Sodium sulfite-bisulfite system

The LCM accurately predicted the vapor pressure of SO and CO2 over sulfite/bisulfite and carbonate/bicarbonate solutions, respectively, for salts of sodium, calcium, and magnesium. Figure 3 plots the LCM predictions of SO2 vapor pressure as a function of theQtotal SO to sodium ratio for a sodium sulfite/bisulfite system at 50 C... 

This recovery process is based on the simple chemistry of the sodium sulfite/bisulfite system. After appropriate pretreatment, the flue gas containing sulfur dioxide enters the absorber, which reduces the sulfur concentration to the required level and can accommodate a wide range of turn-down conditions (Figure 1). 

Hgure 7-14. Equilibrium concentration of SOz in gas over sodium sulfite/bisulfite/ sulfate solutions as a function of pH at i atm pressure and 130 Concentrated system FMC laboratory data, dilute system calculated. Dab ofLegatskietal. (197e)... 

Chemical Properties. The chemistry of sodium metabisulfite is essentially that of the sulfite—bisulfite—metabisulfite—sulfurous acid system. The relative proportions of each species depend on the pH. The pH of a sodium bisulfite solution obtained by dissolving 10 wt % sodium metabisulfite in water at 20°C is 4.9 at 30 wt %, the pH is 4.4. 

In terms of economical synthetic approaches to indoles, the synthesis of this heterocycle from anilines and trialkylammonium chlorides was effected in an aqueous medium (H20-dioxane) at 180°C in the presence of a catalytic amount of ruthenium(III) chloride hydrate and triphenylphosphine together with tin(II)chloride <00TL1811>. Muchowski devised a novel synthetic route to indole-4-carboxaldehydes and 4-acetylindoles 86 via hydrolytic cleavage of W-alkyl-5-aminoisoquinolinium salts 85 to homophthaldehyde derivatives upon heating in a two phase alkyl acetate-water system containing an excess of a 2 1 sodium bisulfite-sodium sulfite mixture <00JHC1293>. 

Sodium sulfite scrubbing can be configured as a regenerative process if the regeneration is performed thermally in an evaporator system. Thermal regeneration removes gaseous sulfur dioxide with the sodium bisulfite being converted back to sodium sulfite. The sulfur dioxide is then reduced to elemental sulfur or converted to sulfuric acid. 

With magnesium-, sodium-, or ammonium-based sytems, the bisulfite and sulfite salts are all soluble at all proportions in the presence of sulfurous acid. Even magnesium sulfite, with a solubility of about 1.25 g/100 mL, cold, is about 160 times as soluble as calcium sulfite at the same temperature and its solubility increases with temperature. So liquor preparation with these sulfite salts is easier, whether for acid sulfite, bisulfite, or NSSC pulping conditions, and even for experimental tests under alkaline conditions. For ammonium-based systems, ammonium hydroxide is contacted with a sulfur dioxide gas stream for liquor preparation. Magnesium-based systems use a magnesium hydroxide slurry to contact the sulfur dioxide gas stream. Sodium-based systems normally employ sodium carbonate lumps in a sulfiting tower, in a method similar to that used for NSSC liquor preparation. Sodium hydroxide may also be used if available at low cost. 

The method of Fan and Dasgupta (1994) relics on tlie reaction of formaldehyde with 1,3-cyclohexane-dione in acidified ammonium acetate to form the fluorescent dihydropyridine derivative in a flow injection analysis system. Formaldehyde trapped in water can be reacted with pararosaniline and sodium sulfite under mild conditions (neutral pH, room temperature equilibration) to produce a colored product that is measured at 570 nm (Petreas et al. 1986). The presence of bisulfite is an interference in this reaction so the method cannot be used to sample atmospheres that contain sulfur dioxide. In addition, the method is reported to suffer from interferences resulting from the presence of other aldehydes and phenol (Hoogenboom et al. 1987). The indirect method of Hoogenboom et al. (1987) relies on the reaction of excess bisulfite in an aqueous solution of formaldehyde with 5,5 -dithiobis(2-nitrobenzoic acid) to form a colored product, the absorbance of which is measured at 412 nm. The method reported by Naruse et al. (1995) relies on the formation of a colored product obtained by reacting the aqueous formaldehyde with acetylacetone and ammonium acetate in acetic acid. Absorbance is measured at 414 nm. 

The sodium sulfite precipitates out of the bisulfite solution and builds a dense slurry of crystals in the evaporator. A portion of this slurry is withdrawn from the evaporator and sent to a dissolving tank where water from the condenser system is added to dissolve the sulfite crystals. The resulting solution is sent to another surge tank and is then fed back into the absorber to complete the process loop. 

Moisture content is another key variable to be controlled during the production of glyceryl ether sulfonates. The minimum amount of water in the system should be enough to keep the sodium sulfite, with its limited solubility, completely dissolved in the system. This is another advantage for using the modified Streckerization reaction since bisulfite is more soluble than sulfite, and as less sulfite is needed, the amount of water required is also reduced. The sulfonate product is also highly viscous with poor heat transfer. Therefore, an overall moisture concentration of 50% is recommended to lower the viscosity of the solution and allow for better temperature control. ... 

On-site generation is necessary because the compressed liquid is explosive at room temperature. It is an unstable gas and, therefore, is not stored or sent in bulk. It is most commonly produced by reacting chlorine with sodium chlorite. There are several generation system choices using chlorine solution, chlorine gas and chlorite solution, or solid chlorite (Figure 3-11). Chlorite solution spills should be neutralized with sodium sulfite. Do not use sodium bisulfite. 

In a perfectly-buffered solution the SO2 vapor pressure will be directly proportional to the total concentration of SO2 and bisulfite, giving a linear equilibrium relationship. In simple alkali sulfite solution without added buffer, the equilibrium relationship is highly nonlinear, because H-1" accumulates as SO2 is absorbed. Under these conditions is it not possible to carry out reversible SO2 absorption/stripping in a simple system, resulting in greater steam requirements than expected with a linear equilibrium relationship. Weak acid buffers such as sodium citrate have been proposed to "straighten" the equilibrium relationship and thereby reduce ultimate steam requirements (Jl, 2, 7). Citrate buffer is attractive because it is effective over a wide range, from pH 2.5 to pH 5.5 in concentrated solutions. 

Although com can be adequately steeped in sterile, aqueous solutions of sulfur dioxide or sodium, magnesium or potassium bisulfite (hydrogen sulfite) in the laboratory,164-166 commercial steeping involves microorganisms. Raw com carries natural populations of bacteria, yeasts and molds which are capable of rapid multiplication in aqueous systems. Wet-millers learned early that com steeped at temperatures of 45-55°C was sweet, but that putrefaction and butyric acid or alcohol production... 

It must be pointed out that the use of the term "active sodium" is simply one of convenience since it is only an indirect indication of the absorptive potential of the liquor. S02 is actually absorbed by or reacts with the sulfite or bicarbonate ions rather than the sodium ion. Also, even though the bisulfite cannot absorb any S02, it can be regenerated to sulfite (as will be discussed later) and, therefore, it is a potentially active species. The limestone dual alkali system operates at "active sodium" concentrations of 1.1 to 1.7 M. 

Although it is possible to convert the SO2 removed from the flue gas to ammonium sulfate, sodium sulfate, or gypsum, the market for such by-products is quite restricted. More recently, interest has centered on processes that recover the SO2 in concentrated form. One such system, the Wellman Lord Process (licensed by Davy-McKee/Davy Corp. Pic.) uses a solution of sodium or potassium sulfite to absorb SO2. The liquid effluent contains a mixture of sulfites and bisulfites from which the less soluble bisulfites are crystallized. The recovered solids are heated to decompose the bisulfites to sulfites with the release of SO2. These sulfites then are redissolved in the liquid recycled to the scrubber. Only a... 

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