Polymers for Fibers and Elastomers - American Chemical Society

16 Effects o f Sulfur a n d M e t a l s o n M e s o p h a s e F o r m a t i o n in C o a l L i q u i d Asphaltene a n d P e t r o l e u m P i t c h 1

YONG-DA GU , VICTORIA A. WEINBERG, MOHAMMAD-ALI SADEGHI, and TEH FU YEN

Downloaded by CORNELL UNIV on July 23, 2016 | http://pubs.acs.org Publication Date: August 29, 1984 | doi: 10.1021/bk-1984-0260.ch016

Environmental and Civil Engineering Department, School of Engineering, University of Southern California, Los Angeles, CA 90089-0242

The effect of elemental sulfur and organic sulfur compounds and organometallics on the mesophase microstructure was investigated. Elemental and organic sulfur compounds and organometallic compounds were added to Catalytic Incorporated coal liquid asphaltene and A240 petroleum pitch. The mesophase microstructure was examined using polarized light microscopy. It was found that organic sulfur compounds have less effect on mesophase microstructure than elemental sulfur but some organometallic compounds greatly inhibit mesophase formation. The properties of manufactured graphites are determined by the microstructure of the carbonaceous mesophase which is formed during pyrolysis* usually between the temperatures of 370 C and 500°C. The characteristics of the final product can be measured in a qualitative way by examination of the mesophase microstructure. Several coal liquid asphaltene and petroleum pitch samples have been screened in this way to determine their suitability as precursors for graphite materials. The physical and chemical properties of the mesophase formed from the samples and their pyrolyses residues were studied(1). It was found that the phenolic oxygen present either in the precursor or by addition during heat treatment suppresses mesophase formation by crosslinking and preventing the development of fluidity(2.)• The effects of other additives on petroleum pitch and PVC pitch such as metals and sulfur have also been studiedQ). The aim of the present work is to investigate the effects of 1

Current address: Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shansi, PRC. 0097-6156/84/0260-0263$06.00/0 © 1984 American Chemical Society

Arthur et al.; Polymers for Fibers and Elastomers ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERS FOR FIBERS AND ELASTOMERS

264

elemental sulfur* organic sulfur and organometallic compounds on the mesophase transformation on coal l i q u i d asphaltene. Some work was also done on A240 petroleum p i t c h .


Experimental The e f f e c t of additives on the asphaltene from the C a t a l y t i c Incorporated (Cat. Inc.) coal l i q u i d product was studied. Asphaltene i s defined as the pentane insoluble but benzene soluble part of the coal l i q u i d . The f r a c t i o n a t i o n procedure has been described i n d e t a i l elsewhere(JL) and i s shown schematically i n Figure 1. Some work was also done with A240 petroleum p i t c h . Elemental analysis f o r the Wyoming sub-bituminous coal* Cat. Inc. coal l i q u i d product* and Cat. Inc. asphaltene and A240 petroleum p i t c h are shown i n Table I . Measured amounts of the additive compounds to be studied were added to the Cat. Inc. asphaltene and petroleum p i t c h . The samples were pyrolyzed and the pyrol y s i s residues examined by cross polarized l i g h t microscopy. Elemental analyses of the residues were done.

Table I . Elemental Analysis (%) and Aromaticity ( f ) * of Coal**, C a t a l y t i c Incorporated (Cat. Inc.) Coal Liquid* and Cat. Inc. Asphaltene and A240 Petroleum Pitch f l

H

C

S

N

0

Ash

f a

Coal Coal Liquid Coal Liquid Asphaltene A240 Petroleum P i t c h

4.8 5.5 5.69 5.6

67.8 88.5 87.25 92.11

1.1 1.3 1.66 0.1

* f estimated from H/C atomic ratio; : **wyoming sub-bituminous

0.6 17.9 0.2 4.3 0.01 4.85 1.8 0.13

7.3 0.3 0.46 0.17

0.76 0.84 0.82 0.88

f = -0.79 H/C + 1.43 a

1. Additives Sublimed elemental sulfur and dibenzothiophene (DBT) were used to study the e f f e c t s of sulfur on the pyrolysis product. A1C1 » Nickel(II) phthalocyanine ( C H i N K N i , copper(II) phthalocyanine (CgH^Nj)^Cu, vanadyl(IV) tetraphenylporphyin (C^H^N^VO) and ferrocene ( C H F e ) were used to introduce metals into the samples. The additives were ground with the samples using an agate mortar. 2. Pyrolysis Pyrolysis experiments were carried out i n a programmed temperature controlled furnace under nitrogen gas at atmospheric 3

8

10

f

2

10


16.

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265

Effects of Sulfur & Metals on Mesophase

COAL LIQUID PRODUCT


pentane

soluble

PENTANE INSOLUBLE

OIL AND RESIN

benzene extract

BENZENE INSOLUBLE

PREASPHALTENE Figure 1.

BENZENE SOLUBLE

ASPHALTENE Flow sheet of f r a c t i o n a t i o n of coal l i q u i d .



266


pressure. The mixtures of Cat* Inc. coal l i q u i d asphaltene and a measured amount of additive were added to the pyrolysis c e l l . This c e l l i s an aluminum tube with a 0.5 mm pinhole i n the cap for free evaporation of the pyrolysis gas. The tubes were placed v e r t i c a l l y into the furnace and purged with nitrogen gas at 10 ml/min. The temperature was programmed at 13 C/hr to 360 C and then 5°C/hr to the f i n a l temperature of 460°C. 3. Microscopy The micrographs of the pyrolyzed residues were obtained using an SM-LUX-POL polarized l i g h t microscope with a camera attachment. Magnification was 200X i n t h i s work. 4. Elemental Analysis of the Pyrolyzed Residues Elemental analyses were done at Huffman Laboratories, Wheatridge, Colorado. The hydrogen and carbon contents were measured using combustion followed by C0 and H 0 determination (±0.3%). Oxygen was determined using pyrolysis followed by oxidation over carbon (±0.5%). Sulfur was measured using combustion to S0 followed by t i t r a t i o n (±0.3%). And ash was determined gravimetrically after combustion to 750 C (±0.3%). 2

2

2

Results and Discussion The cross polarized micrographs of the pyrolyzed residues of the Cat. Inc. o r i g i n a l coal l i q u i d and Cat. Inc. asphaltene are shown i n Figure 2. The microstructures are primarily coarse mosaic textures. The following subsections describe the d i f f e r e n t additives of elemental and organic s u l f u r * organometallies and t h e i r combined e f f e c t s on Cat. Inc. asphaltene during p y r o l y s i s . 1. E f f e c t of Elemental Sulfur Figure 2 also shows the effect of increased amounts of elemental sulfur on the microstructure of Cat. Inc. asphaltene. The microstructure changes from a coarse mosaic f o r 0% and 2% by weight sulfur to a very f i n e mosaic structure at 8% by weight s u l f u r . Figure 3 for the pyrolysis residues of A240 petroleum p i t c h and 8% by weight sulfur shows that the sulfur has less e f f e c t on the microstructure of the p i t c h . The microstructure of the pure p i t c h i s flow type while that of the p i t c h with 8% by weight sulfur i s coarse mosaic. Table II summarizes the results of elemental analysis for the pyrolyzed Cat. Inc. asphaltene and shows how the residual pyrolysis y i e l d increases with sulfur addition. Sulfur acts as a dehydrogenation agent i n Cat. Inc. asphaltene. Loss of hydrogen leaves reactive free r a d i c a l sites open r e s u l t i n g i n increased cross linkage* aromaticity and condensation r e a c t i o n s . These condensation reactions decrease the f l u i d i t y and i n h i b i t the mesophase formation as well as increasing the pyrolysis y i e l d . Petroleum p i t c h i s less affected by the sulfur* possibly because of i t s higher i n i t i a l aromaticity and lower oxygen content.


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16.

F i g u r e 2.

Micrographs of pyrolyses residues of C a t a l y t i c Incorporated (Cat. Inc.) c o a l l i q u i d , C a t . I n c . a s p h a l t e n e and the e f f e c t o f e l e m e n t a l s u l f u r on mesophase f o r m a t i o n i n C a t . I n c « a s p h a l t e n e .


267

268


Table I I , Elemental Analysis of Pyrolyzed Residues of Samples Modified with Elemental Sulfur (Elements i n wt.%)

Samples*


0 4 6 8

C

H

91.82 91.25 91.61 90.61

3.84 3.88 3.73 3.83

0

2.08 2.71 2.47 3.18

N

1.28 1.69 1.55 1.24

S

0.15 0.22 0.04 0.35

Ash

0.12 0.63 0.24 0.71

H/C

Yield (%)**

0.50 0.51 0.49 0.51

52.7 59.5 58.6 64.7

*Each sample used i s Cat. Inc. coal l i q u i d asphaltene; numerals indicated are wt.% S added. **Residual y i e l d s a f t e r p y r o l y s i s (Wt.%).

2. Effect of Dibenzothiophene (DBT) Dibenzothiophene(DBT) was added to Cat. Inc. asphaltene to determine the e f f e c t of sulfur when added as an organic molec u l e . Table I I I shows the amount i n weight percent of DBT that was added to obtain the desired weight percent of s u l f u r . For 8% by weight organic s u l f u r * the sample contains almost half DBT. When DBT i s pyrolyzed alone to 460°C, the pyrolysis y i e l d i s zero. As shown i n Figure 4 the DBT sulfur has no e f f e c t on the microstructure of the pyrolysis residues. I t i s d i f f i c u l t to t e l l i f t h i s i s because most of the DBT vaporizes before mesophase

Table I I I , Effect of Organic Sulfur Exemplified by Dibenzothiophene (DBT) Added to Cat. Inc. Coal Liquid Asphaltene

%s 0 4 6 8

Wt.% 0 24 35 47

(DBT)

Y i e l d (%)* 52.7 45.2 43.8 39.3

Microstructure** CM CM CM CM

•Residua y i e l d s a f t e r p y r o l y s i s (Wt.%) **CM - Coarse Mosaic



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Figure 3.

Figure 4,


Micrographs of pyrolyses residues of A240 Petroleum p i t c h and with 8% by weight elemental sulfur.

The effect of organic sulfur on mesophase formation in Cat. Inc. asphaltene.


269


270

formation begins so that i t does not interact with the Cat. Inc. asphaltene or i f the sulfur i n the DBT molecule i s t i e d up i n the r i n g so that i t cannot act as a dehydrogenation agent. 3 . Effect of Organometallics The e f f e c t of organometallics at 1600 ppm and 800 ppm on the pyrolysis residues of the Cat. Inc. asphaltene are shown i n Figure 5 and Table IV. The additives used were mentioned i n the experimental p a r t . Table IV shows that organic Ni and V i n h i b i t mesophase formation because they promote dehydrogenation and condensation reactions to a greater extent than the other l i s t e d a d d i t i v e s . Pyrolysis y i e l d s are increased because of increased


Table IV, Effect of Organometallics* Added to Cat. Inc. Coal Liquid Asphaltene

Metal 1600

Fe Al Cu Ni V

Y i e l d (%)** ppm 800 ppm

64.5 63.0 — — —

62.7 64.4 64.8 62.3 68.0

Microstructure*** ppm 800 ppm

1600

CM CM —

MM —

CM CM Flow MM FM

•Organometallics used are mentioned i n the experimental part ••Residual yields after pyrolysis (wt.%); also with no additives the y i e l d i s 52.7% and the microstructure i s coarse mosaic •••CM = Coarse Mosaic MM = Medium Mosaic FM = Fine Mosaic

condensation. The Fe, A l and Cu additives are a l l able to increase the y i e l d without changing the microstructure. Mochida, et a l . (4.) have found that Friedel-Crafts catalysts such as A 1 C 1 promote mesophase formation by removing the a l k y l groups that interfere with mesophase order. Our data show that these addit i v e s also can be used to increase the pyrolysis y i e l d s . 4 . E f f e c t of Organometallics with 6% by Wt. Organic Sulfur The combined effects of organometallic additives at 1600 ppm and 800 ppm with 6% by weight organic sulfur* exemplified by dibenzothiophene (DBT)* on the Cat. Inc. asphaltene are shown i n Table V and Figure 6 . It i s shown that the microstructures stay unchanged except for the Ni addition. Also the pyrolysis y i e l d i s increased over that of Cat. Inc. asphaltene and 6% organic sulfur without the organometallic a d d i t i v e s . The effect of S




GU ET AL.

Figure 5.

The e f f e c t of metals on mesophase formation Cat. Inc. asphaltene


272



Figure 6.

The influence of organic sulfur (6% by weight) with organometallic compounds on mesophase formation i n Cat. Inc. asphaltene.


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273

Table V. Effect of Organometallics* and 6% by weight Organic Sulfur, Exemplified by Dibenzothiophene (DBT), Added to Cat. Inc. Coal Liquid Asphaltene

Metal


Fe Ni Cu V

Y i e l d (%)** 1600 ppm 800 ppm

49.1 50.7 — —

47.8 50.4 — —

Microstructure*** 1600 ppm 800ppm

CM FM CM CM

CM FM CM CM

•Organometallics used are mentioned i n the experimental part ••Residual y i e l d s after pyrolysis (Wt.%); also with 6% organic sulfur (DBT) and no metals the y i e l d i s 43.8% and the microstructure i s coarse mosaic •••CM = Coarse Mosaic FM = Fine Mosaic

heat treatment temperature (HTT) on microstructure for the Cat. Inc. asphaltene alone and with the 6% organic sulfur and 800 ppm Ni additive i s compared i n Figures 7 and 8 which show that the Ni additive suppresses mesophase nucleation. Table VI shows the r e s i d u a l yields at d i f f e r e n t pyrolysis temperatures plus t h e i r elemental analysis and aromaticities f o r the combined sample of Cat. Inc. asphaltene* 6% organic sulfur and 800 ppm n i c k e l . Conclusions From t h i s work we can draw three tentative conclusions: 1. The r e s u l t s show that addition of elemental sulfur i n h i b i t s mesophase formation. This e f f e c t i s not as pronounced on materials of higher aromaticity and lower oxygen content such as petroleum p i t c h . We think that t h i s i s because the sulfur acts as a dehydrogenation agent and increases the condensation reaction rate to a point where i t reduces f l u i d i t y and thus suppresses mesophase growth. 2 . The r e s u l t s with organic sulfur addition using DBT are not c l e a r . Either the DBT molecule i s very stable i n the temperature range of mesophase formation or i t vaporizes before the mesophase i s formed. The addition of DBT does not change the microstructure but i t does decrease the o v e r a l l pyrolysis y i e l d . The decrease i n y i e l d i s probably due to the loss of DBT during the heat treatment.




274

Figure 7 * Micrographs of pyrolyses residues of Cat. Inc. asphaltene at d i f f e r e n t f i n a l temperatures.


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Figure 8.

Micrographs of pyrolyses residues at d i f f e r e n t f i n a l temperatures for Cat. Inc. asphaltene with 6% by weight organic Sulfur and 800 ppm N i c k e l .


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275


None Spherrules Larger Spherrules Mozaic

Microstructure

88.56 89.76 89.99 91.19

68.1 64.3

C(%)

81.7 74.4

Yield (%)***

4.58 4.23

5.07 4.83

H(%)

3.02 2.65

4.16 3.37

0(%)

0.09 0.09

0.07 0.07

S(%)

0.60 0.55

0.68 0.64

H/C

0.028 0.025

0.077 0.035

O/C

0.96 1.00

0.89 0.92

a

f ****

•Percent by weight organic sulfur exemplified by dibenzothiophene (DBT) **HTT - Heat Treatment Temperature ***Residua y i e l d s a f t e r pyrolysis (Wt.%) * * * * f - estimated from H/C atomic r a t i o : f = -0.79 H/C + 1.43 a a

428

380 402 413

HTT (°C)**

Table VI. Elemental Analysis of the Sample Residues at Different Pyrolysis Temperatures. Sample: Cat. Inc. Coal Liquid Asphaltene + 6% Organic Sulfur* + 800 ppm Nickel


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277

3. The major c o n c l u s i o n o f t h i s work so f a r i s t h a t t h e t r a c e i n o r g a n i c s A l , Fe and Cu o r g a n o m e t a l l i c a d d i t i v e s w i l l i n c r e a s e t h e p y r o l y s i s y i e l d w i t h o u t a f f e c t i n g t h e mesophase microstructure. A d d i t i o n o f o r g a n o m e t a l l i c s c a n e i t h e r have inhibitory or promotional effects. The p r o m o t i o n a l e f f e c t ( e . g . Cu) i s perhaps due t o t h e t e r m i n a t i o n o f r a d i c a l f o r m a t i o n * whereas t h e i n h i b i t o r y e f f e c t ( e . g . V and N i ) i s due t o t h e i n i t i a t i o n of radical formation. T h i s w i l l be s t u d i e d f u r t h e r u s i n g t h e temperature dependence o f e l e c t r o n s p i n resonance (ESR) studies.


Acknowledgment We a r e g r a t e f u l f o r f i n a n c i a l a s s i s t a n c e Foundation under grant n o . DAR-8008755.

from N a t i o n a l

Science

Literature Cited 1. Weinberg, V.L., Ph.D. Thesis, University of Southern California, Los Angeles, 1981. 2. Weinberg, V.L. and Yen, T.F., unpublished data. 3. O i , S. and Onishi, N., "influence of Organic Sulfur Compounds and Metals on Mesophase Formation"; Carbon 1978, 16, 455. 4. Mochida, I., Ando, T., Maeda, K., Fujitsu, K. and Takeshita, K . , Carbon 1980, 18, 319. RECEIVED May 21, 1984


Polymers for Fibers and Elastomers - American Chemical Society

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