Unstabilized chlorines

Lower chemical reactivity with non-target molecules is useful for another performance-related reason. Microorganisms prefer the protection and luxuriant environment in biofilms (the adherent microbial communities that cause detrimental surface-fouling effects in water cooling systems). Most (>99%) of the viable microorganisms in industrial systems are found in biofilms, not floating around freely in the bulk recirculating water. Compared to unstabilized chlorine or bromine, STABREX more effectively removes and disinfects biofilms as shown in Table 6. 

There are two classes of chlorine commonly used in swimming pools referred to as unstabilized and stabilized. To protect hypochlorous acid from UV degradation cyanuric acid is added to the water. Whether the cyanuric acid is supplied endogenously by the product (stabilized) or whether the cyanuric acid must be added separately (unstabilized) distinguishes the classes. Unstabilized chlorine compounds are chlorine gas, sodium hypochlorite, calcium hypochlorite and lithium hypochlorite. Stabilized chlorine compounds are chlorinated forms of cyanuric acids, sodium dichloro-s-triazinetrione (dichlor) and trichloro-s-triazinetrione (trichlor). It is important to never mix stabilized and unstabilized chlorine products because they are not compatible and can be combustible when mixed as concentrates. 

Unstabilized chlorines. Chlorine gas, sodium hypochlorite, calcium hypochlorite, and lithium hypochlorite do not contain cyanuric acid as part of its makeup and are classified as unstabilized. However, they can be stabilized with the addition of 25 to 150 ppm of cyanuric acid directly to the pool. 

Sodium dichloro-s-triazinetrione sodium dichloroisocyanurate or dichlor) [II, 2L2.6. Sodium dichloro-s-triazinetrione, Dichlor, has been used to sanitize pools and spas since the 1960s. Dichlor is usually sold as white granules in either anhydrous or dihydrate forms. The available chlorine for these chemicals are 63% and 56%, respectively. Several companies have recently introduced dichlor combined with other oxidizers. These blended products vary in their available chlorine content. Dichlor is readily soluble and is the only chlorine product with a nearly neutral pH (6.0, 1% solution 25 "C) (NSPI, 1994). Dichlor is used in both pools and spas as a primary sanitizer. Dichlor will react with most other chemicals, especially unstabilized chlorines. Dichlor is sensitive to moisture. 

At 25°C, pH 7.5, 1.5 ppm FAC, and 25 ppm cyanuric acid, the calculated HOCl concentration is only 0.01 ppm. Although the monochloroisocyanurate ion hydrolyzes to only a small extent, it serves as a reservoir of HOCl because of rapid hydrolysis. Indeed, this reaction is so fast that HClCy behaves like FAC in all wet methods of analysis. Furthermore, since HClCy absorbs uv only below 250 nm, which is filtered out of solar radiation by the earth s atmosphere, it is more resistant to decomposition than the photoactive C10 , which absorbs sunlight at 250—350 nm and represents the principal mode of chlorine loss in unstabilized pools (30). As Httie as 5 ppm of bromide ion prevents stabilization of FAC by cyanuric acid (23) (see also Cyanuric and ISOCYANURIC acids). 

Reactivities of several chlorinated solvents, including chloroform, with aluminum, iron, and 2inc in both dry and wet systems have been deterrnined, as have chemical reactivities in oxidation reactions and in reactions with amines (11). Unstabilized wet chloroform reacts completely with aluminum and attacks zinc at a rate of >250 //m/yr and iron at <250 //m/yr. The dry, uiiinhibited solvent attacks aluminum and zinc at a rate of 250 )J.m/yr and iron at 25 ]lni / yr. 

Charcoal screenings, wet Charcoal, wet Chlorine azide Chlorine dioxide Chloroacetaldehyde Chloroacetone (unstabilized) Chloroacetonitrile Chloroformates, n.o.s. Chloroprene, uninhibited Chlorosulphonic acid Coal briquettes, hot Coke, hot Copper acetylide... 

Charcoal screenings, wet Charcoal, wet Chlorine azide Chlorine dioxide Chloroacetaldehyde Chloroacetone (unstabilized)... 

Index of additive Additive Ratio of rates of dehydro-chlorination of stabilized and unstabilized PVC in 180 min at 175 C, ... 

The oxidation potential of halogens is the result of their strong affinity to electrons. The introduction of any of the unstabilized or stabilized forms of chlorine produce hypochlorous acid (HOCl) and hypochlorite ion (OCl ) when dissolved in water. The total amount of both species is referred to as free available chlorine. Hypochlorous acid is the primary chemical responsible for sanitation. The hypochlorous acid and hypochlorite ion equilibrium is illustrated by the following equation ... 

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