Oil Shale, Tar Sands, and Related Materials - American Chemical

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Synfuel Stability: Degradation Mechanisms and Actual Findings DENNIS W. BRINKMAN—U.S. Department of Energy, Bartlesville Energy Technology Center, P.O. Box 1398, Bartlesville, OK 74003 JOHN N. BOWDEN—Southwest Research Institute, 8500 Culebra Road, San Antonio, TX 78285 JOHN FRANKENFELD and BILL TAYLOR—Exxon Research and Engineering, Box 8, Linden, NJ 07036

While substantial quantities of only a few experimental synfuels have been generated, those which are available have demonstrated the degradation problems that were predicted from work with petroleum. The high heteroatom and unsaturate content of syncrudes derived from shale and coal will necessitate closer attention to processing parameters required to produce a commercially viable product. This paper presents basic and applied data which should aid in the tradeoff decisions between further costly processing and product stability. Because this is a progress report on continuing work, many of the conclusions are preliminary in nature. Degradation Mechanisms Considerable work has been published on degradation mechanisms for compounds found in petroleum(1-4). Much of the previously reported research involved pure compounds in pure hydrocarbon solvents. The work reported here was performed with additive-free #2 diesel fuel or JP-8, both of which are middle distillate fuels in increasing demand. Much of this work is in progress and only preliminary results can be presented here. S t r u c t u r a l E f f e c t s . The r e s u l t s of s t u d i e s on s t r u c t u r a l e f f e c t s which have been c a r r i e d out so f a r are summarized i n Figure 1. Here the n i t r o g e n compounds are grouped as " s t r o n g l y d e l e t e r i o u s " , "moderately d e l e t e r i o u s " and " r e l a t i v e l y harmless" w i t h regard t o t h e i r r e l a t i v e tendencies t o form sludge i n hydrocarbon f u e l s . The d i f f e r e n c e s between groupings, e s p e c i a l l y between s t r o n g l y and moderately d e l e t e r i o u s i s q u i t e l a r g e . These l i m i t e d data seem t o i n d i c a t e t h a t , w i t h few exceptions, the d e l e t e r i o u s compounds are those which contain h e t e r o c y c l i c nitrogens with an a l k y l group adjacent t o n i t r o g e n . F i n a l l y , as observed p r e v i o u s l y Q > A ) the 2,5-dimethyl p y r r o l e (DMP) conf i g u r a t i o n appears s i g n i f i c a n t l y more r e a c t i v e than 2,4-dimethyl 0097-6156/81/0163-0297$05.00/0 © 1981 American Chemical Society

Stauffer; Oil Shale, Tar Sands, and Related Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

formation Structural effects on sediment Figure 1.


20.

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ET

AL.

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Stability

299

p y r r o l e . These observations are based on l i m i t e d data and must be regarded as t e n t a t i v e . However, they do support previous suggestionsC3>4>JL) that sediment from p y r r o l i c compounds a r i s e s from o l i g o m e r i z a t i o n through the adjacent methyl groups (see F i g u r e 2). The p a r t i a l s t r u c t u r e s shown i n Figure 2 are supported by elemental, i n f r a r e d and mass s p e c t r a l analyses(2>A) and provide a p o s s i b l e explanation f o r the need f o r a l k y l groups adjacent to n i t r o g e n f o r l a r g e s c a l e sediment formation. Addit i o n a l work with other model compounds i s being performed to confirm these f i n d i n g s . Compound I n t e r a c t i o n s . I n t e r a c t i o n s may be q u i t e important to storage s t a b i l i t y of s y n t h e t i c f u e l s , e s p e c i a l l y those d e r i v e d from shale and c o a l l i q u i d s . Previous w o r k ^ h a s indicated that c e r t a i n compounds, which do not produce sediment by themselves, can c o n t r i b u t e to or s t i m u l a t e sediment formation i n others ( " p o s i t i v e " i n t e r a c t i o n ) . In some i n s t a n c e s , some mater i a l s i n t e r a c t to i n h i b i t sediment formation ("negative" i n t e r a c t i o n ) . These i n t e r a c t i o n s have been demonstrated f o r thermal s t a b i l i t y a n d , to a very l i m i t e d extent, f o r storage s t a b i l The r e s u l t s of p r e l i m i n a r y i n t e r a c t i o n s t u d i e s i n the present program are summarized i n t h i s s e c t i o n . The r e s u l t s of a p r e l i m i n a r y study to determine whether N-N i n t e r a c t i o n s can occur under c o n d i t i o n s of dark storage are summarized and t h e i r s i g n i f i c a n c e analyzed i n Table 1. In order to determine whether an i n t e r a c t i o n a c t u a l l y occurred the data were analyzed by means of 2 X 2 f a c t o r i a l experiments. A typical design i n v o l v i n g DMP and i s o q u i n o l i n e i s shown i n F i g u r e 3. The a n a l y s i s shown i n F i g u r e 3 i n d i c a t e s a l i k e l y p o s i t i v e i n t e r a c t i o n a f t e r 28 days and c l e a r cut i n t e r a c t i o n a f t e r 56 days. Thus, a f t e r 56 days the t o t a l sediment obtained with both n i t r o g e n compounds together (127.5 mg/100 cc) was more than double the sum of the two which would be expected i f they acted independently (61.8 mg/100 c c ) . To determine the s i g n i f i c a n c e of the r e s u l t s , the data were subjected to Students " t " t e s t , ( i ) R e s u l t s are summarized i n Table 1. These p r e l i m i n a r y r e s u l t s suggest that i n t e r a c t i o n s can occur between DMP and v a r i o u s n i t r o g e n c o n t a i n i n g s p e c i e s . These have important i m p l i c a t i o n s f o r f u e l s t a b i l i t y . C e r t a i n compounds, f o r example, t r i o c t y l a m i n e and i s o q u i n o l i n e , while r e l a t i v e l y innocuous when present alone, can c o n t r i b u t e s i g n i f i c a n t l y to sediment formation i n the presence of compounds such as DMP. On the other hand, some m a t e r i a l s , such as 2-methyli n d o l e , may a c t u a l l y have a s t a b i l i z i n g e f f e c t . The r e s u l t s of the four t e s t s with 2-methylindole are e s p e c i a l l y i n t e r e s t i n g and surprising. They a l l i n d i c a t e a s t a t i s t i c a l l y s i g n i f i c a n t negative i n t e r a c t i o n . This needs to be confirmed i n f u t u r e experiments. Previous work suggested that important i n t e r a c t i o n s can occur between n i t r o g e n and s u l f u r or oxygen compoundsC3 *4>,Z>.§). S e v e r a l of these i n t e r a c t i o n s were "negative" ( i . e . , s t a b i l i z i n g ) . S e v e r a l experiments were performed i n the present program to t e s t


300

OIL SHALE, TAR SANDS, AND RELATED

Figure 2.

Proposed partial structures for dimethylpyrrole

MATERIALS

sediment (5)


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Stability

301

PRESENCE OF COMPOUND A NO

YES

Q 0

1

0.5

40.9(2)

0.0(3)

54.9

U

Pn O W

U

w CO w PH

28-DAYS STORAGE AT 110°F

PRESENCE OF COMPOUND A NO 0

YES

61.3(2)

0.5

1 o w

0.0(3)

§

127.5

CO

s PH

56 DAYS STORAGE AT 110°F

(1) (2) (3)

Sediment shown as mg/100 cc. Amount expected from 150 ppm DMP alone. Amount from 1350 ppm Isoquinoline alone.

Figure 3.

Sediment increase due to interaction between 2,5-dimethylpyrrole 150 ppm) and isoquinoline (B, 1350 ppm) in No. 2 diesel (1)


(A,

Stauffer; Oil Shale, Tar Sands, and Related Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1981. Highly Significant (t = 73, p = 100, p = Significance

Test

( d )

alone.

Not

Significant

Highly Significant Highly Significant Highly Significant

( t =1 1 . 1 ; ( t =7 1 . 0 ; ( t =2 8 . 3 ;

Significant (t= 6 0 ; p = 05) H i g h l y S i g n i f i c a n t ( t =1 3 . 0 ; H i g h l y S i g n i f i c a n t ( t =1 9 . 1 ;

Summary o f I n t e r a c t i o n s Between 2 , 5 - D i m e t h y l p y r r o l e (DMP) and S and 0 Compounds i n No. 2 D i e s e l F u e l

TABLE I I

H W

>

w a

H

m >

a

>

O

>

C/i

>

H

m

o r

ON

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Stability

307

600i

11

I

I

I

I

I

I

2.9

3.0

3.1

3.2

3.3

3.4

3.5

1000 / T

Figure 5.

Arrhenius

1

(°K- )

plot of 2,5-dimethylpyrrole

in No. 2 diesel fuel



308

600

1000/T

Figure 6.

Arrhenius

_ I

(°K )

plot of 2,5-dimethylpyrrole

in JP-8


MATERIALS

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309

Stability

TABLE IV Upgrading E f f e c t on Composition and S t a b i l i t y of J e t F u e l From Shale O i l

Properties S u l f u r , t o t a l , wt-pct Carbon, wt-pct Hydrogen, wt-pct Oxygen, wt-pct Nitrogen, ppm T o t a l gum a f t e r 32 weeks at 110° F, mg/100 ml

Original

Upgraded

0.015 86.2 13.32 0.28 1500

0.005 85.43 14.42 0.05 3.2

6.4

1.8


310


MATERIALS

Table V E l e m e n t a l A n a l y s e s o f O r i g i n a l Syncrude and Gums A f t e r P r o l o n g e d S t o r a g e Elemental A n a l y s i s Element Fuel Gum

532

Naphtha SRC-II ( c o a l )

c H N 0

s Middle D i s t i l l a t e

84.94 12.78 0.32 1.92 0.72

65.99 6.55 8.59 12.91 2.00

86.28 9.05 0.98 3.36 0.32

75.60 6.65 5.46 10.99 0.67

90.13 7.41 1.05 1.53 0.40

88.54 6.73 1.60 2.81 0.31

85.25 12.45 0.223 1.92 0.61

70.01 6.65 6.26 10.27 6.82

85.14 12.56 0.21 1.84 0.21

66.28 6.19 7.21 17-36 2.86

87.67 12.18 0.026 0.90 0.43

82.54 11.38 0.25 0.87 0.55

87.05 12.42 Trace 0.30 0

83.52 8.41 Trace 7.34 0.01

84.80 14.73

75.41 9.08

1629

SRC-II ( c o a l )

c H N 0 S Heavy D i s t i l l a t e

Storage, Weeks

32

32

6434

SRC-II ( c o a l )

c H N 0 S Naphtha-EDS (#6 I l l i n o i s c o a l )

876

c H N 0 S Naphtha-EDS (Wyodak c o a l )

c H N 0

s Gas

Gum, mg/100ml

O i l - T a r Sands

c H N 0 S Kerosene - T a r Sands

c H N 0 S Naphtha - T a r Sands

c H N 0 S

0.015 0.54 0.05

32

1035

32

7438

16

30.1

16

20.7

32

0.05 16.02 0.15


Stauffer; Oil Shale, Tar Sands, and Related Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1981. ^

5

7

Visual

1) 2) 3) 4) 5) 6) 7)

24.5 15 12 15 17 30 4

Spun Tube 34.5 17 24 18 19 35 6

Spot Deposit

For d e t a i l e d d e s c r i p t i o n s , see Ref.(11). Paraho I , N = 1500 ppm. Hydrotreated Athabasca kerosene. Navy sample from W. Kentucky c o a l . Refined from Paraho I m a t e r i a l ; N = 347 ppm. Same as (5), N = 3.2 ppm. Same as (5), N = 146 ppm.

3

Paraho shale o i l J P - 5 ^ 4 Tar sands JP-5^ ) 4 COED c o a l l i q u i d JP-5 (4) 4 Paraho shale o i l J e t A(#4)< > 3 Paraho shale o i l J e t A(#23) ' 4 Paraho shale o i l J e t A(#10)< ) 4 Petroleum based JP-5 1

Description 1/30 0/30 2/30 1/30 0.5/30 1/30 1/30

1/90 0.5/90 76/90 1/90 0.5/90 1/90 1/90

1.5/150 0.5/150 197/150 1/150 0.5/150 1/150 2/150

AP, mm Hg/time, minutes

JFTOT Ratings

JFTOT E v a l u a t i o n s by ASTM Test Method D3241 Conducted f o r 2.5 Hours at 260°C C o n t r o l Temperature

TABLE VI


312

MATERIALS

s h a l e , c o a l , and t a r sands have been subjected to 110°F storage 9 9 f o r up to 32 weeks i n sealed g l a s s c o n t a i n e r s . ^H — ^) It i s normally accepted that one week of storage at 110°F i s e q u i v a l e n t to four weeks storage at ambient f o r middle d i s t i l l a t e s v i z ) , while e q u i v a l e n t to up to ten weeks at ambient f o r l i g h t e r f r a c tions ( i l ) . During t h i s t e s t samples were removed f o r analyses at 4, 8, 16, and 32 weeks and a l l stored samples were aerated every 4 weeks. While the experimental d e t a i l s have been published e l s e w h e r e ( i i > i 2 > i 2 ) , i n general the f u e l s r e f i n e d to meet r e q u i r e ment of petroleum-based f u e l s p e c i f i c a t i o n s showed r e l a t i v e l y good s t a b i l i t y . Table 4 shows an example of a j e t f u e l before and a f t e r upgrading good s t a b i l i t y . Table 4 shows an example of a j e t f u e l before and a f t e r upgrading by a d d i t i o n a l h y d r o t r e a t ment. As can be seen, the more severe the l e v e l of h y d r o t r e a t i n g , the more s t a b l e the f u e l . I t i s f o r t h i s reason that the s t a b i l i t y s p e c i f i c a t i o n s may d i c t a t e the u l t i m a t e p r o c e s s i n g costs. Elemental composition of s e v e r a l s y n f u e l s d e r i v e d from c o a l by two d i f f e r e n t processes and from t a r sands are compared i n Table 5 to the composition of gum produced i n each f u e l during prolonged storage. In some f u e l s c o n s i d e r a b l e q u a n t i t i e s of sediment and gum were formed i n a few weeks, t h e r e f o r e , the aging was d i s c o n t i n u e d before 32 weeks were completed. G e n e r a l l y speaki n g , the heavy d i s t i l l a t e s and gas o i l s (the more v i s c o u s products) produced the l a r g e s t amount of d e p o s i t s followed by the middle d i s t i l l a t e s and then the naphthas. The elemental composit i o n of the gums produced during storage show that the n i t r o g e n , oxygen and s u l f u r compounds tend to p a r t i c i p a t e i n the degradation reactions. In the more v i s c o u s f u e l s the tendency toward h i g h e r heteroatom c o n c e n t r a t i o n i n the gum i s much l e s s , probably because of c o n s i d e r a b l e f u e l entrainment. In some a p p l i c a t i o n s , thermal degradation can be more of a concern than storage s t a b i l i t y . Table 6 presents data on s e v e r a l middle d i s t i l l a t e s y n f u e l s as compared to a petroleum-based f u e l . The tube d e p o s i t s from the J e t F u e l Thermal Oxidation Test (ASTM D3241) are s i g n i f i c a n t l y higher f o r the s y n f u e l s , but the pressure buildup i s normal except f o r one case. This indicates either r a p i d r e a c t i o n s at the hot s u r f a c e or slow agglomeration. In e i t h e r case, the deposit l e v e l i s of concern and may d i c t a t e f u r t h e r upgrading. Conclusion A l l i n f o r m a t i o n p u b l i s h e d to date i m p l i e s that the production of s t a b l e s y n f u e l s i s p o s s i b l e but w i l l r e q u i r e r e f i n i n g processes a l t e r e d from those now r e q u i r e d f o r petroleum. S t a b i l i t y research i s c u r r e n t l y f o c u s s i n g on both b a s i c and a p p l i e d c o n s i d e r a t i o n s , and the r e s u l t s are encouraging. By c o n t i n u i n g these e f f o r t s , i t i s hoped that s t a b i l i t y w i l l not be the l i m i t i n g f a c t o r i n p r o v i d i n g adequate f u t u r e f u e l s u p p l i e s .


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Literature Cited 1. Whisman, M. L., Goetzinger, J. W., and Ward, C. C., "Storage Stability of Aviation Turbine Fuels," BOM RI 7325, 1969, 23 pp. 2. Whisman, M. L., Cotton, F. O., Goetzinger, J. W., and Ward, C. C., "Radiotracer Study of Turbine Aircraft Fuel Stability," BOM RI 7493, 1971, 30 pp. 3. Frankenfeld, J. W. and Taylor, W. F., "Alternate Fuels Nitrogen Chemistry", Final Technical Report for Naval Air Systems Command AIR 310C Contract No. N0001976C0675, November, 1977. 4. Frankenfeld, J. W. and Taylor, W. F., "Continuation Study of Alternate Fuels Nitrogen Chemistry", Final Technical Report for Naval Air Systems Command AIR 310C, Contract No. N0001978-C-0177. 5. Frankenfeld, J. W. and Taylor, W. F., "Continuation Study of Alternate Fuels Nitrogen Chemistry" Quarterly Progress Report No. 1, Naval Air Systems Command, AIR 310C, Contract No. N00019-78-C-0177, May, 1978 6. Taylor, W. F. and Frankenfeld, J. W., Ind. Eng. Chem. Product Research and Development, 17, 86 (1978). 7. Taylor, W. F. and Frankenfeld, J. W., "Development of High Stability Fuel", Final Report for Phase III, Contract No. N000140-74-C-0618, Naval Air Propulsion Test Center, December, 1976. 8. Taylor, W. F. and Frankenfeld, J. W., "Development of High Stability Fuel", Final Report for Phase I, Contract No. N00140-74-C-0618, Naval Air Propulsion Test Center, Jan. 1975. 9. Davies, O. L., Statistical Methods in Research and Production, Hafner Pub. Co., N.Y. (1958). 10. Frankenfeld, J. W. and Taylor, W. F., Ind. Eng. Chem. Prod. Res. Dev. 19 (1) 65 (1980). 11. Brinkman, D. W., Whisman, M. L., and Bowden, J. N., "Stability Characteristics of Hydrocarbon Fuels from Alternative Sources," BETC/RI-78/23, March 1979. 12. Bowden, J. N., "Stability Characteristics of Some Shale and Coal Liquids," BETC/4162-10, September 1980. 13. Bowden, J. N. and Brinkman, D. W., "Hydrocarbon Processing, July 1980, 77 pp. 14. Richie, J., J. Inst. Petrol., 1965, 51 (501). 15. Schwartz, F. G., Whisman, M. L., Allbright, C. S., and Ward, C. C., "Storage Stability of Gasoline," BOM Bulletin 660, 1972, 60 pp. RECEIVED February 18,

1981.


Oil Shale, Tar Sands, and Related Materials - American Chemical

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