联合催化剂预处理对竹纤维热氧化结构及芳构化的影响机制

The multi-catalyst system with inorganic and organosilicon was used to improve the catalytic efficiency of bamboo fiber. Some advantages of this novel ultrasound and impregnation combined pretreatment could be predicted, such as the process of pyrolysis reactions on bamboo fiber at the heat oxidation treatment should be accelerated, and the production of levoglucosan (tar) was decreased. Therefore, the aromatization process and structure was promoted with condensation polymerization of heat oxidation products in the subsequent middle temperature carbonization process. The process of broken and rebuilt of hydrogen bonding of pre-treated bamboo fiber was studied and the mechanism of the swelling of bamboo was illustrated. Meanwhile, with the benefit of the revolutionary spectroscopy instruments, the emergence and development of physical structure and chemical reaction of heat oxidation bamboo fiber in the heat oxidation process will be comprehensively studied by FTIR, XRD with accessories and TG-FTIR characterization techniques, and the activation energy of reaction system was also analyzed. Subsequently, the aromatization of carbon chain in the middle temperature carbonization process was investigated by FTIR, XRD with accessories, 13C NMR analysis with CP/MAS accessories, meanwhile, the microstructure the distribution and calculation of Clement of carbonized products with SEM and XPS was also studied. Finally, from the results of above analysis, the effect of structure of heat oxidation bamboo fiber on the aromatization will be determined and the mechanism of effect of the pre-treatment of bamboo fiber with composite catalyst on the aromatization in the middle temperature carbonization process was illustrated.

本研究拟采用无机/有机硅联合催化剂对竹纤维进行超声-浸渍预处理，加速竹纤维在热氧化处理过程中脱水反应，抑制纤维素热解产物左旋葡萄糖的生成，促进热氧化脱水产物在中温碳化条件下横（纵）向缩聚反应的进行和芳构化结构的生成，为制备高质量的纤维素基碳纤维提供有利条件。首先通过考察分析联合催化剂预处理对竹纤维中氢键的破坏和“重生”的过程及原理，阐明联合催化剂对竹纤维的溶胀机理；然后对预处理竹纤维的热氧化过程进行变温波谱分析，并结合热氧化处理条件对预处理竹纤维反应体系活化能影响的分析计算，阐明联合催化剂预处理竹纤维在热氧化过程中物理结构、化学性质的发生、发展演化机制；进而通过对热氧化纤维中温碳化过程中碳链的芳构化过程分析及其微观构造、碳元素分布及组成的分析计算，最终揭示热氧化纤维结构对芳构化的影响机理，为科学合理的制定和优化联合催化剂预处理和热氧化处理工艺，制备高性能碳纤维提供理论基础和实践依据。

纤维素在高温热解条件下首先发生脱水反应，生成脱水和非脱水纤维素，两者在热解条件下进行竞争反应，而无机催化剂中的酸性试剂可使羟基质子化，这为强化竹纤维在中温阶段的脱水反应提供了思路。项目利用竹纤维制备高温碳化纤维，采用无机化学试剂氯盐（CaCl2和ZnCl2）、有机硅（FMW）、以及有机无机联合催化剂对竹纤维进行预处理，其中：经CaCl2和ZnCl2预处理的竹纤维可在较低温度下使较多的羟基以小分子的形式脱去，有效抑制左旋葡萄糖的产生，同时最大失重率显著降低，碳得率增加；有机硅预处理对竹纤维热性能影响不大，但可以很好的修复竹纤维表面缺陷和沟槽。 CaCl2/ FMW预处理热氧化纤维的结晶度变化不大，而经ZnCl2/FMW和CaCl2/ZnCl2/FMW预处理的热氧化纤维的结晶度稍有下降。利用变温红外FTIR原位分析联合催化剂预处理竹纤维随温度变化过程中的化学结构变化规律，发现在CaCl2预处理作用下，纤维素在210℃时1705，1610cm-1处分别出现了C=O伸缩振动吸收峰和C=C双键的伸缩振动吸收峰，说明纤维素环开始发生高温氧化脱水反应。经CaCl2/FMW、ZnCl2/FMW以及CaCl2/ZnCl2/FMW预处理热氧化纤维在高温碳化结束后得到了不同结构的纤维，其中CaCl2预处理热氧化纤维经高温碳化处理后，钙盐在焦碳表面形成活化中心点，经高温碳化可形成多孔结构，所得碳纤维的比表面积为331.32m2/g，碳纤维的BJH孔容积为0.3307cm3/g，平均孔径为13.6440 nm，中孔孔径在2.06-31.07nm范围内的分布较为集中，说明碳纤维具有较大孔径的孔隙存在。项目研究成果将为竹材产品化学及高温功能性改良提供科学依据，为竹材资源的合理、高效利用提供很好的技术支撑。