Title

ELECTROCHEMICAL OXIDATION OF COAL IN AQUEOUS ELECTROLYTES

Date of Completion

January 1982

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

Up to 50% of North Dakota Lignite coal slurried in NaOH at room temperature and electrolysed using Pt-gauze electrodes became soluble in the electrolyte as humic acids. The potential applied to the cell influences the product distribution; for example, increasing the electrode potential from 1.2 to 2.5 V, SCE gave correspondingly greater humic acid production. Increasing the potential still further however, lowers the amount of humic acid formed. The other reaction products were carbon dioxide and hydrogen which were respectively formed at the anode and the cathode. The rates of reaction increased with increasing temperature. Product analyses by GC-MS and FTIR methods indicate that there are many products and this implys the reaction pathway is complex and involves more than one reaction. A possible reaction mechanism scheme is proposed to explain the formation of various products in the basic media.^ Acidic slurries of NDL and Illinois No. 6 coals were electrolyzed using Pt and graphite electrodes at potentials of 0.8-1.0 V, NHE. This caused pyrite present in the coal to react and dissolve while hydrogen was produced at the cathode with current efficiencies in the range of 90-100%. Cyclic voltammetry applied to either slurry or filtrate indicated that the reversible, one-electron oxidation of Fe(II) to Fe(III) is a major reaction, but chemical assays revealed that sulfide also gets oxidized to elemental sulfur and to sulfate with total sulfur removal from coal being as high as 40%. The dissolved ionic Fe(III) oxidizes not only the pyrite, but also the carbonaceous part of coal by an Electrocatalytic(EC) mechanism where the electrochemical reaction is oxidation of Fe(II) to Fe(III); the latter species generated at the anode could oxidize coal and thus itself would get reduced to Fe(II). However, under application of the applied potentials, Fe(III) would be regenerated continuously at the anode and oxidize the coal particles. A mathematical model for EC mechanism was developed and the chemical rate constant for the NDL coal oxidation was calculated. ^