| 摘要: | 本研究應用兩段式固定床管狀爐反應進行爐外催化裂解反應，探討聚甲基丙烯酸甲酯（Poly (Methyl Methacrylate), PMMA）原料，在控制溫度400℃ - 500℃之條件下，轉化及提升甲基丙烯酸甲酯（Methyl Methacrylate, MMA）純度之可行性研究。並於最佳反應溫度探討添加0.6 M鹽酸改質絲光沸石，控制催化進料比為1.3 wt.%、1.8 wt.%及2.4 wt.%，評估改質催化劑對裂解產物的影響。
研究結果顯示，絲光沸石經過酸改質後，具有較良好之熱穩定性，煅燒處理後維持較高的比表面積109.29 m2/g，並具有中孔可以提升原料轉化率。PMMA裂解後之產物，以可冷凝之揮發性氣體產物為主，主要被後端的活性碳及二氧化矽吸附。至於試驗收集產物中，產率最高的為輕質油，經過化合物物種鑑定主要為PMMA之單體甲基丙烯酸甲酯（Methyl Methacrylate, MMA），其中以400℃及無催化劑條件之輕質油，有最高之單體純度，約為85.36±2.64%。爐外催化裂解試驗後，則係因添加催化劑導致氣體停留時間增加，致使單體純度低於無添加催化劑之試驗結果，其中以400℃及添加1.3 wt.%改質催化劑，PMMA單體之MMA純度約可達80.62±0.86%。此係因催化劑促進不同次級反應，使單體聚合形成二聚體，如2-甲基-5-亞甲基己二酸二甲酯（Hexanedioic acid, 2-methyl-5-methylene-, dimethyl ester）、環己烷-1,4-二甲酸二甲酯（Dimethyl cyclohexane-1,4-dicarboxylate）及2-己烯二酸二甲酯（2-Hexenedioic acid, 2,5-dimethyl-, dimethyl ester）。比較僅煅燒之絲光沸石試驗結果可知，因前述催化劑之酸性位點較高，促進次級反應之現象更為明顯，單體純度則約減少至73.91%。整體而言，本研究已初步建立PMMA之反應特性及裂解機制，未來可朝向改良催化劑特性及提升裂解反應操作效率，將有助於增加PMMA裂解回收單體之潛力。
;This study investigated the thermal pyrolysis of poly (methyl methacrylate) (PMMA) using a two-stage fixed-bed tubular furnace within the temperature range of 400–500 °C. The study focused on the variation in the purity of the recovered monomer, methyl methacrylate (MMA). At the optimal reaction temperature, the effect of mordenite modified by 0.6 M HCl was further examined at catalyst-to-feed ratios of 1.3, 1.8, and 2.4 wt.% in order to evaluate its influence on pyrolysis products. The methodology involved a series of experiments, including acid modification of the catalyst, pyrolysis of PMMA, and analysis of the pyrolysis products.
Acid modification enhanced the thermal stability of mordenite, which retained a higher specific surface area (109.29 m²/g) after calcination. Additionally, the increased mesoporosity enhanced feedstock conversion. PMMA pyrolysis predominantly yielded condensable volatile products, which were subsequently adsorbed on activated carbon and silica gel. Among the collected fractions, light oil exhibited the highest yield and consisted primarily of MMA. The highest monomer purity (85.36 ± 2.64%) was obtained at 400 °C in the absence of a catalyst.
Ex-situ catalytic pyrolysis, a process where the catalyst is added to the pyrolysis products after they have been formed, resulted in reduced MMA purity due to catalyst-induced secondary reactions. At 400 °C with a 1.3 wt.% modified catalyst, MMA purity decreased to 80.62 ± 0.86%. This decline was attributed to catalyst-promoted repolymerization of MMA into dimers, including hexanedioic acid, 2-methyl-5-methylene-, dimethyl ester; dimethyl cyclohexane-1,4-dicarboxylate; and 2-hexenedioic acid, 2,5-dimethyl-, dimethyl ester. Calcined mordenite, with its more substantial acidity, further enhanced these secondary reactions, resulting in a MMA purity of 73.91%. In summary, this work elucidates the fundamental reaction behavior and pyrolysis mechanism of PMMA. The findings underscore the importance of understanding these processes and suggest that future research should focus on tailoring catalyst properties and optimizing operating conditions to improve MMA recovery efficiency from PMMA pyrolysis. |
