Kinetics of the sulfation of NaCl at combustion conditions

SO2 and NaCl react in the presence of O-2 and water vapor to produce Na3SO4 and HCl. The sulfation of solid NaCl was studied in a fixed-bed reactor in the temperature range 400-600 degrees C where NaCl, Na2SO4, and their mixtures are solid. Other experimental conditions were as follows: 0.3-1.1% SO2, 3-11% O-2, 0.5-20% H2O, 2 g of NaCl particles with surface areas of 0.13-0.29 m(2)/g, and a total gas flow rate of 15 cm(3)/s (at 20 degrees C). Under the experimental conditions employed, intraparticle diffusion and external mass transfer did not influence the overall rate, and true kinetic data were obtained. The sulfation rate of the solid NaCl was very slow, with only 0.5-1.1% of the NaCl converted to Na2SO4 in 3 h. The rate was not strongly temperature dependent, and the activation energy was 17 kJ/mol. The reaction rate depended on SO2 partial pressure but not on water vapor and O-2 partial pressures. The observed reaction rate was consistent with a mechanism in which Langmuir-type adsorption of SO2 on the NaCl surface is the rate-limiting step.