Bleaching continuous

SANDOZ CHEMICALS Textile Chemicals(Continued) Bleaching(Continued) ... 

Neutralizing Lotion. The principal active ingredient of cold wave neutralizers is usually an oxidizing agent. The most popular is hydrogen peroxide [7722-84-1J, employed at a concentration of 1—2% it continues to find widespread use. Aqueous solutions of sodium bromate [7789-38-0] at a concentration of 10—20% occasionally are used and are technically preferred over the peroxide formulations because of excellent stabiUty and absence of hair bleaching. Neutralizing powders appear to be on the decline but formulations stiU in use consist of sodium perborate [7632-04-4] combined with hexametaphosphates to improve solubiUty in hard water. 

The copper-chelating abihty of sahcylaldoxime has been used to remove copper from brine in a seawater desalination plant effluent. A carbon—sorbate bed produced by sorption of the oxime on carbon proved to be extremely effective in the continuous process (99). In another apphcation, the chelating abihty of sahcylaldoxime with iron and copper was used to stabilize bleaching powders containing inorganic peroxide salts (100). 

Commercial laundries have used and continue to use sodium hypochlorite as the primary bleaching agent because of its whitening and disinfectant properties. 

Because pulp bleaching agents are, for the most part, reactive oxidising agents, appropriate precautions must be taken in their handling and use. For example, it is important to ensure that the threshold limit values (TLV) (20) in Table 2 are not exceeded in the workplace air. These are airborne concentrations in either parts per million by volume under standard ambient conditions or mg per cubic meter of air. They "represent conditions under which it is beUeved that nearly all workers may be repeatedly exposed, day after day, without adverse effect" (20). TWA refers to a time-weighted average for an 8-h workday STEL is a short-term exposure limit or maximum allowable concentration to which workers can be continuously exposed for 15 minutes. 

After bleaching, the a-sulfonated ester has to be neutralized with sodium hydroxide or some other aqueous base to obtain the salt. Hydrolysis of the ester groups is avoided if the temperature does not exceed 45 °C and the pH is between 7.5 and 9. Neutralization is thus performed in a continuous process to ensure pH control and effective heat removal [33]. The concentration of the NaOH solution has to be calculated so that a slurry is obtained that has a low viscosity so as to facilitate further processing. For example, neutralization can produce a 40% aqueous slurry of sodium palm kernel methyl ester a-sulfonate or a 25% aqueous slurry of sodium tallow methyl ester a-sulfonate [33],... 

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