Chlorination, rate

Continuous chlorination of a cooling water system often seems most pmdent for microbial slime control. However, it is economically difficult to maintain a continuous free residual in some systems, especially those with process leaks. In some high demand systems it is often impossible to achieve a free residual, and a combined residual must be accepted. In addition, high chlorine feed rates, with or without high residuals, can increase system metal corrosion and tower wood decay. Supplementing with nonoxidizing antimicrobials is preferable to high chlorination rates. 

The lack of dependence on ionic strength in the first reaction indicates that it occurs between neutral species. Mono- or dichloramine react much slower than ammonia because of their lower basicities. The reaction is faster with CI2 because it is a stronger electrophile than with HOCl The degree of chlorination increases with decreasing pH and increasing HOCINH mol ratio. Since chlorination rates exceed hydrolysis rates, initial product distribution is deterrnined by formation kinetics. The chloramines hydrolyze very slowly and only to a slight extent and are an example of CAC. 

Amines. Although the chlorination of aqueous aLkylamines is analogous to that of ammonia, mono- and diaLkylarnines generally chlorinate faster because of their higher basicities (13). Bromination rates are significantly faster than chlorination rates, and in some cases, eg, (CH2)2NH... 

Kinetic studies have been carried out using the 1 1-complex iodobenzene dichloride as a source of molecular chlorine. In acetic acid solutions, the dissociation of this complex is slower than the rate of halogenation of reactive aromatics such as mesitylene or pentamethylbenzene, consequently the rate of chlorination of these is independent of the aromatic concentration. Thus at 25.2 °C first-order chlorination rate coefficients were obtained, being approximately 0.2 x 10-3 whilst the first-order dissociation rate coefficient was 0.16 xlO-3 from measurements at 25.2 and 45.6 °C the corresponding activation energies... 

Substituents Relative Arenium Ion stability Relative n-Complex Stability Rate of Chlorination" Rate of Nitration ... 

For chlorine enhanced conversion and initial rate vs. the second order chlorine rate constant (presence of TCE) (Figure 3b), the trends are clear conversion and initial rate increase with increasing kci values. For values of kci above 2e-ll cm molecules i, the enhanced conversion for all corresponding compoimds is greater than 80% per pass. 

Figure 3b Maximum enhanced conversion in a single pass and the enhanced initial rate (TCE added) vs. literature second order chlorine rate constants. (Same symbols as (2a)).

Radiation-induced chlorination of polyisobutene in carbon tetrachloride was studied at various temperatures. The process is a chain reaction with a G value of about 10 to 105, depending on the reaction conditions. At very low dose rates (0.1 to 0.2 rad I sec), the chlorination rate is directly proportional to the dose rate. At higher dose rates, the rate approaches a square-root dependence on the dose rate. The termination reaction and the influence of oxygen are discussed. The reaction is first order with respect to chlorine concentration. An activitation energy of about 4 kcal/mole was obtained. In connection with the chlorination reaction, degradation of the polyisobutene takes place. This degradation was followed by osmometric measurements. The structure of the chlorinated product was briefly investigated by IR spectroscopy. 

Figure 3 shows, on a logarithmic scale, dependence of the chlorination rate on the dose rate used in our experiments. The plot obtained is not linear, as would be the case if Equation 9 holds. The slope of the curve varies from about 1 at low dose rates to about 0.65 at the highest dose rate (1.3 rad/sec). We would like to interpret this... 

The discrepancy from the experimental values is due to the fact that H atoms bound to different types of C atoms are replaced by chlorine at different rates. The substitution of Cfcrt— H takes place via a tertiary radical. The substitution of Csec—H takes place via the somewhat less stable secondary radical, and the substitution of Cprjm—H takes place via even less stable primary radicals (for the stability of radicals, see Table 1.2). According to Hammond s postulate, the rate of formation of these radicals should decrease as the radical s stability decreases. Hydrogen atoms bound to Ctert should thus be substituted more rapidly than H atoms bound to Csec, and these should in turn be substituted by Cl more rapidly than H atoms bound to Cprjm. As the analysis of the regioselectivity of the monochlorination of isopentane carried out by means of Table 1.4 shows, the relative chlorination rates of C —H, C —H, and C. —H are 4.4 33 1, in agreement with this expectation. 

Water is an important reaction component and increases the reaction rate. (Completely dry chlorine and dry calcium hydroxide hardly react at all and the chlorine is merely absorbed). For this reason slaked lime is generally used (e. g. for operation in the chambers and in Hasenclever s apparatus) containing a certain amount (4 to fi per cent) moisture. In the Baekmann apparatus calcium hydroxide with only a very low moisture is used so the chlorination rate is lower, despite the fact that the lime during the reaction is continually raked up by the stirring device. 

Table 5.4 Fluorine chlorine rate ratios for reactions of aUcyl halides [28] ...

Chambers G, Ubbelohde ARJ (1955) The effect of molecular structure of paraffins on relative chlorination rates. J Chem Soc 285-295... 

The chlorination rate was found to be a function of the total copper concentration, cupric/cuprous ratio, and temperature. An empirical expression relating these variables to the space-time yield has been derived. Extensive oxygen mass transfer studies have been carried out in both process and sodium sulfite solutions these taken together make possible the scale-up and design of a commercial reactor with ample safety factor on O2 concentration level. 

The fact that the initial stages of chlorination occur in the diffusion region complicates the investigation of the dose rate dependence of the radiation chlorination rate (7). During the transition to subsequent stages of chlorination, which proceed to a considerable extent in the kinetic region, the dose rate dependence of the chlorination rate is nearly square root (Figure 7). 

Fig. 6-3. Chlorination of propane, at 300 C, Effect of pressure on relative chlorination rates of primary and secondary hydrogen atoms.

The carbon sometimes takes the form of a block of graphite which has a chlorine inlet tube down the middle and is shaped so as to act also as a chlorine distributor, as shown in the small scale chlorinator in Fig. 7.5. Alternatively, the carbon may be in more intimate admixture with the thoria, e.g. when produced by the calcination of a mixture of thoria and starch, followed by grinding. In this case, a reasonable chlorination rate is obtained in the absence of the ferric chloride catalyst, provided the temperature is raised to 900°C. This would probably be the preferred technique for large-scale operation since the removal of an iron catalyst before... 

Redistribute water to individual cells Unplug distribution holes Increase chlorination rate Use biocide... 

In all the photochlorinations, NMR signals pertaining to CHCl groups were never observed in large intensity. It can therefore be concluded that a singly chlorinated CHCl group will continue to react faster than the initial chlorination rate of a new CH2 group. 

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