磁性觸媒應用於催化濕式氧化程序處理水中溶解性污染物之研究

Abstract

本研究以濕式氧化法(wet air oxidation, WAO)及催化濕式氧化法(catalytic WAO, CWAO)處理甲基丙烯酸甲酯(methyl methacrylate, MMA)。於CWAO中，使用自製磁性鉑觸媒(Pt/ZrO2/SiO2/Fe3O4, Pt/ZSM)進行MMA之催化氧化分解並與商用鉑觸媒Pt/γ-Al2O3之催化氧化效能進行比較。研究結果顯示WAO對MMA降解率(ηMMA)及化學需氧量(chemical oxygen demand, COD)礦化率(ηCOD)主要受溫度影響。反應溫度(TST)越高，MMA降解效果越顯著。於WAO中，當TST = 493 K，pO2 = 1.63 MPa (於參考溫度Trf = 493 K時，氧之分壓)，及MMA初始濃度CMMA0 = 500 mg L-1，反應三小時後，ηMMA及ηCOD分別為87％及30％。 超順磁性鉑觸媒Pt/ZSM為次微米顆粒(100~200 nm)，飽合磁化量為6.54 emu g-1，且具有高比表面積(67.46 m2 g-1)及高鉑含量(13.37 wt.% Pt)。其界達電位值(pHZPC)為4.7，故可有效吸附MMA經氧化反應後之中間產物有機酸，並可維持觸媒的催化效能。以添加六氯鉑酸(H2PtCl6．6H2O)之含浸法製備時，水熱還原法可將鉑完全還原；而氣態還原法之Pt以PtCl62-形式存在於表面，殘留的氯離子會影響催化反應。 以氧氣為工作氣體控制反應條件為TST = 453 K，pO2 = 1 MPa (Trf = 453 K)及觸媒添加量(mS) = 1 g時進行CWAO處理MMA及COD，氣態還原法觸媒HG-Pt/ZSM (ηMMA及ηCOD分別為29％及54％) 及水熱還原法觸媒HT-Pt/ZSM (ηMMA及ηCOD分別為46％及36％)之反應性與商用鉑觸媒Pt/γ-Al2O3 (ηMMA及ηCOD分別為39％及39％)相當。反應後之Pt/ZSM觸媒依舊具有超順磁性特性(6.5-7.3 emu g-1)，故應用高梯度磁性分離機(high-gradient magnetic separation, HGMS)分離後，可將觸媒回收再利用，此為Pt/ZSM在固相分離時優於Pt/γ-Al2O3之處。

This study investigated the treatment of methyl methacrylate (MMA) via wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) processes. A superparamagnetic platinum catalyst (Pt/ZrO2/SiO2/Fe3O4, Pt/ZSM) was used to promote the decomposition of MMA and compared with commercial platinum catalyst Pt/γ-Al2O3. Effects of major operating parameters on the system performances in terms of normalized concentrations of MMA and chemical oxygen demand (COD) were investigated. The operating parameters examined included the setting temperature (TST), partial pressure of O2 (pO2), initial concentration of MMA (CMMA0), amount of catalyst used (mS) and reaction time (t). The decomposition efficiencies of MMA and COD (ηMMA and ηCOD) can respectively reach 87 and 30％ after 3 hr reaction time via WAO with reaction conditions at TST = 493 K, pO2 = 2.18 MPa (expressed as value at reference temperature Trf of 493 K) and CMMA0 = 500 mg L-1. The Pt/ZSM exhibits particle size of around 100-200 nm, magnetization of 6.54 emu g-1, specific external surface area of 67.46 m2 g-1, and with high platinum content of 13.37 wt.%. The pHZPC of Pt/ZSM is 4.7 which is favorable for the effective adsorption of acid intermediates on the catalyst surface. The hydrothermal method can reduce the chloride content of the Pt/ZSM which is prepared by the impregnation of Pt precursor H2PtCl6．6H2O on the support of ZSM. At TST = 453 K, pO2 = 1 MPa (Trf = 453 K), and mS = 1 g, the reactivities of HG-Pt/ZSM (Pt/ZSM with Pt reduced via H2 gas) (ηMMA = 29％ and ηCOD = 54％) and HT-Pt/ZSM (Pt/ZSM with Pt reduced via hydrothermal method) (ηMMA = 46％ and ηCOD = 36％) to decompose MMA and COD are as good as those of Pt/γ-Al2O3 (ηMMA = 39％ and ηCOD = 39％). The Pt/ZSM catalyst still holds superparamagnetic property with saturation magnetization of 6.5-7.3 emu g-1 after being used in CWAO process. Thus the used Pt/ZSM can be separated via high-gradient magnetic separation (HGMS) fot the reuse.