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|Title: ||製備新型鎳基MCM－41催化劑應用於稻稈氣化提昇氫氣產量之研究;Enhanced hydrogen production from rice straw gasification by using prepared nickel-based MCM-41 catalyst|
|Authors: ||登阮寶罄;Dang-Nguyen, Bao-Khanh|
|Keywords: ||稻草;氣化;鎳基MCM-41;氫氣;rice straw;gasification;Ni/MCM-41;hydrogen|
|Issue Date: ||2020-06-05 17:47:45 (UTC+8)|
|Abstract: ||本研究嘗試利用自行製備之新型鎳基MCM－41催化劑，探討應用於稻稈氣化提昇產能效率之可行性。研究過程先利用低功率微波消化法合成製備MCM-41，其中二氧化矽來源係從稻稈中萃取，萃取條件主要包括0.05-0.30 M檸檬酸及500-800oC燃燒條件。鎳基催化劑則以濕浸漬方法，將5-15 wt.％的鎳負載於MCM-41之表面，為進一步評估合成之MCM-41及鎳基MCM-41催化劑的效能，研究分別以X光繞射（XRD）、傅立葉轉換紅外光譜（FTIR）、高分辨率透射電子顯微鏡（HRTEM）、Brunauer-Emmett-Teller（BET）及N2吸附/脫附 (N2 adsorption/desorption) 等方法驗證 。催化氣化的反應試驗則是以流體化床反應器進行，控制條件分別包括當量比（ER）為0.2，氣化溫度為800oC。同時5-10 wt.％催化劑則是與矽砂混合後，共同作為砂床的材料。氣化反應產生的合成氣，以GC-FID/TCD進行分析，氣化反應後的催化劑，則以XRD及HRTEM進行相關特徵變化之分析。|
實驗結果顯示，利用0.30 M檸檬酸萃取之二氧化矽，其純度可達95wt.％以上， 且在操作溫度600oC所製備的無定形二氧化矽，較適用於後續作為製備MCM-41之材料。研究同時得知隨著降低合成溫度及延長合成時間，可製備較佳BET表面積之材料。整體而言，基材最佳之BET表面積及孔體積分別為1304.71 m2/g和2.24 nm，均高於商業MCM-41之719.45 m2/g及2.02 nm。根據XRD分析結果顯示，試驗製備之樣品均表現出典型的中孔結構。FTIR分析結果可知，本研究合成之MCM-41與商業型態之MCM-41，均在1065 cm-1、804 cm-1、1640 cm-1及2981-3652 cm-1的寬帶處，出現相似的振動信號，可見本試驗已成功合成MCM-41催化劑。另根據N2吸附/脫附及HRTEM分析結果可知，試驗樣品均屬代表性之IV型等溫線及六邊形結構之催化劑。
稻稈催化氣化產能效率的分析結果顯示，未添加催化劑之試驗條件下，氫組成平均比例及合成氣熱值分别為2.86 vol.％及1.56 kJ/Nm3，同時氫組成比例隨鎳基催化劑添加比例增加而增加，最大氫氣組成比例及合成氣熱值分别約為7.78 vol.％及2.60 kJ/Nm3。此外，當催化劑添加比例由5wt.％增加到10wt.％時，氫氣組成平均比例由3.43 vol.％增加到7.35 vol.％。催化劑之鎳含量由5 wt%增加至10 wt%，其氫氣組成比例亦由6.00 vol.％增加到7.77 vol.％，此係鎳基催化劑提供更多的酸性活性反應位置，促使更多的焦油轉化為合成氣。此外，鎳基催化劑亦促進水氣轉移反應，增加氫氣及二氧化碳的產生。然而，當添加10wt.％含15 %Ni基催化劑之試驗結果顯示，氫氣組成比例稍降低為7.35 vol.％，推測係因稻稈中含鉀成分於氣化反應過程附著於催化劑表面，降低催化劑的反應活性。
;This research investigated the characteristics of prepared nickel-based MCM-41 (Mobile Composite Matter No. 41) and evaluated the performance of enhanced energy conversion efficiency in rice straw gasification amended with different ratio of nickel-based MCM-41 catalyst. The prepared MCM-41 was synthesized using low-power microwave digestion. Silica content was extracted from rice straw by using 0.05 - 0.30 M citric acid and 500 - 800oC operation temperature. Prepared 5 - 15 wt.% nickel-based catalyst was loaded on the MCM-41 surface using wet impregnation method. The synthesized MCM-41 and nickel-based MCM-41 catalysts were all characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), high-resolution transmission electron microscope (HRTEM), Brunauer-Emmett-Teller (BET) and N2 adsorption/desorption methods, respectively. The catalytic gasification was performed in a fluidized bed gasifier controlled at equivalence ratio (ER) 0.2 and 800oC operation temperature. For each run, 5-10 wt.% tested catalyst was mixed with silica sand as bed material. The resulted syngas was analyzed using gas chromatography equipped with flame ionization detector and thermal conductivity detector (GC-FID/TCD). After gasification reaction, the catalyst was separated from the bed material and characterized by using XRD and HRTEM analysis.
The experimental results indicated that extracted silica was obtained from 0.3 M citric acid extraction and approximately higher than 95 wt.%. The amorphous silica form obtained at 600oC was suitable for MCM-41 preparation. It was also found that the BET area was improved with decreasing the synthesis temperature and prolonging the synthesis time. The highest BET surface area and optimal pore volume of MCM-41 were 1304.71 m2/g and 2.24 nm, respectively. To compare with commercial type, prepared MCM-41 has higher BET surface area and pore volume than that of commercial MCM-41. According to XRD results, all the prepared samples demonstrated the typical peaks of mesoporous structure. The FTIR analysis confirmed that the synthesized MCM-41 exhibited similar vibration signals at 1065 cm-1, 804 cm-1, 1640 cm-1, and a broad-band from 2981-3652 cm-1, comparing with the commercial MCM-41. The representative type IV isotherm and hexagonal structure were observed in all samples based on the results of N2 adsorption/desorption and HRTEM analysis.
The rice straw gasification performance was evaluated under different catalyst condition. Without catalyst addition, the average hydrogen produced and syngas heating value were 2.86 vol.% and 1.56 kJ/Nm3, respectively. It was observed that the hydrogen composition enhanced with either nickel content or catalyst addition. The maximum hydrogen content and syngas calorific value were approximately 7.78 vol.% and 2.60 kJ/Nm3, respectively. In the case of catalyst addition increased from 5 wt.% to 10 wt.%, the average hydrogen yield increased from 3.43 vol.% to 7.35 vol.%. The nickel content was also shown a similar trend, the hydrogen composition increased from 6.00 vol.% to 7.77 vol.% with an increase in Ni content increasing from 5 wt.% to 10 wt.%. It could be explained that the tested catalyst provided more acidic active sites for converting more tar content into syngas. Meanwhile the nickel could facilitate the water-gas shift (WGS) reaction, thus, more hydrogen and carbon dioxide were produced in gasification. However, hydrogen composition was a slight decreased to 7.35 vol.% as 15 wt.% Ni-based and 10 wt.% catalyst addition. This is due to the biomass containing potassium species could deposit on the catalyst surface resulted in the catalyst activity reduction. The results were confirmed by the XRD and HR-TEM analysis.
In summary, the prepared MCM-41 has a higher BET surface area and pore diameter characteristics and also exhibited the similar hexagonal structure with commercial MCM-41. The synthesized Ni-based catalyst has been successfully developed for improving quality of syngas in rice straw gasification.
|Appears in Collections:||[環境工程研究所碩士在職專班] 博碩士論文|
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