Chloramines trichloramine

Trichloramine is the most irritant of the chloramines together with dichloramine it is largely responsible for the chlrorine odours and eye irritation. 

Note that trichloramine is an unstable gas that quickly dissociates into its components. The formation of the particular species of chloramines formed is dependent on pH. Trichloramine is formed at pH less than 4.4. Dichloramine is formed at pH 4.4 to 6.0. Monochloramine is the most prevalent species at pH greater than about 7. 

In wastewaters, NH3 originates from the enzymatic attack of nitrogen-containing molecules (e.g., urea and proteins). The hypochlorous acid can then react stepwise with ammonia so as to produce the three chloramines (i.e., mono-, di-, and trichloramine) ... 

Consider the formation of the nitrate ion. The oxidation state of nitrogen in the nitrate ion is +5. Thus, this ion would not be formed from ammonia, because this would need the abstraction of eight electrons. If it is formed from the monochloramine, it would need the abstraction of six electrons, and if formed from the dichloramine, it would need the abstraction of four electrons. Thus, in the chloramine reactions with HOCl, the nitrate is formed from the dichloramine. We will, however, compare which formation forms first from the dichloramine trichloramine or the nitrate ion. The oxidation state of the nitrogen atom in trichloramine is -i-3. Thus, to form the trichloramine, two electrons need to be abstracted from the nitrogen atom. This may be compared to the abstraction of four electrons from the nitrogen atom to form the nitrate ion. Therefore, the trichloramine forms first before the nitrate ion does. 

Now, let us discuss the final fate of trichloramine during disinfection. In accordance with the chloramine reactions [Reactions (17.34) to (17.36)], by the time three moles of HOCl have been added, a mole of trichloramine would have been formed. This, however, is not the case. As mentioned, while the monochloramine decomposes in a stepwise fashion to convert into the dichloramine, its destruction into the nitrogen gas intervenes. Thus, the eventual formation of the dichloramine would be less in fact, much, much less, since, as we have found, formation of the gas is favored over the formation of the dichloramine. In addition, monochloramine and dichloramine, themselves, react with each other along with HOCl to form another gas N2O [NH2CI -1-NHCI2 + HOCl N2O -I- 4H" -I- 4CL]. Also, there may be more other side reactions that could occur before the eventual formation of the dichloramine from monochloramine. Overall, as soon as the step for the conversion of the dichloramine to the trichloramine is reached, the concentration of dichloramine is already very low and the amount of trichloramine produced is also very low. Thus, if, indeed, trichloramine has a disinfecting power, this disinfectant property is useless, since the concentration is already very low in the first place. This is the reason why combined chlorine is only composed of the monochloramine and the dichloramine. Also, it follows... 

As the curve continues to go downhill from point B, the dichloramine converts to the trichloramine, the conversion being complete at the lowest point indicated by breakpoint. As shown, this lowest point is called the breakpoint. In addition, nitrates will also be formed from the dichloramine before reaching the breakpoint. In fact, other snbstances wonld have been formed as decomposition products from monochloramine and dichloramine, as well as other snbstances would have been formed as decomposition prodncts from the chloro-organic compounds and organic chloramines. 

The breakpoint reactions only break down the decomposable fractions of the respective substances. All the nondecomposables will remain after the breakpoint. This will include, among other nondecomposables, the residual organic chloramines, residual chloro-organic compounds, and residual ammonia chloramines. As we have learned, the trichloramine fraction that comes from ammonia chloramines has to be very small at this point to be of value as a disinfectant. All the substances that could interfere with disinfection and all decomposables wonld have already been destroyed, therefore, any amount of chlorine applied beyond the breakpoint will appear as free chlorine residual. 

Figure 11.13. General scheme of breakpoint chlorination difference between total residual Cl and chlorine dose reflects chlorine demand, primarily from ammonium and amines. Before breakpoint, most Cl is in combined forms, primarily mono- and dichloramine after the breakpoint, the combined residual consists of slow-reacting organic chloramines. Added Cl remains in free form after the breakpoint. Sharpness of breakpoint and minimum observed Cl concentration depend on pH, temperature, and time of reaction. Loss of residual Cl at breakpoint is caused by oxidation of di- and trichloramines to Nj according to reactions 33a and 33b and other reactions. (Adapted from Brezonik, 1994.)...

The mix of species produced depends on the ratio of chlorine to ammonia and the pH of the water. In the pH range of 7-8 with a chlorine-to-ammonia ratio (by weight) of 3 to 1, monochloramine is the principal product. At higher chlorine-to-ammonia ratios or at lower pH values (5-7), some dichloramine will be formed. If the pH drops below 5, some nitrogen trichloride (often erroneously called trichloramine ) may be formed. Nitrogen trichloride formation should be avoided because it imparts undesirable taste and odor to the water. To compare the disinfection efficiencies of secondary chlorination with secondary chloramination, a design engineer should also consider the effect of each process on corrosion control (see Appendix A). 

Distribution of mono-, di- and trichloramines depends on pH, temperature, time of reaction and mass ratio of chlorine and ammonia nitrogen. At a certain ratio chloramines are degraded to form elementary nitrogen or dinitrogen monoxide. This process can be represented by the following summary reactions ... 

The chemistry of chloramines has been reviewed by Kovacic et al. (1970). In water, depending on pH and concentration, monochloramine (NH2CI), dichloramine (NHCI2), or trichloramine (NCI3), may be present, in addition to organic chloramines derived from amines. 

Chloramines (referred to as combined chlorine) are formed when water containing ammonia is chlorinated. There are three inorganic chloramine species monochloramine (NH2CI), dichloramine (NHCI2), and trichloramine (NCI3). The species of chloramines that are formed depends on factors such as the ratio of chlorine to ammonia-nitrogen, chlorine dose, temperature, pH, and alkalinity. 

Chlorination of swimming-pool water results in the formation of many chlorinated products. The most frequent derivative is trichloromethane (chloroform) (Camman and Hiibner 1995). Combined with organic nitrogenous compounds (urea, creatinine) generated by swimmers (sweat, urine), active free chlorine produces combined chlorine compounds, such as chloramines, which are irritants. When residual free chlorine levels are lower than 0.3 mg/1, chloramines increase. To decrease chloramine irritant levels and dissociate trichloramines, it is necessary to add chlorine, to provide water renewal and to ensure good air... 

The two chemical species formed by chlorine in water, HOCl and OCl , are known as free available chlorine and are very effective in kilting bacteria and other pathogens. In the presence of ammonia, HOCl reacts with ammonium ion to produce monochloramine (NH2CI), dichloramine (NHCI2), and trichloramine (NCI3), three species collectively called combined available chlorine. Although weaker disinfectants than chlorine and hypochlorite, the chloramines persist in water distribution systems to provide residual disinfection. 

Note that trichloramine is an unstable gas that quickly dissociates into its components. The formation of the specific species of chloramines is dependent on pH and the ratio of chlorine to ammonia. Trichloramine is formed at pH less than 4.4. Dichloramine which is responsible for the swimming pool smell, is formed at pH 4.4 to 6.0. Monochloramine is the most prevalent species at pH greater than about 7. The amount of HOCl fed per pound of ammonia also determines the species that is formed. AA en the ratio of HOCl to NHj is less than 6.7 1, monochloramine is formed. Above this ratio, dichloramine is formed, and above 9.5 1, trichloramine is formed. Breakpoint chlorination occurs at ratios greater than 13.5 1, where all mono- and di-chloramines are destroyed. 

Chloramine, like chlorine, is an oxidizing biocide used for disinfection. Three species collectively make up chloramines, also known as combined chlorine monochloramine, NH Cl dichloramine, NHCl and nitrogen trichloride (trichloramine), NCI3. Of these, monochloramine has the highest standard reduction potential furthermore, it is less prone to impart chlorinous taste and odor to water like other forms of chloramine. As a result, monochloramine is preferred for disinfection applications. 

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