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Preface THE P R O C E S S O F C O N V E R T I N G L O W - V A L U E l i g n o c e l l u l o s i c b i o m a s s t o ethanol v i a fermentation depends keenly o n the development o f e c o n o m i c a l b i o c a t a l y s t s t o a c h i e v e effective d e p o l y m e r i z a t i o n o f t h e c a r b o h y d r a t e c o n t e n t o f b i o m a s s t o sugars. T h i s p r o c e s s shares s e v e r a l features i n c o m m o n w i t h c o n t e m p o r a r y , large-scale uses o f c e l l u l a s e s a n d o t h e r c a r b o h y d r a s e s (i.e., f o o d a n d h o r t i c u l t u r a l p r o c e s s i n g ) , i n c l u d i n g t h e r e q u i r e m e n t f o r cost-effective a n d r e l i a b l e e n z y m e p r o d u c t i o n . H o w e v e r , u n l i k e enzymes used i n the f o o d industry, cellulases used i n ethanologenic p r o c e s s e s n e e d n o t b e d e r i v e d f r o m G R A S ( g e n e r a l l y r e c o g n i z e d as safe) microorganisms. Still, proper stewardship o f environmental concerns must be considered. C e l l u l a s e enzymology research, s u p p o r t e d by the D e p a r t m e n t o f E n e r g y ' s B i o f u e l s P r o g r a m , investigates k e y aspects o f r e d u c i n g t h e s u b stantial cost o f cellulase enzymes used i n industrial processes. T h e driv i n g f o r c e f o r t h i s effort is t h e e x t r a o r d i n a r i l y h i g h r a t i o o f e n z y m e r e q u i r e d t o fully d e p o l y m e r i z e c e l l u l o s e (that is, o n e k i l o g r a m o f c e l l u l a s e f o r 50 k i l o g r a m s o f c e l l u l o s e ) . B e c a u s e n a t i v e b i o m a s s is r e s i s t a n t t o enzymatic action, c h e m i c a l - m e c h a n i c a l methods o f c o n d i t i o n i n g the sub strate must be e m p l o y e d p r i o r to saccharification. T h e s e methods o f "pretreatment" require optimization for different substrates and economies o f conversion to ethanol. F u r t h e r m o r e , the ideal cellulase c o m p l e x used i n biomass processing must be carefully chosen to ensure h i g h a c t i v i t i e s o n t h e a c t u a l substrate u s e d ( s u c h as d i l u t e a c i d p r e t r e a t e d woods, waste paper, a n d agricultural residues). T h e key question to be c o n s i d e r e d f o r e c o n o m i c b i o m a s s c o n v e r s i o n is, " W h i c h p r e t r e a t m e n t a n d c e l l u l a s e system s h o u l d b e c h o s e n f o r t h i s t a s k ? " Enzymatic Conversion of Biomass for Fuels Production features 24 chapters written by many o f the leading international authorities i n the fields o f c e l l u l a s e b i o c h e m i s t r y , b i o f u e l c e l l d e v e l o p m e n t , a n d e t h a n o l o genic fermentation. T h e chapters i n this b o o k highlight the diversity o f approaches used to enhance o u r understanding o f the a c t i o n o f cellulases o n i n s o l u b l e substrates, as w e l l as efforts t o p r e t r e a t a n d f e r m e n t t h e sugars t h u s r e l e a s e d to e t h a n o l . A l s o r e p o r t e d i n t h i s b o o k a r e r e c e n t studies i m p o r t a n t t o t h e p r o d u c t i o n o f b i o d i e s e l fuels a n d e l e c t r o l y t i c f u e l c e l l s . W e b e l i e v e t h e c h a p t e r s i n this b o o k b r i n g , i n d i v i d u a l l y a n d c o l l e c tively, a u n i q u e p e r s p e c t i v e t o t h e f i e l d o f b i o m a s s c o n v e r s i o n .
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Himmel et al.; Enzymatic Conversion of Biomass for Fuels Production ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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Acknowledgments W e are grateful to the B i o t e c h n o l o g y Secretariat o f the A C S for sponsor i n g t h e s y m p o s i u m u p o n w h i c h t h i s b o o k is based. W e a l s o w i s h t o t h a n k t h e o r g a n i z e r s a n d m o d e r a t o r s o f the t h r e e sessions a r o u n d w h i c h t h e s y m p o s i u m a n d b o o k w e r e c o n s t r u c t e d : J o h n O . B a k e r , S e s s i o n I; P a u l G . R o e s s l e r , S e s s i o n II; a n d M i c h a e l E . H i m m e l , S e s s i o n III. T h e i r c o n t r i b u t i o n w a s e s s e n t i a l to t h e success o f t h e s y m p o s i u m a n d b o o k . W e a l s o t h a n k L i z Y a n d a f o r h e r e x p e r t assistance i n p r o d u c t i o n o f t h e f i n a l v e r s i o n s o f a l l 24 c h a p t e r s . O u r e d i t o r at A C S B o o k s was B a r b a r a E . P r a l l e . H e r g u i d a n c e a n d efficient p r o c e s s i n g o f t h e m a n u s c r i p t s w e r e k e y t o t h e t i m e l y p r o d u c t i o n o f t h e b o o k . F i n a l l y , w e t h a n k the s c i e n t i s t s c o n t r i b u t i n g c h a p t e r s to this b o o k . I n a l l cases t h e i r h i g h - q u a l i t y w o r k a n d c a r i n g a t t i t u d e h a v e e n h a n c e d o u r u n d e r s t a n d i n g o f this i n t r i g u i n g field. I n c o n c l u d i n g this preface, w e offer the f o l l o w i n g e x c e r p t f r o m c o l l e g e l e c t u r e n o t e s w r i t t e n d u r i n g t h e 1940s. D e s p i t e t h e e x t r e m e l y e v e n t f u l five decades t h a t l i e b e t w e e n the w r i t i n g o f the n o t e s a n d t h e i r i n c l u s i o n i n t h i s preface, w e b e l i e v e t h a t t h i s e x c e r p t fully c a p t u r e s t h e f u n d a m e n t a l w o r l d v i e w a n d s p i r i t u n d e r l y i n g t h e efforts d e s c r i b e d i n t h i s v o l u m e . A s y o u huddle a r o u n d the campfire o n a dark and chilly night w i t h a group o f friends and quietly watch the tongues o f flame play over the b u r n i n g w o o d , have you ever tried to visualize what is happening before you? H e r e are the pieces o f w o o d w h i c h seem so real. They have form, color, weight, hardness for a moment; and then the next moment they disappear from view. W h i t h e r is this substance going? T h e chemist tells us that all the elements w h i c h were originally taken from the atmosphere as gases are n o w returning to the atmosphere as gases. A l l the materials w h i c h originally came from the soil are n o w returning to the soil as ashes. So most of the substance o f the w o o d is being diffused into space i n a colorless, intangible, transparent form. B u t the leaves o f the tree are able to recapture these ele ments again and convert them into recognizable forms once more. B u t whence all this light and heat? T h e leaves in the forming o f sugar out of carbon dioxide and water capture the sun's energy and convert it into potential energy stored in the w o o d . W h e n the w o o d is burned it combines with oxygen, and the energy captured from the sunlight is again released. So the light and warmth of the campfire is really "canned" sunshine. It is k i n to the rainbow and sunset and glimmerings o f distant stars. T h u s the process of photosynthesis carried on in the leaves and
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the process of oxidation comprise a cycle in which the carbon and oxygen of nature continually move, ever storing and releasing heat in the process. —Edward N . Himmel, Professor of Botany from 1909 to 1958, North Central College, Naperville, IL.
M I C H A E L E. HIMMEL A p p l i e d Biological Sciences Branch
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J O H N O. BAKER A p p l i e d Biological Sciences Branch R A L P H P. O V E R E N D Alternative Fuels Division National Renewable Energy Laboratory 1617 Cole Boulevard Golden, CO 80401-3393 June 16, 1994
xiii Himmel et al.; Enzymatic Conversion of Biomass for Fuels Production ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
