Sulfite solutions

Empty containers may be destroyed in an incinerator or decontaminated by washing with a dilute thiosulfate or sulfite solution. Bulk wastes should be treated by controlled iodine recovery processes. 

In a cychc method selenium is dissolved in hot sodium sulfite solution to form sodium selenosulfate [25468-09-1]. 

The anaerobic reaction of sulfur dioxide with aqueous ammonia produces a solution of ammonium sulfite [10192-30-0]. This reaction proceeds efficientiy, even with a gas stream containing as Httie as 1 wt % sulfur dioxide. The sulfur dioxide can be regenerated at a high concentration by acidulation or by stream stripping of the ammonium sulfite solution, or the sulfite can be made to precipitate and the ammonia recovered by addition of lime (243). The process can also be modified to produce ammonium sulfate for use as fertili2er (244) (see Fertilizers). In a variant of this process, the use of electron-beam radiation cataly2es the oxidation of sulfur dioxide in the presence of ammonia to form ammonium sulfate (245). 

Manufacture. Aqueous sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite solution are treated with sulfur dioxide to produce sodium metabisulfite solution. In one operation, the mother Hquor from the previous batch is reinforced with additional sodium carbonate, which need not be totally in solution, and then is treated with sulfur dioxide (341,342). In some plants, the reaction is conducted in a series of two or more stainless steel vessels or columns in which the sulfur dioxide is passed countercurrent to the alkaH. The solution is cooled and the sodium metabisulfite is removed by centrifuging or filtration. Rapid drying, eg, in a stream-heated shelf dryer or a flash dryer, avoids excessive decomposition or oxidation to which moist sodium metabisulfite is susceptible. 

Sodium Sulfite Solution 25-9 in Oxygen Scavenging, Technical Information Bulletin TlR-13, Rhtjane-Poulenc Basic Chemicals Co., Shelton, Conn., 1991. R. L. Miron, Mater. Peform., 45 (June 1981). 

Regenerable absorption processes have also been developed. In these processes, the solvent releases the sulfur dioxide in a regenerator and then is reused in the absorber. The WelLman-Lord process is typical of a regenerable process. Figure 11 illustrates the process flow scheme. Sulfur dioxide removal efficiency is from 95—98%. The gas is prescmbbed with water, then contacts a sodium sulfite solution in an absorber. The sulfur dioxide is absorbed into solution by the following reaction ... 

In a 4-I. wide-mouthed glass jar, fitted with a mechanical stirrer, is placed a solution of 150 g. (3 moles) of sodium cyanide (Note i) in 500 cc. of water and 318 g. (3 moles) of u.s.P. benz-aldehyde. The stirrer is started and 850 cc. of a saturated solution of sodium bisulfite (Note 2) is added to the mixture, slowly at first and then in a thm stream. The time of addition is ten to fifteen minutes. During the addition of the first half of this solution, 900 g. of cracked ice is added to the reaction mixture, a handful at a time. The layer of mandelonitrile which appears during the addition of the sulfite solution is separated from the water in a separatory funnel. The water is extracted once with about 150 cc. of benzene, the benzene is evaporated, and the residual mandelonitrile is added to the main portion. 

Free iodine, if present, is removed by the addition of 5 per cent sodium sulfite solution. 

Yoshida and Akita (Yl) determined volumetric mass-transfer coefficients for the absorption of oxygen by aqueous sodium sulfite solutions in counter-current-ffow bubble-columns. Columns of various diameters (from 7.7 to 60.0 cm) and liquid heights (from 90 to 350 cm) were used in order to examine the effects of equipment size. The volumetric absorption coefficient reportedly increases with increasing gas velocity over the entire range investigated (up to approximately 30 cm/sec nominal velocity), and with increasing column diameter, but is independent of liquid height. These observations are somewhat at variance with those of other workers. 

Adlington and Thompson (Al) measured the gas-liquid interfacial area in beds of particles of from 0.3- to 3-mm diameter by oxygen absorption in a sodium sulfite solution. They found that the interfacial area decreased with decreasing bed porosity, and was less sensitive to changes in particle size. 

This method involves measurement of the oxidation rate of an aqueous sodium sulfite solution catalyzed by cupric or cobaltous ions. The oxygen absorbed reacts with the sulfite according to the equation ... 

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. 

Calderbank et al. (C1-C4), who worked with systems quite similar geometrically to that of Yoshida and Miura, found that the average bubble diameter for air in water at 15°C ranged from 3 to 5 mm. Westerterp et al. (W2-W4) found the range to be 1-5 mm for air in sodium sulfite solution at 30°C. In addition, they noted that any increase in interfacial area between the bubbles and the liquid was due primarily to the increase in gas holdup, and the average bubble diameter was essentially unaffected by the impeller speed and was approximately 4.5 mm (W3). 

Gal-Or and Resnick (G8) measured average residence time in a system that was geometrically similar to those used by Cooper et al (C9) and Yoshida et al (Y4) with air-distilled water and air-sodium sulfite solutions of the same concentration as used by these investigators. The ratio of impeller to tank diameter was 0.4 in one series (as in the work of Cooper and Yoshida) and 0.3 in a second series. Gal-Or and Resnick reported their results as an average residence time in seconds per foot of gas-free liquid, Bh. The average residence time was calculated from the equation... 

Nowadays economy and ecology render the reuse of the sulfite solution increasingly important. Normally the scrubber liquor is recovered as dilution water directly in the neutralization of sulfonation plant or in the slurry preparation unit of synthetic detergent plants. In some special cases, when the presence of sulfites is incompatible with the slurry composition, it is possible to install as optional a sulfite oxidation unit. This oxidation takes place with atmospheric air. 

Highly active CuCl catalysts for the direct process of methylchlorosilane synthesis were prepared by reducing Cu with a sodium sulfite solution in the presence of dispersing agents. Several well-known dispersants, e.g. SDBS, were used in this study. When SDBS was used, a catalyst in the form of small flakes was obtained that gave the best performance in reactivity, product selectivity and silicon conversion. This provides a convenient way to prepare the CuCl catalyst for use in industrial production. 

Elemental sulfur dissolves in boiling aqueous sodium sulfite solutions with the formation of sodium thiosulfate (Na2S203). The reaction proceeds quantitatively if sulfur and excess sodium sulfite are boiled for some time in weakly alkaline solutions. In the cold, however, practically no reaction occurs. Alternatively, thiosulfate can be produced quantitatively in solution phase by using organic solvents to first dissolve sulfur and then accomplish the reaction with aqueous sulfite. In a parallel reaction, elemental selenium dissolves in alkaline sulfite solution to produce selenosulfate, SeSO ... 

Fig. 12. The hydrogen and cadmium metal concentration at various times of illumination of CdS in a 1 M sulfite solution...

A flowsheet for the Wellman-Lord process is shown in Figure 25.26. Again the gas stream with S02 enters a scrubber into which is sprayed a sodium sulfite solution. This then goes to an evaporator/crystallizer to crystallize out the resulting sodium bisulfite, which converts the sodium bisulfite back to sodium sulfate, releasing the S02. The crystals are dissolved in water and recycled to the scrubber. The effect of the Wellman-Lord process is to produce a concentrated S02 stream from a dilute S02 stream. The resulting concentrated S02 still needs to be treated. 

A violent explosion occurred during the distillation of solvents that had contained the peroxyacid. Although the solvents had been treated by addition of sodium sulfite to reduce the acid, dipropionyl peroxide (which is not reduced by sulfite, and which may have been produced by the sulfite treatment) remained in solution and subsequently decomposed on heating. If the solvent is added to the sulfite solution, the diacyl peroxide is not formed. 

The remaining half of the sulfite solution is subjected to the same treatment, and the total ether extract, after drying, is evaporated on a water bath. The residue is then distilled under reduced pressure, yielding 200-215 g. of almost colorless citral which boils at 84-85°/2 mm. (93-95°/5 mm.). 

A pressure outlet may be used, but the arrangement outlined here is quite sufficient. Citral and pseudoionone are both rapidly polymerized by contact with aqueous sodium hydroxide. This apparatus continuously provides an intimate mixture of the sulfite solution with the ether. On decomposition, the free carbonyl compound is immediately extracted and prolonged contact with sodium hydroxide is thus avoided. 

Wellman-Lord The most widely used regenerable flue-gas desulfurization process. The sulfur dioxide is absorbed in sodium sulfite solution in a wet spray scrubber, forming sodium bisulfite ... 

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