South African Coals and Their Behavior During Liquefaction - ACS

2 South African Coals and Their Behavior During Liquefaction Downloaded by OHIO STATE UNIV LIBRARIES on October 14, 2014 | http://pubs.acs.org Publication Date: October 14, 1980 | doi: 10.1021/bk-1980-0139.ch002

D. GRAY, G. BARRASS, J. JEZKO, and J. R. KERSHAW Fuel Research Institute of South Africa, P.O. Box 217, Pretoria, South Africa 0001

South African coals differ from most Northern Hemisphere coals in their geological age, unusual petrology and their high mineral matter content. If these coals are to be used for conversion to synthetic fuels then criteria must be found to enable predictions of their behaviour under liquefaction conditions to be determined. This paper describes the hydrogenation of a number of South African coals using two different techniques, to ascertain whether well known coal properties can be used to predict their hydrogenation behaviour. The effect of the mineral matter content and of the inorganic sulphur content on the hydrogenation of coal were also studied. GEOLOGICAL ORIGIN OF SOUTH AFRICAN COALS The coal deposits of South Africa were formed during the Permian age just after a retreat of glaciation. This makes it almost certain that the climate was temperate rather than subtropical and may explain the differences between the plant life in South Africa at that time and the flora of the North American

Carboniferous era. The predominance of the inertinite maceral group in South African coals is indicative of drier swamp conditions in which rotting processes as well as peatification played a more dominant role than in the formation of the humic coals of Europe (1) . South African coals were thought to be deposited in deltaic or f l u v i a l environments where fluctuations in water level may have caused deposition of large quantities of mineral matter. South African coals generally have not reached a very high rank although in Natal anthracites are found. This rank increase seems to be due to metamorphism brought about by dolerite intrusions rather than by stratigraphic depth. GEOGRAPHICAL LOCATION AND COAL RESERVES OF SOUTH AFRICA A map showing the coal fields of the Republic of South Africa is shown in Figure 1. The main coalfields l i e in the Highveld area of the Orange Free State, South-Eastern Transvaal 0-8412-0587-6/80/47-139-035$05.00/0 © 1980 American Chemical Society In Coal Liquefaction Fundamentals; Whitehurst, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Downloaded by OHIO STATE UNIV LIBRARIES on October 14, 2014 | http://pubs.acs.org Publication Date: October 14, 1980 | doi: 10.1021/bk-1980-0139.ch002

COAL LIQUEFACTION FUNDAMENTALS

Figure 1.

Coalfields of South A frica

In Coal Liquefaction Fundamentals; Whitehurst, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

2.

GRAY E T

South African

AL.

37

Coals

and N a t a l . Other c o a l f i e l d s are located i n the Northern part of the country, the Waterberg f i e l d on the Botswana border and the Limpopo and P a f u r i f i e l d s on the borders of Zimbabwe/Rhodesia and Mozambique. The l a r g e s t f i e l d i s the Highveld f i e l d (25,407 m i l l i o n metric tons of raw bituminous mineable c o a l i n s i t u ) followed by the Witbank and Waterberg f i e l d s (approximately 17,000 m i l l i o n metric tons) (2).


Table I

Ash

Raw

%

Resources Million Metric Tons

Bituminous Coal Resources

5-10

10-15

15-20

20-25

25-30

30-35 T o t a l

20

1,499

8,620

15,220

18,565

37,350 81,274

Table I shows the raw bituminous c o a l resources f i g u r e s i n m i l l i o n s of metric tons at various ash contents ( 2 ) . The t o t a l f i g u r e of 81,274 m i l l i o n metric tons i s f o r the t o t a l resources of raw bituminous c o a l mineable i n s i t u down to 300 meters. This t o t a l i s the sum of the proven, i n d i c a t e d and i n f e r r e d reserves. Mineable c o a l i n s i t u i s that p o r t i o n of the c o a l i n s i t u which can be mined by e x i s t i n g techniques. The P e t r i c k commission r e p o r t 02) a r r i v e s at a f i g u r e of 24,915 m i l l i o n metric tons of raw bituminous c o a l e x t r a c t a b l e by underground mining. Extract a b l e c o a l i s defined as that p o r t i o n of the mineable c o a l i n s i t u which i s e x t r a c t a b l e i n p r e v a i l i n g or s l i g h t l y l e s s rigorous economic c o n d i t i o n s . The f i g u r e of 24,915 m i l l i o n metric tons f o r a raw bituminous c o a l has been s u b s t a n t i a l l y added to s i n c e 1975 by f u r t h e r e x p l o r a t i o n and could w e l l be of the order of 28,000 m i l l i o n metric tons by t h i s time. I t must a l s o be emphas i z e d that reserves are dynamic, as higher p r i c e s or improved technology may allow the e x p l o i t a t i o n of deposits which are p r e s e n t l y not regarded as reserves. Table I shows that most of the South A f r i c a n bituminous c o a l c o n t a i n high q u a n t i t i e s of mineral matter which i s o f t e n i n t i mately a s s o c i a t e d with the organic matter of the c o a l . About h a l f of the resources y i e l d between 30 and 35 per cent ash. LIQUEFACTION BEHAVIOUR OF A SELECTION OF SOUTH AFRICAN COALS Experimental Two d i f f e r e n t experimental procedures were used i n t h i s study, to i d e n t i f y the c o a l p r o p e r t i e s of importance i n c o a l conversion which are independent of processing c o n d i t i o n s . These were: (i) 'Dry Hydrogénation using a semi-continuous 'hot-rod' reactor. (ii) S l u r r i e d Hydrogénation using a r o t a t i n g autoclave. 1


COAL LIQUEFACTION

38

(i)

FUNDAMENTALS

1

'Hot-Rod Method This method was s i m i l a r to that used by Hiteshue et a l ( 3 ) . In t h i s method sand (50 g, mesh 0.42 - 0.15 mm) was mixed w i t h the c o a l (25 g, mesh 0.5 - 0.25 mm). The a d d i t i o n of sand to the c o a l helped to prevent agglomeration ( 4 ) . A l l the e x p e r i ments used an aqueous s o l u t i o n of stannous c h l o r i d e impregnated on the c o a l as a c a t a l y s t . The amount of c a t a l y s t added on a t i n b a s i s was 1% of the mass of the c o a l . These mixtures were placed i n a 'hot-rod r e a c t o r and heated to 500°C at a h e a t i n g r a t e of 200°C per minute. Residence time at temperature was 15 minutes. Hydrogen at a flow rate of 22 l i t e r s / m i n u t e and a pressure of 25 MPa was c o n t i n o u s l y passed through the f i x e d bed of c o a l / s a n d / c a t a l y s t . The v o l a t i l e products were c o l l e c t e d i n high-pressure c o l d t r a p s . A schematic of the apparatus used i s shown i n F i g u r e 2.


1

(ii)

Rotating Autoclave Method The r e a c t o r was a 1 l i t e r s t a i n l e s s s t e e l r o t a t i n g a u t o c l a v e . In these experiments the r a t i o of anthracene o i l to c o a l was 3:1. Coal (50 g) impregnated with c a t a l y s t (1% Sn as SnCl^) was mixed with sand (200 g ) . The autoclave was p r e s s u r i z e d with hydrogen to 10 MPa at room temperature and heated (ca 7°C/minute) to the f i n a l r e a c t i o n temperature (450°C). The pressure at r e a c t i o n temperature was approximately 25 MPa. The product was washed from the cooled 'hot-rod' r e a c t o r system or autoclave with toluene. The s o l i d residue was e x t r a c ted w i t h b o i l i n g toluene i n a soxhlet e x t r a c t o r f o r 12 hours. The o v e r a l l conversion of c o a l to l i q u i d and gaseous products was obtained from the formula: Percentage conversion =100

1

^Organic m a t e r i a l i n the residue^ ^Organic m a t e r i a l i n the c o a l

In the case of the 'hot-rod' r e a c t o r experiments, the toluene s o l u t i o n s were combined and the toluene removed under reduced pressure. n-Hexane (250 ml) was added to the e x t r a c t and i t was allowed to stand f o r 24 hours with o c c a s i o n a l shaking. The s o l u t i o n was f i l t e r e d to leave a residue (asphaltene) and the hexane was removed from the f i l t r a t e under reduced pressure to give the o i l . P r o p e r t i e s of the coals used The chemical and pétrographie p r o p e r t i e s of the twenty coals used i n the hydrogénation experiments are shown i n Tables I I and I I I . Mineral matter was determined d i r e c t l y using a r a d i o frequency low temperature plasma asher at medium power r a t i n g f o r approximately 48 h per c o a l . The v o l a t i l e matter was c o r r e c t e d f o r the e f f e c t s of the mineral matter by applying the equation used by Given et a l (5). The mean maximum r e f l e c t a n c e of v i t r i n i t e (Ro max) i s the mean of one hundred determinations. The percentage of r e a c t i v e macérais on a volume b a s i s was



1. 2.

47.8 49.1 47.4 45.7 51.4 59.9 48.9 53.8 34.3 56.8 57.3 44.4 56.8 41.5 58.5 56.3 56.4 81.1 17.6 81.9

35.3 34.8 32.8 30.3 32.7 23.3 27.9 29.6 19.8 26.3 25.7 20.8 23.6 22.1 24.9 20.5 17.8 8.9 8.4 6.1

10.9 12.7 14.9 20.2 12.7 14.3 20.6 11.9 38.8 14.3 14.6 27.6 17.4 28.6 13.0 20.8 24.4 8.2 12.2 10.0

H 0

6. 0 3. 4 4. 9 3. 8 3. 2 2. 5 2. 6 4. 7 7. 1 2. 6 2. 4 7. 2 2. 2 7. 8 3. 6 2. 4 1. 4 1. 8 1. 8 2. 0

Ratio 0.83 0.81 0.82 0.80 0.78 0.63 0.79 0.75 0.73 0.72 0.70 0.69 0.71 0.68 0.64 0.66 0.62 0.50 0.47 0.40

0 .5 1 .0 2 .3 2 .9 1 .3 0 .6 0 .8 1 .3 0 .9 0 .8 1 .5 1 .8 1 .9 1 .6 0 .7 0 .8 3 .0 0 .7 1 .7 1 .2 2 .0 1 .5 2 .1 2 .0 2 .1 1 .9 2 .0 1 .9 1 .7 2 .1 2 .0 2 .0 2 .2 2 .0 2 .1 1 .9 2 .3 2 .4 2 .4 2 .2 5. 5 5. 4 5. 4 5. 3 5. 3 4. 4 5. 5 5. 0 4. 5 5. 0 4. 9 4. 7 5. 0 4. 5 4. 7 4. 6 4. 5 3. 8 3. 5 3. 0 78.8 80.6 79.1 79.1 81.6 84.1 82.9 80.3 74.3 83.0 83.5 76.5 84.2 78.4 88.0 83.5 87.0 90.8 89.6 90.9

Atomic

S

Ζ

Ν

%

H

%

C

%

Ultimate Analyses (D.A.F. Basis)

M i n e r a l Matter V o l a t i l e Matter c o r r e c t e d to dry m i n e r a l matter f r e e b a s i s

2

% Fix. Carb.

% Vol. Mat.

% Ash

%

Proximate Analyses ( A i r Dried Basis)

Proximate and Ultimate Analyses of Coals Used i n the L i q u e f a c t i o n Experiments

Mat l a Waterberg New Wakefield Kriel Spitzkop Landau Koornfontein Delmas Sigma T v l . Nav. Springbok Vierfontein Ballengeich Cornelia Phoenix Wolvekrans Newcastle Natal Amm. Utrecht Balgray

Coal

Table I I


10 .3 15 .2 19 .0 22 .3 16 .0 15 .2 22 .8 14 .5 45 .0 17 .2 16 .4 31 .9 19 .9 32 .8 15 .5 21 .4 28 .7 9 .0 14 .8 11 .3

MM

40.1 40.2 38.3 35.9 37.4 25.8 32.9 34.1 28.0 29.9 28.5 26.4 26.4 29.0 28.2 22.4 19.1 8.5 7.5 5.1

VMc

VO

40

COAL LIQUEFACTION FUNDAMENTALS


Table I I I

Pétrographie Composition o f the Coals Used (Mineral Matter Free B a s i s )

Coal

Matla Waterberg New Wakefield Kriel Spitzkop Landau Koornfontein Delmas Sigma T v l . Nav. Springbok Vierfontein Ballengeich Cornelia Phoenix Wolvekrans Newcastle

1 2 3

F u e l Research Institute V+E Volume %

84 94 85 74 63 70 61 54 32 42 38 35 47 29 42 34 50

R

1

max

Ο

0.656 0.720 0.677 0.685

-

0.746 0.787 0.661 0.599 0.748 0.815 0.619 0.858 0.569 0.793 0.760 1.116

South A f r i c a n Iron and S t e e l 2 Corporation Total V+E Volume % 84 94 85 79 62 69 61 54 32 42 38 35 47 24 42 34 50

4 1 5 9 22 16 22 27 53 33 34 33 31 55 33 36 13

Mean Maximum Reflectance o f V i t r i n i t e V i t r i n i t e + Exinite Reactive s e m i - f u s i n i t e


88 95 90 88 84 85 83 81 85 75 72 68 78 79 75 70 63

2.

GRAY E T A L .

South African

41

Coals

determined by two techniques. The v i t r i n i t e and e x i n i t e values were obtained by the Fuel Research I n s t i t u t e and the t o t a l percentage of ' r e a c t i v e macérais was determined by the South A f r i c a n Iron and S t e e l Corporation (ISCOR) ( 6 ) . A number of these c o a l s c o n t a i n large q u a n t i t i e s of r e a c t i v e s e m i - f u s i n i t e (see Table I I I ) . This has important i m p l i c a t i o n s f o r the p r e d i c t i o n of t e c h n o l o g i c a l behaviour and w i l l be d i s c u s s e d l a t e r . 1


RELATIONSHIPS BETWEEN LIQUEFACTION BEHAVIOUR AND COMPOSITION

THE COAL

The e f f e c t of the f o l l o w i n g c o a l property parameters was studied i n r e l a t i o n to l i q u i d y i e l d s and conversions during c o a l hydrogénation using both experimental procedures. 1. 2. 3. 4. 5.

V o l a t i l e Matter Y i e l d H/C Atomic Ratio 'Reactive'Mac era 1 Content Rank M i n e r a l Matter Content and

Composition

Organic Coal P r o p e r t i e s Good c o r r e l a t i o n s are obtained by p l o t t i n g the percentage t o t a l conversion of the c o a l expressed on a dry m i n e r a l matter f r e e b a s i s (dmmf) against the c o r r e c t e d v o l a t i l e matter content f o r both the 'hot-rod' and autoclave modes (see F i g u r e s 3 and 4 ) . The slopes of the r e g r e s s i o n l i n e s are very s i m i l a r i n both modes and the square of the c o r r e l a t i o n c o e f f i c i e n t s are i n both cases very c l o s e to 1. The f a c t that the slopes are s i m i l a r f o r the r e s u l t s from the d i f f e r e n t experimental techniques, i n d i c a t e s that thermal fragmentation i s the o v e r r i d i n g step i n conversion of the c o a l and that any d i f f e r e n c e s are r e l a t e d to the mode of s t a b i l i z a t i o n of the r e a c t i v e fragments formed. F i g u r e s 5 and 6 show that there i s a good c o r r e l a t i o n between the percentage conversion and the H/C atomic r a t i o of the c o a l s f o r both experimental procedures. Thus the c o r r e c t e d v o l a t i l e matter y i e l d and the atomic H/C r a t i o both appear to be good parameters f o r a s s e s s i n g the r e a c t i v i t y of the c o a l s s t u d i e d . There i s a l s o i n t e r c o r r e l a t i o n between the v o l a t i l e matter and the H/C atomic r a t i o f o r the South A f r i c a n c o a l s s t u d i e d . Thus a good c o r r e l a t i o n between conversion y i e l d and one of these p r o p e r t i e s o b v i o u s l y i m p l i e s a s i m i l a r c o r r e l a t i o n w i t h the other property. The c o r r e l a t i o n s between the v o l a t i l e matter y i e l d and the ' r e a c t i v e ' maceral content and between the H/C atomic r a t i o and the ' r e a c t i v e ' maceral content are not s t a t i s tically significant. No data on l i q u i d y i e l d s are a v a i l a b l e f o r the autoclave experiments because i t i s not p o s s i b l e to separate the product o i l , which r e s u l t s from c o a l l i q u e f a c t i o n , from the anthracene o i l and i t s decomposition products. In the case of the 'hotrod' experiments t h i s c o m p l i c a t i o n does not e x i s t .


42

COAL LIQUEFACTION

FUNDAMENTALS

GAS STORAGE


GAS SAMPLE

U ROTAMETER

Figure 2.

Ο

20

Hot rod reactor

40

60

80

100

CONVERSION (DMMF) %

Figure 3.

Percentage conversion against volatile matter yield (hot rod mode)



GRAY E T A L .

South African

Ο

20

Coals

40

60

80

100

CONVERSION (DMMF) %

Figure 4.

Percentage conversion against volatile matter yield (rotating autoclave mode)

0

20

40

60

80

100

CONVERSION (DMMF) %

Figure 5.

Percentage conversion against H/C atomic ratio (hot rod mode)



44

COAL LIQUEFACTION

FUNDAMENTALS

For the l a t t e r technique the y i e l d of toluene s o l u b l e s ( o i l plus asphaltene) i s the most r e l i a b l e of the l i q u i d y i e l d f i g u r e s because of the u n c e r t a i n t y i n estimating the asphaltene y i e l d by p r e c i p i t a t i o n with n-hexane (7). Figure 7 shows the v a r i a t i o n i n toluene s o l u b l e y i e l d w i t h H/C atomic r a t i o and with v o l a t i l e matter y i e l d o f the c o a l s . The best f i t of the data f o r the toluene s o l u b l e s against H/C atomic r a t i o i s a power curve passing through the o r i g i n , whereas f o r the v o l a t i l e matter y i e l d a l i n e a r c o r r e l a t i o n was m a r g i n a l l y b e t t e r . F i g u r e 8 shows the e f f e c t of rank, as measured by the mean maximum r e f l e c t a n c e of v i t r i n i t e , on the o v e r a l l conversion. The conversion was highest f o r c o a l s i n a narrow Ro max range of between 0.65 - 0.70. Cudmore's data on A u s t r a l i a n c o a l s a l s o appears to e x h i b i t a maximum when r e f l e c t a n c e data i s p l o t t e d against conversion (8). I t i s d i f f i c u l t t o i n t e r p r e t t h i s data because of the large v a r i a t i o n i n the v i t r i n i t e and r e a c t i v e s e m i - f u s i n i t e content of these c o a l s . The r e a c t i v i t y of v i t r i n i t e and r e a c t i v e s e m i - f u s i n i t e would be expected to vary with rank but to d i f f e r e n t degrees. F o r s e v e r a l of the lower rank coals v i t r i n i t e i s only a minor component of the c o a l . In Figure 9 the v i t r i n i t e + e x i n i t e content and the 'react i v e maceral content, as determined by ISCOR, are p l o t t e d against the t o t a l conversion f o r the 'hot-rod' technique. Figure 10 p l o t s the same information f o r the autoclave r e s u l t s . The d i f f e r e n t slopes f o r the l i n e s of best f i t f o r ' t o t a l r e a c t i v e s and v i t r i n i t e + e x i n i t e r e f l e c t s the s p e c i a l p e t r o l o gy of the m a j o r i t y of South A f r i c a n coals used i n t h i s study (see Table I I I ) . For these c o a l s the ' r e a c t i v e s ' contain a high p r o p o r t i o n of s e m i - f u s i n i t e i n the i n e r t i n i t e . Several i n v e s t i g a t o r s have t r i e d to c h a r a c t e r i z e the behav i o u r of r e a c t i v e s e m i - f u s i n i t e i n coals during c a r b o n i z a t i o n . Recently there have been reports d e a l i n g with the behaviour of t h i s maceral under l i q u e f a c t i o n c o n d i t i o n s . Ammosov e t a l ( 9 ) c l a s s i f i e d one t h i r d of the s e m i - f u s i n i t e as being r e a c t i v e during coking, w h i l s t the balance together w i t h the m i c r i n i t e are i n e r t . T a y l o r o r i g i n a l l y concluded that s e m i - f u s i n i t e and m i c r i n i t e i n A u s t r a l i a n coals were i n e r t during c a r b o n i z a t i o n but l a t e r observed p a r t i a l f u s i n g of a t r a n s i t i o n a l m a t e r i a l between v i t r i n i t e and s e m i - f u s i n i t e ( 1 0 , 1 1 ) . For American and European coking coals the behaviour of s e m i - f u s i n i t e i s g e n e r a l l y l e s s important since only small q u a n t i t i e s of t h i s maceral are u s u a l l y present. However, South A f r i c a n c o a l used i n coke oven-blends contains as l i t t l e as 40 per cent v i t r i n i t e and as much as 4 5 per cent r e a c t i v e semif u s i n i t e ( 1 2 ) . The p a r t i a l r e a c t i v i t y of the s e m i - f u s i n i t e f r a c t i o n during l i q u e f a c t i o n of A u s t r a l i a n c o a l s has been reported by Guyot et a l (13). They found that the low r e f l e c t i n g i n e r t i n i t e i n two coals up to (a r e f l e c t a n c e from 1.40 to 1 . 4 9 ) was r e a c t i v e . This agrees with the r e s u l t s of Smith and Steyn ( 1 2 ) who consider that the s e m i - f u s i n i t e f r a c t i o n i n South A f r i c a n coals up to V 1 5 (1.50 - 1 . 5 9 ) can be r e a c t i v e to coking. 1

1



GRAY E T A L .

Figure 6.

South African

45

Coals

Percentage conversion against H/C atomic ratio (rotating autoclave mode)

Figure 7. Percentage toluene solubles against H/C atomic ratio (X) and volatile TOLUENE SOLUBLES (DMMF)%

matter yield

(·)



46

COAL

LIQUEFACTION

FUNDAMENTALS

In a d d i t i o n , Shibaoka et a l (14) during hydrogénation of a New South Wales c o a l reported that the i n e r t i n i t e with r e l a t i v e l y low r e f l e c t a n c e became p a r t i a l l y l i q u e f i e d . On the b a s i s of numerous pétrographie analyses of South A f r i c a n coking c o a l s v a r y i n g i n v i t r i n i t e content from 40 per cent up to 90 per cent Smith and Steyn (12) concluded that " s e m i - f u s i n i t e cannot be added to the r e a c t i v e s on a f i x e d a r b i t r a r y b a s i s but need to be counted as a d i s t i n c t group of r e a c t i v e s which can form up to 60 per cent of the t o t a l of semif u s i n i t e plus m i c r i n i t e " . Since the low r e f l e c t i n g unstructured, or only s l i g h t l y s t r u c t u r e d , s e m i - f u s i n i t e i n a c o a l has a s i g n i f i c a n t r o l e i n the coking process, i t i s reasonable to assume that t h i s maceral has an e q u a l l y important r o l e i n l i q u e f a c t i o n processes. For example a c o a l l i k e Sigma having a conv e n t i o n a l l y assessed v i t r i n i t e + e x i n i t e content of only 32 per cent s t i l l gives a conversion y i e l d , on hydrogénation, of 75 per cent (dmmf c o a l b a s i s ) . The t o t a l ' r e a c t i v e maceral content of t h i s c o a l i s 85%. The slopes of the r e g r e s s i o n l i n e s f o r conversion y i e l d against ' r e a c t i v e ' macérais f o r the 'hot-rod' and f o r the r o t a t i n g autoclave modes of hydrogénation are shown by s t a t i s t i c a l a n a l y s i s to be s i m i l a r (compare Figures 9 and 10). This suggests that the r e l a t i o n s h i p between t o t a l ' r e a c t i v e ' macérais and c o a l r e a c t i v i t y as measured by conversion i s not dependent on the conversion technique. However, c o a l r e a c t i v i t y as measured by t o t a l conversion to l i q u i d s and gases becomes l e s s dependent on c o a l parameters as p r o c e s s i n g s e v e r i t y i n c r e a s e s . The e f f e c t of process temperature i n the 'hot-rod' r e a c t o r was studied using three c o a l s of v a r y i n g p r o p e r t i e s . These were Waterberg, Sigma and Landau. At 650°C the conversion y i e l d s of these c o a l s were 89, 90 and 88 per cent of the c o a l (dmmf) r e s p e c t i v e l y . Within experimental e r r o r the conversion y i e l d s had converged to the same v a l u e , whereas at 500°C the conversion y i e l d s were 85, 75 and 65 per cent respectively. 1

THE EFFECTS OF THE

INORGANIC CONSTITUENTS

The e f f e c t s of the i n o r g a n i c c o n s t i t u e n t s i n the c o a l were studied i n two ways. F i r s t l y , to o b t a i n samples with v a r y i n g mineral matter content, a c o a l was subjected to a f l o a t and s i n k s e p a r a t i o n . These f r a c t i o n s were subsequently hydrogenated. The analyses of the f l o a t and s i n k f r a c t i o n s are shown i n Table IV.


GRAY E T A L .

South African


100

Coals

C0NV = 0.88(R)*4.3^ r = 0.85 *

C0NV.= 0.29 (R)+59.0 r = 0.70 . 20

100

40 60 80 CONVERSION (DMMF) %

Fuel

Figure 9.

Percentage conversion against vitrinite + exinite (Φ) and total reactive macérais (X) (hot rod mode) (Π)

r=0.59 0' 0

Figure 10.

1

1

1

20

40 60 80 CONVERSION ( DMMF ) % 1

1

1

1

1

1

1

100

Percentage conversion against vitrinite + exinite (%) and total reactive macérais (X) (rotating autoclave mode)

American Chemical Society Library 16th St. H. W. In Coal Liquefaction Fundamentals; Whitehurst, D.; Washington, D. C. 20036 1155

ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

48

COAL

Table IV

FUNDAMENTALS

Pétrographie Analyses and Ash Y i e l d of Float/Sink Fractions

Relative Density

Vitrinite

Exinite

Inertinite

Volume


LIQUEFACTION

1.4 f l o a t 1.4 - 1.5 1.5 - 1.65 1.65 sink

80.6 78.3 65.6

7.5 8.3 9.1 66.6

Visible Minerals

%

Ash wt % a i r dried basis

5.4 4.3 9.7

6.5 9.1 15.9 33.4

6.7 7.0 16.0 45.3

I t has been demonstrated that c e r t a i n c o a l m i n e r a l s , p a r t i c u l a r l y i r o n compounds, c a t a l y z e the hydrogénation of c o a l derived solvents (15). Mukherjee et a l (16) hydrogenated f l o a t / sink f r a c t i o n s of an Indian c o a l and found that the conversion increased with the amount of mineral matter present i n the fraction. I t i s d i f f i c u l t , however, to assess p r e c i s e l y the e f f e c t that the mineral matter present i n a c o a l has on i t s l i q u e f a c t i o n behaviour. In f l o a t / s i n k f r a c t i o n s of the same c o a l , the pétrographie c o n s t i t u e n t s of the c o a l f r a c t i o n s u s u a l l y change s i g n i f i c a n t l y , with more i n e r t i n i t e being found i n the higher dens i t y f r a c t i o n s . A l s o the mineral matter composition and concent r a t i o n changes from f r a c t i o n to f r a c t i o n , and there may be cons i d e r a b l e v a r i a t i o n i n the mineral matter s u r f a c e areas a v a i l a b l e for possible catalysis. In a d d i t i o n , the combination of the e f f e c t s of increased m i n e r a l matter and decreased ' r e a c t i v e maceral content i n the higher d e n s i t y f r a c t i o n s reduces the agglomeration tendency of the c o a l . This allows more e f f e c t i v e d i f f u s i o n i n the system (4, 14). The r e s u l t s obtained from the f l o a t / s i n k f r a c t i o n s are shown i n F i g u r e 11. I t could be that the increase i n o i l y i e l d obtained with the higher mineral matter f r a c t i o n s i s due to the i n c r e a s e i n s u l f u r content that v a r i e s from 0.5 per cent i n the 1.4 f l o a t to 9 per cent i n the 1.65 s i n k f r a c t i o n . The s i g n i f i c a n c e of these r e s u l t s , at l e a s t as f a r as South A f r i c a n c o a l s are concerned, i s that a h i g h mineral matter content does not n e c e s s a r i l y mean poor performance d u r i n g c o a l l i q u e f a c t i o n . Indeed, t h i s evidence suggests that the mineral matter can be b e n e f i c i a l i n i n c r e a s i n g both the conversion and l i q u i d product y i e l d s . From a p r o c e s s i n g viewpoint, h i g h mineral matter can c r e a t e other problems, and a trade o f f between p o s s i b l e c a t a l y t i c b e n e f i t s and engineering process d i f f i c u l t i e s i s necessary. The second procedure s t u d i e d the e f f e c t s of the s u l f u r content of the c o a l s during hydrogénation. A s u i t e of unwashed 1


2.

GRAY E T A L .

South African

49

Coals

coals was s e l e c t e d so that the only parameter to show s i g n i f i c a n t v a r i a t i o n was the t o t a l s u l f u r content. Of t h i s t o t a l s u l f u r , approximately 1 per cent was o r g a n i c , and the r e s t was i n o r g a n i c s u l f i d e . The maceral content and t o t a l mineral matter content of a l l these samples were very s i m i l a r . Relevant analyses of t h i s s u i t e of c o a l s i s shown i n Table V.


Table V

Analyses of Unwashed Coals Used to Determine the E f f e c t of P y r i t e s

Coal

V+E

A Β C D Ε F G V+E

%

T o t a l Ash %

Moisture %

24 22 26 22 22 24 22

2.4 3.0 2.3 2.8 2.7 2.5 2.4

83.0 83.8 83.7 82.0 82.0 83.2 80.0

6.5 5.7 5.0 4.1 2.2 1.9 1.3 VM

= V i t r i n i t e + Exinite

Sulfur %

VM

%

31.9 29.1 32.2 32.5 32.1 30.2 32.5

= V o l a t i l e Matter

F i g u r e 12 c l e a r l y shows the e f f e c t of i r o n s u l f i d e content of the c o a l on t o t a l conversion and l i q u i d product y i e l d d u r i n g hydrogénation. The conversion increased from about 52 per cent to 70 per cent u s i n g the 'hot-rod r e a c t o r w i t h no added c a t a l y s t . The y i e l d of toluene s o l u b l e product ( o i l p l u s asphaltene) increased from about 30 to 44 per cent with t o t a l s u l f u r i n c r e a s e from 1 to 6.5 per cent. Thus i t would appear that i r o n s u l f i d e can act c a t a l y t i c a l l y i n the 'dry' hydrogénation r e a c t i o n as w e l l as i n s l u r r i e d r e a c t i o n s (15). The i r o n sulphide i n South A f r i c a n c o a l s i s a mixture of p y r i t e and marcasite (18). Although marcasite i s known to t r a n s form i n t o p y r i t e at elevated temperatures, separate s p i k i n g experiments were performed to see i f p y r i t e or marcasite would show a p r e f e r e n t i a l c a t a l y t i c e f f e c t . The a d d i t i o n of p y r i t e and marcasite minerals (-200 mesh), to the c o a l showed e q u i v a l e n t t o t a l conversions, and y i e l d s of o i l and asphaltene. 1

CONCLUSIONS For the South A f r i c a n bituminous f o l l o w i n g conclusions can be made: (i)

c o a l s s t u d i e d here the

Conversion y i e l d s obtained from c o a l l i q u e f a c t i o n under 'dry hydrogénation c o n d i t i o n s and i n the presence of anthracene o i l both show good c o r r e l a t i o n s w i t h H/C atomic r a t i o , the v o l a t i l e matter y i e l d and the ' r e a c t i v e maceral content of the coals. 1

1



50

COAL LIQUEFACTION F U N D A M E N T A L S

PERCENTAGE Figure 11.

ASH

Product distribution vs. ash content of coal (hot rod mode): catalyst = 1 % Sn; Ρ = 25 MPa; Τ = 500°C>

Figure 12. Effect of sulfur content on liquid yields and overall conversion (hot rod reactor): sandxoal = 2:1; Τ = 450°C;V = 25 MPa.



2.

GRAY E T A L .

South African

Coals

51

1

(ii)

'Reactive macérais cannot be defined as the sum of v i t r i n i t e + e x i n i t e f o r these South A f r i c a n c o a l s , but s u b s t a n t i a l portions of the s e m i - f u s i n i t e must be added to obtain t o t a l ' r e a c t i v e s ' .

(iii)

For 'dry' hydrogénation, good c o r r e l a t i o n s are obtained between toluene s o l u b l e y i e l d s and the H/C atomic r a t i o and the v o l a t i l e matter y i e l d of the c o a l s .

(iv)

The i r o n s u l f i d e i n the c o a l appears to a c t benef i c i a l l y i n the 'dry' hydrogénation r e a c t i o n and enhances the o v e r a l l l i q u i d y i e l d . No d i f f e r e n c e was detected i n the r e a c t i v i t y of p y r i t e and marcasite during 'dry' hydrogénation.

LITERATURE CITED 1. Mackowsky, M-Th. "Coal and Coal Bearing Strata". Eds. Murchison, D.G. and Westroll, T.S., Olivier and Boyd, London, 1968. 2. Report of the Commission of Inquiry into the Coal Resources of South Africa. Department of Mines, Pretoria, South Africa, 1975. 3. Hiteshue, R.W., Friedman, S., Madden, R. United States Bureau of Mines, Report of Investigations, 6125, 1962. 4. Gray, D. Fuel, 1978, 57, 213. 5. Given, P.H., Cronauer, D.C., Spackman, W., Lovell, H . L . , Davis, Α., Biswas, B. Fuel, 1975, 54, 40. 6. Smith, W.H. ISCOR, Personal Communication. 7. Steffgen, F.W., Schroeder, K.T., Bockrath, B.C. Anal. Chem., 1979, 51, 1164. 8. Cudmore, J.F. Coal Borehole Evaluation Symposium, Australian Institute of Mining and Metallurgy, 1977, Oct., 146. 9. Ammosov, I . L . , Erexmin, I.V., Sukhenko, S.E., Oshurkova, L.S. Koks i Khimiya, 1957, 12, 9. 10. Taylor, G.H. Fuel, 1957, 36, 221. 11. Taylor, G.H., Mackowsky, M-Th., Alpern, B. Fuel, 1967, 46, 431. 12. Steyn, J.G.D., Smith, W.H. Coal, Gold and Base Minerals (South Africa), 1977, Sept., 107. 13. Guyot, R . E . , Diessel, C.F.K. Australian Coal Industry Research Laboratories, Published Report 79-3, 1978, Dec. 14. Shibaoka, M., Ueda, S. Fuel, 1978, 57, 667. 15. Guin, J . Α . , Tarrer, A.R., Prather, J.W., Johnson, D.R., Lee, J.M. Ind. Eng. Chem. Process Des. Dev., 1978, 17, (2), 118. 16. Mukherjee, D.K., Chowdhury, P.B. Fuel, 1976, 55, 4. 17. Gray, D., Barrass, G., Jezko, J., Kershaw, J.R. Fuel, 1980, 59, 146. 18. Gaigher, J . L . Fuel Research Institute of South Africa, Personal Communication. RECEIVED March 28,

1980.


South African Coals and Their Behavior During Liquefaction - ACS

Recommend Documents