木材热解及金属盐催化热解动力学特性研究

Kinetics of Pyrolysis and Metal-salt Catalized Pyrolysis of Wood

通过不同升温速率下杉木的热重实验，对比分析钾盐催化杉木热裂解动力学特性。借助于DTG重叠峰的分离以及分布活化能模型计算不同转化率条件下的反应活化能，得到钾盐对生物质中半纤维素的低温段分解、纤维素的整个热裂解过程存在催化效果，使失重曲线（200～270℃）肩状峰衰退乃至消失，并促进脱水和交联反应，导致焦炭产率的提高和残碳的有序化，体现为焦炭产量从16．3％提高到25．3％（质量分数），而且80％转化率后残碳分解活化能的急剧提高。基于三组分平行反应机理，采用非线性回归法拟合计算杉木热解动力学参数，得到纤维素的热裂解基本上属于一阶反应，而且钾盐对纤维素和半纤维素的热裂解具有较大程度促进，活化能分别从148．12和235．43kJ／mol下降到108．84和171．41kJ／mol，但对木质素的催化影响并不显著。

According to thermogravimetric analysis under different heating rates, the kinetic characteristics of pyrolysis of Chinese fir wood catalyzed by potassium salt was studied. In response to the separation of DTG ,peaks and the activation energy under different conversion rate calculated by distribution activation energy model, it was found that potassium salt had catalytic effect on decomposition of hemi-cellulose at low temperature, and on the whole pyrolysis process of cellulose. Besides, it weakened or even eliminated the shoulder peak of DTG curves （200-270℃） and promoted dehydration and cross-linking reaction, which improved the char yield, and the ordering of residue carbon, which was represented by the increase of char yield from 16.3 % to 25.3 % and the abrupt increase of activation energy at the residue carbon decomposition stage after 80 % conversion rate. Based on the three-component parallel-reaction mechanism, a non-lineal regression method was adopted to fit and calculate the kinetic parameters for pyrolysis of Chinese fir wood. Results showed that decomposition of cellulose could be regarded as first-order reaction. Potassium salt enhanced the pyrolysis of cellulose and hemi-cellulose, decreased their activation energy from 148.12 and 235.43 kJ/mol to 108.84 and 171.41 kJ/mol respectively, while the catalytic effect on lignin was insignificant.