Sink Float Procedures for Shale Characterization - American Chemical

20

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Sink Float Procedures for Shale Characterization CHARLES J. VADOVIC Exxon Research and Engineering Company, Baytown, T X 77520

A new c h a r a c t e r i z a t i o n procedure has been developed which d i r e c t l y c a l c u l a t e s the organic H/C and N/C r a t i o s i n raw shale from elemental a n a l y s e s . The procedure e l i m i n a t e s the need f o r the a c i d e x t r a c t i o n of kerogen for organic analyses and r e s u l t a n t uncertainty caused by the extraction of basic organic compounds. The procedure i n v o l v e s the accurate analyses of f r a c t i o n s obtained v i a sink f l o a t techniques and has been compared with kerogen analyses for Brazil, Rundle, and Colony shale samples from C o l o r a d o . Good agreement with both the H/C and N/C r a t i o s has been a c h i e v e d . Also, estimates of the hydrogen and n i t r o g e n contents of the mineral matter in raw shales have been obtained. The method appears to be v a l i d f o r raw shale and e l i m i n a t e s the need to e x t r a c t rock with a c i d to obtain kerogen for H/C and N/C a n a l y s e s .

The a n a l y s i s o f t h e o r g a n i c f r a c t i o n i n shale leads t o Important processing insights. However, t h e a n a l y s i s i s comp l i c a t e d by t h e p r e s e n c e o f a s u b s t a n t i a l f r a c t i o n o f r o c k . The r o c k o f t e n c o n t a i n s c a r b o n , a s c a r b o n a t e s , and h y d r o g e n , a s w a t e r o f h y d r a t i o n , w h i c h make i t d i f f i c u l t t o o b t a i n a t r u e o r g a n i c analysis. The r o u t e u s e d most o f t e n t o o b t a i n o r g a n i c a n a l y s e s i s t o i s o l a t e t h e k e r o g e n by a c i d r e m o v a l o f t h e i n o r g a n i c s . This p o s e s numerous p r o b l e m s i n t h a t t h e a c i d s u s e d , HC1 and HF, c a n i n t e r a c t w i t h and be i n c o r p o r a t e d i n t o t h e o r g a n i c m a t r i x . Also b a s i c n i t r o g e n compounds a r e e a s i l y e x t r a c t e d f r o m t h e s h a l e a s w e l l a s i n o r g a n i c n i t r o g e n compounds • The p r e s e n c e o f i n o r g a n i c n i t r o g e n f r o m G r e e n R i v e r s h a l e h a s been d e m o n s t r a t e d and q u a n t i fied i n the literature (1, 2). To o b v i a t e t h e s e d i f f i c u l t i e s a

0097-6156/ 83/0230-0385S06.00/0 ® 1983 A m e r i c a n C h e m i c a l S o c i e t y

Miknis and McKay; Geochemistry and Chemistry of Oil Shales ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

G E O C H E M I S T R Y A N D C H E M I S T R Y OF OIL

386

SHALES

p r o c e d u r e has been d e v e l o p e d w h i c h u t i l i z e s t h e a n a l y s e s o f raw s i n k f l o a t s h a l e samples to c a l c u l a t e the r a t i o s of organic h y d r o g e n and n i t r o g e n t o o r g a n i c c a r b o n . I n a d d i t i o n an e s t i m a t e o f t h e h y d r o g e n and n i t r o g e n c o n t e n t o f t h e m i n e r a l m a t t e r i s obtained•


Sink F l o a t The s t a r t i n g p o i n t f o r t h e p r o c e d u r e o u t l i n e d h e r e i s t h e f l o a t i n g o f m a t e r i a l c o n t a i n i n g r o c k and m i n e r a l m a t t e r a t a predetermined specific gravity. The p r i n c i p l e s i n v o l v e d are d e p i c t e d i n F i g u r e 1. At a low m e d i a s p e c i f i c g r a v i t y e s s e n t i a l l y a l l o f t h e m a t e r i a l w i l l s i n k . As t h e s p e c i f i c g r a v i t y i n c r e a s e s more o f t h e m a t e r i a l f l o a t s . At a s u f f i c i e n t l y h i g h s p e c i f i c g r a v i t y a l l of the m a t e r i a l w i l l f l o a t . D e t a i l s of the beneficiation aspects of the s i n k f l o a t procedure are found i n r e f e r e n c e s 3 t o 7. I n t h e p r o c e d u r e d e s c r i b e d h e r e a method a n a l o g o u s t o t h e c o l l e c t i o n o f d i s t i l l a t i o n c u t s was employed. The s h a l e was subjected t o a low s p e c i f i c g r a v i t y and the f l o a t fraction collected. The s i n k f r a c t i o n was s u b j e c t e d t o an i n c r e m e n t a l l y h i g h e r s p e c i f i c g r a v i t y and t h e f l o a t f r a c t i o n c o l l e c t e d . The p r o c e d u r e was r e p e a t e d u n t i l v e r y l i t t l e m a t e r i a l r e m a i n e d . In t h i s manner a s e r i e s o f s a m p l e s , d i f f e r i n g p r i m a r i l y by o r g a n i c t o r o c k r a t i o , was c o l l e c t e d . The n a t u r e of t h e s h a l e p l a y s a r o l e i n t h e s e l e c t i o n o f t h e media. Heavy h y d r o c a r b o n m e d i a may be u s e d on d r y , impervious s h a l e s s u c h as f r o m C o l o r a d o . For s h a l e s of h i g h moisture cont e n t , s u c h as f r o m t h e R u n d l e d e p o s i t , i t i s more p r a c t i c a l t o use an aqueous b a s e d h e a v y m e d i a s y s t e m . The j u d i c i o u s s e l e c t i o n o f media prevents c o n t a m i n a t i o n o f t h e s h a l e and a l l o w s accurate analysis • Analytical

Procedures

The techniques used f o r a n a l y z i n g s h a l e s b e l o w . Most a r e m o d i f i e d ASTM c o a l m e t h o d s .

are

summarized

Carbon-Hydrogen. The c a r b o n - h y d r o g e n a n a l y s i s was p e r f o r m e d i n a H a l l i k a i n e n c o m b u s t i o n f u r n a c e a t 1000°C. The .2 gram sample was combusted i n a i r f o r 3 m i n u t e s and t h e n combusted f o r 3 m i n u t e s i n o x y g e n . The r e s u l t a n t CO2 and H2O were c o l l e c t e d u s i n g t r a p s s p e c i f i e d by ASTM D3178 and d e t e r m i n e d g r a v i m e t r i c a l l y . Ash. procedure

The a s h (950°C).

was

determined

C0 . Mineral C0 was r e s i d e n c e t i m e o f 45 m i n u t e s • 9

2

by

ASTM D3174 u s i n g

determined

by

ASTM

D1756


the

coke

with

a


1.5 SP.GR.

2.1 SP.GR.

2.1 SG

2.0 SG

2.2 SG

SINK

|FLOAT |

2.3 SG

SINK

FLSAT

2.5 SG

SINK

FLOAT

INORGANIC - S . G . 2.5 TO 3.0

2.4 SG

SINK

FLOAT

2.4 SP. GR.

Figure 1. The mechanism of physical shale beneficiation.

SINK

FLOAT

SINK

FLOAT

LABORATORY FLOAT/SINK TESTS

1.8 SP.GR.

ORGANIC - S . G . 0.9 TO 1.3

NOTE: EACH PARTICLE CONTAINS SOME ROCK OR MINERAL MATTER


388

at

GEOCHEMISTRY A N D CHEMISTRY OF OIL SHALES

Nitrogen. N i t r o g e n was d e t e r m i n e d u s i n g a LECO CHN a c o m b u s t i o n t e m p e r a t u r e o f 1425°C.

analyzer

P r o c e d u r a l D e t a i l s and R e s u l t s The b a s i s f o r t h e p r o c e d u r e balance of the form total . organic i i organic


x

where X ^ o t a l

a

n

d

x

a

r

e

t

h

e

presented .

+

x

/

i t

Q

t

a

l

here

1

Q

i s an

element

0

mineral

a

n

d

o

r

g

a

n

i

c

w

i ht

e

percent

g

o f component i i n t h e s i n k f l o a t s a m p l e , r e s p e c t i v e l y , X ^ i is t h e w e i g h t p e r c e n t o f m i n e r a l s i n t h e sample Y^ i s t h e w e i g h t percent o f component i i n t h e m i n e r a l s and i i s h y d r o g e n o r nitrogen. By a s s u m i n g t h a t t h e w e i g h t p e r c e n t o f m i n e r a l s i s e q u a l t o t h e sum o f t h e a s h and m i n e r a l CO2 c o n t e n t t h e e q u a t i o n n

x

total

=

x

organic

+

Y

minerals

x

(

A

g

h

+

C

o

2

)

/

1

0

e

r

a

0

r

a n i c

i s d e r i v e d . I n d e s c r i b i n g a s e r i e s o f s i n k f l o a t samples x ° S v a r i e s w i t h the organic content of the sample. However as t h e o r g a n i c i s f a i r l y ^ u n i f o r m f r o m one s i n k f l o a t sample t o a n o t h e r the r a t i o X ^ /C rganic s h o u l d be a c o n s t a n t . The above e q u a t i o n c a n be r e w r i t t e n as r g a

C

0

total _ i

( x

organlc i

organic

organic

minerals i

lb c o n v e r t t o an a t o m i c r a t i o t h e m o l e c u l a r and t h e e q u a t i o n r e a r r a n g e d t o 100

X

t 0 t a l

12 ?

4

A

r

g

a

n

i

c

100 C

X

Ash + C 0 2 o

=

MW^C i org i

+

Q

2'

weights

are included

MW

(Ash + C 0 ) 12 2 org 1 — +

i

o

Y

The t o t a l component X j ^ organic carbon are determined by e l e m e n t a l a n a l y s e s . To e f f e c t i v e l y u s e t h e above e q u a t i o n , a s e r i e s o f s a m p l e s c o n t a i n i n g v a r y i n g amounts o f o r g a n i c a n d i n o r g a n i c c o n s t i t u e n t s must be o b t a i n e d . The s i n k f l o a t p r o c e d u r e y i e l d s a s e r i e s o f s a m p l e s w h i c h c o n t a i n v a r i o u s l e v e l s o f o r g a n i c and i n o r g a n i c m a t e r i a l • I t i s assumed t h a t i n t h e s e s a m p l e s v a r i a t i o n s i n b o t h o r g a n i c and i n o r g a n i c composition are minimal • The v a r i a t i o n i n a s h e l e m e n t s for B r a z i l and R u n d l e s h a l e a r e shown i n F i g u r e 2. The a p p r o x i mate m i n e r a l o g y c o r r e s p o n d i n g t o t h e a s h e l e m e n t s c o n t a i n e d i n t h e B r a z i l s h a l e s a m p l e s i s 4 0 % i l l i t e , 30% q u a r t z , 10% a l b i t e , 10% p y r i t e and 10% o t h e r . The a p p r o x i m a t e R u n d l e m i n e r a l o g y i s 5 0 % m o n t m o r i l l i n i t e , 25% i l l i t e , 5% k a o l i n i t e , 15% q u a r t z and 5% other • The v a r i a t i o n s o b s e r v e d i n s i n k f l o a t s a m p l e s f r o m t h e s e ±

a n
r m

Ο τι Ο F

•

H

όο

8 Χ m

Ο m

SO Κ)

Sink Float

Procedures


VADOVIC



394

GEOCHEMISTRY A N D CHEMISTRY OF OIL S H A L E S

Figure 6. Approach applicable to nitrogen.


20.

VADOVIC

395

Sink Float Procedures


The amount o f m i n e r a l h y d r o g e n and n i t r o g e n r e l a t i v e t o t h e t o t a l amount o f h y d r o g e n and n i t r o g e n p r e s e n t i s shown i n T a b l e II, The t o t a l l e v e l s a r e r e p r e s e n t a t i v e o f t h e a v e r a g e y i e l d o f the s h a l e s a n a l y z e d . The a v e r a g e y i e l d s f o r t h e R u n d l e , B r a z i l and C o l o n y o i l s h a l e s t e s t e d a r e 25, 20 and 35 g a l l o n s p e r t o n respectively. The e s t i m a t e d m i n e r a l h y d r o g e n c o n t e n t r a n g e s f r o m 3 t o 15% o f t h e t o t a l h y d r o g e n , and t h e e s t i m a t e d m i n e r a l n i t r o g e n c o n t e n t r a n g e s f r o m 4 t o 31% o f t h e t o t a l .

Table

I I . H&N C o n t e n t •

S m a l l But

Significant

L e v e l s R e p r e s e n t a t i v e of Average o f D e p o s i t

Min, Wt% 0.25 0.28 0.08

Shale Rundle Brazil Colony

Of M i n e r a l s A r e

Hydrogen Total, Wt% 2.16 1.86 2.83

Min/ Total 0.11 0.15 0.03

Min, Wt% 0.13 0.02 0.10

Nitrogen Total Wt% 0.42 0.41 0.83

Min/ Total 0.31 0.04 0.12

Conclusions A method has been d e v e l o p e d , u t i l i z i n g s i n k f l o a t p r o c e d u r e s , which c a l c u l a t e s t h e H/C a n d N/C r a t i o s i n r a w s h a l e s . I n a d d i t i o n t h e t e c h n i q u e e l i m i n a t e s t h e need f o r a c i d e x t r a c t i o n t o o b t a i n kerogen and a l s o e s t i m a t e s t h e H and N c o n t e n t o f t h e mineral matrix. The p r o c e d u r e has been t e s t e d o n B r a z i l , R u n d l e and C o l o r a d o s h a l e s a n d agreement w i t h e x t r a c t e d k e r o g e n a n a l y s e s h a s been achieved. Acknowledgments The a u t h o r w i s h e s t o t h a n k Z. B a s e t , R. G u e r r e , T. H e b e l and W. B r e w e r f o r t h e i r a s s i s t a n c e . Literature 1.

2. 3. 4. 5.

R. N a d k a r n i ,

Cited

Forsman, J. P.; Hund, J. M. in "Habitat of Oil"; L. G. weeks, Ed. American Association of Petroleum Geologists, 1958; p. 223. Cooper, J. E.; Evans, W. S. SCIENCE 1983, 219, 492-3. Dismant, J. H. The Mines Magazine 1961, 15-22. Frost, I. C.; Stanfield, K. E. Anal. Chem. 1950, 22, 491-2. Fahlstrom, P. H. in "Proceedings of 12th Oil Shale Symposium" Colorado School of Mines, 1979.


396

6.

7. 8.

GEOCHEMISTRY A N D CHEMISTRY OF OIL S H A L E S

Larson, O. A., Schultz, C. W. and Michaels, E. L. in "Oil Shale Tar Sands and Related Materials"; ACS SYMPOSIUM SERIES No. 163, ACS:Washington D.C. 1981; 139-154. Reisberg, J. ibid; 155-166. Pevear, D., personal communication.


RECEIVED June 30, 1983


Sink Float Procedures for Shale Characterization - American Chemical

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