Hypochlorites membrane cell process

Depleted brine will be physically saturated with chlorine, and some chlorine wUl react to form hypochlorite (Section 7.5.9.1). This chlorine value represents an economic asset to be recovered and, particularly in the case of membrane cells, an intolerable contaminant in the brine treatment system. There are several approaches to this problem [208], and we cover these below. We divide them into methods aimed at recovery of the bulk of the chlorine in a useful form (primary dechlorination Section 7.5.9.2) and those whose purpose is to reduce the active chlorine to chloride and safeguard the environment or other parts of the process (secondary dechlorination Section 7.5.9.3). Some of the hypochlorite that forms in the anolyte will continue to react to form chlorate. This is a much less harmful impurity in the cells, and higher concentrations are tolerable. Many plants keep the chlorate concentration under control by natural or deliberate purges from the brine system (Section 7.5.7.2A). In others, it is necessary to reduce some of the chlorate ion to chloride in order to maintain control (Section 7.5.9.4). 

Caustic soda is a likely source of nickel from the corrosion of the evaporators (Section 9.3.2.1). The nickel content of 50% NaOH can be reduced by addition of a corrosion inhibitor to the evaporation process (Section 9.3.4.2). Nickel can be avoided in integrated on-site production of hypochlorite by using less-concentrated NaOH from membrane cells, without evaporation. 

The direct electrochemical oxidation (no cell divider membrane) of wastewater has been employed in the textile industry. Typically, this industry produces an organic-contaminated wastewater that also contains sodium chloride sodium chloride is desirable in promoting anodic oxidation. The presence of sodium chloride is fortuitous for textile manufacturers since the hypochlorite byproduct produced in the electrochemical oxidation process is used for textile bleaching operations.24... 

The more suitable purification method for the bacterial cellulose calls upon distilled water, sodium hydroxide and sodium hypochlorite solutions, since it guarantees the elimination of bacteria cells and culture medium residues from the membrane. For clinical applications, the suitable sterilization processes are gamma radiation and ethylene oxide treatment, but the latter should be avoided for bacterial cellulose dry or wet membrane, because it can cause allergic reactions, mostly when used internally. 

The chlorine evolution reaction and the hydrogen evolution reaction at the anode and the cathode, respectively, in a chlor-alkali cell are controlled by the electrochemical and/or chemical steps rather than by mass transfer. However, the transport phenomena across the separator, either a porous diaphragm or an ion-exchange membrane, are governed by the solution flow near the surface. The disproportionation reaction of hypochlorites in a chlorate cell is diffusion-controlled process. Consequently, knowledge... 

It is possible to neutralize the invading OH ions in the membrane process by addition of hydrochloric acid into the anode compartment and to decrease the pH value down to 2. Then, hypochlorite and chlorate formation is stopped, and the oxygen content in the anode gas is reduced to 0.5 vol.%. No OH ions are formed within the electrolysis cell of the amalgam process so that the oxygen content of chlorine gas is less than 1 vol.%. 

Brine Dechlorination. In the mercury and membrane processes, the depleted brine leaving the cells must be dechlorinated before resaturation. Further acidification with hydrochloric acid to pH 2-2.5 reduces the solubility of chlorine by shifting the equilibrium point of hydrolysis and inhibits the formation of hypochlorite and chlorate. Chlorine discharged in the anolyte tank prior to dechlorination may be fed into the chlorine system. The dissolved chlorine of the brine then is still 400 -1000 mg/L, depending on pH and temperature. The brine is passed down a packed column or sprayed into a vacuum of 50 - 60 kPa, which reduces the chlorine concentration in the brine to 10-30 mg/L. The vacuum is produced by steam jet or liquid-ring vacuum pump. The pure chlorine gas obtained is fed into the chlorine stream. 

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