Modification of Lignins for Use in Phenolic Resins - ACS Symposium

Chapter 5 Modification of Lignins for Use in Phenolic Resins Downloaded by PURDUE UNIV on July 8, 2016 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch005

G . G r a h a m A l l a n , J o n A. D a l a n , and N o r m a n C . Foster Department of Chemical Engineering and College of Forest Resources University of Washington Seattle, W A 98195

The high temperature phenolysis of a commercially available, spray-dried, spent ammonium sulfite liquor from the pulping of softwood has been investigated under both batch and continuous regimes as a route to a phenol substitute for use in phenol-formaldehyde resins. During the phenolysis reaction, the ammonium ion content of the lignin sulfonate rapidly decreased, and up to 0.9 mol of phenol per mol of lignin C repeating units could be chemically attached to the lignin by reaction at 246 ° C for 2 hours. Phenolation also reduced the water solubility and the molecular weight of the lignin sulfonate. The kinetics of phenolysis under autogeneous pressure are second order with respect to phenol and lignin concentrations and the rate constant between 150 and 250 ° C is -4.7 ( ± 0.7) x 10 exp(-22,000 ± 600 c a l / R T ) L / m o l min. 9

7

L a r g e v o l u m e s o f w o o d composites are b o n d e d w i t h p h e n o l - f o r m a l d e h y d e adhesives. T h e U . S . o u t p u t o f p h e n o l i n 1987 w i l l l i k e l y set a record o f more t h a n 3 b i l l i o n p o u n d s , a n d a p p r o x i m a t e l y 4 0 % o f t h i s w i l l be used as a c o m o n o m e r w i t h f o r m a l d e h y d e i n adhesive a p p l i c a t i o n s (1). T h e p a r t i a l replacement o f some o f t h i s p h e n o l w i t h l i g n i n s has l o n g represented a n a p p a r e n t l y a t t r a c t i v e m a r k e t o p p o r t u n i t y because t h e p h e n o l used i n w o o d adhesives is w o r t h a b o u t $528 M M p e r year w h e n p h e n o l is 44 cents a p o u n d , w h i c h was t h e A u g u s t 1987 b u l k price o f p h e n o l w i t h a l l allowances taken i n t o account (#). R e a l i s t i c a l l y , however, i t w o u l d be u n l i k e l y t h a t m o r e t h a n 2 5 % o f the t o t a l of t h i s adhesive p h e n o l c o u l d be replaced. T h i s a s s u m p t i o n decreases t h e value o f the p o t e n t i a l m a r k e t o p p o r t u n i t y t o $132 M M p e r year. Since t h e p h e n o l 0097-6156/89/0385-0055$06.00/0

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1989 American Chemical Society

Hemingway et al.; Adhesives from Renewable Resources ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Downloaded by PURDUE UNIV on July 8, 2016 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch005

s u b s t i t u t e w i l l have t o sell for less t h a n p h e n o l i t s e l f (say b y 2 5 % ) , the e s t i m a t e o f the size o f the f i n a n c i a l o p p o r t u n i t y w i l l have t o be s t i l l f u r t h e r reduced t o $100 M M p e r year. T h e f i n a l d e f i n i t i o n o f the m a g n i t u d e o f the possible f i n a n c i a l g a i n u l t i m a t e l y depends, o f course, u p o n the difference between the cost o f the p h e n o l a n d the cost o f the replacement l i g n i n s . F o r each cent t h a t the cost o f t h e l i g n i n s u b s t i t u t e is below t h a t o f the replaced p h e n o l , the g a i n w o u l d be $3 M M per year. T h i s n u m b e r is i n d e p e n d e n t o f the m a r k e t price o f p h e n o l . T h e s e c a l c u l a t i o n s show t h a t i f renewable resources s u c h as l i g n i n s are t o f i n d use as s u b s t i t u t e s for p h e n o l i n w o o d adhesives, the cost differential between these m a t e r i a l s m u s t be m a x i m i z e d t o a t t r a c t i n v e s t m e n t c a p i t a l . C l e a r l y , the p u l p l i g n i n s a l r e a d y b e i n g p r o d u c e d are l i k e l y t o be the lowest cost renewable resource a v a i l a b l e for t h i s purpose. T h o s e generated i n the k r a f t process are a l r e a d y recycled for t h e i r fuel value i n the recovery furnace a n d are not easily accessible. T h e r e is o n l y one U . S . c o m p a n y s e l l i n g k r a f t l i g n i n , a n d i t s lowest b u l k price is 40 cents a p o u n d ( 3 ) . I n c o n t r a s t , the l i g n i n s f r o m the sulfite p u l p i n g processes are r e a d i l y a v a i l able i n c o m m e r c i a l q u a n t i t i e s f r o m several p u l p producers i n different countries. M o r e t h a n e n o u g h is a v a i l a b l e a n n u a l l y t o replace the entire o u t p u t o f s y n t h e t i c p h e n o l . I n aqueous s o l u t i o n , the price o f these l i g n i n sulfonates c a n be as low as 3 cents a p o u n d o n a d r y basis. T h e s p r a y - d r i e d forms sell for a b o u t 15 cents a p o u n d (4). C l e a r l y , the process of s p r a y d r y i n g is not i n e x p e n s i v e . W h y t h e n are these l i g n i n sulfonates n o t used as a p a r t i a l replacement for p h e n o l i n p h e n o l - f o r m a l d e h y d e - b a s e d w o o d adhesives? T h e first reason is t h a t the presence o f the sulfonate groups confers a water s e n s i t i v i t y t o the adhesive. T h i s s e n s i t i v i t y is exacerbated b y the presence o f w a t e r - s o l u b l e c a r b o h y d r a t e s . A second reason is the low r e a c t i v i t y o f the l i g n i n sulfonates w i t h f o r m a l d e h y d e a n d the consequent low level o f crosslink density achieved i n the f i n a l adhesive. A t h i r d reason is the m o l e c u l a r size o f some of the l i g n i n sulfonates. L a r g e m o l e c u l a r weight m a t e r i a l cannot penetrate the cell walls o f the w o o d to f o r m a n adhesive c o n t i n u u m between contiguous w o o d p a r t i c l e s . Before l i g n i n sulfonates c a n be usefully i n c o r p o r a t e d i n t o p h e n o l i c w o o d adhesives, these s h o r t c o m i n g s m u s t be remedied i n a cost-effective way relative t o the price o f p h e n o l . T h e r e m e d i a l a p p r o a c h selected i n t h i s w o r k has been t o investigate the phenolysis o f c o m m e r c i a l l i g n i n sulfonates w i t h c o m m e r c i a l grade p h e n o l . Experimental Procedures and Results S e l e c t i o n o f L i g n i n S u b s t r a t e . T h e l i g n i n sulfonate chosen for the i n i t i a l e x p e r i m e n t s was a n a m m o n i u m salt r a t h e r t h a n the c o r r e s p o n d i n g c a l c i u m , m a g n e s i u m , or s o d i u m c o u n t e r p a r t s , w h i c h are the other c o m m e r c i a l forms a v a i l a b l e . T h i s selection was m a d e o n the basis t h a t a m m o n i u m l i g n i n s u l fonates a c t u a l l y differ s i g n i f i c a n t l y i n p h y s i c a l a n d c h e m i c a l properties f r o m the


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s u p e r f i c i a l l y analogous m e t a l s a l t s . P e r h a p s the m o s t s t r i k i n g difference is t h a t a m m o n i u m l i g n i n sulfonates are soluble i n a v a r i e t y o f o r g a n i c solvents, whereas, the c a l c i u m , m a g n e s i u m , a n d s o d i u m salts are o n l y s o l u b l e i n w a t e r . T h i s s o l u b i l i t y difference i m p l i e s t h a t the a m m o n i u m salts m a y have c h e m i c a l properties q u i t e d i s t i n c t f r o m the other m e m b e r s o f the l i g n i n sulfonate c l a n . C e r t a i n l y , d u r i n g the p u l p i n g process, m a n y of the l i g n i n fragments det a c h e d f r o m the w o o d m u s t react w i t h the a m m o n i a present, since c a r b o n y l f u n c t i o n s exist i n a l l l i g n i n s , a n d these groups r e a d i l y c o m b i n e w i t h a m m o n i a . T h e existence o f t h i s r e a c t i o n is evidenced b y the fact t h a t o n l y a p o r t i o n of the n i t r o g e n content o f the a m m o n i u m l i g n i n sulfonates c a n be d i s t i l l e d off as a m m o n i a u n d e r a l k a l i n e c o n d i t i o n s . A m m o n i u m salts a n d a m i d e s , o f course, are q u a n t i t a t i v e l y converted t o a m m o n i a u n d e r these c o n d i t i o n s ; a m i n e s a n d i m i n e s are n o t . T h e s e observations w o u l d also a p p l y t o c a r b o h y d r a t e m a t e r i a l a d m i x e d w i t h the a m m o n i u m l i g n i n sulfonates. T h e n a t u r e of the covalently b o u n d n i t r o g e n i n a m m o n i u m l i g n i n sulfonates or the associated c a r b o h y d r a t e s has n o t yet b e e n r e p o r t e d , b u t i f i t is present as a p r i m a r y or secondary a m i n e , the r e a c t i v i t y t o w a r d f o r m a l d e h y d e w o u l d l i k e l y be increased (5) a n d the crosslink density o f the r e s u l t a n t adhesive t h e r e b y augmented. C h o i c e o f t h e L i g n i n M o d i f i c a t i o n R e a c t i o n . T h e p h e n o l y s i s r e a c t i o n was selected as a means o f m o d i f y i n g the s t r u c t u r e a n d r e a c t i v i t y o f the a m m o n i u m l i g n i n sulfonate for three m a i n p r a c t i c a l reasons. F i r s t , because t h i s l i g n i n d e r i v a t i v e is soluble i n ( a n d w i l l u l t i m a t e l y be used i n c o n j u n c t i o n w i t h ) l i q u i d p h e n o l itself; second, because u n r e a c t e d p h e n o l , u n l i k e other r e a c t i o n solvents, w o u l d not have t o b e removed f r o m the p h e n o l a t e d p r o d u c t after r e a c t i o n a n d before conversion t o the adhesive resin; a n d t h i r d , because l i g n i n s a n d c a r b o h y drates are k n o w n t o react w i t h phenols under a c i d i c c o n d i t i o n s (6,7). A discussion o f the various possible facets o f the c h e m i s t r y of the i n t e r a c t i o n s o f l i g n i n s a n d c a r b o h y d r a t e s w i t h p h e n o l lies b e y o n d the scope o f t h i s a r t i c l e . However, i n a general way, i t c a n be s t a t e d t h a t , because o f the excess of p h e n o l i n the r e a c t i o n m i x t u r e , the c o m b i n a t i o n w i t h either l i g n i n or carb o h y d r a t e s is m o s t l i k e l y to involve o n l y one o f the three reactive p o s i t i o n s o n the a r o m a t i c r i n g o f the p h e n o l . C o n s e q u e n t l y , the r e a c t i v i t y of the m o d i f i e d l i g n i n s a n d c a r b o h y d r a t e s t o f o r m a l d e h y d e ought t o be enhanced r e l a t i v e t o the p r e p h e n o l y z e d m a t e r i a l because, for every reactive p o s i t i o n lost b y c o m b i n a t i o n , two new reactive p o s i t i o n s are created b y the a d d e d p h e n o l moiety. P h e n o l y s i s R e a c t i o n P r o c e d u r e . T o explore the concept o f p h e n o l a t i o n , m i x t u r e s o f a c o m m e r c i a l s p r a y - d r i e d softwood a m m o n i u m l i g n i n sulfonate (10 g, O r z a n A , 6 0 % a m m o n i u m l i g n i n sulfonate ( M W = 228), 2 8 % sugars, 6 . 2 % sulfur, 2 . 5 % a s h , I T T - R a y o n i e r , S h e l t o n , W a s h i n g t o n a v a i l a b l e i n b u l k at 17 cents a p o u n d (8) a n d c o m m e r c i a l grade p h e n o l (15 m L , R e i c h h o l d C h e m i c a l s Inc., T a c o m a , W a s h i n g t o n ) c o n t a i n e d i n s m a l l pressure b o m b s (30 m L , P a r r I n s t r u m e n t C o m p a n y , M o l i n e , I l l i n o i s ) were heated by suspension i n a h y d r a u l i c 0


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fluid h e a t i n g b a t h m a i n t a i n e d at 200 ± 3 ° C for v a r i o u s p e r i o d s of t i m e . A f t e r b e i n g heated a n d before b e i n g o p e n e d , the sealed b o m b s were c o o l e d for 5 m i n u t e s i n a n ice b a t h .


F a t e o f A m m o n i u m I o n D u r i n g L i g n i n P h e n o l a t i o n . A l i q u o t s (1-5 g) of the r e a c t i o n p r o d u c t s were t h e n d i l u t e d w i t h water (200 m L ) a n d a n a l y z e d for t h e i r a m m o n i u m i o n content. T h e procedure c o m p r i s e d t r e a t m e n t w i t h a n aqueous s o l u t i o n of N a O H ( 2 0 % w / v , 100 m L ) , d i s t i l l a t i o n w i t h c o l l e c t i o n of the d i s t i l l a t e (175 m L ) i n a n aqueous s o l u t i o n of b o r i c a c i d ( 4 % w / v , 50 m L ) , a n d t i t r a t i o n w i t h a s t a n d a r d s o l u t i o n of s u l f u r i c a c i d . T h e results o b t a i n e d are c o m p i l e d i n T a b l e I.

T a b l e I. Effect of D u r a t i o n of H e a t i n g o n the A m m o n i u m I o n C o n t e n t o f a M i x t u r e of A m m o n i u m L i g n i n S u l f o n a t e a n d P h e n o l (61.5%) D u r a t i o n of H e a t i n g (min)

A m m o n i u m Ion Content

0 10 20 30 40 50 60

(%) 3.63 2.43 1.84 1.95 1.81 1.76 1.74

75 80 120 134

2.01 2.01 1.81 1.70

T h e d a t a i n the t a b l e d e m o n s t r a t e t h a t a b o u t h a l f o f the water-soluble a m m o n i u m i o n content is converted i n t o some new f o r m o f n i t r o g e n , the n a t u r e of w h i c h has yet t o be d e t e r m i n e d . C o n c u r r e n t t o t a l n i t r o g e n analyses b y the use o f a m o d i f i e d K j e l d a h l procedure (9) c a p a b l e of c l e a v i n g h e t e r o c y c l i c s t r u c tures confirmed t h a t no detectable a m o u n t of n i t r o g e n h a d been lost f r o m the phenolysis reaction system. It is also evident f r o m the results i n T a b l e I t h a t the t r a n s f o r m a t i o n of the a m m o n i u m i o n is essentially complete w i t h i n a 2 0 - m i n u t e r e a c t i o n p e r i o d . T h i s is a n i m p o r t a n t f i n d i n g i n terms of the s i z i n g a n d o p e r a t i o n of a continuous reactor, details of w h i c h (10) w i l l be r e p o r t e d elsewhere. P h e n o l y s i s P r e s s u r e s i n L a r g e r B a t c h R e a c t o r . Because of the difficulties of w o r k i n g w i t h s m a l l a m o u n t s of m a t e r i a l , the foregoing e x p e r i m e n t s were repeated i n a larger c a p a c i t y (500 m L ) s t i r r e d b a t c h reactor. T h i s enabled


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measurement of the pressures generated d u r i n g p h e n o l y s i s . T h e pressure d a t a collected are s h o w n i n T a b l e I I .

T a b l e I I . C o m p a r i s o n of T o t a l Pressure G e n e r a t e d b y H e a t e d P h e n o l a n d a P h e n o l - A m m o n i u m L i g n i n S u l f o n a t e (38.5%) M i x t u r e in a Stirred B a t c h Reactor


Duration of H e a t i n g (min) 0 2 4 6 7 8 10 11 14 15 18 20 25 30 40 50 55 60 70

G a u g e Pressure ( k N / m ) G e n e r a t e d b y Phenol-Ammonium Phenol L i g n i n Sulfonate 2

0 14 41 83 103 110

1

0

14 41

131

152 -

164 165 166 166 166

-

-

207

145

234 289 289

-

289 310 310 310

M u l t i p l y b y 0.145 t o convert t o p s i .

F r o m the d a t a i n T a b l e I I , i t seems t h a t the pressures i n v o l v e d i n c a r r y i n g out the p h e n o l y s i s m o d i f i c a t i o n do n o t pose any s p e c i a l engineering p r o b l e m s since the m a x i m u m encountered is o n l y 45 p s i . Subsequently, however, i n a n o t h e r set of e x p e r i m e n t s t h a t were c a r r i e d o u t for longer h e a t i n g p e r i o d s , the pressures observed rose t o m u c h higher levels (cf. T a b l e V I I I ) . T h i s m a y be due t o the presence of water generated b y d e h y d r a t i o n reactions. T h e conversion o f a m m o n i u m ions achieved i n t h i s larger s t i r r e d reactor was v e r y s i m i l a r t o t h a t a c c o m p l i s h e d i n the s m a l l e r P a r r b o m b s . However, because o f the heat c a p a c i t y of the larger reactor, the t i m e necessary t o raise the t e m p e r a t u r e t o secure a n equivalent extent o f r e a c t i o n was lengthened to 70 minutes.


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S o l u b i l i t y o f P h e n o l a t e d L i g n i n S u l f o n a t e s . Since the presence of a m m o n i u m sulfonate moieties tends t o confer water s o l u b i l i t y , t h e i r disappearance s h o u l d be reflected i n a r e d u c t i o n of t h i s c h a r a c t e r i s t i c . T h e extent of t h i s effect was assessed b y m e a s u r i n g the s o l u b i l i t y of a s t i r r e d a l i q u o t (1-4 g) of the 200 ° C phenolysis p r o d u c t i n water (200 m L ) . T h e r e s u l t a n t suspension was filtered a n d the residue d r i e d for a b o u t 2 days at 22 ° C t o constant w e i g h t . T h e results o b t a i n e d u n d e r a v a r i e t y of r e a c t i o n c o n d i t i o n s are s u m m a r i z e d i n T a b l e III.

T a b l e I I I . Effect of D u r a t i o n of H e a t i n g o n A m m o n i u m I o n C o n t e n t a n d W a t e r - S o l u b i l i t y of a M i x t u r e of P h e n o l (61.5%) a n d A m m o n i u m L i g n i n Sulfonate Duration of Heating (min) 0 20 30 40 50 60 70

Ammonium Ion Content

Y i e l d of Water-Insolubles

(%) 3.62 2.30 2.21

(%) 0.0 0.8 21.0

1

2.08

1.86

23.4 27.5 28.8

E x p r e s s e d i n t e r m s of the a m m o n i u m l i g n i n s u l fonate feed. 1

A n o t h e r related set o f e x p e r i m e n t s was also c a r r i e d o u t t o d e t e r m i n e the effect of t e m p e r a t u r e o n the i n s o l u b i l i z a t i o n of t h e a m m o n i u m l i g n i n sulfonate b y p h e n o l y s i s for a p e r i o d of 2 h o u r s . T h e results o b t a i n e d , w h i c h are s u m m a r i z e d i n T a b l e I V , show t h a t m o r e t h a n o n e - t h i r d of the c o m m e r c i a l p r o d u c t c a n be m a d e w a t e r - i n s o l u b l e b y t h i s procedure. F o r subsequent adhesive p r o d u c t i o n , i t is i m p o r t a n t t o note t h a t a l l the r e a c t i o n m i x t u r e s were c o m p l e t e l y soluble i n 0 . 1 % a n d 1% aqueous s o d i u m h y d r o x i d e s o l u t i o n . T h e s o l u b i l i t i e s i n 0 . 1 N a n d I N aqueous s u l f u r i c a c i d s o l u t i o n s were 81.9 a n d 7 5 . 4 % , respectively. P h e n o l y s i s o f C a r b o h y d r a t e s . T h e c a r b o h y d r a t e s are also m o d i f i e d b y rea c t i o n w i t h p h e n o l under c o m p a r a b l e c o n d i t i o n s as has been d e m o n s t r a t e d b y M a t h u r (11). A m o n g the p r o d u c t s identified were l e v u l i n i c a c i d , f u r f u r a l , a n d h y d r o x y m e t h y l f u r f u r a l . A l l are capable of f o r m i n g c a r b o n - c a r b o n b o n d s w i t h phenol. D e g r a d a t i o n o f L i g n i n M o l e c u l a r W e i g h t . I n a d d i t i o n t o these t r a n s f o r m a t i o n s of the water-sensitive c a r b o h y d r a t e s , the phenolysis r e a c t i o n also affects


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the m o l e c u l a r weight of the l i g n i n sulfonate. T h i s is evidenced b y c o m p a r i son of the v i s c o s i t y of the phenolysis m i x t u r e after r e a c t i o n at two different m e a n residence t i m e s i n a continuous t u b e reactor. T h e v i s c o s i t y was m e a s u r e d i n a B r o o k f i e l d viscometer ( B r o o k f i e l d E n g i n e e r i n g C o m p a n y , S t o u g h t e n , M a s sachusetts, M o d e l N o . R V F ) f i t t e d w i t h a N o . 3 s p i n d l e r o t a t i n g at 20 r p m a n d c a l i b r a t e d w i t h g l y c e r o l . W h e n the residence t i m e s were 9.7 a n d 20.0 m i n u t e s , the viscosities measured were 1770 a n d 1170 centipoise, respectively.

T a b l e I V . Effect of R e a c t i o n T e m p e r a t u r e o n E x t e n t of P h e n o l y s i s a n d Degree of W a t e r I n s o l u b i l i t y C o n f e r r e d u p o n a C o m m e r c i a l A m m o n i u m L i g n i n Sulfonate A d m i x e d w i t h P h e n o l (61.5%) a n d H e a t e d for 2 H o u r s Reaction Temperature

Y i e l d of W a t e r Insolubles

(°C) 134 135 139 150 162 170 181 196 212 224 246

(%) 2.4

1

--

5.2 10.2 14.2 19.4 23.6 31.0 32.8 36.1

Recoverable Phenol (%) 95.9 95.3 95.9 98.2 96.3 93.0 89.8 90.6 89.3 85.4 85.7

Combined Phenol per L i g n i n U n i t (mol) 0.15 0.19 0.15 0.01 0.13 0.34 0.54 0.49 0.57 0.82 0.80

E x p r e s s e d i n t e r m s of the a m m o n i u m l i g n i n sulfonate feed.

C o l l a b o r a t i v e c h e m i c a l evidence for the b r e a k d o w n o f the l i g n i n sulfonates was the discovery t h a t the s t e a m d i s t i l l a t e of phenolysis m i x t u r e s , b a t c h - r e a c t e d at 224 ° C , c o n t a i n e d g u a i a c o l , m e t h y l g u a i a c o l , a n d c a t e c h o l . T h e s e are t y p i c a l fragments r e s u l t i n g f r o m the high-energy d e g r a d a t i o n of l i g n i n s (12). Further d a t a s h o w i n g the extent of d e g r a d a t i o n of the l i g n i n sulfonates d u r i n g p h e n o l y s i s have been gathered b y the use of gel f i l t r a t i o n c h r o m a t o g r a p h y (13) a n d w i l l be r e p o r t e d elsewhere. K i n e t i c S t u d y o f t h e P h e n o l y s i s R e a c t i o n . W i t h the d e m o n s t r a t i o n t h a t a l l of the a l r e a d y o u t l i n e d deficiencies of a m m o n i u m l i g n i n sulfonates as a p h e n o l replacement c a n be reduced b y phenolysis, a t t e n t i o n was t u r n e d t o c o n s i d e r a t i o n of the c o n s t r u c t i o n of a p i l o t p l a n t scale continuous t u b e reactor. T h i s is needed i n order t o prepare the large a m o u n t s of p h e n o l y z e d l i g n i n sulfonates r e q u i r e d for resin synthesis a n d t e s t i n g u n d e r p l y w o o d p r o d u c t i o n c o n d i t i o n s .


62


S u c h t e s t i n g , t o be r e p o r t e d i n d e t a i l l a t e r , showed t h a t the p h e n o l y z e d p r o d u c t


c a n be successfully used i n adhesive f o r m u l a t i o n s for p l y w o o d

(14).

A s a prelude t o the design of the t u b e reactor (10), a k i n e t i c s t u d y of the p h e n o l y s i s procedure as a f u n c t i o n of t e m p e r a t u r e was c a r r i e d o u t o n a larger scale. T h e e q u i p m e n t used was a stainless steel pressure reactor ( M o d e l 4 5 0 1 , P a r r I n s t r u m e n t C o m p a n y , M o l i n e , I l l i n o i s ) . T h i s reactor is fitted w i t h a n i n t e r n a l s t i r r e r , a n e x t e r n a l electric heater, a n d a c o n t i n u o u s s a m p l i n g device. A m i x t u r e of the c o m m e r c i a l a m m o n i u m l i g n i n sulfonate (668 g) a n d m o l t e n p h e n o l (1000 m L ) was sealed i n t o the reactor a n d h e a t e d t o the designated t e m p e r a t u r e s . A p p r o x i m a t e l y 3 hours were needed t o heat the reactor f r o m r o o m t e m p e r a t u r e t o 200 ° C . A s i m i l a r p e r i o d of t i m e was r e q u i r e d t o c o o l the reactor a n d i t s contents back t o 22 ° C after c o m p l e t i o n of a r u n . A f t e r a r e a c t i o n p e r i o d n o m i n a l l y l a s t i n g 2 h o u r s , the u n r e a c t e d p h e n o l was s t e a m distilled f r o m the reaction m i x t u r e and the amount measured by comparative U V spectroscopy. T h e results o b t a i n e d a n d s u m m a r i z e d i n T a b l e I V show t h a t a s u b s t a n t i a l a m o u n t of p h e n o l becomes c h e m i c a l l y c o m b i n e d w i t h the renewable resource feedstock. T h e effect o f h e a t i n g t i m e o n the extent of phenolysis i n t h i s larger reactor was also s t u d i e d at 220 ° C , a n d the r e s u l t i n g d a t a secured are s u m m a r i z e d i n T a b l e V . It was necessary t o use a h e a t i n g t i m e correction because the exotherm i c i t y of the phenolysis r e a c t i o n at 200 ° C increased the t e m p e r a t u r e of the react ants as the t i m e of r e a c t i o n progressed.

T a b l e V . Effect o f T i m e - C o r r e c t e d D u r a t i o n of H e a t i n g at 220 ° C o n E x t e n t of P h e n o l y s i s of a C o m m e r c i a l A m m o n i u m L i g n i n Sulfonate A d m i x e d w i t h P h e n o l (61.5%) Time-Corrected Duration of Heating (min)

Combined Phenol

5 10 16 22 48

0.08 0.13 0.19 0.23 0.40

per L i g n i n U n i t (mol)

A n a l y s i s o f K i n e t i c D a t a . T o gather the d a t a necessary for t h i s t y p e of a n a l y s i s , yet another set of phenolysis e x p e r i m e n t s was c a r r i e d o u t ; t h i s t i m e i n a s m a l l P a r r b o m b t h a t was i m m e r s e d i n a n o i l b a t h m a i n t a i n e d at 220 ° C for r e l a t i v e l y short p e r i o d s o f t i m e . T h e d a t a collected a n d s u m m a r i z e d i n T a b l e V I were correlated for zero, first, a n d second order k i n e t i c models b y the use


5.

ALLAN E T AL.

63


of a n i n t e g r a l m e t h o d (15). T h e c o r r e l a t i o n coefficents for the fit w i t h these orders of r e a c t i o n k i n e t i c s were 0.93, 0.875, a n d 0.975, respectively. W i t h t h i s d e m o n s t r a t i o n t h a t the k i n e t i c s of the phenolysis r e a c t i o n are second order i n n a t u r e , a n A r r h e n i u s rate constant m o d e l jfe = k exp(-E /RT) 0

(1)

0

was a p p l i e d (15) to the t e m p e r a t u r e a n d t i m e d a t a i n T a b l e V I I for t e m p e r a t u r e s between 150 a n d 246 ° C . T h e c a l c u l a t e d a c t i v a t i o n energy, E , d e t e r m i n e d b y t h i s p r o c e d u r e was 23,075 c a l / m o l K . Downloaded by PURDUE UNIV on July 8, 2016 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch005

0

T a b l e V I . K i n e t i c D a t a for the P h e n o l y s i s of A m m o n i u m L i g n i n S u l f o n a t e i n P h e n o l (61.5%) T i m e of Immersion Heating (min)

C o n c e n t r a t i o n of Phenol

Concentration of Lignin Units

[P] (mol/liter)

M (mol/liter)

In [ P ] / [ L ]

0 5 10 15 20 30 60

7.71 7.54 7.44 7.33 7.34

1.20 1.03 0.93 0.82 0.83 0.75 0.42

1.86 1.99 2.07 2.19 2.17

7.26 6.90

2.27 2.80

T h i s v a l u e , together w i t h t h e h e a t i n g a n d c o o l i n g t i m e s o f the reactor t h a t are s u m m a r i z e d i n T a b l e V I I I , was used t o correct the rate constant d a t a i n T a b l e V I I . T h i s c o r r e c t i o n is based o n the r e c o g n i t i o n t h a t for second order kinetics ^

(2)

= -kC C a

b

where C a n d C& denote the concentrations o f species A a n d B , respectively, at t i m e t w h i l e k represents the rate constant o f the r e a c t i o n . a

B y s u b s t i t u t i o n of e q u a t i o n (1) i n t o (2) a n d i n t e g r a t i o n , e q u a t i o n (3) is o b t a i n e d where t h e o r i g i n a l concentrations are designated as C a n d Cb · ao

ln(CaC JC C ) h

h

ao

= (C

bo

-

C )k exp(-E /RT)t ao

0

0


0

(3)


x

4

3

2

T h e d e n s i t y of the i n i t i a l r e a c t i o n m i x t u r e was 1.18 g / m L . T h e i n i t i a l c o n c e n t r a t i o n of p h e n o l was 7590 m m o l / L . T h e i n i t i a l c o n c e n t r a t i o n of l i g n i n u n i t s was 1250 m m o l / L . M e a s u r e d after a p e r i o d of phenolysis of 120 m i n .

1

3

4

T a b l e V I I . D a t a for C a l c u l a t i o n of A c t i v a t i o n E n e r g y of the P h e n o l y s i s of A m m o n i u m L i g n i n S u l f o n a t e i n P h e n o l (61.5%) u s i n g the A r r h e n i u s R a t e C o n s t a n t M o d e l (15) C o n c e n t r a t i o n of R a t e of L i g n i n Phenolysis Phenolysis A m o u n t of Phenol Combined Phenol* Lignin U n i t s U n i t C o m b i n a t i o n Rate Constant Temperature ( L / m o l min) m m o l / k g R e a c t a n t s (m m o l / L ) (mmol/L) ( m m o l / L min) (°C) 1.52 1.92 154 7406 1068 130 1064 1.52 7402 1.93 135 155 154 1.52 1.92 139 7406 1068 104 1.22 150 7465 1127 1.03 162 239 7305 968 2.35 3.33 3.22 170 328 7201 863 5.18 181 527 6966 629 5.18 11.82 196 707 6753 415 6.96 24.80 212 6602 835 265 8.21 46.98 224 1005 6402 64 9.89 241.38 246 6414 995 76 9.78 200.63



5.

ALLAN ET A L

65


T a b l e V I I I . T e m p e r a t u r e a n d Pressure V a r i a t i o n i n the P h e n o l y s i s R e a c t o r as a F u n c t i o n of H e a t i n g T i m e D u r a t i o n of Heating (min) 0 25 35 50 70 90 142 160 178 200 250 292 326 340

1

Temperature in Reactor (°C) 43 50 63 83 102 122 140 157 177 205 208 208 208 0

G a u g e Pressure of Reactor (kN/m ) 2

0 69 76 76 83 90 103 166 248 1028 1559 2014 2379 855

A f t e r t h i s h e a t i n g p e r i o d , the reactor was c o o l e d by i m m e r s i o n i n ice water. 1


66


W h e n t w o i d e n t i c a l sets of reactants are m a i n t a i n e d at different t e m p e r a tures, the extent of r e a c t i o n of each is also i d e n t i c a l o n l y w h e n the p r o d u c t s of the rate constants a n d r e a c t i o n t i m e s ( t a n d t ) are e q u a l , so t h a t b

a

i k exp(E /RT ) a

0

0

U _


U

(4)

= t k exp(E /RT )

a

b

0

0

b

exp(Eg) (l/RT

a

, *

- 1/ΛΓ»)

V

;

E q u a t i o n (5) was used t o correct the h e a t i n g t i m e s i n T a b l e V I I , a n d new re a c t i o n rate constants were t h e n c a l c u l a t e d . T h e r e a f t e r , a new a c t i v a t i o n energy was o b t a i n e d b y a second A r r h e n i u s fit of the corrected d a t a . T h i s procedure was repeated u n t i l the difference i n the c a l c u l a t e d a c t i v a t i o n energy f r o m two successive i t e r a t i o n s was less t h a n the s t a n d a r d d e v i a t i o n of the error of the fit of the d a t a . T h e f i n a l a c t i v a t i o n energy value o b t a i n e d was 22,182 ± 612 c a l / m o l K , a n d the c o r r e l a t i o n coefficient was t h e n 0.996. T h i s value of the a c t i v a t i o n energy, together w i t h the corrected rate constants for each t e m p e r a t u r e , was e m p l o y e d t o evaluate the p r e - e x p o n e n t i a l c o n s t a n t , k , i n the A r r h e n i u s rate constant m o d e l . T h e value t h u s d e r i v e d was 0

k

0

= -4.7 ( ± 0 . 7 ) χ 1 0

7

L/mol min

where the error is the s t a n d a r d d e v i a t i o n f r o m the m e a n value. T h e final corrected v a l u e for t h e a c t i v a t i o n energy was also used t o adjust for the e x o t h e r m i c h e a t i n g observed i n the s m a l l b o m b r u n s , w h i c h m o d i f i e d the i n i t i a l k i n e t i c d a t a . T h e a d j u s t e d t i m e values were 4.60, 8.31, 14.53, 20.18, 25.08 a n d 31.77 m i n u t e s , c o r r e s p o n d i n g t o the values 5, 10, 15, 20, 30 a n d 60 listed i n Table V I . A s a n e x a m p l e of the consequence of t h i s t i m e a d j u s t m e n t , the v a l u e of the rate constant for the p h e n o l a t i o n r e a c t i o n at 220 ° C becomes k = -4.5 ( ± 0 . 3 ) χ 1 0 "

3

L/mol min

T h e c o r r e l a t i o n coefficient, after e l i m i n a t i o n o f the d a t a p o i n t s at 20 a n d 25 n o m i n a l m i n u t e s b y i n v o k i n g C h a u v e n e t ' s c r i t e r i o n (16), was f o u n d t o be 0.986. Conclusions G i v e n a l l the foregoing i n f o r m a t i o n , i t is clear t h a t the p h e n o l y s i s of a m m o n i u m l i g n i n sulfonates ameliorates the several s h o r t c o m i n g s of t h i s renewable resource as a c o m p o n e n t of p h e n o l - f o r m a l d e h y d e adhesives. M o r e o v e r , the s i m p l i c i t y of the phenolysis process suggests t h a t i t is a feasible route t o a n e c o n o m i c a l l y a t t r a c t i v e a n d m a r k e t a b l e replacement for p h e n o l . T h e k i n e t i c d a t a established w i l l enable a large-scale continuous t u b e reactor t o be designed t o convert a m i x t u r e o f c o m m e r c i a l grade a m m o n i u m l i g n i n sulfonates (40%) i n p h e n o l (60%) i n t o a m o b i l e b l a c k o i l s u i t a b l e for use i n adhesive f o r m u l a t i o n s .


5.

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67


Literature Cited 1. Chemical & Engineering News, 1987, 65, No. 16, 11. 2. Price data, August 24, 1987, Dow Chemical Co., Midland, M I 48674. 3. Price data, August 24, 1987, Westvaco Corp., Charleston Heights, S C 29415-0848. 4. Price data, August 24, 1987, Reed Inc., Quebec, P . Q . , Canada, G1K 7N1. 5. Allan, G . G . ; Baxter, G . F . ; Freeman, H . G. U.S. Patent 3 518 159, June 30, 1970.


6. Hergert, H . L. In Lignins, Occurrence, Formation, Structure and Reactions, Κ. V . Sarkanen and C . H . Ludwig, Eds., Wiley-Interscience, John Wiley & Sons, Inc., New York, 1971, p. 288. 7. Dubois, M . ; Billes, Κ. Α . ; Hamilton, J . K . ; Rebers, P. Α . ; Smith, F . Anal. 1956, 28, 350.

Chem.,

8. Price data, August 24, 1987, ITT-Rayonier Inc., Seattle, W A 98188. 9. Allan, G . G . ; Mauranen, P.; Desert, M . D.; Reif, W . M . Pa-peri Puu, 1968, 50, 529. 10. Dalan, J. A . M . S . Thesis, University of Washington, Seattle, 1974, p. 38. 11. Mathur, V . K . P h . D . Thesis, University of Washington, Seattle, 1982, p. 69. 12. Allan, G . G . ; Mattila, T. In Lignins, Occurrence, Formation, Structure and Reactions, Κ. V . Sarkanen and C . H . Ludwig, Eds., Wiley-Interscience, John Wiley & Sons, Inc., New York, 1971, p. 577. 13. Edelman, D . L. P h . D . Thesis, University of Washington, Seattle, 1979, p. 59. 14. Foster, N . C . P h . D . Thesis, University of Washington, Seattle, 1978, p. 31. 15. Levenspiel, O . Chemical Reaction Engineering, 2nd. E d . , John Wiley & Sons, Inc., New York, 1972, p. 45. 16. Holman, J. P. Experimental Methods for Engineers, 2nd. E d . , McGraw-Hill, Inc., New York, 1971, p. 56. R E C E I V E D September 12, 1988


Modification of Lignins for Use in Phenolic Resins - ACS Symposium

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