KINETICS OF THE SODIUM BICARBONATE-SULFUR DIOXIDE REACTION

A parallel reaction path model has been developed to explain the reaction between sodium bicarbonate (NaHCO3) particles and sulfur dioxide (SO2) gas. This reaction is atypical compared to other alkali and alkaline compounds with SO2 in that the optimum reaction temperature occurs where thermal decomposition of the parent particles is pronounced. The model accounts for the concomitant thermal decomposition reaction which occurs at the temperatures where this reaction is industrially significant. The subsequent reaction between the product of the thermal decomposition, micro-grains of sodium carbonate (Na2CO3) and SO2 is considered in the reaction path by the use of a pore plugging model. The model has been applied to published kinetic data for the NaHCO3-SO2 reaction in order to obtain the reaction rate constants which are shielded from observation by the thermal decomposition reaction and the subsequent reaction between Na2CO3 and SO2. An expression for the reaction rate constant for the reaction of NaHCO3 with SO2 has been found and is of the form k1 = 2.2625 X 106 e- 13.512/RT. The model has been applied to conversion of the bicarbonate particles for up to 600s reaction time, with good agreement with the data. This model can be used to predict the reactivity of NaHCO3 with SO2 in typical gas-solid reactors.