15 Electron Optical and IR Spectroscopic Investigation of Coal Carbonization
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch015
J. J. FRIEL, S. M E H T A , and D. M . FOLLWEILER Bethlehem Steel Corporation, Homer Research Laboratories, Bethlehem, PA 18016
The chemistry of coal carbonization was studied i n an attempt to better understand the changes that take place as metallurgical coal becomes plastic. Infrared spectroscopy was used to study the transformation from coal-mesophase-semicoke and to relate the changes to those observed i n the electron microscope. Spectra of semicokes produced from three different coals at various heat-treatment temperatures show changes that can be related to the fluid properties of the coals. Evidence of mesophase i n the fluid range of temperature can be obtained from changes in the region of the spectra assigned to aromatic hydrogen out-of-plane bending modes. Heat-treatment temperatures above the fluid range result in condensation of the mesophase as hydrogen i s lost. Various metallurgical coals with different coking properties were examined i n an attempt to learn more about the carbonization process. In our previous studies, we observed three basically different microstructures i n different coals during heating stage experiments i n the transmission electron microscope (1). A Pittsburgh No. 8 coal with good coking properties readily formed mesophase spheres that coalesced before solidification to a semicoke (Figure 1). An I l l i n o i s No. 6 sample of similar rank but l i t t l e fluidity exhibited only isolated small mesophase spheres (Figure 2). A Lower Kittanning low-volatile coal formed not only spheres but rods (Figure 3). The purpose of the present study was to examine the coal-tocoke transformation away from the heating stage of the electron microscope. We carbonized samples at various heat-treatment temperatures in a plastometer. The plastometer has the advantage over the electron microscope hot stage not only i n that i t is the apparatus we used i n the fluidity test but also i n that i t minimizes thermal gradients across the sample. Semicokes thus 0097-6156/82/0205-0293$06.00/0 © 1982 American Chemical Society
In Coal and Coal Products: Analytical Characterization Techniques; Fuller, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch015
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COAL
Figure 1.
AND
COAL
PRODUCTS
Electron micrograph of coalesced spheres in Pittsburgh No. 8 vitrinite on the heating stage of the TEM.
Figure 2.
Electron micrograph of isolated spheres in Illinois No. 6 vitrinite.
In Coal and Coal Products: Analytical Characterization Techniques; Fuller, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch015
15.
FRIEL
ET AL.
Spectroscopic Investigation of Carbonization
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produced were examined i n the e l e c t r o n microscope and by i n f r a r e d spectroscopy. Studies on c o a l s t r u c t u r e and i t s decomposition products u s i n g F o u r i e r transform i n f r a r e d spectroscopy (FTIR) were r e c e n t l y reported by Solomon ( 2 ) . While t h i s technique produces a g r e a t e r peak-to-background r a t i o than i s p o s s i b l e w i t h the c o n v e n t i o n a l i n f r a r e d technique, we were s t i l l able t o o b t a i n u s e f u l informat i o n w i t h the c o n v e n t i o n a l d i s p e r s i v e instrument by means o f m u l t i p l e accummulations. P a i n t e r and Coleman a l s o used the FTIR technique on c o a l and c a r e f u l l y assigned a b s o r p t i o n s t o s p e c i f i c f u n c t i o n a l groups ( 3 ) . Our aim was t o study the d i f f e r e n c e s among c o a l s of d i f f e r e n t coking p r o p e r t i e s and r e l a t e the growth of mesophase i n these c o a l s t o the changes that take place upon c a r b o n i z a t i o n . The p r o p e r t i e s of the c o a l s s t u d i e d a r e l i s t e d i n Table I . Inasmuch as i n f r a r e d s p e c t r a of c o a l s o f d i f f e r e n t rank are s i m i l a r , i t was necessary t o s e l e c t c o a l s o f markedly d i f f e r e n t coking p r o p e r t i e s t o improve our chances o f seeing differences. Experimental Technique Coal ground t o
