A coal desulfurization process via sodium metaborate electroreduction with pulse voltage using a boron-doped diamond thin film electrode

Abstract

A preliminary study was conducted on the coal desulfurization process via NaBO₂ electroreduction with pulse voltage using a boron-doped diamond (BDD) thin film electrode. It has been proved that NaBO₂ was converted into NaBH₄ by ¹¹B NMR. The factors that influence the conversion rate of NaBO₂ into NaBH₄ and coal desulfurization efficiency were investigated. Under the conditions of −1.5 V forward pulse voltage, +0.5 V reverse pulse voltage, 0.2 mol L⁻¹ NaBO₂ concentration, 0.5 mol L⁻¹ NaOH concentration, 2 s forward pulse duration, 1 s reverse pulse duration, 50 g L⁻¹ coal concentration, 0.8 mmol L⁻¹ NiCl₂ concentration and 2.5 h electrolytic time, a higher desulfurization efficiency (64%) was obtained compared with the common electrochemical desulfurization (ECDS) process using a Pt electrode. By analyzing and comparing the coal samples and electrolytes before and after desulfurization it was indicated that the removed S from the coal sample in the form of gaseous H₂S was mainly converted into Na₂S and Na₂S_x and boron (B) recycling was realized during coal desulfurization. Particularly, the combustion characteristics of coal were improved after desulfurization. Finally, the desulfurization mechanism was proposed. All these results indicated that the desulfurization process via NaBO₂ electroreduction with pulse voltage using a BDD thin film electrode is effective and highly promising for coal desulfurization.