Chapter 8
Mobile Phase in Coal Viewed from a Mass Spectrometric Perspective 1
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Yongseung Yun , Henk L. C. Meuzelaar , Norbert Simmleit , and Hans-Rolf Schulten 3
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Center for Micro Analysis and Reaction Chemistry, University of Utah, Salt Lake City, UT 84112 Chemical and Biological Laboratories, Institut Fresenius, D-6204 Taunusstein-Neuhof, Germany Department of Trace Analysis, Fachhochschule Fresenius, Dambachtal 20, 6200 Wiesbaden, Germany 2
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Seven Argonne Premium coal samples ranging from lignite to low volatile bituminous in rank were analyzed by Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS) in order to determine the existence and structural nature of a thermally extractable "mobile phase". In addition, Curie-point Pyrolysis-Low Voltage Mass Spectrometry (Py-LVMS) was employed to demonstrate the importance of mild oxidation on the thermally extractable mobile phase components. Py-FIMS results clearly reveal the existence of a thermally extractable, bitumen-like fraction which is chemically distinct from the remaining coal components. In lignite, several biomarker compounds were noticeable in the mobile phase components while bituminous coals contain various alkylsubstituted aromatic compounds in the mobile phase. Blind Canyon coal, which contains 11% resinite, exhibits mobile phase components believed to originate from terpenoid aromatization. Curie-point Py-LVMS results illustrate the importance of the oxidation status of coal for studying the mobile phase since mild air oxidation severely changes the structural characteristics of the thermally extractable mobile phase.
In recent years f e w t o p i c s h a v e generated a m o r e s p i r i t e d d i s c u s s i o n a m o n g c o a l s c i e n t i s t s t h a n the i s s u e o f the p u t a t i v e b i n a r y ( m o b i l e + n e t w o r k ) phase nature o f c o a l s (1). I n i t i a l l y b a s e d o n N M R o b s e r v a t i o n s (2), the c o n c e p t o f a " m o b i l e phase" i n c o a l s o o n c a m e to e n c o m p a s s a b r o a d range o f m o r e o r less r e a d i l y e x t r a c t a b l e a n d / o r d i s t i l l a b l e l o w e r m o l e c u l a r w e i g h t ( M W ) c o m p o n e n t s , v a r i o u s l y referred to as "guest m o l e c u l e s " (3), "clathrates" (1,4) o r s i m p l y , a n d p e r h a p s m o s t s u c c i n c t l y , " b i t u m e n " (5).
0097-6156/91/0461-0089$06.50/0 © 1991 American Chemical Society
Schobert et al.; Coal Science II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
C O A L SCIENCE II
90 N o n e o f these terms appears to b e c o m p l e t e l y satisfactory.
T h e concept o f
" m o b i l i t y " i n N M R s p e c t r o s c o p y is q u i t e different f r o m that i n the f i e l d o f s e p a r a t i o n s c i e n c e , w h e r e m o b i l i t y g e n e r a l l y requires a m e a s u r a b l e degree o f s o l u b i l i t y a n d / o r distillability
in
liquid
or
gaseous
media,
respectively.
For
example,
p o l y m e t h y l e n e - l i k e m o i e t i e s , s u c h as f o u n d i n s o m e c o a l c o m p o n e n t s (6), are h i g h l y " m o b i l e " i n N M R terms (1), w i t h o u t n e c e s s a r i l y b e i n g e x t r a c t a b l e b y s o l v e n t s o r distillable b y nondestructive
heating.
T h e t e r m "guest m o l e c u l e s " , o r i g i n a l l y i n t r o d u c e d to i n d i c a t e s p e c i f i c a l l y l a b e l e d m a r k e r m o l e c u l e s used i n N M R studies o f c o a l (7), is e q u a l l y unsatisfactory for m o b i l e p h a s e c o m p o n e n t s i n d i g e n o u s to the c o a l itself. A l s o , there appears to b e
Downloaded by GEORGETOWN UNIV on November 2, 2016 | http://pubs.acs.org Publication Date: May 6, 1991 | doi: 10.1021/bk-1991-0461.ch008
i n s u f f i c i e n t e v i d e n c e for the presence o f s i z e a b l e quantities o f true "clathrates" to r u l e out
other
p o s s i b i l i t i e s , e.g.,
strong
noncovalent
b o n d i n g rather t h a n
physical
entrapment. F i n a l l y , c o m p l e t e l y e q u a t i n g the " m o b i l e phase" w i t h s o l v e n t (e.g. p y r i d i n e ) e x t r a c t a b l e " b i t u m e n " i n c o a l i g n o r e s the p o t e n t i a l presence o f c o l l o i d a l p a r t i c u l a t e matter i n the p y r i d i n e extracts as w e l l as p o s s i b l e s o l v e n t - i n d u c e d s c i s s i o n o f w e a k chemical bonds.
F u r t h e r m o r e , the s o l v e n t - e x t r a c t a b l e f r a c t i o n m a y w e l l i n c l u d e
m a c r o m o l e c u l a r c o m p o n e n t s , s u c h as resinites. M a s s s p e c t r o m e t r i c o b s e r v a t i o n s h a v e thus far p l a y e d a rather l i m i t e d r o l e i n the " m o b i l e phase" d i s c u s s i o n s (1) but are s t a r t i n g to s h e d s o m e l i g h t o n the k e y q u e s t i o n : is there c o n c l u s i v e e v i d e n c e f o r the p r e s e n c e o f a c h e m i c a l l y a n d / o r p h y s i c a l l y d i s t i n c t " m o b i l e phase", as o p p o s e d to a c o n t i n u u m o f p o s s i b l e m o l e c u l a r s i z e s a n d structures? I f the m o b i l e p h a s e is present i n a s i g n i f i c a n t c o n c e n t r a t i o n , as suggested b y the results o f s o l v e n t e x t r a c t i o n studies (1,8), the p r a c t i c a l m e a n i n g o f the m o b i l e p h a s e to c o a l c o n v e r s i o n processes m a y be p r o f o u n d . In c o a l l i q u e f a c t i o n , t w o stage processes e m p h a s i z i n g the m o b i l e phase a n d the m a c r o m o l e c u l a r structure separately c o u l d w e l l be most e c o n o m i c a l .
I n d e v o l a t i l i z a t i o n k i n e t i c s , at least t w o sets o f
k i n e t i c parameters are necessary to m o d e l the d e v o l a t i l i z a t i o n p h e n o m e n a
associated
w i t h the m o b i l e p h a s e a n d the m a c r o m o l e c u l a r structure r e s p e c t i v e l y s i n c e the m o b i l e p h a s e c o m p o n e n t s d e v o l a t i l i z e at m u c h l o w e r temperatures than the m a c r o m o l e c u l a r structure c o m p o n e n t s (9). In a d d i t i o n , the m o b i l e p h a s e appears to h a v e a s i g n i f i c a n t i n f l u e n c e o n the t h e r m o p l a s t i c properties o f c o a l (5) a n d thereby o n c o k e q u a l i t y . In the c o n t e x t o f the present d i s c u s s i o n the t e r m " m o b i l e p h a s e " w i l l be u s e d to
describe
those c o m p o n e n t s
w h i c h can
be
thermally
extracted
("distilled",
"desorbed") u n d e r v a c u u m at temperatures b e l o w the t h e r m a l d e g r a d a t i o n range o f the c o a l . T h e residue, d e s i g n a t e d as the n o n m o b i l e ( " n e t w o r k " ) phase, is t h e r m a l l y d e g r a d e d i n the p y r o l y s i s temperature range. O f c o u r s e , the onset o f p y r o l y s i s m a y v a r y c o n s i d e r a b l y , d e p e n d i n g o n h e a t i n g rate, r a n k a n d c o a l t y p e ( 1 0 ) . Experimental Seven A N L - P C S (Argonne National Laboratory - P r e m i u m C o a l Sample) coals were analyzed by P y - F I M S i n time resolved ( T R ) mode.
C o n v e n t i o n a l characterization
data o n A N L - P C S c o a l s h a v e b e e n d e s c r i b e d e l s e w h e r e (11). A b o u t 1 0 0 μ g o f - 1 0 0 m e s h c o a l w e r e transferred
i n t o a quartz c r u c i b l e a n d i n t r o d u c e d i n t o the h i g h
3
v a c u u m ( 1 0 ' P a ) o f the i o n s o u r c e ( 2 0 0 ° C ) . T h e i n s t r u m e n t a l setup u s i n g a F i n n i g a n
Schobert et al.; Coal Science II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
8. YUN ET AL.
Mobile Phase in Coal
91
M A T 7 3 1 d o u b l e - f o c u s s i n g m a s s spectrometer, a c o m b i n e d E I / F I / F D / F A B i o n s o u r c e a n d a n A M D Intectra d i r e c t i n t r o d u c t i o n s y s t e m , has b e e n p r e v i o u s l y d e s c r i b e d i n d e t a i l ( 1 2 ) . T h e s a m p l e s w e r e heated l i n e a r l y f r o m 5 0 ° C to 7 5 0 ° C at a rate o f 1 0 0 K/min.
In g e n e r a l , 3 5 F I m a s s spectra w e r e r e c o r d e d i n the m / z 5 0 - 9 0 0 m a s s range. In a d d i t i o n , a c o a l s a m p l e w a s o b t a i n e d f r o m a fresh c h a n n e l - c u t i n the
H i a w a t h a s e a m i n E m e r y C o u n t y ( U t a h ) a n d i m m e r s e d i n w a t e r p r i o r to b e i n g c r u s h e d a n d m i l l e d to
