Decarboxylation of Beypazari Lignite by the Catalytic Effect of Cu2+, Zn2+, and Ag+ Ions

Abstract

Decarboxylation of the Beypazari lignite with Cu2+, Zn2+, and Ag+ metal ions used as catalysts was investigated. Change in the calorific values after decarboxylation of the raw and demineralized coal with these metal ions was determined. Heating the raw and demineralized Beypazari lignite samples to temperatures between 100°C and 230°C for 10–60 min, the calorific values seemed to increase to about 10–20% higher values than those of the unheated samples. Heating the samples of Beypazari lignite charged with metal cations yielded products of higher calorific values than those of untreated lignite. The optimum metal concentration to obtain decarboxylated lignites with the highest calorific value for each metal-lignite group in the decarboxylation experiments were found as 4% Ag+, 3% Cu2+, and 1% Zn2+ for the raw lignite and 1% Ag+, 3% Cu2+, and 3% Zn2+ for the demineralized lignite. Addition of metals to the raw and demineralized samples decreased the activation energy of decarboxylation reactions. Cu2+ seemed to be the most effective catalyst by reducing the activation energy to about 7–8 kJ/mol both in the decarboxylation reactions of raw and demineralized lignite samples. 13C NMR measurements revealed that the aromaticity of the decarboxylated products of the raw lignite seemed to stay constant and those of demineralized lignite increased slightly. The sequence of the rate of loss of the oxygen functional groups in decarboxylation reactions for all of the metal charged sample was found to be carbonyl > carboxyl > carboxylate > hydroxyl. If the metal ions were compared in terms of effectiveness in decarboxylation reaction, the order was as follows: Cu2 > Ag > Zn2 (for raw lignite samples) and Cu2 > Zn2 > Ag (for demineralized lignite samples).