Sodium carbonate, dechlorination

Mono-substitution occurs most readily in the stepwise replacement of the halogen substituents of 2,4,6-trichloro-s-triazine with aqueous methanol and sodium bicarbonate (30°, 30 min), the monomethoxy derivative (324) is obtained on heating (65°, 30 min), the disubstitu-ted derivative is formed and on brief heating (65°) with the more basic sodium carbonate or methanolic sodium hydroxide (25°, 3 hr) complete methoxylation (320) occurs. Ethanolic ethoxide (25°, 1 hr) or sodium carbonate (35°) is sufficient to give complete ethoxy-dechlorination. The corresponding phenoxy derivatives are obtained on treatment with one (0°), two (15°, 1 hr), or three equivalents (25-70°, 3 hr) of various sodium phenoxides in aqueous acetone. The stepwise reaction with phenols, alcohols, or thiols proceeds in better yield in organic solvents (acetone or chloroform) with collidine or 2,6-lutidine as acid acceptors than in aqueous sodium bicarbonate. ... 

The ion-exchange catalyst dechlorinates the plastics (e.g. PVC) and therefore avoids issnes with HCl generation and chlorine contamination of the diesel. The company claims to have processed cable waste consisting of almost 100% PVC and the catalytic depolymerization process produced diesel fuel with a chlorine content below the detection limit. The catalyst needs to be activated before use via ion exchange using soda (sodium carbonate) and lime (calcium hydroxide) in order to insert the sodium and calcium ions... 

Figure 24. Schematic diagram of a brine circulation system in the mercury cell process a) Electrolysis cell b) Anolyte tank c) Vacuum column dechlorinator d) Cooler e) Demister f) Vacuum pump g) Seal tank h) Final dechlorination i) Saturator k) Sodium carbonate tank I) Barium chloride tank m) Brine reactor n) Brine filter o) Slurry agitation tank p) Rotary vacuum filter q) Vacuum pump r) Brine storage tank s) Brine supply tank...

CASRN 127-20-8 molecular formula C3H3Cl2Na02 FW 164.95 Soil. Undergoes dechlorination and the liberation of carbon dioxide in soil. The residual activity is limited to approximately 3-4 months (Hartley and Kidd, 1987). The average half-life for dalapon-sodium in soil incubated in the laboratory under aerobic conditions was 15 d (Namdeo, 1972). 

The most common method for achieving aromatization of compounds such as 72 is with phosphorus oxytrichloride and the addition of dimethylformamide (DMF Scheme 1) (see, for example, <1996CHEC-II(7)921>, and more recently, <2004M283, 1997S567>). Reductive dechlorination of 73 with palladium on carbon in the presence of sodium hydroxide affords the corresponding heterocycle 74 (Scheme 1) <2004M283>. 

Water from the wastewater treatment plants of paper mills, power plants, etc., contains high chlorine residues in aqueous media, which causes environmental concern. Several methods have been used for dechlorination, including granular activated carbon, hydrogen peroxide, sodium thiosulfate, ammonia, sodium sulfite, and metabisulfite. In addition, ferrous sulfate hep-tahydrate has also been proposed for the removal of chlorine residues. 

Chlorine can be removed from RO feed water using sodium bisulfite or carbon filtration (see Chapters 8.2.4 and 8.1.4, respectively). As discussed in Chapter 8.1.4, carbon in carbon filters can aide the growth of microbes so carbon filtration is typically not recommended for dechlorination of RO feed water unless the concentrations of organics is high enough to warrant its use, or if the dosage of sodium bisulfite is too low for accurate control. 

Effluents from sewage treatment plants are not allowed to contain residual chlorine in excess of tolerable values as determined by water quality standards. For example, in discharges to trout streams, the residual chlorine should not exceed 0.02 mg/L. Thus, chlorinated effluents should be dechlorinated. Sulfur dioxide, sodium sulfite, sodium metabisullite, and activated carbon have been used for dechlorination. Because sulfur dioxide, sodium sulfite, and sodium metabisulfite contain sulfur, we will call them sulfur dechlorinating agents. Dechlorination is an oxidation-reduction reaction. The chemical reactions involved in dechlorination are discussed next. 

To eliminate residual free chlorine from hquid, granular activated carbon adsorption or chemical reduction (with reducing agents, such as sulfur dioxide, sodium bisulfite, and sodium metabisulfite) are the most common processes for dechlorination. Ultraviolet (UV) irradiation process is gaining wider acceptance as a dechlorination process (30,45,46, 60,61). 

Another example of a liquid-phase reaction used to produce precursors for nonoxide powders involves reductive dechlorination of halide solutions. An example is the reaction between silicon tetrachloride, carbon tetrachloride, and sodium in heptane at 300°C ... 

As remarkable as the performances of these membranes are, aU aromatic PA membranes have one severe drawback their susceptibility to degradation by chlorine. The removal of chlorine prior to membrane separation by activated carbon, sodium sulphite (Na2S03), or sodium bisulphite (NaHSOa) addition is, therefore, mandatory. Dechlorination by NaHSOs in stoichiometric excess can, however, be ineffective in seawater feed because dissolved oxygen in seawater reacts with the chemical. Further, the absence of chlorine can lead to biofouling that is often irreversible. 

Free chlorine (CI2) is an oxidant. Polyamide RO and NF membranes are sensitive to chlorine. Hence, water must be dechlorinated by passing it through an activated carbon filter or by the addition of a reducing chemical such as sodium sulphite, sodium bisulphite, or sodium metabisulphite to feed water. However, it is necessary for CA membranes to protect them from bacterial attack. 

---