一次性废竹筷制备活性炭及热解过程分析

Preparation of activated carbon from waste disposable bamboo chopsticks and analysis of pyrolysis process

以一次性废竹筷为原料,K2CO_3为活化剂,通过炭化和活化2步制备活性炭。采用全自动比表面和孔径分布分析仪、傅里叶变换红外光谱仪(FTIR)、X射线衍射分析仪(XRD)对样品的孔隙性质、表面官能团和晶相变化进行了表征,并研究了活性炭对亚甲基蓝的吸附等温线。利用热重分析(TGA)对活性炭的制备过程进行了研究,并用Coats-Redfern法确定了热解反应活化能和反应模型。结果表明,活性炭的比表面积为1 262 m^2·g-1,总孔体积为0.624 cm^3·g-1。K2CO_3活化可导致热解炭的脂肪烃侧链断裂,并发生脱氢缩聚,其石墨微晶的轴向(100)堆积被破坏,径向(002)芳香环网状结构则更为有序。活性炭对亚甲基蓝的吸附过程符合Langmuir模型,最大吸附量为336 mg·g-1。废竹筷的2个主要热解阶段符合一维扩散模型和二级反应模型,其热解反应活化能分别为76.23和104.24 k J·mol-1;活化过程中残存木质素的热解可由一维扩散模型描述,K2CO_3浸渍使其热解反应活化能降低了44.28 k J·mol-1。

Activated carbon was prepared from waste disposable bamboo chopsticks by K2CO_3 activation via 2-step method. The activated carbon was analyzed by N2-adsorption/desorption,FTIR and XRD,and the adsorption isotherm was quantified using methylene blue. The preparation process was investigated by TGA,and the pyrolysis kinetic and model were studied using Coats-Redfern method. Experimental results demonstrated that the BET surface area and total pore volume of the activated carbon were 1 262 m^2·g^-1and 0. 624 cm^3·g^-1,respectively. Aliphatic chains and oxygen-contained groups on the char surface were removed during K2CO_3 activation. Larger aromatic layers were formed at（100） planes,but the graphite-like microcrystallites at（002） planes were destroyed. The methylene blue adsorption data followed Langmuir model with a maximum adsorption capacity of 336 mg·g^-1. The two main pyrolysis stages of the waste disposable bamboo chopsticks can be described by one-dimensional diffusion model and second order reaction model,with the activation energies of 76. 23 and104. 24 kJ·mol^-1,respectively. The pyrolysis of the residual lignin in the char fitted one-dimensional diffusion model,and the activation energy was lower by 44. 28 kJ·mol^-1due to K2CO3 impregnation.