Decomposition of Coal Model Compounds During Simulated Chemical Coal Cleaning with Molten Hydroxides

Abstract

Abstract Coal model compounds, such as dibenzothiophene, its analogs and the hydroxylated derivatives of these compounds. were treated with molten hydroxides to evaluate the importance of nucleophilicity for the different alkali-metal hydroxides. The soluble hydroxylated model compounds were decomposed and desulfurized by RbOH or CsOH at lower temperatures and in less time than when decomposed by KOH or NaOH, indicating that molten hydroxides have varying degrees of nucleophilicity, the progression of nucleophilicity being CsOH > RbOH ≥ KOH > NaOH. The discrepancy of these results with previously published studies, suggesting NaOH is as effective as KOH in desulfurizing coal, is discussed. Increased solubility of the hydroxylated derivatives in molten hydroxide led to faster reaction rates under homogeneous reaction conditions. Aryl ethers decomposed more readily than did aryl sulfides. Sulfur-carbon bond cleavage was more facile in sulfur compounds with conformational mobility.