钾元素对生物质及其三组分热解的影响

采用机械混合法将KCl加入到纤维素、半纤维素、木质素以及稻壳和稻壳模拟物等生物质中,得到了一系列不同K含量的生物质样品,通过热重(TG)实验考察了K元素对生物质热解特性的影响.结果表明,K元素对生物质三组分热解特性的影响比较复杂,纤维素的最大热解失重速率随着KCl添加量的增加而降低,但KCl对半纤维素和木质素热解特性的影响不显著.无论是否添加KCl,模拟生物质的热解特性均可以认为是三组分热解的简单叠加.但酸预处理稻壳三组分间的稳定结构,导致其DTG曲线在300 ℃左右的热解峰由稻壳模拟物的尖峰变为肩峰,其热解焦炭收率也比稻壳模拟物的略低.此外,实验还采用浸渍法向酸预处理稻壳中添加了KCl.TG实验结果表明,K元素的存在对生物质热解具有一定的催化作用,但KCl的添加方式不同,生物质的热解特性有明显差别,生物质样品经机械混合添加KCl后,其热解焦炭收率呈下降趋势(纤维素除外),浸渍法添加的KCl导致酸预处理稻壳的最大热解失重速率和焦炭收率升高.

Effect of potassium on pyrolysis of rice husk and its components

Different rice husk samples and their components (cellulose, hemicellulose and lignin) were investigated with emphasis on the influence of potassium on their pyrolysis behaviors by using thermogravimetric (TG) analysis. The results indicate that the maximum weight loss rate of cellulose decreases with the addition of KCl. However, no significant differences are observed for the pyrolysis behavior of hemicellulose and lignin. The TG/DTG curve of a model rice husk (a mixture of cellulose, hemicellulose and lignin) could be obtained by superposition of that for each component. However, during pyrolysis the raw stable structure of basic components in the rice husk results in a change from a sharp peak for the model rice husk to a shoulder peak for the AW rice husk (pretreated with HCl to remove K and the other mineral matters) at around 300 ℃. In addition, the effect of KCl addition on pyrolysis of the AW rice husks was also studied. The results show that potassium has a remarkable catalytic effect on pyrolysis of the rice husk samples. The pyrolysis characteristics vary depending on the addition methods of KCl. While char yields decrease with the addition of KCl using mechanical method (except for the cellulose), the char yield and the maximum weight loss rate of impregnated AW rice husk increase gradually with the increase of KCl content.