Material and Energy Balances in the Production of Ethanol from Wood

13 Material and Energy Balances in the Production of

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 18, 2015 | http://pubs.acs.org Publication Date: January 26, 1979 | doi: 10.1021/bk-1979-0090.ch013

Ethanol from W o o d MORRIS WAYMAN, JAIRO H . LORA, and E D M U N D GULBINAS Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A4 I n t e r e s t i n renewable r e s o u r c e s as raw m a t e r i a l s f o r chemi c a l s and energy has i n t e n s i f i e d i n r e c e n t y e a r s as a r e s u l t o f a n t i c i p a t e d s h o r t a g e s o f p e t r o l e u m a n d n a t u r a l g a s (1,2_ 3). A s i g n i f i c a n t p a r t of t h i s e f f o r t has been devoted to the p r o d u c t i o n o f a l c o h o l s , p a r t i c u l a r l y m e t h a n o l and e t h a n o l , f r o m wood ( 4 - 8 ) . M e t h a n o l i s t h e m a i n c o n s t i t u e n t o f " w o o d a l c o h o l " , made f o r a g r e a t many y e a r s b y t h e d e s t r u c t i v e d i s t i l l a t i o n o f w o o d , e s p e c i a l l y hardwoods (9). F r o m a t o n o f h a r d w o o d , one c o u l d e x p e c t a b o u t 60 l b , t h a t i s 7 . 5 g a l l o n s o f m e t h a n o l , a l o n g w i t h a v a r i e t y of other chemicals. Wood a l c o h o l i s n o l o n g e r m a d e . The p r o cesses discussed i n recent reports (4,5), are quite d i f f e r e n t , b e i n g b a s e d on wood g a s i f i c a t i o n , f o l l o w e d b y r e a c t i o n s s i m i l a r t o those employed i n s y n t h e s i s of methanol from n a t u r a l gas. The e x p e c t a t i o n h a s b e e n h e l d o u t t h a t 80 g a l l o n s o f m e t h a n o l c o u l d be o b t a i n e d f r o m a t o n o f w o o d , a b o u t 10 t i m e s t h e y i e l d o f t h e o l d wood a l c o h o l . W h i l e t h e r e i s g e n e r a l agreement t h a t wood gas c o u l d p r o b a b l y be c o n v e r t e d t o m e t h a n o l , t o t h i s d a t e no one has done i t , and t h e r e a r e no d a t a , l a b o r a t o r y o r o t h e r w i s e , t o i n d i c a t e what p r o b l e m s m i g h t be e n c o u n t e r e d i n the c o n v e r s i o n , o r what the economics might b e . The r e c e n t s u g g e s t i o n t h a t m i x t u r e s o f w o o d g a s a n d r e f o r m e d n a t u r a l g a s may b e a g o o d s o u r c e o f m e t h a n o l i s m o s t t i m e l y . O u r c a l c u l a t i o n s s u g g e s t t h a t t h i s may now b e t h e c h e a p e s t r o u t e t o m e t h a n o l i n many p l a c e s . 9

The s i t u a t i o n w i t h r e g a r d t o e t h a n o l i s much c l e a r e r : there i s l o n g i n d u s t r i a l experience i n the manufacture of ethanol from wood, by f e r m e n t a t i o n of the sugars i n the waste e f f l u e n t s of pulp m i l l s , o r o f t h e s u g a r s made b y w o o d h y d r o l y s i s ( 9 ) . In the years f o l l o w i n g W o r l d War I I , wood h y d r o l y s i s p l a n t s h a v e b e e n u n a b l e t o compete e c o n o m i c a l l y w i t h p e t r o l e u m - b a s e d e t h a n o l synthesis, m a i n l y b y h y d r a t i o n o f e t h y l e n e , a n d t h e y h a v e b e e n s h u t down i n most c o u n t r i e s . H o w e v e r , i n t h e S o v i e t U n i o n , we u n d e r s t a n d , t h e r e a r e s t i l l a b o u t 30 w o o d h y d r o l y s i s p l a n t s i n o p e r a t i o n (10). Many o f t h e s e a r e u s e d f o r f o d d e r y e a s t p r o d u c t i o n (11) b u t t h e wood s u g a r s a r e a l s o a v a i l a b l e f o r e t h a n o l p r o d u c t i o n . Recent

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T h i s chapter not subject to U . S . C o p y r i g h t . P u b l i s h e d 1979 A m e r i c a n C h e m i c a l S o c i e t y .

In Chemistry for Energy; Tomlinson, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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served t o s t i m u l a t e i n t e r e s t i n ethanol p r o d u c t i o n from renewable r e s o u r c e s once a g a i n . The B r a z i l i a n n a t i o n a l p r o g r a m f o r e x t e n d i n g g a s o l i n e a n d e v e n s u b s t i t u t i n g f o r i t by e t h a n o l (12) h a s been p a r t i c u l a r l y noteworthy. The B r a z i l i a n e x p e r i e n c e h a s b e e n b a s e d on f e r m e n t a t i o n o f t h e b y - p r o d u c t s o f cane s u g a r m a n u f a c t u r e , and some e t h a n o l h a s been p r o d u c e d t h e r e f r o m c a s s a v a s t a r c h . W h i l e e t h a n o l f r o m wood s u g a r s h a s n o t b e e n p a r t o f t h a t p r o g r a m , the s u c c e s s f u l s u b s t i t u t i o n o f e t h a n o l f o r g a s o l i n e c o m m e r c i a l l y has r a i s e d t h e p r o s p e c t o f a l a r g e m a r k e t o u t l e t , a n d t h e r a p i d l y i n c r e a s i n g p r i c e o f g a s o l i n e here suggests that the economics, i f n o t f a v o r a b l e now, may become s o i n a f o r e s e e a b l e f u t u r e . Of t h e v a r i o u s t e c h n o l o g i c a l a d v a n c e s w h i c h h a v e b e e n made i n wood t r e a t m e n t i n r e c e n t y e a r s , t h e two most r e l e v a n t t o e t h a n o l p r o d u c t i o n a p p e a r t o be t h e a u t o h y d r o l y s i s - e x t r a c t i o n p r o c e s s f o r hardwoods ( 1 3 ) a n d t h e e n z y m a t i c h y d r o l y s i s o f c e l l u l o s i c m a t e r i a l s ( 1 4 ) . By t h e a u t o h y d r o l y s i s - e x t r a c t i o n p r o c e s s , wood i s s e p a r a t e d i n t o i t s t h r e e main components, c e l l u l o s e , h e m i c e l l u l o s e and l i g n i n . The c e l l u l o s e s o p r o d u c e d i s a v a i l a b l e f o r h y d r o l y s i s by e i t h e r a c i d o r c e l l u l a s e , w h i l e t h e h e m i c e l l u l o s e s and l i g n i n a r e a v a i l a b l e f o r t h e c o - p r o d u c t i o n o f c h e m i c a l s o r e n e r g y . By a u t o h y d r o l y s i s , t h a t i s steaming under c a r e f u l l y c o n t r o l l e d c o n d i t i o n s o f t i m e and t e m p e r a t u r e , t h e h e m i c e l l u l o s e s a r e s o l u b i l i z e d and c o n v e r t e d t o s u g a r s , f u r f u r a l , a c e t i c a c i d a n d o t h e r p r o d u c t s , w h i l e t h e l i g n i n i s s o m o d i f i e d a s t o be e x t r a c t a b l e w i t h c a u s t i c soda under moderate c o n d i t i o n s a t atmospheric p r e s s u r e , l e a v i n g r e l a t i v e l y pure c e l l u l o s e undissolved. I n t h i s p a p e r we r e p o r t o u r s t u d i e s o f t h i s c e l l u l o s i c r e s i d u e , b y h y d r o l y s i s and f e r m e n tation to ethanol. The a d v a n c e s made i n e n z y m a t i c h y d r o l y s i s o f c e l l u l o s i c m a t e r i a l s (14) a r e a l s o o f i n t e r e s t . This technology i n v o l v e s o n l y moderate temperature p r o c e s s e s i n s i m p l e equipment w h i c h p r o m i s e s t o be o f s i g n i f i c a n t l y l o w e r c a p i t a l c o s t t h a n t h e p r e s s u r e e q u i p m e n t a s s o c i a t e d w i t h c o n v e n t i o n a l a c i d wood h y d r o l y s i s p r o cesses. A l l o f t h e s e c o n s i d e r a t i o n s combined t o l e a d us t o s t u d y p r o c e s s e s f o r e t h a n o l p r o d u c t i o n f r o m wood, e s p e c i a l l y i n a n e f f o r t t o o b t a i n d a t a f o r m a t e r i a l and energy b a l a n c e s , and p o s s i b l y f o r the economics. Pretreatment

o f t h e Wood

The p a r t i c u l a r wood s p e c i e s we c h o s e f o r t h i s s t u d y i s a s p e n ( P o p u l u s t r e m u l o i d e s ) , w h i c h i s p l e n t i f u l i n Canada and i n t h e n o r t h e r n U.S.A. The c h e m i c a l c o m p o s i t i o n we f o u n d t o be g l u c a n 53.4%, x y l a n 1 4 . 9 % , t o t a l c a r b o h y d r a t e 79.0%, l i g n i n 1 7 . 1 % a n d e x t r a c t i v e s 3.8%. We w o u l d e x p e c t t o t a l f e r m e n t a b l e s u g a r s o f about 56% i n t h i s sample o f aspen i n anhydro form ( T i m e l l has r e p o r t e d a b o u t 6 0 % i n a n o t h e r s a m p l e ( 1 5 ) ) w h i c h upon h y d r o l y s i s w o u l d y i e l d a b o u t 1,250 l b wood s u g a r s p e r t o n o f wood ( d r y b a s i s ) , from t h e s t o i c h i o m e t r y . T h e o r e t i c a l c o n v e r s i o n o f t h i s s u g a r t o e t h a n o l w o u l d y i e l d 640 l b o r 81.1 g a l l o n s o f a n h y d r o u s



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e t h a n o l , o r 85 g a l l o n s o f t h e 95% a z e o t r o p e . The wood, i n c h i p f o r m , was t r e a t e d by a u t o h y d r o l y s i s ( 1 4 ) . The c h i p s , w i t h i n i t i a l m o i s t u r e o f a b o u t 50%, w e r e h e a t e d w i t h s t e a m t o 195°C and h e l d a t t h i s t e m p e r a t u r e f o r 30 m i n u t e s . This t i m e - t e m p e r a t u r e r e s u l t s i n f o r m a t i o n o f v o l a t i l e s s u c h as f u r f u r a l , w a t e r - s o l u b l e h e m i c e l l u l o s e and a l k a l i - s o l u b l e l i g n i n . T y p i c a l l y a b o u t 12% o f t h e wood s u b s t a n c e was c o n v e r t e d t o v o l a t i l e s , and a b o u t 12% o f h e m i c e l l u l o s e s was o b t a i n e d i n t h e w a t e r w a s h i n g s o f t h e r e s i d u e . A b o u t 75% o f t h e wood s u b s t a n c e r e m a i n e d as r e a d i l y d i s i n t e g r a t e d f i b r o u s p u l p . A u t o h y d r o l y s i s was c a r r i e d o u t i n two d i f f e r e n t w a y s , c o n t i n u o u s and b a t c h . C o n t i n u o u s a u t o h y d r o l y s i s was c a r r i e d o u t i n a r e a c t o r i n t h e p l a n t o f S t a k e T e c h n o l o g y L i m i t e d , O t t a w a ( 1 6 ) . The r e a c t o r was a h o r i z o n t a l t u b e a b o u t 10 i n c h e s i n d i a m e t e r and 8 f e e t l o n g e n c l o s i n g a h e l i c a l screw conveyor. I t was f e d c o n t i n u o u s l y by a p l u g - f o r m i n g h e l i x a t one e n d , and d i s c h a r g e d f o r a few s e c o n d s o u t o f e a c h m i n u t e a t t h e o t h e r end. Steam was a d m i t t e d a t a b o u t 250 pounds p e r s q u a r e i n c h p r e s s u r e n e a r t h e f e e d e n d , and measurements i n d i c a t e d t h a t the temperature r o s e t o the d e s i r e d v a l u e instantaneously. The d i s c h a r g e t h r o u g h an o r i f i c e t o a t m o s p h e r i c pressure s u f f i c e d to completely d i s i n t e g r a t e the chips to a very fine pulp. B a t c h a u t o h y d r o l y s i s was c a r r i e d o u t i n 300 m l p r e s s u r e v e s s e l s i n a p r e h e a t e d s i l i c o n e b a t h , w i t h due a l l o w a n c e f o r t e m p e r a t u r e e q u i l i b r a t i o n t o a c h i e v e as n e a r l y as p o s s i b l e 195°C f o r 30 m i n u t e s . C h i p m o i s t u r e was a d j u s t e d t o 50% f o r t h e b a t c h autohydrolysis. F o r some e x p e r i m e n t s , t h e a u t o h y d r o l y s e d p u l p was s u b j e c t e d t o h y d r o l y s i s , e i t h e r a c i d o r e n z y m a t i c , as f o r m e d , w i t h o u t washing or e x t r a c t i o n . For other experiments, the autohydrolysed p u l p a f t e r t h o r o u g h w a t e r w a s h i n g , was e x t r a c t e d w i t h s o d i u m h y d r o x i d e s o l u t i o n ( 2 0 % NaOH on p u l p , 70°C, 2 h o u r s ; 4% NaOH on p u l p consumed) t o remove t h e l i g n i n . A b o u t 20 t o 22% o f t h e s t a r t i n g wood s u b s t a n c e was r e c o v e r e d as l i g n i n f r o m t h e e x t r a c t by a c i d i f i c a t i o n . The c e l l u l o s i c r e s i d u e , a b o u t 97% c e l l u l o s e , was t h e n a b o u t 50% o f t h e s t a r t i n g wood s u b s t a n c e . I t was t h o r o u g h l y washed and l i g h t l y a c i d i f i e d b e f o r e h y d r o l y s i s . As a r e s u l t o f t h e s e v a r i o u s p r e t r e a t m e n t s , t h e h y d r o l y s i s e x p e r i m e n t s w e r e c a r r i e d o u t on t h r e e d i f f e r e n t s t a r t i n g m a t e r ials: a u t o h y d r o l y s e d a s p e n wood made e i t h e r i n b a t c h o r i n c o n t i n u o u s e q u i p m e n t ; and t h e c e l l u l o s i c r e s i d u e o f t h e a u t o h y d r o l y s i s - c a u s t i c extraction process. Acid Hydrolysis A c i d h y d r o l y s i s was c a r r i e d o u t i n s m a l l (30 m l ) p r e s s u r e v e s s e l s i n s i l i c o n e o i l b a t h s a t 190°C w i t h d i l u t e s u l p h u r i c a c i d . Upon c o m p l e t i o n , t h e v e s s e l s w e r e c o o l e d r a p i d l y , t h e r e s i d u e was t h o r o u g h l y washed w i t h h o t w a t e r , d r i e d and w e i g h e d . The l i q u o r and wash w a t e r s w e r e c o l l e c t e d and t h e s u g a r c o n t e n t d e t e r m i n e d by


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t h e a n t h r o n e method ( 1 7 ) . S t u d i e s were made o f t h e e f f e c t o f v a r y i n g s u l p h u r i c a c i d c o n c e n t r a t i o n s , l i q u o r t o s o l i d s r a t i o , and s i n g l e s t a g e compared w i t h m u l t i - s t a g e h y d r o l y s i s . S i n g l e stage a c i d h y d r o l y s i s of the c e l l u l o s i c r e s i d u e of a u t o h y d r o l y s i s and e x t r a c t i o n a t 190°C w i t h 0.5 t o 4.0% E $0 on the w e i g h t of the c e l l u l o s e gave r a t h e r u n s a t i s f a c t o r y r e s u l t s . The maximum s a c c h a r i f i c a t i o n a c h i e v e d was a b o u t 42% o f t h a t t h e o r e t i c a l l y p o s s i b l e . Degradation r e a c t i o n s caused the sugar y i e l d t o d r o p . I n m u l t i s t a g e h y d r o l y s i s , t h e s u g a r was removed a s s o o n a f t e r f o r m a t i o n as p o s s i b l e . F i g u r e 1 shows t h e r e s u l t s o f a m u l t i - s t a g e h y d r o l y s i s w i t h 2.0% l^SOi* on c e l l u l o s i c r e s i d u e by h e a t i n g f o r 20 m i n u t e s a t 190°C, r e m o v i n g t h e l i q u o r , w a s h i n g t h e r e s i d u e w i t h hot w a t e r , then r e p e a t i n g the h y d r o l y s i s w i t h f r e s h acid. The r e s u l t s show t h e c o n s i d e r a b l e y i e l d a d v a n t a g e o f t h e m u l t i s t a g e a c i d h y d r o l y s i s , o v e r 80% b e i n g o b t a i n e d . This i s u n d o u b t e d l y due t o t h e r e m o v a l o f t h e s u g a r f o r m e d i n e a c h s t a g e of the a c i d h y d r o l y s i s , thereby p r e v e n t i n g i t s d e s t r u c t i o n on prolonged a c i d treatment. The same e f f e c t c a n , o f c o u r s e , be a c h i e v e d i n o t h e r ways s u c h as by p r e s s u r e p e r c o l a t i o n o r by continuous h y d r o l y s i s i n a p r o p e r l y designed r e a c t o r . The c e l l u l o s i c r e s i d u e u s e d i n t h e s e e x p e r i m e n t s i s a d v a n t a g e o u s f o r a c i d h y d r o l y s i s compared t o u n t r e a t e d wood. The c e l l u l o s i c r e s i d u e i s f i n e l y d i v i d e d , and o f h i g h e r d e n s i t y t h a n wood c h i p s , 0.5 g / m l compared t o 0.36, and has a v e r y l o w l i g n i n content. As a r e s u l t , t h e o u t p u t o f f e r m e n t a b l e s u g a r s f o r a g i v e n s i z e o f d i g e s t e r w i l l be a b o u t t w i c e t h a t o b t a i n a b l e w i t h chips. 2


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Enzyme H y d r o l y s i s C e l l u l a s e enzyme, p r o d u c e d by T r i c h o d e r m a r e e s e i , a v a r i a n t o f T. v i r i d a e , was k i n d l y s u p p l i e d by D r . M a n d e l s o f t h e N a t i c k l a b o r a t o r y , and u s e d f o r e n z y m a t i c h y d r o l y s i s a t pH 4.8, 50°C o f a u t o h y d r o l y s e d a s p e n wood o b t a i n e d by c o n t i n u o u s h y d r o l y s i s , and c e l l u l o s i c r e s i d u e from the a u t o h y d r o l y s i s - e x t r a c t i o n p r o c e s s . Sugar was d e t e r m i n e d by t h e d i n i t r o s a l i c y c l i c a c i d (DNSA) method o f M i l l e r (18) as m o d i f i e d by t h e N a t i c k c e l l u l a s e l a b o r a t o r y ( 1 9 ) . The N a t i c k l a b o r a t o r y h a d a l r e a d y t e s t e d a u t o h y d r o l y s e d wood s a m p l e s p r e p a r e d i n t h e c o n t i n u o u s r e a c t o r , w i t h e n c o u r a g i n g results. F i g u r e 2 i l l u s t r a t e s our r e s u l t s . I t shows a v e r y r a p i d i n i t i a l r e a c t i o n , s l o w i n g c o n s i d e r a b l y a f t e r 24 h o u r s . The r e s u l t s i n F i g u r e 2 a l s o show i n c r e a s i n g s a c c h a r i f i c a t i o n when h i g h e r amounts o f c e l l u l a s e a r e u s e d . When 20% o f t h e enzyme, b a s e d on a u t o h y d r o l y s e d wood w e i g h t , was u s e d , t h e y i e l d o f s u g a r s was 77% o f t h e o r y i n 3 d a y s . I n a n o t h e r s e t o f e x p e r i m e n t s u s i n g 10% by w e i g h t o f c e l l u l a s e , t h e a c t i o n o f t h e enzyme was continued f o r 13 d a y s . The y i e l d a f t e r 3 d a y s was 5 2 % , i n agreement w i t h t h e r e s u l t s shown i n F i g u r e 2, b u t t h e a c t i o n o f t h e enzyme c o n t i n u e d , new s u g a r b e i n g f o r m e d a t t h e r a t e o f a b o u t 3% a day. At 13 d a y s , when t h e e x p e r i m e n t was d i s c o n t i n u e d , t h e y i e l d was 90%



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Hydrolysis Stages Figure

1. Multistage due, 2.0% H SO t

k

hydrolysis of autohydrolyzed-extracted lignocellulosic resi on lignocellulosic residue; each stage 20 min at 190°C


187


188

CHEMISTRY

F O R E N E R G Y

Weight % Cellulase 0.125IuB/mg (filter paper activity) PH 4.8 50° C

Time (days) Figure

2.

Enzymatic

hydrolysis

of autohydroly hydrolysis)

zed aspen wood (continuous


auto-


13.

W A Y M A N

E T

AL.

Material

and

Energy

Balances

in Ethanol

Production

189

of t h e o r y , and t h e c u r v e had n o t l e v e l l e d o f f , s u g g e s t i n g t h a t s t i l l h i g h e r y i e l d s were p o s s i b l e from the o r i g i n a l a d d i t i o n o f cellulase. Such c u r v e s may be s e e n i n F i g u r e 3, w h i c h shows t h e r e s u l t s of c e l l u l a s e h y d r o l y s i s o f v a r i o u s s u b s t r a t e s . In these e x p e r i ments a b s o r b e n t c o t t o n was o n l y s l i g h t l y a t t a c k e d by t h e enzyme, w h i l e the f o u r o t h e r s u b s t r a t e s were r a p i d l y a t t a c k e d i n the f i r s t 24 h o u r s . T h e r e a f t e r , t h e c e l l u l a s e c o n t i n u e d i t s s a c c h a r i f i c a t i o n a c t i o n , s u g a r y i e l d s o f a b o u t 90% b e i n g o b t a i n e d i n 12 d a y s from shredded f i l t e r paper. T h e r e were o t h e r v e r y l a r g e d i f f e r ences o b s e r v e d . A u t o h y d r o l y s e d aspen prepared i n the c o n t i n u o u s r e a c t o r was a l m o s t as good a s u b s t r a t e a s t h e f i l t e r p a p e r , w h e r e a s t h e same p r o c e s s c a r r i e d o u t i n t h e b a t c h r e a c t o r s p r o d u c e d m a t e r i a l h i g h l y r e s i s t a n t to enzymatic h y d r o l y s i s . The b a t c h a u t o h y d r o l y s e d a s p e n r e a c h e d 30% s a c c h a r i f i c a t i o n i n 1 d a y , t h e n r e s i s t e d f u r t h e r e n z y m a t i c a t t a c k . The d i f f e r e n c e i s a t t r i b u t a b l e to the p h y s i c a l form, s i n c e the d i s c h a r g e from t h e c o n t i n u o u s d i g e s t e r i n v o l v e s an i n s t a n t a n e o u s change f r o m a b o u t 200 pounds p e r s q u a r e i n c h p r e s s u r e t o a t m o s p h e r i c p r e s s u r e . T h i s i s accomp a n i e d by f l a s h i n g o f f o f s t e a m and v o l a t i l e s . The wood s u b s t a n c e i s t h e r e b y d i s r u p t e d , and t h e c e l l s s e p a r a t e d and e x p o s e d . Upon e x t r a c t i o n o f t h e b a t c h a u t o h y d r o l y s e d m a t e r i a l w i t h NaOH, i t became much more s u s c e p t i b l e t o e n z y m a t i c h y d r o l y s i s , s u g a r y i e l d s of a b o u t 65% b e i n g o b t a i n e d i n 12 d a y s , b u t a s i s e v i d e n t f r o m Figure 3 i t d i d not reach the r a t e of s a c c h a r i f i c a t i o n achieved w i t h t h e c o n t i n u o u s l y a u t o h y d r o l y s e d wood. F i g u r e 4 shows t h e e f f e c t o f m u l t i s t a g e e n z y m a t i c h y d r o l y s i s of c o n t i n u o u s l y a u t o h y d r o l y s e d a s p e n wood. A t t h e end o f 2 d a y s o f c e l l u l a s e h y d r o l y s i s a t pH 4.8, 50°C w i t h 10% o f enzyme on wood, t h e s u g a r s o l u t i o n and enzyme w e r e removed and t h e r e s i d u e was washed w i t h h o t w a t e r . F r e s h enzyme was t h e n added and t h e h y d r o l y s i s c o n t i n u e d f o r a n o t h e r d a y , when a g a i n s u g a r s and enzyme w e r e removed, and a new h y d r o l y s i s s t a r t e d . I t i s e v i d e n t from t h e r e s u l t s o f F i g u r e 4 t h a t by t h e end o f day 5, 97.2% s a c c h a r i f i c a t i o n was o b t a i n e d , and a f t e r 9 d a y s t h e y i e l d was 9 9 . 9 % , t h e r e s i d u e b e i n g a v e r y f i n e l y d i v i d e d b l a c k powder, most l i k e l y residual lignin. The r e s u l t s o f m u l t i s t a g e enzyme t r e a t m e n t s u g g e s t s t h a t f u r t h e r study of c e l l u l a s e a c t i o n i s f u l l y warranted. One h o p e f u l a r e a w o u l d be t o d e c r e a s e t h e h y d r o l y s i s t i m e and enzyme c o n c e n t r a t i o n , and i n c r e a s e t h e number o f s t a g e s . Another a p p r o a c h w o u l d be t o remove t h e s u g a r s by some o t h e r means, s u c h as d i a l y s i s o r f e r m e n t a t i o n ( 2 0 ) . Fermentation S o l u t i o n s o f wood s u g a r s w e r e f e r m e n t e d a n a e r o b i c a l l y by o r d i n a r y F l e i s c h m a n n s y e a s t (Saccharomyces c e r e v i s i a e ) . After 2 d a y s t h e brews w e r e t e s t e d f o r r e s i d u a l s u g a r . A l s o s a m p l e s o f t h e b r e w w e r e d i s t i l l e d and t h e d i s t i l l a t e s a n a l y s e d f o r e t h a n o l 1



190

CHEMISTRY

F O R E N E R G Y

ο Shredded filter paper α Continuous autohydrolysed aspen • Lignocellulosic residue of NaOH extracted batch autohydrolysed aspen

100

90

δ Batch autohydrolysed aspen • Absorbent cotton

80

IT

7

0

φ

c ο

50

CO

ϋ ο ϋ CO

40

30

CO

20

10

0.

Figure

3.

Enzymatic

I

I

ι

I

4

hydrolysis

I

I

I

I

6

8

Time

(days)

>

of various substrates strate, pH 4.8,50°C

i

10

I

ι

12

by cellulase,

ι

ι

14

10.0% on sub



13.

W A Y M A N

E T

A L .

Material

and Energy

Balances

in Ethanol

Production

Time (days) Figure 4. Enzymatic hydrolysis of autohydroly zed aspen wood (continuous autohydrolysis), 10.0% cellulase on wood, pH 4.8,50°C, single and multi-stage



192

CHEMISTRY

FOR

ENERGY

u s i n g gas c h r o m a t o g r a p h y . C o m p l e t e f e r m e n t a t i o n o f t h e s u g a r s o c c u r e d when t h e s u g a r s w e r e d e r i v e d f r o m a u t o h y d r o l y s e d e x t r a c t e d wood c e l l u l o s i c r e s i d u e s , b u t o n l y 72% o f t h e s u g a r s were f e r m e n t e d i n t h e 2 day p e r i o d when t h e y w e r e o b t a i n e d by h y d r o l y s i s of a u t o h y d r o l y s e d but not e x t r a c t e d p u l p . The s u g a r s i n the a u t o h y d r o l y s i s l i q u o r s , t h a t i s the h e m i c e l l u l o s e s o l u t i o n s , w e r e o n l y 27% f e r m e n t e d i n t h a t p e r i o d . T h i s was n o t s u r p r i s i n g s i n c e most o f t h e h e m i c e l l u l o s e o f a s p e n i s x y l a n , a s u g a r n o t f e r m e n t a b l e by t h i s y e a s t . A l c o h o l r e c o v e r y f r o m t h e f e r m e n t a t i o n brews was l e s s t h a n c o m p l e t e i n most c a s e s , w h i c h may be a t t r i b u t a b l e t o l e s s t h a n i d e a l c o n d i t i o n s . The b e s t y i e l d s , 60 t o 97% o f t h e o r y , w e r e o b t a i n e d w i t h s u g a r s o b t a i n e d by h y d r o l y s i s o f c e l l u l o s i c r e s i d u e s of the a u t o h y d r o l y s i s - e x t r a c t i o n process. Unextracted pulps, or t h e h e m i c e l l u l o s e s o l u t i o n s , gave p o o r e t h a n o l f o r m a t i o n , w h i c h suggests i n h i b i t i o n . I n t h e c a l c u l a t i o n o f m a t e r i a l and e n e r g y b a l a n c e s w h i c h f o l l o w s , we h a v e assumed 95% y i e l d s o f e t h a n o l f r o m wood s u g a r s , w h i c h i s r e a d i l y a c h i e v e d i n i n d u s t r i a l p r a c t i c e and w h i c h we b e l i e v e t o be a c h i e v a b l e w i t h o u r wood s u g a r s as w e l l . M a t e r i a l and E n e r g y

Balances

The c h a r t o f F i g u r e 5 shows m a t e r i a l and e n e r g y b a l a n c e s f o r e t h a n o l p r o d u c t i o n f r o m a s p e n wood f o l l o w i n g a u t o h y d r o l y s i s and c a u s t i c e x t r a c t i o n , i n c l u d i n g the r e s u l t s of a c i d h y d r o l y s i s of t h e l i g n o c e l l u l o s i c r e s i d u e , and t h e c o r r e s p o n d i n g f i g u r e s f o r e n z y m a t i c h y d r o l y s i s . The numbers i n b o t h c a s e s a r e b a s e d upon t h e d a t a o b t a i n e d i n e a c h s t a g e o f p r o c e s s i n g as d e s c r i b e d above in this report. From t h e c h a r t o f F i g u r e 5, we c a n e x p e c t t o o b t a i n f r o m one t o n o f a s p e n wood ( d r y b a s i s ) , f o l l o w i n g a u t o h y d r o l y s i s , c a u s t i c e x t r a c t i o n , a c i d h y d r o l y s i s and f e r m e n t a t i o n , 452.6 pounds o r 57.3 g a l l o n s o f 100% e t h a n o l , o r 58.4 g a l l o n s o f t h e 95% e t h a n o l water azeotrope. I f enzyme h y d r o l y s i s i s e m p l o y e d i n s t e a d o f a c i d h y d r o l y s i s , somewhat more e t h a n o l i s o b t a i n e d , 533.6 pounds o r 67.6 g a l l o n s o f 100% e t h a n o l , c o r r e s p o n d i n g t o 68.9 g a l l o n s o f 95% e t h a n o l . As was s t a t e d a b o v e , t h e t h e o r e t i c a l e x p e c t a t i o n i f a l l s t a g e s gave 100% y i e l d s w o u l d be 649 l b s o r 81.1 g a l l o n s . The e x p e r i m e n t a l r e s u l t s r e p o r t e d h e r e s u g g e s t t h a t we may expect r e c o v e r y o f e t h a n o l by t h e s e two p r o c e s s e s a t 70.7% and 83.4% o f this theoretical level. I n a d d i t i o n we may e x p e c t t o r e c o v e r 426 l b o f s o l i d l i g n i n and 246 l b o f r e c o v e r a b l e v o l a t i l e s m a i n l y f u r f u r a l and a c e t i c and f o r m i c a c i d s . The l i g n i n so o b t a i n e d may be u s e d as a s o l i d f u e l , o r i t may be c o n v e r t e d t o u s e f u l c h e m i cals. The f u r f u r a l i n t h e v o l a t i l e s i s r e a d i l y c o n d e n s e d and i s also a u s e f u l chemical. A c e t i c and f o r m i c a c i d s a r e a l s o a r t i c l e s o f commerce. E n e r g y b a l a n c e s shown on t h e c h a r t s o f F i g u r e 5 a r e b a s e d on heat values re-determined here. T h e s e h e a t v a l u e s a r e shown i n Table I .



13.

W A Y M A N

Material

E T A L .

and Energy

Balances

in Ethanol

Production

193

Aspen Wood Chips 2000 l b s . (Dry Basis) 18.49 MM BTU

autohydrolysis

Volatiles ( a c e t i c a c i d , formic acid, f u r f u r a l , etc.) 246 l b s .

Wash Water (hemicelluloses) 258 l b s .

Pulp (pulp + l i g n i n ) 1496 l b s . 12.00 MM BTU

I

(20%)

*• Ethanol 16.6 l b s . 0.24 MM BTU

Reducing Sugars Detected - Determined 164 l b s . extraction (20% NaOH)

1

Lignin 452 l b s .

Pulp (mainly c e l l u l o s e ) 1009 l b s . 8.17 MM BTU

I Solids 426 l b s . 3.80 MM BTU

Remained i n S o l u t i o n 26.4 l b s .

enzyme h y d r o l y s i s (95%) a c i d h y d r o l y s i s (80%) Glucose 1065 l b s .

Glucose 897 l b s . fermentation (95%)

Ethanol 517 l b s . 6.70 MM BUT

Ethanol 436 l b s . 5.65 MM BTU Figure

fermentation (95%)

5.

Material

and energy balance. Acid and enzyme autohydrolysis and caustic extraction.

hydrolysis

following


194

CHEMISTRY

F O R

ENERGY

TABLE I Heat o f C o m b u s t i o n D a t a Heat o f C o m b u s t i o n BTU/lb


Substance aspen c h i p s a u t o h y d r o l y s e d aspen lignin l i g n o c e l l u l o s i c pulp ethanol (absolute)

9,246 10,010 11,106 8,098 12,968

U s i n g t h e s e d a t a we h a v e t h e f o l l o w i n g g r o s s e n e r g y p e r t o n o f a s p e n wood: 10 acid hydrolysis ethanol lignin volatiles

6

5.88 3.80 + 9.68 + =52.35 +%

recovery

BTU enzyme h y d r o l y s i s 6.93 3.80 + 10.73 + =58.03+%

T h i s g r o s s e n e r g y r e c o v e r y makes no a l l o w a n c e f o r p r o c e s s i n g energy, i n c l u d i n g a u t o h y d r o l y s i s , a c i d h y d r o l y s i s and a l c o h o l distillation. We c a n e s t i m a t e i t a s f o l l o w s : 10 acid hydrolysis autohydrolysis caustic extraction hydrolysis distillation net energy

recovery

0.6 0.1 0.6 1.7 3.0 =37.1%

b

BTU enzyme h y d r o l y s i s 0.6 0.1 0.2 2.0 2.9 =42.3%

From t h e s e e s t i m a t e s i t i s a p p a r e n t t h a t t h e l i g n i n r e c o v e r e d i s capable o f p r o v i d i n g a l l o f the energy r e q u i r e d t o operate the processes, w i t h a l i t t l e l e f t over. The c h a r t o f F i g u r e 6 r e p r e s e n t s t h e r e s u l t s o f a c i d h y d r o l y s i s and f e r m e n t a t i o n o f a u t o h y d r o l y s e d a s p e n . The y i e l d o f e t h a n o l i s s l i g h t l y l e s s than t h a t obtained from autohydrolysed c a u s t i c e x t r a c t e d a s p e n b e i n g 436 l b o r 55.2 g a l l o n s o f 100% e t h a n o l , o r 56.3 g a l l o n s o f 9 5 % e t h a n o l b e i n g o b t a i n e d p e r t o n o f wood. The h y d r o l y s i s r e s i d u e , a m o d i f i e d l i g n i n , i s o b t a i n e d a t t h e r a t e o f 455 l b p e r t o n o f wood, a n d a b o u t 500 l b h e m i c e l l u l o s e s and v o l a t i l e s a r e a l s o a v a i l a b l e f o r v a r i o u s u s e s . The g r o s s



13.

W A Y M A N

E T

A L .

Material

and Energy

Balances

in Ethanol

195

Production

Aspen Wood Chips 2000 l b s . (Dry B a s i s ) 18.49 MM BTU

autohydrolysis

v o l a t i l e s and s o l u b l e s acid hydrolysis

Glucose 1087 l b s .

Residue ( l i g n i n ) 455 l b s . 4.06 MM BTU

fermentation 90%

Ethanol 436 l b s . 5.64 MM BTU Figure

6.

Material

and energy balance

acid hydrolysis

of autohydroly

zed


aspen


196

CHEMISTRY

F O R

ENERGY

e n e r g y r e c o v e r y i s 5 2 . 4 3 % . S i n c e t h e r e i s no c a u s t i c e x t r a c t i o n s t a g e , a l i t t l e e n e r g y w i l l be s a v e d i n p r o c e s s i n g , and t h e n e t e n e r g y r e c o v e r y i s e s t i m a t e d a t 36.8%. As b e f o r e , t h e r e i s enough l i g n i n residue to f u e l the process. When a u t o h y d r o l y s e d a s p e n was t r e a t e d w i t h c e l l u l a s e enzyme, p o o r r e s u l t s were o b t a i n e d . B a s e d on a t o n o f d r y wood, o n l y a b o u t 300 l b o f f e r m e n t a b l e s u g a r s w e r e o b t a i n e d , and t h e f e r m e n t a t i o n was v e r y i n e f f i c i e n t w i t h l o w y i e l d s o f e t h a n o l . These r e s u l t s compare p o o r l y w i t h t h o s e shown i n F i g u r e 5 when a u t o h y d r o l y s e d - c a u s t i c e x t r a c t e d a s p e n was t r e a t e d w i t h c e l l u l a s e enzyme, and t h e n f e r m e n t e d . I t would appear from these r e s u l t s t h a t t h e c a u s t i c e x t r a c t i o n s t e p f o r l i g n i n r e m o v a l w o u l d be n e c e s s a r y i f t h e e n z y m a t i c h y d r o l y s i s p r o c e s s w e r e t o be a d o p t e d and a d v i s a b l e when a c i d h y d r o l y s i s i s u s e d . E c o n o m i c s o f t h e Two

Processes

The d a t a a b o v e e n a b l e u s t o make some r o u g h e s t i m a t e s o f c o s t s a s s o c i a t e d w i t h two p r o c e s s e s : ( i ) ACID, t h a t i s a s p e n wood-autohydrolysis-caustic extraction-acid hydrolysis-fermentat i o n - d i s t i l l a t i o n ; and ( i i ) ENZYME, t h a t i s a s p e n w o o d - a u t o h y d r o l y s i s - c a u s t i c extraction-enzymatic hydrolysis-fermentationdistillation. For purposes of comparison, the product i n both c a s e s w i l l be assumed t o be 10 m i l l i o n g a l l o n s o f 9 5 % e t h a n o l p e r y e a r , a minimum e c o n o m i c s i z e .

Wood r e q u i r e m e n t , c h i p s , d r y t o n s / d a y Capital Costs, $ c h i p s t o r a g e and d i s t r i b u t i o n a u t o h y d r o l y s i s stage c a u s t i c e x t r a c t i o n stage h y d r o l y s i s stage fermentation distillation steam system water system m a t e r i a l s t o r a g e and h a n d l i n g pollution control b u i l d i n g s and l a n d total physical plant engineering construction overhead, contingency working

capital

Acid

Enzyme

490

415

1,000,000 4,000,000 1,000,000 4,000,000 2,800,000 1,800,000 1,600,000 150,000 1,000,000 150,000 3,500,000 21,000,000

850,000 3,500,000 1,000,000 2,000,000 3,500,000 1,800,000 800,000 400,000 1,000,000 150,000 3,500,000 18,500,000

4,000,000 25,000,000 3,000,000 $28,000,000

4,000,000 22,500,000 3,000,000 $25,500,000



13.

W A Y M A N

ET

AL.


Annual Operating Costs $ Wood c a u s t i c soda sulphuric acid fermentation chemicals p a c k a g i n g and d i s t r i b u t i o n t o t a l variable costs utilities labour maintenance m a t e r i a l s other t o t a l fixed costs t o t a l annual operating costs 20% o f i n v e s t m e n t t o t a l annual costs

197

Acid

Enzyme

4,300,000 200,000 600,000 1,000,000 6,100,000 100,000 2,000,000 200,000 200,000 2,500,000 8,600,000 5,600,000 $14,200,000

3,630,000 200,000 1,000,000 1,000,000 5,830,000 100,000 2,000,000 200,000 200,000 2,500,000 8,330,000 5,100,000 $13,430,000

P r i c e per g a l l o n , i n c l u d i n g d i s t r i b u t i o n and p r o f i t , b u t no t a x

$1.42

$1.34

The above r o u g h e c o n o m i c s s u g g e s t a s i g n i f i c a n t a d v a n t a g e f o r t h e e n z y m a t i c p r o c e s s , a b o u t 10% i n c a p i t a l c o s t s and 6% i n p r o d u c t " c o s t " , o r , s i n c e i t i n c l u d e s an a l l o w a n c e f o r a d e q u a t e r e t u r n on i n v e s t m e n t , p r i c e . The p r i c e p e r g a l l o n w o u l d make t h i s ethanol c o m p e t i t i v e w i t h i n d u s t r i a l a l c o h o l today, but i t i s t o o e x p e n s i v e t o be c o n s i d e r e d f o r m o t o r f u e l a t p r e s e n t g a s o l i n e prices. The c a p i t a l c o s t s g i v e n a r e b e l o w t h o s e g i v e n by M i t r e ( 2 1 ) , o r by K a t z e n ( 2 2 ) , b u t a r e i n l i n e w i t h t h o s e e s t i m a t e d by R o b e r t s o n , N i c k e r s o n ( 2 3 ) . I t w o u l d t a k e more d a t a t h a n a r e a v a i l a b l e t o c h o o s e among t h e s e e s t i m a t e s . Our e s t i m a t e i s b a s e d on a f l o w s h e e t , i n q u i r i e s o f e q u i p m e n t c o s t s and e s t i m a t e s b a s e d on o t h e r e x p e r i e n c e . D i r e c t e x p e r i e n c e i s , so f a r , n o t a v a i l a b l e . What i s b a d l y n e e d e d i s a d e m o n s t r a t i o n p l a n t . The d i s t r i b u t i o n o f f a c t o r s w h i c h e n t e r i n t o t h e p r i c e may be summed up as f o l l o w s : variable operating costs capital related fixed operating costs

43% 39% 18% 100%

The m a j o r f a c t o r w h i c h e n t e r s i n t o v a r i a b l e o p e r a t i n g c o s t s i s wood, h e r e t a k e n as $25.00 p e r d r y t o n , a r e a s o n a b l e c u r r e n t p r i c e f o r a s p e n c h i p s i n s e v e r a l l o c a t i o n s i n Canada. Under some s p e c i a l c i r c u m s t a n c e s t h i s c a n be r e d u c e d c o n s i d e r a b l y : w a s t e a s p e n c h i p s , f o r e x a m p l e , w o u l d c o s t $18.00 p e r t o n . If available in a d e q u a t e q u a n t i t y , s u c h c h i p s w o u l d c u t t h e c o s t o f e t h a n o l by



198

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a b o u t 10 t o 12c p e r g a l l o n . Government i n t e r e s t i n i n d u s t r i a l employment m i g h t r e s u l t i n s u b s i d i e s w h i c h c o u l d e f f e c t i v e l y c u t the c a p i t a l c o s t i n h a l f . T h i s w o u l d r e d u c e t h e c o s t by 25 t o 28c per g a l l o n . T h u s , i t i s c o n c e i v a b l e t h a t a p r o p e r l y l o c a t e d and f u n d e d p r o j e c t c o u l d b r i n g t h e p r i c e o f t h i s e t h a n o l t o $1.00. T h i s w o u l d r e p r e s e n t a v e r y good p r i c e f o r i n d u s t r i a l e t h a n o l . I t i s s t i l l too h i g h f o r g a s o l i n e , even t a k i n g i n t o account expected g a s o l i n e p r i c e s as now p r o j e c t e d f o r t h e n e x t d e c a d e , u n l e s s u n f o r s e e n s h o r t a g e s impose s p e c i a l a d v a n t a g e s f o r t h i s t y p e o f motor f u e l . Discussion The p r e s e n t r e s u l t s s u g g e s t t h a t t h e e n z y m a t i c h y d r o l y s i s process i s at l e a s t c o m p e t i t i v e w i t h the a c i d h y d r o l y s i s p r o c e s s . The m a i n d i f f i c u l t y w i t h i t i s t h e l o n g t i m e r e q u i r e d f o r t h e h y d r o l y s i s , compared w i t h t h e a c i d p r o c e s s . The p r e s e n t w o r k s u g g e s t e d a mechanism f o r o v e r c o m i n g t h i s p r o b l e m , w h i c h i s t o remove t h e s u g a r s as f o r m e d , p e r h a p s by c o m b i n i n g t h e e n z y m a t i c h y d r o l y s i s and t h e f e r m e n t a t i o n i n one v e s s e l a t t h e same t i m e . I n s u c h a combined p r o c e s s , t h e r e m o v a l o f t h e s u g a r s f r o m t h e s o l u t i o n as s o o n as t h e y a r e f o r m e d by t h e f e r m e n t a t i o n w o u l d be e x p e c t e d t o i n c r e a s e b o t h t h e y i e l d and t h e r a t e o f h y d r o l y s i s . T h i s w o r k a l s o s u g g e s t s o t h e r r e s e a r c h and d e v e l o p m e n t d i r e c t i o n s n e e d e d t o b r i n g t h e p r i c e o f e t h a n o l down t o an a u t o m o t i v e fuel level. We n e e d a l o w e r c a p i t a l c o s t h y d r o l y s i s p r o c e s s w h i c h can produce a c o n c e n t r a t e d sugar s o l u t i o n . We a l s o n e e d a f e r m e n t a t i o n process adaptable to concentrated sugar s o l u t i o n s to lower a l c o h o l p u r i f i c a t i o n c o s t s . F i n a l l y we n e e d t o r e c o v e r and i n clude by-product values - l i g n i n , f u r f u r a l , a c i d s , methanol, e t c . i n our income. We s h o u l d a l s o t r y t o a c h i e v e economy o f s c a l e , w h i c h w o u l d r e d u c e u n i t c o s t c o n s i d e r a b l y . B a s e d on p l a n t a t i o n h y b r i d p o p l a r ( 1 ) , p l a n t s o f 100 t o 200 m i l l i o n g a l l o n s p e r y e a r c a n be b u i l t 10 t o 20 t i m e s as l a r g e as t h e example u s e d i n t h e s e c a l c u l a t i o n s . T h i s w o u l d r e d u c e b o t h c a p i t a l and raw m a t e r i a l c o s t s . P e r h a p s we n e e d t o be b o l d e r i n o u r a p p r o a c h t o d e s i g n o f e t h a n o l f r o m b i o m a s s . Summary and

Conclusions

1. Y i e l d s o f e t h a n o l f r o m a s p e n wood a r e 70.7% and 83.4% o f t h e o r e t i c a l where a c i d h y d r o l y s i s and e n z y m a t i c h y d r o l y s i s w e r e e m p l o y e d . These w e r e , r e s p e c t i v e l y , 58.4 g a l l o n s and 68.9 g a l l o n s o f 95% e t h a n o l p e r t o n o f a s p e n wood. I n a d d i t i o n 426 l b l i g n i n w i t h h e a t o f c o m b u s t i o n o f 11,100 B T U / l b w e r e obtained. 2. G r o s s e n e r g y r e c o v e r i e s ( e t h a n o l + l i g n i n ) by t h e two p r o c e s s e s w e r e 52.4% and 5 8 . 0 % , r e s p e c t i v e l y . Taking estimates of proc e s s e n e r g y i n t o a c c o u n t , n e t e n e r g y r e c o v e r i e s were 3 6 . 1 % and 42.3%.



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199

3. M u l t i - s t a g e h y d r o l y s i s was b e n e f i c i a l , compared to s i n g l e stage h y d r o l y s i s , for both a c i d and enzymatic h y d r o l y s i s . Sugar y i e l d s of 80% of theory were obtained i n 5-stage a c i d hydro l y s i s , and over 99% i n 3-stage enzymatic h y d r o l y s i s . These r e s u l t s w i t h enzyme h y d r o l y s i s suggest that constant removal of sugar as formed, by d i a l y s i s or by fermentation, may g r e a t l y improve present enzymatic h y d r o l y s i s procedures. 4. Wood p r e t r e a t e d by a u t o h y d r o l y s i s and e x t r a c t i o n i s necessary f o r s u c c e s s f u l enzymatic h y d r o l y s i s , and advantageous for a c i d hydrolysis. 5. Economic estimates show a s i g n i f i c a n t advantage i n c a p i t a l and o p e r a t i n g costs for enzymatic h y d r o l y s i s e t h a n o l . The i n v e s t ment r e q u i r e d f o r a p l a n t to make 10 m i l l i o n g a l l o n s per year of aspen-based ethanol would be about $25 to $28 m i l l i o n . The p r i c e of the product, i n c l u d i n g a reasonable r e t u r n on i n v e s t ment , would be about $1.34 to $1.42 per g a l l o n . About one quarter of the cost i s wood c o s t , and another t w o - f i f t h s i s capital related. By a proper choice of l o c a t i o n w i t h good p r o x i m i t y to cheap aspen c h i p s , and by s u i t a b l e funding arrange ments, the p r i c e of 95% ethanol c o u l d be reduced to $1.00 per g a l l o n . This would be a good p r i c e f o r i n d u s t r i a l a l c o h o l . I t i s too high to be considered as a gasoline s u b s t i t u t e , unless unforseen shortages impose s p e c i a l advantages f o r t h i s type of motor f u e l . Acknowledgements We acknowledge w i t h thanks the c o - o p e r a t i o n of Stake Technology, e s p e c i a l l y Mr. Robert Bender, i n the continuous a u t o h y d r o l y s i s , and of the N a t i c k group under D r . Leo Spanο i n p r o v i d i n g c e l l u l a s e . We have r e c e i v e d f i n a n c i a l a s s i s t a n c e from the N a t i o n a l Research C o u n c i l of Canada and from the U n i v e r s i t y of Toronto.

Abstract Experimental production of ethanol from aspen wood gave yields of 70.7% or 83.4% of theory when acid hydrolysis or enzy matic hydrolysis were used after autohydrolysis and extraction of lignin. These were, respectively, 58.4 and 68.9 gallons of 95% ethanol per ton of aspen wood (dry basis). In addition 426 lb of lignin with heat of combustion 11,100 BTU/lb were obtained per ton of wood. Gross energy recovery (ethanol + lignin) was 52.4 and 58.0% by the two processes, or allowing for processing energy, net energy recovery was 36.1 and 42.3% respectively. Multi stage hydrolysis was beneficial for both acid and enzymatic hydrolysis, 80% and over 99% of theoretical yields of sugar being obtained by the two processes. Economic estimates show a significant advantage in investment and operating costs for the enzymatic process. The price of 95% ethanol, including a reasonable return on investment by this process is estimated at $1.34/gallon. This would be a


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good price for industrial ethanol, but would be quite high for gasoline use under prevailing circumstance. Literature Cited


1.

2. 3. 4.

5.

6.

7. 8. 9. 10.

11. 12.

13.

Lora, J . H . , M.A.Sc. Thesis, University of Toronto, 1976; Lora, J.H. and Wayman, Μ., Fast Growing Hybrid Poplar: A Renewable Source of Chemicals, Energy and Food, Forest Research Informa tion Paper No. 102, Ontario Ministry of Natural Resources, Toronto, 1978; Wayman, M. and Lora, J . H . , Wood-fired Electri city Generation in Eastern Ontario, Royal Commission on Electric Power Planning, Toronto, Ontario, 1978 (including references to many recent symposia and studies). Lewis, C.W., Fuels from Biomass - Energy Outlay Versus Energy Returns: A Critical Appraisal. Energy (1977) 2(3), 241-248. Davies, D.S., The Changing Nature of Industrial Chemistry. Chemical and Engineering News (March, 1978) 22-27. InterGroup Consulting Economists, Economic Pre-Feasibility Study: Large-Scale Methanol Fuel Production from Surplus Cana dian Forest Biomass. Fisheries and Environment Canada, Ottawa, 1976. Mackay, D. and Sutherland, R., Methanol in Ontario. Ontario Ministry of Energy, Toronto, 1976; Mackay, D., Boocock, D.G.B. and Sutherland, R., The Production of Synthetic Liquid Fuels for Ontario. Ontario Ministry of Energy, Toronto, 1978. Azarniouch, M.K. and Thompson, K.M., Alcohols from Cellulose Production Technology, presented at Symposium: Canadian Society for Chemical Engineering and Canadian Society for Mechanical Engineering, Toronto, 1976. Clark, D.S., Fowler, D.B., Whyte, R.B. and Wiens, J . K . , Eth anol from Renewable Resources. The Canadian Wheat Board, Ottawa, 1971. Robertson, Nickerson Limited, Saskatchewan Industrial Fermen tation Complex, Regina, 1976. Wenzl, H.F.N., "The Chemical Technology of Wood", Academic Press, New York, 1970. Tokarev, B . I . , Hydrolysis of Wood, Chapter XXIV in "The Chem istry of Cellulose and Wood", by N.I. Nikitin. Translated from the Russian by Israel Program for Scientific Translations, Jerusalem, 1966. Wayman, Μ., Food from Wood, Forest Commission Bulletin 56. Her Majesty's Stationery Office, London, 1976. Linderman, R.L. and Rochioli, C., Ethanol in Brazil: A Brief Summary of the State of the Industry in 1977, The Seagram Lecture, the Second Joint Chemical Institute of Canada -American Chemical Society Conference, Montreal, 1977. Gaden, E . L . , Jr., Mandels, M.H., Reese, E.T. and Spano, L . A . , Enzymatic Conversion of Cellulosic Materials: Technology and Applications. Interscience-Wiley, New York, 1976.



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14. Lora, J.H. and Wayman, Μ., Delignification of Hardwoods by Autohydrolysis and Extraction, Tappi (1978) 61(6) 47-50. 15. Timmel, T., Tappi (1957) 40(1) 30. 16. Stake Technology Limited, 20 Enterprise Avenue, Ottawa, Ontario, Canada, K2A 0A6. 17. Kohler, L.H., Differentiation of Carbohydrates by Anthrone Reaction Rate and Color Intensity, Anal. Chem. (1952) 24(10) 1576-1579. 18. Miller, G.L., Anal. Chem. (1959) 31, 426. 19. Mandels, M.H. and Sternberg, D., Recent Advances in Cellulase Technology. Cellulase Technology (1976) 54(4) 267-286. United States Army Natick Development Center. Production and Appli cations of Cellulase: Laboratory Procedures, Natick, Mass., 1974. 20. Myers, S.G., Ethanolic Fermentation During Enzymatic Hydroly sis of Cellulose. Second Pacific Chemical Engineering Congress, Denver, Colorado, 1977. 21. Blake, D. and Salo, D., Solar Related Technologies. Vol. IX. Biomass Fueld Production and Conversion Systems, The Mitre Corporation, McLean, Virginia, 1977. 22. Hokanson, A.E. and Katzen, R., Chemicals from Wood Waste. Ralph Katzen Associates, Cincinnati, Ohio, 1977. 23. Saskatchewan Industrial Fermentation Complex. Robertson, Nickerson Group Associates, Ottawa, 1976. RECEIVED July 24,1978.


Material and Energy Balances in the Production of Ethanol from Wood

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