The degradation kinetics of two pharmaceutical intermediates [5-methyl-1,3,4-thiadiazole-2-methylthio (MMTD-Me) and 5-methyl-1,3,4-thiadiazole-2-thiol (MMTD)] have been studied in order to assess the effectiveness and the feasibility of UV processes for the degradation water polluted by such intermediates. Experiments were carried out, at 25°C, treating, in a batch reactor, aqueous solutions (1 and 100 mg/L) of both compounds by UV radiations (254 nm) in the presence or absence of hydrogen peroxide. For both substrates, the results showed that: (i) no degradation occurred when H2O2 alone was used; (ii) UV and UV/H2O2 processes were both effective for degrading the substrates; (iii) substrates degradation by photo-oxidation was always faster than by direct photolysis; (iv) during direct photolysis, a lower substrate initial concentration lead to a faster and more efficient degradation. The quantum yields of the photolytic process were experimentally measured for both substrates resulting 14.1 1.5 and 12.0 0.7 mmol/einstein-1 for MMTD-Me and MMTD, respectively. Carrying out photo-oxidation experiments using excess of peroxide [i.e., initial substrate concentration of 1 mg/L and H2O2/substrate molar ratios of 50/1, 42/1, 34/1 and 23/1], first- and second-order rate constants for MMTD-Me and MMTD degradation were calculated. In particular, the values of these latter resulted (8.30.8)108 and (1.60.5)1010 M-1s-1, respectively. Our results show that to remove a few g/L of the pharmaceutical intermediates, a H2O2 dose of 1 mg/L, 99% would only need 55 min for (MMTD-Me) and 2.7 min (MMTD)
Kinetic investigation on UV and UV/H2O2 degradations of pharmaceutical intermediates in aqueous solution
Lopez A;Mascolo G;
2003
Abstract
The degradation kinetics of two pharmaceutical intermediates [5-methyl-1,3,4-thiadiazole-2-methylthio (MMTD-Me) and 5-methyl-1,3,4-thiadiazole-2-thiol (MMTD)] have been studied in order to assess the effectiveness and the feasibility of UV processes for the degradation water polluted by such intermediates. Experiments were carried out, at 25°C, treating, in a batch reactor, aqueous solutions (1 and 100 mg/L) of both compounds by UV radiations (254 nm) in the presence or absence of hydrogen peroxide. For both substrates, the results showed that: (i) no degradation occurred when H2O2 alone was used; (ii) UV and UV/H2O2 processes were both effective for degrading the substrates; (iii) substrates degradation by photo-oxidation was always faster than by direct photolysis; (iv) during direct photolysis, a lower substrate initial concentration lead to a faster and more efficient degradation. The quantum yields of the photolytic process were experimentally measured for both substrates resulting 14.1 1.5 and 12.0 0.7 mmol/einstein-1 for MMTD-Me and MMTD, respectively. Carrying out photo-oxidation experiments using excess of peroxide [i.e., initial substrate concentration of 1 mg/L and H2O2/substrate molar ratios of 50/1, 42/1, 34/1 and 23/1], first- and second-order rate constants for MMTD-Me and MMTD degradation were calculated. In particular, the values of these latter resulted (8.30.8)108 and (1.60.5)1010 M-1s-1, respectively. Our results show that to remove a few g/L of the pharmaceutical intermediates, a H2O2 dose of 1 mg/L, 99% would only need 55 min for (MMTD-Me) and 2.7 min (MMTD)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
