Effects of Reaction Conditions on the Aqueous ... - ACS Publications

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch007

Effects of Reaction Conditions on the Aqueous Thermochemical Conversion of Biomass to Oil P. M . MOLTON, R. K. MILLER, J. A. RUSSELL, and J. M . DONOVAN Batelle Pacific Northwest, P.O. Box 999, Richland, WA 99352

Thermochemical liquefaction of biomass is basically a simple process whereby it is heated with alkali under pressure at temperatures up to 400°C. This simple procedure converts the biomass to a mixture of gas (2-10%), char (5-40%). and oil (up to 40%), on a weight basis. It is one of several methods available for conversion of biomass to potential liquid fuels, the others being direct heating of dry matter (destructive distillation, pyrolysis) (1), fermentation (or anaerobic digestion) (2), and gasification (partial oxidation) (3) followed by liquefaction to methanol. There are variants on all of these processes. The most interesting variant on the basic thermochemical liquefaction process involves the addition of an overpressure of carbon monoxide and hydrogen to the reaction, which is also performed in a non-aqueous solvent (anthracene oil or recycled product oil). Yields of oil up to 70% of the weight of the Douglas fir wood feedstock have been reported in an investigation by Elliott (4-8), Elliott and Walkup (9) and Elliott and Giacoletto (10). This process variant (also known as the Albany, PERC, or CO-Steam Process) is described in more detail in the Results and Discussion section. The t h e r m o c h e m i c a l l i q u e f a c t i o n process a n d its variants are of interest because t h e y appear t o have several a d v a n t a g e s over t h e o t h e r m e t h o d s . T he y d o n o t require p r e l i m i n a r y d r y i n g o f t h e f e e d s t o c k ; t h e y operate at a

0O97-6156/81/0144-0137$06.50/0 © 1981 American Chemical Society

Klass; Biomass as a Nonfossil Fuel Source ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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relatively l o w t e m p e r a t u r e ; a n d t h e y c o n v e r t all of t h e biomass. leaving o n l y a relatively small u n u s a b l e residue w h i c h is as little as 5% of t h e feedstock. In a d d i t i o n , t h e c r u d e l i q u i d p r o d u c t separates s p o n t a n e o u s l y f r o m t h e a q u e o u s phase after t h e reaction. Historically, t h e a q u e o u s d e g r a d a t i o n of b i o m a s s in t h e f o r m of n e w s p r i n t or c o t t o n w a s e x a m i n e d by Berl a n d S c h m i d t (11-13) a n d Berl. S c h m i d t , a n d Koch (14). a n d by others w h o w e r e p r i m a r i l y interested in t h e m e c h a n i s m of g e o l o g i c a l f o r m a t i o n of coal f r o m plant material (e.g.. 15). T h e alkaline reaction of cellulose w a s f u r t h e r i n v e s t i g a t e d by a series of a u t h o r s , n o t a b l y S a m u e l s o n (16-28) a n d H e i n e m a n n (29). T h e reactions of cellulose at t e m p e r a t u r e s u p t o 180°C have long been of interest in t h e paper p u l p i n g i n d u s t r y . A l t h o u g h c o n d i t i o n s in p u l p i n g have s o m e relevance t o t h e c o n v e r s i o n of cellulose t o o i l . as d i s c u s s e d in m o r e detail later, t h e y are generally m i l d e r (since d i s s o l u t i o n of t h e cellulose is d e f i n i t e l y not required). O t h e r c h e m i c a l s are also a d d e d , s u c h as s o d i u m sulfide in Kraft p u l p i n g , a n d no a t t e m p t is m a d e t o e x c l u d e o x y g e n f r o m t h e reaction. T h e d e v e l o p m e n t of t h e r m o c h e m i c a l l i q u e f a c t i o n t e c h n i q u e s f o r c o n v e r s i o n of b i o m a s s t o oil has been r e v i e w e d by M o l t o n a n d D e m m i t t (30). T h e effect of alkali o n cellulose has been r e v i e w e d by Richards (31) a n d M e l l e r (32). In 1 9 2 4 . W a t e r m a n a n d K o r t l a n d t (33) o b s e r v e d t h a t s e m i c o k e o b t a i n e d f r o m lignite w a s liquefied m o r e rapidly if t h e r e w a s an overpressure of h y d r o g e n a n d / o r c a r b o n m o n o x i d e . Fischer a n d S c h r a d e r (34) o b s e r v e d t h a t s o d i u m f o r m a t e in large a m o u n t s f a c i l i t a t e d t h e l i q u e f a c t i o n of various materials i n c l u d i n g peat a n d cellulose at 4 0 0 ° C . T h e effect of f o r m a t e or c a r b o n m o n o x i d e o n t h e rate of b i o m a s s l i q u e f a c t i o n w a s r e p o r t e d in 1 9 6 0 by A p p e l l , W e n d e r , a n d Miller (35) w o r k i n g at t h e Bureau of M i n e s in P i t t s b u r g h . In a series of p u b l i c a t i o n s (36-40). these a n d o t h e r w o r k e r s at t h e Bureau of M i n e s s h o w e d a d e f i n i t e effect of c a r b o n m o n o x i d e o n t h e alkaline l i q u e f a c t i o n of biomass. A s a result of t h e Bureau of M i n e s w o r k , a pilot p l a n t w a s c o n s t r u c t e d at A l b a n y , O r e g o n . This w a s d e s i g n e d t o liquefy b i o m a s s as a slurry in r e c y c l e d p r o d u c t oil in t h e presence of 5% a q u e o u s s o d i u m c a r b o n a t e at 2 9 0 - 3 7 0 ° C . T h e residence t i m e w a s e s t i m a t e d at 2 0 m i n t o 1 hr in a stirred t a n k reactor. Initially, w o o d f l o u r w a s used as t h e b i o m a s s source, after h a m m e r - m i l l i n g a n d p r e - d r y i n g . T h e p i l o t p l a n t s t a r t e d o p e r a t i o n in 1 9 7 7 . a l t h o u g h s i g n i f i c a n t a m o u n t s of oil p r o d u c t w e r e not o b t a i n e d u n t i l several m o n t h s later. O p e r a t i o n of t h e pilot plant has been d o g g e d by p r o b l e m s of p l u g g i n g and c o r r o s i o n of pipes a n d m e c h a n i c a l difficulties.


7.

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A t t h e t i m e of pilot plant c o m p l e t i o n , o n l y t h e original Bureau of M i n e s w o r k w a s available for e s t i m a t i o n of process parameters. This w o r k w a s used in t h e d e s i g n o f t h e A l b a n y pilot plant. T h u s , t h e original c o n d i t i o n s f o r o p e r a t i n g t h e pilot plant w e r e a s s u m e d , w i t h n o g u a r a n t e e t h a t t h e y w e r e o p t i m u m c o n d i t i o n s . Since pilot plant s t a r t u p , laboratory i n v e s t i g a t i o n s have been p e r f o r m e d in s u p p o r t of t h e pilot plant (4-10). a n d have i n c l u d e d w o r k o n process o p t i m i z a t i o n .


For s o m e years w e have been w o r k i n g o n t h e d e t e r m i n a t i o n o f t h e c h e m i s t r y i n v o l v e d in biomass l i q u e f a c t i o n , u s i n g pure cellulose (Solka-floc) as o u r initial m o d e l (41-43). W e believe t h a t a c o m p a r i s o n of o u r results u s i n g pure cellulose in an a q u e o u s s y s t e m , w i t h results o b t a i n e d in a closer s i m u l a t i o n of t h e A l b a n y pilot plant c o n d i t o n s . is useful in p r e d i c t i n g s o m e o f t h e c o m p l e x c h e m i s t r y o c c u r r i n g in t h e pilot plant. A m o r e d i r e c t c o m p a r i s o n u s i n g w o o d substrate

a n d recycle oil is d i f f i c u l t

d u e t o t h e great

complexity and

v a r i a b i l i t y in t h e s y s t e m . In t h i s paper, w e report t h e results of s o m e of o u r e x p e r i m e n t s o n t h e v a r i a t i o n o f reaction p a r a m e t e r s a n d p r o d u c t f o r m a t i o n f r o m pure cellulose in an a q u e o u s s y s t e m closely related t o t h e A l b a n y pilot plant c o n d i t o n s . MATERIALS AND METHODS T h r o u g h o u t this w o r k w e used pure cellulose (Solka-floc; B r o w n Co., NJ) as our m o d e l biomass source because of its h i g h purity. Use of n e w s p r i n t or w o o d w o u l d have m a d e o u r results d i f f i c u l t t o r e p r o d u c e d u e t o t h e h e t e r o g e n i t y of s u c h materials. T h e effect o f t h e l i g n i n c o m p o n e n t o f w o o d on t h i s l i q u e f a c t i o n process is b e i n g i n v e s t i g a t e d in a separate series of e x p e r i m e n t s . T h e Solka-floc t h a t w e o b t a i n e d w a s o f 9 5 . 8 % p u r i t y , a n d c o n t a i n e d w a t e r (3.9%), ash (0.3-0.5%) a n d n i t r o g e n (0.004-0.0034%). Solkafloc o f t h e g r a d e used b y us c o n t a i n s over 9 0 % alpha-cellulose, is greater t h a n 5 0 % crystalline, a n d consists o f a 3:1 m i x t u r e of fibers w i t h degree of p o l y m e r i z a t i o n (DP) o f 6 0 0 a n d 1 1 0 0 . The average DP is therefore a b o u t 7 5 0 , c o m p a r i n g w i t h Douglas f i r cellulose o f DP a b o u t 8 0 0 . T h e degree o f c r y s t a l l i n i t y (44) a n d t h e DP v a l u e (45.46) have b o t h been s h o w n t o exert h i g h l y s i g n i f i c a n t effects o n t h e rate o f d e g r a d a t i o n of cellulose. A n h y d r o u s s o d i u m c a r b o n a t e (Fisher c e r t i f i e d ACS grade) w a s of m i n i m u m 9 9 % p u r i t y . A l l w a t e r w a s d i s t i l l e d , a n d all solvents w e r e o f a n a l y t i c a l reagent grade. E x p e r i m e n t s t o d e t e r m i n e t h e effect o f c a r b o n m o n o x i d e o n oil p r o d u c t yield w e r e p e r f o r m e d in 2.5 a n d 10 g a l l o n a u t o c l a v e s ; e x p e r i m e n t a l c o n d i t i o n s are s h o w n in Table I. Cellulose, s o d i u m c a r b o n a t e , a n d w a t e r w e r e m i x e d in a 3 0 % cellulose slurry, a n d t h e slurry w a s p o u r e d into t h e a u t o c l a v e , w h i c h w a s



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t h e n sealed a n d f l u s h e d w i t h pure n i t r o g e n for 5 m i n t o e x c l u d e o x y g e n . T h e a u t o c l a v e w a s t h e n raised t o t h e c o r r e c t t e m p e r a t u r e (heating t i m e 2.5 hr), m a i n t a i n e d at t h i s t e m p e r a t u r e for 2 0 t o 6 0 m i n . a n d c o o l e d (cooling t i m e 3.5 hr). T h e c a r b o n m o n o x i d e , w h e r e a d d e d , w a s a d d e d after t h e n i t r o g e n f l u s h , at 2 5 0 or 5 0 0 psig initial pressure. A f t e r c o o l i n g , t h e gas w a s v e n t e d a n d t h e a u t o c l a v e o p e n e d . T h e a q u e o u s phase w a s separated a n d t h e oil residue a n d c h a r p o u r e d off a n d d r i e d . T h e p r o d u c t oil of c h i e f interest in t h e s e e x p e r i m e n t s w a s o b t a i n e d by a 3-day S o x h l e t e x t r a c t i o n of t h e tar plus c h a r f r a c t i o n , u s i n g a c e t o n e as t h e e x t r a c t i n g solvent. A f t e r r e m o v a l of t h e a c e t o n e u n d e r r e d u c e d pressure, t h e oil y i e l d w a s d e t e r m i n e d o n a w e i g h t basis. T o d e t e r m i n e t h e e f f e c t s of alkali c o n c e n t r a t i o n , final reaction t e m p e r a t u r e , a n d reaction t i m e o n t h e kinetics of t h e o i l - f o r m i n g reactions, a d i f f e r e n t p r o c e d u r e had t o be used. For t h e s e e x p e r i m e n t s , s m a l l reactors w e r e used, of a p p r o x i m a t e l y 7 m l t o t a l v o l u m e . A f t e r m i x i n g t h e cellulose w i t h w a t e r a n d alkali, i n s e r t i n g t h e m i x t u r e i n t o t h e b o m b a n d f l u s h i n g w i t h n i t r o g e n , t h e reactors w e r e i m m e r s e d in a sand b a t h already at t h e c o r r e c t t e m p e r a t u r e . Heating time was thus reduced to 5 min, and cooling time to 7 min, a p r o c e d u r e w h i c h m i n i m i z e d t h e reactions o c c u r r i n g d u r i n g t h e h e a t i n g a n d c o o l i n g periods. H o w e v e r , because of t h e s m a l l a m o u n t s of m a t e r i a l in these reactors, a p r o d u c t y i e l d c o u l d n o t be o b t a i n e d . Instead, t h e o i l - f o r m i n g reactions w e r e m o n i t o r e d by gas c h r o m a t o g r a p h y o n a Perkin-Elmer 9 0 0 i n s t r u m e n t . T h e n u m b e r a n d d i s t r i b u t i o n of volatile p r o d u c t s w e r e used as an index of t h e degree of reaction. Further i d e n t i f i c a t i o n of p r o d u c t s w a s p e r f o r m e d o n a H e w l e t t Packard 5 9 9 2 G C / M S i n s t r u m e n t . A series of e x p e r i m e n t s w a s p e r f o r m e d w i t h t h e s m a l l reactors, based u p o n statistical e x p e r i m e n t a l d e s i g n t e c h n i q u e s . A B o x - B e h n k e n d e s i g n w a s used, w i t h t h e e x p e r i m e n t a l p a r a m e t e r s s h o w n in Tables II t o IV for d e t e r m i n a t i o n of t h e effects of reaction t i m e , t e m p e r a t u r e , a n d alkali c o n c e n t r a t i o n . A f t e r r e a c t i o n , t h e a q u e o u s a n d oil phases w e r e separated a n d e x a m i n e d separately. In t h e s e e x p e r i m e n t s , for p u r p o s e s of c o m p a r i s o n of p r o d u c t d i s t r i b u t i o n as a f u n c t i o n of t h e variable e x p e r i m e n t a l parameter, t h e GC t r a c e of t h e u n t r e a t e d a q u e o u s phase w a s used. Further w o r k is b e i n g p e r f o r m e d t o i d e n t i f y t h e o r g a n i c c o m p o n e n t s of t h e p r o d u c t oils a n d a q u e o u s phases t o d e t e r m i n e t h e r e a c t i o n m e c h a n i s m s i n v o l v e d in oil f o r m a t i o n . A q u e o u s phase c o m p o n e n t s w e r e f o u n d t o be similar in c o m p o s i t i o n t o m o s t oil c o m p o n e n t s , b u t are better resolved o n t h e GC. There is a possibility t h a t higher m o l e c u l a r w e i g h t oil c o m p o n e n t s m a y c h a n g e i n d e p e n d e n t l y of l o w e r m o l e c u l a r w e i g h t c o m p o n e n t s , b u t w e have no w a y of t e s t i n g t h i s as t h e s e p a r a t i o n a n d i d e n t i f i c a t i o n of h i g h m o l e c u l a r w e i g h t materials in s u c h a c o m p l e x m i x t u r e are b e y o n d o u r c u r r e n t a n a l y t i c a l capabilitites.


MOLTON ET A L .

Oil from Biomass


Table 1. EFFECT OF CARBON MONOXIDE ON CELLULOSE LIQUEFACTION • Pressure Alkali Cone. (psig) (N) 0 0.3 0 0.3 0 0.3 250 0.3 250 0.3 250 0.3 0 0.6 0 0.6 0 0.6 0 0.6 0 0.6 0 0.6 250 0.6 250 0.6 250 0.6 500 0.6 0 1.18 0 1.18 250 1.18 500 1.18 500 1.18 0 1.79 250 1.79 500 1.79 0 2.37 0 2.37 500 2.38

Final Temp. Time at Temp. (min) (°C) 20 318 350 20 407 60 20 293 300 60 60 332 317 20 337 30 304 60 60 337 60 360 60 385 299 20 20 318 60 359 20 268 307 20 324 20 20 321 20 268 307 20 20 275 20 268 20 275 20 291 20 343 20 270

Yield(%) 31 22 23 14 28 33 31 26 29 29 26 21 34 34 28 26 19 27 33 31 27 18 24 23 4 11 15

* Based on original weight of cellulose added.

Table II. CONDITIONS U8ED FOR ΒΟΧ-ΒΕΗΝΚΕΝ STUDIES OF CELLULOSE LIQUEFACTION, 250-290°C

Run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Temp. (°C) 270 270 270 250 290 290 290 270 250 250 250 290 270 270 270

Time (hr) 1.0 3.5 6.0 3.5 1.0 3.5 6.0 3.5 1.0 3.5 6.0 3.5 1.0 3.5 6.0

[Na C( (N) 0.6 0.3 0.0 0.0 0.3 0.0 0.3 0.3 0.3 0.6 0.3 0.6 0.0 0.3 0.6 2


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T a b l e I I I . C O N D I T I O N S U S E D FOR N O N B O X - B E H N K E N KINETIC STUDIES OF CELLULOSE L I Q U E F A C T I O N , 1 5 0 - 2 3 0 ° Temp.

Time

[Na C0 ]

(C°)

(min)

(N)

1

210

2

210 170 170 150 150 190 190 230 230

45 60 60

0.3 0.3 0.3 0.3 0.3 0.3 0.3


Run

3 4 5 6 7 8 9 10 11

45 45 60 45 60

15 16 17

15 30 60 45 30

210 210 170 170 150 150

18 19 20

3

0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

15 30

190 190 230 230

12 13 14

2

15 15 30 30 15

0.3 0.3

T a b l e I V . C O N D I T I O N S U S E D FOR F I G U R E S O F G C T R A C E S OF CELLULOSE LIQUEFACTION PRODUCTS Temp.

Time

[Na C0 ]

Figure

(°C)

(hr)

(N)

1 a 1 b 1 c 2a 2b 2c 3a

270 270 270 150 210 290

1.0 3.5 6.0 1.0 1.0 1.0

270 270 270 270

3.5 3.5 6.0 6.0

0.6 0.3 0.6 0.3 0.3 0.3 0.07 0.03 0.6 0.0

3b 4a 4b

2


3

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RESULTS A N D DISCUSSION Effect of Carbon M o n o x i d e T h e results o f 2 7 a u t o c l a v e e x p e r i m e n t s w i t h cellulose are s h o w n in Table I. Oil yields range f r o m 4 % t o 3 4 % of t h e original w e i g h t of cellulose a d d e d , w i t h n o clear p a t t e r n e m e r g i n g . In part t h i s m a y be due t o t h e m a s k i n g effect of 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 f o r t h e autoclaves. Based o n pure cellulose, t h e t h e o r e t i c a l yield of a h y d r o c a r b o n oil ( C H i o ) % Y weight; with 8% o x y g e n , as is c h a r a c t e r i s t i c o f t h e A l b a n y pilot plant p r o d u c t , t h i s is increased t o 55%. Hence, o u r h i g h e s t oil yield is 3 4 / 5 5 X 100, or 6 2 % of t h e o r e t i c a l . L i g n i n a n d h e m i c e l l u l o s e are of m o r e variable c o m p o s i t i o n , b u t t h e t h e o r e t i c a l yields o f oil c o n t a i n i n g 8 % o x y g e n are a b o u t 7 5 % a n d 5 0 % respectively. Based o n t h i s d a t a , a c r u d e e s t i m a t e o f t h e t h e o r e t i c a l oil yield f r o m w o o d c o n t a i n i n g 5 0 % cellulose, 2 5 % l i g n i n , a n d 2 5 % h e m i c e l l u l o s e is 6 0 % . Elliott a n d W a l k u p (9) have presented data for t h e A l b a n y m o d e l s y s t e m s h o w i n g oil yield t o be a f u n c t i o n of c a r b o n m o n o x i d e overpressure in t h e range of 2 5 0 - 1 5 0 0 psig initial pressure, w i t h a m a x i m u m oil yield of 7 0 % . This indicates t h a t a t h e o r e t i c a l oil yield can be a c h i e v e d at h i g h CO overpressure, w i t h t h e possibility of s o m e i n c o r p o r a t i o n o f CO i n t o t h e p r o d u c t a l t h o u g h one e x p e r i m e n t carried o u t w i t h C O d i d not result in C i n c o r p o r a t i o n into t h e oil p r o d u c t . i s

5

1

b


6

1 4

1 4

Elliott (7) has reported s o m e e x p e r i m e n t s using w o o d flour, l i g n i n , a n d cellulose w i t h o u t a n y a d d i t i o n of CO. A t 3 5 0 ° C final t e m p e r a t u r e f o r 1 hr, w i t h 1 8 % s u b s t r a t e slurry, t h e oil yields w e r e 3 9 , 2 3 , a n d 3 0 % respectively. T h e result w i t h cellulose is in a g r e e m e n t w i t h our d a t a . T h e effect of c a r b o n m o n o x i d e a d d i t i o n t o a n a q u e o u s s y s t e m w i t h a 3 0 % cellulose slurry w a s t o increase oil yield b y o n l y 3 - 4 % in o u r e x p e r i m e n t s , u p t o 5 0 0 psig initial CO pressure. This is also in a g r e e m e n t w i t h Elliott's data. T h e C O - e n h a n c e m e n t effect o n oil yield is t h u s barely n o t i c e a b l e w i t h cellulose at CO pressures b e l o w 5 0 0 psig. The o n l y o t h e r n o t i c e a b l e effect o f v a r i a t i o n of t h e e x p e r i m e n t a l parameters s h o w n (Table I) is a n e g a t i v e effect of h i g h alkali c o n c e n t r a t i o n o n oil y i e l d , w h e n t h e s o d i u m c a r b o n a t e c o n c e n t r a t i o n is raised t o 2.37 Ν (12.6%) at 2 7 0 3 4 3 ° C . This is c o u n t e r t o Elliott a n d Giacoletto's results (10). T h e effect of alkali o n cellulose c h a i n peeling a n d cleavage w a s f o u n d t o be d i r e c t l y p r o p o r t i o n a l t o alkali c o n c e n t r a t i o n at l o w e r t e m p e r a t u r e s (185°C) (47). Since h i g h alkali c o n c e n t r a t i o n s favor t h e h y d r i d e - transfer m e d i a t e d Cannizzaro reaction t o yield acid salts a n d alcohols f r o m a l d e h y d e s and some ketones, w e s u g g e s t t h a t perhaps t h e l o w e r oil yield m a y be d u e t o removal of c a r b o n y l i n t e r m e d i a t e s f r o m t h e reaction.


144


SOURCE

Because of t h e m a s k i n g effect of l o n g h e a t i n g a n d c o o l i n g t i m e s in large a u t o c l a v e s ( 2 . 5 , 1 0 gallon), w e c o n t i n u e d o u r e x p e r i m e n t s in small reactors of 7 m l t o t a l v o l u m e . This p e r m i t t e d us t o a c h i e v e short h e a t i n g a n d c o o l i n g t i m e s , b u t because of t h e small a m o u n t of reactants. p r e v e n t e d us f r o m assessing oil yields. Since w e are c u r r e n t l y interested in reaction c h e m i s t r y , t h i s w a s not c o n s i d e r e d an o v e r r i d i n g d i s a d v a n t a g e . W e w e r e able

to

e s t i m a t e t h e degree of cellulose c o n v e r s i o n f r o m t h e gas c h r o m a t o g r a p h traces of t h e p r o d u c t s , as s h o w n b e l o w , b u t t h e s e d o n o t represent a Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch007

q u a n t i t a t i v e yield e s t i m a t e . Effect of Reaction Time Figure I s h o w s t h e GC traces o b t a i n e d f r o m d i r e c t i n j e c t i o n of λμί q u a n t i t i e s of t h e a q u e o u s phases f r o m t h r e e e x p e r i m e n t s . W e c h o s e t o use t h e a q u e o u s phases because t h e y c o n t a i n l o w e r m o l e c u l a r w e i g h t materials t h a n t h e oils, a n d h e n c e p r e s u m a b l y p r o d u c t s f o r m e d earlier in t h e oil g e n e r a t i o n reaction s e q u e n c e , a n d because t h e a q u e o u s phases g i v e cleaner GC traces t h a n t h e oils, w h i c h are very d i f f i c u l t t o resolve.Only m i n o r differences are n o t i c e a b l e b e t w e e n t h e traces f r o m r e a c t i o n s carried o u t for 1,3.5. a n d 6 hr at a c o n s t a n t t e m p e r a t u r e of 2 7 0 ° C . T h i s t e m p e r a t u r e is m u c h l o w e r t h a n t h e t e m p e r a t u r e n o r m a l l y used in w o o d l i q u e f a c t i o n (370°). y e t m o s t of t h e cellulose w a s dissolved. T h e yield of c h a r or insoluble residue w a s generally less t h a n 2 0 % of t h e w e i g h t of cellulose a d d e d . Effect of Reaction Temperature T h e GC traces f r o m t h r e e e x p e r i m e n t s r u n at t e m p e r a t u r e s of 150. 2 1 0 . a n d 2 9 0 ° C a n d c o n s t a n t t i m e (1 hr). alkali c o n c e n t r a t i o n of (0.30 N), a n d w i t h o u t c a r b o n m o n o x i d e , are s h o w n in Figure II. A t t h e t w o l o w e r t e m p e r a t u r e s t h e m o s t noticeable feature is a pair of large peaks close t o t h e i n j e c t i o n point. One of these has been i d e n t i f i e d as a c e t o n e . T h e q u a n t i t y of a c e t o n e is less at t h e higher t e m p e r a t u r e 2 9 0 ° C . w h i c h i n c i d e n t a l l y is t h e l o w e s t o p e r a t i n g t e m p e r a t u r e at A l b a n y . T h e r e m a i n d e r of t h e peaks are p r o d u c t s d e r i v e d in part f r o m c o n d e n s a t i o n of a c e t o n e u n d e r alkaline c o n d i t i o n s (Aldol c o n d e n s a tion), a n d increase in a m o u n t w i t h increasing t e m p e r a t u r e , a l t h o u g h t h e d i s t r i b u t i o n remains relatively c o n s t a n t . T h e c o n c l u s i o n s t o be r e a c h e d f r o m these e x p e r i m e n t s are clear: Acetone is an early major product from cellulose, is produced at a much lower temperature than generally assumed (150°C and above), and then condenses to other products in a series of reactions which are constant over the range 150-290°C T h e nature of these reactions is still b e i n g e l u c i d a t e d , a l t h o u g h it appears t h a t a c e t o n e is o n l y one of at least t h r e e major small m o l e c u l e i n t e r m e d i a t e s leading t o t h e f o r m a t i o n of oil, t h e others b e i n g acrolein a n d a c e t o i n . A t t h e l o w e r reaction


Figure 1. Effect of reaction time




146

BIOMASS AS A N O N F OSSIL F U E L

2a

150°C

Figure 2.

Effect of temperature


SOURCE

7.

MOLTON ET A L .

Oil from Biomass

147

t e m p e r a t u r e s 150°C a n d 2 0 0 ° C . very little cellulose w a s dissolved (it w a s merely b r o w n e d ) . T h e volatile p r o d u c t s o b s e r v e d a c c o u n t for an e s t i m a t e d 2 3% o f t h e t o t a l c a r b o n in t h e reactor.


Effect of Alkali Concentration A level o f 5% s o d i u m c a r b o n a t e based o n o r g a n i c feed material is used at A l b a n y . T h e a q u e o u s s t r e a m is a d d e d t o t h e reaction m i x t u r e as 2 0 w t % c a r b o n a t e i n w a t e r . Because t h e A l b a n y s y s t e m is m a i n l y n o n - a q u e o u s , t h e a c t i v i t y o f t h e s o d i u m c a r b o n a t e is u n k n o w n . A t t h e o p e r a t i n g t e m p e r a t u r e of t h e A l b a n y reactor, t h e a m o u n t o f l i q u i d w a t e r r e m a i n i n g has n o t been d e t e r m i n e d ; t h e s o d i u m c a r b o n a t e m a y be dispersed in t h e oil vehicle. Some w a t e r is p r o d u c e d d u r i n g t h e l i q u e f a c t i o n process, a n d s o m e acidic materials w h i c h w i l l react w i t h c a r b o n a t e are p r o d u c e d , so t h e c h e m i c a l f o r m a n d a c t i v i t y o f t h e c a t a l y s t is d i f f i c u l t t o d e t e r m i n e i n t h e A l b a n y process. O u r reactions w e r e all carried o u t in t h e a q u e o u s s y s t e m , so t h e s o d i u m c a r b o n a t e is readily available f o r reaction at t h e a d d e d c o n c e n t r a t i o n , rather t h a n at s o m e u n d e t e r m i n e d l o w e r c o n c e n t r a t i o n . In t w o e x p e r i m e n t s s h o w n in Figure III, s o d i u m c a r b o n a t e c o n c e n t r a t i o n s o f 0.07 a n d 0.30 Ν resulted in r o u g h l y t h e same total volatile o r g a n i c material c o n c e n t r a t i o n in t h e a q u e o u s phase o f t h e p r o d u c t . There are s o m e differences in relative p r o d u c t c o n c e n t r a t i o n s , b u t t h e overall GC traces are very similar. A c t u a l i d e n t i t y o f each c o m p o n e n t w i l l be c o n f i r m e d b y G C / M S b u t is irrelevant here. In Figure IV, a GC t r a c e at an alkali c o n c e n t r a t i o n o f 0.60 Ν b u t w i t h a reaction t i m e o f 6 hr gave a very similar p r o d u c t d i s t r i b u t i o n t o t h a t o b s e r v e d after 3.5 hr (Figure III). H o w e v e r , a zero alkali c o n c e n t r a t i o n (Figure IVa) resulted in o n l y traces o f p r o d u c t u n d e r t h e same c o n d i t i o n s . T h e c o n c l u s i o n s f r o m t h i s series o f e x p e r i m e n t s are also clear: Alkali c o n c e n t r a t i o n has little effect o n t h e l i q u e f a c t i o n reaction over t h e range 0.07 t o 0.6 N. T h e reaction proceeds t o t h e same p r o d u c t s at c o n c e n t r a t i o n s as l o w as 0.07 N. T h e presence o f s o m e alkali is necessary f o r t h e reaction t o p r o c e e d , even t h o u g h in all o f o u r e x p e r i m e n t s , t h e p H at t h e c o n c l u s i o n o f t h e e x p e r i m e n t d r o p p e d t o t h e acid side (5-6 on average). Results o b t a i n e d b y Lai a n d Sarkanen (47) s h o w e d t h a t t h e rate o f cellulose d e g r a d a t i o n is d i r e c t l y p r o p o r t i o n a l t o t h e alkali c o n c e n t r a t i o n . Elliott a n d G i a c o l e t t o U 0 ) have also e x a m i n e d t h e effect o f s o d i u m c a r b o n a t e c o n c e n t r a t i o n in t h e oil-based l i q u e f a c t i o n s y s t e m a n d have s h o w n n o c h a n g e i n alkali effect over t h e range o f 6 - 1 8 % a d d i t i o n b y w e i g h t . They e s t i m a t e t h a t a c o n c e n t r a t i o n o f 3 % m a y be p r a c t i c a b l e before a n adverse effect o n l i q u e f a c t i o n is o b s e r v e d , w h i l e o u r l o w e s t value o f 0.07 Ν (0.37%) is a l m o s t 10x l o w e r t h a n t h i s in t h e c e l l u l o s e / w a t e r s y s t e m .

Menem Chemlol Society Library

16ft ft. N. w. Klass;1155 Biomass as a Nonfossil Fuel Source ACS Symposium Series; American Chemical WetMagtot, 0. C. Society: 20038Washington, DC, 1981.


B I O M A S S AS A N O N F O S S I L

3i

FUEL

3.5 HR / 0.30AUCALI

Figure 3.

4a

6HR

Effect of alkali (3.5 h)

0 ALKALI

Figure 4.

Effect of zero and 0.6Ή alkali


SOURCE

7.

MOLTON

ET AL.

149

Oil from Biomass

A great deal o f w o r k has been d o n e o n t h e effect of a q u e o u s alkali o n cellulose, f r o m t h e v i e w p o i n t of t h e p u l p i n g i n d u s t r y (e.g.. 1 6 - 2 8 , 4 8 - 5 9 ) . T h e m i n o r o r g a n i c volatile p r o d u c t s o b s e r v e d here at similar t e m p e r a t u r e t o t h o s e used

in Kraft

pulping

(150-180°C)

eventually

lead t o colored

product

f o r m a t i o n , w h i c h is o f c o n c e r n t o t h e paper industry. T h e f o r m a t i o n o f a c e t o n e f r o m cellulose has long been k n o w n . Generally, m o s t interest has been s h o w n in t h e nature of t h e residual cellulose after alkali t r e a t m e n t , n o t in t h e nature o f t h e volatiles. From t h e v i e w p o i n t

of d e t e r m i n i n g t h e


c h e m i s t r y o f oil f o r m a t i o n f r o m cellulose, t h e i n t e r m e d i a t e volatile p r o d u c t s are a l l - i m p o r t a n t a n d t h e residual cellulose is of little interest. In o u r v i e w , t h e e c o n o m i c s o f t h e A l b a n y pilot plant c o u l d be i m p r o v e d s o m e w h a t b y using a l o w e r s o d i u m c a r b o n a t e c o n c e n t r a t i o n . This w o u l d also reduce t h e c h a n c e of alkali stress c o r r o s i o n . Oil C o m p o s i t i o n W e are c u r r e n t l y s t u d y i n g t h e v a r i a t i o n in oil p r o d u c t c o m p o s i t i o n a n d a q u e o u s phase o r g a n i c p r o d u c t c o m p o s i t i o n as a f u n c t i o n o f reaction t i m e , t e m p e r a t u r e , a n d alkali c o n c e n t r a t i o n . This w o r k is in its p r e l i m i n a r y stages, a n d should e v e n t u a l l y lead t o a d e t a i l e d u n d e r s t a n d i n g o f t h e c h e m i c a l reactions o c c u r r i n g d u r i n g l i q u e f a c t i o n . A t present, w e have i d e n t i f i e d 7 8 c o m p o n e n t s of t h e oils a n d a q u e o u s phases d e r i v e d f r o m l i q u e f a c t i o n of pure cellulose. These c o m p o u n d s are listed in Table V. They i n c l u d e a w i d e range of a l i p h a t i c a n d a r o m a t i c alcohols, p h e n o l s , h y d r o c a r b o n s , s u b s t i t u t e d furans, a n d a l i c y c l i c c o m p o u n d s . Their i n d i v i d u a l c o n c e n t r a t i o n s are n o r m a l l y less t h a n 1 % o f t h e t o t a l o r g a n i c c o n t e n t o f t h e p r o d u c t . The available e v i d e n c e s u p p o r t s a d e g r a d a t i o n o f cellulose t o a c e t o n e , acrolein, a n d a c e t o i n ( a m o n g o t h e r p r o d u c t s ) . These small m o l e c u l e s t h e n re-condense u n d e r t h e alkaline c o n d i t i o n s o f t h e reaction t o give t h e observed p r o d u c t s . A r o m a t i c h y d r o c a r b o n a n d p h e n o l f o r m a t i o n f r o m these m o l e c u l e s under these c o n d i t i o n s appears t o involve a variant o f t h e A l d o l c o n d e n s a t i o n . These c o n c l u s i o n s w e r e also reached b y Theander, Popoff, a n d c o - w o r k e r s a n d reported in a n earlier series of articles (60-66). O u r results s u p p o r t their conclusions and proposed mechanisms. For e x a m p l e , 1,4-addition o f t h e a c e t o n e c a r b a n i o n t o acrolein w o u l d be a facile reaction under t h e reaction c o n d i t i o n s used for cellulose l i q u e f a c t i o n (both o f these i n t e r m e d i a t e s are f o r m e d f r o m cellulose). T h e p r o d u c t , 5 k e t o h e x a n a l , c o u l d cyclize t o 3 - h y d r o x y c y c l o h e x a n o n e , w h i c h w o u l d t h e n d e h y d r a t e a n d d e h y d r o g e n a t e t o p h e n o l a n d related a r o m a t i c p r o d u c t s . This route t o an observed p r o d u c t (phenol) is still s p e c u l a t i v e , b u t w e have s h o w n t h e m o r e d i r e c t route t o p h e n o l f r o m c y c l o h e x a n o n e does not o c c u r u n d e r t h e


150


SOURCE

Table V. PRODUCTS IDENTIFIED FROM CELLULOSE LIQUEFACTION


OPEN CHAIN ALIPHATICS Aliphatic Hydrocarbons c i s - or t r a n s - 3 - h e x e n e 3-heptene 4-octyne 2,5.-dimethyl-2,4,-hexadiene 2.5.-dimethyl-traos-3-hexene octene decyne 2 . 6 . 1 0 . 1 4 - t e t r a m e t h y I-

Probability T* Τ

τΡ τ τ τ

Mol. Wt. 84 98 110 110 112 112 138

Ρ

296

Aliphatic Alcohols ethylene glycol

Ρ

3-methyl-1-butanol diethylene glycol

τΗ

62 88 106

(2- or 3-) m e t h y l - 2 . 4 , - p e t a n e d i o l diethylene glycol. monoethyl ether

Η

118

Η

134

2-(2-butoxyethoxy) ethanol

Η

162

Τ Ρ Ρ

98 100 114

τ τ

116 124

Ρ

126

τ

170

heptadecane

Aliphatic Ketones 4-methyl-pent-3-en-2-one 4-methyl-2-petanone 3-heptanone 4-hydroxy-4-methyl2-pentanone 3-octadienone 2-methyl-hepten3-one acrolein hydrate monotrifluoroacetate'''


7.

MOLTON ET A L .

151

Oil from Biomass

Table V. PRODUCTS IDENTIFIED FROM CELLULOSE LIQUEFACTION (continued) CYCLIC COMPOUNDS Cyclic Hydrocarbons 1-ethyl c y c l o h e x e n e


e t h y l - or d i m e t h y l - c y c l o h e x a n e methyl-n-propylcyclopentene methyl ethyl cyclohexane 1.5.5,6-tetramethyl1.3-cyclohexadiene (1.1)-. (1.2)-. ( 1 , 3 ) - d i m e t h y l i n d a n

Probability

Mol. W t .

Ρ Τ

110

τ τ

112 124 126

τΡ

136

τ

160

Ρ Ρ

86 100

Η Τ Ρ Η Η Τ Η

84 98 98 98 110 112 112

Η

112

Τ Τ Τ

124

τ

152

Ρ Ρ

86

Η

100

Τ Ρ

102

146

1.1-dimethyl-1.2.3.4tetrahydronaphthalene Cyclic Alcohols cyclopentanol cyclonhexanol Cyclic Ketones cyclopentanone 2-methyl cyclopentanone 3-methyl cyclopentanone cyclohexanone 2,5-dimethyl cyclopentanone 2,4-dimethyl cyclopentanone 2-ethylcyclopentanone 3-methylcyclopentanone c y c l o h e x e n e - 1-enyI m e t h y l ketone 4.4.5-trimethylcyclohex-2-enone 2-cyclopentyl-1 -cyclopentanone ethyl-2-methyl-cyclohex -1-enyI ketone Furans 8 - b u t y r o l a c t o n e (keto f o r m o f 2-hydroxy-4,5-dihydrofuran) 2,4-dimethyl furan 2,5-dimethyltetrahydrofuran 2-hydroxy-2-methyltetrahydrofuran 2.3.4-trimethyl furan ethyl methyl furan

τ

138 152

96

110 110


152

BIOMASS AS A NONFOSSIL

FUEL

SOURCE

Table V. PRODUCTS IDENTIFIED FROM CELLULOSE LIQUEFACTION (Continued)


Alkyl Benzenes

Probability

Mol. Wt.

propyl furan

Τ

110

2-iso-propyl furan 2.5-diethyl furan

Τ Τ

butyl furan

τΡ

110 124 124

2-methylbenzofuran pentyl furan heptyl furan

τ τ

132 138 166

AROMATICS ο-, p-. or m - x y l e n e e t h y l benzene 2-methyl styrene 1 - m e t h y l - 2 - e t h y l benzene 1 - m e t h y l - 3 - e t h y l benzene η - p r o p y l benzene o-allyl t o l u e n e 1 - m e t h y l - 2 - n - p r o p y l benzene c y c l o p e n t y l benzene 1 - m e t h y l - 4 - i s o b u t y l benzene 2-phenyl-3-methyl butane Phenol Derivatives phenol o-cresol m-cresol p-cresol 2-ethyl phenol

Η Η Ρ Η Η Η Τ Η Τ Ρ

τ Η Η Η Η Τ

106 106 118 120 120 120 132 134 146 148 148

o-methoxyphenol 2-phenoxyethanol 2 - h y d r o x y - 4 - m e t h y I-

Η Η

94 108 108 108 122 124 138

acetophenone η - p r o p y l cresol 4 - t - b u t y l (o- or m-) cresol

Ρ Τ Ρ

150 150 164

Ρ

112 162

POLYFUNCTIONALS 2-formyl-2.3-dihydro-pyran 2,5-dimethylterephthaldehyde

τ


7.

MOLTON

ET AL.

153

Oil front Biomass

The a b o v e c o m p o u n d s w e r e i d e n t i f i e d f r o m 18 samples. Eleven samples w e r e analyzed o n a H e w l e t t - P a c k a r d 5 9 8 0 G C / M S ; 3 samples o n a 50-ft. stainless steel L B 5 5 0 X c o l u m n p r o g r a m m e d f r o m 7 0 ° C t o 140°C at 4 7 m i n w i t h a 2 m i n initial h o l d ; a n d 8 samples o n a 3 0 - m glass capillary S P 2 1 0 0 c o l u m n p r o g r a m m e d f r o m 5 0 ° at 2 6 0 ° at 4 ° / m i n w i t h a 4 m i n initial h o l d . Six samples w e r e analyzed o n a H e w l e t t - P a c k a r d 5 9 9 2 G C / M S o n a 6-ft stainless steel Carbowax 2 0 m c o l u m n , using 3 programs: 5 0 ° / 2 min, 2 ° / m i n t o 1 9 0 ° ; 8 5 7 1 0 m i n . 8 7 m i n t o 1 1 5 ° ; a n d 1 1 5 7 5 m i n . 2 7 m i n t o 150°. A 7 t h s a m p l e analyzed o n t h i s i n s t r u m e n t w a s at 3 4 7 2 m i n , 2 7 m i n t o 1 3 5 ° o n a 6 - f t stainless steel O V - 1 7 c o l u m n .


f

* Τ - Tentative (10-30%)

Ρ - Probable

Η - Highly Probable

(31-75%)

(75-99%)

+ Identified in a t r i f l u r o a c e t y l a t e d o i l sample.


154


SOURCE

c o n d i t i o n s used for cellulose l i q u e f a c t i o n . Similar A l d o l - t y p e c o n d e n s a t i o n s c a n a c c o u n t for m a n y m o r e of t h e o b s e r v e d p r o d u c t s . Little else of relevance t o t h e present d i s c u s s i o n c a n be said at present r e g a r d i n g t h e m e c h a n i s m s of f o r m a t i o n of t h e s e p r o d u c t s .


T h e n a t u r e of t h e p r o d u c t s a l l o w s us t o p r e d i c t t h a t t h e oil w i l l s l o w l y p o l y m e r i z e d u e t o r e a c t i o n b e t w e e n t h e p h e n o l s a n d f u r a n s . w i t h side reactions f r o m u n s a t u r a t e d h y d r o c a r b o n s . T h e oil w i l l also be rather corrosive because of t h e a c i d i c n a t u r e of t h e phenols. W e have o b s e r v e d b o t h of these in practice. Oil p r o d u c t s are stable o n l y if kept in a freezer, a n d syringes used for i n j e c t i o n of s a m p l e s i n t o t h e G C / M S i n s t r u m e n t c h a r a c t e r i s t i c a l l y seize. P l u g g i n g of pipes t o g e t h e r w i t h rather serious c o r r o s i o n p r o b l e m s have o c c u r r e d in p r a c t i c e at A l b a n y , a n d are c o n s i s t e n t w i t h o u r o b s e r v a t i o n s o n oil c o m p o s i t i o n . U n d e r these c i r c u m s t a n c e s , t o s u g g e s t d i r e c t use of t h e oil as a fuel in c o n v e n t i o n a l boiler e q u i p m e n t w i t h o u t p r e t r e a t m e n t is u n w i s e . Implications for Albany T h e e x p e r i m e n t a l w o r k r e p o r t e d here deals w i t h o p t i m u m r e a c t i o n c o n d i t i o n s for t h e l i q u e f a c t i o n of t h e m a j o r b i o m a s s c o m p o n e n t , cellulose, in an a q u e o u s s y s t e m . W h i l e l i g n i n in w o o d m a y c h a n g e t h e results q u a l i t a t i v e l y , w e d o n o t e x p e c t t h a t transfer of our c o n c l u s i o n s t o a w o o d - b a s e d s y s t e m w i l l i n v a l i d a t e these results. H o w e v e r , t h e r e are s o m e differences a n d o u r results s h o u l d be used as i n d i c a t o r s rather t h a n q u a n t i t a t i v e measures of p e r f o r m a n c e in o t h e r s y s t e m s . For i n s t a n c e , at A l b a n y , t h e reactor is a stirred t a n k , a n d c o n s e q u e n t l y s o m e of t h e oil has a longer residence t i m e , w h i l e s o m e proceeds t h r o u g h rapidly. This causes s o m e d i f f e r e n c e b e t w e e n results at A l b a n y a n d o u r e x p e r i m e n t s , w h i c h w e r e p e r f o r m e d in small autoclaves. Here w e s i m p l y a p p l y t h e results of o u r w o r k generally t o biomass l i q u e f a c t i o n s y s t e m s , w i t h A l b a n y as an e x a m p l e , w i t h o u t a t t e m p t i n g t o c l a i m a 1:1 c o r r e s p o n d e n c e . In a n y e v e n t , l a b o r a t o r y w o r k in s u p p o r t of t h e A l b a n y pilot p l a n t is p r o c e e d i n g separately at o u r l a b o r a t o r y (4-10), w h i l e t h e research r e p o r t e d here is basic in n a t u r e (41-43). In T a b l e V I , w e s h o w a c o m p a r i s o n b e t w e e n t h e r e a c t i o n c o n d i t i o n s used by us a n d t h o s e u s e d a t A l b a n y . Cellulose l i q u e f a c t i o n in a n a q u e o u s s y s t e m is i m p r o v e d o n l y s l i g h t l y by t h e a d d i t i o n of u p t o 5 0 0 psig of c a r b o n m o n o x i d e , w h i l e use of w o o d a n d larger a m o u n t s of c a r b o n m o n o x i d e results in i m p r o v e d oil yields. There are p r o b l e m s w i t h t h e use of an oil v e h i c l e at A l b a n y , s u c h as t h e c o n t i n u e d p o l y m e r i z a t i o n of t h e v e h i c l e w i t h repeated passes t h r o u g h t h e reactor. T h e o r i g i n a l i n t e n t in u s i n g recycle oil w a s t o r e d u c e reactor o p e r a t i n g pressure since w a t e r at 3 7 0 C generates a very h i g h pressure. A l s o , it w a s felt t h a t there c o u l d be s o m e h y d r o g e n d o n o r s o l v e n t e


Klass; Biomass as a Nonfossil Fuel Source ACS Symposium Series; American Chemical Society: Washington, DC, 1981. 2

Water

Water

290-370

150-407 2

2

2

2

3

3

3

Na C0 (5%)

2

3

Na C0 (5%)

2

Na C0 (5%)

Catalyst

CO.C0 . Na C0 N (0.37-12.6%)

2

CO:H 60:40

Heavy c y c l e C O : H oil 60:40

290-370

CO

Gas

Anthracene oil

Media

290-370

Temperature, (°C)

20-360

90

60

5-12

Residence T i m e , (min)

T a b l e V I . C O M P A R I S O N OF REACTION P A R A M E T E R S : B A T T E L L E - N W , A N D A L B A N Y , OR PILOT P L A N T


Feedstock

Cellulose (Solka-floc)

Acid-hydrolyzed D o u g l a s Fir

D o u g l a s Fir

D o u g l a s Fir


156

BIOMASS AS A NONFOSSEL F U E L

SOURCE

effect in using recycle oil. This effect does operate t o s o m e e x t e n t as s h o w n by Elliott a n d G i a c o l e t t o (10). A l l of t h e e x p e r i m e n t s o n t h e effect of CO overpressure a b o v e 5 0 0 psig have been p e r f o r m e d in an oil v e h i c l e ; if t h e s a m e y i e l d - i n c r e a s i n g effect c a n be s h o w n t o o c c u r in an a q u e o u s s o l v e n t t h e n m a n y of t h e v e h i c l e - a s s o c i a t e d p r o b l e m s at A l b a n y c o u l d be e l i m i n a t e d by u s i n g w a t e r as t h e vehicle. This w o u l d of course affect t h e e c o n o m i c s of t h e process, as t h e o p e r a t i n g pressure w o u l d increase, b u t t o s o m e e x t e n t t h i s w o u l d be alleviated by s i m p l i f i c a t i o n of t h e p r o d u c t separation step — w a t e r a n d oil separate s p o n t a n e o u s l y (leaving an oil p r o d u c t c o n t a i n i n g Ι Ο Ι 5% w a t e r ) , a n d t h e r e w o u l d be a l o w e r load o n t h e c e n t r i f u g e . Polymerization a n d c o r r o s i o n p r o b l e m s m i g h t still occur. T h e a q u e o u s s o l v e n t , c o n t a i n i n g s o m e of t h e w a t e r - s o l u b l e p r o d u c t s , c o u l d in p r i n c i p l e be r e c y c l e d t o p r o v i d e a d d i t i o n a l oil. T h e h y d r o g e n d o n o r s o l v e n t - e f f e c t s h o u l d still o p e r a t e w i t h an a q u e o u s v e h i c l e , since p r o d u c t oil w o u l d dissolve m o s t of t h e early reaction p r o d u c t s ; t h e s e b e i n g o r g a n i c in n a t u r e , w o u l d t e n d t o dissolve readily in oil already f o r m e d . H y d r o g é n a t i o n of i n t e r m e d i a t e p r o d u c t s w o u l d t h u s still be e x p e c t e d t o o c c u r , even t h o u g h w a t e r is a poor d o n o r solvent. Polymerization of t h e p r o d u c t oil d u r i n g r e p e a t e d r e c y c l i n g is n o t s u r p r i s i n g , since m a n y of t h e r e a c t i o n p r o d u c t s are reactive. Fu. Illig, a n d M e t l i n (67) o b s e r v e d t h i s p o l y m e r i z a t i o n p h e n o m e n o n d u r i n g an i n v e s t i g a t i o n i n t o oil d e r i v e d f r o m b o v i n e m a n u r e ; t h e y f o u n d t h a t t h e p o l y m e r i z a t i o n c o u l d be p r e v e n t e d by i n t e r m e d i a t e h y d r o g é n a t i o n of t h e initial p r o d u c t over a c o b a l t m o l y b d a t e catalyst. If recycle oil is f o u n d t o be an essential part of t h e A l b a n y process, s u c h an i n t e r m e d i a t e h y d r o g é n a t i o n c o u l d increase v e h i c l e stability. Regardless of t h e v e h i c l e used, it appears t h a t t h e alkali c o n c e n t r a t i o n used at A l b a n y is t o o h i g h . Our results w i t h cellulose i n d i c a t e t h a t a r e d u c t i o n of up t o 13x m a y be possible w i t h o u t i n t e r f e r i n g w i t h p r o d u c t composition (not yield), w h i l e Elliott a n d Giacoletto's results (10) i n d i c a t e t h a t a 2x r e d u c t i o n is possible w i t h o u t a f f e c t i n g oil yield from w o o d . It is d i f f i c u l t t o d e t e r m i n e an o p t i m u m t i m e or t e m p e r a t u r e for t h e l i q u e f a c t i o n process because reaction t i m e a n d t e m p e r a t u r e are i n t e r a c t i v e variables. Reaction t e m p e r a t u r e is t h e m o s t i m p o r t a n t f a c t o r a c c o r d i n g t o our research, in a g r e e m e n t w i t h w o r k r e p o r t e d by Corbett a n d Richards (68) in t e r m s of t h e a m o u n t of v o l a t i l e p r o d u c t s f o r m e d f r o m cellulose. Inclusion of l i g n i n a n d h e m i c e l l u l o s e in a w o o d s u b s t r a t e m a y alter t h e o p t i m u m t e m p e r a t u r e , b u t s h o u l d n o t alter t h e f a c t t h a t reaction t e m p e r a t u r e is c o n t r o l l i n g . H o w e v e r , oil yield itself m a y not be a suitable p a r a m e t e r for m e a s u r i n g t h e e f f i c i e n c y of t h e l i q u e f a c t i o n process. A h i g h yield of oil m a y


7.

MOLTON ET A L .

Oil from Biomass

157


be a c h i e v e d at t h e e x p e n s e o f a l o w heat c o n t e n t t h r o u g h i n c o r p o r a t i o n o f o x y g e n into t h e p r o d u c t . F u r t h e r m o r e , there m a y be o t h e r trade-off f a c t o r s t o be t a k e n into c o n s i d e r a t i o n , s u c h as t h e c h e m i c a l c o m p o s i t i o n a n d c o r r o s i v i t y of t h e p r o d u c t . M a x i m i z a t i o n of t h e heat c o n t e n t o f t h e p r o d u c t as a d u a l f u n c t i o n of t i m e of reaction a n d m a x i m u m t e m p e r a t u r e has n o t y e t been s t u d i e d b u t w o u l d be very useful. A c c o r d i n g t o o u r results w i t h cellulose, t h e p r i m a r y o i l - f o r m i n g reactions leading t o volatile c a r b o n y l c o m p o u n d s are c o m p l e t e at 2 3 0 ° C after 1 hr. w i t h s u b s e q u e n t reactions i n v o l v i n g i n t e r m e d i a t e s already f o r m e d a n d leading t o increased v i s c o s i t y a n d m o l e c u l a r w e i g h t . Earlier w o r k s h o w e d d i s s o l u t i o n of c o t t o n h y d r o cellulose in 0.5 hr at 100°C in 0.5 Ν alkali (68-71). a l t h o u g h t h e m o l e c u l a r w e i g h t o f t h e h y d r o c e l l u l o s e w a s n o t disclosed. This is m u c h l o w e r t h a n t h e 3 7 0 ° C c u r r e n t l y used at A l b a n y , a l t h o u g h l i q u e f a c t i o n o f t h e l i g n i n c o m p o n e n t of w o o d m a y w e l l require a m u c h higher t e m p e r a t u r e t h a n required f o r cellulose l i q u e f a c t i o n . Regarding t h e d e s i g n o f t h e process, w e feel t h a t a c o n t i n u o u s p l u g f l o w reactor is i n h e r e n t l y b e t t e r t h a n t h e stirred t a n k c u r r e n t l y in use. A p l u g f l o w reactor w o u l d also give greater c o n t r o l over t h e reaction parameters. W e also feel t h a t m o r e careful a t t e n t i o n s h o u l d be g i v e n t o t h e relationship b e t w e e n reaction p a r a m e t e r s a n d p r o d u c t y i e l d a n d q u a l i t y in f u t u r e d e s i g n o f biomass l i q u e f a c t i o n plants, since o u r w o r k , a n d t h a t o f Elliott (4-10) d e m o n s t r a t e s t h a t a n u m b e r o f e r r o n e o u s a s s u m p t i o n s w e r e m a d e in d e s i g n i n g t h e pilot plant at A l b a n y . SUMMARY The d i r e c t t h e r m o c h e m i c a l c o n v e r s i o n o f w o o d y biomass t o oil is o n e m e t h o d of p r o d u c i n g l i q u i d fuel. This m e t h o d is c u r r e n t l y b e i n g e x a m i n e d in a pilot plant at A l b a n y , O r e g o n . A t A l b a n y , w o o d is liquefied at a t e m p e r a t u r e of 2 9 0 - 3 7 0 ° C , a pressure of over 3 0 0 0 psig, a n d a residence t i m e of 2 0 - 9 0 m i n in t h e presence of a 6 0 : 4 0 m i x t u r e o f c a r b o n m o n o x i d e : h y d r o g e n , a n d a catalyst c o n s i s t i n g o f 5% s o d i u m c a r b o n a t e . In our w o r k o n t h e f u n d a m e n t a l c h e m i s t r y o f this l i q u e f a c t i o n t e c h n i q u e , laboratory studies using pure cellulose as a m o d e l c o m p o u n d s h o w e d t h a t l i q u e f a c t i o n o c c u r s rapidly at 3 0 0 ° C a n d b e l o w at a pressure o f 2 8 0 0 psig of s t e a m w i t h n o a d d e d gas. in less t h a n 1 hr. F u r t h e r m o r e , t h e effect of t h e s o d i u m c a r b o n a t e " c a t a l y s t " o n t h e early l i q u e f a c t i o n reactions is i n d e p e n d e n t o f its c o n c e n t r a t i o n t o a level of b e l o w 0.8%. Gas c h r o m a t o g r a p h i c a n d mass s p e c t r o m e t r i c e x a m i n a t i o n o f t h e p r o d u c t oil s h o w s its c o m p o s i t i o n t o be a l m o s t c o n s t a n t over t h e w h o l e range o f reaction c o n d i t i o n s used. A r e - e x a m i n a t i o n o f reactor d e s i g n o f f u t u r e biomass l i q u e f a c t i o n plants appears w a r r a n t e d in light of these results.


158

BIOMASS AS A N O N F O S S L L

FUEL

SOURCE

ACKNOWLEDGEMENT W e g r a t e f u l l y a c k n o w l e d g e s u p p o r t for t h i s w o r k u n d e r c o n t r a c t n u m b e r EY7 6 - C - 0 6 - 1 8 3 0 f r o m t h e U.S. D e p a r t m e n t of Energy, D i v i s i o n of C h e m i c a l Sciences, Office of Basic Energy Sciences.


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