Wood Technology: Chemical Aspects

5 Thermal Deterioration of W o o d

Downloaded by PRINCETON UNIV on September 26, 2013 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0043.ch005

FRED SHAFIZADEH and PETER P. S. CHIN Wood Chemistry Laboratory, University of Montana, Missoula, Mont. 59801

When wood is heated at elevated temperatures, it w i l l show a permanent loss of strength resulting from chemical changes in its components. The thermal decomposition can start at temperatures below 100°C if wood is heated for an extended period of time. Figure 1 shows that wood heated at 120° loses 10% of i t s strength in about one month, but it takes only one week to obtain the same loss of strength if it i s heated at 140° (1). Heating at higher temperatures gives v o l a t i l e decomposition products and a charred residue. The pyrolytic reactions and products control the combustion process and relate to the problems of c e l l u l o s i c f i r e s , chemical conversion of c e l l u l o s i c wastes and u t i l i z a t i o n of wood residues as an alternative energy source. In our laboratory, the pyrolytic reactions of wood and its major components have been investigated by a variety of analytical methods. Thermal analysis of cottonwood and i t s major components (2), as shown in Figures 2 and 3, indicates that the thermal behavior of wood reflects the sum of the thermal responses of i t s three major components, c e l l u l o s e , hemicellulose (xylan) and l i g n i n . A l l these substrates are i n i t i a l l y dried on heating at 50-100°. The hemicellulose component is the least stable and decomposes at 225-325°. Cellulose decomposes at higher temperatures within the narrower range of 325-375°. Lignin, however, decomposes gradually within the temperature range of 250-500°. The c e l l wall polysaccharides provide most of the v o l a t i l e pyrolysis products, while l i g n i n predominantly forms a charred residue. Since the thermal reactions of the wood components are highly complex and additive, they have been studied i n d i v i d u a l l y . Among the three major components, the pyrolysis reactions of cellulose have been most extensively studied. At temperatures above 300°, rapid cleavage of the glycosidic bond takes place,

57

In Wood Technology: Chemical Aspects; Goldstein, I.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


WOOD

TECHNOLOGY:

1 hr.

CHEMICAL

.

Journal of the Forest Products Research Society

Figure 1. Effect of time and tempera ture on the modulus of elasticity of wood: (A) 10%,

(B) 2 0 % , and (C) 40%

Ί

m1n

'

fro

loss of modulus of elasticity (I),

50

150

250

îfe

ïfc—

im>. vo

350

450

Temperature (°C) Figure 2.

Differential thermal analysis of wood and its components


ASPECTS

Thermal

AND CHIN

Deterioration


SHAFizADEH

1 ^ fc I 110

130

I 10

I 15 I

150

I 20 I

170

I 25 I

190

1 30

min.

1 210

230

°C

R e t e n t i o n time (min) Temperature (degrees) Figure 4. Chromatogram of cellulose pyrolysis tar after reduction with NaBH : a, unknown; b, l,6-anhydro~β-Ό-glucopyranosè; c, lfi-anhydro-fi-O-glucofuranose; d, 3-deoxyhexitols; e, Ό-glucitol; f, oligosac charide derivatives i



60

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

producing 1,6-anhydro-g-D-glucopyranose (levoglucosan) and other t a r r y p y r o l y s i s products t h a t have been analyzed by chromatographic methods (see Figure 4) and are l i s t e d i n Table I ( 3 ) . This cleavage o f g l y c o s i d i c groups proceeds through a t r a n s g l y c o s y l a t i o n mechanism w i t h the p a r t i c i p a t i o n o f one of the f r e e hydroxyl groups, producing mainly 1,6-anhydro-6 -D-glucopyranose, which i s more s t a b l e than other anhydro sugars. The t a r f r a c t i o n a l s o contains randomly l i n k e d o l i g o - and p o l y s a c c h a r i d e s , p r o duced by secondary t r a n s g l y c o s y l a t i o n and condensation r e a c t i o n s . P y r o l y s i s of c e l l u l o s e under vacuum gives a high y i e l d of the v o l a t i l e p r o d u c t s , p a r t i c u l a r l y l e v o g l u c o s a n . At atmospheric p r e s s u r e , however, the y i e l d of levoglucosan drops s h a r p l y , due to f u r t h e r decomposition, which increases the y i e l d o f char. The t r a n s g l y c o s y l a t i o n r e a c t i o n s are preceded and accompanied by dehydration and e l i m i n a t i o n r e a c t i o n s t h a t produce wat e r and other dehydration products such as furan d e r i v a t i v e s and 1,6-anhydro-3,4-dideoxy-&-D-gjycero-hex-3-enopyranos-2-ulose (levoglucosenone) . The a d d i t i o n o f a c i d i c a d d i t i v e s , such as phosp h o r i c a c i d , diammonium phosphate, diphenyl phosphate and z i n c c h l o r i d e , can s i g n i f i c a n t l y c a t a l y z e the l a t t e r r e a c t i o n s . This i s i l l u s t r a t e d i n Figure 5 and Table I I . Figure 5 shows the enhanced y i e l d s o f levoglucosenone and 2-furaldehyde due to the a d d i t i o n of diphenyl phosphate, a strong Arrhenius a c i d , and Table II shows the e f f e c t o f H 3 P O 4 on promoting the production of levoglucosenone from various _Q-glucose-containing m a t e r i a l s i n c l u d i n g pure c e l l u l o s e , s t a r c h and wastepapers. The formation of levoglucosenone from the p y r o l y t i c dehydration o f c e l l u l o s e has r e c e n t l y been reported by d i f f e r e n t l a b o r a t o r i e s ( 4 - 6 ) . This compound was b e l i e v e d to be produced through the formation o f levoglucosan as shown i n Scheme 1, however, t h i s i s the s u b j e c t of some controversy ( 6 , 7 ) . In summary, the thermal degradation of c e l l u l o s e i n the temperature range of 300-350° can be dep i c t e d as shown i n Scheme 2. At higher temperatures, the i n t e r m e d i a t e s , i n c l u d i n g l e v o glucosan and the condensation products f u r t h e r p y r o l y z e to g i v e various products by f i s s i o n o f the carbohydrate u n i t s and r e a r rangement of the intermediate p r o d u c t s . Table I I I shows the p r o ducts obtained from the p y r o l y s i s of c e l l u l o s e and t r e a t e d c e l l u lose a t 600° ( 8 ) . The s i g n i f i c a n t increase i n the y i e l d s o f wat e r and char and decrease i n the y i e l d o f t a r i n the a c i d t r e a t e d c e l l u l o s e v e r i f i e s the p r e v i o u s l y mentioned promotion of dehydrat i o n and c h a r r i n g reactions by a c i d i c a d d i t i v e s . The p y r o l y s i s r e a c t i o n s i n v o l v e d i n h e m i c e l l u l o s e , i . e . , x y l a n , are s i m i l a r t o those i n v o l v e d i n c e l l u l o s e p y r o l y s i s . Table IV shows the p y r o l y s i s products formed from x y l a n at 300° (9). The p y r o l y s i s of x y l a n y i e l d s about 16% of t a r which cont a i n s 17% of a mixture of o l i g o s a c c h a r i d e s . Upon a c i d h y d r o l y s i s , they g i v e an approximately 54% y i e l d o f J - x y l o s e . Structural a n a l y s i s of the polymers shows t h a t they are branched-chain


SHAFizADEH

AND CHIN

Thermal

Deterioration


15

Scheme 1.

Pyrolysis of cellulose (A) to levoglucosan (B) and levoglucosenone (C )



62

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

polymers, i n d i c a t i n g t h a t they are d e r i v e d from random condensat i o n of x y l o s y l u n i t s which are formed by cleavage of the g l y c o s i d e groups s i m i l a r to t h a t occuring i n c e l l u l o s e p y r o l y s i s . The a d d i t i o n of a Lewis a c i d , i . e . , Z n C ^ s i g n i f i c a n t l y decreases the production of t a r and enhances the production of char due to the enhanced dehydration r e a c t i o n s . A t higher temperatures the g l y c o s y l u n i t s and the random condensation products are f u r t h e r degraded to a v a r i e t y o f v o l a t i l e p r o d u c t s , as shown i n Table V ( £ ) . Comparison o f t h i s t a b l e with the high temperature p y r o l y s i s products l i s t e d f o r c e l l u l o s e i n Table I I I shows t h a t the products of both f r a c t i o n s are b a s i c a l l y s i m i l a r . The s i g n i f i cant increase i n the y i e l d s o f 2 - f u r a l d e h y d e , water and char and decrease i n the y i e l d o f t a r by the a d d i t i o n of Z n C K v e r i f i e s the enhanced, dehydration and i s s i m i l a r t o observed e f f e c t s i n cellulose pyrolysis. Compared w i t h the p y r o l y s i s o f p o l y s a c c h a r i d e s , the p y r o l y s i s of 1 i g n i n i s r e l a t i v e l y unexplored. While the thermal r e a c t i o n s of l i g n i n occur over a wide temperature range of 2 5 0 - 5 0 0 ° , the decomposition i s most r a p i d between 3 1 0 - 4 2 0 ° , as i n d i c a t e d by the y i e l d o f gas and d i s t i l l a t e produced. Due to the complex s t r u c t u r e of l i g n i n , the mechanism of i t s thermal degradation i s not w e l l understood. Table VI l i s t s the major p y r o l y t i c products from l i g n i n ( 1 0 ) . The most abundant product i s c h a r , a h i g h l y condensed carbonaceous r e s i d u e , obtained i n about 55% y i e l d . The second f r a c t i o n of the p y r o l y t i c products i s an aqueous d i s t i l l a t e , produced i n about 20% y i e l d . I t contains mainly water and some methanol, acetone and a c e t i c a c i d . The y i e l d o f methanol f o r hardwood l i g n i n i s about 2%, twice as much as f o r softwood l i g n i n because i t c o n t a i n s a s y r i n g y l r a t h e r than guaiacy1 s t r u c t u r e . The y i e l d of a c e t i c a c i d from hardwood l i g n i n i s a l s o s i g n i f i c a n t l y higher than from softwood 1 i g n i n ; prèsumably i t o r i g i nates from the propanoid s i d e c h a i n s . The t h i r d f r a c t i o n of the p y r o l y t i c products i s t a r , which i s produced i n about 15% y i e l d . I t i s a mixture of p h e n o l i c compounds c l o s e l y r e l a t e d to phenolguaiacol and 2,6-dimethoxy-phenol, w i t h s u b s t i t u e n t s a t the p o s i t i o n para t o the hydroxyl group. The l a s t p y r o l y t i c f r a c t i o n i n cludes v o l a t i l e products such as CO, C H 4 , C 0 and ethane, p r o duced i n about 12% y i e l d . The 1 i s t o f p y r o l y s i s products of cottonwood shown i n Table VII (11) r e f 1 e c t s the summation of the p y r o l y s i s products of i t s three major components. The higher y i e l d s of acetone, p r o p e n a l , methanol, a c e t i c a c i d , C 0 , water and char from cottonwood, as compared to those obtainea from c e l l u l o s e and x y l a n , are l i k e l y a t t r i b u t e d to l i g n i n p y r o l y s i s . Other res u l t s are s i m i l a r to those obtained from the p y r o l y s i s o f c e l l - w a l l p o l y s a c c h a r i d e s . This f u r t h e r v e r i f i e s t h a t there i s no s i g n i f i c a n t i n t e r a c t i o n among the three major components during the thermal degradation of wood. The p y r o l y s i s products o f wood can be broadly grouped i n t o three c a t e g o r i e s as shown i n Scheme 3 , i . e . , the combustible 2

2


Thermal

Deterioration


SHAFIZAJDEH A N D C H I N



64

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

v o l a t i l e s , t a r and char. Upon f u r t h e r p y r o l y s i s , t a r i s f i n a l l y converted to v o l a t i l e s and c h a r . In the presence o f oxygen, the combustible v o l a t i l e s lead to f l a m i n g combustion w h i l e char r e acts by glowing combustion. The r a t e of combustible v o l a t i l e formation can be measured as a f u n c t i o n o f temperature by thermal e v o l u t i o n a n a l y s i s (TEA). This i n s t r u m e n t a t i o n u t i l i z e s a temperature programmed furnace combined w i t h a flame i o n i z a t i o n d e t e c t o r which responds i n a p r e d i c t a b l e manner to the evolved gases. The TEA of cottonwood i s shown i n Figure 6. I t shows the e v o l u t i o n o f combustible v o l a t i l e s i n two o v e r l a p p i n g stages due to the decomposition o f h e m i c e l l u l o s e and c e l l u l o s e f r a c t i o n s , r e s p e c t i v e l y . A previous study i n our l a b o r a t o r y revealed a good c o r r e l a t i o n between c a l o r i f i c values of the p y r o l y s i s products and t h e i r carbon c o n t e n t s , as shown i n Figure 7 (12). The TEA data can thus be used f o r c a l c u l a t i n g the heat content o f the v o l a t i l e s . An example i s given i n F i g u r e 8 (13), which shows the o r i g i n a l TEA data on the s c a l e on the l e f t and the converted heat values on the r i g h t f o r Douglas f i r needles before and a f t e r a sequence of e x t r a c t i o n s . P a r t Β of t h i s f i g u r e i s the o r i g i n a l cumulative d a t a , and Part A i s the data c a l c u l a t e d f o r d i f f e r e n t temperature i n t e r v a l s . This data i s important i n terms of p r e d i c t i n g the f l a m m a b i l i t y of the samples, s i n c e i t r e f l e c t s the f r a c t i o n of the t o t a l heat content a c t u a l l y made a v a i l a b l e through gas phase com b u s t i o n to propagate the f i r e . The c h a r r i n g o f c e l l w a l l polysaccharides i n v o l v e s a s e r i e s o f r e a c t i o n s i n c l u d i n g d e h y d r a t i o n , condensation and c a r b o n i z a t i o n . The dehydration and the e f f e c t of a c i d i c a d d i t i v e s i n p r o moting dehydration have been d i s c u s s e d . The dehydration products f u r t h e r undergo condensation r e a c t i o n s , e s p e c i a l l y i n the p r e sence o f Z n C l . The unique e f f e c t of ZnClo on promoting conden s a t i o n r e a c t i o n s i s i l l u s t r a t e d i n F i g u r e 9 {S) which shows that the a d d i t i o n of Z n C l s i g n i f i c a n t l y reduces the evaporation of levoglucosenone by promoting the condensation o f t h i s dehy d r a t i o n product to n o n v o l a t i l e m a t e r i a l s that are charred on f u r t h e r h e a t i n g . The c a r b o n i z a t i o n r e a c t i o n s i n v o l v e f u r t h e r e l i m i n a t i o n o f the s u b s t i t u e n t s , production o f s t a b l e f r e e r a d i c a l s and formation of new carbon bonds on f u r t h e r h e a t i n g . A study of the temperature dependence of f r e e r a d i c a l form a t i o n o f wood and i t s three major components by ESR i s shown i n Figures 10-13. This data i n d i c a t e s that up t o 3 5 0 ° , the f r e e r a d i c a l s formed from heating of wood are mainly from c e l l w a l l polysaccharides. L i g n i n , at t h i s temperature range, generates very small concentrations of f r e e r a d i c a l s . The a d d i t i o n of a c i d i c a d d i t i v e s lowers the decomposition temperature o f wood and i t s components, i n c l u d i n g 1 i g n i n . However, they promote f r e e r a d i c a l formation o n l y i n the c e l l wall p o l y s a c c h a r i d e s , not i n l i g n i n . An exception i s Z n C l which produces a s l i g h t increase i n f r e e r a d i c a l formation i n f i g n i η at temperatures above 3 0 0 ° . 2

9

2

2


SHAFizADEH

AND

Thermal

CHIN

Deterioration

65


5.

î

Figure 7.

I

I

30

40

I

1

50 60 P e r c e n t Carbon

I

70

Heat of combustion at 4O0°C vs. percent carbon: V • char, Ο vohtiles

fuels,


WOOD TECHNOLOGY:

CHEMICAL

ASPECTS


ËS BEFORE REMOVAL OF EXTRACTIVES Π AFTER REMOVAL OF ETHER EXTRACTIVES Μ AFTER REMOVAL OF TOTAL EXTRACTIVES

100

200

300

400

500

TEMPERATURE (*C) • BEFORE REMOVAL OF EXTRACTIVES • AFTER REMOVAL OF ETHER EXTRACTIVES • AFTER REMOVAL OF TOTAL EXTRACTIVES

3500

2500

8 ο 1500

S 500

300

500

TEMPERATURE ( C) e

Figure 8. Evolution of carbon and heat from Douglas-fir foliage (A) in tem perature intervals and (B) cumulative, based on dry weight of the unextracted sample


In Wood Technology: Chemical Aspects; Goldstein, I.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. (degrees)

Figure 9. Thermal analysis of levoglucosenone samples: (a) neat, (b) -\-5% zinc chloride, (c) + 5 % diammonium phosphate, and (d) + 5 % diphenyl phosphate (D.t.a., differential thermal analysis; T.g., thermogravimetry; D.t.g., derivative of thermogravimetry)

Temperature


CHEMICAL

ASPECTS


WOOD TECHNOLOGY:

Jo

i


55

.BP


Figure 11.

The rate of free radical formation (—A—)

(«Ο

and weight loss ( — Δ — )

Temp,

on heating xylan and treated xylan


CD

pi


Figure 12.


(«Ο

and weight loss ( — Δ — )

Temp.

on heating of lignin and treated lignin



Figure 13.


(«ς)

and weight loss (--A--)

Temp,

on heating of wood and treated wood



72

WOOD TECHNOLOGY:

CHEMICAL

ASPECTS

This i n d i c a t e s t h a t the thermal decomposition o f 1 i g n i n at temperatures below 350° i s h e t e r o l y t i c , most 1 i k e l y o c c u r r i n g by the cleavage o f s i d e c h a i n s . This i s true i n neat 1 i g n i n as w e l l as i n the presence o f a c i d c a t a l y s t s . However, the r a t e of f r e e r a d i c a l formation of l i g n i n samples increases s h a r p l y at 3 5 0 ° , i n d i c a t i n g the homolytic f i s s i o n o f l i g n i n predominates at h i g h er temperatures. The ESR data from c e l l w a l l polysaccharides shows a twostage f r e e r a d i c a l f o r m a t i o n ; a low temperature f r e e r a d i c a l formation stage which corresponds to the i n i t i a l decomposition of the carbohydrate polymers, and a high temperature f r e e r a d i c a l formation stage which corresponds t o the f i n a l c h a r r i n g r e a c t i o n s between 300 and 3 5 0 ° . This two-stage f r e e r a d i c a l forma t i o n phenomena i s e s p e c i a l l y c l e a r f o r the Z n C ^ t r e a t e d x y l a n sample. This i s due to the low decomposition temperature f o r t h i s sample, which produces a c l e a r separation between these two s t a g e s . These phenomena i n d i c a t e t h a t during the i n i t i a l decomposition o f carbohydrate polymers, the h e t e r o l y t i c r e a c t i o n s , such as t r a n s g l y c o s y 1 a t i o n , are accompanied by homolytic react i o n s . The low temperature f r e e r a d i c a l formation i s probably a s s o c i a t e d with the dehydration and e l i m i n a t i o n r e a c t i o n s and the condensation of unsaturated p r o d u c t s . The increased r a t e of high temperature f r e e r a d i c a l formation i n c e l l w a l l polysacchar i d e s i s accompanied by a small weight l o s s , i n d i c a t i n g t h a t t h i s f r e e r a d i c a l formation i s caused by c r a c k i n g of the bonds i n the char substrate r a t h e r than by cleavage of the s u b s t i t u e n t s . The f r e e r a d i c a l formation i n wood i s roughly the summation of t h a t f o r i t s three major components. Tables V I I I and IX are a b r i e f summary o f r e s u l t s from work r e l a t e d to the use o f c e l l u l o s i c f u e l s as an energy source, both i n terms of propagation o f f i r e and as a renewable a l t e r n a t i v e energy source. Table V I I I shows the heats of combustion o f the f u e l and i t s p y r o l y s i s p r o d u c t s . Table IX shows the d i s t r i b u t i o n of the heat content i n the v o l a t i l e and char f r a c t i o n s . The energy released i n the gas phase i s much higher f o r c e l l u l o s e than f o r l i g n i n , although the heats o f combustion o f l i g n i n and i t s gaseous p y r o l y s i s products are much higher than those o f c e l l u l o s e . Consequently, softwood, although i t s heat of combustion i s over 500 cal/g more than that o f hardwood, produces very l i t t l e more heat i n the gas phase. This i s because the higher o r i g i n a l heat content o f softwood i s due t o i t s higher l i g n i n content. These data a l s o c l e a r l y p o i n t out the value o f these f u e l s as an energy source, e i t h e r a f t e r c a r b o n i z a t i o n or i n t h e i r o r i g inal state.


5.

SHAFizADEH

and

chin

Thermal

Deterioration

73

Appendix


TABLE I.

ANALYSIS OF THE PYROLYSIS PRODUCTS OF CELLULOSE AT 300° UNDER NITROGEN

Condition

Atm. pressure

1.5 Mm Hg, 5% S b C l

1.5 Mm Hg

3

Char

34.2%

17.8%

25.8%

Tar

19.1

55.8

32.5

levoglucosan

3.57

28.1

6.68

1,6-anhydro-e-Ilglucofuranose

0.38

5.6

0.91

trace

trace

2.68

^-glucose hydro!yzable material s

TABLE I I .

6.08

11.8

20.9

YIELDS OF LEVOGLUCOSENONE FROM THE PYROLYSIS OF DIFFERENT MATERIALS AT 3 5 0 ° *

Material

Neat

(55)

5% H P0 - t r e a t e d 3

4

Cellulose

1.2

11.1

Starch

0.3

9.0

Newsprint (with ink)

Tb

9.1

K r a f t shopping bags

Τ

10.2

a.

Determined by p y r o l y z i n g 5 mg samples and d i r e c t l y the v o l a t i l e s by GLC.

b.

Τ = t r a c e amount.

(%)

analyzing


74

WOOD

TABLE I I I .

PYROLYSIS PRODUCTS OF CELLULOSE AND TREATED CELLULOSE AT 600°

Product


TECHNOLOGY: CHEMICAL ASPECTS

Neat

Acetaldehyde

1.5

Furan

+5% H P 0 3

4

+5% ( N H ) H P 0 4

2

4

+5% ZnCl 2

0.9

0.4

1.0

0.7

0.7

0.5

3.2

Propenal

0.8

0.4

0.2

Τ

Methanol

1.1

0.7

0.9

0.5

Τ

0.5

0.5

2.1

2.0

2.0

1.6

1.2

2.8

0.2

Τ

0.4

Acetic acid

1.0

1.0

0.9

0.8

2-Furaldehyde

1.3

1.3

1.3

2.1

5-Methyl-2furaldehyde

0.5

1.1

1.0

0.3

Carbon dioxide

6

5

6

3

11

21

26

23

5

24

35

31

66

41

26

31

2-Methylfuran 2,3-Butanedione l-Hydroxy-2- . propanone I J

Glyoxal

Water Char Balance

(tar)

a

Percentage, y i e l d based on the weight of the sample; Τ = trace amounts.


SHAFizADEH

AND


TABLE IV.

CHIN

Thermal

Deterioration

PYROLYSIS PRODUCTS OF XYLAN AND TREATED XYLAN AT 300°

Product

Neat

Liquid condensate

30.6

+10X Z n C l

a

45.3

7.9

7.5

Char

31.1

42.2

Tar

15.7

3.2

Carbon dioxide

High mol. wt. component

(17)*

D-xylose from hydrolysis

(54)

2

C

Percentage, y i e l d based on the weight of the sample. ^Based on the weight of the tar 'Based on the weight of oligosaccharides.


76

WOOD TECHNOLOGY:

TABLE V.

Neat

Xylan +10% Z n C l

2

0-Acetylxylan +10% ZnCl Neat

0.1

1.0

1.9

Τ

2.0

2.2

3.5

0.3

Τ

1.4

Τ

1.3

1.0

1.0

1.0

Τ

Τ

Τ

Τ

1-Hydroxy-2propanone

0.4

Τ

0.5

Τ

3-Hydroxy-2butanone

0.6

τ

0.6

Τ

Acetic acid

1.5

τ

10.3

9.3

2-Furaldehyde

4.5

2.2

5.0

Carbon d i o x i d e

8

7

8

6

Water

7

21

14

15

10

26

10

23

64

32

49

35

Acetaldehyde

2.4

Furan Acetone

^

Propionaldehyde Methanol 2,3-Butanedione

Char Balance

ASPECTS

PYROLYSIS PRODUCTS OF XYLAN AND TREATED XYLAN AT 500*

Product


CHEMICAL

(tar)

a

10.4

Percentage, y i e l d based on the weight of the sample; Τ = trace amounts.


2


12 20 15 55

water, methanol, acetone, acetic a d d

phenolic compounds

carbonaceous residue

Liquid

Tar

Char

Yield

carbon monoxide, méthane» carbon d i o x i d e , ethane

Products

PYROLYSIS PRODUCTS OF LIGNIN AT 450-550°

Volatile

Fraction

TABLE V I .


(Ï)

WOOD TECHNOLOGY:

78


TABLE V I I .

CHEMICAL

PYROLYSIS PRODUCTS OF WOOD AND TREATED WOOD AT 600° +52

ZnCl

Product

Neat

Acetaldehyde

2.3

Furan

1.6

7.9

1.5

0.9

Propenal

3.2

0.9

Methanol

2.1

2.7

Acetone

%

Propionaldehyde

J

a

4.4

2>

2-Methylfuran

b

2,3-Butanedione

2.0

1.0

1-Hydroxy-2-propanone

2.1

Τ

Glyoxal

2.2

Τ

Acetic acid

6.7

5.4

2-Furaldehyde

1.1

5.2

Formic acid

0.9

0.5

5-Methyl-2-furaldehyde

0.7

0.9

2-Furfuryl alcohol

0.5

Τ

Carbon dioxide

12

6

Water

18

18

Char

15

24

28

22

Balance

ASPECTS

(tar)

Percentage, y i e l d based on the weight of the sample; Τ = trace amounts. ^Not c l e a r l y i d e n t i f i a b l e for wood.


2

SHAFiZADEH

AND

CHIN

Thermal

Deterioration


5.


79


Douglas F i r

Populus ssp.

Softwood

Hardwood

heated at 400° for 10 min.

Klason

Lignin

a

-4375

F i l t e r paper

Cellulose

-1546

-1987

-1050

Type

Source

a

Char ( c a l / g fuel)

-3072

-3169

-1995

-3093

a

Gas ( c a l / g fuel)

-4618

-5156

-6370

-4143

Total (cal/g)

DISTRIBUTION OF THE HEAT OF COMBUSTION OF WOOD AND ITS COMPONENTS

Fuel

TABLE I X .


5. SHAFIZADEH AND CHIN

81

Thermal Deterioration

Literature Cited 1.

Seborg, R.M., Tarkow, Η., and Stamm, A.J., J. Forest Prod. Res.

2.

16, 3.

Soc.,

(1953),

3,

59.

Shafizadeh, F. and McGinnis, G.D., Carbohyd. Res.,

(1971),

273-277.

Shafizadeh, F. and Fu. Y.L., Carbohyd. Res.,

(1973),

29,


113-122.

4.

Halpern, Y., Riffer, R., and Broido, A., J. Org. Chem.,

5.

Shafizadeh, F. and Chin,

(1973),

38,

204-209.

P.P.S.,

Carbohyd. Res.,

(1976),

46,

149-154. 6.

7.

Fung, D.P.C., Wood Science, ( 1 9 7 6 ) , 9, 5 5 - 5 7 . Broido, A., Evett, Μ., and Hodges, C.C., Carbohyd. ( 1 9 7 5 ) , 44,

Res.,

267-274.

8.

Chin, P.P.S., Ph.D. Dissertation, University of Montana

9.

Shafizadeh, F., McGinnis, G.D., and Philpot, C.W., Carbohyd.

(1973). Res.,

10. 11.

(1972),

25,

23-33.

A l l a n , G.G. and M a t t i l a , T., Lignins, Sarkanen, K.V. and Ludwig, C.H., Eds., Wiley-Interscience Publishers, New York, 1 9 7 1 , p. 5 7 5 . Philpot, C.W., Ph.D. Dissertation, University of Montana (1970).

12. 13.

Susott, R.A., DeGroot, W.F., and Shafizadeh, F. J. Fire and Flammability, ( 1 9 7 5 ) , 6 , 3 1 1 - 3 2 5 . Shafizadeh, F., Chin, P.P.S., and DeGroot, W.F., Forest Science, in press.


Wood Technology: Chemical Aspects

Recommend Documents