Supercritical Fluid Extraction of Lignin from Wood - ACS Symposium

Chapter 4

Supercritical Fluid Extraction of Lignin from Wood Lixiong Li and Erdogan K i r a n

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Department of Chemical Engineering, University of Maine, Orono, Downloaded by RUTGERS UNIV on February 22, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch004

ME 04469

Reactive extraction of lignin from red spruce has been studied using supercritical methylamine and methylamine-nitrous oxide binary mixtures. The wood residues and precipitated fractions after extractions have been characterized by chemical and spectroscopic procedures. The molecular weights and molecular weight distributions of the extracted lignins have been determined by gel permeation chromatography. The effect of extraction time, temperature, pressure, and composition of extraction fluid on molecular weights of the extracted lignins has been studied. The molecular weight distribution of the lignins extracted by methylamine-nitrous oxide binary mixture is observed to be similar to that of kraft lignin (Indulin AT). In contrast, lignins extracted by pure methylamine display much broader molecular weight distributions. Molecular weight distributions become broader with an increase in extraction time, temperature, or pressure. Supercritical fluid extraction is a new separation technique that finds a number of applications in the natural products, biochemicals, food, pharmaceuticals, petroleum, fuel, and polymer industries (1-8). There is now an interest in applying this technology in the pulp and paper industry (9,10). In a recent comprehensive study on the interaction of supercritical fluids with lignocellulosic materials, it has been shown that lignin can be not only extracted from wood by reactive supercritical fluids but also separated as solid products in solvent-free form by reducing the extraction fluid pressure from a supercritical to sub critical level (11,12). Address correspondence to this author.

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0097-6156/89/0397-0042$06.00/0 C 1989 American Chemical Society

In Lignin; Glasser, Wolfgang G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Downloaded by RUTGERS UNIV on February 22, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch004

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A m o n g the various e x t r a c t i o n fluids, s u p e r c r i t i c a l m e t h y l a m i n e a n d m e t h y l a m i n e - n i t r o u s oxide b i n a r y m i x t u r e s have been f o u n d to be espec i a l l y effective i n the selective removal o f l i g n i n f r o m w o o d . T h i s has been verified by c h e m i c a l ( K l a s o n l i g n i n d e t e r m i n a t i o n ) , t h e r m a l ( t h e r m o g r a v i m e t r i c a n a l y s i s ) , a n d spectroscopic (infrared) analyses of the w o o d residues a n d the e x t r a c t e d fractions. It has been s h o w n t h a t l i g n i n r e m o v a l increases w i t h e x t r a c t i o n t i m e , t e m p e r a t u r e , pressure, a n d the m e t h y l a m i n e content ( i n the b i n a r y m i x t u r e of m e t h y l a m i n e - n i t r o u s oxide). A m o t i v a t i o n i n the use of b i n a r y m i x t u r e s i n v o l v i n g one of the components w i t h selective r e a c t i o n c a p a b i l i t y t o w a r d l i g n i n (such as m e t h y l a m i n e ) is the p o s s i b i l i t y of i n d u c i n g a l i m i t e d f r a g m e n t a t i o n of l i g n i n u p o n w h i c h its d i s s o l u t i o n is achieved i n the s u p e r c r i t i c a l fluid m e d i a . If t h i s is i n fact the case, the m o l e c u l a r weight of the lignins m a y be expected to be larger t h a n t h a t of lignins o b t a i n e d b y conventional p u l p i n g processes. T o test t h i s h y p o t h e sis, i n f o r m a t i o n o n the m o l e c u l a r weight a n d m o l e c u l a r weight d i s t r i b u t i o n ( M W D ) of l i g n i n f r o m s u p e r c r i t i c a l fluid e x t r a c t i o n is needed. T h e present paper is focused o n t h i s p a r t i c u l a r aspect. T h e l i t e r a t u r e o n m o l e c u l a r weight a n d M W D of l i g n i n s r e s u l t i n g f r o m various conventional c h e m i c a l treatments is quite extensive (13-15). In the selection of p r o p e r solvents for G P C analysis of l i g n i n , i n f o r m a t i o n o n s o l u b i l i t y of lignins i n various solvents documented b y m a n y researchers (17-19) is very useful. T h e c o m m o n l y used solvents are either aqueous s o l u t i o n s (20-23) or organic c o m p o u n d s such as t e t r a h y d r o f u r a n ( T H F ) , d i m e t h y l f o r m a m i d e ( D M F ) , d i m e t h y l s u l f o x i d e ( D M S O ) , a n d dioxane (24-28). M o r e recently, the use of h i g h performance gel p e r m e a t i o n c h r o m a t o g r a p h y w i t h s t y r e n e - d i v i n y l b e n z e n e copolymer gel c o l u m n s to characterize l i g n i n molecu l a r weight has been reported (29-31). A m o n g the various solvents, D M F is reported to be the most effective organic solvent to dissolve k r a f t lignins (19). It has also been suggested t h a t association effects of nonacetylated l i g n i n molecules i n D M F can be s u b s t a n t i a l l y reduced b y a d d i n g l i t h i u m b r o m i d e to D M F solvent (31-33). In the present s t u d y , G P C analyses were carried out i n D M F + 0 . 1 M L i B r using W a t e r s U l t r a s t y r a g e l c o l u m n s . G P C results of the e x t r a c t e d l i g n i n s have been interpreted w i t h respect to e l u t i o n volumes, a n d c o m p a r e d w i t h the results of k r a f t pine l i g n i n ( I n d u l i n A T ) to d i s t i n g u i s h different molecu l a r weight features. Experimental Extraction System. T h e flow-through e x t r a c t i o n s y s t e m used i n t h i s s t u d y is s h o w n i n F i g u r e 1. T h e s y s t e m is operable u p to 400 b a r at 200°C. It c o n sists of solvent delivery systems ( F l u i d 1, F l u i d 2, F l u i d 3), a flow-through reactor ( F R ) , a set of separator traps ( T P 1 , T P 2 ) , a n d the t e m p e r a t u r e a n d pressure c o n t r o l u n i t s . T h e reactor, t r a p s , m i c r o m e t e r i n g valves, a n d t u b i n g connections are housed i n a heated oven. In a t y p i c a l e x t r a c t i o n e x p e r i m e n t , a k n o w n a m o u n t of w o o d (about 3 g) i n sawdust f o r m is first loaded into the reactor. B o t h the reactor a n d the separators are heated under a gentle n i t r o g e n flow (10 c c / m i n ) to the



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F i g u r e 1. E x p e r i m e n t a l s y s t e m for s u p e r c r i t i c a l f l u i d e x t r a c t i o n . L F = l i n e filter; P G = pressure gauge; S V = shut-off valve; C V = check valve; P H C = p r e h e a t i n g c o i l ; T C = t h e r m o c o u p l e ; M V = m i c r o m e t e r i n g valve; T P = separator t r a p ; subscripts: r = reactor; 1,2 = t r a p 1,2.

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desired e x t r a c t i o n t e m p e r a t u r e . T h e n the e x t r a c t i o n fluid is i n t r o d u c e d i n t o the reactor. B y a d j u s t i n g the m i c r o m e t e r i n g valve ( M V ) , the pressure i n the reactor is m a i n t a i n e d at a desired level. A f t e r the r e a c t i o n , the s y s t e m pressure is reduced to atmospheric level either d i r e c t l y or i n a stagewise fashion w i t h the a i d of the m i c r o m e t e r i n g valves M V i a n d M V 2 . T h e e x t r a c t i o n is continued for a specified t i m e . A t the end of each r u n , the w o o d residue i n the reactor ( F R ) a n d the precipitate i n the t r a p s ( T P 1 a n d T P 2 ) are collected a n d a n a l y z e d . In the present s t u d y reactor t e m p e r a t u r e , pressure, a n d e x t r a c t i o n t i m e are varied i n the range f r o m 175 to 185°C, 170 to 275 b a r , a n d 0.5 to 5 h r , respectively. T h e pressure i n the first t r a p is m a i n t a i n e d at 1 b a r . Downloaded by RUTGERS UNIV on February 22, 2016 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch004

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Materials. T h e w o o d s a m p l e , red spruce (Picea rubens), was o b t a i n e d l o c a l l y a n d used i n sawdust f o r m collected f r o m a 1 m m sieve. K r a f t pine l i g n i n ( I n d u l i n A T ) was o b t a i n e d f r o m Westvaco. T h e e x t r a c t i o n fluids, n i t r o u s oxide ( A i r c o , 99.9 w t . % p u r i t y ) a n d m e t h y l a m i n e ( L i n d e S p e c i a l t y Gases, 98.0 w t . % p u r i t y ) were used w i t h out further p u r i f i c a t i o n . E l u e n t s o l u t i o n ( D M F + 0 . 1 M L i B r ) for G P C analysis was prepared w i t h H P L C grade d i m e t h y l f o r m a m i d e ( B u r d i c k a n d J a c k s o n ) a n d l i t h i u m b r o m i d e ( F i s h e r Scientific C o . ) , w h i c h were used w i t h o u t further p u r i f i c a tion. G P C performance was tested using polystyrene s t a n d a r d s dissolved i n the same solvent. T h e polystyrene standards (average m o l e c u l a r weights: 300,000, 100,000, 50,000, 35,000, 17,500, 4,000, 2,000 w i t h p o l y d i s p e r s i t y < 1.06) were o b t a i n e d f r o m the Pressure C h e m i c a l C o m p a n y . Critical Properties. T h e c r i t i c a l t e m p e r a t u r e , pressure a n d v o l u m e for m e t h y l a m i n e , n i t r o u s oxide a n d their b i n a r y m i x t u r e s were e x p e r i m e n t a l l y d e t e r m i n e d a n d have been p r e v i o u s l y reported (34). T h e c r i t i c a l t e m p e r atures of the m i x t u r e s are i n t e r m e d i a t e between those of the pure c o m p o nents ( T m e t h y l a m i n e = 156.9°C; T n i t r o u s oxide = 36.5°C). T h e c r i t i c a l pressure goes t h r o u g h a m a x i m u m between the pure c o m p o n e n t values ( P m e t h y l a m i n e = 7.43 b a r ; P n i t r o u s oxide = 72.4 b a r ) . T h e m a x i m u m (92.5 bar) is observed at about 46 w t . % m e t h y l a m i n e content. T h e e x t r a c t i o n conditions reported i n the present s t u d y are a l l above the c r i t i c a l T a n d P of the fluids used. c

c

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Chemical and Spectroscopic Analyses. A c i d insoluble l i g n i n ( K l a s o n l i g n i n ) contents of w o o d species before a n d after extractions were d e t e r m i n e d u s i n g a m o d i f i e d procedure s u i t a b l e for s m a l l samples (35). A D i g i l a b F T I R spectrophotometer ( M o d e l F T S - 6 0 ) was used to o b t a i n I R s p e c t r a of samples before a n d after e x t r a c t i o n s . S t a n d a r d K B r pellets c o n t a i n i n g 1% b y weight s a m p l e were used. GPC Analysis. M o l e c u l a r weight characterizations were c a r r i e d out u s i n g a W a t e r s 840 G e l P e r m e a t i o n C h r o m a t o g r a p h e q u i p p e d w i t h b o t h a n u l t r a violet ( U V ) ( M o d e l 481) a n d a refractive index ( R I ) detector ( M o d e l 410). T w o U l t r a s t y r a g e l c o l u m n s , i n the r u n n i n g order of 1,000 a n d 10,000A pore



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size, were used. T o prevent the c o l u m n f r o m clogging w i t h i m p u r i t i e s t h a t m a y exist i n the mobile phase, a 2 - m i c r o n g u a r d c o l u m n was connected i n series before the 1000A c o l u m n . T h e i n s t r u m e n t was operated at 1.0 c c / m i n solvent flow w i t h 30 m i n r u n t i m e . T h e c o l u m n s a n d the sample a n d reference cell i n the R I detector were m a i n t a i n e d at 40°C. T h e sample concentration was 0 . 1 % ( w / v ) a n d the i n j e c t i o n v o l u m e was 25 pi. T h e wavelength of the U V detector was set at 268 n m . Because l i g n i n s c o n t a i n a large n u m b e r of p h e n o l i c , m e t h o x y l , a n d a r y l ether f u n c t i o n a l groups (36,37), interactions between l i g n i n molecules themselves, a n d between l i g n i n molecules a n d gel m a t e r i a l , m a y not be c o m pletely avoided regardless of the nature of a given solvent. S u c h molecular interactions, especially i n the case of u n d e r i v a t i z e d l i g n i n s , result i n a b a c k pressure rise across the c o l u m n s a n d t a i l i n g i n the c h r o m a t o g r a m w h i c h m a y be observed when the system is continuously used over an e x t e n d e d t i m e p e r i o d . A consequence of c o l u m n back-pressure rise is a r e d u c t i o n i n the a c t u a l solvent flow rate a n d an increase i n the observed e l u t i o n v o l umes. I n the present study, to test the r e l i a b i l i t y of e l u t i o n times, s t a n d a r d polystyrene samples were r u n i n between several runs w i t h l i g n i n samples. Results and Discussion F i g u r e 2 shows the extent of dissolution of red spruce i n m e t h y l a m i n e , the a m o u n t of p r e c i p i t a t e collected i n the first t r a p u p o n complete depressuri z a t i o n to 1 b a r , a n d the K l a s o n l i g n i n content i n the w o o d residue after e x t r a c t i o n , as functions of e x t r a c t i o n t i m e . T h e t o t a l d i s s o l u t i o n a n d prec i p i t a t i o n are n o r m a l i z e d w i t h respect to oven d r y weight of i n i t i a l w o o d . T h e e x t r a c t i o n conditions were 185°C, 275 b a r , a n d 1 g / m i n solvent flow rate. A s s h o w n i n the figure, d i s s o l u t i o n i n i t i a l l y increases w i t h t i m e a n d levels off at about 2 8 % by weight. T h e precipitates w h i c h were collected as solids follow a s i m i l a r t r e n d . T h e K l a s o n l i g n i n content of the w o o d residue decreases w i t h e x t r a c t i o n t i m e , f r o m a n i n i t i a l value of 2 6 . 5 % d o w n to 1 0 . 1 % after 5 h of e x t r a c t i o n . T h e residues a n d precipitates f r o m the above t i m e dependent e x t r a c t i o n s t u d y were further characterized by F T I R . T h e most d i s t i n c t i v e I R absorbance b a n d for l i g n i n is observed at 1510 c m " due to a r o m a t i c r i n g v i b r a t i o n s (37). A s shown i n F i g u r e 3, the a b s o r p t i o n i n t e n s i t y of the residues at 1510 c m " decreases w i t h increasing e x t r a c t i o n t i m e . W h e n c o m p a r e d to the s p e c t r u m of red spruce at this same absorbance region, i t is easy to see t h a t the relative a m o u n t of l i g n i n i n the w o o d samples decreases to a lower level after m e t h y l a m i n e e x t r a c t i o n . F i g u r e 4 shows the I R s p e c t r a of I n d u l i n A T a n d the precipitates f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce a n d I n d u l i n A T , respectively. W e observe f r o m this c o m p a r a t i v e p l o t t h a t the I R s p e c t r a of the precipitates f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce a n d m e t h y l a m i n e e x t r a c t i o n of I n d u l i n A T are nearly i d e n t i c a l , suggesting t h a t the precipitate f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce is indeed l i g n i n - l i k e m a t e r i a l . T h e figure also shows the I R s p e c t r u m of the precipitate f r o m a m m o n i a e x t r a c t i o n of red spruce. T h e s p e c t r u m of the 1

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• KLRSON LIGNIN o DISSOLUTION a PRECIPITATION

uJ a ID CL

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F i g u r e 2. D i s s o l u t i o n (%) o f red spruce i n m e t h y l a m i n e ( O ) , K l a s o n l i g n i n content (%) i n t h e residues after e x t r a c t i o n ( • ), a n d t h e a m o u n t (%) o f precipitates i n the first t r a p (at 1 b a r ) ( A ) , as functions o f e x t r a c t i o n t i m e . E x t r a c t i o n c o n d i t i o n s : 185°C, 275 b a r , a n d 1 g / m i n solvent flow rate.

American Chemical Society Library 115516th St.. N.w.

In Lignin; Glasser, Wolfgang G., et al.; O.C. Society: 20036 Washington, DC, 1989. ACS Symposium Series;Washington. American Chemical



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F i g u r e 3. Infrared s p e c t r a of red spruce ( A ) , a n d red spruce residues after 1 h ( B ) , 2 h ( C ) , 3 h ( D ) , a n d 5 h ( E ) m e t h y l a m i n e e x t r a c t i o n at 1 8 5 ° C , 275 b a r a n d 1 g / m i n solvent flow rate.



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Figure 4. Infrared spectra of kraft lignin, Indulin A T (D), and the precipitates collected i n the first trap (at 1 bar) after methylamine extraction of Indulin A T (C), methylamine extraction of red spruce (B), and ammonia extraction of red spruce ( A ) . Extraction conditions: 2 h extraction at 185 ° C, 275 bar, and 1 g/min solvent flow rate.


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p r e c i p i t a t e f r o m a m m o n i a e x t r a c t i o n displays a different absorbance p a t t e r n , i n d i c a t i n g t h a t t h i s p r e c i p i t a t e m a y be a m i x t u r e of dissolved l i g n i n as w e l l as carbohydrates f r o m red spruce. F u r t h e r details of e x t r a c t i o n results w i t h other fluids a n d lignocellulosic m a t e r i a l s a n d the results of c h e m i c a l analyses are presented elsewhere (11,12). H a v i n g identified the precipitate f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce as b e i n g p r i m a r i l y e x t r a c t e d l i g n i n s , we investigated their m o l e c u l a r weights a n d m o l e c u l a r weight d i s t r i b u t i o n s by G P C . A l l G P C results i n t h i s paper are presented o n the basis of relative s a m p l e e l u t i o n v o l u m e ( i n d i c a tive of m o l e c u l a r weight) a n d relative e l u t i o n v o l u m e range a n d i n t e n s i t y ( i n d i c a t i v e of m o l e c u l a r weight d i s t r i b u t i o n ) . T h e s a m p l e c h r o m a t o g r a m s presented i n F i g u r e s 5 to 10 are traces of the U V absorbance detected at 268 n m . These c h r o m a t o g r a m s show the effects of e x t r a c t i o n t i m e , t e m p e r ature, pressure, a n d c o m p o s i t i o n o n the m o l e c u l a r weight o f the e x t r a c t e d lignin. F i g u r e 5 shows the c o m p a r a t i v e c h r o m a t o g r a m s of five l i g n i n samples o b t a i n e d f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce. T h e e x t r a c t i o n c o n d i tions were m a i n t a i n e d at 185°C, 275 b a r , 1 g / m i n solvent flow rate, except t h a t e x t r a c t i o n t i m e was v a r i e d f r o m 0.5 h to 5 h . A s the e x t r a c t i o n t i m e increases, the detector s i g n a l intensity corresponding to lower m o l e c u l a r weight range (at higher e l u t i o n volume) becomes more d i s t i n c t , a n d the base of the s a m p l e peaks extends more to the left ( i n d i c a t e d by s m a l l a r rows). These changes i n the c h r o m a t o g r a m s are i n d i c a t i v e of a n increase i n the r e l a t i v e f r a c t i o n of b o t h s m a l l a n d large sized molecules, w h i c h lead t o a broader M W D . T h u s , longer e x t r a c t i o n t i m e w i t h m e t h y l a m i n e appears to produce lignins w i t h broader M W D . T h e effect of e x t r a c t i o n t e m p e r a t u r e o n the M W D ' s of the e x t r a c t e d lignins is s h o w n i n F i g u r e 6. T h e l i g n i n samples were o b t a i n e d f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce at temperatures r a n g i n g f r o m 175 to 185°C, w h i l e m a i n t a i n i n g other e x t r a c t i o n conditions at 275 b a r , 3 h , a n d 1 g / m i n solvent flow rate. T h e figure shows t h a t the M W D ' s of the l i g n i n s b e c o m e broader w i t h increasing e x t r a c t i o n t e m p e r a t u r e . I n a s i m i l a r way, a n i n crease i n e x t r a c t i o n pressure leads t o a broader M W D of the l i g n i n s ( F i g . 7). These lignins were o b t a i n e d f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce at 185°C. T h e e x t r a c t i o n t i m e was 3 h at 1 g / m i n solvent flow rate i n the pressure range f r o m 172 to 275 b a r . F i g u r e 8 shows the c o m p a r a t i v e c h r o m a t o g r a m s of l i g n i n samples o b t a i n e d f r o m e x t r a c t i o n of red spruce a n d m e t h y l a m i n e - n i t r o u s oxide b i n a r y m i x t u r e at five different compositions (0.2, 0.4, 0.6, 0.8, 1.0 weight f r a c t i o n of m e t h y l a m i n e , at 185°C, 275 b a r , 2 h , a n d 1 g / m i n solvent flow r a t e ) . T h e apparent M W D ' s of the lignins f r o m the b i n a r y solvent e x t r a c t i o n s are narrower t h a n those of the lignins o b t a i n e d w i t h pure m e t h y l a m i n e e x t r a c t i o n . O n the other h a n d , l i g n i n s f r o m pure m e t h y l a m i n e e x t r a c t i o n appear to have the largest average m o l e c u l a r weight a m o n g the l i g n i n s s h o w n i n F i g u r e 8. T o compare lignins p r o d u c e d f r o m s u p e r c r i t i c a l fluid e x t r a c t i o n of w o o d w i t h lignins f r o m conventional p u l p i n g processes, a k r a f t pine l i g n i n



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F i g u r e 5. G P C analyses o f the precipitates collected i n the first t r a p (at 1 b a r ) after 0.5 h ( A ) , 1 h ( B ) , 2 h ( C ) , 3 h ( D ) , a n d 5 h ( E ) e x t r a c t i o n o f red spruce w i t h m e t h y l a m i n e at 185°C, 275 b a r , a n d 1 g / m i n flow rate.

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F i g u r e 6. G P C analyses o f the precipitates collected i n t h e first t r a p (at 1 b a r ) after e x t r a c t i o n of red spruce w i t h m e t h y l a m i n e at 170°C ( A ) , 175°C ( B ) , 180°C ( C ) , 1 8 5 ° ( D ) . O t h e r conditions m a i n t a i n e d at 3 h e x t r a c t i o n t i m e , 275 b a r , a n d 1 g / m i n solvent flow rate.



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Retention Time (min) F i g u r e 7. G P C analyses o f the precipitates collected i n the first t r a p (at 1 b a r ) after e x t r a c t i o n o f r e d spruce w i t h m e t h y l a m i n e at 172 b a r ( A ) , 207 b a r ( B ) , 241 b a r ( C ) , 275 b a r ( D ) . O t h e r c o n d i t i o n s m a i n t a i n e d at 3 h e x t r a c t i o n t i m e , 185° C , a n d 1 g / m i n solvent flow rate.



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Retention Time (min) F i g u r e 8. G P C analyses o f the precipitates collected i n the first t r a p (at 1 b a r ) after extractions o f red spruce w i t h b i n a r y m i x t u r e s o f m e t h y l a m i n e n i t r o u s oxide at m e t h y l a m i n e weight fractions of 0.2 ( A ) , 0.4 ( B ) , 0.6 ( C ) , 0.8 ( D ) , 1.0 ( E ) . O t h e r conditions m a i n t a i n e d at 2 h e x t r a c t i o n t i m e , 185°C, 275 b a r , a n d 1 g / m i n solvent flow rate ( T h e e x t r a c t i o n c o n d i t i o n s are above the c r i t i c a l T a n d P o f the b i n a r y m i x t u r e s ; see ref. 34.)


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( I n d u l i n A T f r o m Westvaco) a n d the p r e c i p i t a t e f r o m m e t h y l a m i n e e x t r a c t i o n of I n d u l i n A T were also a n a l y z e d w i t h G P C . A s shown i n F i g u r e 9, t h e precipitates f r o m 1 h , 3 h , a n d 5 h m e t h y l a m i n e e x t r a c t i o n o f I n d u l i n A T at 185°C, 275 b a r , a n d 1 g / m i n solvent flow rate do n o t show a n appreciable difference i n their apparent M W D ' s f r o m t h a t of I n d u l i n A T . T h i s i n d i cates t h a t no significant c h e m i c a l t r a n s f o r m a t i o n s t h a t m a y alter m o l e c u l a r weight d i s t r i b u t i o n o f I n d u l i n A T occur d u r i n g m e t h y l a m i n e e x t r a c t i o n s . In F i g u r e 10, the c h r o m a t o g r a m s o f the precipitates f r o m m e t h y l a m i n e a n d m e t h y l a m i n e - n i t r o u s oxide e x t r a c t i o n of r e d spruce, a n d m e t h y l a m i n e e x t r a c t i o n of I n d u l i n A T are c o m p a r e d a l o n g w i t h the c h r o m a t o g r a m o f I n d u l i n A T . T h e lignins o b t a i n e d f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce has the broadest apparent M W D . E x t r a c t i o n w i t h m e t h y l a m i n e - n i t r o u s

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Retention Time (min) Figure 9. G P C analyses of kraft pine lignin, Indulin A T ( A ) , and the precipitates collected i n the first trap (at 1 bar) after 1 h (B), 3 h (C), and 5 h (D) extraction of Indulin A T with methylamine at 185 ° C, 275 bar, and 1 g/min solvent flow rate.



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Retention Time (mln) Figure 10. G P C analyses of Indulin A T (A), and the precipitates corresponding to chromatogram C in Figure 9 (B), chromatogram C in Figure 8 (C), and chromatogram D in Figure 5 (D).

oxide b i n a r y m i x t u r e produces l i g n i n s w h i c h display a n apparent M W D s i m i l a r to t h a t of I n d u l i n A T . These observations are i m p o r t a n t i n t h a t b y m a n i p u l a t i n g the c o m p o s i t i o n of the e x t r a c t i o n fluid, the m o l e c u l a r weight d i s t r i b u t i o n of the l i g n i n can be altered a n d p o s s i b l y r e g u l a t e d . Conclusions T h e results t h a t have been presented i n d i c a t e t h a t s u p e r c r i t i c a l fluid ext r a c t i o n can achieve not o n l y separation of l i g n i n f r o m w o o d , b u t also m a y p e r m i t c o n t r o l of the l i g n i n m o l e c u l a r weight a n d M W D b y m a n i p u l a t i o n of e x t r a c t i o n t e m p e r a t u r e , pressure, t i m e , or the c o m p o s i t i o n of the ext r a c t i o n solvents. A m o n g these e x t r a c t i o n variables, the influence of ext r a c t i o n t i m e a n d solvent c o m p o s i t i o n are greater. T h e l i g n i n s p r o d u c e d f r o m m e t h y l a m i n e e x t r a c t i o n of red spruce generally show higher average m o l e c u l a r weight t h a n t h a t of kraft pine l i g n i n ( I n d u l i n A T ) . I n the b i n a r y ( m e t h y l a m i n e - n i t r o u s oxide) solvent s y s t e m , lignins w i t h narrower M W D


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are o b t a i n e d w i t h a n increase i n n i t r o u s oxide f r a c t i o n . A n increase i n e x t r a c t i o n t i m e , pressure or t e m p e r a t u r e tends t o broaden the M W D o f the lignins o b t a i n e d f r o m either m e t h y l a m i n e or m e t h y l a m i n e - n i t r o u s oxide e x traction. A cknowledgment s T h i s research has i n p a r t been s u p p o r t e d b y the N a t i o n a l Science F o u n d a tion (Grant N o . CBT-8416875).


Literature Cited 1. Schneider, G. M.; Stahl, E.; Wilke, G., Eds. Extraction with Supercritical Gases; Verlag Chemie: Deerfield Beach, F L , 1980. 2. Williams, D. F. Chem. Eng. Sci. 1981, 36, 1769. 3. Randall, L. G. Sep. Sci. Technol. 1982, 17, 1. 4. Paulaitis, M . E.; Krukonis, V. J.; Kurnik, R. T.; Reid, R. C. Rev. Chem. Eng. 1983, 1, 178. 5. Paulaitis, M . E.; Penninger, J . M . L.; Grey, R. D.; Davidson, P., Eds. Chemical Engineering at Supercritical Conditions; Ann Arbor Science: Ann Arbor, MI, 1983. 6. Penninger, J. M . L.; Radosz, M.; McHugh, M . A.; Krukonis, V. J . , Eds. Supercritical Fluid Technology; Elsevier: New York, 1985. 7. McHugh, M . ; Krukonis, V. Supercritical Fluid Extraction, Principles and Practice; Butterworths: Boston, 1986. 8. Stahl, E.; Quirin, K. W.; Gerard, D. Dense Gases for Extraction and Refining; Springer-Verlag: New York, 1988. 9. Kiran, E . Tappi 1987, 70, 23-24. 10. Kiran, E . Am. Papermak. 1987, 11, 26-28. 11. Li, L.; Kiran, E . Paper presented at AIChE Ann. Meet., New York, NY, Nov., 1987. 12. Li, L.; Kiran, E . Ind. & Eng. Chem.-Res. 1988, 27, 1301-12. 13. Kringstad, K. P.; Månsson, P.; Mörck, R. SPCI Intl. Symp. Wood % Pulp. Chem. (Stockholm) Preprints 1981, 5, 91-93. 14. Kolpak, F. J.; Cael, J . J . Proc. TAPPI Ann. Meet. (Atlanta) 1983, p. 55. 15. Kolpak, F. J.; Cietek, D. J.; Fookes, W.; Cael, J . J . Proc. IPUAC Macromol. Symp. (Amherst, MA) 1982, p. 449. 16. Wagner, B. A.; To, T.; Teller, D. E.; McCarthy, J . L. Holzforschung 1986, 40, Suppl., 67-73. 17. Schuerch, C. J. Amer. Chem. Soc. 1952, 74, 5061-67. 18. Brown, W. J . Appl. Polym. Sci. 1967, 11, 2381-96. 19. Kim, H. Ph.D. Thesis, Univ. of Maine, Orono, M E , 1985. 20. Simonson, R. Svensk Papperstidn. 1967, 21, 711-14. 21. McNaughton, J . G.; Yean, W. Q.; Goring, D. A. I. Tappi 1967, 50, 548-52. 22. Gupta, P. R.; McCarthy, J . L. Macromolecules 1968, 1, 236-44. 23. Pellinen, J.; Salkinoja-Salonen, M. J. Chromat. 1985, 322, 129-38. 24. Hütterman, A. Holzforschung 1978, 32, 108-11.



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25. Connors, W. J . Holzforschung 1978, 32, 145-47. 26. Connors, W. J.; Sarkanen, S.; McCarthy, J. L. Holzforschung 1980, 34, 80-85. 27. Marchessault, R. H.; Coulombe, S.; Morikawa, H.; Robert, D. Can. J. Chem. 1982, 60, 2372-82. 28. Lewis, N. G.; Goring, D. A. I.; Wong, A. Can. J. Chem. 1983, 61, 416-420. 29. Faix, O.; Lang, W.; Salud, E . C. Holzforschung 1981, 35, 3-9. 30. Himmel, M.; Oh, K.; Sopher, D. W.; Chum, H. L. J. Chromat. 1983, 267, 249-65.] 31. Chum, H. L.; Johnson, D. K.; Tucker, M . P.; Himmel, M . E . Holzforschung 1987, 41, 97-108. 32. Sarkanen, S.; Teller, D. C.; Hall, J.; McCarthy, J . L. Macromolecules 1981, 14, 426-34. 33. Glasser, W. G.; Barnett, C. A.; Muller, P. C.; Sarkanen, K. V. J. Agric. Food Chem. 1983, 31, 921-30. 34. Li, L.; Kiran, E . J. Chem. & Eng. Data 1988, 33, 342-44. 35. Effland, M . J . Tappi 1977, 60, 143. 36. Sarkanen, K. V.; Ludwig, C. H., Eds. Lignins: Occurrence, Formation, Structure and Reactions; Wiley: New York, 1971. 37. Fengel, D . ; Wegener, G. Wood: Chemistry, Walter de Gruyter: New York, 1984.

Ultrastructure,

Reactions;

RECEIVED March 17,1989


Supercritical Fluid Extraction of Lignin from Wood - ACS Symposium

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