微波誘發裂解生質廢棄物之研究

Microwave-Induced Pyrolysis of Biomass Waste

黃于峯(Yu-Fong Huang)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.01796

摘要

本研究係應用單向（聚焦）式的微波照射方式，誘使生質廢棄物進行熱裂解反應，以獲致具有高熱值或經濟價值的產物。在本研究中主要是以稻稈作為研究對象，並輔以其他常見生質廢棄物之實驗結果進行比較。微波功率的增加可提升熱裂解反應之升溫速率及最高溫度，進而有更高的原物料減量比。因此藉由微波功率的增加，縮短微波照射時間是可預期的。此外，原物料的顆粒大小亦會影響反應效果，推論是較小的原物料增加了容積密度及顆粒間接觸面積，因此提升原物料內部的熱傳效果，使得整體的熱裂解反應能更為快速。
產物分析結果方面，藉由固相產物（焦炭）的比表面積分析及界達電位分析結果，可預估固相產物具有應用在水處理及廢水處理中陽離子吸附去除之價值。銅吸附實驗結果顯示，即使是在pH 5的酸性條件下，固相產物對於銅離子的吸附去除率仍可達到90 %以上。氣相產物（燃料氣）之主要成份為H2、CO2、CO、CH4，其H2含量（50.67 vol.%）高於傳統熱裂解法的25 vol.%，顯示出微波誘發裂解生質能源技術具有可生產富氫燃料氣之潛力。依據氣相產物定量分析結果進行化學計量分析，可歸納出一近乎平衡的化學反應式。液相產物（焦油）中主要乃包括有三種類別的化合物：(1) 長鏈的飽和脂肪族化合物；(2) 極性化合物，如酚及其衍生物；(3) 低環數的多環芳香族化合物。由於液相產物中多環芳香族化合物的含量不高，且多為低環數者，故應有較低的毒性。氣相、固相、液相產物之重量百分比各為54.31 wt.%、28.07 wt.%、17.62 wt.%，故超過一半的稻稈樣品經由微波誘發裂解後可轉化為氣相產物，此部分亦優於傳統熱裂解方法。
本研究並針對稻稈、稻殼、玉米葉、咖啡殼、竹葉、甘蔗渣與甘蔗皮七種生質廢棄物，以及半纖維素、纖維素、木質素進行熱分析－質譜實驗。研究結果顯示氣相產物的主要生成乃發生於生質廢棄物重量損失最快之時，惟獨H2在較高溫（667∼749 °C）時亦會出現一明顯的生成情形。各生質廢棄物的H2半定量分析結果，其中以稻殼及玉米葉的產量較少，而以咖啡殼為最多。本研究將生質廢棄物的熱裂解視為擬一級反應，並應用Arrhenius方程式進行化學動力分析。各生質廢棄物的活化能及頻率因子差異頗大，並呈現出反比的趨勢，可能主要歸因於其成份比例的差異。一般生質廢棄物皆含有纖維素、半纖維素及其他物質，由於其含量比例的不同，使得有這般差異。然而此差異情形在反應速率常數並沒有出現，各生質廢棄物的差異最多僅在一個級數以內，進而造成頻率因子與有效碰撞機率二者之間呈現出此消彼長的情形。
微波誘發裂解稻稈的氣相產物可在300 W的微波功率下有效生成，且最大反應溫度可在10 min的反應時間內達到。在此條件下所得到的氣相產物總熱值約佔所需輸入能量的29.34 %，若加上固相及液相產物的熱值則可增加為57 %左右。因此，在微波誘發裂解反應中，大約有43 %的輸入能量應主要是使用於微波的產生，少部份則可能為實驗過程中因反射的微波功率所造成之額外能量消耗。微波誘發裂解之技術可行性係藉由SWOT分析進行評估。其可行性首重於內部本身的技術成熟度、效能、產物的質與量等因素，以及外部環境的政策、經濟、能源等因子。微波誘發裂解技術之推廣應從掌握並強化技術的產能、效能開始以提高競爭力，並尋求、開發適用的市場以增加技術能見度與市場比重。依據目前國內外之能源環境與政策走向，再生能源之需求理應會持續增加。然而技術種類眾多，強化微波誘發裂解技術之優勢並減低劣勢相信是使其脫穎而出的不二法門。

關鍵字

微波誘發裂解 ； 生質廢棄物 ； 焦炭 ； 焦油 ； 燃料氣 ； 氫氣

並列摘要

This study utilized the microwave irradiation of single (focused) mode to induce the pyrolysis of biomass waste. Thus products with high heating values or economic worth can be obtained. In this study, rice straw was chosen to be the primary researching target. Some other common biomass waste was also researched for the purpose of results comparison. The increase of microwave power helped to promote the heating rate and maximal temperature of pyrolysis, so higher mass reduction ratio of feedstock can be achieved. Thus by applying higher microwave power, it is expectable that the irradiation time of microwave can be shortened. Besides, particle size of feedstock affected the reaction performance as well. This might imply that the smaller feedstock had the higher bulk density and the more contact area between particles. Therefore, the heat transfer inside the feedstock was enhanced, and the entire pyrolysis reaction turned to be more rapid.
By the results of specific surface area analysis and zeta potential analysis, it is expectable that the solid product (char) can be applied in the cation adsorption in the water and wastewater treatment. The result of copper adsorption experiment shows that, even under the acidic condition (pH 5), the adsorption removal rate of copper can be over 90%. The primary components of gas product (fuel gas) were hydrogen, carbon dioxide, carbon monoxide, and methane. The hydrogen content (50.67 vol.%) of the gas product was higher than of traditional pyrolysis (25 vol.%). Thus the technology of microwave-induced pyrolysis shall have the high potential to produce hydrogen-rich fuel gas. According to the result of quantitative analysis of gas product, stoichiometric analysis was also executed to conclude to a nearly balanced chemical equation. There were mainly three categories of compounds in the liquid product (tar): (1) long-chained aliphatic compounds; (2) polar compounds (e.g., phenol and its derivatives); (3) low-ringed polycyclic aromatic hydrocarbons (PAHs). The liquid product shall be low poisonous due to the low content of PAHs and their low ring numbers. The gravimetric percentages of gas, solid, and liquid product were 54.31 wt.%, 28.07 wt.%, and 17.62 wt.%, respectively. Over half of rice straw sample can be converted into gas product. This result is also better than the traditional manner of pyrolysis.
This study also researched relevant characteristics of rice straw, rice husks, corn leaves, coffee hulls, bamboo leaves, sugarcane bagasse, sugarcane peel, hemicellulose, cellulose, and lignin by means of thermal analysis-mass spectrometry (TA-MS) experiments. The result showed that the primary production of gas product occurred during the highest mass-loss rate of biomass waste. However, there was also an obvious production of hydrogen at higher temperatures (667-749 °C). From the semi-quantitative analysis of hydrogen content, both rice husks and bamboo leaves had lower hydrogen production, and coffee hulls had the most. The pyrolysis of biomass waste was assumed to be pseudo first-order reaction, and the Arrhenius equation was applied to the analysis of chemical kinetics. The activation energy and frequency factor of biomass waste differed a lot from each other, and showed an inverse proportion. This might be due to the difference among the contents of biomass waste. Besides, the reaction rate constants of biomass waste did not differ much, which was about one order at the most. This might be the reason why there was an inverse relationship between the frequency factor and the effective collision probability.
The gas product of microwave-induced pyrolysis of rice straw can be effectively generated under microwave power of 300 W, and the maximal reaction temperature can be reached in 10 minutes. Under this condition, the total heating value of the gas product was about 29.34 % of input energy needed. This percentage can be increased to about 57 % when adding heating values of the solid and liquid product. Therefore, in the microwave-induced pyrolysis, there was about 43 % of input energy that might be used for microwaves generation or extra energy consumption due to reflectional microwave power.
The technology feasibility of microwave-induced pyrolysis was assessed by SWOT analysis. The result shows that inner factors of technology maturity, performance, quality and quantity of products, and outer factors such as government policy, economy and energy, are most important for the feasibility. The promotion of microwave-induced pyrolysis should start with enhancement of technology productivity and performance to raise its competitiveness, and try to expand suitable market to increase its visibility and market proportion. According to the international and domestic energy situation and policy direction so far, the demand of renewable energy shall keep increasing. However, there are so many technologies relevant to renewable energy. It is believed that to maximize advantages and to minimize disadvantages of microwave-induced pyrolysis are best policies to make it more favorable.

並列關鍵字

microwave-induced pyrolysis ； biomass waste ； char ； tar ； fuel gas ； hydrogen

參考文獻

Antal, M.J., Allen, S.G., Schulman, D., Xu, X.D., and Divilio, R.J., “Biomass gasification in supercritical water,” Ind. Eng. Chem. Res., 39, 4040-4053 (2000).

Afridi, H.I., Kazi, T.G., Jamali, M.K., Kazi, G.H., Arain, M.B., Jalbani, N., and Shar, G.Q., “Analysis of heavy metals in scalp hair samples of hypertensive patients by conventional and microwave digestion methods,” Spectr. Lett., 39, 203-214 (2006).

Banyasz, J.L., Li, S., Lyons-Hart, J.L., and Shafer, K.H., “Cellulose pyrolysis: the kinetics of hydroxyacetaldehyde evolution,” J. Anal. Appl. Pyrol., 57, 223-248 (2001).

Bilali, L., Benchanaa, M., El harfi, K., Mokhlisse, A., and Outzourhit, A., “A detailed study of the microwave pyrolysis of the Moroccan (Youssoufia) rock phosphate,” J. Anal. Appl. Pyrolysis, 73, 1-15 (2005).

Bradbury, A.G.W., Sakai, Y., and Shafizadeh, F., “A kinetic model for pyrolysis of cellulose,” J. Appl. Polym. Sci., 23, 3271-3280 (1979).