Decomposition of Sulfamethoxazole by Catalytic Wet Peroxide Oxidation

촉매습식과산화(CWPO)를 이용한 설파메톡사졸의 분해

Abstract

Sulfamethoxazole (SMX) is sulfaamide-based synthetic antibiotics, which are widely prescribed pharmaceutical compound to treat bacterial infections in both human and animals. Most of them are not completely decomposed as refractory substances. The environmental impact of pharmaceuticals as emerging contaminants has generated severe concerns. In this study, catalytic wet peroxide oxidation (CWPO) of SMX was carried out with $Cu/Al_2O_3$ catalyst and investigated the optimum reaction conditions of temperature, dosage of catalyst and concentration of $H_2O_2$ to completely decompose the SMX. It was observed that SMX was completely decomposed within 20 min using 0.79 mM $H_2O_2$ and 6 g $Cu/Al_2O_3$ catalyst at 1 atm and $40^{\circ}C$, but SMX was not fully mineralized and converted to intermediates as hydroylated-SMX, sulfanilic acid, 4-aminobenzenesulfinic acid and nitrobenzene. After that these are completely mineralized through organic acid. We proposed the decomposition reaction path ways of SMX by analyzing the behavior of these intermediates. To investigate the durability of heterogeneous catalyst, decomposition of SMX was observed by continuously recycling catalysts. When the heterogeneous catalyst of 10 wt% $Cu/Al_2O_3$ was continuously reused 5 times, decomposition of SMX was a little lowered, but the activity of catalyst was overall very stable.

설파메톡사졸(sulfamethoxazole, SMX)은 박테리아 치료를 위해 사람과 동물에게 널리 사용되어 온 설파아미드계열의 합성 항생제이다. 이들 대부분은 난분해성 물질로서 분해되지 않고 환경생태계에 노출되어 심각한 환경문제를 일으키게 된다. 본 연구에서는 난분해성 SMX를 분해하기 위하여 $Cu/Al_2O_3$ 촉매를 이용한 촉매습식과산화(catalytic wet peroxide oxidation, CWPO) 공정을 수행하였고, SMX를 완전히 분해하기 위한 최적의 온도, 촉매 주입량, 과산화수소($H_2O_2$)의 농도 등을 조사하였다. 1기압, $40^{\circ}C$에서 $H_2O_2$ 0.79 mM과 6 g의 10 wt% $Cu/Al_2O_3$ 촉매를 사용하여 20분 이내에 SMX가 완전히 분해되는 것으로 관찰되었다. 그러나 SMX는 완전히 무기화 되지 못하고, 중간생성물인 hydroylated-SMX, sulfanilic acid, 4-aminobenzenesulfinic acid, nitrobenzene을 거쳐 유기산으로 분해된 후 최종적으로 무기화 되었다. 이들 중간생성물의 거동을 파악하여 SMX의 분해 반응경로를 예측하였고 불균일 촉매의 내구성을 알아보기 위하여 10 wt% $Cu/Al_2O_3$ 촉매를 연속적으로 재사용 하여 SMX 분해율을 조사하였다. SMX의 분해율은 촉매를 5회 이상 재 사용하였을 때 다소 낮아졌지만 촉매의 활성도는 전반적으로 매우 안정적이었다.

Figure 1. Decomposition of SMX by CWPO at 1 atm and 40 ℃.

Figure 2. Decomposition of SMX with change of H₂O₂ concentration at 1 atm, 20 ℃ and 2 g 10 wt% Cu/Al₂O₃ .

Figure 3. Decomposition of SMX with change of 10 wt% Cu/Al₂O₃ catalyst loading amount at 1 atm, 20 ℃ and 0.197 mM H₂O₂.

Figure 4. Decomposition of SMX with change of temperature at 1 atm, 2 g 10 wt% Cu/Al₂O₃ and 0.197 mM H₂O₂.

Figure 5. Effects of 10 wt% Cu/Al₂O₃ catalysts and H₂O₂ concentration on CWPO of SMX at 20 ℃; (a) 0.197 mM H₂O₂, (b) 0.395 mM H₂O₂, (c) 0.790 mM H₂O₂.

Figure 6. Effects of temperature and H₂O₂ concentration on CWPO of SMX at 2 g 10 wt% Cu/Al₂O₃; (a) 20 ℃, (b) 40 ℃, (c) 80 ℃.

Figure 7. Effects of 10 wt% Cu/Al₂O₃ catalysts loading amount and temperature on CWPO of SMX at 0.197 mM H₂O₂; (a) 2 g 10 wt% Cu/Al₂O₃, (b) 4 g 10 wt% Cu/Al₂O₃, (c) 6 g 10 wt% Cu/Al₂O₃.

Figure 8. Effects of pH on CWPO of SMX at 1 atm, 40 ℃, 6 g 10 wt% Cu/Al₂O₃ and 0.790 mM H₂O₂.

Figure 9. Decomposition of SMX by CWPO with continuously recycling catalysts at 1 atm, 40 ℃, 6 g 10 wt% Cu/Al₂O₃ and 0.790 mM H₂O₂.

Figure 10. SEM micrographs of 10 wt% Cu/Al₂O₃ catalyst; (a) fresh catalyst (b) 5 times used catalyst.

Figure 11. The change of decomposition intermediates of SMX by CWPO at 1 atm, 40 ℃, 6 g 10 wt% Cu/Al₂O₃ and 0.790 mM H₂O₂.

Figure 12. Reaction pathways of SMX by CWPO.

Table 1. BET analysis of fresh and 5 times used 10 wt% Cu/Al₂O₃ catalysts

Table 2. Identified intermediates of sulfamethoxazole