Threshold inhibitors

The most commonly used scale inhibitors are low molecular weight acrylate polymers and organophosphoms compounds (phosphonates). Both classes of materials function as threshold inhibitors however, the polymeric materials are more effective dispersants. Selection of a scale control agent depends on the precipitating species and its degree of supersaturation. The most effective scale control programs use both a precipitation inhibitor and a dispersant. In some cases this can be achieved with a single component (eg, polymers used to inhibit calcium phosphate at near neutral pH). 

Threshold dose, 25 233. See also TD50 estimating, 25 235 Threshold gain, 14 665 Thresholding process, 18 148 Threshold inhibitors, 26 139 Threshold limit values (TLV), 1 819,... 

Threshold inhibitor blends For example, polyvinylcaprolactam + tetrabutylammonium bromide, BP (Duncan et al., 1996) <10... 

In some applications, such as the desalination of a well water, suspended solids and colloids may be negligible and the pretreatment section may consist of pH adjustment and addition of a threshold inhibitor. At the other extreme is the desalination of surface waters, municipal wastes and industrial wastes which may require all of the steps outlined above. 

One method of preventing precipitation is to operate the reverse osmosis unit at a recovery which will not concentrate the feed/reject stream to the compound saturation level. Another method of preventing precipitation is to add a threshold inhibitor, such as sodium hexametaphosphate, certain polyacrylates, organophosphates or phosphonates, to the feedwater. The threshold inhibitors are added at the rate of 1 to 5 mg/fi of feedwater, and they serve to disrupt the formation of a crystalline precipitate during the residence time of the feedwater in the reverse osmosis unit. In doing this, they broaden the solubility limits of the sparingly soluble compounds. 

Sulfuric acid and sodium hexametaphosphate (SHMP) are injected in the feedwater line upstream of the cartridge filters. The sulfuric acid is injected to adjust the feedwater pH to a level of between 4 and 6. The purpose of acid injection is twofold. The primary purpose is to mitigate the possibility of calcium carbonate deposition by conversion of bicarbonate to carbon dioxide. Coincidentally, the rejection performance of the thin film composite membrane is pH sensitive and the optimum performance is at the operating pH level. SHMP is added to the feedwater as a threshold inhibitor to inhibit the crystalline growth of sparingly soluble salts such as calcium sulfate. 

Scale inhibitors or anti-sealants (A/S) are generally organic compounds containing sul-phonate, phosphonate, or carboxylic acid functional groups and chelating agents such as carbon, alum and zeolites that sequester and neutraUse a particular ion that may be formed. The majority of scale inhibitors can be classified as threshold inhibitors. In... 

The above requirements can be met by a class of mineral crystal growth modifiers often referred to as threshold inhibitors. Threshold inhibitors are surface active molecules, usually simple polyelectrolytes, that modify mineral crystal growth at some "threshold" concentration below stoichiometric concentrations of scaling ions in a given system (5-74). BaS04 scale inhibition is usually attempted by treatment of aqueous brines with surface active polyelectrolytes of various chemical functionality, but with only limited success. 

A proprietary class of inhibitors, threshold inhibitors, are also added in small concentration to inhibit crystal growth. 

Uses Sequestrant, deflocculant, threshold inhibitor in cooling water treatment stabilizer for biocides such as chlorine and bromine dispersant for scale formation corrosion inhibitor for carbon steel... 

Uses Sequestrant, deflocculant, threshold inhibitor for water treatment, oilfield treatment, pulp/paper chems., leather treatment chems., textile additives dispersant for solid particles Features Hydrolytic stability... 

Uses Threshold inhibitor for calcium and magnesium water hardness applies. Incl. process aid in detergent mfg. general purpose cleaners heavy duly llqs. dishwasher liqs. hard surf, cleaners Properties M.w. 2500 vise. 60 cps pH 6.3 45% NV Rhodoline DF 6120 [Rhodia Novecare)... 

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