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ELECTROCHEMICAL IBTERACTIOS OF BEYPAZARI LIGNITEIS STROHG ACIDIC MED1AHaluk Özyörük a , Kadir Pekmez a & Yuda Yürüm aa Department of Chemistry , Hacettepe University , Beytepe, Ankara, 06532, TurkeyPublished online: 16 Jun 2010.

To cite this article: Haluk Özyörük , Kadir Pekmez & Yuda Yürüm (1987) ELECTROCHEMICAL IBTERACTIOS OF BEYPAZARILIGNITE IS STROHG ACIDIC MED1A, Fuel Science and Technology International, 5:6, 677-696, DOI: 10.1080/08843758708915870

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FUEL SCIENCE B TECHNOLOGY INT'L., 5 ( 6 ) , 677-696 (1987)

BLECTRM:HEIICAL IBTERACTIOB OF BEYPAZARI LIGNITE IB STRONG ACIDIC KEDlA

Haluk Bzy6riik. Kadir Pekmez and Yuda Yiirijm

Hacettepe University. Department of Chemistry Beytepe. Ankara 06532

Turkey

ABSTRACT

Beypazari lignite was extracted with acetonitrile and acetonltrilelHCl0~ and electrnchemical hydrogenation of the lignite in acetonitrilelLiCI0, in the Dresence of HC10- was investi~ated. Controlled poten'tial electrolysis experiments were carried out at -0.5 V vs a AalAnCl electrode. Infrared scectra of the - - products were measured and yields of extraction were determined. Extraction yields in acetonitrile and a~etonitrilelHC10~ were 9 and 17.3 Z, respectively. The yield of extractable material did not increased in the electrochemical environment. Acetonitrile extraction produced residual mtter with less hydroxyl groups. Stirring the lignite in acetonitrilelHClOn for 7 hours oxidized both the extract and the residue. The residue seemed to contain less hydroxyl groups than that of the acetonitrile extraction residue and it has new carbonyl and etheric groups that were absent in the original lignite. It was found that the material extracted during electrochemical treatment by acetonitrile/HClOn was hydrogenated and the coal matrix remained intact. As the quantity of HCIOn consumed in electrolysis was increased the armunt of methyl groups in the extract also increased. Higher potentials are probably neccessary to hydrogenate the coal matrix by the electrochemically produced hydrogen atoms.

Copyright 0 1987 by Marcel Dekker. Inc

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OZYORUK, PEKMEZ, AND YURUM

Recently, 6zy6riik and co-workers (1987) concluded

that tetraphenylcyclopentenone could be forned by

direct reduction of tetraphenylcyclopentadienone

<tetracyclone) in acetonitrile < A l i ) , with the

electrolytically produced hydrogen atoms if HClOa was

present in the medium. Cyclopentenone is formed

directly by the attack of hydrogen atoms to

tetracyclone. The similar technique can be applied to

hydrogenate coal extracts and the coal matrix. The aim

of this report is to investigate the interaction of

coal slurries under the electrolytic conditions

described by 6zy6riik et al. 1987. .

Coal is now considered t o contain

a macromolecular structure (Green et al. '1982). which

sbould be depolymerized to smaller parts before it can

be used as a chemical feedstock. Host contemporary

degrading procedures involve combined pyrolysis and

hydrogenation, Blectrochemical methods to hydrogenate

or oxidize the coal ~~!acromolecule m y be advantageous

in 'the requirement of energy and the degradation

reactian can be controlled more efficiently. The idea

of electrochemical coal hydrogenation using ethylene

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE 679

diamine as the solvent and lithium chloride as the

supporting electrolyte was suggested by Sternberg and

co-workers (1963). Dogru and co-workers (1975)

utilizing the same method hydrogenated high

temperature coal tar and found that the intensity of

1450 cm-' band due to asymmetric methylene and methyl

bending vibrations in the infrared spectra of the

products was increased about 100 percent passing

0.5 ampers for 15 hours through the electrochemical

cell. Gasification by using a coal slurry as an anodic

depolarizer has been suggested by Coughlin and

Parooque (1979a. 1979b and 1979~). They found that.

coal was oxidized at the platinum anode in sulphuric

acid solution producing carban dioxide or carbon

monoxide. Recently. Coughlin and Parooque (1982)

reported that after the electrochemical oxidation of

several coals slurried in aqueous sulphuric acid, the

solid residues were enriched in oxygen and depleted in

hydrogen and volatile nmtter content. Potentiostatic

reaction seemed to have lower selectivity for

consumption of volatile matter over fixed carbon than

did galvanostatic reaction. Baldwin and co-workers

(1981) investigated the voltammetric and electrolytic

behaviour of several coal slurries and H-coal liquids

in both aqueous and organic solvents. They found that

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680 OZYORUK, PEKMEZ, AND YURUU

the electroactive species always appeared to consist

largely of material extracted from the coal matrix.

The extract from the aqueous coal slurries contained

significant amounts of iron and oxidation of Fe*' to

Fe3' a s found to be responsible for the anodic

currents at +0.4 V. It was observed that no iron was

extracted by AH. Bertle and co-worker6 (1986) reported

chemical and electrochemical oxidation of coal as

a potential route to coal liquids and other derived

products. They concluded that anodic oxidation, after

preliminary dissolution, at a voltage below that

required for evolution of carbon dioxide avoids the

presence of spent reagent. Anodic decorboxylation of

coal acids to hydrocarbons yielded products with

nolecular mass distribution appropriate for these to

comprise fuel oils or feedstocks for upgrading to

transport fuels.

In the present study the electrochemical

interaction of Beypazari lignite in the presence of

HClO- and AH at a Pt cathode is reported. Products of

the electrolysis were investigated mainly by infrared

spectroscopy. It was observed that meterial extracted

from the coal matrix was hydrogenated while the

residue remained intact in the electrolytic

cnnditions.

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ELECTROCHEHICAL INTERACTION OF BEYPAZARI LIGNITE

Beypazari lignite was used in this study.

Elemental analysis of the lignite is presented in

Table I. Tbe lignite was ground and sieved to -177 pm

(-80 mesh ASTIO and stored under a nitrogen

atmosphere.

HClOn was used as a strong proton donor and LiClO.

was the supporting electrolyte. The purification of AB

are described in Sertel et al. (1986). The

measureloents were carried out under oxygen free

nitrogen atmosphere in a three electrode cell using

a PAR Hodel 173 Potentiostat and Hodel 179 Digital

Coulometer. Exhaustive controlled potential

electrolysis experiments were carried out in a cell

with a Pt macroworking electrode. The counter

electrode was a Pt wire in A 8 / 0 . 1 M tetra n-butyl

ammonium perchlorate (TBAP) separated from the

TABLE I

Elexrental Analysis of Beypazari Lignite

Carbon 64.8 Hydrogen 5 . 1 nitrogen 2 . 0 Sulphur 5 . 1 Oxygen (by diff.) 23.0 Mineral Matter (dry) 3 9 . 7

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682 OZYORUK, PEKHEZ, AND YURUH j

solution under investigation by a G4 sintered glass

disc. The reference electrode consisted of a silver

Chloride coated Ag wire in Ali10.1 I TBAP which was

a160 separated from the electrolysis solution by

a sintered glass disc. Controlled potential

electrolysis experiments were carried out at -0.5 V vs

a Ag/AgCl electrode. The quantity of electrons

transferred to the protons produced by the

dissociation of perchloric acid was determined

coulometrically. The scheme of dissociation and

electrode reactions is as f0110w~.

HClo. + H* + C10.-, in solution

8' + e- + H.. at cathode.

In order to investigate the effects of the

solvents used in the electrochemical system. 40 mg of

lignite was first stirred tosether with 25 m l of AE

for 7 hours. The extract and residue of this

experiment were separated by filtration. AE in the

extract solution was evaporated and the extract was

stored under a nitrogen atmosphere for infrared

spectroscopy. The residue was washed with water at

room temperature to extract the AE retained and dried

at llO°C under a nitrogen atmosphere then weighed to

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE 683

llleasure yield of extraction. In a second blank

experiment 40 mg of lignite was stirred with 25 ml of

AE and 40 millilloles of HClO. for 7 hours which is the

equivalent period for the consumption of the acid if

the electrolytical conditions were applied. The

liquids and residue of this experiment were separated

as described above and their infrared spectra were

measured. In an electrolysis experiment 40 mg lignite,

25 ml AB were stirred with 40 millilloles of HCIOn. The

amount of HClO. was increased to 50. 60 and

00 milliwles in other experiments. Hlectrolysis was

continued until all the acid was consumd. Liquids

obtained after the electrolysis experiments were

separated by filtration. AE present in the extract was

evaporated in an evaporator under a nitrogen

atmosphere. Residual lignite was washed with water

until all of the AB retained was extracted and then

dried in an oven at 100°C under a nitrogen atmosphere

and weighed. Infrared spectra of solid and liquid

products were measured with a Hitachi 270-30 infrared

spectromter with KBr technique. KBr pellets were

prepared by grinding 2.5 mg sample with 200 mg KBr.

Pellets were pressed in an evacuated die at 10 tons

and dried at 100°C for 72 hours under a nitrogen

atmosphere to rewve water.

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OZYORUK, PEKMEZ, AND YURUN

and Ace-

Preatment

The infrared spectrum of Beypazari lignite is

presented in Fig. 1 A . The spectrum is typical for

a low r a d coal. The infrared spectrum has a strong

transmittance in the 3000-3600 cm-' region. This broad

and intense band is attributed to D H bond and is due

to extensive intramolecular hydrogen bonding between

hydroxyl groups and other functional groups existing

within the coal matrix. Some of these functional

groups are very polar and capable of entering into

hydrogen bonding. such polar constituents conti-ibute

greatly to the secondary structure of coal. This is

especially true for low rank coals. The 0-H band may

also be due to intermolecular hydrogen banding between

the material adsorbed and the coal matrix. This

strong background can be reduced by Walkylation

(Liotta, 1979) or by specific extraction that will

take out the polar material rich in hydroxyl

functionalities. The infrared spectrum of the residual

lignite after A H extraction is given in Pig. 1 B . This

spectrum is similar to the one in Fig. 1 A except the

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE

, 7-- , , , - 7 3500 3000 2500 2000 1600 1200 800

WAVENUMBER. crn.1'

FIG. 1. Infrared spectra of A> Beypazari lignite, B) residual lignite after AB extraction. and C) A l l extract.

strong background is highly reduced in this case. It

seemed that after the Al l extraction the residual.

lignite contained relatively low hydroxyl

concentration. The infrared spectrum of the material

extracted by Al l (Fig. 1C) confirms this claim. The

spectrum contained fewer peaks than expected for

an infrared spectrum of a coal product; a very intense

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686 OZYORUK, PEKMEZ, AND YURUM

hydroxyl band near 3500 cm-' and a strong aromatic

ring stretching band at 1600 cm-' (Svehla. 1976).

Absence of other peaks c o m n to a coal product is

quite interesting. The aliphatic absorption near

2950 cm-' seemed to be very weak, but the absorption

in the out-of-plane aromatic substitution range

(900-700 c indicated the presence of s o w

aliphatic groups in the material. The relative

intensities of 3500 cm-' bands due to hydroxyl

functionalities with respect to the intensities of

CHa groups near 2950 cm-' for the original lignite.

residue after AB extraction and AH extract were

63. 41 and 58. respectively. m i l e the hydroxyl

intensities of both original lignite and the extract

were almost identical. intensity of hydroxyl bands in

the infrared spectrum of the residue was reduced about

34 percent after the extraction process. This nay be

a verification to the strong background in the

infrared spectrum of lignites due to intermolecular

hydrogen bonding between the coal matrix and

extractable adsorbed material. All extraction produced

a residue which has less hydroxyl groups than the

original lignite and therefore the strong background

due to 0-8 bands in the infrared spectrum (Fig. 1B)

was extensively reduced.

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE

-,---?- -r 3 i00 3000 2500 2000 1600 ' 1 h 0 ' 8b0 ' 1

WAVENUMBER. cm-'

FIG. 2. Infrared spectra of A ) residue and B) extract obtained after ABlHClOa treatment.

Stirring Beypazari lignite in AH and 40 millimoles

HCIOn for 7 hours oxidized both the extract and

residual lignite. Pig. 2 A presents the infrared

spectrum of the residue obtained after this treatment.

The structure of the residual matter seems to be

different than that of obtained after AB extraction.

It has all the features of an oxidized coal substance;

a shoulder at 1700 cm-' due to carbonyl absorption and

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688 OZYORUK, PEKUEZ, AND YURUM

a band near 1100 cnr' due to etheric oxygen

functionalities (Liotta, 1979; Yiriim. 1987) denotes

the changes occurred in the structure of coal matrix.

The relative intensity of hydroxyl absorption with

respect to alkyl absorption reduced from 41 in the

All residue to 35 in the residue after acid treatment.

The residue after AB/tlCIOn seemed to have less

hydroxyl. groups than that of AB residue and it

contained new carbonyl and extra etheric groups that

were absent in the original lignite and residue after

AB extraction. The main difference in the infrared

spectrum of the extract obtained after AB/HClO-

treatment (Fig. 2 ~ ) from that of the All extract (Fig.

LC) was the presence of stroq 1100 c c ' band due to

etheric groups. Absorption due to carbonyl groups was

absent. It might be expected that carbonyl

functionalities would be observed in this sample.

HClOa is a very strong oxidizing agent. It seemed that

since the oxidation reaction took place in a liquid

medium and the interaction between the acid and

the mterial extracted occurred very fast, besides the

cnrbonyl groups produced in the first step of

the oxidation process etheric groups might also be

formed in the drastic oxidation conditions <Y6riim,

1967). This speculation of course should be checked

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ELECTROCHEMICAL INTERACTION O F BEYPAZARI L I G N I T E 689

with molecular weight determinations because ether

groups produced would probably be bridging groups

between primary raterial extracted and thus the

extract after AB/HClOn treatment should be of higher

molecular weight. Ve observed carbonyl functionalities

in the residue after the acid treatment. This was due

to the oxidative effect of HC10a on the coal matrix by

a liquid-solid interaction. Because of the resistance

to mass transfer in a liquid-solid interaction the

oxidation reactions would be expected to proceed more

slowly than those occurring io a liquid =dium.

Carbonyl groups produced on the coal surface were not

further oxidized and therefore bridging etheric groups

might not be produced due to steric and mass transfer

limitations.

In Fig. 3 and Fig. 4 the infrared spectra of the

residual material and extracts, respectively,

obtained after electrolysis are presented. The basis

of the present work depended on the use of

electrochemically nascent hydrogen atoms produced

in the cathode compartment of the electrolysis cell in

the hydrogenation of the coal itself or of any product

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OZYORUK, PEKHEZ, AND YURUM

-- 8 , , , , , , 3500 3000 2500 2000 1600 1200 800

WAVENUMBER. c m l

FIG. 3. Infrared spectra of residual lignite after electrolysis. A) 40 millimoles. B) 50 millimolee. C ) 60 millimoles and D) 80 millimoles HClOa consumption.

obtained from the coal slurry. The infrared spectra in

Fig. 3 are similar to the one obtained after AB/HCIO1

treatment without electrolysis Wig. 2A). The relative

intensities of alkyl (2950 cm-'), carbonyl (1700 cs')

and ether (1100 cm-') bands in the spectra Of Fig. 3

and in Fig. 28 are approximately identical. It oeemd

that the coal rmatrix was not hydrogenated by the

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE

3 i n n 3dnn 25100 20bo l i o n l i o n I eon Cbn

WAVENUMBER. cm"

PIG. 4. Infrared spectra of extracts obtained after electrolysis, A) 50 milliwles. B) 60 milliwlea and C) 80 millinoles HClO. consumption.

TABLE I1

Extraction Yields of Beypazari Lignite After AH, ABIHClO. Treatment and Electrolysis

Yield. %

AH Extraction 9.0 ABIHC10- Treatment 17.3 AHIHC~OI Electrolysis 18.0

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692 OZYORUK, PEKMEZ, AND YURUM

hydrogen atoms produced in the electrochemical

environment. The solubility data in the Table 11

supports this claim. The yield after AB extraction was

9.0 X . The yield increased to 17.3 X in the AHIHClO.,

treatment. 18.0 X of the lignite was extracted a*ter

an electrochemical experiment. Electrolytic conditions

alwst did not change the yield of extraction and it

appeared that the residue remained intact in the

electrochemical enviroment.

Fig. 4 gives the spectra of the extracts obtained

after electrolysis experiments. These spectra are

different than that of in Fig. 2B. The spectrum in

Fig. 2B was of the extract obtained after AHlHClOa

treatment. It seemed that HC10, oxidized the raterial

extracted by AH. In the case of spectra of Fig. 4 the

situation is quite variant. Ye can see that the

material obtained after electrolysis experiments is

hydrogenated. The alkyl bands absent in the AH

extracts (Fig. 1C and Fig. 2B) appeared in these

extracts. As the severity of the electrolysis was

increased from 50 milliwles of HClO. consumption to

80 milliwles the intensity of nethylene bands in the

region of 2850-2920 cm-' also increased. In addition

to this the bands in the 1380-1457 cm-I region due to

s v t r i c and asymmetric methyl bending vibrations

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ELECTROCHEMICAL INTERACTION OF BEYPAZARI LIGNITE 693

became w r e complex as the quantity of HCIOn consumed

in the electrolysis was increased. This designated

that new alkyl structures at positions of different

symmetries were formed after electrolysis. This of

course needs verification by methods other than

infrared spectroscopy. The change in the intensity of

the etheric bands near 1100 cm-' is significant. After

the electrolysis experiment of 50 millimnles HClOn

consumption, the etheric band which was absent in the

original AH extract started io emerge. As the armunt

of HClOn consumed in the electrolysis was enlarged the

intensity of the etheric bands also increased. This is

because of the oxidative effect of HCIOn ; although

HCIOn was used as a strong proton donor in the

experimental conditions it seemed that its oxidizing

properties were also effective. Thus, there may be

an optimum concentration for the HClOn in order to

prevent its oxidative action. Results of electrolysis

experiments performed indicated that concentrations

less than 40 millimoles of HCIOp were sufficient for

hydrogenation purposes.

The data presented in this work points out to the

possibilty of in situ hydrogenation of the coal

liquids during extraction procedures. It was also

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694 OZYORUK, PEKMEZ, AND YURUM

found that using a potential of - 0 . 5 V the

electrochemical hydrogenation of the coal matrix

itself was not practicable. This is probably due to

the rmrss transfer resistance offered by the coal

particles in a liquid-solid interaction. Higher

cathodic potentials would probably force the electrons

produced directly into the coal matrix in addition to

=re hydrogen atom production. The results of Dogru

and co-wurkers (1975) verify this claim. These workers

in order to maintain a constant current of 0 . 5 amperes

through the cell had to raise the cathodic potential

to higher values. Thus they were able to hydrogenate

the coal matrix itself. The results reported in the

present study are significant in terms of energy

consumption. Hydrogenation of the extract was achieved

by the use of a potential as low as - 0 . 5 V. The

current passed through the cell was 12 miliiamperes at

the beginning of electrolysis and it reduced virtually

to zero as HC10. was completely consuloed. This result

indicated that Inore than a coal particle itself.

compounds produced by the coal that were soluble in

AB and HClOa were reduced by the electrochemically

produced hydrogen atoms. This is in accord with the

conclusion of Baldwin and co-workers (1981) who found

that the electroactive species appeared to consist

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ELECTROCHEMICAL INTERACTION OF FEYPAZARI LIGNITE 695

largely of material extracted from the coal matrix.

Dhooge and co-workers (1982) stated that rather than

coal particles, compounds or ions from the coal that

are soluble were responsible for the electrochemical

phenomena. Since no iron bras extracted by AU (BBldwin.

1981). then the electroactive species responsible in

electrochemical hydrogenation should be the organic

material extracted from the coal matrix. The detailed

mechanism of hydrogenation of coal liquids in the

present work was not comprehended, work is currently

under progress in our laboratory using model chemicals

for better understanding of the hydrogenation

mechanism reported in this paper.

Bartle, K.D.. Pappin. A. J.. Taylor, B. and Mills. D.G. 1986. Fuel Process. Technol. .l4, 183.

Coughlin, R.V. and Farooque, 11. 1979a. Bature,219.301.

Coughlin. R. V. and Farooque, M. 1979b. Bature. ZBJ2.666.

Coughlin. R . V . and Farooque. 11. 1979~. Fuel.5&705.

Coughlin. R . V . and Farooque. 11. 1982. Ind. Eng. Chem. Process Des. Dev. , 21,559.

Dogru. R., Gaines. A.F. and Yiiriim. Y. 1975. Proc. of 5th Science Congress of Turkey. T. B. T. A. K. Publication Bo: a. 291.

Dooge. P. 11.. Stilwell. D.E. and Park, S-M. 1982. J. Electrochem. Sac. ,129,1719.

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696 OZYORUK, PEKMEZ, AND YURUM

Green. T., Kovac, J . , Brenner. D. and Larsen. J . V . 1982, The Macromolecular Structure of Coals, In, R.A. Keyers. (ed.). Coal Structure, Academic Press. Hew York.

Liotta. R. 1979. Fuel. ZQ.724.

&y6rijk, H . . Peklmz, K. and Yildiz. A. 1987. Electrochemical Reduction of Tetraphenyl Cyclopentadienones, Electrochimica Actn, in press.

Sertel. M . Yildiz. A. and Baumgartel. H. 1986. Electrochimica Acta, X. 1625.

Sternberg, H . V . , IIarkby, R.E. and Vender, I. 1963, J. Electrochem. Soc. . U. 425. Svehla, G. 1976. Comprehensive Analytical Chemistry. Vol. 6. Analytical Infrared Spectroscopy, Elsevier, Amsterdam.

Yirriim, Y. 1987, Interaction of Coals with Dxygen at Temperatures up to 600°C. Thermochimica Acta, in press.

RECEIVED: A p r i l 14, 1987 ACCEPTED: May 11. 1.987

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