- 學位論文
電漿改質銅鋅鋁系觸媒轉化合成氣產製甲醇及二甲醚之研究
Plasma-assisted preparation of Cu/ZnO/Al2O3 catalyst for DME synthesis
摘要
本研究於Cu/ZnO/Al2O3觸媒製備過程中導入電漿改質程序，以氫氣、氧氣電漿改質鍛燒後之Cu/ZnO/Al2O3觸媒，並嘗試以電漿取代傳統熱鍛燒步驟。電漿改質與電漿鍛燒之觸媒透過BET、XRD、Cu0 surface area、ICP-AES、TGA、FE-SEM分析了解電漿處理程序前後觸媒物化性質的變化；電漿改質與電漿鍛燒程序的同時利用OES電漿放射光譜觀察電漿中物種組成，推測觸媒於電漿環境下可能的反應機制。觸媒經電漿處理後用於合成氣轉化二甲醚反應(STD reaction)以瞭解各觸媒活性差異。 電漿改質鍛燒後觸媒，BET全比表面積均比熱鍛燒觸媒小些，晶相上則無太大差異，由ICP-AES分析結果發現電漿改質有效去除觸媒殘餘不純物，金屬銅比表面積亦略為提升。觸媒活性提升以O2-CP60觸媒最大，CO轉化率達70 %，DME產率2.3 g-DME/g-cat*h大於Blank-C觸媒的1.08 g-DME/g-cat*h；電漿鍛燒觸媒從ICP-AES分析發現隨電漿鍛燒時間的增加，觸媒不純物有漸少的趨勢，但含量仍高於Blank-C觸媒，XRD圖譜上亦可觀察到仍有前驅物型態結晶，但CuO晶粒有變小、分散性增加的現象。O2-PC240觸媒於STD反應活性略高於Blank-C觸媒，而H2-PC240觸媒則與Blank-C觸媒相當。 透過實驗數據的回歸，本研究建立了Blank-C與O2-CP60觸媒之反應動力學模型，用以預測不同反應條件之出口組成，同時提供產製二甲醚製程最適化之參考。由動力學模型計算目前製程之最佳化參數，反應溫度應增加至310℃左右，反應壓力越高壓越利於DME產率，合成氣最佳進料流量在200 sccm，H2/CO最佳比例約在2.2至2.4之間。
並列摘要
In this work, a novel radio frequency (RF) glow discharge plasma modified Cu/ZnO/Al2O3 catalysts were prepared by conventional coprecipitation method, with the goal to improve its performance on the dimethly ether synthesis from syngas. Not only plasma modified process, the feasibility of using plasma to replace traditional calcination process were also investigated. To further understand the interplay between plasma species and catalyst surface, we used optical emission spectroscopy (OES) as a diagnostic tool to observe the concentration of active species in the plasma. The results show that although the catalysts’ BET surface areas after plasma modification or plasma calcination were lower than the traditional-calcined and non-calcined catalyst, but the copper surface area and metal dispersion of the catalysts increased after plasma modification. By the cross examination between OES diagnostics and ICP/AES analysis, we confirmed that plasma is responsible for the decomposition of carbonates and impurity which contented in the catalyst. The catalytic performances of H2, O2 plasma modified catalysts (after calcination) are better than traditional-calcined catalyst. Moreover, the catalyst activity enhanced after O2 plasma calcination which compared with traditional-calcined catalyst, due to the remarkable decrease of the copper oxide crystalline size according to XRD analysis. A kinetic model were also established for the dimethly ether synthesis from syngas over the catalyst. The kinetic parameters of the model reactions were determined by regression from experimental data. The kinetic model was found to predict well on the product flowrate and reactant conversion of syngas to DME (STD) reaction under different conditions (temperature, pressure, syngas feed ratio, etc.), which is required for future reactor design and optimization of DME synthesizing process.