Control of chlorination

Chlorination of methane may yield any one of four organic products, depending upon the stage to which the reaction is carried. Can we control this reaction so that methyl chloride is the principal organic product That is, can we limit the reaction to the first stage, wo/iochlorination  

We might at first expect—naively, as it turns out—to accomplish this by providing only one mole of chlorine for each mole of methane. But let us see what happens if we do so. At the beginning of the reaction there is only methane for the chlorine to react with, and consequently only the first stage of chlorination takes place. This reaction, however, yields methyl chloride, so that as the reaction proceeds methane disappears and methyl chloride takes its place. 

As the proportion of methyl chloride grows, it competes with the methane for the available chlorine. By the time the concentration of methyl chloride exceeds that of methane, chlorine is more likely to attack methyl chloride than methane, and the second stage of chlorination becomes more important than the first. A large amount of methylene chloride is formed, which in a similar way is chlorinated to chloroform and this, in turn, is chlorinated to carbon tetrachloride. When we finally work up the reaction product, we find that it is a mixture of all four chlorinated methanes together with some unreacted methane. 

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If the water is found fit for consumption, with respect to both its mineral and biological content, the problem of sanitization can still arise. Public supply invariably has a very small residual chlorine level. This suppresses biological growth and maintains water quality even when the line is stagnant. As with other forms of treatment, the scale of private supply is usually too small to allow good control of chlorinating equipment. 

Any biological deterioration of cellulose acetate membranes is always by "accidental". To prevent this kind of deteriorations, chlorine injection to feed water is common practice. Inadequate control of chlorine injection may result in the enzymic deterioration of cellulose acetate membrane. 

Gates D. 1999b. Practieal suggestions for meeting USEPA compliance monitoring requirements and in-plant operational control of chlorine dioxide in drinking water. Ozone Sei Eng 21 433-445. 

In the control of chlorine disinfectant systems, the effective use of the chlorine for its intended purpose is assumed if the treated water considerably downstream from the chlorinalor contains a residual of chlorine. Depending upon use. lull-contact tinte may be assumed alter len miuules. or the interval may be extended lo several hnurs. The systems also are usually carefully monitored by bacteriological testing. Normally a dose of I lo 2 milligrams of chlorine per liter is adequate lo destroy all bacteria and leave an effective residual. Residuals of 0.1 to 0.2 milligrams per liter are usually maintained in the diluent streams front water-treatment plants as a factor of safely for consumers. 

Intermittent free residuals may exist at levels of 0.3 to 1.0 ppm, depending on the particular cooling system dynamics, which, as has been said previously, may present additional corrosion risks if the free reserve is too high. Good control of chlorine is essential ... 

Chlorine content. One method for process monitoring and control of chlorine concentration is measurement of thermal conductivity. 

Although the flowsheet shown in Fig. 4.7a is very attractive, it is not practical. This would require careful control of the stoichiometric ratio of decane to chlorine, taking into account both the requirements of the primary and byproduct reactions. Even if it was possible to balance out the... 

CH2=CHC = CCH = CH2. a colourless liquid which turns yellow on exposure to the air it has a distinct garlic-like odour b.p. 83-5°C. Manufactured by the controlled, low-temperature polymerization of acetylene in the presence of an aqueous solution of copper(I) and ammonium chlorides. It is very dangerous to handle, as it absorbs oxygen from the air to give an explosive peroxide. When heated in an inert atmosphere, it polymerizes to form first a drying oil and finally a hard, brittle insoluble resin. Reacts with chlorine to give a mixture of chlorinated products used as drying oils and plastics. 

Chlorine Trifluoride. Chlorine trifluoride is produced commercially by the continuous gas-phase reaction of fluorine and chlorine ia a nickel reactor at ca 290°C. The ratio of fluorine to chlorine is maintained slightly in excess of 3 1 to promote conversion of the chlorine monofluoride to chlorine trifluoride. Sufficient time ia the reactor must be provided to maintain high conversions to chlorine trifluoride. Temperature control is also critical because the equiHbrium shift of chlorine trifluoride to chlorine monofluoride and fluorine is significant at elevated temperatures. 

Other burners are used for low capacity operations. A cascade or checker burner, ia which molten sulfur flows down through brick checkerwork countercurrent to a flow of air, is used ia small units with a sulfur trioxide converter to condition gases entering electrostatic precipitators at boiler plants operating on low sulfur coal. A small pan burner, which is fed with soHd, low carbon sulfur, is used to produce sulfur dioxide for solution ia irrigation water to control the pH and maintain porosity ia the soil. The same type of burner is used to disiafect wastewater ia this case sulfur dioxide is used iastead of chlorine. 

The misconception that vinyl gives off dioxin when it is incinerated is misleading. A study conducted by ASME in 1995 (162) found that the presence, or absence, of chlorine-containing wastes in incinerators had no effect on the levels of dioxin produced. Rather, it was found that incinerator operating conditions (primarily temperature) were the key to controlling dioxin formation. More recentiy, German officials examined the issue of incinerating vinyl waste and decided there was no cause for concern (180). 

Most microbes in cooling systems can be controlled by chlorine or bromine treatment if exposed to a sufficient residual for a long enough time. A free chlorine residual of 0.1—0.5 ppm is adequate to control bulk water organisms if the residual can be maintained for a sufficient period of time. 

Water Quality Maintenance. In addition to controlling algae and microorganisms such as bacteria, proper swimming pool maintenance requires control of free and combined available chlorine, pH, alkalinity, hardness, and saturation index. Ranges for various swimming pool parameters (Table 2) are recommended by The National Spa and Pool Institute (14). 

Granular) control of algae and bacteria in ponds—5—10 mg/L residual chlorine for 12—24 h ... 

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