Kinetic Studies of the Desulphurization of a Nigerian Coal Sample Using Sulphuric Acid and Hydrogen Peroxide

The kinetics of desulphurization of Onyeama coal with hydrogen peroxide and sulphuric acid solutions was studied in this work. The influence of temperature, concentrations of hydrogen peroxide and sulphuric acid as well as particle size, were studied. It was found that the dissolution curves for total sulphur follow the kinetic model of the shrinking core model, with diffusion through the product layer as the rate-determining step. The calorific value of the coal sample was relatively unaffected. The desulphurization reaction followed the pseudo-first order kinetics. The process activation energy, enthalpy, entropy and free energy are  kJ mol^-1, 8.43 kJ mol^-1, ^-2 kJ mol^-1, and  kJ mol^-1 respectively. The negative activation energy indicates a complicated process mechanism. The positive free energy can be attributed to the steric hindrance by large aromatic rings present in the coal. The findings from the experimental tests showed that the desulphurization process of coal was best achieved with hydrogen peroxide stabilized with dilute sulphuric acid. The reaction kinetics can be described by the semi-empirical model:

1 –2/3  .X_B–〖(1-X_B)〗^(2/3)= 0.467C_([H_2 〖SO〗_4])-0.133(H_2 〖SO〗_4  /H_2 O_2)-0.110 (p)-0.304 exp (-1345/T) t.