Effect of some parameters on the formation of chloroform during chloramination of aqueous solutions of resorcinol
Résumé
The effects of various factors (N/Cl ratio used to prepare monochloramine, monochloramine doses, pH and contact time) on the monochloramine demand and on the chloroform yield during chloramination of resorcinol have been investigated. Chloramination experiments were carried out at 24 ± 1 °C, at pH values ranging from 6.5 to 12 using a bicarbonate/carbonate buffer and preformed monochloramine solutions prepared at pH 8.5 with N/Cl ratios ([NH4Cl]0/[Total free Cl2]0 ranging from 1.0 to 150 mol/mol). Kinetic experiments ([Resorcinol]0 = 5 or 100 μM, [NH2Cl]0/[Resorcinol]0 = 20 mol/mol, pH = 8.5 ± 0.1) showed a slow increase of the monochloramine consumption with reaction time. The monochloramine demands after reaction times of 7 days ([Resorcinol]0 = 100 μM) and 14 days ([Resorcinol]0 = 5 μM) were equal to 8.5 mol of NH2Cl/mole of resorcinol and were higher than the chlorine demands (≈7.3 mol/mol). Chloroform yields from monochloramination of resorcinol were lower than 8% (<80 mmol of CHCl3/mole of resorcinol) and were less than the yields obtained by chlorination (0.9-0.95 mol/mol). Chloroform productions increased with increasing monochloramine dose and reaction time and decreased with increasing pH values within the pH range 6.5-10. Chloroform formation markedly decreased when the N/Cl ratio increased from 1 to 1.5 mol/mol and was suppressed at N/Cl > 100 mol/mol. The data obtained in the present work suggest that free chlorine released from monochloramine hydrolysis plays a significant role on the formation of chloroform during chloramination of resorcinol at N/Cl ratios close to unity (1.0 < N/Cl < 1.5).
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