Mass sulfite oxidation method

Measurement of the absorption rate of carbon dioxide in aqueous solutions of sodium hydroxide has been used in some of the more recent work on mass-transfer rate in gas-liquid dispersions (D6, N3, R4, R5, V5, W2, W4, Y3). Although this absorption has a disadvantage because of the high solubility of C02 as compared to 02, it has several advantages over the sulfite-oxidation method. For example, it is relatively insensitive to impurities, and the physical properties of the liquid can be altered by the addition of other liquids without appreciably affecting the chemical kinetics. Yoshida and... 

In 1960, Yoshida et al. (Y4), working with a geometrically similar system and with the sulfite-oxidation method, confirmed the results reported by Cooper et al. They also showed that the gas film does not offer any resistance to the mass transfer of oxygen from air to the sodium sulfite solution. In addition, they found that the mass-transfer coefficient per unit area was equal for water and for aqueous sodium sulfite. 

In spite of its wide application, the mechanisms of this reaction remain obscure. Many diverse arguments have been published since the reaction was first investigated in 1897 (Bl, C5, C9, F7, J6, M5, P9, R2, S5, W2, W4, Yl, Y4). Cooper et al. (C9) introduced this method as a yardstick for the measurement of volumetric mass-transfer coefficients in gas-liquid contacting. Karow et al. (Kl) later concluded that the sulfite oxidation is suitable for fermentation process scale-up studies. Cooper et al. established that the reaction proceeds at a rate independent of sulfite ion concentration over wide concentration ranges. In their work they considered the sulfite oxidation to be of zero order with respect to both sulfite and sulfate concentration. 

It is possible to influence the size of the dispersion spots in liquid-gas systems (specific phase contact surface) and therefore, the mass transfer efficiency, by changing the method of reactant introduction. During the motion of the gas-liquid flows in tubular turbulent reactors, an increase of the gas supply branch pipe diameter results in a slight decrease of the sulfite number of the reactor (Table 4.4), which can be seen from the decrease of the phase contact surface as d 2 grows by 15%. Similarly, with the decrease of the coaxial liquid-phase supply branch pipe diameter from 10 to 5 mm, SuR equals 13.5 and 14 g02/h, respectively. Thus, there is almost no dependence of the rate of sodium sulfite oxidation in aqueous solution, by atmospheric oxygen, on the method of reactant introduction. This is related to the fact that changes in the method of the liquid- and gas-phase introduction, in particular, the diameters of the feeding branch pipes, do not influence the mass delivery coefficient in the liquid phase. 

Beyond this physical method using photography or light scattering for measuring a, the chemical method based on sulfite oxidation is often successfully used despite disadvantages due to different fluid properties. According to the theory of mass transfer with simultaneous chemical reaction, A can be calculated from... 

Mass-transfer rates have been determined by measuring the absorption rate of a pure gas or of a component of a gas mixture as a function of the several operating variables involved. The basic requirement of the evaluation method is that the rate step for the physical absorption should be controlling, not the chemical reaction rate. The experimental method that has gained the widest acceptance involves the oxidation of sodium sulfite, although in some of the more recent work, the rate of carbon dioxide absorption in various media has been used to determine mass-transfer rates and interfacial areas. 

Measurements Using Liquid-Phase Reactions. Liquid-phase reactions, and the oxidation of sodium sulfite to sodium sulfate in particular, are sometimes used to determine kiAi. As for the transient method, the system is batch with respect to the liquid phase. Pure oxygen is sparged into the vessel. A pseudo-steady-state results. There is no gas outlet, and the inlet flow rate is adjusted so that the vessel pressure remains constant. Under these circumstances, the inlet flow rate equals the mass transfer rate. Equations (11.5) and (11.12) are combined to give a particularly simple result ... 

In order to estimate the efficiency of the mass transfer in gas-liquid flows, a sulfite method [22], based on the catalytic oxidation of sodium sulfite by atmospheric oxygen, was used ... 

Sulfur in coal that is burned to generate electricity is a major source of acid rain and SO2 air pollution. In Eschka s method to measure S, coal is fused with 5 times its mass of a 2 1 (by mass) mixture of MgO and anhydrous Na2C03 at 800°C for 4 h in air. Sulfur ends up as sulfate (SO ) and sulfite (SOf") salts. The fused mass is dissolved in 6 M HCl and boiled with aqueous Br2 to oxidize S03 to SO . Excess Br2 is evaporated. The solution is adjusted to pH 3 and aqueous BaCl2 is added to precipitate BaS04, which is filtered, washed, dried by ignition, and weighed. 

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