Treating processes hypochlorite

In another process, hypochlorite filtrate is treated with lime slurry to precipitate dibasic crystals that are filtered. The filtrate is mixed with strong caustic, chlorinated, and filtered to remove NaCl crystals. The filtrate containing Na and Ca hypochlorite is mixed with dibasic crystals and chlorinated producing a slurry of Ca(OCl)2 is filtered the cake goes to a dryer and the filtrate to the dibasic crystallizer (195). 

The abatement of chlorine vents and the subsequent destruction of the resulting sodium hypochlorite has been the subject of many studies. There are a variety of approaches to the waste hypochlorite destruction including chemical dosing, homogeneous and slurry catalysis as well as fixed-bed catalysis. For the most part these processes treat the hypochlorite at its natural strength the stoichiometric equivalent strength of the caustic soda fed to the scrubber. 

Lime is used in the paper industry to produce the bleaching agent calcium hypochlorite (Ca(OCl)2). Slaked lime is used to recover sodium hydroxide from soda ash after the pulping process ( )2( ) + Na2C03(a(i) —> 2NaOH(a(j) + CaC03(s). The recovered calcium carbonate can be used to regenerate lime. Lime is also used to treat process water in the paper industry. 

Raw lac is first treated to remove water-soluble carbohydrates and the dye that gives lac its red color. Also removed are woody materials, insect bodies, and trash. It is further refined by either hot filtration or a solvent process. In the heat process, the dried, refined lac is filtered molten through cloth or wine screens to produce the standard grades of orange shellac. In the solvent process, lac is dissolved and refluxed in alcohol solvents, filtered to remove dirt and impurities, and concentrated by evaporation. The lac can be further decolori2ed in this process to produce very pale grades. Bleached shellac is prepared by treatment with dilute sodium hypochlorite and coalesced into slabs. 

Chlorine relieved through process venting of the plants, or released inside one of the buildings handling liquefied chlorine will be scrubbed, i.e. treated through absorption in a solution of sodium hydroxide to generate sodium hypochlorite. 

Traditionally, processes have used a single destruction technique, and this has historically been the case also for HYDECAT . Thus, nearly all installed processes treat the waste hypochlorite at the concentration it exits the scrubbing system down to concentrations suitable for discharge (Fig. 26.2). The key aspect in the re-evaluation described herein is to question the practices of firstly single technology and secondly end-of-pipe treatment the destruction of the hypochlorite exclusively in the blowdown stream from the scrubber. That is, it is questioned whether installation of a single treatment technique solely to process the effluent at its natural concentration from the scrubber loop is necessarily the best process option. This chapter will consider the two parts of the question paraphrased above sequentially. 

How -elimination reactions and subsequent processes under alkaline conditions affect the carbonyl groups and the Mw of an oxidized cotton linters is shown in Fig. 2. The initial concentration of carbonyls is 30 pmol/g, introduced by hypochlorite treatment at pH 7. The sample was treated with a buffer solution of pH 11 at 40 °C. The Mw suffers a steep decrease within the first 5 hours, the drop in carbonyls proceeds at a significantly lower rate. While the changes in Mw level off after approx. 20 hours of treatment, the carbonyl groups are slightly decreasing further (unpublished results). 

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