摘要
深入理解水在褐煤上的吸附是褐煤干燥提质技术的理论基础之一。采用傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)和低温氮吸附/脱附试验分析了褐煤的含氧官能团和孔隙结构,利用水蒸气吸附/脱附试验和分子动力学(MD)模拟探究了水蒸气在褐煤孔隙中的吸附行为。研究结果表明:褐煤样品丰富的含氧官能团和较多的微孔、中孔(孔径约2 nm),为水蒸气提供了吸附位点和吸附场所。水蒸气在煤样上的吸附过程可分为3个阶段。第1阶段,相对蒸气压(P/P_(0))<0.21,水分子直接吸附于含氧官能团上,此时的吸附速度最大;第2阶段(P/P_(0)=0.21~<0.71),水分子与已吸附的水分子相互作用,促使水团簇逐渐生长;第3阶段(P/P_(0)≥0.71),水团簇填充孔隙,并发生毛细凝聚,此时的吸附速度略大于第2阶段。根据Dent模型对水蒸气吸附等温线的拟合结果,吸附类型属于多级吸附,包括初级吸附(第1阶段)和次级吸附(第2、3阶段)。初级吸附能(-48.77 kJ/mol)显著大于水的液化热(E L=-43.99 kJ/mol),而次级吸附能(-42.28 kJ/mol)略小于E L,表明吸附于褐煤的水呈液态。水蒸气脱附过程存在明显的脱附迟滞现象,表明水蒸气吸附稳定,较难去除,其中高压迟滞发生在P/P_(0)≈0.4~0.9,主要由毛细凝聚和“墨水瓶”效应引起;而低压迟滞发生在P/P_(0)<0.4,由水分子与含氧官能团间强相互作用引起。MD模拟结果与水蒸气吸附/脱附等温线分析结果一致,水分子优先吸附在孔隙中,与孔隙壁的含氧官能团形成氢键,且其扩散系数(2.98×10^(-5)cm^(2)/s)与液态水的分子扩散系数相近。
Deeply understanding the adsorption of water on lignite is one of the theoretical foundations of lignite drying and upgrading technology.The oxygen-containing functional groups and pore structure of lignite were analyzed using Fourier Transform Infrared Spectroscopy(FTIR),Scanning Electron Microscopy(SEM),and low-temperature nitrogen adsorption/desorption experiments.The adsorption behavior of water vapor in the pores of lignite was investigated using water vapor adsorption/desorption experiments and Molecular Dynamics(MD)simulations.Results show that the rich oxygen-containing functional groups and numerous micropores and mesopores(with the pore size mainly around 2 nm)in lignite samples provide adsorption sites and places for water vapor.The adsorption process of water vapor on the coal sample can be divided into three stages.In the first stage,with the relative vapor pressure(P/P_(0))<0.21,water molecules directly adsorbe on oxygen-containing functional groups,and the adsorption speed is the highest.In the second stage(P/P_(0)=0.21-<0.71),water molecules interact with adsorbed water molecules,promoting the gradual growth of water clusters.In the third stage(P/P_(0)≥0.71),water clusters fill the pores and the capillary condensation appeared,the adsorption speed in this stage is slightly higher than in the second stage.According to the fitting results of the Dent model on the water vapor adsorption isotherm,the adsorption type belonged to multi-stage adsorption,including primary adsorption(first stage)and secondary adsorption(second and third stages).The primary adsorption energy(-48.77 kJ/mol)is significantly greater than the liquefaction heat of water(E L=-43.99 kJ/mol),while the secondary adsorption energy(-42.28 kJ/mol)is only slightly less than E L,indicating that the water adsorbed on lignite is liquid.There is a significant desorption hysteresis phenomenon during the water vapor desorption process,indicating that the water vapor adsorbes stably and is difficult to remove.High pressure hysteresis occurr
作者
王成勇
邢耀文
王市委
陈鹏
李吉辉
桂夏辉
WANG Chengyong;XING Yaowen;WANG Shiwei;CHEN Peng;LI Jihui;GUI Xiahui(School of Mining and Mechanical Engineering,Liupanshui Normal University,Liupanshui 553004,China;Chinese National Engineering Research Center of Coal Preparation and Purification,China University of Mining and Technology,Xuzhou 221116,China;School of Chemical and Environmental Engineering,China University of Mining and Technology-Beijing,Beijing 100083,China)
出处
《洁净煤技术》
CAS
CSCD
北大核心
2024年第5期162-171,共10页
Clean Coal Technology
基金
贵州省基础研究(自然科学)资助项目(黔科合基础-ZK[2022]一般532)
贵州省教育厅资助项目(黔教技[2023]087号)
六盘水师范学院学科(培育)团队资助项目(LPSSY2023XKTD02)。
关键词
褐煤
孔隙结构
含氧官能团
水蒸气吸附
Dent模型
分子动力学模拟
lignite
pore structure
oxygen-containing functional group
water vapor adsorption
Dent model
molecular dynamics simulation
