o n , h y d r o l y z e d , n e u t r a l i z e d and then the n i t r i t e s a l t recovered a f t e r l i q u i d s t r i p p i n g . L i t e r a t u r e a v a i l a b l e on the recovery of DMF from aqueous systems i n d i c a t e d that acceptable y i e l d s could be obtained by d i s t i l l a t i o n . (5) The d i s t i n c t d i f f e r e n c e between schemes (a) and (b) was t h a t i n scheme (a) , the DMF would n o t r e q u i r e d i s t i l l a t i o n . H o p e f u l l y t h i s would have l e d t o lower economics f o r scheme (a) than scheme (b).



62

S O L V E N T S P U N R A Y O N , MODIFIED C E L L U L O S E FD3ERS

c.) Countercurrent e x t r a c t i o n of the aqueous-DMF spent s p i n bath - t h i s would o n l y a p p l y f o r aqueous s p i n baths. Commercial methods f o r c o u n t e r c u r r e n t e x t r a c t i o n of DMF from aqueous-DMF s o l u t i o n s were d e s c r i b e d i n d e t a i l i n the l i t e r a t u r e . ( 6 ) A v a r i e t y of e x t r a c t a n t s i n c l u d i n g chlorocarbons and hydrocarbons were e v a l u a t e d . The c o n c l u s i o n of t h i s l i t e r a t u r e study was that methylene c h l o r i d e was the most e f f i c i e n t e x t r a c t a n t and t h a t the process was economically f e a s i b l e when the aqueous-DMF contained l e s s than 10% DMF. R e s u l t s i n t h i s l a b o r a t o r y d i d not show p r o mise p r o b a b l y because the aqueous DMF spent s p i n baths contained a c i d or s a l t components which complicated e x t r a c t i o n . Recovery of the coagulant p o r t i o n of the s p i n b a t h , i . e . water or an a l c o h o l would be, i n a s i n s e , a l i m i t i n g f a c t o r s i n c e , depending on the composition of the s p i n b a t h , v e r y l a r g e volumes would be i n v o l v e d i n the recovery as w i l l now be exp l a i n e d . Although some e a r l y s p i n n i n g work was done using 8/25/67 cellulose/NoO^/DMF s o l u t i o n s , a d e c i s i o n was made, based on comparative s t u d i e s between 8/25/67 and 8/15/77 s p i n n i n g s o l u t i o n s , t o make the d e t a i l e d process e v a l u a t i o n on an 8/15/77 c e l l ulose/N204/DMF s o l u t i o n . T h i s r e q u i r e s t h a t 1.88 l b s . of N 04 and 9.63 l b s . of DMF be r e c y c l e d per 1.00 l b . of processed f i b e r i n a d d i t i o n t o the coagulant p o r t i o n of the s p i n b a t h . For example, i f the s p i n bath were at e q u i l i b r i u m and were 58/31/5/6, i s o p r o p y l a l c o h o l (i-PrONO/DMF/HN0 /isopropyl n i t r i t e (i-0r0N0) then a t o t a l of/-' 28.3 l b s . (9.63 l b s . DMF and 18.64 l b s . of i-PrONO) of l i q u i d would have t o be r e c y c l e d per 1.00 l b . of f i b e r processed. I f the s p i n bath were aqueous-DMF at a l e v e l of 20% H2O then a minimum of 12.0 l b s . of l i q u i d would be r e c y c l e d per 1.00 l b . of processed f i b e r . These represent examples of how the s p i n b a t h composition s e t s a lower l i m i t on the amount of chemic a l s which must be processed. Therefore the economics of a comm e r c i a l process depend g r e a t l y on the s p i n b a t h composition. I n i t i a l s p i n n i n g experiments i n d i c a t e d t h a t alcohol-DMF s p i n baths produced b e t t e r f i b e r s than aqueous-DMF s p i n b a t h s . Pure methyl-, e t h y l - or i s o p r o p y l - a l c o h o l as coagulant-regenerants produced f i b e r s w i t h approximately e q u i v a l e n t p h y s i c a l p r o p e r t i e s . Since methyl n i t r i t e i s a t o x i c gas and e t h y l n i t r i t e has a v e r y low b o i l i n g p o i n t , they are d i f f i c u l t t o handle at an e x p e r i mental l e v e l . However, i s o p r o p y l n i t r i t e (i-PrONO) i s reasona b l y easy t o handle and t h e r e f o r e i-PrOH was chosen as the coa g u l a n t - régénérant f o r d e t a i l e d recovery s t u d i e s . The p h y s i c a l p r o p e r t i e s of f i b e r s coagulated i n alcohol-DMF systems decreased as the l e v e l of DMF i n c r e a s e d , the b e s t f i b e r s having been spun from pure a l c o h o l primary s p i n b a t h s . However, i t was apparent t h a t , f o r economic reasons, some l e v e l of a l c o h o l i n DMF would have to be chosen and the f i b e r p r o p e r t i e s maximized f o r t h i s chosen system. An i-PrOH/DMF r a t i o of 2/1 was chosen and thus when r e c o v e r y s t u d i e s were begun, s y n t h e t i c spent s p i n baths of 2

3



b. )

80.5 95.5

165.2 99.5

78.0 96.7

76.9

164.3

75.4

96.8

41.1

79.1

23.4

18.5

39.8

5.1 11.0

0.0

0.0

2.4

2

H0

39.8

0.0

0.0

0.0

0.0

HNO3 g.

76.9

i-PrONO g.

T h i s 67.Ig. of DMF i s composed of DMF which i s a v a i l a b l e f o r r e c y c l e by simply d i s t i l l i n g the l i q u i d (28.6g.) and DMF which i s bound to the HNO3 and can be recovered i f the complex i s broken by n e u t r a l i z a t i o n .

a. ) T h i s 76.9g. represents 52.7g. i-PrOH

93.4

408.7

s t a r t i n g s p i n bath

% accounted f o r

381.6

totals

0.0

67.1

120.6

bottoms

4

62.5

4.9

32-46/1

3

18.9

i-PrOH

76.4

88.7

25-32/1

2

-

g.

82.9

95.9

r.t./10

1

DMF

3.4

T o t a l Wt. g.

Conditions bp. °C/mm. Hg

F r a c t i o n No.

Recovery of Process Chemicals by Vacuum D i s t i l l a t i o n of the Crude S p i n Bath

TABLE I I I


g.

S O L V E N T SPUN R A Y O N , MODIFIED

64

FD3ERS

2/1 i-PrOH/DMF i n which Ν 0 was added t o b r i n g the HN0 l e v e l near 3, 5 and 10% were e v a l u a t e d . These s o l u t i o n s were vacuum d i s t i l l e d without n e u t r a l i z a t i o n to e s t a b l i s h e x a c t l y how such an a c i d i c s o l u t i o n would behave i n a recovery process. Table I I I shows a synopsis of the d i s t i l l a t i o n of a s p i n bath a t the 10% a c i d l e v e l . The i-PrONO and i-PrOH d i s t i l l e d together as the p r e s s u r e was reduced. The next f r a c t i o n contained i-PrOH/DMF and q u i t e unexpectedly, no HNO3 was found i n t h i s f r a c t i o n . I n f a c t , pure DMF was obtained as d i s t i l l a t e i n the next f r a c t i o n u n t i l the bottom r e s i d u e contained n e a r l y 1.0 mole HNO3/I.O mole DMF. This r e s i d u e was f r a c t i o n a l l y d i s t i l l e d t o g i v e a c l e a r , c o l o r l e s s , o i l y l i q u i d , bp. 94-95°C/8 mm Hg. The l i q u i d had a d e n s i t y of 1.21 g/ml and contained 47.07% HNO3 ( t i t r a t i o n w i t h standard c a u s t i c ) and 48.98% DMF (gas chromatographic a n a l y s i s ) . The t h e o r e t i c a l values are 1.14 g/ml as the d e n s i t y and 46.32% HNO3, 53.68% DMF. Thus, t h i s new m a t e r i a l represents a 1:1 molar mix t u r e o f HNO3 and DMF i n which there i s o b v i o u s l y some i n t e r a c t i o n between the two molecular s p e c i e s , i . e . complexation t o some ex t e n t . T h i s i n t e r a c t i o n i s a l s o suggested by n u c l e a r magnetic resonance (NMR) s t u d i e s which showed a d o w n f i e l d s h i f t o f t h e DMF-aldehyde and N-methyl protons i n the mixture as compared t o these protons i n pure DMF. As these s p e c t r a were taken i n the neat l i q u i d s , no s o l v e n t e f f e c t s could i n t e r f e r e w i t h the r e s u l t s . This d o w n f i e l d s h i f t was a l s o present when the s p e c t r a were taken i n CDCI3/TMS. A t a b u l a t i o n of these s h i f t s a r e shown i n Table I V . 2


CELLULOSE

4

3

TABLE IV NMR S h i f t s i n DMF and DMF/HNO3 Complex a

Sample

/(ppm)( ->

DMF-HNO3

3.09

3.24

8.28

DMF

2.80

2.98

8.03

0.29

0.26

0.25

a.) Chemical s h i f t s i n ^(ppm) d o w n f i e l d from the i n t e r n a l s t a n dard TMS. The DMF-HNO3 b i n a r y mixture i s i n t r i g u i n g s i n c e i t provides a method of s e p a r a t i n g most of the DMF from the HNO3 even though the b o i l i n g p o i n t of DMF (154°C) i s much g r e a t e r than t h a t of HNO3 (83°C). The d o w n f i e l d chemical s h i f t of the aldehyde and N-methyl resonances i n d i c a t e a decrease i n e l e c t r o n d e n s i t y at




5.

Cellulose-N O DMF t

65

Solution

r

the amide carbon atom which i s c o n s i s t e n t w i t h a weak complexing of the amide and HNO3. Attempts t o d i s s o l v e c e l l u l o s e i n t h i s b i n a r y mixture were u n s u c c e s s f u l . Thus vacuum d i s t i l l a t i o n o f a s y n t h e t i c s p i n bath a t concent r a t i o n s expected i n a commercial process gave s e p a r a t i o n of a l l components except that p o r t i o n of the DMF which was i n v o l v e d i n a DMF/HNO3 b i n a r y mixture. This DMF c o u l d be r e l e a s e d by a d d i t i o n of a base and v a r i o u s bases were s t u d i e d f o r t h i s purpose but those d e r i v e d from c a l c i u m were chosen f o r s e v e r a l reasons as e x p l a i n e d below. Calcium carbonate (CaC03>, c a l c i u m hydroxide (Ca(CH)«) or c a l c i u m oxide (CaO) were used t o r e l e a s e the DMF from t h i s DMF/HNO3 mixture. The r e s u l t a n t c l e a r t h i c k s o l u t i o n was vacuum d i s t i l l e d t o recover the DMF l e a v i n g a c a l c i u m n i t r a t e (Ca(N03) ) r e s i d u e . This s o l i d r e s i d u e gave when p y r o l y z e d . Thus, t h i s sequence e s t a b l i s h e d t e c h n i c a l l y t h a t i t was p o s s i b l e t o f r a c t i o n a t e the s p i n bath, recover i-PrOH, i-PrONO and IMF from HN0 and o b t a i n N 0 from the HNO3 p o r t i o n of the bath. The choice of c a l c i u m bases f o r n e u t r a l i z a t i o n r e s u l t s from a study which was done on the s t a b i l i t y of DMF under a c i d i c and b a s i c c o n d i t i o n s . The data c l e a r l y showed that DMF i s reasonably s t a b l e i n the presence of a c i d as long as water i s excluded b u t t h a t dimethylamine (DMA) i s formed by h y d r o l y s i s when water i s present. By c o n t r a s t , DMF decomposed r a p i d l y when NaOH o r KOH was added w i t h no a d d i t i o n a l H 0. When C a ( 0 H ) , CaO or CaC03 was added t o DMF, even w i t h a d d i t i o n a l H 0 , no measurable amount of DMA was formed even on prolonged standing a t room temperature. I n a d d i t i o n , the recovery o f N 0 from C a ( N 0 o ) by p y r o l y s i s i s a commercial process r e l a t e d t o the phosphoric a c i d i n d u s t r y and l i t e r a t u r e references were found t o i n d i c a t e t h a t good y i e l d s of N 0 from p y r o l y s i s of C a ( N 0 3 ) were customary.(2) F o l l o w i n g an extensive l i t e r a t u r e search, a p r o j e c t was e s t a b l i s h e d to study the p r o d u c t i o n of N 0 v i a p y r o l y s i s o f v a r i o u s metal n i t r a t e s and n i t r i t e s . A m u f f l e furnace was modif i e d t o h o l d a p y r o l y s i s tube c o n t a i n i n g the s a l t under study. A s t a i n l e s s s t e e l p y r o l y s i s chamber was b u i l t so t h a t d i f f e r e n t sweep gases could be used t o create the d e s i r e d atmosphere i n the p y r o l y s i s tube and t o sweep the product N2O4 gases i n t o a capt u r i n g s o l u t i o n of 1-pentyl a l c o h o l i n IMF. The amount of N 0 c o u l d then be determined by UV-VIS. a n a l y s i s of the amount of 1 - p e n t y l n i t r i t e formed i n the c a p t u r i n g s o l u t i o n . References i n the l i t e r a t u r e i n d i c a t e d good N 0 y i e l d s could be obtained from C a ( N 0 ) a t 600°C i n a C 0 atmosphere (2) or NaN0 i n a CO atmosphere (5) b u t no data were a v a i l a b l e on the p y r o l y s i s o f KNO3 or n i t r i t e s a l t s . I n a d d i t i o n t o o b t a i n i n g the N 0 y i e l d , i t was necessary t o measure the content of unpyrolyzed n i t r a t e and n i t r i t e i n the p y r o l y s i s s a l t r e s i d u e t o determine the s e l e c t i v i t y of the process. Methods f o r these determinations were developed· 2

3

2

4

2

2

2

2

2

2

4

2

4

2

4

2

2

3

2

2

4

3

2

4


4

66


The expected s a l t m i x t u r e which would be obtained from the recovery process would be an equimolar m i x t u r e o f c a l c i u m n i t r a t e / c a l c i u m n i t r i t e . N i t r i t e s a l t s decompose t o produce one mole of NO and one mole of NO2 per mole of n i t r i t e s a l t thus a d d i t i o n a l o x i d a t i o n i s r e q u i r e d t o o b t a i n N2O4 from t h i s system. Equations 6 and 7 are examples of the c h e m i c a l changes accompanying the r e l e a s e of N2O4 d u r i n g the decomposition of Ca(N0 ) . Although the byproducts v a r y w i t h the d i f f e r e n t sweep gases and s a l t s , the decomposition of c a l c i u m n i t r a t e , Ca(NO^) and c a l c i u m n i t r i t e , Ca(N02>2 i n the presence of CO2 should serve as adequate examples. 3

2


2

6.

Ca(N0 )

2

+ C0 —>CaC0

3

+ 2N0

7.

Ca(N0 )

2

+ C0 —*CaC0

3

+ N0

3

2

2

2

2

+ 1/2

2

+

0

2

NO

When a m i x t u r e o f n i t r a t e and n i t r i t e i s p y r o l y z e d , 1/2 mole of oxygen i s produced, which i s the r e q u i r e d amount t o convert the NO from n i t r i t e decomposition t o N 2 O / . However, i n the l a b o r a t o r y experiments, oxygen was mixed w i t h the e f f l u e n t gases i n o x i d a t i o n chambers which were p l a c e d b e f o r e the c a p t u r i n g cham bers f o r a l l p y r o l y s i s runs which i n c l u d e d n i t r i t e . This assured the b e s t p o s s i b l e y i e l d s . Y i e l d s of N2O4 r e s u l t i n g from p y r o l y s i s experiments are shown i n Table V. The r e s u l t s i n t h i s t a b l e show t h a t 93% N2O4 y i e l d s can be obtained from the p y r o l y s i s of a 1:1 ( C a ( N 0 ) / C a ( N O o ) m i x t u r e a t 800°C i n a C 0 a t mosphere. I f the HONO o r C a ( N 0 ) 2 could be o x i d i z e d t o H N 0 or C a ( N 0 > 2 , then the ^ 0 , recovery would i n v o l v e the p y r o l y s i s of C a ( N 0 o ) which r o u t i n e l y gave 98% y i e l d s of N 0, i n C 0 or N at 800°C. T h i s p a r t of the i n v e s t i g a t i o n e s t a b l i s h e d a route to N 0^ r e c o v e r y , i . e . by p y r o l y s i s of a C a ( N 0 ) / C a ( N 0 2 ) 2 mixture. S i n c e the Ν2Ο4 which i s produced by t h i s p y r o l y s i s i s a c o r r o s i v e , o x i d i z i n g gas, a s p e c i f i c study was made to determine the requirements f o r c o n s t r u c t i o n m a t e r i a l s f o r the p y r o l y s i s furnace. Conferences w i t h f a c u l t y members a t the Engineering School, Rutgers U n i v e r s i t y , New Brunswick, N.J. r e s u l t e d i n the s u g g e s t i o n t h a t a ceramic m a t e r i a l would be r e q u i r e d f o r the i n s i d e of the f u r n a c e . The m a t e r i a l of p r e f e r e n c e was A l 2 0 which i s f r e q u e n t l y used f o r furnace l i n i n g s . P r o t o t y p e l a b o r a t o r y p y r o l y s i s tubes of A 1 0 were designed and obtained from Duramic P r o d u c t s , Inc. P r e l i m i n a r y p y r o l y s i s data from a l i m i t e d number of experiments u s i n g pure c a l c i u m n i t r a t e i n d i c a t e t h a t the y i e l d s of N2O4 are s i m i l a r t o those obtained when s t a i n l e s s s t e e l tubes were used. One of the important remaining steps was c o n v e r s i o n of i s o p r o p y l n i t r i t e i n t o the c a l c i u m n i t r i t e s a l t f o r p y r o l y s i s . Hy d r o l y s i s of i-Pr0N0 to HN0 ( n i t r o u s a c i d ) and n e u t r a l i z a t i o n of 3

2

2

2

2

3

3

2

2

2

2

s

2

3

2

3

2

3

2


a

l

t


g)

f)

c) d) e)

b)

a)

2

2

3

2

2

3

2

3

2

d

e

2

2

e

e

e

2

2

2

75.3/86.5 67.7/84.8 93.3/100.1 97.8/97.8 76.8/84.6 61.9/68.8 57.8/92.8/-

Carbon Dioxide

2

11

-/-/-

53.1/54.1 28.8/33.9

-/-/-

35.0/58.0 11.9/36.6

Carbôn Monoxide

2

2

2

2

-/-

9.6/63.9 6.0/69.2 38.2/95.2 98.1/98.1 20.1/31.7 28.8/38.5 34.0/78.8/-

2

2

13.9/41.0 26.0/84.4/-

-/-

-/-

-/-

-/-

Air

Nitrogen

b

These results are averages of 2-4 pyrolysis experiments. If the salts were not thoroughly dried, lower N 0^ yields resulted. The sweep gas flow rates were 100 ml./min. Stainless steel (310) pyrolysis chambers were used. Results are expressed as % y i e l d of N 04/total % of the starting salt which i s accounted for by the sum of the N 04 yield plus analysis of the pyrolysis residue. Pyrolysis at 600°C resulted i n very low N2O4 yields. Pyrolysis at 800°C resulted i n very low N 04 yields. The pyrolysis of a n i t r i t e salt produces a mole of NO per mole of N0 . Therefore 0 was mixed at 50 ml./min. with the pyrolysis effluent to oxidize any NO to N 04 for capture. Carbon monoxide can reduce N0 to NO by the equation CO + N0 -•NO + C0 therefore 0 was mixed at 50 ml ./min. with these pyrolysis effluent streams. When these measurements were made, no method of residue analysis was available.

3

2

3

C

NaN0 /800/90 KNOJ800/90 Ca(N0 ) /600/120 Ca(N0 ) /800/90 NaN0 :NaN0 /1000/90 KNO3:KNO /1000/90 » Ca(N0 )2 :Ca(N0 ) /600/120 > 8 Ca(N0 )2 :Ca(N0 ) /800/90 » 8

c

Salt/Temp. °C/Time (min.)

3

a

The Effect of Temperature and Sweep Gas on N2O4 Yields from the Pyrolysis of Nitrate Salts or 1:1 Nitrate/Nitrite Salt Mixtures >

TABLE V


3

3

S*

Ο ?

ΐ s:

ο

I

r

Ο

ο

01


Spin Bath

3

I ο η

t i I I a t

8

D i

£ 2

Kiln

—a—

2

C0

2

2

2

H 0

3

CaC0 |

Ca(N03>2 ]Ca(N0 ^ Neutraliz ation DMF ΗΝΟ^,ΗΝΟο,1 i-PrOH, DMF, i - P r O H

H2O

DMF

DMF

CaO

Cellulose Fiber

i-PrOH

->>

H 0 Cycle (alternate) Η NO 3, H N 0 , DMF

{Hydrolysis

i-PrONO

DMF/HNO3

L

i-PrOH

4

trace DMF

2

Ca2

ι

Pyrolysis

t

k

Figure 4. Final technically proven total recycle and recovery system for spinning rayon fibers from CellOH-N O -DMF solutions

i-PrOH,HN0

i-PrONO,DMF

Solu.

DMF

Ν2θ



5.


Cellulose-N0 -DMF Solution t

4

69

t h i s HONO appeared reasonable. Although t h i s approach was f o l lowed, the problem of e f f i c i e n t c o n v e r s i o n of i-PrONO t o HONO remained one of the weak p o i n t s i n the recovery scheme. A f t e r d e t a i l e d study, i t appeared t h a t the c h o i c e medium f o r the hyd r o l y s i s was the HNO3/DMF obtained as the bottoms f r a c t i o n from d i s t i l l a t i o n o f the crude s p i n b a t h . T h i s was expected s i n c e h y d r o l y s i s i s a c i d c a t a l y z e d . I n a d d i t i o n , the DMF caused the i-PrONO t o be m i s c i b l e w i t h the H2O added f o r h y d r o l y s i s whereas normally i-PrONO and H2O are not m i s c i b l e . The progress i n development of t h i s aspect o f the recovery c y c l e was impeded by one p a r t i c u l a r f a c t o r . A method f o r monit o r i n g e i t h e r the c o n c e n t r a t i o n of i-PrONO o r HNO2 i n the DMF/HNO3/H2O h y d r o l y s i s s o l u t i o n s was not known. The UV-VIS. s p e c t r a of i-PrONO and HNO2 are o v e r l a p p i n g so t h a t t h i s was not a u s e f u l method. A method f o r gas chromatographic a n a l y s i s o f n i t r i t e s , ( i s o p r o p y l , amyl, isoamyl o r c y c l o h e x y l ) was not found s i n c e the n i t r i t e apparently decomposes during chromatography. In fact,_under a l l o f the c o n d i t i o n s attempted, a peak f o r the parent a l c o h o l was observed when the n i t r i t e was i n j e c t e d . I n a d d i t i o n , s e v e r a l peaks, a t t r i b u t a b l e t o n i t r o g e n oxide gases were present i n these chromatograms. The temperature o f the i n j e c t i o n p o r t and the column as w e l l as the gas f l o w r a t e were changed as was the column composition but no s u i t a b l e c o n d i t i o n s were found under which pure n i t r i t e d i d not f u l l y decompose t o i t s parent a l c o h o l . One method f o r a n a l y s i s may be NMR s p e c t r o scopybut t h i s was not r e a d i l y a v a i l a b l e . Thus, the amount of hyd r o l y s i s was c r u d e l y measured by aqueous t i t r a t i o n w i t h standard caustic. M i x t u r e s o f n i t r i t e s , i s o p r o p y l as w e l l as model a l k y l n i t r i t e s , were s t u d i e d i n DMF and H2O w i t h or without a c i d . A m i x t u r e of i-Pr0N0/H20/DMF was s l u r r i e d f o r 15 minutes a t room temperature and then n e u t r a l i z e d w i t h Ca(0H)2 o r CaO. I t was not e f f i c i e n t t o use CaC03. T h i s new mixture was vacuum d i s t i l l e d t o g i v e a powdery r e s i d u e which gave N2O4 on p y r o l y s i s . A d d i t i o n a l experimentation i n d i c a t e d t h a t i t was p o s s i b l e t o r e cover unhydrolyzed n i t r i t e by c a r e f u l f r a c t i o n a l d i s t i l l a t i o n of the n e u t r a l i z e d i s o p r o p y l n i t r i t e h y d r o l y s i s m i x t u r e . A t o t a l recovery of HNO2 (by t i t r a t i o n ) p l u s the recovered unchanged i-PrONO (by d i s t i l l a t i o n ) was 94%, suggesting the p o s s i b l e use of m u l t i p l e h y d r o l y s i s u n i t s . The e n t i r e recovery and r e c y c l e scheme based on t h i s work i s shown i n F i g u r e 4. This i s e s s e n t i a l l y s i m i l a r t o t h a t proposed i n F i g u r e 3 except t h a t a l l o f the loops have been c l o s e d . A r e covery and r e c y c l e scheme such as t h i s should not r e l e a s e any e f f l u e n t t o the environment because i t i s t o t a l l y c y c l i c a l w i t h a l l steps i n c l u d e d i n c l o s e d loops. Conclusions I t has been d e f i n i t i v e l y proven t h a t the m a t e r i a l which i s r e c o v e r a b l e by c o a g u l a t i o n o f a p y r i d i n e s t a b i l i z e d c e l l u l o s e /



70

plex


N2O4/DMF s o l u t i o n i s c e l l u l o s e n i t r i t e . However, although i t seems reasonable t h a t c e l l u l o s e n i t r i t e i s formed i n the absence of p y r i d i n e t h i s f a c t o r does not l i m i t the u t i l i t y o f the p r o posed r e c y c l e and recovery scheme because t h a t scheme i s d i c t a t e d by the s p i n n i n g system which i s r e q u i r e d t o make the most com m e r c i a l l y acceptable rayon f i b e r s . In t h i s case, the s p i n n i n g system of c h o i c e was based on i s o p r o p y l a l c o h o l and t h i s a l c o h o l immediately forms i s o p r o p y l n i t r i t e when i t c o n t a c t s the c e l l u lose/N204/DMF s o l u t i o n i r r e g a r d l e s s of whether the c e l l u l o s e i s complexed or d e r i v a t i z e d . A l l chemical steps r e q u i r e d t o recover and r e c y c l e the DMF, coagulant and N2O4 from the spent s p i n bath have been d e l i n e a t e d and proven to be f e a s i b l e from a t e c h n i c a l s t a n d p o i n t . Abstract The d i s s o l u t i o n of cellulose i n DMF/N O is d i s c u s s e d in terms of t h r e e p o s s i b l e mechanisms, one i n v o l v i n g derivatization of the cellulose and two d e s c r i b i n g dissolution in terms of com f o r m a t i o n . Chemical and s p e c t r a l s t u d i e s on the p y r i d i n e stabilized cellulose/N O /DMF s o l u t i o n s t r o n g l y support the mechanism of derivatization of the cellulose by NO. A total recovery and r e c y c l e scheme has been proposed and proven to be t e c h n i c a l l y f e a s i b l e . This scheme i n v o l v e s separa tion of the crude spent s p i n b a t h , which c o n t a i n s DMF, NO, i-PrOH and i-PrONO, into four major fractions. These are a.) pure i-PrONO, b.) pure i-PrOH, c.) pure DMF and d.) a 1:1 molar DMF/HNO complex. The DMF/HNO complex is used to c a t a l y z e hy drolysis of the i-PrONO to i-PrOH and HNO . T h i s HNO /HNO combination is n e u t r a l i z e d w i t h CaO and the r e s u l t a n t Ca(NO ) / Ca(NO ) is p y r o l y z e d in a CO atmosphere t o recover N O f o r r e c y c l e . Calcium carbonate r e s u l t i n g from the p y r o l y s i s of Ca(NO ) /Ca(NO ) i n CO is converted t o CaO and CO t o continue the cyclical p r o c e s s . 2

2

4

4

2

4

2

3

4

3

2

3

2

3

2

2

3

3

2

2

Literature 1. 2.

3. 4. 5. 6.

2

2

2

2

4

2

Cited

Schweiger, R.G., U.S. P a t e n t No. 3,702,843 (1972). D e l a s s u s , M a r c e l ; Copin, Robert; Hofman, Theophile; S i n n , Robert, S. A f r i c a n Patent No. 68 0155809 (Aug. 1968). CA 70 Ρ 89317z. Industrie-Werke K a r l s r u h e A k t . Ges. German Patent No. 1,014,086 August 22, 1957 CA 53P11412C. Monograph-DMF: A Review of Catalytic Effects and S y n t h e t i c A p p l i c a t i o n s , E . I . duPont de Nemours and Co., Inc., page 3. Monograph-DMF: Recovery and Purification, E . I . duPont de Nemours and Co., I n c . , page 10. Monograph-DMF: Recovery and Purification, E . I . duPont de Nemours and Co., I n c . , page 12.


Chemistry of the Cellulose-N2O4-DMF Solution: Recovery and

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