Coal softening route to binder pitch for carbon electrodes

Short Communications

Coal softening

route

to binder

pitch

for carbon

electrodes

S. R. Richards, K. T. Tran and D. A. Abbenes Industrial Processing Division, D.S.I.R., (Received 28 November 1988)

PO Box 31-310,

Lower

Hutt,

New

Zealand

New Zealand Buller coal has been found to behave like a very hard coal-tar pitch and solvent refined coal. Autoclave treatments of Buller coal/solvent mixtures at around 360°C and moderate pressures beyond about 1 MPa have shown that the coal can be homogeneously softened (without hydrogenation) from its natural softening point range of 35@4OO”C to any desired softening point, depending upon the solvent type, the coal:solvent ratio and the autoclaving conditions. It is suggested that pitches synthesized from this low-ash coal could be substituted for traditional pitches used in metallurgical electrode manufacture. Further laboratory work to test the synthetic pitches in carbon anode preparation and consumption is planned. (Keywords: pitch; ash; coal)

In the early 1980s Sheat’ demonstrated that the ash in high volatile, bituminous Buller coal was discrete and could be lowered to less than 0.2 % by laboratory sink/float separations. This led to an investigation into the production of anode carbon for aluminium smelting’, which concluded that, at that time (198384), there was little likelihood of a cost saving over petroleum coke. However, some spin-off ideas which arose from the were worthy of follow-up, study especially in view of the aluminium industry’s open-minded attitude to sources of carbon-based materials for electrode manufacture. Two related research extensions were pursued: one involved continued research into the conversion of Buller coal into dense coke3 and the other is the subject of this the potential for namely, paper, converting Buller coal into a substitute coal-tar pitch. The present work was based on the idea that low-ash Buller coal could be considered to be a very hard coal-tar pitch. Later on it was compared with solvent refined coal (SRC). Work done by the National Coal Board during the anode carbon investigation2, showed that Buller coal was readily dissolved in recycle oil solvent under their normal SRC production conditions (coal:solvent ratio 1:3, 2MPa, 400°C). Thus it was considered worthwhile to investigate the conditions required to soften Buller coal to the range of binder pitches. 00162361/89/030391-06$3.00 0 1989 Butterworth & Co.

(Publishers) Ltd

Since 1980 more than one million tonnes of Buller coal (Webb/Stockton blend) have been exported to Japan, ostensibly for blending with other coals for the production of metallurgical coke. From Table 1 it can be seen that the chemical analysis of selectively-mined and/or washed Buller coal is similar to that of solvent relined coal, and as such could be considered for higher-valued carbon products than blast furnace coke. As a replacement for petroleum coke in aluminium anode manufacture Buller coal coke would have to be made from cleaned coal to maintain the silicon and iron levels acceptably low. Fricker and Minehan have demonstrated’ that a 0.70% ash feed coal can be upgraded by conventional industrial washing techniques to a 0.25% ash coal. An anode coke made from this coal would just meet the specified iron and silicon levels (500 ppm) for petroleum coke. Vanadium levels would be much lower than (the typical 250 ppm) in petroleum coke, since vanadium levels in the coal ranged from 0.1 to 20ppm’. This investigation involved treating finely ground Buller coal with various commercially available coal-derived liquids under a range of test conditions and testing the physical properties of the resulting synthetic pitches. The primary screening parameter used was softening point as measured by the ring and ball method9 or by a hot stage melting point apparatus. The specifications for various

electrode binder pitches are given in Table 2. These were taken as guidelines in this study.

EXPERIMENTAL Materials

The coal used in this study was from the Webb opencast mine. It was milled to pass 3.2 mm mesh and stored in a sealed plastic bag, when surface oxidation may have occurred. Gieseler fluidity measurements on Webb coal” have shown a strong tendency of weathering/oxidation to reduce fluidity. However, no such influence on its solubility or softening behaviour was evident over the duration of this work. The < 1 y0 ash coal was air dried at the -3.2mm particle size and ground io pass 150pm mesh just prior to softening treatment.

Figure 1 Autoclave arrangement for coal softenink e^periments

FUEL, 1989, Vol 68, March

391

Short Communications Table 1

Properties of Webb coal, solvent refined coal and Koppers pitch Low-ash Webb coal

Proximate analysis (air-dried basis) Moisture, % Ash, % Sulphur, %

1.0

O.l-> 10

1.0

0.5-7

34.8

Fixed carbon, %

64.0

Specific energy, MJ kg-’

34.9 9-9+ +

85.0

Koppers pitchb

0.4

0.29

0.34

0.28

1.03

29-36

9+

Ultimate analysis, (ash-free basis) Carbon, %

SRC”

l-2

0.2

Volatile matter, %

Swelling number

Buller coal ranges“

0.44

43.6

53.2

55.7

46.2

36.7

_

37.0 _

S&mid5 87.6

93.3 4.08

Hydrogen, %

5.4

5.6

Nitrogen, %

1.3

2.2

1.17

Sulphur, %

1.0

0.6

0.44

Oxygen, % (by difference)

6.4

3.8

1.02

Ash constituents Si02, %

2045

27.8

A&O,, % b03, %

2&45 140

1.1

CaO, % Na,O, % K,O, %

l-9 0.2-9 0.5-3.5 l-10

Ti02, %

0.02-2.2

P,Os, % SOB, % Petrographic analysis6 Vitrinite, ~01%

93

Exinite, ~01%

4

Inertinite, ~01%

3

Reflectance, Rm,

1.05

“This work, sample supplied by Reynolds Metals Company, Alabama *This work, sample supplied by Comalco Research Centre. Melbourne

High and low temperature tars and creosotes were tested as softeners. Table 3 lists the coal liquids used in this work, which included tars and creosotes from subbituminous and bituminous coals. Apparatus

The synthetic pitches were prepared in a 500ml Parr Instrument Company Type 4022 rocking autoclave. The general arrangement is presented schematically in Figure 1. Procedure

Preparations were carried out on two scales: 50-1OOg batches of mixtures of coal/solvent (referred to as macro-scale) and < 1 g batches of mixtures (referred to as micro-scale). Up to 11 Pyrex test tubes containing various coal/solvent mixtures could be tested simultaneously in the micro runs. A weighed amount of ground coal (about 2@4Og) was premixed with the chosen solvent in a predetermined ratio between 1:3 and 1 :l. coal:solvent.

392

FUEL,

1989,

Vol 68, Mimh

The mixture was transferred to the autoclave, which was then assembled, placed in the heater and connected to the gas control system (Figure 1). The autoclave was evacuated to remove air and then pressurized to about half the final pressure with nitrogen from a gas cylinder. The heater was switched on and temperatures and time were recorded on a chart recorder. As the autoclave heated up, excess pressure was bled off until the temperature stabilized. Timing of a run commenced when the operating temperature was reached. After the time allotted, the autoclave was cooled before releasing the pressure and opening. The contents were either chipped or scraped out of the autoclave and stored in sealed glass bottles ready for testing. Testing

The pitches produced were routinely examined by determining their softening and/or melting points. The ring and ball method’ was used for the macro runs,

while a Reichert hot stage melting point apparatus (HSMPA) was used for the micro runs. Figure 2 correlates HSMPA softening and melting against the ring and ball method. Other tests performed on selected samples included toluene insolubles (TI), quinoline insolubles (QI),

J

I”

Ring & ball softening

point, “C

Figure 2 Coal softening measurement: calibration melting point of hot-stage apparatus versus ring and ball method

Short Communications Table 2

Specifications

for electrode

binder

pitches Aluminium

Property Softening Coking

point,

“C

residue/value,

Benzene (toluene), Quinoline Alpha

% min

insolubles,

insolubles,

resin,

% min

Pechiney”

Comalco’2

80 f 2 (K-S)6

90+2

1088112 (Cube in air)

65 f 5 (K-S)”

42

45

55565

36

28

30

30

20

Beta resin, % max Water content, ?< max

Iron,

0.3

0.3

6

20 0.05

0.3

0.75 0.3

0.3

viscosity,

0.05 1.32 (15°C)

1.25 (20°C)

CP

at 140°C

5500

at 160°C

1000

at 180°C

300

Distillate,

16.5

0.05

% max

Silicon, % max Real density, kg dme3 Dynamic

CP-13

20

0.3

Sulphur content, y/, max Ash content, ‘Z/,max

(K-S)6

8815

20

7; max

Other electrode uses Impregnation of graphite”

anodes

Soderberg’i

10

y< max

smelting Prebaked

‘:/, max 0

Amb.~270”C 27s300°C 309360°C

4

Amb.-360°C

5

’ Determined bDetermined

Table 3

4.0

by Kraemer-Sarnow method, which gives results about 10°C lower than ring and ball method’ by cube in air method, which gives results similar to the ring and ball methodI

Coal-derived

solvents

tested as coal softeners

Code

Solvent

Parent

coal

Source _

Low temperature

tar

WT

Waikato

subbituminous

Low temperature

creosote

WC

Waikato

subbituminous

IT

Liverpool

KT

Coking

blend, bituminous

Koppers tar, probably BHP Steelworks

KC

Coking

blend. bituminous

Koppers Austrlia Pty. Ltd Distillation of KT

Gasworks

tar

Cokeovens

tar

High temperature

creosote

bituminous

210

.i

190

.r 5E

170

z

130

150

KT

Ltd

Distillation

of WT

Invercargill

Gas Co. Ltd ex

370” a sharp increase in softening temperature occurred, brought on, perhaps, by the development of condensation reactions during incipient coking. This view is strengthened by the appearance of discrete particles which remained unmelted and undissolved at the end of the melting point tests for the higher temperature runs. Most runs were conducted at around 355”C, which appeared to be about the optimum for Webb coal. Effect of pressure Figure 4 illustrates the effect of pressure on coal softening. Because the effect of

;g

a 110 c” 330 ._

n

blend

Carbonisation

determinations of moisture, ash, real density, Conradson coking value and distillate to 360°C. Several macro-scale thermopitches were analysed gravimetrically (TGA) in a nitrogen atmosphere to obtain weight loss versus temperature data, distillates up to 360°C and coking residues. Some pitch ashes were analysed for iron and silicon.

0

“;

Waikato

3

RESULTS

=\ 350

370

Run temperature,

390

410

“C

Figure 3 Webb coal softening: ring and ball softening point versus run temperature

Effect of temperature Figure 3 shows the shortness of the workable range of process temperatures, about 340-380°C. Below 340°C solvent action was sluggish and incomplete, leaving undissolved coal. Above

_.

c

n

0

2

4

6

8

10

12

Pressure, MPa

Figure 4 Webb coal softening: softening point versus pressure

ring and ball

FUEL, 1989, Vol 68, March

333

Short Communications Coal:KT=l:Z /

or perhaps volatile solvent losses from the mixtures due to condensation on the cooler part of the autoclave. Effect of solvent type and coaksolvent ratio

100 80

’ ’ 0.0 0.4

0.8

1.2

1.6

2.0

2.4

Run time, (h)

Figure 5 Webb coal softening: trends of time at temperature

pressure on softening was much reduced above 0.5 MPa, some dependences of softening behaviour on other parameters have been examined, including data obtained over a range of pressures (210 MPa). ESfect of time Figure 5 depicts the change in softening

high with time, using behaviour temperature creosote as an example. Other conditions were coal:solvent ratio 1:2, 355°C and 7MPa. Presumably the decreasing softening points up to about one hour resulted from increasing solvolysis up to that time, and the increases after that time resulted from opposing effects, such as polymerization

The chemical nature of the coalderived solvent was very important. Low temperature carbonization coal tar (WT) and creosote (WC) from subbituminous coal showed no sign of softening Webb coal at all. On the other hand, high temperature carbonization coal liquids from bituminous coals showed good softening abilities. Figure 6 demonstrates the effects of solvent type (different methods of production and different boiling fractions from one carbonization method). The greater softening of Webb coal achieved by high temperature creosote than by its parent tar suggests that lower molecular weight polynuclear aromatic compounds may be the more effective agents in coal

20

0.3

I

’

’

’

’

’

L -

0.4 0.5 0.6 0.7 Coal:solvent ratio Figure 6 Webb coal softening: ring and ball softening point versus ratio

Koppers and Kyowa pitches do not lose > 20% volatiles up to 36O”C,cf. 4% max. specified). DISCUSSION Related processes and materials Jastrzebski and others”*‘2m14(and J. C. Nixon, 1983; J. T. Keniry, 1987, private communications) have described the properties as they relate to electrode the factors affecting tar and pitch properties as they related to electrode manufacture. Pitch production includes refining and/or modifying processes to meet specifications for particular end uses, such as Soderberg electrode paste, pre-baked carbon anodes, cathodes or impregnation pitches for improving

softening. Some test results Table 4 displays some typical test results. Two points worth noting, perhaps, are the decrease in quinoline insolubles with decreasing pressure, and the thermogravimetric method of establishing a distillation curve appears to give a different result from liquid-vapour distillations (assuming equilibria

Comparison between coal-tar pitches and synthetic pitches

Table 4

Synthetic pitches Property

Run 37 Run 63 Run 66 Run 62 Run 50 Run 68 Run 59 Run 57

Koppers Kyowa Run 54 pitch pitchd

Comalco spec. CP- 13

Softening point, “C (R and B) 107

117

163

125

137

180

130

144

175

97

104

108-l 12

30.3

32.0

31.1

31.2

42.0

45.0

31.0

28.1

44.3

21.3

22.3

30 min.

Quinoline insolubles (QI), % 12.3

6.7

6.1

21.3

7.1

2.3

12.1

11.0

7.1

18.1

13.3

16.5 max.

Beta resin (TI-QI), %

18.0

25.3

25.0

15.9

34.3

42.1

18.3

11.1

36.7

2.1

9.0

20 min.

Water, %

0.22

0.52

0.32

0.20

0.20

0.16

0.24

0.21

0.19

0.14

0.20

0.05 max.

Toluene insolubles (Tl), %

Sulphur, %

<0.5

< 0.5

<0.5

< 0.5

< 0.5

(0.5

< 0.5

<0.5

< 0.5

0.44

Ash, %

0.51

0.18

0.11

0.45

0.44

0.60

0.59

0.44

0.78

0.24

0.13

Iron (Fe), %

0.001

0.001

0.01

0.008

0.009

0.006

0.008

0.006

0.008

0.002

0.002

0.05 max.

Silicon (Si), %

0.13

0.20

0.15

0.01

0.07

0.14

0.13

0.09

0.19

0.01

0.03

0.05 max.

Real density, kg dm- 3

1.232

1.205

1.253

1.291

1.309

1.359

1.328

1.279

1.356

1.396

1.295

1.320 min.

48.9

Distillate at 36O”C, %b Coking value (Conradson), Coke residue (TGA), xb

48.3

47.8

21.6

25.2

20.0

26.5

27.1

26.2

20.9

22.4

5.0 max.

41

41.5

54

51

58

54

55

61

61

61

55-65

38

39

39

41

51

52

49

52

49

45

47

KC

KC

KC

KT

KT

KT

IT

IT

IT

J

d

d

d

J

J

J

J

0.2

0.1

10.5

0.2

0.1

10.5

0.4

0.2

Ratio 0.5, temperature 355°C. time 0.5 h J 10.5 Pressure, MPa (absolute)

“Determined by Karl Fischer method bDetermined by thermogravimetric analysis ‘See Table 3 for key to solvents d Sample obtained from University of Auckland Department of Chemical and Materials Engineering

394

0.3 max.

%42.5

Run conditions Solvent’

0.75 max.

FUEL, 1989, Vol 68, March

Short Communications density and electrical properties in graphites. Pitch treatments are aimed at adjusting softening point, softening range, volatile components and introducing structure or conductivity enhancers, such as mesophase precursors. They mainly involve thermal treatments between 350 and 5oa”C in vertical reactors under pressure for periods of up to 40h to harden the pitch. Sometimes air or steam blowing is used when oxidation and gas-scrubbing can achieve hardening while still keeping other parameters within specification. Of greater similarity with this present work are the softenmg of hard pitch with a coalderived oil/creosote of boiling point 250°C or higherI and certain stages of the SRC process’. Both processes straight-forward polymeric involve solute/solvent plasticising treatments, but in the SRC process hydrogen pressure adds a further depolymerizing influence through the hydrogenation of doublebonded carbon and sulphur, nitrogen and oxygen The similarity atoms. between the SRC and coal softening processes stops at the initial dissolution stage, cf. Tuble 5. However, the similarity does raise the question: could SRC be used as a coke binder in electrode manufacture? The probable answer is yes, as it, too, could be modified just as we have done with Buller coal. Schmid’ gives the range of fusion points of typical SRCs as 149-204°C and a single using an experiment we did SRC:Koppers tar ratio of 0.67, 355”C, and 7 MPa for 0.5 h, resulted in a pitch with a ring and ball softening point of 7l”C, lower than could be achieved using Webb coal and the same conditions. Thus, the technology for synthesizing electrode pitches from Buller coal could be adapted from SRC technologies, but because of the extremely low ash levels in washed Buller coal, the coal solution (presumed to be liquid under preparative conditions) wouid not have to be filtered. The filtration step in the SRC process is troublesome and is therefore to be avoided, if possible. Improvements in synthetic pitch quality may be attainable conditions under hydrogenation (Including hydrogen donor solvents), but present indications are that the extra cost may not be necessary.

Synthetic

pitch quality

Table 4 compares the ranges of properties obtained with some synthetic pitches against two commercially available binder pitches. The results demonstrate the scope for controlling pitch properties using this type of preparation. Obviously the synthetic pitches fail short of the Comalcu specification for pre-baked anode binder pitch, especially on ash and silicon contents and perhaps on distillate up to

Table 5 Comparison of ranges of operating variables in SRCs and Buller coal softening processes

SRC 42-82 Temperature, “C 7-17.5 Pressure, MPa Coal:solvent ratio, wt:wt 0.33-0.67 Time, h f-1 Gas feed rate, Nm3/ tonne of coal 95c-1900 Hydrogen concentration in feed gas, mol :< 6&95 ---

Coal softening

--

34&380 IL7 0.4-0.6 fl make-up

NZ

360°C. As would be expected, higher distillate figures were obtained for pitches made with creosote as solvent (lower boiling range). However, no attempts were made to modify pitch properties by additional treatments such as those discussed by Jastrzebski et al.’ 3 Some of the test results obtained may not be comparative beyond this study, because they were measured using non-standard methods, e.g., the distillate by TGA. However, TGA has been recently evaluated for the characterization of petroleum bitumenslS and it could be applied to coal pitches as well. TGA gave the following information: 1. 2. 3. 4. 5.

loss of water and volatiles

up to 105°C loss of volatile matter up to 360°C loss of volatiles after 0.5 h at 360°C pyrolysis data to 900°C carbon residue at 900°C.

By changing over to carbon dioxide or air at 9oo”C, reactivity data and ash content could also have been determined. Providmg that representivity is not a problem (in view of the very small sample size required), perhaps TGA could be considered as a cheaper and more efficient way of routinely testing and characterizing pitches for the electrode industries.

Process prospects An industry using local resources to produce a substitute for imported binder pitch would be much-needed in the New Zealand coal industry. This study has shown that in addition to about SOOOtpa of low-ash Biiikr coal, abaut 15000 tpa of high temperature coal tar would be required to satisfy the pitch demand of the local aluminium industry alone. Insufficient quantities of high temperature tars are produced in New Zealand, and, in fact, tar production continues to dwindle as the remaining gasworks close down. Therefore, coal tar would have to be imported, or new capacity for local production installed.

Such local production would lend synergistic support for the development other carbon-based of potential industries, such as electrode carbons, arc furnace electrodes, silicon, ferrosilicon, ferrovanadium, silicon carbide, calcium carbide and smokeless fuel productions, and lead to economies of scale. The concept of importing coal-tar rather than hard coal-tar pitch has the attraction of being cheaper, (about $300 versus about $500 f.o.b./tonne), but the prospects of an overall cheaper synthetic pitch are not clear at this stage. The next phase of development will be to produce sufficient quantities of synthetic pitch to carry out laboratory anode forming, baking and consumption tests. If these are successful, then perhaps that will be the time to look at the economics and how other potential carbon-based industries may be affected.

ACKNOWLEDGEMENTS The senior author (S.R.R.) would like to thank the following people: Mr B. H. Hamilton of IPD for analyses, Dr J. Donbavand of MWD Central Laboratories for TGA and Mr A. G. Urane of Koppers Australia, Mr A. Peattie of Waikato Carbonisation, Mr D. J. Kubrycht of Invercargill Gasworks, Dr N. E. Richards of Reynolds Metals Company and Professor B. J. Welch of the University of Auckland for various samples. Funds in support of this investigation were made available by the New Zealand Ministry of Energy.

REFERENCES Sheat, A. W. Proceedings Chemeca 81, 9th ChrIstchurch, N.Z., 30 Aug.-4 Sept., 1981, pp. 207-214 Marshall. T Anode Carbon Task Force report to Ministers of Energy and Scrence, DSIR Industrial

Processing Division Report No. IPDTTSCI6014. MOE ReDort No. ET/024, Aug. lb83 ’ Smith, M A. and Welch, B. J. 1st Ejennxa? Coal Research Conference, Wellington, 15-17 Oct. 1985, paper 30.1 Gray, V. R. Coal Research Association of New Zealand, Internal report, The Chemical Properties of Buller Coals, 1981 Schmid, B. K. in ‘EncyCIOpedJa of Chemical Processing and Design’, (Ed. J. J. McKetta) Marcel Dekker Inc.. New York, 19i6, pp. 35&86 Black, P. M. NZERDC Report NO. 5 I, 1980 Fricker, A. G. and Minehan. P. J. DSIR Industrial Processing Division, internal intenm report No. 4 to Anode Carbon Task Force, 1983 Gainsford, R. Chemistry

DSIR Analysis Anode Carbon

FUEL,

1989,

Division, Report No. 30/153/l to Task Force, 1983

Vol 68,

March

395

Short Communications 9 10 11 12

ASTM D36-70 Clemens, A. H. and Matheson, T. W. Fuel 1987,66, 1009 Jastrzcbski, J. Freiberger Forschungsheffe A 1980,618, 147 Jastrzebski, J., Bogucki, J. and Skmpel, z. U.N. Economic

Simultaneous

13

Commissions for Europe, Symposium on the Gasification and Liquitication of Coal, Katowice, Poland, 23-27 April

14

1979

15

Jastrzebski, J., Bogucki, J. and Szen, A. Freiberger

A

1980,

Forschungshejie A 1980,618, 97 Donbavand, J. Australian Rood Research Board Proceedings 1984,

12(2), 71

618, 167

desulphurization

Katsuki Kusakabe, Masafumi Koichiro KusunokP

Forschungshefte

Fica, J., Nermanowska, J. and Jastrzebski, J. Freiberger

and demineralization

Orita, Koji Kato, Shigeharu

Morooka,

of coal

Yasuo Kato and

Department of Applied Chemistry, Kyushu University 36, Fukuoka 812, Japan * Department of Chemical Engineering, Kyushu University 36, Fukuoka 872, Japan (Received 8 July 1988)

Pulverized coals were treated in a molten bath of NaOH and KOH at 623 K. Over 90 wt% of the total sulphur and ash was removed in a 1 h reaction but the mass of the molten alkali had to be at least twice the mass of coal. To reduce the amount of alkali, a new reaction method was proposed. Coal particles were coated with alkali by being soaked in an aqueous alkali solution and dried in a vacuum oven, before being heated at 648 K in a nitrogen stream. When the amount of alkali exceeded 20-30 wt % of the initial coal weight, the removal of total sulphur and ash was increased and nearly equal to that obtained by the molten alkali bath method. The loss in gross heating value of coal treated by alkali impregnation was only 2.5 wt % after 2 h reaction at an alkali level of 43 y0 of the initial coal weight.

(Keywords:desulphurization; demineralization; alkali)

Desulphurization and demineralization of coal prior to combustion are important technologies as regards environmental protection. Chemical methods, including partial oxidation, chlorination, hydrodesulphurization, alkali displacement reaction, and microwave heating are effective for advanced coal cleaninglm9, but only the molten alkali method can remove both mineral and organic sulphur. In a previous paper, a high sulphur bituminous coal (Miike, Japan) was treated with molten KOH and NaOH mixtures”. More than 95 wt % of the organic sulphur and mineral matter contained in the coal was removed. The gasification of the coal was not serious under optimum reaction conditions. In the present study, some typical coals were treated in a molten alkali bath, and the effect of coal species on desulphurization and demineralization was studied. Subsequently the reaction method was improved to reduce the amount of alkali used. The effect of the amount of alkali used on the efficiency of removal of sulphur and mineral matter was studied to determine the minimum amount of alkali required. 00162361/89/030396C4S3.00 0 1989 Butterworth & Co. (Publishers) Ltd.

396

FUEL, 1989, Vol 68, March

EXPERIMENTAL Apparatus Alkali

and procedure bath

method. The coals used, Illinois No. 6 (USA), Great Greta (Australia), Santa Catarina (Brazil) and Oldben (Canada), were pulverized to <2OCl~m for the studies. Sodium hydroxide (2wt% moisture) and potassium hydroxide (15 wt y0 moisture) of reagent grade were used without further purification. The water content in the reagents was measured with a thermobalance. The sodium and potassium hydroxide was heated in a nickel crucible equipped with a nickel agitating plate. The temperature was measured with a nickel sheathed chromel-alumel thermocouple. The fraction of potassium hydroxide in the molten bath was 46wt%, and the reaction temperature was kept at 623 K, these conditions being found to be an optimum previouslylo. The alkali (70g) was heated to the desired temperature, pulverized coal (3g) was added and the reaction was continued for 1 h under nitrogen. The reactants were then quenched by immersing the crucible in a

cold water bath. The solidified alkali was dissolved in water, and coal particles were recovered by filtration. The coal particles were washed with hot water and a 1M hydrochloric acid solution and again with hot water. The dehydrated coal was dried for 45 h at 343 K in uacuo. Alkali impregnation method. Coal particles (log) were mixed in an aqueous solution containing a prescribed amount of alkali and stirred overnight at room temperature. After most of the moisture was removed in a rotary evaporator, the coal particles were dried at 343 K in uacuo. Alkali-coated coal samples were also prepared by mixing coal and alkali in

a ball mill under a nitrogen atmosphere. The amount of impregnated alkali was determined by washing the coal sample with a 1M HCI solution and by measuring the Na and K concentration in

the solution by atomic absorption spectrophotometry. The concentration was expressed with respect to the initial coal weight. The KOH fraction in the alkali mixture was fixed at 52 wt %. This value was somewhat higher than the