Catalytic oxidation of sodium sulfite in a gas–liquid tubular ejector: optimization of the operational conditions by Simplex method

A process of the production of medical analyses reagents releases a gaseous effluent containing HCl and SO2. These gasses are absorbed and neutralized by an aqueous solution of sodium hydroxide. The liquid effluent of this neutralization stage, having an average flow rate of 12 000 l/day, is an aqueous solution of sodium sulfite and sodium chloride with the concentrations of around 0.8 and 1 M, respectively. This study concerned the determination of the optimum experimental conditions in order to oxidize all the sodium sulfite at 1 day of operation with a minimum number of ejectors installed parallel to each other. We have used the Simplex method to optimize this oxidation with two variables: temperature and the concentration of the catalyst. The limits of the experimental domain were defined as 20 and 50 °C for the temperature and 10−4 and 10−3 mol/l for the concentration of the catalyst, while the other operating conditions like the initial pH of the solution, gas and liquid flow rates and the initial concentration of sodium sulfite were kept constant. The results of this optimization have showed us that the totality of the effluent could be treated using an installation of 17 parallel ejectors in 20 h of operation at a temperature of 34 °C and with a catalyst concentration of 1.2×10−3 mol/l.