氯化钙催化纤维素热裂解动力学研究

Kinetics analysis of cellulose pyrolysis catalyzed by calcium chloride

用差示热重分析仪对氯化钙纤维素热裂解动力学催化影响进行了研究。结果表明,氯化钙对焦炭的形成具有强烈的促进效果,使热裂解最终残留物产率从5%提升到10%以上,氯化钙的存在影响到热失重初始阶段活性纤维素的生成,使热重曲线向低温侧移动,并在低温段产生了小的失重速率峰。通过热重分析发现,氯化钙催化条件下纤维素热裂解动力学参数被分为了三段,分别对应于活性纤维素的生成、炭化和活性纤维素转化为挥发分产物三个区间,并依次成为整体失重过程的控制步骤。结合B ro ido-Shafizadeh机理分析以及与纯纤维素热裂解动力学参数的对比,氯化钙对这三个主要反应步骤都产生了促进效果,其中以催化焦炭的生成最为明显,在促进焦炭化的过程中,降低了气体产物的生成比率。

Experiments on pyrolysis of cellulose added with calcium chloride （CaCl2 ） were done on a thermo- gravimetric （TG） balance to study the catalytic mechanism of the process. Compared with the TG curves of pure cellulose pyrolysis, those added with CaCl2 show that CaCl2 has a strong effect on the formation of char, which increases the char yield from 5% to above 10%. In addition, it affects the formation of active cellulose by moving TG curve towards lower temperature, and leads to a small weight loss peak at the initial stage of decomposition process, which reveals the emission of small gas are improved in the process of de-polymerization of long chain biomass molecule. By kinetic analysis, the pyrolysis process of cellulose with CaCl2 is divided into three stages, respectively, corresponding to the formation of AC, carbonization and conversion into volatiles, which control the weight loss process sequentially. Based on the Broido-Shafizadeh model, those kinetic parameters calculated by narrow temperature zone method show that CaCl2 enhances all these three reactions. Especially in the low temperature the formation of char is catalyzed strongly, whose active energy has a sharp decrease. Because of the catalytic selectivity of CaCl2 on different reactions, CaCl2 has an especial effect on the formation of char, and decreases the emission of gas during the carbonization process, which indicates the char catalyzed by CaCl2 has high aliphatic degree.