The effect of ash and ash constituents on the liquefaction yield of Turkish lignites and asphaltites

The effect of ash and ash constituents on the liquefaction yield of Turkish lignites and asphaltites Mualla Oner, Gibes and Solih Dincer

Oner”, Esen Bolat, Giilseren

Yalin, Ceqminaz

Kavlak

Yildiz Technical University, Chemical Engineering Department, Sisli, Istanbul, Turkey (Received 16 July 1993)

The objective of this work was to study mineral matter effects in coal liquefaction. A suite of 16 lignites and two asphaltites have been liquefied in a batch autoclave under a standard set of reaction conditions. Experiments were performed at 44o”C, 60 min residence time and 8 MPa hydrogen pressure (cold charge).

All experiments were carried out in solvents, like anthracene oil, creosote oil, tetralin and TUPRAS vacuum residual oil, at a solvent:lignite ratio of two. The ash content of lignites and asphaltites ranged from 7.73 (dry) to 59.99% (dry). It was found that, generally, as the ash content increased, the total conversion of lignite and conversion to tetrahydrofuran (THF), toluene or hexane solubles increased; total conversion, THF and toluene solubles yields appear to remain constant at high ash contents. Multiple regression analysis was employed to relate yield and conversion data with specific ash minerals. (Keywords:ash; liquefaction yield; effect)

Catalysts in coal conversion processes are of great importance, because they increase the yields and substantially reduce the sulfur content in the final product. Mineral catalysis, as it relates to coal conversion processes, is very important because it represents a readily available, abundant, inexpensive source for use in accelerating liquefaction reactions in coal liquefaction. Commercial catalysts, such as nickel or cobaltmolybdenum, tend to produce the highest conversion yields; however, these catalysts are susceptible to deactivation by sintering, carbon deposition and metal deposition’. In addition, these commercial catalysts are expensive, and recycling of these spent catalysts is costly and inefficient. Therefore, mineral matter provides an inexpensive alternative. The ash, or more precisely, the mineral matter content of coal is more important in liquefaction processes, particularly in single stage processes such as the solvent refined coal (SRC) process2. It has been demonstrated that mineral phases present in many coals do exhibit a catalytic effect in SRC processes’. In two stage processes the catalytic effect of the ash content is not as important, since hydrocracking and rehydrogenation of the solvent takes place in the second stage before which the ash has been removed by filtration. Many studies have shown that mineral matter behaves in a beneficial manner during coal conversion. Given et ~1.~9”made the observation that the highest liquefaction yields from a series of fractions obtained from a lignite by float and sink methods were given by the sample with the highest total mineral and pyrite contents. Mukherjee and Mitra’ found that the overall percentage * Present address: The University of Arizona, Department Science and Engineering, Tucson, AZ 85721, USA 0016-2361/94/10/165849 c 1994 Butterworth-Heinemann

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of Materials

conversion increased continuously with the amount of mineral matter present in the fraction. They improved the conversion of Assam (India) bituminous coal by impregnating it with titanium oxide or kaolin. Wright and Severson observed that conversion of lignite in a continuous reactor increased as the potassium and sodium concentration rose. They also showed that iron, in the form of filter cake residues from coal liquefaction experiments, was active for increasing the hydrogen donor quality of anthracene oil. Coal minerals have also been reported to catalyse hydrogenation of creosote oil and anthracene oils, resulting in enhanced hydrogen transfer capacity for these solvents’. It was found that pyrite was the most important coal mineral matter constituent having catalytic activity during liquefaction’. The catalytically active form of iron in coal liquefaction has not been identified conclusively, but it is thought to be pyrrhotite. Under liquefaction conditions, FeS, is transformed into a non-stoichiometric iron sulfide, Fe,_,S (0 < x < 0.125). Thomas et al.’ studied the kinetics of this decomposition under coal liquefaction conditions, and concluded that the catalytic activity of FeS, is associated with radical initiation resulting from the pyrite-pyrrhotite transformation. Mazzocco et al.” have shown that run-of-mine coals were more reactive than corresponding washed coals which contained less mineral matter. The liquefaction reactivity was regained when pyrite concentrate was added to the washed coals in sufficient quantity. Furthermore, there is a considerable literature”*12 reporting increased reactivities in carbonaceous materials owing to the presence of certain inorganic compounds, such as metallic oxides. High ash coals are known to contain these minerals, which may increase hydrogenation reactivity.

Effect of ash on coal liquefaction yield: M. Oner et al.

In this study, a series of batch reactor experiments have been performed to develop correlations between ash and ash constituents of 16 lignites and two asphaltites, with yield data obtained in tetralin, anthracene, creosote and vacuum residue oils, at 440°C and 8 MPa (cold hydrogen pressure). An attempt will not be made to review the effects of all classes of minerals, but will only consider those minerals which have shown a large effect on coal conversion processes. The terms minerals, mineral matter and ash will be used synonymously in this paper. EXPERIMENTAL Materials

Experiments were carried out with 16 lignites and two asphaltites using tetralin, TUPRAS vacuum residue oil, anthracene and creosote oils as solvents. Creosote and anthracene oils used in this study were obtained from Karabuk Demir Celik Fabrikalari AS and vacuum residual oil (VR) was provided by TUPRAS, Turkey. Tetralin was supplied by Merck company, and it was used as-received. The creosote oil used has a carbonhydrogen ratio of 1.24 (90.78 wt% C, 6.12 wt% H and 0.70 wt% N); anthracene oil has a carbon-hydrogen ratio of 1.27 (91.50 wt% C, 6.01 wt% H and 0.75 wt% N); vacuum residual oil has a carbon-hydrogen ratio of 0.64 (85.58 wt% C, ll.O6wt% H and 0.50wt% N). The elemental analysis for carbon, hydrogen and nitrogen was done by Beller Microanalysis Laboratories in Germany. The ash samples prepared at 800°C were analysed with inducted coupled plasma (ICP), Leeman, Model PSlOOO Series. Procedure

The liquefaction experiments were carried out in a 250 ml magnetically stirred and electrically heated stainless steel autoclave manufactured by Ernst Haage. Based on the literature and evaluation of previous work’3-‘7, the reaction temperature, pressure and reaction time for these experiments were chosen as 44o”C, 8 MPa hydrogen (cold charge) and 1 h, respectively. Solvent-lignite or asphaltite ratio was chosen as two, dry basis (db). At the completion of a liquefaction experiment, the autoclave was cooled overnight to room temperature and the gases were analysed by Shimadzu Moduline GC-9A model gas chromatograph. The liquid products and solid residue washed from the autoclave with toluene and fractionated by Soxhlet extraction into oil (hexane soluble material), asphaltene (toluene soluble, hexane insoluble material), preasphaltene [tetrahydrofuran (THF) soluble, toluene insoluble material] and residue (THF insoluble material). The blank runs for all sets of experiments with no lignite present were carried out with all solvents to evaluate the reactivity of the lignite samples alone. The total conversion (TC) was calculated from the formula: TC (%)=

lignite input(daf) - residue(daf) lignite input(daf)

The hydrogen consumption (HC) in the gas phase was estimated from the pressure difference (end pressure minus initial pressure) at room temperature. The oil yield (0) was calculated from the following expression: O(%)=lOO+HC-A-PA-G-R

In the above expression HC, A, PA, G and R stand for the weight percentages of hydrogen consumption, asphaltene, preasphaltene, gas and residue, respectively. Those percentages were obtained from the ratio of the respective weights to the lignite input (daf).

RESULTS

AND DISCUSSION

There have been a number of studies which have established relations between hydrogenation performance and organic and inorganic coal characteristics’8-2’; however, these have been directed primarily toward higher rank coals or groups of coals exhibiting wide variation in rank. This work is concerned with 16 lignite and two asphaltite samples showing big variations in ash and ash constituents. The complete experimental data were reported in previous works13-‘7. The lignite and asphaltite characteristics used in this study are listed in Table 1. The analysis of ash results are given in Table 2. The experimental data used for this study are given in Figures 14.

In a discussion of mineral matter effects relative to non-catalytic liquefaction, one should consider the changes in total conversion and liquid yield data as a function of ash content. Such ash effects were studied using lignites and asphaltite in which ash contents range from 7.73 (dry) to 59.99% (dry). The results are summarized in the following paragraphs. Conversion of hexane soluble products (0) and toluene soluble products (0 + A) from the initially insoluble coal is perhaps the most important overall criterion of liquefaction effectiveness. The data show that conversion and yield data are affected by the ash content of the feed lignite. As shown in Figure 5 oil yield increases from 11.10 to 62.20 (wt% daf), 10.70 to 55.80 (wt% daf) and 12.90 to 61.90 (wt% daf) as ash content increases from 7.73 to 59.99 (wt% dry) when anthracene, creosote and vacuum residual oil are used as solvents, respectively. The total conversion [toluene solubles (TS) and THF solubles (THFS)] yields also increase with increasing ash content; the yields appear to remain constant at high ash contents as shown in Figure 6. It seems that the catalytic effect of ash may saturate when ash contents are 35-40 (wt% dry). In high ash contents, reactor capacity is adversely affected, also there is a ballasting effect with the recoverable distillable yield 22. Ash content appears to have little or no effect on the production of preasphaltene and asphaltene. An attempt was made to correlate ash contents against total conversion (TC, wt% daf), oil (0, wt% daf), asphaltene (A, wt% da& preasphaltene (PA, wt% daf), toluene solubles (TS, wt% daf), tetrahydrofuran solubles (THFS, wt% daf) yield data. For this purpose, a linear regression was performed on the data obtained by using four different solvents. It was found that, generally, good correlations did not exist between ash content, yield and conversion data. In a very few cases square of correlation coefficients (r2) exceeded 0.4. The best correlation coefficients were obtained with oil yield (0, wt% daf) as the dependent variable. The correlation coefficient of experiments using anthracene oil as solvent was better than other solvents. The equations obtained by using ash content in the simple linear regression are: O,, (wt% daf) = 0.78 ash + 10.82 (SE and SL excluded)

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Effect of ash on coal liquefaction yield: M. Oner et al. Table 1

Analytical

data for lignites and asphaltites

WC

Lignite used

(atomic)

;;

dry)

;:

Ash (% dry)

daf)

BE

64.90

5.61

2.19

1.04

5.69

35.61

64.39

BS

60.14

5.90

2.34

1.18

2.05

42.08

57.92

53.21

CA

66.38

4.82

1.67

0.87

4.23

37.53

62.47

27.15

49.88

CH

60.06

5.19

2.21

1.04

4.37

31.72

68.28

44.12

EL

65.95

4.97

2.48

0.90

5.82

54.78

45.22

28.19

GO

63.46

4.97

2.32

0.94

1.57

35.41

64.59

13.58

IL

68.19

5.11

1.27

0.90

2.95

40.32

59.68

33.61

KE

65.08

5.74

1.85

1.06

3.94

39.88

60.12

19.01

KN

67.66

4.52

2.78

0.80

5.63

62.93

37.07

38.50 49.20

KR

66.92

5.55

2.09

0.99

0.79

49.43

50.57

OR

66.78

5.43

0.91

0.97

2.76

36.48

63.52

7.73

SA

61.32

4.73

1.60

0.93

4.97

48.21

51.79

59.99

SE

71.97

4.70

2.32

0.78

1.45

48.65

51.35

24.87

SL

74.82

7.06

1.35

1.13

6.95

14.25

85.75

28.00

so

64.10

5.62

1.47

1.05

0.80

39.69

60.31

55.51

SR

87.91

6.13

1.29

0.92

0.92

32.10

67.90

41.53

TU

78.30

5.65

3.03

0.87

1.37

31.59

68.41

18.59

YA

63.65

4.87

1.59

0.92

5.11

44.41

55.59

25.35

Table 2

Chemical

analyses

of ash (g 100 g-

Lignite

Si

Fe

Al

Mg

BE BS CA CH EL GO IL KE KN KR OR SA SE SL so SR TU YA

22.06 N.d.” 8.24 N.d. 5.47 N.d. 9.36 N.d. 11.35 33.26 N.d. 32.55 9.02 N.d. 27.65 N.d. 5.48 4.30

6.70 6.30 3.26 3.62 1.45 1.11 2.88 1.56 1.69 3.70 0.79 14.42 6.87 1.37 3.64 3.03 2.29 3.28

6.60 16.48 5.55 4.18 2.69 1.17 6.88 2.13 7.20 3.91 0.37 18.19 I .94 1.56 17.80 3.34 3.52 2.97

2.59 1.22 0.13 4.94 0.74 0.68 0.96 0.79 0.84 0.81 0.50 4.03 1.12 1.08 1.07 1.63 0.47 0.54

’ organic matter)

a

Ca

K

Na

6.89 5.20 1.18 9.47 6.87 2.22 3.75 2.47 8.64 2.34 1.60 5.49 2.18 6.68 8.05 9.73 0.37 4.23

1.14 1.77 0.27 0.32 0.20 0.09 1.60 0.17 0.52 2.44 0.02 2.88 0.13 0.21 1.50 2.06 0.27 0.25

3.54 0.41 0.12 1.67 0.12 0.34 2.06 0.10 0.29 0.42 0.02 0.40 0.34 0.15 0.46 0.23 0.03 0.07

a N.d., not determined

TC m

BE ES

CA CE

THFS m

EL GO IL

TS 0

KE KN

0

KR

OR

SA St3 SL

SO SR

T" YA

Figure 1 The results of liquefaction experiments with anthracene P = 8 MPa hydrogen; T= 44O’C; reaction time = 1 h; S/L = 2 100

oil:

,

Im

TCM

THFSm

TSn

0

KE KN

KR OR SA

00

rz = 0.755 1, SEOE = 7.38, solvent = anthracene

oil. 00

Oco (wt% daf)=0.62 ash+ excluded)

11.71 (SE, SL and YA 70

r2 = 0.5713, SEOE = 9.11, solvent = creosote

oil.

OVR (wt% daf) = 0.93 ash + 20.28 (BS, SA and TU excluded) r2 = 0.4902, SEOE = 13.73, solvent = vacuum residual oil. The efect of specljic minerals in ash The observed relation between the concentration of the ash and conversion and yield data was further evaluated with respect to the concentration of ash constituents (g 100 g-’ of organic matter). The bulk of the ash forming material in lignite occurs as inherent inorganic matter in the form of exchangeable cations

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z :

60

E

50

z j:

40 SO 20 10 0 BE

RS CA CII

EL GO

IL

SE

SL SO SR T”

Figure 2 The results of liquefaction experiments with creosote P = 8 MPa hydrogen; T= 440°C; reaction time = 1 h; S/L = 2

YA

oil:

Effect of ash on coal liquefaction @j

TC m

THFS m

TS 0

28.20 to 13.90 (wt% daf) and 3.70 to 0.10 (wt% daf), respectively. The conversion and yield data increased with the Fe content up to a point corresponding to 6.87 g Fe 100 gg ’ of organic matter. The data for the next higher Fe content of lignite remain constant in spite of an increase in Fe to 14.12g lOOg-’ organic matter. Asphaltene and preasphaltene contents decrease as Fe content increases, as shown in Figure 8. Fe, especially pyrite has been cited as an important mineral catalyst. It was found to be an active mineral catalyst, as measured

0

100 00 80

70 = 4

yield: M. Oner et al.

60

!.5 so % 40 ;; 30

t 90

20

v

0 OA.0. ’ oe.0.

%.R.

00

10 0 BE

BS lx

CH

EL

GO IL

KS

KN KR OR

Figure 3 The results of liquefaction P = 8 MPa hydrogen; T= 440°C; reaction

SA BE SL

so

SR T”

experiments with time = 1 h; S/L = 2

70

YA

tetralin:

V

0

60

V T g

V

V

WV

lV

50

V

0 V

0

m

TC w

THFS

TS 0

I!

0

i

100

.e”

0 40

a

OO

.z

c?

0

30

v

v

0

0

8.

0 l

V 0

20

01

I

0

10

I

I

I

,

1

20

30

40

50

80

70

Ash @dry) Figure 5 Variation of the oil (0) yields with ash for hydroliquefaction of lignites in anthracene (O,,), creosote (O,,) and vacuum residual oil (Ova)

BE

BS

CA CA EL

GO IL

i-3 KN KR

OR Sk SE

SL SO

SR T” YA

loo1

Figure 4 The results of liquefaction experiments with vacuum residual oil: P = 8 MPa hydrogen; T= 440°C; reaction time = 1 h; S/L = 2

present as salts of carboxylic acids. These include the cations such as Na, Ca, Mg, Fe and Al. In this study total Fe, Al, Si, Mg, Ca, Na and K concentrations were chosen as the independent variables, since the active form of the minerals has not been ascertained. The major constituents of the lignite ashes are silica, alumina, iron and calcium. There appears to be a direct correlation between oil (0), toluene solubles (0 + A), THF solubles (0 +A+ PA) and total conversion from the liquefaction experiments with ash constituents, but the dependence is not marked. The scatter can be attributed to the variation of other properties in the samples. In all cases conversion and oil yield were found to be more sensitive to ash content. Conversion of coal and production of oils increased with increasing Fe content of the ash as shown in Figure 7. In the case of creosote oil used as solvent, oil production increased from 10.70 to 55.80 (wt% daf) as the Fe concentration increased from 0.79 to 14.42 (g 100 g-’ organic matter) as shown in Figure 8. Asphaltene and preasphaltene yields decreased from

z

90

-

00

-

70-

if7 2 .f

60

30

I 0

I

I

I

I

I

I

I

10

20

30

40

50

60

70

Ash

@dry)

Figure 6 Variation of the total conversion (TC,,), tetrahydrofuran solubles (THFS,,) and toluene solubles (TS,,) with ash in anthracene oil

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Effect of ash on coal liquefaction yield: M. Oner et al.

100 90

experiments showed that the total conversion, oil, tetrahydrofuran and toluene solubles yield data increase continuously with the amount of Al present up to a level of 7.20 g lOOg-’ organic matter and then level out (Figure 9). The preasphaltene (PA) and asphaltene (A) yield data also show a tendency to decrease with increasing Al content, though with more scatter than in the case of oil and conversion (Figure 10). The rate of decrease appears to remain constant at high Al contents. In this study no detectable trends were observed with Si contents of ash.

8 l 0

60

l

70

l

l

;

a

t 80 0” c

0

50

0,

V

V

V V V

E

40

V

V

lv

V

0 %J..

vv

30

100

l TSA.cL

l

v O,.,.

l l

0.

’ 0

0

I

I

I

I

t

2

4

6

0

10

Fe

(g/100

g organic

I

i

12

14

l

16 C

60

(TC,,), oil (O,,) and of the ash in anthracene

?-?.

0

-

:

l V

50-

0

0

0

E c

40

-

30

V -

0

O0

0O

0

0

0 OA.0.

70 20-

0

60

v T%o ..

10

0

0

0’

0

t 6

I

1

I

1

I

I

I

I

2

4

6

6

10

12

14

16

16

21

Figure 9 Variation of the total conversion (TC,,), oil (O,,) toluene soluble (TS,,) yields with Al content of the ash in anthracene

and oil

0

50

0

Al (g/100

40

T%.cJ.

l

0

y 0

l l V

J

matter)

Figure 7 Variation of the total conversion toluene solubles (TS,,) yields with Fe content oil

V l

g organic

matter)

s ‘p .c

l

30 50

0 AA.&

20

0

l

cb

10

v

v 67

I

0 0

2

4 Fe

6 (g/lOOg

, a organic

I

I

10

12

I” _

14

16

0

matter)

Figure 8 Variation of the oil (Oc,), asphaltene (PA,,) with Fe content of ash

Fuel 1994

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0

0

(A,,) and preasphaltene 0

by hydrogenation activity and decrease in asphaltene content, in coal liquefaction6.23. It is reported that acidic components of coal minerals would enhance the rate of coal liquefaction, because they increase the rate of decomposition or aromatic ether structuresz4. The acidic effect of coal minerals was concluded to be mainly due to alumina or silica-alumina. Alumina-silicate minerals are the major mineral impurities in coals, and these may act as cracking catalysts at the temperatures prevailing during coal hydrogenation. The

1662

pAA.0.

l

73 Number

10

l;,::, ‘,:‘,

0

2

4

6 Al

(g/lOOg

6

,

10 organic

,

12

( 14

.,; 16

16

20

matter)

Figure 10 Variation of preasphaltene (PA,,) yields with Al content of the ash in anthracene

and asphaltene oil

(AAo)

Effect of ash on coal liquefaction yield: M. Oner et al. 100 90 v

60

vb’_ le*

70 t C

vvQ “v*v

v

v

V l

.

.

“,:

60-

:

ve

??

50-

f F

40

-

30

-O

0

00 0

0

a@

0

0

0 O&O. l

0

20

v TCA.0.

0 10

0’

t

0

0

1

2 Yg (g/100

Figure 11 conversion

TSA.0.

3 g organic

4

5

Matter)

Variation of oil (O,,), toluene solubles (TS,,) and total (TC,,) yields with Mg content of ash in anthracene oil

In this study, an examination of the conversion data for all samples studied did not reveal any statistically significant correlations with Na and K content of the ash. This may be due to the relatively low Na and K contents, where any catalytic effect due to these minerals may be masked by variations in the hydrogenation reactivity due to other factors. However, SA and BE lignite samples with high Na and K contents consistently demonstrated relatively high hydrogenation reactivity. The catalytic effects of Na and K on hydrogenation have been reported in the literaturez5 and are exploited in several coal liquefaction processes under development. A considerable proportion of the ash forming constituents are present as cations associated with the carboxylic acid groups in the coal. It was found that sodium associated with carboxyl groups has a beneficial catalytic effect with regard to the quality of the liquid producP. Appell et ~1.‘~have reported alkali metal carbonates as catalysts and have mentioned the alkaline ash content of lignite. Further, the superiority of CO steam compared to hydrogen, in the non-catalytic hydrogenation of lignite, has been attributed again to the catalytic effects of alkali and alkali earth metals present in the coal, which are known to be effective catalysts in the carbon-steam and carbon monoxide-steam reactions2’. A similar inspection of the conversion and yield data shows a tendency to increase with increasing Ca and Mg contents, though the relationship did not reveal any significant correlation with hydrogenation reactivity (see Figure 11). As shown in Figure I I, the yield data obtained in anthracene oil pass through a maximum at about 2.59 g 100 gg’ Mg content; toluene solubles and total conversion tend to be constant at higher Mg contents, whereas oil yield drops somewhat at 5 g 100 gg ’ Mg content. The preasphaltene and asphaltene contents of the liquid product decrease with increasing Mg content, although the points lie somewhat scattered around the line (see Figure 12).

In general, the conversion and yield data obtained by using anthracene, creosote and vacuum residual oil give stronger relations with ash and ash constituents than do tetralin data. These differences may be explicable in terms of the different levels of inherent inorganic constituents which may catalyse the transfer of hydrogen to the coal to give a consistently higher relationship, while this mechanism may contribute less to conversion and yield data when tetralin is used as solvent. It is known that either molecular hydrogen or hydrogen donor species must be available to transfer hydrogen to the coal for liquefaction processes. A direct relationship exists between the degree of dissolution and hydrogen transfer, i.e. the more hydrogen transferred, the greater the liquefaction. Coal mineral matter most likely cannot directly catalyse hydrogen transfer to coal, either from molecular hydrogen dissolved in the carrier solvent or from hydrogen donor species. The catalytic effect of inorganic constituents of coal has been attributed to in situ hydrogenation of the liquefaction solvent, resulting in enhanced hydrogen transfer to the dissolving coal. Coal minerals have been reported to catalyse hydrogenation of creosote oil and anthracene oil, resulting in enhanced hydrogen transfer capacity of the solvent23. It has been shown that under thermal iiquefaction conditions, tetralin is not produced by the hydrogenation of naphthalene26. That is, once the donor capacity is exhausted the tetralin must be externally regenerated and is not replenished by in situ mineral matter catalysis. Derbyshire et ~1.~~ found that a three-ring compound like phenanthrene can be hydrogenated to some extent by the catalytic effect of ash in liquefaction reactions. They have also found that both dihydropyrene concentration and conversion correlated directly with the coal ash content. It is known that anthracene, creosote and vacuum residual oils contain the above-mentioned polyaromatic compounds. Therefore, the catalytic effect of ash is more pronounced than tetralin under these experimental conditions.

Mg (g/100

g organic

matter)

Figure 12 Variation of preasphaltene (PA,,) and asphaltene yields with Mg content of ash in anthracene oil

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(AAo)

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Effect of ash on coal liquefaction Table 3

Results ofmultiple

r’Pi Solvent = AO; tiAo = Fe - 66.76 Al Mg -111.51 Ca 2.02 K Na

442.03

analysis for oil yield (0, % daf)

Yt

82.94; Rtio = 0.9963; SEOE = 2.26 0.9463 14.59 0.9576 -0.75 -2.16 0.9433 0.11 0.9463 62.15 0.9046 - 8.73 0.8489 _ _ 0.9689

-

Solvent = CO; mco = Fe -25.87 Al -16.73 Mg -90.12 Ca 5.78 K 445.93 Na - 16.72

regression

yield: M. Oner et al.

-345.57 30.34

0.9831 0.9049

75.08 - 10.77

59.38; RtSo = 0.9951; SEOE =2.00 0.8704 6.70 0.9202 -0.30 0.9711 _ 0.03 0.9580 16.04 0.9567 0.9046 -0.37 0.7900 ~ 0.9770 -277.05 0.9771 46.38 0.9522 _ _

Solvent = TET; aTET= 109.77; Rt&, =0.9862; SEOE Fe -64.31 0.9321 12.48 0.9347 Al 16.73 0.8024 - 3.64 0.8982 Mg -94.66 0.9341 16.04 0.9288 Ca 10.56 0.9522 -0.72 0.9195 K 202.44 0.8989 - 121.98 0.8795 Na _ _ _ Solvent = VR; txvR= Fe 25.59 Al - 12.27 Mg -54.93 Ca -30.33 K 147.60 Na 63.12

Table 4 Results (TC, % daf)

= 2.47 -0.57 0.15 21.13 _

52.89; R& = l.oooO; SEOE =0.08 0.9999 - 2.50 0.9995 0.08 0.9999 0.47 0.9999 0.9999 _ 0.98 1.0000 7.49 1.0000 -0.41 0.9997 - 146.86 0.9999 37.98 1.0000 -12.17 1.0000 -

of multiple

regression

analysis

Solvent = AO; aAO = 51.46; Rt:,=0.9947; Fe 7.30 0.9711 -0.68 Al 8.71 0.9375 - 1.07 Mg - 15.69 0.5911 28.07 Ca -7.18 0.7802 2.78 K _ _ Na 5.34 0.6168 -

SEOE= 0.9598 0.9171 0.8847 0.9058 _

Solvent = CO; ace = 38.09; RtSo = 0.9864; Fe 14.57 0.8552 1.34 Al 4.79 0.6993 Mg 19.31 Ca _ 1.24 K -49.97 0.5099 Na - 60.28 0.8356 57.27

SEOE = 2.50 0.6896 _ -0.01 0.4990 - 4.03 0.9282 -0.11 _ 7.58 0.7856 - 12.70

0.9678 0.9500 0.8598 _ 0.9851 0.9243 0.9171 0.9608 _ _ 0.9732

0.9343 0.9068

_ 0.8425

0.9991 0.9997 0.9999 0.9999

_

0.03 - 4.96 -0.23

0.8589 0.9064 0.9365

- 1.95

0.9373

_

0.8704 0.5113 0.8996 0.5363 0.7728 0.9871 0.9850 0.9738 0.9949 0.9969 _

Solvent = VR; avR= Fe 64.80 Al -20.27 Mg -20.86 -48.73 53.86

59.81; R&=0.9995; 0.9948 - 9.67 0.9773 2.51 0.9950 -

SEOE = 1.01 0.9930 0.42 0.9710 - 0.09 _ _

0.9923 0.9720 _

0.9975 _ 0.9953

0.9980 0.9667 0.9960

0.9979 0.9676 _

12.77 -21.09 -13.32

-0.81 8.81 -

The effects of individual minerals were not easily assessed as noted above. This was primarily due to the fact that the individual ash constituents were highly cross-correlated, therefore they could not be independently varied. It is not possible to select coals in

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Fuel 1994 Volume 73 Number 10

BiXi+

~ i=l

yiXi2+

~ i=l

6,X?

where y is a dependent variable (values of 0, TS, THFS and TC); x is the independent variable (values of Fe, Al, Mg, Ca, Na and K content of ash); and tlO,Bi, yi and 6i are constant values obtained by regression. The application of multiple regression analysis consists of solving the set of equations, as a result of which one finds the regression coefficients and the constants. Rt2 is the square of the multiple correlation coefficient, i.e. variance explained; r& rt and ri are the square of partial correlation coefficients for introduction of each property. The regression coefficients Rt2, r2 and standard error of estimate (SEOE, i.e. the standard deviation of the actual conversion and yield data about the regression line) obtained are given in Tables 3-6. Thus, the equation in Fe, Fe2 and Fe3 alone explained 94.63, 95.76 and 96.78% of the variance, respectively, and use of all other

Table 5 Results (TS, % daf)

of multiple

regression

analysis

for toluene

solubles

_

Solvent =TET; aTET= 96.73; Rt$,, =0.9995; SEOE = 0.32 Fe -0.17 0.9674 0.016 Al 6.97 0.9903 - 0.74 0.9905 0.02 Mg -3.64 0.8137 6.61 0.9687 - 1.16 Ca -4.71 0.9833 1.75 0.9927 0.14 K -96.67 0.9953 83.01 0.9965 - 18.98 Na _ -0.79 0.9565 -

Ca K Na

y=Cr,+ ~ i=l

for total conversion

1.50 -

which only one mineral varied while the others remained constant. It must be emphasized that proper regression analysis requires the widest possible range of independent variables. It is important to realize, therefore, that the multiple regression analyses can, at best, suggest specific mineral effects. The multiple regression analysis was employed, and the Microstat Statistical Package Program was used for this purpose. This program performs multiple linear regression, including as independent variables percentages of Fe, Al, Mg, Ca, Na and K in ash. The dependent variables in this regression are the per cent conversion (TC), oil (0), toluene solubles (TS) and tetrahydrofuran solubles (THFS). The data are readily adaptable to multiple regression, where the model to be fitted is:

Solvent = AO; G(,,,~= 45.84; Rt:,=0.9999; Fe _ 0.31 Al 10.79 0.9990 - 1.58 Mg - 37.41 0.9977 44.92 Ca - 12.90 0.9985 4.47 K 43.00 0.9969 - 16.79 Na 24.06 0.9975 - 13.92

SEOE =0.26 0.9953 - 0.036 0.9993 0.05 0.9989 - 7.43 0.9993 -0.36 0.9973 0.9990 -

0.9982 0.9990 0.9989 0.9995

Solvent = CO; ace = 45.81; RtSo = 0.9987; SEOE = 1.03 Fe 8.80 0.9962 _ - 0.086 Al _ _ _ Mg - SO.46 0.9725 58.21 0.9845 - 9.86 Ca - 5.23 0.8202 2.61 0.9515 -0.22 K -54.59 0.9559 -71.54 0.9827 20.83 Na - 63.45 0.9859 64.12 0.9938 - 15.50

0.9861 0.9697 0.9891 0.9960

Solvent = TET; aTET= 82.89; Rt&, = 0.9996; SEOE = 0.44 _ Fe _ _ 0.023 Al 7.13 0.9894 - 1.00 0.9926 0.03 Mg - 5.00 0.7357 -9.19 0.9309 1.84 Ca - 6.93 0.9841 2.24 0.9907 -0.16 K - 42.98 0.9679 45.97 0.9844 -11.72 Na - 9.47 0.9567 4.63 0.9765 -

0.9920 0.9906 0.9546 0.9912 0.9887 _

Solvent = VR; avR = Fe 66.78 Al -23.73 Mg - 13.70 Ca - 53.77 K Na

83.20

0.9956

46.74; Rt& =0.9811; 0.8337 - 10.63 0.6063 3.17 0.8329 0.9167 14.09 _

SEOE = 5.50 0.7947 0.49 0.5821 -0.13 _ _

0.7878 0.6089 _

0.9320 _

0.9325 _

0.7413

0.6356

- 46.46

-0.91 _ 6.70

0.5101

Effect of ash on coal liquefaction Table 6 Results (THFS, % daf) i

of multiple

Pi

r’B,

regression

analysis

for THF

Solvent =CO; a,o=51.51; Rrfo=0.9984; Fe 8.59 0.9960 _ Al Mg -44.38 0.9639 52.19 Ca -7.94 0.9112 2.92 K 60.37 0.9628 - 76.88 Na - 63.07 0.9853 63.18

SEOE = 1.96 0.9697 -0.73 0.9720 0.23 0.9641 ~ 0.9543 0.9793 29.14 0.9389 3.22 SEOE= _ _ 0.9804 0.9599 0.9846 0.9935

Solvent = VR; xva = 48.05; Rt& =0.9867; Fe 65.12 0.8636 - 10.18 Al -21.08 0.6173 2.68 Mg - 15.25 0.8914 - 54.95 -

0.9385 _

Na

84.29

0.7962

14.47

0.9596 0.8954

0.09

0.9954 _

- 8.89 -0.23 22.47 - 15.06

0.9825 0.9712 0.9904 0.9957

0.9505

_

_

_

SEOE =4.77 0.8251 0.47 0.5698 -0.11 _ -0.94

0.6782

5.99

REFERENCES 1

2

0.9892 0.995 1 0.9682 0.9926

0.8182 0.5964 0.9511

_ -44.32

ACKNOWLEDGEMENTS

0.9698 0.9737

1.04

Solvent = TET; aTtT = 89.70; Rt&, = 0.9998; SEOE = 0.43 Fe _ 0.07 0.8770 0.02 Al 6.89 0.99 14 - 1.01 0.9955 0.03 Mg -8.71 0.942 1 - 7.09 0.9435 1.56 Ca - 10.05 0.9964 2.74 0.9979 -0.18 K - 34.55 0.9687 41.98 0.9882 -11.41 Na - 8.69 0.9750 4.00 0.9849 -

et al.

We appreciate the support of Volkswagen Stiftung (Project No. I/61628) and YUAF (Project No. 91-B-0408-10) for the accomplishment of this work.

Yi

Solvent = AO; aAo = 110.52; R&,=0.9969; Fe - 84.67 0.9670 16.46 Al 22.56 0.9443 - 5.56 Mg - 90.32 0.9621 18.16 CL 8.27 0.9566 -0.91 K 424.35 0.9818 - 223.64 Na _ - 18.21

Ca K

solubles

yield: M. Oner

0.5246

constituents (i.e. Al, Mg, Ca, K and Na) explained 99.63% of the variance when anthracene oil was used as solvent. When the same operations were performed for the tetralin data, the Fe, Fe2 and Fe3 alone explained 93.21, 93.47 and 93.43% of the variance, respectively, but the effect of Na was not observed as shown in Table 3. The only inference one can draw is that the role of Na becomes less important when tetralin is used as solvent. An increase in credibility of the equations was attained by using six variables, yielding a reduced standard error of the estimate to 0.08, and the variance explained increased to 1.000 for oil yields using vacuum residue as the solvent. Inspection of the regression results in Tables 3-6 indicates that Fe, Al, Mg and Ca in the model contribute more significantly to the variance of the liquefaction data than either Na or K.

11 12 13

I4 15 16 17 18 I9 20 21

22 23

24 25 26

CONCLUSIONS The batch reactor liquefaction experiments have been completed using 16 Turkish lignites, two asphaltites and four different solvents, namely tetralin, anthracene, creosote and vacuum residual oils. It was found that the ash content of the lignite has an influence on liquefaction yields. Application of the simple and multiple linear regression analysis showed that the lignite ash and ash constituents, such as Fe, Al, Ca, Mg, Na and K contents, appear to correlate well with total conversion and liquid yield data for four different solvents. It should be recognized that the results presented in this paper are based on a representative number of Turkish lignites. Further work involving additional lignites would be required to confirm and extend the trends presented here.

Kang, C. C. and Johanson, E. C. in ‘Liquid Fuels from Coal’ (Ed. R. T. Ellington), Academic Press, New York, 1977, pp. 899101 Tarrer, A. R., Guin, J. A., Pitts, W. S., Henley, J. P., Prather. J. W. and Stvles. G. A. in ‘Liauid Fuels from Coals’ (Ed. R. T. Ellington), Academic Press, New York, 1977, pp. 45-61 Given, P. H., Cronauer, D. C., Spackman, W., Lowell, H. L., Davis, A. and Biswas, B. Fuel 1975, 54, 34 Given, P. H., Cronauer, D. C., Spackman, W., Lowell, H. L., Davis, A. and Biswas, B. Fuel 1975, 54,40 Mukherjee, D. K. and Mitra, J. R. Fuel 1984, 63, 722 Wright, C. H. and Severson, D. E. Am. Chem. Sot. Div. Fuel Chem., Prepr. 1972, 16, 68 Gangwer, T. E. and Prasad, H. Fuel 1979, 58, 577 Brooks, D. G., Guin, J. A., Curtis, C. W. and Placek, T. D. Ind. Eng. Chem. Process Des. Dev. 1983, 22 (3), 343 Thomas, M. G., Granoff, B., Noles, G. T. and Boca, P. M. Am. Chem. Sot. Div. Fuel Chem., Prepr. 1978, 23, 42 Mazzocco, N. J., Klunder, E. B. and Krastman, D. Report No. DOE/PETC/TR-81/l, Pittsburgh Eng. Tech. Center, Pittsburgh, PA, March 1981 Walker, P. L., Shelef, M. and Anderson, P. A. Chem. Phys. Carbon 1968, 4, 287 Marsh, H. and Adair, R. R. Carbon 1975, 13, 327 Dincer, S., Bolat, E., Oner, M. and Yalin, G. ‘Liquefaction of Turkish Lignites’, Volkswagen Stiftung Project No. I/61628, Annual Report, 1990 Oner, M., Bolat, E. and Dincer, S. Energy Sources 1990,12,407 Oner, M., Bolat, E. and Dincer, S. Energy Sources 1992,14,81 Bolat, E., Oner, M., Yalin, G. and Dincer. S. Fuel Sci. Tech&. Int. 1992, 10 (3), 371 Bolat, E., Kavlak, C., Yalin, G. and Dincer, S. Fuel Process Technol. 1992,31, 55 Abdel-Baset, M. B., Yarzab, R. G. and Given, P. H. Fuel 1978, 51, 89 Garr, G. T., Lytle, J. M. and Wood, R. E. Fuel Process Technol. 1979,2, 179 Yarzab, R. F., Given, P. H., Spackman, W. and Davis, A. Fuel 1980, 59, 81 Mori, K., Tariuchi, M., Kawashima, A., Okuma, 0. and Takahashi, T. in ‘Coal Liquefaction Fundamentals’ (Ed. D. D. Whitehurst), Am. Chem. Sot. Symposium Series Vol. 139, American Chemical Society, Washington, DC, 1980, pp. 75-96 Peel, R. B., Diaz, J. S. and Luengo, C. A. Fuel 1979, 58, 298 Tarrer, A. R., Guin, J. A., Pitts, W. S., Henley, J. P., Prather, J. W. and Styles, G. A. Am. Chem. Sot. Div. Fuel Chem., Prepr. 1976, 21 (5), 59 Kamiya, Y., Nagae, S. and Oikawa, S. Fuel 1983, 62, 31 Appell, H. R., Wender, I. and Miller, R. D. Am. Chem. Sot. Div. Fuel Chem., Prepr. 1969, 13 (4), 39 Derbyshire, F. J., Varghese, P. and Whitehurst, D. D. in ‘International Conference on Coal Science’, Dusseldorf, September 1981, Verlag Gliickauf GmbH, Essen, 1981, pp. 356-361

NOMENCLATURE A A0 BE BS CA CH co daf db EL FC

Asphaltene Anthracene oil Beypazari Beysehir Can Cayirhan Creosote oil Dry ash free Dry basis Elbistan Fixed carbon

Fuel 1994

Volume

73 Number

10

1665

Effect of ash on coal liquefaction yield: M. Oner et al. G GO

Gas

HC IL KE KN KR 0 OR PA r2 R Rt2 St

Goynuk Hydrogen consumption Ilgin Keles Kangal Karliova Oil Orhaneli Preasphaltene Square of the partial correlation coefficient Residue Square of the multiple correlation coefficient Total sulfur

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Fuel 1994 Volume 73 Number 10

SA SE SEOE SL so SR TC TET THFS TS TU VM VR YA

Saray Seyitomer Standard error of estimation Silopi Soma Sirnak Total conversion Tetralin Tetrahydrofuran solubles Toluene solubles Tuncbilek Volatile matter Vacuum residual oil Yatagan