页岩氮气吸附BET比表面积测定误差校正方法

基于多分子层吸附理论的BET模型是最成熟、最常用于比表面测试的计算方法,然而,针对页岩样品在液氮温度下的氮气吸附数据,选取0.05~0.30间的相对压力点(适用于中孔材料)进行BET比表面计算时,将出现回归曲线相关系数较差、常数C为负值(无物理意义)情况,这一问题往往被测试者忽视。通过页岩的二氧化碳吸附数据运用DFT模型,计算出页岩的微孔分布可知,页岩含有大量0.5~1.0 nm之间的微孔,页岩纳米级孔隙分布范围广的特点是出现上述问题的根本原因,即页岩并非孔径分布较窄的介孔材料。通过调整相对压力点的选取范围,在相对压力0.05~0.20下计算页岩比表面其相关系数能达到0.999 9以上,且在Y轴上产生正截距,该相对压力范围更为合理,计算出的BET比表面更为可靠。

The accurate determination method for BET specific surface based on nitrogen adsorption of shale sample

The theory of BET model which based on multi-molecular layer adsorption is the most commonly and mature method used for specific surface testing. For the nitrogen adsorption data of shale samples which at liquid nitrogen testing temperature, slectting the relative pressure from 0.05 to 0.3 between (indicated for mesoporous materials) we can calculate the BET specific surface of the sample, but it will appear the problem of poor correlation coefficient and negative C constant which is not allowed to happen, the problem is often subject to ignore. The micropore pore size distribution calculated by carbon dioxide adsorption data using the DFT model shows shales contain a mount of microporous which aperture between 0.5 ~ 1.0nm. The characteristics of shales nanometer pore distribution is the fundamental reason for the emergence of above problems. In other words, shale is not the mesoporous materials and narrower pore size distribution. On the contrary, by selecting the relative pressure which from 0.05 to 0.20 calculating the specific surface, the correlation coefficient reached more than 0.9999, and emerged positive intercept on the Y axis, the relative pressure range is more reasonable, and the calculated BET specific surface is more reliable.