10% carbon monoxide mixture using CoMo and CoW catalysts

Hydrocracking of Point of Ayr coal liquid with hydrogen and 90% hydrogen/IO% carbon monoxide mixture using CoMo and COW catalysts Paul W. Doughty,

Graham

Harrison

and Gregory

J. Lawson*

Department of Chemistry and Biology, Staffordshire Polytechnic, College Road, Stoke-on- Trent, Staffordshire, ST4 2DE. UK *Department of Chemical Engineering, University of Birmingham, Birmingham B 152TT. (Received 2 1 November 1988; revised 7 Nfarch 1989)

UK

Catalytic hydroliquefaction experiments on a Point of Ayr coal liquid were performed in autoclaves fitted with a falling/spinning basket. The bimetallic catalysts CoMo and COW on an acidic alumina support were used at different contents of MO and W in oxide and presulphided forms. Some experiments used H, alone and some used 90vol%H,/10vol%CO. The hydroliquefied products were characterized by vacuum distillation and g.1.c. into 13 product groups. The carbon, hydrogen and sulphur contents of the washed catalysts were determined. Generally, conversions to material boiling below 475°C were <80%, and conversions to lower boiling point material were influenced by the presence of CO, the composition of the catalyst, the run time and by presulphidation. On many occasions, increased conversion to low boiling point material resulted only from breakdown of the recycle solvent fractions, and not from increased conversion to material boiling below 475°C. It was apparent that on altering the metal content of catalysts or after presulphiding, the catalysts CoMo behaved differently from COW. (Keywords:

hydroliquefaction;

catalyst;

carbon

monoxide)

Hydroliquefaction processes need to induce good conversions of coal to lower molecular weight material while maintaining a consistent quality of recycle solvent. The processes are usually designed to operate with pure hydrogen and multifunctional catalysts. The hydrogen would be produced by gasification followed by the shift reaction and chemical clean-up operations to remove CO. By using the gas mixture after the shift reaction, the clean-up operation could be omitted allowing savings to be made on hydrogen production costs. However, the presence of small amounts of CO (e.g. 10~01%) may reduce conversions and negate the savings made in hydrogen production. A recent paper’ has shown that 90 ~01% Hz/10 vol%CO with a CoMo catalyst can be used for the hydroliquefaction of Point of Ayr coal liquid at conversions around 50-60wt% of the daf coal feed. However, it appeared that little hydrogenation was occurring over the 2 h and that cracking reactions were period studied, predominant. Since cracking reactions will depend principally on the acidity of the alumina support, which was not altered, the potential of the metals on the support for hydrogenation and the effect of possible preferential adsorption of CO at the metal sites were hardly tested. Consequently, there was a need to extend the study to cover conditions where hydrogenation should occur to a greater extent. Under such conditions, the type and concentration of the metal in the catalyst should influence conversions and recycle solvent compositions, and the presence of CO could become more important. It has been shown that catalysts other than CoMo can be effective in the presence of CO for hydroliquefaction

001~2361/89/101257-07$3.00 0 1989 Butterworth & Co. (Publishers)

Ltd.

of a coal liquid produced by dissolving coal in hydrogenated anthracene oil (HAO)‘,‘. In particular, bimetallic tungsten catalysts have shown potential. However, the content of hydroaromatic compounds in the HA0 after dissolution of coal remained high, and cracking of these compounds could progress without the need for prior hydrogenation. Hence, again the hydrogenation capacity of the catalyst may not have been properly tested, the catalyst performances being dictated by the alumina support. This paper reports results from a study devised to examine the effectiveness of CoMo and COW for the hydroliquefaction of a coal liquid with either pure H, or 90 vol%H,/10vol%CO under various reaction conditions. The composition of the gas mixture was selected to represent the probable maximum level of CO in an ‘impure’ hydrogen feed, and the experimental programme was confined to using a coal liquid so that the possible influence of CO on the yields and compositions of particular boiling point ranges could be established. EXPERIMENTAL Materials

The sample of coal liquid was supplied by British Coal Research Establishment (CRE) and was produced by dissolving a Point of Ayr coal in a recycle solvent. Details of the coal and the coal liquid are shown in Table 1. The specifications of the alumina support for the catalysts have been reported previously’. All chemicals were of Analar grade.

FUEL, 1989, Vol 68, October

1257

Hydrocracking

of Point of Ayr coal liquid: P. W. Doughty

Table 1 Analyses

of Point

Proximate analysis Moisture Ash Volatile matter

(wt% ad)

Ultimate C H 0 N s

analysis

of Ayr coal (drum

7/84) and coal liquid

3.8 14.6 30.9 (wt% db) 68.4 4.1 8.4 1.34 2.59

Point of Ayr Coal liquid B.p. fraction “C

Wt%

<260 <275 215475 >475

2.7 5.6 65.1 29.3

“Values

supplied

by CRE

Equipment All hydrocracking experiments were performed in one of two 500 ml capacity stainless steel autoclaves, of similar design. Each autoclave was fitted with a special mesh basket that retained the catalyst above the coal liquids until the reaction temperature was achieved. The stirrer was driven magnetically, and heating was provided by a quick release electrical unit. Full design details of the autoclaves are presented elsewhere3. Carbon, hydrogen, nitrogen and sulphur analyses were made using elemental analysers. Procedure Each hydrocracking experiment used approximately 100 g of coal liquid and 4 g of catalyst, and was conducted at a gas pressure of 19-20 MPa and a reaction temperature of 400°C. For catalyst preparation, the technique of incipient wetness was used following the procedure described previously2. Presulphiding of the catalysts was carried out by adding 5 ml of CS, to 20 g of the dried oxide catalyst (which was retained in the specifically designed basket), and reacting in the autoclave at 300°C and 18 MPa for 24 h. After venting the gas from the autoclave, the catalyst was removed and stored without further treatment under nitrogen until required. The hydrocracked products were separated by vacuum distillation in a glass apparatus, into fractions of equivalent boiling point at atmospheric pressure of < 275,275-300 and 300-475”C. A cold trap fraction was collected using an acetone-dry ice cold mixture. The fractions were separated by gas chromatography (following the procedure reported previously’) and 13 product groups defined from g.1.c. analysis on appropriate marker compounds. Briefly the groups were: 1, single ring compounds; 2, hydronaphthalenes; 3, naphthalene; 4, methylhydronaphthalenes and methylnaphthalenes; 5, dimethylnaphthalenes and dimethylhydronaphthalenes; 6, acenaphthene and fluorene; 7, perhydrophenanthrenes; 8, hydrophenanthrenes; 9, phenanthrene; 10, anthracene; 11, hydropyrenes; 12, pyrene; and 13, b.p. >pyrene. The amounts in each of the product groups were calculated from the masses of the distillation fractions and the integrated areas of the g.1.c. peaks. Full details of the definition of the 13 product groups and the procedure

1258

FUEL, 1989, Vol 68, October

et al. for calculating their amounts are presented elsewhere’. Product groups l-4 represent materials of b.p. < 26OOC; groups l-5, material b.p. < 275°C; groups 6-l 3, material b.p.275 to 475”C, constituted the recycle solvent fraction.

RESULTS I%eldsfrom vacuum distillation and g.1.c. The yields of the 13 product groups and the amounts of material of b.p. ~260, < 275, ~475 and 275475”C, for the various hydrocracking experiments at 4OO”C, are shown in Table 2 as wt% of the hydrocracked coal liquid. Within the table, results are presented for experiments with H, alone and with 90vol%H2/10vol%C0 for oxide and presulphided CoMo or COW catalysts and for run times of 2, 6 and 24 h; all values are averages from duplicate experiments and a coding system for each column identifies the operating parameters. Generally, agreements between duplicate experiments were: for conversions to material boiling ~475 and 275-475”C, f2%; for conversions to material boiling ~260 and <275”C, i4%; and for individual groups, f 10%. The catalyst compositions in Table 2 relate to the mass of the metal oxide as a percentage of the mass of support. For example, 15%M0/3%C0 would contain 15 g of MOO, and 3 g of Co0 on 1OOg of alumina support. The yields in Table2 are based on the mass of the recovered material, and do not include the gas produced from hydrocracking. (No coking was observed in any of the reactions, and gas production was estimated to be small so the yields relative to the coal feed would be similar to those stated in Table2). It can be seen that overall conversion to material boiling ~475°C was always greater than 70% and for 24 h experiments with CoMo (column 4) conversion was above 80%. Overall conversion was not significantly affected by alterations in reaction conditions, unlike conversions to material boiling < 260°C and ~275°C. The two main product ranges lay in groups 8 and 11. Since group 8 contained about 80 wt% of the di-, tetra- and octa-hydroderivatives of phenanthrene and group 11 contained a significant proportion of hydropyrenes, the recycle solvent fraction (b.p. 275 to 475°C) will contain a large proportion of three- and four-ring hydrogen donors. Effect of gas mixture and of presulphiding To assess the influence of the presence of CO and the effect of sulphiding the catalysts, the ratios of yields with 90vol%H2/10vol%C0 to those with H, alone and of yields with sulphided catalysts to those with oxide catalysts, were calculated, as shown in Table 3. According to the experimental errors stated earlier, a change of 0.1 in the values of these ratios should be significant. It can be seen that in only one case was the ratio for total conversion to material boiling <475”C different from 1.0, and consequently it can be assumed that total conversion was not dependent upon the presence of CO or on sulphiding of the catalyst. For the yields of the other fractions, more changes in the ratios were apparent, the changes being greater for sulphiding of the catalysts than for the presence of CO. For the 90%H,/lO%CO: H, ratios it can be seen that significant differences were formed for ~260 and < 275°C material; for CoMo catalysed reactions, only experiments over 6 h with the

2 ads

4.2

2.3

0.7

5.3

8.4

3.9

4.2

15.1

8.8

0.9

14.5

4.0

4.3

76.6

12.5

20.9

55.7

1 ado

3.0

1.6

1.0

3.9

4.2

3.8

5.8

17.8

12.0

1.1

18.5

2.7

3.1

78.5

9.5

13.7

64.8

or W/3%Co;

Group no.

I

2

3

4

5

6

7

8

9

10

11

12

13

<415”C

< 260°C

<275”C

275-475”C

a, 15%Mo

l-13,

b, lO%Mo

3.7 4.2 15.1 8.4

4.7 13.0 8.8

17.2

10.8

15.4 3.9 7.2

14.1 4.0 5.3

19.6

c, 5%Mo

63.7

59.6

16.3

8.4

15.9

6.3

4.1

14.5

1.7

8.8

17.4

3.5

3.3

59.4

17.3

9.7

76.7

10.0

3.2

16.5

1.9

4.6

15.3

4.9

3.0

7.6

4.4

4.2 7.9

0.6

1.8

2.9

9 aeo

0.7

1.6

1.9

8 cds

59.2

16.0

8.9

75.2

10.4

3.7

15.1

1.4

7.5

14.0

3.6

3.5

7.1

4.1

0.8

1.6

2.4

10 ado

~_._~.

58.8

14.4

6.8

73.2

7.4

3.8

14.7

0.7

8.9

15.7

4.4

3.2

7.6

3.5

0.5

1.1

1.7

11 ads

57.5

-

18.1

10.4

75.6

58.0

16.6

8.7

74.6

3.4 16.0 9.9 0.5 13.4 4.2 9.0 75.4 8.5 16.5 58.9

3.6 14.0 6.9 1.0 16.2 3.7 11.2 72.5 6.1 13.0 59.5

catalysts

2.5

4.3

3.4

8.0

0.8

0.5

6.9

1.4

2.9

2.0

1.0

16 aeo

0.7 3.6 6.9

0.8 4.0 8.3 3.6

4.2 8.8

16.0 9.2 0.6 14.8 4.1 5.7

15.1 9.2 0.6 13.9 4.1 6.9

20.3 10.7

58.8

16.3

7.5

75.1

2.4

4.6

9.6

1.1

71.9 7.1 14.0 57.9

73.0 7.9 16.2 56.8

-.

4.1

4.0 3.4 4.1

54.7 _-

19.1

10.6

-7 73.8

2.9

P

2

!!$

2

b

$

2 3.7

2 10.4

0,

s

0.9

10.4

18.0

3

8.5 4.3 3.5 6.2

s

z z z 0

0.6

4.9

1.5

3.3

20 ces

0.9

1.2

1.5

1.7

19 ceo

1.1

18 beo

1.2

-

1.9

17 aes

90%H,/lO%CO

1.2

15 ads

COW catalysts

s, sulphide

57.6

16.5

9.2

74.1

11.0

11.9 9.0

4.3 3.5

4.2

14.8

0.8

7.5

13.6

2.5

3.1

7.3

4.6

0.9

1.6

2.1

14.2

1 .o

6.0

13.9

4.7

2.8

1.9

4.6

0.7

1.8

1.6

14 ado

at 400°C

15.1

0.9

7.5

14.6

3.7

2.5

7.7

4.7

0.9

2.0

2.8

12 aeo

H, alone 13 aes

experiments

d, 2 h run time; e, 6 h run time; f, 24h run time; o, oxide catalysts;

59.0

53.9

49.8 or W/3%Co;

16.2

20.6

14.6

9.2

12.9

10.2

33.6

75.2

74.5

78.3

26.6

2.9

2.5

1.1

0.8

0.9

7.0

83.4

6.9

3.7

13.8

3.7

13.4

7.0

3.2

2.8

4.4

1.7

0.7

1.0 4.3

2.2

2.0

4.7 2.1

7 bds

6 ads

90%H,/lO%CO

for hydrocracking _~__

Yields (wt% of coal liquid after hydrocracking)

< 26O”C, < 275°C and 275475°C .~

5.1

4.3

1.2

1.5

3.2

ado _.

5

<475”C,

catalysts

boiling

CoMo

5.3

3.0

7.0

9.7

0.8

6.2

9.9

4 afo

material

or W/3%Co;

58.8

18.3

13.1

77.1

7.2

4.0

15.4

1.5

6.4

15.0

6.0

3.3

5.2

5.4

0.9

2.1

4.7

3 aeo

H, alone

groups

Yields of product

Table 2

Hydrocracking

of Point

of Ayr coal liquid:

et al.

P. W. Doughty

oxide catalyst produced significant differences, while COW catalysed experiments changes were apparent in all cases apart from 2 h experiments with oxide catalysts. For the sulphided: oxide ratios, the more significant differences arose in the yields of < 260 and ~275°C material but, particularly for CoMo-catalysed experiments, the amount of material in the recycle solvent fraction was less with sulphided catalysts. For 15 wt%Mo/ 3 wt%Co catalysts, presulphiding improved conversion to material boiling ~275°C by 40-50%, but for similar W-containing catalysts, yields were only 70-90% of those with oxide catalysts. For the 5 wt%W/3 wt%Co catalysts, presulphiding increased the yield of material boiling ~275°C by 40% and material boiling < 260°C by 50%. Effect of reuction

catalysts with the gas mixture. Generally increases were greater for experiments with H, alone, and increases in conversion to material boiling < 260°C were greater than those for conversion to material boiling ~275°C. apart from the two cases in which no increase in material boiling ~260°C was observed. For COW catalysts, there was no significant change with time either in the composition of the low boiling point material (< 260 or < 275°C) or in the composition of the recycle solvent fraction. For CoMo catalysts, the amount of group 1 material (b.p. < decalin) increased by 60 wt% when the reaction time was increased from 2 to 6 h (columns 1 and 3 respectively in Table 2), and by over 300 wt% on increasing to 24 h (column 4 in Table 2). The amounts of material in group 2 (boiling above decalin but below naphthalene), group 4 (mainly methylsubstituted naphthalenes and hydronaphthalenes) and group 5 (mainly dimethylhydronaphthalenes and dimethylnaphthalenes) also increased as the reaction time was lengthened, but the amount of naphthalene (group 3) remained relatively constant. For the recycle solvent, the contents of phenanthrene (group 9) and hydrophenanthrenes (group 8) after 2 h contacts were similar to those in the coal liquid feed. After 6 h, the hydrophenanthrene content still remained about the same but the phenthrene content was less, reflecting the progress of hydrogenation of phenanthrene. After 24 h, both the hydrophenanthrene and phenanthrene contents were reduced, the hydrophenanthrene content being about 65% of that after 2 h contacts. The content of perhydrophenanthrene remained roughly constant throughout, probably reflecting an equilibrium concentration.

time

Changes with time in the yields of materials boiling ~260 and ~275°C are summarized in Table4 as percentage increases compared with corresponding 2h experiments. In two cases no increase in yield of material boiling < 260°C was observed, both of these using oxide Table 3 Yield ratios; 90vol%H,/10vol%CO: oxide catalysts Ratio-yield

CoMo

H, alone and sulphide:

with 90vol%H,/lOvol%CO: yield with H, alone

catalysts

COW catalysts

Fraction b.p.“C

2h

2h

6h

2h

2h

6h

6h

0

s

0

0

S

0

S

<260 <275 275415 <475

1.1 1.1 1.0 1.0

1.0 1.0 1.0 0.9

0.7 0.9 1.0 1.0

1.o 1.0 1.0 1.0

1.0 0.9 0.9 1.0

0.8 0.9 1.0 1.0

0.9 1.0 1.0 1.0

Efect of changes in MO and Wcontent of the catalysts Figure 1 shows how the amounts of the various boiling point fractions changed with the MO or W contents of the catalysts. The experimental conditions were 2 h with sulphided catalysts for CoMo and 6 h with oxide catalysts for COW. It is apparent that changes in the content of MO produced different results from changes in the content of W. Increasing the W content of the catalysts increased the amount of material boiling <475”C, whereas increasing the MO content reduced such material; however for MO, the changes in conversion were small and were not much greater than the spread between duplicate experiments. The amounts of low boiling materials, both ~260 and <275”C, increased with

Ratio-yield with sulphided catalysts: yield with oxide catalysts _. COW catalysts

CoMo catalysts

~---

Fraction b.p.“C

2h H,

2h Hz/CO

2h H,

2h HJCO

6h H,

6h HJCO

6h

< 260 <275 275475 <475

1.3 1.5 0.9 1.0

1.3 1.4 0.8 1.0

0.8 0.9 1.0 I.0

0.7 0.8 1.0 1.0

0.8 0.9 1.0 1.0

0.9 1.0 1.0 1.0

1.5 1.4 0.9 1.0

“5 wt%W/3 wt%Co (remainder are 15 wt%W o, oxide catalysts; s, sulphide catalysts

Table 4

Changes

in conversion

H&O

or MO/~ wt%Co)

to low boiling

point material

with respect

to 2 h experiments

Run time

Increase b.p. < 260°C

in material

(wt%) b.p. ~275

Form +/composition’ of catalyst

Gas compositiot?

15 wt%Mo(o)

HZ

6

15 wt%Mo(o)

Hz/CO

6

-ve

15 wt%Mo(o)

HZ

24

180

145

15 wt%W(o)

H*

6

17

13

15 wtW(0)

Hz/CO

6

-ve

0

15 wt%W(s)

HZ

6

28

15

15 wt%W(s)

Hz/CO

6

23

25 ~_

“All catalysts contained 3 vol%Co bGas mixturee9Ovol% H,/lOvol%CO o, oxide catalysts; s, suphide catalysts

1260

FUEL,

1989,

Vol 68, October

(h)

38

34 18

C

Hydrocracking

MO or W content Figure 1

Table 5

Variation

Analysis

of yields of boiling

point fractions

CoMo

cow

of catalysts

(wt%)

C

H

S

N

ado ado ads ads(co) bds(co) cds(co)

19.2 20.2 19.0

2.0 2.0 2.1

2.0 1.8 5.1

1.3 1.3 _

19.0 18.7

2.0 2.1

4.7 2.9

_

21.2

2.5

2.0

ado ado ads ads(co) aeo aeo(c0) aes aes(c0) beo(co) ceo(c0) ces(c0)

19.6 19.2 16.5

2.1 2.0 1.9

0.9 0.8 3.1

_ _ _

16.1 18.5 19.0 15.3 16.0 17.1 17.6 16.1

1.7 2.3 2.1 1.7 1.8 1.8 1.9 1.7

3.1 1.1 0.8 3.0 2.9 0.7 0.7 1.7

_ _ _ _ _ _

a, lSwt%Mo or W/3 wt%Co; b, lOwt%Mo or W/3wt%Co; c, 5 wt%Mo or W/3 wt%Co; d, 2 h experiments; e, 6 experiments; o, oxide catalysts; s, sulphide catalysts; co, experiments using 90vol%H,/10vol%CO

increasing MO or W content, but the increase was much larger for MO-containing catalysts. The amount of recycle solvent decreased with increasing MO content but remained relatively unchanged for W-containing catalysts, the spread in results probably reflecting experimental error. Therefore it would appear that increased conversion to low boiling point material resulted from breakdown of the recycle solvent for MO-containing catalysts, but from increased conversion to material boiling ~475°C for W-containing catalysts.

of Ayr coal liquid:

P. W. Doughty

I

I

I

5

IO

15

et al.

(wt%)

liquid) with metal content

Analysis Analysis

Catalyst

of catalysts

(wt% of hydrocracked

of catalysts

Operating conditions

of Point

of catalysts

of catalysts

The results of CHNS analysis of the washed catalysts for some of the experiments are shown in Table5. It is apparent that considerable deposition had occurred, indicating some catalyst deactivation. However, it has been found that if the used catalyst is recontacted with more coal liquid under similar experimental conditions, the conversions, the distribution of material among the products, and the specific surface area of the catalysts, are not significantly affected, and the amount of carbon deposited does not increase3. Therefore, it would appear that in the type of autoclave reactor employed, the catalyst was rapidly deactivated and thereafter the amount of deposition remained constant. Although presuphided COW catalysts tended to have a lower level of deposition, generally the extent of deposition was independent of the composition of the gas and of the type and amounts of the metals in the catalyst. DISCUSSION Proton and 13C n.m.r. analysis of asphaltene fractions of extracts produced by dissolution of coal in hydrogenated anthracene oil at 400°C have indicated average molecular structures containing small aromatic clusters linked by ether, methylene or phenyl-phenyl bridges4. A test involving the reaction of diphenyl ether with 9,10-dihydrophenanthrene at 400°C showed that, in the presence of either H, alone or 90 vol%H,/lO vol%CO, the addition of a CoMo catalyst to the charge increased the rate of cleavage of the ether bridge by a factor of about fifty’. Since this type of bond cleavage will not require prior hydrogenation of aromatic rings, it will depend less on the adsorption of hydrogen at metal sites on the catalyst surface. In the early stages of catalytic hydroliquefaction, the concentration of these bridged aromatic compounds will

FUEL, 1989, Vol 68, October

1261

Hydrocracking

of Point

of Ayr coal liquid:

P. W. Doughty

be relatively high, and much of the lower molecular weight material in the products could be derived by rupture of the bridges. Evidence for the extent of hydrogenation can be assessed from the effect of variable time experiments in which the phenanthrene content of the hydrocracked product was similar to that of the coal liquid after 2 h but became less after 6 h. In experiments on the hydrogenation of phenanthrene, it was found6 that under similar conditions, 80 wt% of the phenanthrene was converted (mainly to its hydroaromatic derivatives) after 2 h. Therefore, it would appear that the early stages in the hydroliquefaction of the coal liquid are dominated by bridge cleavage and are not significantly dependent upon hydrogen adsorption, i.e. they will not be significantly affected by adsorption of CO at hydrogenation sites. As the reactions progress, more of the lower molecular weight material will arise from hydrocracking of aromatic ring clusters, and hence the rates of reaction will become more dependent on the ability of the catalyst to adsorb hydrogen, which will be influenced by the types and concentrations of the metals in the catalyst and the adsorption of CO at hydrogenation sites. Although the partial pressure of H, would be lower for experiments with the gas mixture, the difference would be small in relation to the total hydrogen pressure, and it has been found that the rates of hydrogenation of various polycyclic aromatics (phenanthrene, pyrene, fluorene) are not significantly affected by the partial pressure of hydrogen over the range of difference in this study, i.e. pseudo first order reaction kinetics can be assumed6. Consequently, adsorption of CO at hydrogenation sites seemed to be responsible for the lower conversions to material boiling < 260 and < 275°C when the reaction rates become dependent upon the rate of hydrogenation of polycyclic aromatic compounds. It is well known that presulphiding of MO- and W-containing catalysts can enhance their catalytic ability provided that the sulphiding is controlled7. The present results showed that presulphiding of CoMo catalysts enhanced conversions to low boiling point material but for W-containing catalysts only 5 wt%W/3 wt%Co enhanced conversion. The initial sulphur levels of the catalysts e.g. 6.4wt% for 15 wt%Mo/3 wt%Co and 3.6 wt% for 15 wt%W/3 wt%Co corresponded to the stoichiometric formation of CoS with MO& and WS, respectively, and the sulphur contents of the used catalysts, after correction for deposited material, would indicate no decomposition of the sulphides. Therefore, it would seem that for the hydrocracking of coal liquids, presulphiding W-containing catalysts will not necessarily enhance catalyst activity. For both CoMo and COW catalysts, increasing the metal concentration resulted in increased conversion to low b.p. material; for COW catalysts the increases came about from improved overall conversion to material boiling ~475°C whereas for CoMo catalysts the increases were caused by breakdown of the recycle solvent. The increases might have resulted from the higher metal content creating more hydrogenation sites, or from a synergistic effect, or from a combination of both these effects. In the case of CoMo catalysts, conversion increased markedly as the MO content was changed from 10 to 15 wt %, and it is likely that synergism develops over this range. Some evidence for synergism

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FUEL, 1989, Vol 68, October

et al. with COW catalysts over the 10 to 15 wt% W range could be found in the greater increase in conversion to material of b.p. <475”C. Some recent papers ’ ~ i2 have reported promotion of the activities of CoMo, NiMo and NiW catalysts for hydrogenation and desulphurisation over a certain range of promoter metal (Co or Ni) to main metal (MO or W) atomic ratios. The Co:Mo atomic ratio for the CoMo catalysts denoted 15, 10 and 5 wt% MO and 3 wt% Co are 0.38, 0.58 and 1.15, respectively, so that synergism appears to develop at an atomic Co:Mo ratio of between 0.38 and 0.58. These values are consistent with those reported for the desulphurisation of thiophene with CoMo catalysts’ and for the hydrogenation of cyclohexene by the similar catalyst NiMo”. Only when the reaction time for the CoMo catalyst was extended to 24 h was overall conversion to material boiling ~475°C significantly increased. (For the COW catalysts, overall conversion was influenced by the W content but only reached that produced by CoMo catalysts at 15 wt% W). Improvements in conversions to low boiling point material for CoMo catalysts mainly resulted from breakdown of the recycle solvent fraction whose mass and composition need to be relatively constant. The proportion of the recycle solvent is the controlling factor for a materials balance in a continuous process. Only for 2 h runs with oxide catalysts was the proportion of the recycle solvent fraction similar to that in the coal liquid feed. For longer reaction times and sulphided catalysts, a lower boiling point cut at about 260°C would have to be taken to maintain the mass balance, producing a recycle solvent with a higher content of hydroaromatics based on naphthalene and a lower content of hydrophenanthrenes and hydropyrenes. It has been shown that 3- and 4-ring hydroaromatics are better hydrogen donors than 2-ring hydroaromaticsi3-’ 5. For instance, McMillen et ~1.” found that dihydrophenanthrene donated hydrogen at an order of magnitude faster than tetralin. Consequently, although sulphiding the catalysts or extending the run time improved conversion to material boiling ~260°C the recycle solvent fraction produced might be less effective at dissolving coal, resulting in reduced overall liquefaction. CONCLUSIONS The results have shown that 90 vol%H,/lO vol%CO can be used for the hydrocracking of a Point of Ayr coal extract without detriment to the catalyst compared with H, alone. Over 2 h contacts with CoMo or COW catalysts the presence of CO tends to promote conversion to low boiling point material (b.p. ~260 and < 275°C). However, this promotion is lost with sulphided catalysts and for 6 h contacts with oxide catalysts, and conversions, particularly to material boiling < 260°C can be less when the gas mixture is used, probably because CO molecules occupy H, sites at the catalyst surface. Changing the MO or W content of the catalysts does affect conversions but to different extents. Increasing the MO content increases the amount of low boiling point material as a result of breakdown of the recycle solvent, whereas increasing the W content increases the amount of low boiling point material because of improved breakdown of material boiling >475”C. For sulphided CoMo catalysts there is

Hydrocracking

evidence of synergism developing between atomic Co :Mo ratios of 0.38 and 0.58. Conversion to material boiling <475”C of > 80% could only be achieved by using a contact time of 24 h with 15 wt%Mo/3 wt%Co in its oxide form. However, the content of the recycle solvent fraction in the product was greatly reduced, and only with 2 h contacts with oxide catalysts was the amount of material in the 275475°C range similar to that in the coal liquid feed.

I 2 3 4 5

I 8

The authors express their gratitude to SERC for providing financial support (grant reference number GR/D 06827), to British Coal, Coal Research Establishment for supply of the Point of Ayr coal liquid and to Akzo Chemie, Netherlands, for providing the alumina support for the catalysts.

of Ayr coal liquid: P. W. Doughty

et al.

REFERENCES

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ACKNOWLEDGEMENTS

of Point

9 10 11 12 13 14 15

Doughty, P. W., Harrison, G. and Lawson, G. J. Fuel 1989, 68, 298 Doughty, P. W., Harrison, G. and Lawson, G. J. Fuel 1986, 65, 931 Doughty, P. W., PhD 7hesis, Staffordshire Polytechnic, 1988 Cahill, P. and Harrison, G. Second International Rolduc Symposium on Coal Science 21-25 May, 1989, paper 39 Harrison, G. and Bate, K. to be presented at International Conference on Coal Science, Tokyo, Japan 23-27 Ott, 1989 Bate, K. and Harrison, G. to be presented at International Conference on Coal Science, Tokyo, Japan 23-27 Ott, 1989 Weisser, 0. and Landa, S. in ‘Sulphide Catalysts. Their Properties and Applications’, Pergamon Press, London, 1973 Ledoux, M. J., Michaux, O., Agostinin, G. and Panissad, P. J. Catal. 1985, 96, 189 Bachelier, J., Duchet, J. and Cornet, D. J. Catal. 1984,87,283 Thakur, D. S., Grange, P. and Delman, B. J. Catal. 1985,91,3 18 Bachelier, J., Tilliette, M. J., Duchet, J. C. and Cornet, D. J. Catal. 1984, 87, 292 Topsoe, H., Candra, R., Topsoe, N. Y. and Clausen, B. S. Bull. Sot. Chim. Bely. 1984, 93, 783 Kamiya, Y. and Nagae, S. Fuel 1985,64, 1242 Kamiya, Y., Ohta, H., Fukushima, A., Aizawa, M. and Mizuki, T. ‘Proc. Int. Conf. Coal Sci.‘, Pittsburgh 1983, p. 195 McMillen, D. F., Malhortra, R., Chang, S., Ogier, W. C., Nigenda, S. E. and Fleming, R. H. Fuel 1987, 66, 1611

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