Oxidation of high sulphur coal. Part 2. Desulphurisation of organic sulphur by hydrogen peroxide in presence of metal ions

This paper describes a simple oxidative method of desulphurisation of coal organic sulphur carried out by using hydrogen peroxide as an oxidant. Desul phurisation achieved up to the extent of 3.70-6.25 wt% in 1-4 h whereas at 24 h, it increases to 9.24 wt%. When metal ions are externally added to the system containing coal and hydrogen peroxide, desulphurisation is reduced considerably in the presence of Ni2+ ion while the presence of Cu+, Co2+, S n2+, Pd2+ and Sb3+ ions enhance the rate of desulphurisation in 1-4 h. At 2 4 h, except Cu+ and Sn2+ ions, the presence of other metal ions increases t he magnitude of desulphurisation. Highest desulphurisation is obtained in a short time period with Pd2+ ion (28.14 wt%) whereas it is 31.12 wt% in the presence of Sb3+ ion at 24 h. The desulphurisation reaction follows pseudo -first order kinetics in all the systems and the rate constants fall in the range of (1.02-8.68) x 10(-5) s(-1) implying a slow, steady process which is supported by the exceptionally low frequency factor. The activation ener gy for desulphurisation in the systems falls in the range of 8.74-13.67 kJ mol(-1). The positive value of Gibbs free energy of activation represents a non-spontaneous reaction. The reaction proceeds with the absorption of hea t (endothermic) as revealed by the positive value of enthalpy of activation . Sufficiently low positive values of entropy of activation and frequency f actors attribute an associated reaction and proceed through the initial for mation of activated complexes. Model study reveals that the process is effe ctive with aliphatic sulphur compounds. The non-spontaneous nature of the r eaction is largely due to the resistance offered by the macro-aromatic sulp hur compounds. Pragmatic desulphurisation has been achieved in the process developed here and is therefore of considerable technological interest. (C) 2001 Elsevier Science Ltd. All rights reserved.