以高級氧化法及濕式氧化法處理壓克力樹脂廢水

Abstract

本研究探討如何處理彩色濾光片玻璃（color filter glass, CFG）再生製程之鹼性廢水（alkaline wastewater, A-water）及其壓克力樹脂相關成分之合成廢水。CFG再生製程之A-廢水含有4 M的氫氧根離子及由溶解的壓克力樹脂所形成的化學需氧量（chemical oxygen demand, COD）80,446 mg L-1。A-廢水經過濾程序去除懸浮固體物（suspended solid, SS）後的濾液（effluent after filtration, F-water），再以高級氧化程序（advanced oxidation processes, AOPs）如臭氧（ozonation, O3）、臭氧/紫外光（O3/ultra-violet, O3/UV）、鉑催化臭氧/紫外光（catalytic O3/UV with Pt/γ-Al2O3, O3/UV/Pt）三種方式進行處理。過濾程序使用0.5 µm 鐵氟龍濾紙（PTFE filter）， 其濾液（F-廢水）相對於原廢水（A-廢水）的COD去除率（removal efficiency of COD (ηC) relative to A-water, ηC,FA ）約為 30.7% 。相近的去除率亦可以重力沉降（gravity sedimentation, GS）7.5 h達到（33.7%）。以高級氧化方式處理F-廢水，於反應時間為60 h時，其相對於F-廢水所含COD之去除率ηC,OF 約為 8-12%。相對於A-廢水的整體COD去除率ηC,OA可以達 36.2-39.1%。 為進一步瞭解製程基本成分之去除效能，本研究亦討論如何藉由催化濕式氧化法來處理壓克力樹脂相關成分甲基丙烯酸甲酯（methyl methacrylate, MMA）的人工廢水。藉由改變系統的主要操作參數來評估MMA及COD的相對去除率（ηMMA = (1 - CMMA/CMMA0)及ηC = (1 - CCOD/CCOD0)）。這些參數包括1）所設定的操作溫度（setting temperature, TST）；2）鉑催化劑（Pt/Al2O3）的有無；3）工作氣體的有無或種類；4）催化劑的量(mPt)及5）氧的分壓(pO2)。此外，實驗過程中亦持續監測pH的變化，以瞭解其與MMA的分解或COD的礦化情形相關性。實驗結果顯示，在沒有觸媒的狀況下，TST對CMMA/CMMA0具有極為顯著的影響，CMMA/CMMA0 由TST = 180 ºC時的0.89降到TST = 200 ºC時的0.62；再降到220 ºC 時的0.09（反應時間reaction time (tFR) = 180 min, pO2 = 2 MPa，由參考溫度 Trf = 180 ºC所得）。相對於此，TST對CCOD/CCOD0則影響較小，在 tFR = 180 min且TST 為 160-220 ºC時，CCOD/CCOD0 僅為 0.78-0.87 。當以mPt = 30.38 g鉑觸媒（Pt/Al2O3）進行催化濕式氧化，反應時間 tFR = 180 min 且TST 在 160 ºC 及 180-220 ºC 時，CMMA/CMMA0分別為0.15及0.01-0.05；其CCOD/CCOD0在TST為160-220 ºC時也降低到0.16-0.34。亦即，使用鉑觸媒不僅增進MMA及COD的去除效率，也降低了反應所需的溫度以減少所需能源。此結果也顯示，以氧作為氧化氣體可以藉由催化濕式氧化有效將COD礦化。然而且儘管較高的氧氣分壓（1-2 MPa）可以在催化濕式氧化系統的液相中提供較高的溶氧，但並未顯著增進反應效率。此外，催化濕式氧化對COD的去除效率較文獻中以其他高級氧化程序如UV、O3及UV/ O3處理MMA為高。 本研究亦以高級氧化（AOPs）與催化濕式氧化（CWAO）兩種方式來處理壓克力樹脂另一主要成分甲基丙烯酸（methacrylic acid, MAA）的人工廢水。所探討之三種AOPs程序為UV、O3和O3/UV。UV程序的CMMA/CMMA0與CCOD/CCOD0幾乎接近1，顯示無處理效果。O3和O3/UV二者的處理效果則相近，CMMA/CMMA0均近於0，而CCOD/CCOD0則均為0.5左右，此結果顯示O3及O3/UV對酸性物質之礦化有其瓶頸之處。當O3處理效能已受侷限時，UV之助益亦有限。濕式氧化部分，在未先通氮氣的狀況下，當pO2 = 0與1 MPa，反應時間tFR = 180 min時，其CMAA/CMAA0值分別為0.85和0.42，CCOD/CCOD0值分別為0.85和0.40，因此pO2之增加可有效降低MAA與COD之濃度。在先通氮氣的狀況下以CWAO程序處理MAA，在pO2 = 1-2 MPa觸媒mPt = 10 g狀況下，於t = 30及60 min時，CMAA/CMAA0可降至0.08及~0%；CCOD/CCOD0於t = 60 min時可降至0.14-0.19%，同時pH則在t = 30 min後，由3.3逐漸增高至約5.18-5.43。顯示觸媒確實會改變反應機制以增加反應速率。但增加mPt為20及30 g時，其結果與mPt = 10 g時的定性與定量結果相近。顯示過量添加觸媒，其增進效果不大。比較CWAO及AOPs對MAA之處理效果，結果顯示前者優於後者。此結論與MMA之處理效果一致。本研究所得到的結果可供半導體工業未來處理含PMMA（poly MMA, 聚甲基丙烯酸甲酯）、MMA及MAA廢水的參考。

The treatment of alkaline wastewater (noted as A-water) from cleaning of color filter glass (CFG) was studied. The A-water contains hydroxide ion and dissolved acrylic resin of high concentrations of 4 M and 80,446 mg L-1 chemical oxygen demand (COD), respectively. The suspended solid (SS) of A-water was removed via filtration. The effluent after filtration process (noted as F-water) was further treated via advanced oxidation processes (AOPs) such as ozonation (O3), O3/ultra-violet (UV) irradiation (O3/UV) and catalytic O3/UV with Pt/γ-Al2O3 (O3/UV/Pt). The filtration process employing 0.5 µm PTFE filter yielded the F-water containing 55,749 mg L-1 COD with the removal efficiency of COD (ηC) relative to A-water (ηC,FA) of about 30.7% for treating the A-water. It was noted that about 33.7% COD of A-water can be also removed using the gravity sedimentation (GS). However, the GS time was as long as about 7.5 h. The values of ηC relative to F-water (ηC,OF) via AOPs for treating the F-water were about 8-12% at the reaction time of 60 h. The overall ηC relative to A-water (ηC,OA) can reach about 36.2-39.1% after filtration process and AOPs. The results indicate that the combined processes using filtration and AOPs are applicable for treating the A-water from cleaning of CFG. Noting that the acrylic resin of A-water was manufactured using substances including methyl methacrylate (MMA) and methacrylic acid (MAA), this study then conducted the treatment of MMA-containing wastewater via catalytic wet oxidation (CWAO) as an alternative of AOPs. Effects of major operating parameters on the system performances in terms of the normalized concentrations of MMA and 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 (pO2). 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 ºC to 0.62 at 200 ºC and 0.09 at 220 ºC with pO2 = 2 MPa (based on the reference temperature Trf of 180 ºC). 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 ºC. 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 ºC and in 180-220 ºC, respectively, while the CCOD/CCOD0 decreases to about 0.16-0.34 with TST in 160-220 ºC. The use of Pt/Al2O3 not only improves the removals of MMA and COD but also reduces the TST required for the efficient removals 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 pO2 is not significant if the supplied pO2 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 O3 and combined process of O3 and UV for the effective removal of COD in the treatment of MMA. As a major componet, methacrylic acid (MAA) was treated via AOPs and CWAO process. The results reveal that the CMMA/CMMA0 and CCOD/CCOD0 via UV process are near 1, indicating no effect of UV process. As for O3 and O3/UV processes, the treatment efficiencies are about the same with CMMA/CMMA0 of near 0 and CCOD/CCOD0 of 0.5. The results via WAO process without pre-purge using N2 show that, at pO2 = 0 and 1 MPa and tFR = 180 min, the values of CMAA/CMAA0 are 0.85 and 0.42, while those of CCOD/CCOD0 are 0.85 and 0.40, respectively. It illustrates that the values of CMAA and CCOD are effectively reduced with increasing pO2. The results of CWAO process using Pt catalyst (mPt = 10 g) with pre-purge employing N2 indicate that, at pO2 = 0 to 1 MPa, the value of CMAA/CMAA0 are 0.08 and ~0% at tFR = 30 and 60 min, respectively; at tFR = 60 min, CCOD/CCOD0 is 0.14-0.19%; the pH value icreases from 3.3 at beginning to 5.18-5.43 after tFR = 30 min. Thus, the catalyst may change the reaction mechanism to improve the reaction rate. Note that the increasing use of mPt (say, 20 and 30 g) does not enhance the reaction rate extent significantly. The information obtained in this study is useful for the proper operation and rational design of the AOPs and CWAO systems for the effective treatment of PMMA-, MMA- and MAA-containing wastewater from the semiconductor industry.