Cellulose Chemistry and Technology

18 Pyrolysis of Cellulose after Chlorination or Addition of Zinc Chloride

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 11, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch018

YUAN Z. LAI, FRED SHAFIZADEH, and CRAIG R. McINTYRE W o o d C h e m i s t r y L a b o r a t o r y , U n i v e r s i t y of M o n t a n a , M i s s o u l a , MO 59812

We have been c o n c e r n e d w i t h t h e mechanism o f p y r o l y t i c r e actions involved i n the i n i t i a t i o n , propagation and suppression o f c e l l u l o s i c f i r e s (!_-([). S i n c e c h l o r i n e d e r i v a t i v e s a n d s a l t s are e x t e n s i v e l y used as flame r e t a r d a n t s , p y r o l y s i s o f c e l l u l o s e a f t e r c h l o r i n a t i o n o r a d d i t i o n o f z i n c c h l o r i d e has been i n v e s t i g a t e d i n order t o determine t h e reactions and p r i n c i p l e s i n volved i n suppressing t h e production o f flammable v o l a t i l e s which fuel t h e flaming combustion. P r e p a r a t i o n o f Samples Samples o f 6 - c h l o r o - 6 - d e o x y c e l l u l o s e w i t h v a r y i n g d e g r e e s o f c h l o r i n a t i o n were p r e p a r e d b y t r e a t i n g m i c r o c r y s t a l l i n e c e l l u l o s e i n DMF w i t h m e t h a n e s u l f o n y l c h l o r i d e a t 63°C ( 7 ) . T h e p r o d u c t s and t h e i r p r o p e r t i e s a r e l i s t e d i n T a b l e 1. Samples o f c e l l u l o s e c o n t a i n i n g v a r y i n g amounts o f Z n C l p were p r e p a r e d b y a d d i n g t h e c a l c u l a t e d p r o p o r t i o n o f c a t a l y s t i n methanol a n d e v a p o r a t i n g t h e s o l v e n t u n d e r vacuum. Discussion Thermal Reactions o f C h l o r i n a t e d C e l l u l o s e s . T h e thermogram o f p u r e c e l l u l o s e i s shown i n F i g u r e 1. I n t h i s f i g u r e , t h e DTA, T G a n d DTG c u r v e s r e f l e c t t h e s e q u e n c e o f p h y s i c a l t r a n s f o r m a t i o n s a n d c h e m i c a l r e a c t i o n s as t h e s a m p l e i s h e a t e d a t a constant rate. The DTA c u r v e c o n t a i n s a b r o a d d e c o m p o s i t i o n e n d o t h e r m i n the range o f 300-375°C centered a t 3 4 0 ° C t h a t i s accompanied by a r a p i d w e i g h t l o s s l e a v i n g 6.5% o f c a r b o n a c e o u s r e s i d u e a t 4 0 0 ° C 256

In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

LAI ET AL.

18.

Pyrolysis of Cellulose

257

TABLE 1 Preparation o f 6-Chloro-6-deoxycellulose


Sample

Reaction Conditions Temp Time (hr) (°c)

Color

Product Chlorine

D.S.

3

(%)

A

63

1.5

White

0.40

0.018

B

63

2.5

White

0.50

0.023

C

63

3.7

White

1.16

0.053

D

63

7.1

White

1.96

0.091

E

63

19.6

Tan

4.12

0.192

F

63

48.6

Tan

5.72

0.270

Degree o f s u b s t i t u t i o n c a l c u l a t e d from t h e c h l o r i n e c o n t e n t . The DTG c u r v e , i n d i c a t i n g t h e r a t e o f w e i g h t l o s s , shows a s h a r p peak a t 3 5 1 ° C C h l o r i n a t e d samples gave e n t i r e l y d i f f e r e n t thermograms. They decomposed a b o u t 100°C l o w e r a n d gave more c h a r r e d r e s i d u e , as i l l u s t r a t e d i n F i g u r e 2, f o r a sample (B) w i t h a d e g r e e o f s u b s t i t u t i o n (D.S.) o f 0.023. T h i s s a m p l e shows a b r o a d endot h e r m i n t h e r a n g e o f 2 0 0 - 3 6 0 ° C w i t h o v e r l a p p i n g peaks; n e a r 225° a n d 2 8 0 ° C , a n d a r e s i d u e o f 30% a t 4 0 0 ° C , w i t h t h e maximum r a t e of weight loss o c c u r r i n g a t 3 0 0 ° C The n a t u r e o f c h e m i c a l r e a c t i o n s a n d w e i g h t l o s s o c c u r r i n g w i t h i n t h e r a n g e o f 1 5 0 - 3 0 0 ° C were i n v e s t i g a t e d by m o n i t o r i n g the v o l a t i l e p r o d u c t s f o r m e d a n d a n a l y s i s o f t h e r e s i d u e s . Hydrogen c h l o r i d e , d e t e c t e d as A g C l , s t a r t e d t o e v o l v e a t ^ 2 0 0 ° C , i n d i c a t i n g t h a t t h e f i r s t e n d o t h e r m i c peak i n v o l v e s d e h y d r o h a l o g e n a t i o n o f t h e m o l e c u l e . More t h a n 8 0 % o f t h e comb i n e d c h l o r i n e d i s a p p e a r e d on h e a t i n g t h e s a m p l e t o 250°C. T h e endotherm a t 225°C, c o r r e s p o n d i n g t o t h e d e h y d r o h a l o g e n a t i o n , became more p r o m i n e n t w i t h a h i g h e r d e g r e e o f c h l o r i n a t i o n . F o r example, s a m p l e F, w i t h D . S . o f 0.27, showed o n l y a b r o a d endot h e r m i c peak a t 2 2 0 ° C , a*s i l l u s t r a t e d i n F i g u r e 3. ESR s c a n n i n g o f t h e p y r o l y s i s r e s i d u e s w i t h i n t h e r a n g e o f 150-300°C i n d i c a t e d t h a t t h e i n i t i a l d e c o m p o s i t i o n r e a c t i o n s a r e h e t e r o l y t i c , b u t s u b s e q u e n t r e a c t i o n s , w h i c h t a k e p l a c e above 2 3 0 ° C a r e a c c o m p a n i e d by t h e f o r m a t i o n o f s t a b l e f r e e r a d i c a l s . #


In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Figure

1.

Thermal

analysis

curves of microcrystalline

cellulose


I

S I

Ο

•

Hi

I

η

Μ

C/5

ο

Ρ

η

Si


Figure 2.

Thermal analysis curves of 6-chloro-6-deoxy cellulose (B, D.S. of 0.023)



Figure

3.

Thermal

analysis curves of 6-chloro-6-deoxy

cellulose ( F , D.S. 0 / 0.270)


to

i

ο

I

Ο

*!

§

Ω

Μ

ο

Ρ ε

s


18.

LAI ET AL.

Pyrolysis

of

Scheme 1.

Cellulose

261

Production of levoglucosenone

The s c a n n i n g mass s p e c t r o s c o p y d a t a f o r t h e v o l a t i l e s formed a t v a r i o u s t e m p e r a t u r e s a r e summarized i n F i g u r e 4. T h e s e d a t a show t h e e v o l u t i o n o f w a t e r (m/e 1 7 ) , c a r b o n d i o x i d e (m/e 4 4 ) , 2 - f u r a l d e h y d e (m/e 95 a n d 9 6 ) , 5 - m e t h y l - 2 - f u r a l d e h y d e W e 109 and 1 1 0 ) , β - a n g e l i c a l a c t o n e (m/e 98) a n d l e v o g l u c o s e n o n e X"l»6anhydro-3,4-dideoxy^-D-glycero-hex-3-enopyranos-2-ulose) (m/e 98 a n d 126) o c c u r r e d a l t h e e a r l y s t a g e s o f h e a t i n g . Formation o f these ions i s c o n s i s t e n t with the chemical a n a l y s i s o f v o l a t i l e p r o d u c t s shown i n T a b l e 2. T h e r e s u l t s show t h a t c h l o r i n a t e d s a m p l e s , i n c o n t r a s t t o p u r e c e l l u l o s e , g i v e a s u b s t a n t i a l amount o f l e v o g l u c o s e n o n e as shown i n Scheme 1. T a b l e 3 a n d F i g u r e 5 summarize t h e t h e r m a l a n a l y s i s f e a t u r e s o f c h l o r i n a t e d c e l l u l o s e with v a r i o u s degrees o f c h l o r i n a t i o n . T h e y show t h a t c h a r r i n g i n c r e a s e s w i t h t h e d e g r e e o f s u b s t i t u t i o n up t o a D.S. o f 0.023. A d d i t i o n a l c h l o r i n a t i o n a f t e r t h a t has l i t t l e o r no e f f e c t . T h u s , o n l y a s m a l l q u a n t i t y o f com b i n e d h a l o g e n i s n e c e s s a r y t o a c h i e v e t h e maximum c h a r r i n g e f f e c t . A l s o , p r e - h e a t i n g t h e sample c a u s e s a s h a r p d e c r e a s e i n t h e f o r m a t i o n o f l e v o g l u c o s e n o n e a n d 2 - f u r a l d e h y d e . F o r example, sample Β on p r e - h e a t i n g t o 250°C l o s t ^ 8 0 % o f i t s o r i g i n a l c h l o r i n e c o n t e n t and gave o n l y 3.2% o f l e v o g l u c o s e n o n e on f u r t h e r h e a t i n g as compared t o 12.5% l e v o g l u c o s e n o n e o b t a i n e d f r o m t h e u n h e a t e d sample. T h i s i n v e s t i g a t i o n shows t h a t h y d r o g e n c h l o r i d e , l i b e r a t e d i n the early stages o f heating, could c a t a l y z e a s e r i e s o f d e h y d r a t i o n r e a c t i o n s . F u r t h e r c o n d e n s a t i o n and c a r b o n i z a t i o n o f t h e d e h y d r a t i o n p r o d u c t s , s u c h as l e v o g l u c o s e none, r e d u c e s t h e p r o d u c t i o n o f c o m b u s t i b l e v o l a t i l e s . T h e c o n d e n s a t i o n and c a r b o n i z a t i o n r e a c t i o n s a r e c a t a l y z e d more e f f e c t i v e l y by L e w i s a c i d s , s u c h as Z n C l , t h a n by A r r h e n i u s a c i d s ( δ λ Thermal r e a c t i o n s o f c e l l u l o s e a f t e r a d d i t i o n o f z i n c c h l o r i d e , shown i n F i g u r e 6, r e f l e c t t h e c h a r r i n g r e a c t i o n s . T h e t h e r m a l a n a l y s i s c u r v e s o f a sample o f c e l l u l o s e c o n t a i n i n g 5% o f Z n C l ? shows a b r o a d d e c o m p o s i t i o n e n d o t h e r m i n t h e r a n g e o f 200-358*C, w h i c h peaks a t 333°C w i t h a s h o u l d e r n e a r 2 7 5 ° C The d e c o m p o s i t i o n endotherm i s a c c o m p a n i e d by * 64% o f w e i g h t l o s s , l e a v i n g 36% o f c h a r r e d r e s i d u e a t 4 0 0 ° C . The i n i t i a l d e c o m p o s i t i o n r e a c t i o n s o c c u r r i n g w i t h i n t h e 2



Figure 4.

Mass spectrometry of the pyrolysis products of 6-chloro-6-deoxy cellulose (F, D.S. of 0.270)

Temperature, °C


In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. 3.0 3.1

0.3 0.3

2 8

5.1

7.1

220

240

250

260

0.270

—

—

0.192

—

—

0.9

0.6

0.6 0.6 0.6

1.1 1.3 1.1

0.4

0.4

0.4

Τ 0.2 1.2 1.2

13.4. 10.6 11.4 8.3

0.6

0.3

29.5

300 1.0

1.3

0.3

17.8

280

—

1.3

0.3

10.2

—

3.2

0.4

0.091

0.053

3.3

Τ

12.5

0.2

0.7

2.1

Τ

12.8

200

Τ

L e v u l i n i c Acid

1.4

0.8

0.4

0.2

1.0

0.5

—

—

0.023

—

1.2 0.7

—

0.018

—

Products Formed on Rapid Heating to 500°C {%) 2-Furaldehyde 5-Methyl-2- 3-AngelicaLevoglucosenone furaldehyde lactone

1.8

—

Substrate Preheat- Weight ing °C Loss {%)

0.000

D.S.

V o l a t i l e Products of 6-Ch1oro-6-deoxycel1ulose and i t s P a r t i a l l y Degraded Residue Formed on Rapid Heating t o 500°C

TABLE 2


In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Figure

5.

Pyrolysis

products

of 6-chloro-6-deoxy-cellulose

at 500°


F

ο

i

M en

S

M

f

w

to


Figure

6. Thermal

analysis curves of cellulose

in the presence

of 5% zinc

chloride


to

o S*

s-

ce

•

g

h-» po

CELLULOSE CHEMISTRY AND TECHNOLOGY

266


TABLE 3 Thermal

Analysis Features o f 6-Chloro-6-deoxycellulose

Sample

Degree o f Substitution

D . t . a . peaks D . t . q . peaks Range Peak Dec. °ç °C °C 6-Chloro-6-deoxy c e l l u l o s e a

300 ,335

a

T.g. Residue a t 4 0 0 ° C (%) a

12.0

A

0.018

210-360

225 ,285

Β

0.023

200-360

225 ,280

C

0.053

200-350

225,280

285

D

0.091

200-345

225,280

230 ,280

9

32.0

Ε

0.192

205-340

225,275

215,260

31.5

F

0.270

190-340

220

240

31.5

351

6.5

a

a

300,325

a

30.0 29.2

Cellulose 300-375

340

A shoulder r a n g e o f 200-330°C w e r e i n v e s t i g a t e d b y p h y s i c a l and c h e m i c a l a n a l y s i s o f the r e s i d u e s o b t a i n e d a t d i f f e r e n t temperatures. The a n a l y t i c a l r e s u l t s a r e s u m m a r i z e d i n T a b l e 4. T h e IR d a t a showed t h a t f o r m a t i o n o f c a r b o n y l 1710 cm" ) and u n s a t u r a t e d 1610 cm" ) g r o u p s r e s u l t i n g f r o m d e h y d r a t i o n r e a c t i o n s t a k e s p l a c e i n t h e e a r l y s t a g e s o f h e a t i n g . The f i n e s t r u c t u r e o f . c e l l u l o s e , i n d i c a t e d by t h e f i n g e r p r i n t r e g i o n (1500-800 c m " ) , was p r a c t i c a l l y d e s t r o y e d on h e a t i n g t o 3 1 0 ° C w i t h 32% o f w e i g h t l o s s . The w a t e r - s o l u b l e f r a c t i o n , a f t e r b o r o h y d r i d e r e d u c t i o n and a c i d h y d r o l y s i s , was f o u n d t o c o n s i s t m a i n l y o f u n h y d r o l y z a b l e c o n d e n s a t i o n p r o d u c t s and s m a l l e r q u a n t i t i e s o f J - g l u c o s e and 3,6-anhydro-D-glucose. ESR s p e c t r o s c o p y o f t h e h e a t e d s a m p l e c o n t a i n i n g 5% Z n C ^ showed t h a t t h e r a d i c a l f o r m a t i o n a s s o c i a t e d w i t h t h e c h a r r i n g r e a c t i o n s t a k e s p l a c e a t a r e l a t i v e l y low t e m p e r a t u r e o f 2 3 0 ° C , c o r r e s p o n d i n g t o 4% w e i g h t l o s s . T h e r e f o r e , i t was c o n c l u d e d t h a t ZnCl2 c a t a l y z e s the n o n g l y c o s i d i c c o n d e n s a t i o n and c h a r r i n g r e a c t i o n s a t the very e a r l y stages o f h e a t i n g . T h i s accounts f o r t h e low y i e l d o f monomeric p r o d u c t s and l a r g e p r o p o r t i o n o f r e s i dues d i s c u s s e d a b o v e . 1

1

1


In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. (Π.2)

J-glucose (%)

(1.9) (T)

(2.2)

(n.o) (13.3) (11.2)

a

5.8

Very Weak

Strong

(3.7)

12.4

Weak

Moderate

Strong

(3.5)

8.6

Moderate

Weak

Number in parentheses are percentages of the water-soluble fraction.

(1.4)

3,6-anhydro-Dglucose (%) "*

After reduction and acid hydrolysis a

9.2

Water-soluble material (%)

9.8

Moderate

Strong

1

Fingerprint region for cellulose (1500-800 cm" )

Weak Weak

Very Weak

Unsaturation , groups (1610 cm" )

Carbonyl group -ι (1700-1720 cm"')

IR spectra Moderate

Black

Deep Brown

Brown

Brown

Gray

Moderate

54.33

67.64

83.09

85.9

94.5

Color

45.67

32.36

16.91

14.1

Residue

Weight Loss {%)

5.5

330°

310°

υ

Temperatures, °C 280"

27ϋ

Z3b"

Properties

Analysis of Cellulose Samples Containing $% Zinc Chloride Pyrolyzed to Different Temperatures

TABLE 4


268

CELLULOSE CHEMISTRY AND TECHNOLOGY

TABLE 5 Thermal A n a l y s i s F e a t u r e s o f C e l l u l o s e C o n t a i n i n g Z i n c C h l o r i d e


Additive

D . t . a . peaks Range Peak °C °C

D . t . q . peaks °C

T.g. Residue a t 4 0 0 ° C (%)

Neat

300-375

340

351

6.5

IX

275-365

345

340

12.2

3%

200-360

333

275 ,327

5%

200-358

7%

175-340

275 ,333 a a 225 ,310

10%

175-330

210 ,260 ,305

3

a

3

a

a

30.5

275 ,327

3

31.0

265,310

40.0

265,310

41.3

A shoulder The t h e r m a l a n a l y s i s f e a t u r e s o f c e l l u l o s e c o n t a i n i n g v a r y i n g amounts o f Z n C l g a r e summarized i n T a b l e 5. T h e s e d a t a show that higher proportions o f c a t a l y s t lower the decomposition t e m p e r a t u r e even f u r t h e r a n d r e s u l t i n a v e r y b r o a d e n d o t h e r m w i t h no d i s t i n c t p e a k s , a p p a r e n t l y d u e t o t h e o v e r l a p p i n g o f a v a r i e t y o f c o n c u r r e n t and c o n s e c u t i v e r e a c t i o n s . A l s o , t h e e x t e n t o f c h a r r i n g i n c r e a s e s as t h e p r o p o r t i o n o f t h e a d d i t i v e i s i n c r e a s e d a n d r e a c h e s t h e maximum v a l u e o f 4 0 % a t * 7% a d d i t i o n . I s o t h e r m a l P y r o l y s i s . I s o t h e r m a l p y r o l y s i s a t 500°C p r o v i d e d a c r o s s - s e c t i o n o f t h e p r o d u c t s formed by t h e s e q u e n c e o f p y r o l y t i c r e a c t i o n s . T h e s e p r o d u c t s , l i s t e d i n T a b l e 6, c o n s i s t e d o f t a r , c h a r , water, carbon d i o x i d e , hydrogen c h l o r i d e , a n d a v a r i e t y o f v o l a t i l e o r g a n i c compounds, namely 2 - f u r a l d e h y d e , 5-methyl-2-furaldehyde, and levoglucosenone, d e r i v e d mainly from dehydration reactions. G.L.C. a n a l y s i s o f t h e t a r f r a c t i o n , b e f o r e and a f t e r a c i d h y d r o l y s i s , g a v e t h e r e s u l t s shown i n T a b l e 7. T h e s e d a t a i n d i c a t e that the t a r f r a c t i o n , i n general, c o n s i s t e d mainly o f u n h y d r o l y z a b l e c o n d e n s a t i o n p r o d u c t s , a n d s m a l l amounts o f l e v o g l u c o s a n , i t s furanose isomer, and 3,6-anhydro-J-glucose as t h e monomeric p r o d u c t s . However, t h e t a r f r a c t i o n s f r o m Z n C ^ t r e a t e d s a m p l e s , b o t h b e f o r e and a f t e r a c i d h y d r o l y s i s , c o n t a i n


In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Τ Τ

Cellulose Chemistry and Technology

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