外源酸催化对木材半纤维素热降解规律的影响  

Effects of exogenous acid catalysis on the thermal degradation law of wood hemicellulose

作　　者：雒翠梅 王旭洁 母军[1] 漆楚生 Luo Cuimei;Wang Xujie;Mu Jun;Qi Chusheng(MOE Key Laboratory of Wooden Material Science and Application,School of Materials Science and Technology,Beijing Forestry University,Beijing 100083,China)

机构地区：[1]木质材料科学与应用教育部重点实验室,北京林业大学材料科学与技术学院,北京100083

出　　处：《北京林业大学学报》2022年第4期147-156,共10页Journal of Beijing Forestry University

基　　金：国家自然科学基金项目(31971589、31870536)。

摘　　要：【目的】高温热处理可使木材半纤维素部分降解,改善木材的尺寸稳定性。使用外源酸可降低木材半纤维素热降解温度,因此有必要明确其热降解规律。【方法】采用碱法分离的方式提取出杨木和杉木的半纤维素,通过傅里叶红外光谱仪和热重分析法研究引入外源酸条件下(两种外源酸AlCl_(3)和H_(3)PO_(4),每种外源酸的浓度分别为0.1和0.3 mol/L)半纤维素的热降解规律。【结果】碱法分离出的木材半纤维素,其红外谱图符合阔叶材和针叶材半纤维素的基本特征。经AlCl_(3)和H_(3)PO_(4)处理后,相比未处理的半纤维素,羟基峰发生红移,且半纤维素的特征吸收峰强度显著降低。热重分析显示:两种外源酸预处理的木材半纤维素的起始降解温度(T_(5%))从200℃左右降低至95~150℃,且主要降解温度范围从200~300℃降低至100~150℃。在相同浓度下,AlCl_(3)处理后半纤维素的T_(5%)(150℃)大于H_(3)PO_(4)的(95℃)。当AlCl_(3)浓度增大时,半纤维素热分解速率加快,但T_(5%)无明显变化。随H_(3)PO_(4)浓度增大时,半纤维素热分解速率和T_(5%)均减小。相比未处理的杨木半纤维素热解活化能(199.68 kJ/mol)和杉木半纤维素热解活化能(231.12 kJ/mol),AlCl_(3)和H_(3)PO_(4)处理后的热解活化能显著降低。在相同浓度0.3 mol/L的条件下,AlCl_(3)处理后杉木半纤维素的平均活化能(112.31 kJ/mol)要低于H_(3)PO_(4)的(125.82 kJ/mol)。【结论】本研究采用的两种外源酸均可显著降低半纤维素的热降解温度。总体来讲,AlCl_(3)催化效果优于H_(3)PO_(4),杉木半纤维素对H_(3)PO_(4)较为敏感。可根据针、阔叶材半纤维素的差异性选择不同的外源酸性介质作为催化剂,加速热解反应速率,从而为外源酸在木材低温热处理的应用提供一定的理论支撑。[Objective]High-temperature heat treatment can partially degrade wood hemicellulose and improve wood dimensional stability.The use of exogenous acid can reduce the thermal degradation temperature of wood hemicellulose,so it is necessary to clarify its thermal degradation law.[Method]In this study,hemicelluloses from poplar and Chinese fir were separated by alkali method.Thermal degradation of hemicellulose(The two exogenous acids were AlCl_(3)and H_(3)PO_(4),and the concentration of each acid was 0.1mol/L and 0.3mol/L,respectively)under different acidic conditions were investigated by Fourier Infrared Spectrometer(FTIR)and thermogravimetric(TG)analysis.[Result]The FTIR spectra of wood hemicelluloses isolated by alkali method were consistent with the basic characteristic of hemicellulose of softwood and hardwood.After being treated with AlCl_(3)and H_(3)PO_(4),the hydroxyl peak showed red shift,and the characteristic absorption peak intensity of hemicellulose decreased significantly compared with the untreated hemicellulose.TG analysis showed that the initial degradation temperature(T_(5%))of wood hemicellulose ranged from 200℃to 95–150℃after being pretreated by two kinds of exogenous acids,and the main degradation temperature ranged from 200–300℃to 100–150℃.At the same concentration,the T_(5%)value of hemicellulose(150℃)after AlCl_(3)treatment was greater than that of H_(3)PO_(4)(95℃).When the concentration of AlCl_(3)increased,the thermal decomposition rate of hemicellulose accelerated,but it had almost no effect on T_(5%).When the concentration of H_(3)PO_(4)increased,the thermal decomposition rate of hemicellulose and T_(5%)both decreased.Compared with untreated poplar wood hemicellulose(199.68 kJ/mol)and Chinese fir hemicellulose(231.12 kJ/mol),the pyrolysis activation energy was significantly reduced after AlCl_(3)and H_(3)PO_(4)treatment.When the concentration was 0.3M,the average activation energy of Chinese fir hemicellulose(112.31 kJ/mol)after AlCl_(3)treatment was lower than that of H_

关 键 词：磷酸 路易斯酸 催化 针叶材 阔叶材 半纤维素 热降解 

分 类 号：S781.46[农业科学—木材科学与技术]