基于量子化学的木质素热裂解中环类化合物形成的理论及实验研究

利用傅里叶变换红外光谱仪分析木质素微观结构,应用裂解气相色谱-质谱联用技术(Py-GC/MS)进行木质素的热裂解产物分析。研究结果表明:300和400℃时没有检测到多环芳烃等复杂结构,可见在该温度下,裂解产物并未发生二次缩合作用;在800℃下,苯和甲苯的GC含量增加,苯酚基本保持不变,并开始出现多环芳烃化合物。以密度泛函理论B3LYP/6-31G(d,p)为基础对木质素的裂解反应过程进行了分子动力学模拟研究,对比分析实验数据和模拟数据,推断出木质素热裂解中环类化合物的形成演化机理:300~400℃主要发生CC键的断裂和羟基脱落(路径R5-1)以及C1—Cα键的断裂(路径R5-2);400~800℃发生的C1—Cα键断裂反应(路径R4-1),苯环上甲氧基官能团脱去反应(路径R4-4)和苯环上甲氧基均裂(路径R5-3);与苯环上甲氧基官能团均裂反应(路径R4-3)相比,苯环C1—Cα断裂反应(路径R4-2)发生的可能性更大;路径2、路径3和路径5的产物量均在800℃左右达到最大,其产物分别为联苯、菲以及芘。

Theoretical and Experimental Study on Cyclic Compound Formation in Lignin Pyrolysis Based on Quantum Chemistry

The microstructure of lignin was analyzed by using Fourier transform infrared spectrometer ( FT-IR) , and the pyrolysis products of lignin were analyzed by gas chromatography mass spectrometry ( Py-GC/MS ) .The results showed that the second condensation reaction of the cracking product did not occur at 300 and 400 ℃, and the complex structures such as polycyclic aromatic hydrocarbons were not detected .At 800 ℃, the relative contents of benzene and toluene increased while the phenol content was stable .Meanwhile , the polyaromatic hydrocarbons were observed .The molecular dynamics simulation of the cracking reaction process of lignin was carried out based on the density functional theory B 3LYP /6-31G(d, p).The comparison between the calculated and experimental results showed that the fracture of C C bond, the loss of hydroxyl (path R5-1) and the fracture of C1—Cαbond ( path R5-2 ) appeared at 300 -400 ℃.The fracture of C1—Cαbond ( path R4-1 ) , the detachment of methoxyl functional groups on the benzene ring ( path R4-4 ) and the homolytic reaction of methoxyl functional groups on the benzene ring (path R5-3) were proceeded at 400 -800 ℃;C1—Cαbond (path R4-2) was fractured, more likely than the homolytic reaction of methoxyl functional groups on the benzene ring (path R4-3).The products of paths 2, 3 and 5 could be obtained as the temperature was over than 800℃, and their corresponding products were phenanthrene , biphenyl and pyrene , respectively .