挥发性有机物(VOCs)是光化学反应形成细颗粒物(PM2.5)、臭氧(O3)等2次污染物的重要前驱体，对大气环境和人体健康具有严重的危害。多孔炭吸附法具有效率高、成本低、可再生等优点，在VOCs处理技术中应用广泛。然而目前国内生产的煤基多孔炭以中低端产品为主，存在孔隙不够发达、传质过程受限等问题。围绕多孔炭制备过程的结构原位调控以及VOCs在孔道内的扩散/吸附机制开展了深入的研究。以褐煤为原料，KOH为活化剂，通过酸洗脱灰和Ca(NO3)2浸渍预处理，在碱煤质量比为2∶1的条件下制备煤基多孔炭，并选择甲苯作为目标VOCs进行吸附机制研究。结果表明，Ca(NO3)2改性后制备得到多孔炭的石墨芳香片层堆叠高度(Lc)减小、层间距离(d002)增大，说明Ca(NO3)2改性导致石墨微晶的破坏程度加深，有利于发达孔隙结构的形成。以甲苯分子动力学直径(0.57 nm)作为孔径范围的划分尺度，发现PC-Ca0.2在甲苯分子直径1～3倍(0.57～1.71 nm)具有最高的孔容积，同时也具有最高的甲苯吸附容量(746.2 mg/g)。采用Weber-Morris颗粒内扩散模型分析甲苯吸附的速率控制步骤，发现吸附过程由内扩散和外扩散共同控制，PC-Ca0.2具有最大的吸附速率常数和最小的扩散边界层常数。因此，当多孔炭在甲苯分子动力学直径1～3倍内具有较大的孔容积时，其孔隙结构更有利于甲苯吸附过程的扩散传质。

Volatile organic compounds (VOCs) are important precursors of secondary pollutants such as fine particulate matter (PM2.5) and ozone (O3),which are harmful to the atmospheric environment and human health.Adsorption technology by porous carbon is widely used in VOCs treatment.However,traditional coal-based porous carbon exhibits underdeveloped pore structures,which may limit the mass transfer process.The in-situ structure control during synthesis process of porous carbon and the diffusion/adsorption mechanism of VOCs were studied in this paper.Porous carbon was prepared from lignite by acid washing together with Ca(NO3)2 impregnation pretreatment,and toluene was chosen as adsorbate.Results showed that the stacking height (Lc) of aromatic structure decreased after Ca(NO3)2 modification,while the interlayer spacing (d002) increased.This indicated the deep damage of carbon microcrystalline,which was favorable to the formation of pores.The molecular diameter of toluene (0.57 nm) was used as the dividing scale of pore size range.PC-Ca0.2 exhibited the largest pore volume in the range of 1-3 times of toluene molecular diameter (0.57-1.71 nm),which also had the highest toluene adsorption capacity of 746.2 mg/g.Weber-Morris intraparticle diffusion model was used to study the rate determining step of toluene adsorption.It was found that the adsorption process was controlled by both internal and external diffusion.PC-Ca0.2 had the maximum adsorption rate constant and the minimum diffusion boundary layer constant.Therefore,when the porous carbon had a larger pore volume in the range of 1-3 times of molecular diameter,it was more conductive to the diffusion and mass transfer in the adsorption process.

1 试验

   1.1 煤样分析

   1.2 样品制备

   1.3 表征测试

   1.4 吸附性能评价

2 结果与讨论

   2.1 Ca(NO3)2改性对煤基多孔炭结构的影响

   2.2 煤基多孔炭对甲苯的吸附性能

   2.3 甲苯在多孔炭上的吸附平衡

   2.4 甲苯在孔道内的吸附和扩散机制

3 结论