Sodium ions, carbon sequestration

FIG. 8.13 Sequestration of water hardness ions by detergent builders. Sodium polyacrylate Mw = 170,000, STPP (sodium tripolyphosphate), NTA (nitrilotriacetic acid), EDTA (ethylenediamine tetraacetic acid), sodium citrate, CMOS (sodium carboxymethoxysucci-nate), sodium carbonate, zeolite A. (Reproduced from Nagarajan, M.K., J. Am. Oil Chem. Soc., 62, 949, 1985. With permission.)... 

Alkali carbonates and silicates precipitate out Ca + ions as CaCOj, and can leave insoluble deposits on clothes and washing machines. Organic bnilders, in spite of good sequestration capacity, have found limited use because of unfavorable cost-performance benefits. Citrates have replaced sodium TPP, and because of high solubility and lower effective pH, they make good builders in enzyme formulations. Polycarboxylate salts such as EDTA and NTA, in spite of their efficiency as chelators, are not widely used. NTA, because of its toxicity profile, has very limited use as a builder. Zeolite A, an insoluble builder, has also been used as a nonphosphate bnilder. 

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