18
1
H-NMR
T h e r m a l Scanning M e t h o d s for Studying
Oil S h a l e P y r o l y s i s L. J. LYNCH and D. S. WEBSTER
Downloaded by CORNELL UNIV on May 26, 2017 | http://pubs.acs.org Publication Date: August 1, 1983 | doi: 10.1021/bk-1983-0230.ch018
CSIRO Physical Technology Unit, 338 Blaxland Road, Ryde, NSW, 2112, Australia
1
This paper reports on the use of H NMR thermal scanning for studying the pyrolysis of o i l shales. The strength and sensitivity of the H NMR signals of o i l shales are sufficient such that pulsed NMR techniques afford a means of dynamically observing thermal transformation processes. Parameters can be extracted from the NMR data that relate to the hydrogen content, phase structure, molecular mobility and free radical content of the specimen. The temperature dependencies of these parameters reveal chemical and physical transformations that occur in the nature of the kerogen materials and the pyrolysis products. Examples of H NMR thermal scanning of Australian o i l shales are presented which illustrate this method of H NMR thermal analysis. 1
1
1
Dynamic experimental techniques by which non-equilibrium states of a system can be observed during thermally induced transformations allow the kinetics of pyrolysis mechanisms to be directly studied. This paper reports on the novel use of simple low resolution proton nuclear magnetic resonance (^H NMR) measurements as a reaction time probe to monitor the state of o i l shales during heating from room temperature to ^87OK. The method involves the observation of the NMR transverse relaxation transient at regular intervals during heating. Similar studies of coal pyrolysis (1-6) and a description of the apparatus (7) used have been previously reported. In these reports the ability to obtain non-equilibrium data during fossil fuel pyrolysis despite the limited scope for signal averaging and the deterioration of signal-to-noise of the 4l nmr signal with rise in temperature was demonstrated. This method of thermal analysis has a particular advantage over conventional thermal analysis methods such as thermogravimetry and differential thermal analysis in that i t is highly selective of the organic kerogen to the exclusion of the inorganic parts of the shale. 0097-6156/ 83/0230-0353S06.00/0 © 1983 American Chemical Society Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
354
GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
The experiments r e p o r t e d here i n v o l v e measurements o f t h e 1H NMR during p y r o l y s i s o f shale specimens contained i n open tubes and f l u s h e d w i t h dry n i t r o g e n gas so t h a t v o l a t i l e p y r o l y s i s products are q u i c k l y removed. A number o f d i f f e r e n t parameters e x t r a c t e d from the data are i n v e s t i g a t e d f o r t h e i r u s e f u l n e s s i n monitoring changes that occur i n the p r o p e r t i e s o f the specimen. These parameters r e l a t e t o the l o s s o f hydrogen from the specimen and changes t h a t occur i n the molecular s t r u c t u r e and m o b i l i t y as a consequence o f chemical and p h y s i c a l t r a n s f o r m a t i o n s . The r e s u l t s presented are not part o f a systematic study o f o i l shale p y r o l y s i s but r a t h e r those o f v a r i o u s experiments s e l e c t e d t o demonstrate the u t i l i t y and p o t e n t i a l o f the method. Downloaded by CORNELL UNIV on May 26, 2017 | http://pubs.acs.org Publication Date: August 1, 1983 | doi: 10.1021/bk-1983-0230.ch018
Experimental The specimens f o r measurement c o n s i s t e d o f 300-500 mg o f f i n e l y ground m a t e r i a l p r e d r i e d under n i t r o g e n a t 378K and contained i n open g l a s s tubes. The ^-H NMR measurements were made at 60 MHz u s i n g high temperature specimen probes and temperature c o n t r o l apparatus described p r e v i o u s l y ( 7 ) . Specimens were p o s i t i o n e d w i t h i n the i n n e r 2/3 o f the measurement radio-frequency c o i l o f the NMR probe and were continuously f l u s h e d w i t h a stream of dry n i t r o g e n gas throughout t h e h e a t i n g c y c l e s which r a p i d l y removed v o l a t i l e products formed from the measurement zone. Thus at a l l stages during an experiment the *Η NMR s i g n a l o f a l l the r e s i d u a l m a t e r i a l was recorded. R e s u l t s a r e r e p o r t e d here f o r experiments made on a Sydney b a s i n o i l s h a l e from Glen Davis and on a J u l i a Creek shale and i t s demineralized organic r e s i d u e . These specimens were obtained from CSIRO D i v i s i o n o f F o s s i l Fuels and CSIRO D i v i s i o n o f Energy Chemistry r e s p e c t i v e l y . We ds
\ \
Ι
Ο
k.
Β
\ν VS. \ \
\
