| 摘要: | 本研究利用爐外催化裂解反應，探討低密度聚乙烯(Low-Density Polyethylene, LDPE)、高密度聚乙烯(High-Density Polyethylene, HDPE)、聚丙烯(Polypropylene, PP)以及聚乳酸(Polylactic Acid, PLA)等四種常見農業薄膜材質，轉換為能源之可行性。試驗條件分別控制反應溫度600℃，不同模擬農業薄膜材料之摻混比例(3:1、1:1及1:3)，以及添加2.5%之自製鎳基催化劑等條件，期進一步評估共同裂解與催化裂解之產物分布及物種變化之影響。
研究結果顯示，試驗選擇之四種塑膠材質，經裂解反應之產物皆以氣體為主，產量可達80 wt.%以上。至於裂解油產量，其中LDPE及HDPE分別為6.71 w.t%及5.28 w.t%。由於裂解油品中出現類似蠟之產物，試驗經爐外催化裂解反應後，裂解油品中蠟產量明顯下降，且裂解油產量分別增加至13.31 w.t%及11.54 w.t%。此外，PP及PLA之裂解油產量，分別為7.61 wt.%及2.36 wt.%，然經氣相催化反應後，裂解油產量分別下降至6.14 wt.%及0.66 wt.%，此係受到催化劑促進液相產物轉換成氣相產物之影響，整體而言，隨爐外催化反應之影響，試驗四種塑膠之裂解油產量變化，主要原因在於鎳為高活性之金屬，有助於提供活性位點，並促進斷鍵反應之發生。
根據裂解油品之元素分析結果顯示，LDPE、HDPE及PP經裂解反應衍生之輕質油及重質油，主要為碳及氫元素，而PLA衍生之裂解油品，則以碳及氧元素為主。LDPE、HDPE與PP於不同試驗條件下，油品之熱值介於10,994 kcal/kg–11,580 kcal/kg，PLA油品之熱值則介於3,893 kcal/kg–5,386 kcal/kg，前述油品熱值之變化，主要受到油品中碳、氫及氧含量之影響。至於LDPE、HDPE及PP之H/C比及O/C比，分別介於1.74–1.99及0.00–0.03，而PLA之H/C及O/C比則分別介於1.74–2.19及0.45–0.81，受到結構中的氧元素影響，根據H/C比及O/C比之變化範圍可知，與LDPE共裂解衍生之裂解油，O/C比隨著PLA摻混比例增加而增加，有促進油品老化現象發生之潛勢。
輕質油及重質油之化合物物種分析結果顯示，碳數分布分別集中在C7–C9及C10–C16化合物，惟PLA衍生之輕質油及重質油，碳數分布分別集中在C5-C6及C7-C9化合物。LDPE及HDPE衍生之裂解油物種則以脂肪族為主；PP之裂解油物種，以脂肪族及芳香族為主；PLA衍生之裂解油物種則以含氧化合物為主。爐外催化試驗結果顯示，所有試驗之裂解油中>C21之化合物比例下降，並使芳香族化合物比例增加，顯示催化劑有助於斷鍵反應，並促使芳香化反應之發生。在產能評估結果中，氣體產物皆有最高之碳分布及能源密度，分別達78%及0.8以上，能達到能源轉換應用之目的。整體而言，本研究已成功模擬驗證LDPE、HDPE、PP及PLA等農膜塑膠材質，應用裂解及催化裂解轉換能源之可行性，並依據衍生裂解油之物種鑑定及能源密度之評估，將有助於提供後續工程應用之參考依據。;This research investigated the feasibility of converting common agriculture film materials, including Low-Density Polyethylene (LDPE), High-Density Polyethylene (HDPE), Polypropylene (PP), and Polylactic Acid (PLA), into energy by ex-situ catalytic pyrolysis. The condition operates at the temperature of 600°C, the blending ratio (3:1, 1:1, and 1:3) of stimulated agriculture film materials, and 2.5% prepared nickel-based catalyst addition. These conditions aim to investigate the influence of blending ratio and catalyst on the distribution and the variations in speciation of the pyrolysis products.
Experimental results showed that the gaseous product is dominant for four types of selected plastic materials after pyrolysis reaction, and the yield is up to 80 wt.%. Regarding pyrolytic oil, the yields of LDPE and HDPE are 6.71 wt.% and 5.28 wt.%, respectively. The wax-like products significantly appeared in the pyrolytic oil. However, the wax-like product yield also significantly decreased after catalytic reaction and increased the yield of pyrolytic oil to 13.31 wt.% and 11.54 wt.% for LDPE and HDPE, respectively. Furthermore, the yield of pyrolytic oil for PP and PLA are 7.61 wt.% and 2.36 wt.%, respectively. However, the pyrolytic oil yields also decreased to 6.14 wt.% and 0.66 wt.% for PP and PLA after the gas-phase catalytic reaction. This is attributed to the catalyst promoting the conversion of liquid-phase products into gas-phase products. Overall, the prepared nickel-based catalyst could provide highly active sites and facilitate the occurrence of cracking reactions in the pyrolysis of the tested plastic materials.
According to the elemental analysis of the pyrolytic oil, the light and heavy fractions of pyrolytic oil derived from LDPE, HDPE, and PP are mainly composed of carbon and hydrogen, while that of pyrolytic oil derived from PLA is composed of carbon and oxygen. Under different experimental conditions, the calorific values of oils derived from LDPE, HDPE, and PP ranged from 10,994 kcal/kg to 11,580 kcal/kg. However, the calorific value of oils derived from PLA ranged from 3,893 kcal/kg to 5,386 kcal/kg. The carbon, hydrogen, and oxygen content of pyrolytic oil primarily influences the variations in the calorific values. The H/C ratio and O/C ratio of the pyrolytic oil derived from LDPE, HDPE, and PP ranged from 1.74 to 1.99 and 0.00 to 0.03, respectively. In the case of pyrolytic oil derived from PLA, the H/C and O/C ratios ranged from 1.74 to 2.19 and 0.45 to 0.81, respectively. Based on the variation in H/C and O/C ratios, the result showed that the O/C ratio increases with the PLA blending ratio increasing in the co-pyrolysis of LDPE and PLA. It implied the potential for a promotion in the aging of the oil products due to the PLA containing oxygen.
The speciation analysis of the light and heavy fractions of pyrolytic oil indicates that the carbon distribution dominates in C7–C9 and C10–C16. Except for the PLA conditions, the carbon distribution of the light and heavy fractions of oils dominates in C5–C6 and C7–C9. The main speciation of pyrolytic oil derived from LDPE and HDPE are aliphatic compounds. However, the speciation of the pyrolytic oil derived from PP is both aliphatic and aromatic compounds. On the other hand, oxygen-containing compounds are the dominate species of pyrolytic oil derived from PLA. In the results of the ex-situ catalytic experiments, the proportion of >C21 compounds in the pyrolytic oil decreased, while the proportion of aromatic compounds increased, indicating that the catalyst enhanced the cracking reactions and aromatic formation. Based on the energy density analysis results, the gaseous products have the highest carbon distribution and energy density, up to 78% and 0.8, implying that could provide a great energy conversion efficiency. Overall, this study successfully verified the feasibility of converting simulated agricultural film plastics such as LDPE, HDPE, PP, and PLA into energy through pyrolysis and catalytic pyrolysis. Meanwhile, based on the speciation identification and the energy density of pyrolytic products, the relevant results will be helpful for the subsequent selection of pyrolysis technologies and references for engineering applications. |
