木質素磺酸鹽製備炭材特性之研究

Abstract

本實驗利用工業木質素—木質素磺酸鹽作為研究材料，探討木質素磺酸鹽原材料性質及生產炭材的製程及其產物性質，不同的製程條件包括熱裂解加熱溫度、升溫速率和持溫時間以及後續的不同洗滌處理（去離子水超音波振盪水洗或磷酸浸泡酸洗）。分析項目可分為：表面形態和孔隙性質、化學性質以及熱性質。表面形態及孔隙性質包括了掃描式電子顯微鏡及比表面積、孔隙率和孔徑分析；化學性質分析包括了熱裂解氣相層析質譜分析了解化合物組成，元素分析了解碳元素含量變化，傅立葉轉換紅外線光譜分析了解化學官能基變化，X-射線繞射分析及近邊緣X光吸收近邊緣結構光譜分析了解石墨化程度和芳香環碳及羧酸碳的變化，界面電位分析了解材料分散性、表面電荷及等電位點；熱性質包括了示差掃描熱量分析及熱重分析，分析材料吸放熱情形及熱穩定性。研究結果顯示，木質素磺酸鹽經高溫熱裂解後從原本棕色的粉末顆粒狀變成了黑色的固塊狀，顆粒相互熔融在一起，表面佈滿孔洞以及出現顆粒膨脹變形的情況，推測為在熱裂解過程中，因自活化及高溫所發生的交聯反應和氣化反應導致氣體蒸散所造成炭材的多孔性。此外，炭材的碳含量會隨著熱裂解溫度上升而增加，但熱裂解溫度上升會使產率下降。對於炭材的洗滌處理，結果顯示，水洗處理和酸洗處理皆有效去除焦油和灰分等雜質使產物的碳含量增加，且酸洗會優於水洗。但水洗處理的炭材卻有最佳的熱穩定性及分散性。研究結果也顯示，當熱裂解溫度上升時，水洗處理炭材中的芳香環的碳結構呈增加趨勢，而羧酸的碳結構則是呈下降趨勢，熱裂解溫度需超過600°C時，才會有較多的芳香環的碳，形成石墨化的結構。而水洗處理炭材的平均孔徑會隨熱裂解溫度增加而變小，而比表面積會隨著熱裂解溫度上升，會呈先上升後下降的趨勢，熱裂解溫度為900°C時有最高的比表面積，為688.5 m2 g-1。而炭材的孔隙度大小則跟熱裂解溫度沒有太大的相關，整體都落在70–80%之間。而吸脫附等溫線和孔徑分佈的結果都顯示了木質素磺酸鹽炭材的孔隙結構為微孔的構造。

In this study, the properties of lignin-based charcoal materials made by lignosulfonate (a technical lignin) through different process parameters were investigated, such as pyrolysis temperature, heating rate, holding time and washing treatment (Deionized water washing with ultrasonicator, acid washing by phosphoric acid). Analysis tests include surface morphology and pore properties, chemical properties and thermal properties. Surface morphology and pore properties include scanning electron microscope, surface area porosity and pore diameter analysis. Chemical properties include pyrolysis-gas chromatography/mass spectrometry, elemental analysis, fourier transform infrared spectroscope, X-ray diffraction, near edge X-ray absorption fine structure and zeta potential. Thermal properties include differential scanning calorimetry and thermogravimetric analysis. Results show that after pyrolysis processing, lignosulfonate particles would form porous charcoal spheres, caused by self-activation, cross-linking and gasification reaction caused by high temperature, gas emission during pyrolysis resulted in the porous structures for the lignin-based charcoals, producing the more porous structures for lignin-based charcoals. Furthermore, the carbon content of lignin-based charcoals has significantly increased with elevating pyrolysis temperatures. As the degreaser, deionized water and phosphoric acid can remove impurity of lignin-based charcoal increased the carbon content. In contrast to carbon content, the yields of lignin-based charcoals decreased with elevating pyrolysis temperatures and washing treatment. Acid washing charcoals have the highest carbon content, but deionized water washing charcoals have the best thermal stability and dispersibility. The results also show that the charcoal’s aromatic ring structure would increase and carboxylic carbon would decrease when pyrolysis temperature was increased. However, the graphitized structure could form only when the pyrolysis temperature was over 600°C. And the average pore diameter of the lignin-based charcoals washing by deionized water were decreased when the pyrolysis temperature was increased, but the surface area would first rise and then fall, the lignin-based charcoal has the highest surface area (688.5 m2 g-1) when the pyrolysis temperature was at 900°C. The porosity of the charcoals has no significance to pyrolysis temperature, the porosity of all lignin-based charcoals washing by deionized water was between 70–80%. The results of adsorption isotherms and pore size distribution both show that the pore structures of lignin-based charcoals are micro-pore.