Treatment of methyl methacrylate from semiconductor wastewater by catalytic wet oxidation

Abstract

Treatment of methyl methacrylate (MMA) from semiconductor wastewater via catalytic wet oxidation (CWAO) was studied. Effects of major operating parameters on the system performances in terms of the normalized concentrations of MMA and chemical oxygen demand (COD) relative to their initial values, namely C MMA/ C MMA0 and C COD/ C COD0, were investigated. These parameters include (1) the setting temperature T ST of operation, (2) the presence of catalyst Pt/Al 2O 3, (3) the presence of working gas, (4) the amount of Pt/Al 2O 3 ( m Pt) and (5) the partial pressure of O 2 ( p O 2 ). The change of pH value during the course of CWAO was also examined to elucidate the extents of decomposition of MMA and mineralization of COD. The results indicate that the effects of T ST on the C MMA/ C MMA0 are very vigorous for the case of sole wet oxidation (WAO) without catalyst. At the reaction time t FR = 180 min, the C MMA/ C MMA0 decreases from 0.89 at T ST = 180 °C to 0.62 at 200 °C and 0.09 at 220 °C with p O 2 = 2 MPa (based on the reference temperature T rf of 180 °C). The effects of T ST on the C COD/ C COD0 are not strong for the WAO, reducing the C COD/ C COD0 only to about 0.78–0.87 at t FR = 180 min with T ST in 160–220 °C. As for the CWAO in the presence of Pt/Al 2O 3 with m Pt = 30.38 g, the C MMA/ C MMA0 reduces greatly to 0.15 and 0.01–0.05 at t FR = 180 min with T ST at 160 °C and in 180–220 °C, respectively, while the C COD/ C COD0 decreases to about 0.16–0.34 with T ST in 160–220 °C. The use of Pt/Al 2O 3 not only improves the removal of MMA and COD but also reduces the T ST required for the efficient removal of MMA and COD, saving the energy needed. The results also reveal that the oxidizing gas such as O 2 is required for effective mineralization of COD via CWAO. However, the enhancement effect of increasing p O 2 is not significant if the supplied p O 2 is high enough, say 1–2 MPa, to proceed the CWAO in liquid phase with sufficient dissolved oxygen. Further, the CWAO is more efficient than the advanced oxidation processes of direct ultra violet irradiation (UV), sole ozonation (OZ) and combined process of OZ and UV for the effective removal of COD in the treatment of MMA. The information obtained in this study is useful for the proper operation and rational design of the CWAO system for the effective treatment of MMA-containing wastewater from the semiconductor industry.