Kinetics of oxidation of sodium dithionite by flow thermal method

Abstract

The homogeneous kinetics and inhibition of sodium dithionite oxidation in an aqueous solution were studied by means of a flow thermal method. Results on the oxidation study of dithionite solutions at 3OoC show that the reaction is first order with respect to dithionite and zero order with respect to oxygen. An activation energy of 17.5 kcal/g-mole has been calculated for this reaction. The inhibiting effects of manganese chloride, manganese sulfate, and triethanolamine were inversely proportional to 0.8, 0.9, and 0.2 power, respectively.A free radical chain mechanism has been proposed, and the rate expres- Solutions nf sodium dithionite are used as powerful and rapid reducing agents for vat dyeing, bleaching, and for manufacture of various chemicals. The inherent instability of this compound with respect to atmospheric oxidation in aqueous solutions, however, lowers the efficiency of the solutions after prolonged storage. Therefore, a considerable excess of sodium dithionite over stoichiometric amounts must be used. It would be very desirable to minimize the excess consumption of sodium dithionite in industrial applications, and it is essentially in regard to this problem that the kinetics of sodium dithionite oxidation in aqueous solutions has been studied in some detail. The resulting information, however, is contradictory in many ways and thus remains inconclusive. The earliest oxidation study of dithionite was probably conducted by Meyer (1903); he computed first-order rate constants which drifted over a wide range. Nicloux (1933) and Lynn (1954) proposed an overall stoichiometry for the reaction. Lynn (1954) reported that the rate of atmospheric oxidation was first order, involving dithionite in solutions of 0.1M. Morello et al. (1964) reported that the reaction is first order with respect to dithionite and zero order with respect to molecular oxygen at operating concentrations between 8 )( 10-5 M and 47.5 X M dithionite and 10 X lop5 for oxygen. In contrast, Rinker et al. (1960) observed that the reaction is half order with respect to dithionite and first order with respect to oxygen. The pH of the reacting medium was held approximately at the value used by iMorello et al. Jhaveri and Sharma (1968) found the reaction to be first order with respect to dithionite for concentrations below 0.08 M/1 and second order for concentrations above 0.08 M/1. In the case of oxygen, the reaction was observed to proceed with zero order.The kinetic analysis has not been projected as a focal point because of the existing controversy in the experimental results. It should also be noted that substances such as manganese compounds, trialkanolamines, sodium phosphate, ammonium thiocyanate, etc. are known to inhibit the oxidation of sodium dithionite solutions; however, there seems to be no reported data on kinetics and inhibition. In the present investigation, the reaction rate of homogeneous liquid-phase oxidation of sodium dithionite solutions was studied by a flow-thermal method similar to that employed by Hartridge and Rou...

Determination of Interfacial Areas in a Bubble Column by Different Chemical Methods

“…[8][9][10] The aim of this work is to compare the results obtained by three different chemical methods: Danckwerts'method, based on the absorption of CO 2 in sodium or potassium carbonate buffer solutions, 11 and the sulfite and dithionite methods, which involves the oxidation of sulfite or dithionite ions by oxygen, 12,13 respectively. For all of them, the influence of the surfactants' presence on the interfacial area was also determined.…”

Kinetics of Reaction of Sodium Hypochlorite and Sodium Sulfite by Flow Thermal Method

“…The rapid-mixing apparatus, differential measurements of the temperature, experimental procedure, and the method of data reduction have been described elsewhere (Mishra and Srivastava, 1975;Singh et al, 1978).…”

Density and Viscosity of Aqueous Solutions of Sodium Dithionite, Sodium Hydroxide, Sodium Dithionite + Sucrose, and Sodium Dithionite + Sodium Hydroxide + Sucrose from 25 °C to 40 °C

“…Most authors agree on zero order for oxygen, and some authors have even suggested that the reaction is of first order with respect to dithionite in the range of dithionite concentration <0.1 mol‚dm -3 and of second order in the range of dithionite concentration >0.1 mol‚dm -3 (Hikita et al, 1978). The absorption rate decreased with an increase of the pH of the solution (Singh et al, 1978) in the pH range of 8-11, while it is independent of the pH between 12.0 and 13.7 (Camacho et al, 1992).…”