Preparation and Testing of Cationic Flocculants from Kraft Lignin

Chapter 21

Preparation and Testing of Cationic Flocculants from Kraft Lignin Erkki Pulkkinen, Airi Mäkelä, and Hannu Mikkonen Department of Chemistry, University of Oulu, SF-90570 Oulu, Finland

Kraft lignin has been reacted to a quaternary ether derivative over several hours at temperatures ranging from room temperature to 65°C. Based on the nitrogen content (2.7-3.7%) of the purified product, 42-61% of the hydroxyl groups of lignin were etherified. The yield with respect to reagent was usually over 50%. In laboratory tests the lignin-based cationic ether effectively precipitated inorganic colloids from wastewaters. It is w e l l k n o w n t h a t the a c e t y l a t i o n , for e x a m p l e , of a r o m a t i c a n d a l i p h a t i c h y d r o x y l groups i n kraft l i g n i n can d r a s t i c a l l y change the s o l u b i l i t y of l i g n i n . T h e same occurs w h e n h y d r o x y l groups of kraft l i g n i n are reacted w i t h epoxy reagents h a v i n g q u a t e r n a r y a m m o n i u m groups i n the molecule.

NaOH *

iin-OH + C H o - C H C H ~

v

-

z

,

—

s

l

o

w

Ο

ν

glycidyltrimethylammonium chloride

Hgnin-OC^CHC^i^C^^CI

G

CH CHCH N®(CH3) CI + NaOH 2

CI

2

\

3

OH

N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride 0097-6156/89A)397--0284$06.00A) © 1989 American Chemical Society

0

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E v e n t h o u g h 3.0-4.4 m m o l s (from a t o t a l of 7.2 m m o l s ) of h y d r o x y l groups per g r a m of l i g n i n were c a t i o n i z e d b y these reagents, the p r o d u c t s were c o m p l e t e l y water soluble a n d effective flocculants. I n t h i s p a p e r we discuss the p r e p a r a t i o n a n d testing these c a t i o n i c l i g n i n derivatives.

Experimental Materials. C o m m e r c i a l k r a f t l i g n i n , I n d u l i n A T (Westvaco C o r p . ) , has a c o m b i n e d phenolic a n d a l i p h a t i c h y d r o x y l group content of 7.2 m m o l / g as d e t e r m i n e d b y q u a n t i t a t i v e S i N M R spectroscopy (1). T h e p i n e k r a f t l i g n i n f r o m the N u o t t a s a a r i m i l l of V e i t s i l u o t o C o r p . , F i n l a n d , has a corr e s p o n d i n g h y d r o x y l content of 7.7 m m o l / g . T h e g l y c i d y l t r i m e t h y l a m m o n i u m chloride reagent, c o n t a i n i n g 6 3 . 3 % e p o x y f u n c t i o n a l i t y , was a p r o d u c t of R a i s i o C o r p . , F i n l a n d . N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride was prepared i n the l a b o r a t o r y (2,3). P r a e s t o l 41 I K ( S t o c k hausen C o r p . ) was used as a reference c a t i o n i c flocculant. 2 9

Flocculation Tests (4). A conventional j a r test procedure w i t h a s i x - p l a c e m u l t i p l e stirrer s y s t e m ( P h i p p s & B i r d , Inc.), a n d c r y s t a l l i n e s i l i c a p a r ticles ( M i n - U - S i l 5, P e n n s y l v a n i a G l a s s a n d S a n d C o r p . ) , or a l t e r n a t i v e l y m a t e r i a l dredged f r o m the b o t t o m of a waterway, were used as a c o l l o i d a l reference. A f t e r s t i r r i n g the m a i n b a t c h of the s i l i c a (600 or 1800 m g M i n U - S i l 5 i n 4000 m L of deionized water) for a n h o u r , 2 m L aqueous H C 1 was a d d e d a n d the p H adjusted w i t h s o l i d N a H C 0 3 to 4. T h e d r e d g i n g effluent (3700 m g / l i t e r , p H 5.1) was used as such as a s e t t l i n g reference. T o p e r f o r m the j a r test, 600 m L of the b a t c h d i s p e r s i o n was i n t r o d u c e d i n t o each 800 m L decanter flask a n d the dispersions were s t i r r e d at 100 r p m w h e n the flocculant dosages were a d d e d . Thereafter s t i r r i n g was c o n t i n u e d at 100 r p m for 20 m i n . , at 30 r p m for 20 m i n . , a n d t h e n allowed t o settle for 30 m i n . u n d i s t u r b e d . R e s i d u a l t u r b i d i t i e s were measured b y a H a c h t u r b i d i m e t e r o n 25 m L a l i q u o t s of the s u p e r n a t a n t l i q u i d s t a k e n 2 c m b e low the surface a n d p l o t t e d as f o r m a z i n t u r b i d i t y percent u n i t s (% F T U ) against flocculation dosage i n p p m solids. Stability of Floe. A f t e r s e t t l i n g for 30 m i n u t e s a n d m e a s u r i n g the r e s i d u a l t u r b i d i t y , a dispersion (600 m L ) was p o u r e d i n t o another flask a n d b a c k t o the o r i g i n a l flask. T h e p o u r i n g back a n d f o r t h was t h e n repeated t w i c e . A f t e r s e t t l i n g for 30 m i n . , the r e s i d u a l t u r b i d i t i e s were measured as before. Gelling of Lignin with Formaldehyde. A 5.12 g s a m p l e of a s o d i u m salt of l i g n i n ( 4 0 % nonvolatiles ( N . V . ) , 1 5 % N a O H d i g n i n ) was reacted w i t h 3 7 % C H 0 (0.71 m o l e / 1 0 0 g l i g n i n ) at 9 0 ° C i n a test tube (height 10 c m , w i d t h 2 cm) u n t i l g e l l i n g occurred after 130 m i n . T h e gel t i m e was measured w i t h a T e c a n G e l a t i o n T i m e r , G T 3 (disc 14 m m ) . 2

Reaction of Lignin and Gelled Lignin with Glycidyltrimethylammonium Chloride. G l y c i d y l t r i m e t h y l a m m o n i u m chloride was added t o a preprepared s o d i u m salt of l i g n i n (pre-stirred i n a s t e a m b a t h for 2 h) a n d the r e a c t i o n m i x t u r e was s t i r r e d at 60-70°C for 3 h ( T a b l e I). C a t i o n i z i n g the gelled l i g n i n (reacted w i t h C H 2 O for 130 m i n . ) was essentially

LIGNIN: PROPERTIES AND MATERIALS

286

c a r r i e d out i n the same way except t h a t the solids content of the r e a c t i o n m i x t u r e was 2 9 % i n s t e a d of 4 4 % . I n the r e a c t i o n of l i g n i n w i t h N - ( 3 - c h l o r o 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride the m o l a r r a t i o s of reagent to N a O H was 1:1 a n d h y d r o x y l groups to reagent 1:1. T h e r e a c t i o n was c a r r i e d out at r o o m t e m p e r a t u r e at 5 2 % N . V . T a b l e I. R e a c t i o n of K r a f t L i g n i n w i t h G l y c i d y l t r i m e t h y l a m m o n i u m C h l o ride 0

Weight Components Indulin A T Total O H hydroxyl carboxyl Reagent (63.2%) NaOH H 0 2

a

grams

grams

2.09

2.0

2.64 0.3 4.0

1.67 0.3

9.03

3.97

mmoles 17.2 14.4 2.8 11.0 7.5

Molar Ratio 1 1 0.76

Nonvolatiles

1 0.68

0.43

(N.V.):

44%

A f t e r r e a c t i n g at 60-70°C for 3 h , the isolated a n d d r i e d p r o d u c t weighed 4.5 g a n d , after p u r i f i c a t i o n w i t h b o t h e t h a n o l a n d u l t r a f i l t r a t i o n , p r o v i d e d 2.34 g p r o d u c t c o n t a i n i n g 2.7 a n d 2 . 9 % N , respectively. T h e l i g n i n recoveries i n p u r i f i c a t i o n were 80.3 a n d 8 2 . 8 % .

Purification of Cationized Lignin. T h e p u r i f i c a t i o n was c a r r i e d out either b y u l t r a f i l t r a t i o n of the n e u t r a l i z e d p r o d u c t m i x t u r e t h r o u g h a D i a f l o U M 2 m e m b r a n e ( A m i c o n C o r p . , exclusion l i m i t 1000 M W ) or b y s l u r r y i n g a finely g r o u n d 1 g s a m p l e of d r y crude c a t i o n i c ether at r o o m t e m p e r a t u r e i n 160 m L 9 4 % e t h a n o l . T h e filtered powder was washed w i t h 50 m L 9 4 % e t h a n o l a n d t h e n w i t h 10 m L d i e t h y l ether a n d b r o u g h t to a constant weight i n a v a c u u m desiccator. T h e u l t r a f i l t r a t i o n was preferred w h e n the n i t r o g e n content of the p u r i f i e d c a t i o n i c ether exceeded 3%. Results A s is presented i n F i g u r e 1, the flocculation test w i t h s i l i c a as a c o l l o i d a l reference can be used to o p t i m i z e the reaction t i m e . B y l e t t i n g the r e a c t i o n w i t h l i g n i n a n d N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride advance at r o o m t e m p e r a t u r e for 100 h i n s t e a d of 50 h , the dosage req u i r e m e n t of the r e a c t i o n m i x t u r e was reduced to about half. T h e r e s i d u a l t u r b i d i t y already was sufficiently reduced after r e a c t i n g for 50 h . F i g u r e 2 indicates t h a t the flocculation performance of the c a t i o n i c l i g n i n ether p u rified b y u l t r a f i l t r a t i o n ( 2 . 9 % N ) or b y w a s h i n g w i t h e t h a n o l ( 2 . 7 % N ) was equal.

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F i g u r e 2. Effect of p u r i f i c a t i o n o n flocculation p e r f o r m a n c e : (O) unpurified; ( φ ) purified b y leaching w i t h e t h a n o l ; ( Δ ) purified b y u l t r a f i l t r a t i o n .

288

LIGNIN: PROPERTIES AND MATERIALS

A s seen i n T a b l e I, there was enough e p o x y reagent to convert o n l y 7 6 % of h y d r o x y l groups to the c a t i o n i c ether. A s s u m i n g t h a t the n i t r o ­ gen content (2.9%) f o u n d i n the purified s a m p l e ( 8 0 . 2 % l i g n i n recovery) is e q u a l l y d i s t r i b u t e d t h r o u g h the whole c a t i o n i c l i g n i n , one can e s t i m a t e t h a t 4 2 % of the h y d r o x y l groups were reacted a n d 5 5 % of the reagent was c o n s u m e d i n the d e r i v a t i z a t i o n . F i g u r e s 3 a a n d 3b show t h a t the flocculation performance of the p u ­ rified c a t i o n i c l i g n i n d e r i v a t i v e , prepared under the c o n d i t i o n s described i n T a b l e I, is e q u a l to t h a t o f the c o m m e r c i a l reference ( P r a e s t o l 41 I K ) . F i g u r e s 4 a a n d 4 b , o n the other h a n d , reveal t h a t the same c a t i o n i c l i g n i n derivative behaves p o o r l y i n the s t a b i l i t y test when c o m p a r e d to the c o m ­ m e r c i a l reference. F i g u r e s 4 a a n d 4b further show t h a t b y condensing the s o d i u m salt of l i g n i n w i t h formaldehyde ( 1 5 % N a O H d i g n i n , 0.7 mole C H 2 O per 100 g l i g n i n ) at 9 0 ° C for 130 m i n . , a n d subsequently r e a c t i n g the gelled p r o d u c t w i t h g l y c i d y l t r i m e t h y l a m m o n i u m chloride, the flocculation perfor­ m a n c e i n the s t a b i l i t y tests was i m p r o v e d , b u t d i d not reach t h a t of the c o m m e r c i a l reference. It can be assumed t h a t the b r i d g i n g a b i l i t y of l i n e a r c a t i o n i c p o l y a c r y l a m i d e s contributes p o s i t i v e l y i n the s t a b i l i t y test. A n i m p r o v e m e n t i n the flocculation a b i l i t y of the p u r i f i e d c a t i o n i c l i g n i n ether due to a n increase i n the m o l e c u l a r weight is clearly seen i n F i g u r e 5. T h e same figure reveals a moderate g a i n i n the flocculation perfor­ m a n c e relative to P r a e s t o l 41 I K w h e n the c a t i o n i c l i g n i n ether h a d 3.4% Ν i n s t e a d of 2 . 9 % Ν as i n the j a r test s h o w n i n F i g u r e 3a. A series of reactions was c a r r i e d out i n order to o p t i m i z e the r e a c t i o n conditions. A s seen i n T a b l e II, at best 3.7% of n i t r o g e n was f o u n d i n the p u r i f i e d c a t i o n i c l i g n i n , w h e n the r e a c t i o n t i m e was 5 or 8 h at 5 5 ° C ( E x p e r i m e n t s 1 a n d 3). P e r h a p s the reaction t i m e a n d t e m p e r a t u r e s h o u l d be lowered f u r t h e r . A t 3.7% Ν some 6 2 % of the h y d r o x y l groups, p r e s u m a b l y i n c l u d i n g a l l p h e n o l i c O H groups, were reacted. Since the procedure i n these e x p e r i m e n t s i n c o r p o r a t e d a smaller a m o u n t of water to avoid a base-catalyzed o p e n i n g of the o x i r a n e r i n g , h i g h solids contents (52-64%) were encountered. It is a d v i s a b l e to a d d p o w d e r e d l i g n i n first to the alkaline s o l u t i o n a n d m i x i n i t i a l l y at r o o m t e m p e r a t u r e a n d t h e n at the r e a c t i o n t e m p e r a t u r e . A s a m i x i n g device we used a r o u n d b o t t o m flask a t t a c h e d to a r o t a r y evaporator at a t m o s p h e r i c pressure a i d e d w i t h m a g n e t i c s t i r r i n g i n the flask. W h e n the s o d i u m salt o f l i g n i n a p p e a r e d to be homogeneous, the c a t i o n i c reagent was i n t r o d u c e d . T h e i n c o m p l e t e recovery b y u l t r a f i l t r a t i o n (56-92%) i n the e x p e r i m e n t s s h o w n i n T a b l e II engenders a n error when the n i t r o g e n content of the retentate is projected to represent t h a t of the whole s a m p l e . A s a m a t t e r o f fact, i n E x p e r i m e n t 1 we o b t a i n e d 1 g c a t i o n i c l i g n i n h a v i n g 3.7% n i t r o g e n b y u l t r a f i l t r a t i o n whereas b y e t h a n o l w a s h i n g 0.65 g w i t h 3.2% n i t r o g e n was o b t a i n e d . P o s s i b l y the l a t t e r m a t e r i a l was of higher m o l e c u l a r weight.

Reaction Mechanism U n d e r the e x p e r i m e n t a l c o n d i t i o n s there w i l l be c o m p e t i t i o n between

a

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F i g u r e 3. T e s t i n g of flocculation performance against (a) s i l i c a d i s p e r s i o n ; (b) d r e d g i n g effluent; ( Q ) c a t i o n i c l i g n i n ether; ( # ) P r a e s t o l 4 1 1 K .

LIGNIN: PROPERTIES AND MATERIALS

290

F i g u r e 4. C o m p a r i s o n of flocculation performance i n s t a b i l i t y test (a) against s i l i c a d i s p e r s i o n ; (b) against d r e d g i n g effluent; (O) c a t i o n i c l i g n i n ether; ( Δ ) C H 0 - c o n d e n s e d c a t i o n i c l i g n i n ether; (φ) P r a e s t o l 41 I K . 2

21. P U L K K I N E N E T A L

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291

% FTU

60 Γ

50 Γ

40 Γ

30 L

20 r*

10 h

0.02

0.04

0.06

0.08

0.1

0.12

ppm

F i g u r e 5. Effect o f m o l e c u l a r weight o n flocculation p e r f o r m a n c e o f c a t i o n i c l i g n i n d e r i v a t i v e : (Ç)) I n d u l i n A T , M 23000, N : 3.3%; ( Δ ) I n d u l i n A T , M 6300, N : 3.7%; ( * ) P r a e s t o l 41 I K , M i n - U - S i l 5 450 m g / l i t e r . w

w

292

LIGNIN: PROPERTIES AND MATERIALS

T a b l e II. C o n d i t i o n s for C a t i o n i z i n g L i g n i n

a

Reaction Cationic Lignin Exp. No.

Molar Ratios OH:Reagent:NaOH

Temp. °C

Time h

% Ν

% Recovery

Reagent % Yield

Reaction with Glycidyltrimethylammonium Chloride 1 2 3 4 5 6

1:0.9:0.2 1:0.9:0.2 1:0.9:0.2 1:1.0:0.2 1:1.0:0.2 1.1.0:0.2

Reaction with 7 8 9

52 52 52 65 65 65

74 65 69 51 58 42

56 65 63 68 61 92

3.7 3.6 3.7 3.3 3.4 2.7

5 8 8 5 8 20

N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride

1:0.9:0.9 1:1.0:1.0 1:0.6:0.6

r.t. 65 65

50 51 44

70 65 74

2.9 3.2 2.1

50 10 12

4

E x p e r i m e n t s 1-6 were carried out i n a 1 g s a m p l e of I n d u l i n A T at 5 6 % N . V . I n e x p e r i m e n t 7 a 2 g s a m p l e of I n d u l i n A T was reacted at 5 2 % N . V . N u o t t a s a a r i l i g n i n (2 a n d 5 g) was reacted i n e x p e r i m e n t s 8 a n d 9 at 64 a n d 5 8 % N . V . , respectively. A l l the samples were p u r i f i e d b y u l t r a f i l t r a t i o n a n d the l i g n i n % recovery was d e t e r m i n e d f r o m the % n i t r o g e n a n d the y i e l d of the retentate. Reagent y i e l d s are corrected for u l t r a f i l t r a t i o n losses. R o o m temperature.

Lignin-O® + CHg-CHCHgN^CH^CI® H 0 2

lignin-OCH CHCH N®(CH3) CP 2

2

—=->

3

lignin-OCH CHCH N«iCH3) CP 2

2

3

OH O r P + CH -CHCH N®(CH ) CP 2

2

3

3

H 0 2

CH^CHCH^CHgJgCI© • OH

O® 9

CH -CHCH N®(CH ) Cr + OH© 2

OH OH

2

3

3

21. P U L K K I N E N E T A L .

Preparation and Testing of Cationic Flocculants 293

n u m b e r o f nucleophiles for opening the oxirane r i n g . Since t h e m o l a r a m o u n t o f s o d i u m h y d r o x i d e , w h i c h is first i n t r o d u c e d i n t o t h e r e a c t i o n m i x t u r e , nearly reaches t h e corresponding contents o f phenolic a n d c a r b o x y lie acid groups (Table I ) , l i g n i n phenoxide a n d c a r b o x y l a t e moieties must be t h e d o m i n a n t nucleophilic species a t the b e g i n n i n g . T h e m a i n reactions can be expressed b y the following equations. W h e t h e r o r n o t the reagent w i l l react w i t h t h e secondary h y d r o x y l group generated i n each r i n g o p e n i n g is at present u n k n o w n . T h e c h l o r o h y d r i n reaction w i t h s o d i u m h y d r o x i d e is assumed t o b e a two-step process i n w h i c h a r a t e - d e t e r m i n i n g i n t r a m o l e c u l a r displacement of chloride i o n b y negatively charged oxygen follows a p r i o r e q u i l i b r i u m between the h y d r o x i d e i o n a n d the h y d r o x y l group o f the h a l o h y d r i n (5). CI

CI

CHo-CHo + O H

ι

2

2

9

^

f a S t

^ CHo-CHo

*

I

OH

O

CI I CHo-CHo

ι

slow _ — >

2

9

CHo-CH + C r

9

\

y Q Ο Indeed, we have found t h a t N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride is r e a d i l y converted w i t h s o d i u m h y d r o x i d e t o g l y c i d y l t r i ­ m e t h y l a m m o n i u m chloride, w h i c h obviously further reacts a t a slower rate w i t h l i g n i n nucleophiles t o f o r m cationic l i g n i n derivatives. 2

2

0

Conclusion E v e n a p a r t i a l conversion o f t h e h y d r o x y l groups o f kraft l i g n i n i n t o a c a t i o n i c ether derivative c o n t a i n i n g quaternary a m m o n i u m groups i m p a r t s water s o l u b i l i t y t o the derivative w h i c h is a p r o m i s i n g c a n d i d a t e as a p o t e n ­ t i a l flocculant i n l i q u i d / s o l i d separations i n i n d u s t r i a l a n d m u n i c i p a l water treatment. Literature C i t e d 1. 2. 3. 4.

Nieminen, M . ; Pulkkinen, E . ; Rahkamaa, E . Holzforschung, in press. Paschall, E . F . U.S. Patent 2 876 217, 1959. Paschall, E . F.; Minkema, W . H . U.S. Patent 2 995 513, 1961. Hudson, R. E., Jr.; Wagner, E . G . J. Am. Water Works Assoc. 1981, 40, 218-23. 5. Frost, Α. Α.; Pearson, R. G . Kinetics and Mechanism; John Wiley & Sons: New York, 1962; C h . 12, p. 288.

RECEIVED March 17,1989