Effect of blending on liquefaction of coals

Effect of blending Koji Ouchi, Shoichi Masataka Makabe, Takekawat

Ibaragi, Hironori

on liquefaction

of coals*

Ataru Kobayashi, Kazuyuki Tanimoto, Itoh, Kenji Matsubarat and Tomei

Faculty of Engineering, Hokkaido University, Sapporo, 060, Japan t Technical Research Center, Nippon Kokan K.K., Kawasaki, 2 10, Japan (Received 16 May 1983; revised 13 June 1983)

Aftersolvent extraction of Taiheiyo, Miikeand Balmercoals using wash oil under nitrogen atmosphereat 370°C for 30 min, the extraction yield is always within the additivity law. Further studies used Yallourn, Soyakoishi, Taiheiyo, Horonai, Miike, Shin Yubari, Balmer coals and their blends which were hydrogenated in tetralin, wash oil or creosote oil, with or without catalyst, at 400-45OC under 10 or 3 MPa of initial hydrogen pressure. When hydrogen is available, the additivity law exists for blended coals, but when the hydrogen supply isdeficient, the experimental conversion of blended coals isalways lower than calculated conversions. This may be due to the faster consumption of the hydrogen by more reactive coals and thus the less reactive coals were unable to react with hydrogen. (Keywords: coal; liquefaction;

blending)

Many authors have discussed the different conditions required for coal liquefaction; coal blending is particularly important. When coals are blended it is expected that once one coal has dissolved in the solvent, it would have a beneficial effect on the solubility of the other coal; in particular the bituminous coals, which have larger aromatic structural units, and are thought to have better dissolving power. If this phenomenon takes place, it favours the hydrogenation reaction, because the solute would react more readily than the solid. However, it would also be expected that when the hydrogen supply is insufficient, the more reactive coal in the blend takes the hydrogen preferentially. Thus the total liquefaction yield may be smaller than could be calculated for each coal independently hydrogenated. This Paper assesses these possibilities. Sato et al.’ examined hydrogenation without solvent at 500°C for 10 s under 15 MPa pressure. They reported that blending of Newdell (Australia) and Miike (Japan) coals gave an unexpected tendency ; namely, at a SO/SOblending ratio the liquefaction yield was smaller than the calculated values and at a 20/80 blending ratio it was larger. But there are doubts about the precision of the experimental results in their report. They also reported that the liquefaction of Miike and Taiheiyo (Japan) coals at 400 and 420°C for 30 min under an initial hydrogen pressure of 7.8 MPa in creosote oil shows the additivity rule. Clarke et al.2 and Ueda et d3 reported that blending coals gave additive results and they found no interaction between the coals. Later Ueda et a1.4 showed that a slight increase in the liquefaction yield was found with Yallourn and Shin Yubari (Japan) coals on blending. Such contradictions in the literature must be clarified and the issue of which reaction will or will not lead to additivity, must be elucidated. *Part of this Paper was presented at the 46th Annual Meeting of the Chemical Society of Japan, 1982 00162361/84/010078-06%3.00 @ 1984 Butterworth & Co. (Publishers)

78

FUEL, 1984, Vol63,

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This Paper aims to ascertain the additivity in liquefaction yield in hydrogenation of coals and to clarify under which conditions this additivity will appear, by varying the reaction conditions.

EXPERIMENTAL Coal samples

Yallourn, Taiheiyo, Miike, Shin Yubari and Bahner (Canada) coals were used after a float and sink separation to concentrate the vitrinite. Other Yallourn, Soyakoishi (Japan) and Horonai (Japan) coals were used as received. These coals were ground to pass a 100 Tyler mesh (149 pm) and dried. The ultimate analyses are listed in Table 1. Solvent extraction

With the Taiheiyo, Miike and Bahner coals, 15 g of sample for the extraction of each coal or a blend of 7.5 g of each coal and 45 g of wash oil (180-310°C) were charged into 500 ml rocking autoclave with 10 stainless steel balls. The atmosphere was replaced with 3 MPa of nitrogen and the autoclave heated to 370°C with a heating rate of 3.54.o”C min- ’ and held for 30 min at this temperature, then cooled. The gases were analysed by g.c. The product was removed using 300 ml of benzene and extracted by shaking for 10 h at room temperature. Part of the benzene-insoluble residue was extracted with 100 times its weight of pyridine in the same way as before. As it is difficult to separate wash oil from the product, the conversion was calculated from the weight of extraction residue using the following equations : Benzene conversion (BC) %=[ 1 -c_isi]

x 100

Effect of blending

on coal liquefaction:

K. Ouchi et al.

Reaction with wash oil or creosote oil Table 1 Ultimate

analytical

data of coal samples (% daf)

With red mud and sulphur as catalyst using wash oil. 10 g

Coal

C

H

N

S

0 (diff .I

Yallourn (Australia) Soyakoishi (Japan) Taiheiyo (Japan) Horonai (Japan) Miike (Japan) Shin Yubari (Japan) Balmer (Canada)

66.9 70.7 77.9 78.9 83.9 87 .o 89.5

5.3 5.1 6.3 6.5 6.3 6.0 5.5

0.6 1 .7 1 .l 1 .3 1 .2 1 .3 1.3

0.3 1 .o 0.2 0.2 2.1 0.5 0.3

26.9 21.5 14.5 13.1 6.5 5.2 3.4

Pyridine conversion (PC) % = Pl-gx

Ash

lP&:x

Ash

BI -Ash

‘M-Ash

1

x100

of Taiheiyo or Miike coal (in the case of blended coals, 5 g of each coal) were charged into the same autoclave with 20 g of wash oil, 1 g of red mud and 0.1 g of sulphur. The initial hydrogen pressure was 10 MPa and the reaction temperature was 400°C. Other procedures and gas analyses were the same as before. For Yallourn and Shin Yubari coals, 15 g of coal, 30 g ofwash oil, 1.5 g of red mud and 0.15 g of sulphur were used. The product in the autoclave after reaction was recovered with 250 ml of n-hexane. The mixed solution was shaken for 10 h at room temperature to separate nhexane-solubles and insolubles (HS and HI). The HI was filtered and dried under vacuum. As before, the separation of wash oil was difficult and n-hexane conversion (HC) % was estimated from the amount of HI. HI -(Catalyst

+ Ash) x 1oo

Coal (daf) where: M = weight of sample coal; Ash = weight of ash in M; BZ = weight of benzene-insoluble material; PE = weight of BI used for pyridine extraction; and PI = weight of pyridine-insoluble material. Hydrogenation liquefaction Reaction with tetralin as solvent.

Tetralin was used after vacuum distillation. Taiheiyo coal (5 g) and Miike coal (5 g) were charged into a 500 ml rocking autoclave with 100 g of tetralin and 10 stainless balls. The autoclave was pressurized with hydrogen to 10 MPa, then heated to 400 or 440°C with the heating rate of 3.5-4.O”C min- ’ and maintained at this temperature for 30 min. The resultant gases were analysed by g.c. Each coal (10 g) was also hydrogenated separately in the same way. The product in the autoclave was recovered with 15& 200ml tetralin and filtered to separate the tetralin-soluble (TS) and insoluble (TI) parts. The TI was washed with a suitable amount of tetralin and methyl alcohol and dried. The mixed solution of tetralin and methyl alcohol was added to the tetralin solution mentioned above. This solvent was distilled under vacuum to concentrate the TS portion and finally separated by steam distillation. To quantify the conversion, the TS and TI were extracted in parallel with pyridine, benzene and n-hexane by shaking (the ratio of sample/solvent = l/40). Solventsoluble fractions were recovered by vacuum distillation and dried. The extraction yields were determined by the following equations : Pyridine-soluble

(PS) % = Pyridine-soluble in TI +TS x loo Coal (daf)

1

n-hexane-insoluble (HI) was extracted with benzene and pyridine in parallel, to estimate the pyridine and benzene conversion (PC and BC). Extraction procedures were as described above. BC % = 1 _ Benzene-insoluble in HI -(Catalyst Coal (daf)

1

+ Ash) x 1oo

PC %=

1

1 _ Pyridine-insoluble in HI - (Catalyst + Ash) x 1oo Coal (daf) Wth red mud and sulphur as catalyst using creosote oil and the as received coals. 50 g of coal, 75 g of creosote

oil, 5 g of red mud and 1 g of sulphur were charged in a rocking autoclave with 10 stainless balls. The atmosphere was replaced with 10 MPa hydrogen and the autoclave heated to the reaction temperature (400,420 and 45O’C) for 30 min. After reaction, the gases were analysed by g.c. and the product filtered. Solubles and residues were extracted with THF, benzene and n-hexane using Soxhlet apparatus and the conversion was calculated from the weight of residues. Wthout catalyst. Taiheiyo, Miike and Balmer coals and their blends were also reacted without catalyst. Most procedures were the same as described in (a), except for the amount of sample: coal 15 g (in the case of blending, 7.5 g each): wash oil, 30 g; and initial hydrogen pressure of 3 MPa.

Benzene-soluble (BS) % = Benzene-soluble in TI and TS x 1oo Coal (daf)

RESULTS AND DISCUSSION Solvent extraction

n-Hexane-soluble

(HS) % = n-hexane-soluble in TS x100 Coal (dal)

Results of solvent extraction at 370°C under 3 MPa nitrogen pressure are shown in Figures Z-3. All the experiments were duplicated and the error was within f 1%. There exists a clear linear relation for conversion

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1984,

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79

Effect of blending on coal liquefaction: K. Ouchi et al.

loo/

60-

2ol-----l 0. Concentmtlon

of Miike

0

100

50

0

Concentmtion

50 of Taihetvo

,

100 coal (wt%)

Figure 2

Solvent extraction of blend of Taiheiyo and Balmer coals, 370°C 30 min. N2, 3 MPa, wash oil. 0, Pyridine conversion; A, benzene conversion; 0, gases

yield and this means that each coal dissolves independently in the solvent. Usually larger aromatic molecules like phenanthrene or pyrene dissolve better than smaller molecules like benzene or naphthalene, and the higher ranks ofcoal have larger average aromatic ring size (57) (for example, the average aromatic ring number of Taiheiyo coal is l-2, that of Miike 2-3 and that of Balmer 4). It could be concluded that the dissolved part of higher rank coals increases the solubility of the other coals in the blend; but this is not the case. Hydrogenation Under a sufjicient supply of hydrogen.

Results of the reaction in tetralin under 10 MPa hydrogen, at 400 and 440°C for 30 min are shown in Table 2. Conversions at

80

FUEL, 1984, Vol 63, January

coal (wt%)

Solvent extraction of blend of Miike and Balmer coals, 370°C. 30 min, N,, 3 MPa, wash oil. 0, Pyridine conversion; A, benzene conversion; 0, gases

I

I

0

of Miike

Figure 3

Figure 7 Solvent extraction of blend of Taiheiyo and Miike coals, 370°C. 30 min. NS, 3 MPa, wash oil. 0, Pyridine conversion; A, benzene conversion; 0, gases

OL ’

1OC

50 Concentration

coal (wt%)

440°C did not show any difference between the calculated and experimental values (run 22). The difference was within f 1.5%. The data on conversion at 400°C is scattered, but the calculated values are similar to the experimental ones. From these results it can be concluded that there was no blending effect on the conversion under these conditions, namely there is an additivity between these coals. Results of the reaction with wash oil and catalyst under 10 MPa of hydrogen pressure at 400°C for 30 min are shown in Table 3. Again, there is no signiticant difference between calculated and experimental values. Therefore under these reaction conditions with catalyst, there was no influence on liquefaction due to blending the coals. Ueda et aL4 reported that the blend of Yallourn and Shin Yubari coals increases the liquefaction yield. To check their result the present authors also tried a similar reaction, using the same conditions as above. The result is shown in Table 4. There is no favourable effect and the liquefaction yield was consistent with the additivity law. The effect of reaction temperature was examined using Yalloum, Soyakoishi, Horonai coals (coals as received) and their blends using creosote oil. The results are shown in Figures 4 and 5. Although the data are somewhat scattered, these also show additivity at any temperature. In the hydrogenation reaction using 10 MPa initial hydrogen pressure and catalyst, hydrogen is supplied in sufficient quantity to the reaction system. This is the reason why each coal reacts independently from each other in the reaction system. In hydrogenation, it is understood that the initial reaction is the splitting of the bridging bonds to make radicals and that these radicals then take hydrogen to stabilize themselves thus producing smaller molecules. When hydrogen is supplied in sufficient quantity, all the radicals can be stabilized allowing no interaction between radicals, the reaction for each coal proceeding independently of the other coals. Moreover the dissolution of each coal into the solvent, wash oil, is also independent as mentioned above. This also does not accelerate liquefaction.

Effect of blending on coal liquefaction: K. Ouchi et al. Table 2

Liquefaction

with tetralin.

1 2

pressure, 10 MPa; reaction

time, 30 min

Absorbed hydrogen

Product

Tetralin-

gases

soluble

Coal (9)

(“Cl

(mg)

(96)

(%I

HS

BS

Taiheiyo, 10 Miike, 10

400 400

99 45

4.3 1 .4

75.6 75.7

19.9 14.9

55.3 53.2

71

2.8

75.7

17.1

54.1

93.4

400

100

2.9

75.0

23.5

46.6

90.5

440 440

225 135

10.0 6.1

93.4 92.9

33.5 32.0

179

a.0

93.1

la5

a.5

91 .o

Average of run 1 and 2 21 Taiheiyo, 5 Miike, 5 3 4

100 g; hydrogen

Reaction temp.

Run no.

Tetralin,

Taiheiyo, 10 Miike, 10

Average of run 3 and 4 22 Taiheiyo, 5 Miike, 5

440

Percentages are based on solid recovery

Conversion

89.5 96.3

al.8

97.3

78.1

103.0

32.6

79.6

100.6

32.9

75.1

97.2

Wash oil, 20 g; red mud, 1 .O g; sulphur, 0.1 g; initial hydrogen

pressure, 10 MPa;

Conversion Absorbed Coal fg)

PS

fdaf)

Tab/e 3 Liquefaction with wash oil and catalyst. temperature, 400°C; time, 30 min

Run no.

1%)

hydrogen

fmg)

(o/o)

Product gases HC

f%)

ac

PC -

23 Miike, 10 24 Taiheiyo, 10 Average of run 23 and 24 25 Miike, 5 Taiheiyo, 5

297 510 407

4.6

6.3

37.6 52.7 45.1

77.0 80.4 78.7

99.8 101.9 100.9

375

6.8

46.6

80.6

102.2

a.1

I

Tab/e 4 Liquefaction with wash oil and catalyst. temperature, 400°C; time, 30 min

Wash oil, 30 g; red mud, 1.5 g: sulphur,

0.15

g; initial hydrogen

pressure, 10 MPa;

Conversion Run no.

Absorbed Coal fg)

38 Yallourn, 15 39 Shin Yubari, 15 Average of run 38 and 39 40 Yallourn, 7.5 Shin Yubari, 7.5

hydrogen

f%)

Product gases

(mg)

f%)

HC

BC

PC

701 430 565

20.1 5.1 12.5

49.8 25.8 37.8

73.0 57.0 65.0

103.3 105.9 104.6

574

10.9

37.5

61.7

103.7

Under a deficient supply ofhydrogen. For reactions without catalyst and under a lower initial hydrogen pressure of 3 MPa using wash oil at 400°C for 30 min (Table 5) the experimental values of conversion for the blended coals were lower than those of the calculated ones. Table 5 and Figure 6 show clearly this decrease in conversion. In Figure 6, if the additivity law applies, the conversion values should be at the middle point of the line connecting the conversion values of each coal, but in all cases the experimental values are lower than these values. The reason may be as follows. With an insufficient hydrogen supply, the more reactive and more soluble

coals preferentially consume the available hydrogen around them very quickly and the hydrogen concentration in the reaction system is thus decreased. The lower reactive and lower soluble coals therefore have little chance to react with the hydrogen, accelerating the polycondensation reaction leading to a lower liquefaction yield. The reaction condition adopted in this case is similar to the SRC production process. Namely, the working pressure was about 7-8 MPa and the reaction time was 30 min at 400°C. Thus under the conditions operating in an SRC plant, blending of coals must be carefully controlled, as blending can sometimes lower the liquefaction yield.

FUEL,

1984,

Vol 63, January

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Effect of blending on coal liquefaction: K. Ouchi et al. 42O’C u

1oc

n r\

0 A

0

” 80

B( B 60

4c

0

0

O

0

4(

C

C

0

0 ~ ”

0

100

0

80

*

u

0 m

D

450°C A ”

0

2(

C

lO(

u

60 B 40

20

B

3 -

0

’

w 50

I 0

Concentration

,‘,E /

ca 100

of Horonar coal (wt %I

Figure 4 Liquefaction of Soyakoishi and Horonai coals with creosote oil. Coal, 50 g; creosote oil, 75 g; red mud, 5 g; sulphur, 1 g; initial hydrogen pressure, 10 MPa; temperature, 420 and 450°C; time, 30 min. A, gases; B, oil+ water; C, asphaltene; D, preasphaltene; E, residue

45O’C n v

A

0

0

lO(

8(

6( B 4(

Figure 5 Liquefaction of Yallourn and Horonai coals and their blends with creosote oil. Coal, 50 g; creosote oil, 75 g; red mud, 5 g; sulphur. 1 g; initial hydrogen pressure, 10 MPa; temperature, 400. 420 and 450°C; time, 30 min. A, gases; B, oil+water; C, asphaltene; D, preasphaltene; E, residue

2( 1

f3

0

C 0

0

u ,D
I

W

50

0

Concentration

82

FUEL, 1984, Vol63,

January

0

C

of

Horonai

coal

(wt

V. 1

Effect of blending on coal liquefaction: K. Ouchi et al. Table 5

Run no. 27 28 30

Liquefaction

with wash oil and without

catalyst.

Walsh oil, 30 g; initial hydrogen

pressure, 3 MPa; temperature,

Product

Conversion

400°C:

time, 30 min

(%)

Sample

Absorbed hydrogen

gases

Coal

(g)

(mg)

f%)

HC

BC

PC __---

Taiheiyo Miike Balmer

15 15 15

237 157 a7

14.1 5.1 4.4

25.1 16.8 3.6

39.5 41.3 14.5

61 .l 96.4 31.4

Average of run 27 and 28 29 Taiheiyo Miike

7.5 7.5

Average of run 28 and 30 Balmer 31 Miike Average of run 27 and 30 32 Taiheiyo Balmer

I

7.5

197

9.6

21 .o

40.4

78.8

165

6.5

15.3

37.5

77.4

122

4.9

10.2

27.8

63.8

110

4.8

3.8

22.2

54.3

162

9.2

14.3

27.0

46.2

146

10.5

9.4

19.8

37.0

7.5 I 7.5 7.5

REFERENCES 1 Sato, Y. Fuel 1982,61, 875 Clarke, J. W., Kimber, G. M., Rantal, T. D. and Shipley, D. E., ‘Coal Liquefaction Fundamentals’,(Ed. D. D. Whitehurst) Am. Chem. Sot. Symp. Ser. 1980, 139, 112 3 Nakata, Y., Ueda, S., Sakai, N., Shibaoka, M. and Maekawa, Y., Paper presented at 45th Annual Meeting of Chemical Sot. Japan, II, 1286, 1981 Nakata, Y., Ueda, S. and Maekawa, Y., Paper presented at 19th conference on Coal Science in Japan, 218, 1982 Iwata, K., Itoh, H. and Ouchi, K. Fuel Proc. Trchnol. 1980,3,221 Makabe, M. and Ouchi, K. Fuel 1979,58, 43 Iwata, K., Itoh, H. and Ouchi, K. Fuel Proc. Trchnol. 1980, 3, 25

2

Figure 6

Liquefaction of Taiheiyo, Miike and Balmer coals and their blends. Coal, 15 g; wash oil, 30 g; initial hydrogen pressure,

3 MPa; temperature, 4OOT; time, 30 min. 0, Pyridine conversion of each coal; 0, pyridine conversion of coal blends; A, benzene conversion of each coal; A, benzene conversion of coal blends; 0, n-hexane conversion of each coal; n , n-hexane conversion of coal blends; x, calculated conversion of coal blends

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