Batch chlorination of toluene

Table 1. Distributions of Reactor Products from Batch Chlorination of Toluene...

Fio. 4.6. Batch chlorination of toluene in a well-mixed bubble-column reactor (Example 4.4)... 

Conventional Chlorination of Toluene. In the batch chlorination of toluene (e.g., at 50 °C in the presence of FeClj catalyst), a crude mixture is formed in which the monochlorotoluene fraction contains small amounts of meto-chlorotoluene, with the two isomers ortho- and para-chlorotoluene in a practically statistical distribution in the ratio ortho para = 1.92 [128]. 

The batch chlorination of toluene (with continuous CI2 flow) was studied in a BCR by Lohse et al. [10]. At low catalyst concentrations (FeCl3) and in the presence of trace impurities of water the reaction takes place in the slow reaction regime. The chlorination of toluene (T) and the consecutive chlorination of monochloro toluene to dichloro toluene... 

Fig. E 1 Description of experimental data of batch chlorination of toluene in BCR (Ccat(FeCl3) = 2.96 x 10"3 mol/1, CI2 inlet mol fraction = 0.6, T = 298 K)[10]. Reprinted with permission from Chem. Engng. Sci. 38, Lohse M., E. Alper and W.-D. Deckwer, Modeling of Batch Catalytic Cheorination of Toluene. Copyright (1976), Pergamon Press...

Regardless of the exact mechanism at work, HCl catalyst pretreatment have been demonstrated to enhance the photocatalytic oxidation of toluene at low concentrations [68,69]. The apparent deactivation of the photocatalyst is noticeably delayed over HCl-pretreated catalyst samples in a manner similar to that seen with cofed toluene and TCE (Fig. 13). However, the pseudo-steady-state level of conversion appears to be nearly identical on both untreated and HCl-pretreated catalysts. Because the batch HCl pretreatment process incorporates a limited quantity of HCl into the catalyst surface structure, this similarity in longterm activity may be the result of surface chlorine depletion. 

The example is concerned with a batch chlorination process. At the beginning, the fresh toluene charged to the reactor will contain no dissolved chlorine. After bubbling of the chlorine has commenced, a period of time will need to elapse before the concentration of the dissolved chlorine rises to a level that just matches the rate at which it is being removed from the solution by reaction. To avoid such a complication in this example, calculations are carried out for the stage when, after chlorine bubbling has continued at a steady rate, the fractional conversion of the toluene has reached a value of 0.10. It is then assumed that, at any instant in time, the rate of mass transfer of chlorine from the gas phase is just equal to the rate at which it reacts in the bulk of the liquid, i.e. the rate is given by equation 4.17. 

Jahnisch et al. used an IMM falling-film microreactor for photochlorination of toluene-2,4-diisocyanate [38] (see also Chapter 4.4.3.3, page 161). As a result of efficient mass transfer and photon penetration, chlorine radicals were well distributed throughout the entire film volume, improving selectivity (side chain versus aromatic ring chlorination by radical versus electrophilic mechanism) and spacetime-based yields of l-chloromethyl-2,4-diisocyanatobenzene compared to those obtained using a conventional batch reactor. 

Toluene is to be chlorinated in a batch-operated bubble column such that, for any particular gas rate chosen, the height of the dispersion in the column is 2.2 m. The reactor will operate at a temperature of 20eC and a pressure of 1 bar (any effect of hydrostatic pressure differences in the column may be neglected). The catalyst will be stannic chloride at a concentration of 5 x 10 4 kmol/m3. 

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