Treatment of methyl methacrylate from semiconductor wastewater by catalytic wet oxidation

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 CMMA/CMMA0 and CCOD/CCOD0, were investigated. These parameters include (1) the setting temperature TST of operation, (2) the presence of catalyst Pt/Al2O3, (3) the presence of working gas, (4) the amount of Pt/Al2O3 (mPt) and (5) the partial pressure of O2 (pO2pO2). 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 TST on the CMMA/CMMA0 are very vigorous for the case of sole wet oxidation (WAO) without catalyst. At the reaction time tFR = 180 min, the CMMA/CMMA0 decreases from 0.89 at TST = 180 °C to 0.62 at 200 °C and 0.09 at 220 °C with pO2=2 MPapO2=2 MPa (based on the reference temperature Trf of 180 °C). The effects of TST on the CCOD/CCOD0 are not strong for the WAO, reducing the CCOD/CCOD0 only to about 0.78–0.87 at tFR = 180 min with TST in 160–220 °C. As for the CWAO in the presence of Pt/Al2O3 with mPt = 30.38 g, the CMMA/CMMA0 reduces greatly to 0.15 and 0.01–0.05 at tFR = 180 min with TST at 160 °C and in 180–220 °C, respectively, while the CCOD/CCOD0 decreases to about 0.16–0.34 with TST in 160–220 °C. The use of Pt/Al2O3 not only improves the removal of MMA and COD but also reduces the TST required for the efficient removal of MMA and COD, saving the energy needed. The results also reveal that the oxidizing gas such as O2 is required for effective mineralization of COD via CWAO. However, the enhancement effect of increasing pO2pO2 is not significant if the supplied pO2pO2 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.