ISSN 1068�364X, Coke and Chemistry, 2011, Vol. 54, No. 6, pp. 208–210. © Allerton Press, Inc., 2011.Original Russian Text © G.A. Mandrov, 2011, published in Koks i Khimiya, 2011, No. 6, pp. 30–32.

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Currently available technologies permit the extrac�tion of as much as 95% of the organic combustiblemass from lignite. One such technology breaks lignitedown into three components: humic acids, fulvicacids, and metal salts [1].

In Fig. 1, we show the surface of these components.We see that the surface texture of fulvic acids (a) ischaracterized by strict structure, while that of humicacids (b) is amorphous. Humic acids are insoluble atpH < 2; fulvic acids are soluble at all pH values.

According to current concepts, humic acids andfulvic acids may be categorized as nonstoichiometricacids characterized by irregular structure, heteroge�neous structural elements, and polydispersity [2].They are best described not by molecules but by amolecular ensemble. The conversion of such anensemble to compounds with known molecular massand structure is of definite scientific interest.

In the present work, we consider humic acids andfulvic acids derived from humic lignite (Kuznetsk

Basin, Barandatsk deposit, rank B2), with the follow�ing characteristics: moisture content 5 wt %; ash con�tent 9.8 wt %, yield of volatiles 45.8 wt %, Cdaf =72.9%; Hdaf = 5.3%; 21% (O + N + S).

The acids are obtained by the method in [1]; thisinvolves mechanically activated treatment of the lig�nite. The fulvic acids are separated from the metal saltsand used in organic synthesis within aqueous–ethan�olic systems. The IR spectra are recorded on anInfralum FT�801 instrument; microphotographs ofthe samples are obtained on a Jeol JSM 6390 LA ana�lytical scanning microscope. Chromatograms of theconversion products of the humic and fulvic acids arerecorded on an Agilent 6890N/5973 Inert chromato�graph, with a 30 m × 0.25 mm HP�5SMS capillary col�umn (5% diphenyl + 95% dimethylglyoxal); the car�rier gas is helium. The chromatograph is equippedwith an Agilent mass�spectrometric detector.

In Fig. 2, we show the IR spectra of the initialhumic and fulvic acids. We see that the acids have dif�

CHEMISTRY

Electrochemical Oxidation of Lignite’s Humic and Fulvic AcidsG. A. Mandrov

Coal Institute, Siberian Division, Russian Academy of Sciences, Kemerovo, Russiae�mail: catalys01@rambler.ru

Received March 28, 2011

Abstract—The electrochemical oxidation of lignite’s humic and fulvic acids in an aqueous–ethanolic alka�line medium is studied. Complex lignite components may be converted to chemical compounds with simpleand known structure (predominantly phthalates), without tar formation.

DOI: 10.3103/S1068364X11060032

(a) 50 µm 10 µm

30 µm

(b) (c) 009

Fig. 1. Microphotographs of the surface of fulvic acids (a), humic acids (b), and metal salts (c).

COKE AND CHEMISTRY Vol. 54 No. 6 2011

ELECTROCHEMICAL OXIDATION OF LIGNITE’S HUMIC AND FULVIC ACIDS 209

Fig. 2. IR spectra of humic acids (a) and fulvic acids (b).

ferent functional groups and are capable of chemicalreaction in certain conditions.

The electrochemical oxidation of the humic andfulvic acids is undertaken in aqueous–ethanolic alka�line medium, within a standard glass cell, with peri�odic mixing of the electrolyte. The cell has platinumanodes and does not contain a diaphragm.

Coal powder is suspended in an aqueous solution ofmetal halides and then subjected to electrolysis in aseparate anode space of the tank, by the method in [3].After a certain time, the chlorinated products (molec�ular mass ~500) and polycyclic polycarbonic acids(molecular mass ~1000) are removed from the anolyte.

These products subsequently undergo hydration, crack�ing, oxidation, and other types of processing.

In the light of the results, it is of interest to investi�gate electrochemical oxidation not of the coal itselfbut of its conversion products (humic and fulvicacids). At the same time, we want to establish whichproducts are formed with complete decolorization ofthe solutions in the electrolyte containing aqueoussolutions of metal hydroxides, to which ethanolicsolutions of fulvic acids or humic acids are added.

At the end of electrolysis, the reaction products areprepared and the ethanolic extracts of the organicmaterials formed are investigated by chromatomassspectrometry. In Figs. 3 and 4, we show the chromato�

1.0

0500100015002000250030004000 3500

Wave number, cm–1

Absorption, rel. %

0.5

Holding time, min

3348

2974

2928

2889

1923

1651

1573

1414

1088

1382

13371273

880

1049(a)

(b)

50454035305 5515 252010

1

2

Fig. 3. Chromatogram (a) and IR spectrum (b) of complex phthalic�acid esters obtained by electrochemical oxidation of fulvicacids.

210

COKE AND CHEMISTRY Vol. 54 No. 6 2011

MANDROV

grams and IR spectra of the products formed in theelectrochemical oxidation of humic and fulvic acids.

It is evident from Fig. 3a that the electrochemicaloxidation of fulvic acids results in two products: thediisobutyl ester of phthalic acid (1); and the mono�2�ethylhexyl ester of phthalic acid (2).

For the electrochemical oxidation of humic acids(Fig. 4a), we see six products: tritetracontane (1); thedibutyl ester of phthalic acid (2); tetratriacontane (3);tetratetracontane (4); the mono�2�ethylhexyl�ester ofphthalic acid (5); and heptacosane (6). The degree ofidentity is ≥90 for all the materials except hepta�cosane, for which the corresponding figure is 87.

In Figs. 3 and 4, we also show the IR spectra of thecomplex phthalic�acid esters obtained by electro�chemical oxidation of humic and fulvic acids. The mainabsorption bands (3348 cm–1 and 3370 cm–1) corre�spond to valence vibrations of the hydroxyl groups. Thedouble bands in the range 2974–2889 cm–1 indicatevalence vibrations of the aliphatic groups –CH2 and–CH3. The intense narrow bands at 1048 cm–1 and1049 cm–1 correspond to valence vibrations of theC–O group in complex esters CH3C(O)O–R.

Complex phthalic�acid esters are observed in natu�ral water, according to [4]. Our results suggest that,besides the other factors that facilitate phthalate accu�mulation in natural water, we should note the role ofthe oxidation of humic and fulvic acids by oxygen dis�solved in the water.

We conclude that the electrochemical oxidation oflignite’s humic and fulvic acids may result in the for�mation of organic compounds with known structureand molecular mass, without tar formation.

REFERENCES1. Potapov, V.P., Schastlivtsev, E.L., and Mandrov, G.A.,

Russian Patent 75 656, Byull. Izobret., 2008, no. 23.2. Perminova, I.V., Analysis, Classification, and Predic�

tion of the Properties of Humic Acids, Doctoral Disser�tation, Moscow, 2000.

3. Petrova, G.I. and Bychev, M.I., Elektrokhimicheskayapererabotka burykh uglei (Electrochemical Processingof Lignite), Yakutsk: YF, Izd. SO RAN, 2001.

4. Rokosova, N.N., Rokosov, Yu.V., and Schastlivtsev, E.L.,Active Nonwoven Carbon�Based Material in the Anal�ysis of Organic Water Pollutants, Koks Khim., 2009,no. 11, pp. 42–45.

Fig. 4. Chromatogram (a) and IR spectrum (b) of complex phthalic�acid esters obtained by electrochemical oxidation of humicacids.