Sulfite systems, sodium-base

The sodium-base sulfite systems present experience with sulfur recovery processes that may have wide application outside the paper pulp industry. The basic chemistry involved is historically very old (122). Essentially, four steps underlie the various processes ... 

Numerous sulfite chemical pulping recovery systems are in use today. Heat and sulfur can be recovered from all liquors generated however, the base chemical can only be recovered from magnesium and sodium base processes. See Smook s Handbook12 for more information. 

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. 

Where water softening is provided and there is no reduction in system water TDS, treatments are primarily based on inorganic corrosion inhibitor blends (nitrite, molybdate, etc.). Under these circumstances, there is no benefit in using an expensive organic oxygen scavenger to keep the TDS level low, and a common chemical such as catalyzed sodium sulfite may be used. 

An efficient synthesis of 1,4-oxazepines has been developed based on iodine-sodium bicarbonate-promoted intramolecular cyclisation of the enamides 237, which were derived in turn from the p-formyl enamides 236 by sodium borohydride reduction. Reductive removal of the iodo-substituent in 238 was readily achieved using sodium sulfite. The R1 and R2 groups were part of a ring system, for example a steroid system [01SC3281],... 

Oh et al. [16] have demonstrated that a microemulsion based on a nonionic surfactant is an efficient reaction system for the synthesis of decyl sulfonate from decyl bromide and sodium sulfite (Scheme 1 of Fig. 2). Whereas at room temperature almost no reaction occurred in a two-phase system without surfactant added, the reaction proceeded smoothly in a micro emulsion. A range of microemulsions was tested with the oil-to-water ratio varying between 9 1 and 1 1 and with approximately constant surfactant concentration. NMR self-diffusion measurements showed that the 9 1 ratio gave a water-in-oil microemulsion and the 1 1 ratio a bicontinuous structure. No substantial difference in reaction rate could be seen between the different types of micro emulsions, indicating that the curvature of the oil-water interface was not decisive for the reaction kinetics. More recent studies on the kinetics of hydrolysis reactions in different types of microemulsions showed a considerable dependence of the reaction rate on the oil-water curvature of the micro emulsion, however [17]. This was interpreted as being due to differences in hydrolysis mechanisms for different types of microemulsions. 

It has been shown that the addition of a small amount of the anionic surfactant sodium dodecyl sulfate (SDS) to a microemulsion based on nonionic surfactant increased the rate of decyl sulfonate formation from decyl bromide and sodium sulfite (Scheme 1 of Fig. 2) [59,60]. Addition of minor amounts of the cationic surfactant tetradecyltrimethylammonium gave either a rate increase or a rate decrease depending on the surfactant counterion. A poorly polarizable counterion, such as acetate, accelerated the reaction. A large, polarizable counterion, such as bromide, on the other hand, gave a slight decrease in reaction rate. The reaction profiles for the different systems are shown in Fig. 12. More recent studies indicate that when chloride is used as surfactant counterion the reaction may at least partly proceed in two steps, first chloride substitutes bromide to give decyl chloride, which reacts with the sulfite ion to give the final product [61]. 

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). 

A water system naturally contains sulfate-based compounds, but when sulfite is added to a closed water system as an oxygen scavenger and corrosion inhibitor, the sodium sulfite is oxidized to sodium sulfate, as indicated in Equation 18.1 (Yuzwa 1991) ... 

Method B Through the column heated at 340-350°C, 21 g methyl a-methylphenethyl sulfite was dropped in about 1 h. After all the liquid had been passed through, the system was swept with nitrogen for 15 min, then the column was taken off and the receiver was stoppered and heated on a steam bath under a pressure of 5 mmHg to bring all volatile products into the dry ice trap. A residue of 4 g unchanged sulfite was left in the flask. The liquid that had collected in the dry ice trap was dissolved in ether and washed with water to eliminate sulfur dioxide and methanol. After the elimination of the ether, 9 g of liquid remained (96% based on unrecovered sulfite). The refractive index did not change after distillation from sodium. 

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