Sulfite, electrolytic oxidation

Dithionates may be prepared by the electrolytic or chemical oxidation of sulfurous acid and sulfites. Chemical oxidation is accomplished by the action of chlorine, iodine, hydrogen peroxide, or oxygen in an acid medium by the action of chromates or permanganates in neutral solution - ... 

Franke [47] undertook a comprehensive electroanalytical study of K2S207 mixtures with K2S04, which is formed by Eqs. (47) and (48) and V2Os, a widely-used oxidation catalyst for S02. Pure pyrosulfate under N2 or air (Fig. 38a,b) shows only the reduction to S02 and sulfate, Eq. (48) (all potentials are vs. Ag/Ag+). When S02 is added, a new reduction and oxidation peak appear (Fig. 38c,d). When the electrolyte was pre-saturated with K2S04 (ca. 4 wt.%) (Fig. 39) the gas composition had no direct effect on the voltammetry. Although the equilibrium for Eq. (49) lies well to the right at this temperature, 400 °C, the kinetics are quite slow in the absence of a catalyst. The equilibrium between pyrosulfate and sulfate, Eq. (47), lies well to the left (K = 2 x 10-6), but will proceed to the right in the absence of S03. Thus, the new peaks are sulfate oxidation, Eq. (43), and S03 reduction to sulfite ... 

By media variables we mean the solvent, electrolyte, and electrodes employed in electrochemical generation of excited states. The roles which these play in the emissive process have not been sufficiently investigated. The combination of A vV-dimethylformamide, or acetonitrile, tetra-n-butylammonium perchlorate and platinum have been most commonly reported because they have been found empirically to function well. Despite various inadequacies of these systems, however, relatively little has been done to find and develop improved conditions under which emission could be seen and studied. Electrochemiluminescence emission has also been observed in dimethyl sulfite, propylene carbonate, 1,2-dimethoxyethane, trimethylacetonitrile, and benzonitrile.17 Recently the last of these has proven very useful for stabilizing the rubrene cation radical.65,66 Other electrolytes that have been tried are tetraethylam-monium bromide and perchlorate1 and tetra-n-butylammonium bromide and iodide.5 Emission has also been observed with gold,4 mercury,5 and transparent tin oxide electrodes,9 but few studies have yet been made1 as to the effects of electrode construction and orientation on the emission character. 

It is a well-known fact that bubbles produced by mechanical force in electrolyte solutions are much smaller than those in pure water. This can be explained by reduction of the rate of bubble coalescence due to an electrostatic potential at the surface of aqueous electrolyte solutions. Thus, k a values in aerated stirred tanks obtained by the sulfite oxidation method are larger than those obtained by physical absorption into pure water, in the same apparatus, and at the same gas rate and stirrer speed [3]. Quantitative relationships between k a values and the ionic strength are available [4]. Recently published data on were obtained mostly by physical absorption or desorption with pure water. 

Culture media usually contain some electrolytes, and in this respect the values of A in these media might be closer to those obtained by the sulfite oxidation method than to those obtained by experiments with pure water. 

Tano T, Ito T, Takesue H, Sugio T, Imai K (1982) B-type cytochrome, an electron carrier in the sulfite-oxidation system of Thiobacillus thiooxidans. J Ferment Technol 60 181-187 Taya M, Shiraishi H, Katsunishi T, Tone S (1991) Enhanced cell density culture of Thiobacillus ferrooxidans in membrane-type bioreactor with electrolytic reduction unit for ferric ion. J Chem Eng Jpn 24 291-296... 

SO2 produced by this process can be scrubbed using aqueous NaOH or (NH4)0H solutions to form Na2S03 or (NH4)2SOg solutions. Aqueous sulfite solutions can be further oxidized via electrolytic or photolytic processes, producing sulfate based fertilizer and hydrogen according to ... 

To avoid the cost and disposal problems of once-through processes employing alkali metal compounds, a considerable amount of research and development effort has been expended on techniques for regenerating this type of absorbent. Processes used employ precipitation of insoluble compounds (double alkali), and thermal decomposition (Wellman-Lord and Elsorb). Processes under development or which have been investigated include precipitation of insoluble compounds (zinc oxide), low-temperature reduction of sulfite (citrate and potassium formate processes), high-temperature reduction (aqueous carbonate process), electro-dialysis (SOXAL), and electrolytic (Stone Webster/Ionics Process). Descriptions of some of these processes are provided in subsequent sections. 

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