Dedicated t o P r o f . Dr. K a r l K r a t e l ABSTRACT C h a r g e -t r a n s f e r complexes were found t o o c c u r between k r a f t l i g n i n and a n added model quinone, 3 , 5 -d i -~-b u t y 1 -1 , 2 -b e n z o q u i n o n e . The o c c u r r e n c e of c h a r g e -t r a n s f e r i n t e r a c t i o n s was a l s o a p p a r e n t i n an o x i d i z e d k r a f t l i g n i n w i t h a n i n c r e a s e d quinone c o n t e n t . I n t h e s e systems, f r e e p h e n o l i c groups w i t h i n t h e l i g n i n were cons i d e r e d t h e donor s p e c i e s and ortho-quinones t h e complementary a c c e p t o r m o i e t i e s . Carbon-I4 l a b e l i n g r e v e a l e d t h a t t h e quinone c o n t e n t of t h e i n v e s t i g a t e d k r a f t l i g n i n averaged 3%. These q u i n o n e s were determined t o have a molar a b s o r p t i v i t y of 528 L/mol-cm. Upon sodium borohydride r e d u c t i o n of t h i s l i g n i n , o n l y o n e -t h i r d of t h e absorbance d e c r e a s e c o u l d be accounted f o r by t h i s number of quinones. The remaining t w o -t h i r d s of t h e d e c r e a s e i n absorbance was a s s i g n e d t o t h e d i s r u p t i o n of c h a r g e -t r a n s f e r complexes. The quinones, t h e r e f o r e , played a d u a

Chelation and removal of transition metals from the kraft lignin employed in this study did not reduce the lignin's visible absorbance.Likewise, hydrogenation of carbon-carbon double bonds in this lignin also had no effect on its visible spectrum. This indicated that extended conjugated systems were not a significant contributor to the color of this lignin. Of the structures investigated, quinones were found to be the major visible-light absorbing chromophores. Since a large component of the quinone's absorption results 1 from their participation in charge-transfer complexes (CTC's), CTC's were a significant contributor to the color of this lignin.

During the drying and pyrolysis phases of kraft black liquor combustion, significant swelling of individual liquor particles occurs. Swollen volumes can reach 20 to 30 times the original volume during combustion. The swelling process can conceivably affect the combustibility of black liquor and the amount of carryover in a recovery furnace.The composition of black liquor was found to have a large influence on swelling. A combination of sugar acids and kraft lignin swelled to a larger extent than when either component was pyrolyzed separately. A 1:1 ratio of these two components resulted in maximum swelling for the various ratios tested. The molecular weight of kraft lignin had an effect on swollen volume with higher molecular weight fractions producing lower swelling chars.Other components were found to reduce the swelling of black liquors. Extractives interfered with the swelling by appearing to change the deformable properties of the pyrolyzing material. Inorganic salts acted as a diluent.Analysis of the surface characteristics of chars revealed that good swelling chars were composed of small bubbles 50 to 150 microns in diameter. Poor swelling liquors did not exhibit this phenomenon. The formation of bubbles was found to be initiated at 240°C, which closely corresponded to the thermal decomposition temperature of a sugar acid. Kraft lignin appeared to have a major influence on the viscous properties of the pyrolyzing particle. The composition of black liquor determines to a large extent the surface active and viscous forces present in black liquor; these forces are believed to be responsible for the extent to which kraft black liquors deform and swell during pyrolysis.

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