亚临界水解预处理稻草秸秆制备活性炭及表征

Preparation and Characterization of Activated Carbon from Rice Straw Pre-treated by the Subcritical Hydrolysis

通过以稻草秸秆的亚临界预处理中产生的残渣作为实验材料,以氯化锌作为活化剂制备具有吸附性能的活性炭,研究了活化温度,活化时间,浸渍时间以及浸渍比等4个因素对生成活性炭的性能影响,设计正交实验制备活性炭.以低温液氮吸附测定活性炭的比表面积和孔容、孔径分布,以扫描电子显微镜(SEM)观测活性炭表面形貌,并以亚甲基蓝(MB)作为吸附质,研究了活性炭对亚甲基蓝的吸附动力学和吸附等温线.结果表明,活化温度900℃,活化时间60 min,浸渍比1∶5,浸渍时间12 h,当氯化锌质量分数为20%时,制得相应活性炭的碘值为1 122.79 mg.g-1,亚甲基蓝吸附值为136.50 mg.g-1.亚甲基蓝在活性炭上的吸附基本符合Langmuir方程,且准二级动力学模型能很好地描述活性炭对亚甲蓝的吸附过程;热力学研究表明,吸附吉布斯自由能(ΔG0)<0,而焓变(ΔH0)>0,说明吸附为吸热的自发反应过程,升温有利于吸附.

Activated carbons were prepared from waste residue which was obtained from rice straw dealt with subcritical water by chemical activation with ZnCl2.It was also considered that the variations of activation temperature,activation time,impregnation time and impregnation ratio influenced the performance of activated carbon.Adsorption isotherm and scanning electron microscopy（SEM） were used to characterize the pore structure and surface morphology of carbon.Adsorption kinetics and isotherms of methylene blue,used here as a reference compound,were studied.The results show that when zinc chloride content was 20%,the optimum conditions of activated carbon produced are obtained-reaction temperatures of 900℃,activation time of 60 min,impregnation ratio of 1∶5 and impregnation time of 12 h.The number of iodine and methylene blue of activated carbon is 1 122.79 mg·g-1,136.50 mg·g-1,respectively.Adsorption of methylene blue on activated carbon fits the Langmuir equation and pseudo-second kinetic model can well describe the adsorption process of methylene blue.The negative change in free energy（ΔG0） and positive change in enthalpy（ΔH0） indicate that the adsorption is a spontaneous and endothermic process.