简介

相比于动态穿透曲线法，静态法测量气体等温线简单便捷。然而，静态测量不能模拟实际动态情况下的气体和混合气组分。 因此穿透实验在优化研究过程中是非常有必要的，可以在不同压力条件下测量气体等温线。
这篇应用笔记给大家介绍如何用穿透曲线分析仪BTA测量不同压力条件下的吸附等温线来研究气体吸附量随着压力的变化。这与静态法是完全不同的，气体的流速对吸附等温线有非常大的影响，尤其是在穿透柱有压降或者存在传质问题的情况下。

实验过程

Zeolite 13X was used to measure high pressure carbon dioxide adsorption on the Micromeritics BreakThrough Analyzer at varying pressures between 1 bar and 10 bar (absolute). These measurements were collected at 30 °C and a total flowrate of 21 sccm. The flow consisted of 10 sccm N₂, 10 sccm CO₂, and 1 sccm He. Helium was used as a tracer gas in these experiments to determine the start of the breakthrough experiment. A tracer gas was used as the total flowrate of gas remained the same regardless of pressure, however the deadtime of each experiment would change due to the compression of gas in the same volume of total dead space. Prior to each analysis, zeolite 13X was activated at 100 °C for one hour before increasing to 200 °C for an additional 12 hours. After each measurement, the sample required full activation to completely regenerate the material, while room temperature activation was sufficient at 1 bar, higher activation temperature were required for greater pressure measurements. Additionally, the mass spectrometer would become saturate with CO₂ after each measurement and required a brief 1 – 2 hour bake-out before proceeding to the next analysis.

实验结果

Breakthrough measurements were collected on zeolite 13X at 1, 2, 3, 5, 7, and 10 bar absolute pressure. For each measurement the flowrate of CO₂ was 10 sccm. Figure 1 shows the results of all breakthrough measurements. Time zero corresponds to the breakthrough of helium in the measurement such that the deadtime of the experiment has already been subtracted out.

All the zeolite 13X breakthrough curves show sharp peaks signifying that there are little to no mass transfer limitations. This behavior is expected as zeolite 13X has shown excellent capabilities to adsorb CO₂ and the pore window is much larger than the kinetic diameter of CO₂. Additionally, no pressure drop was observed in the system, this was also expected as zeolite 13X was analyzed as-is in its pelletized form.

Figure 2 below shows the isotherm that is generated when solving the breakthrough equation and
plotting the total quantity adsorbed for each breakthrough measurement. Table 1 also displays the
quantities adsorbed at each pressure.

结论

实验结果表明1-10 bar绝对压力内，Zeolite 13X是非常有效的CO₂ 吸附剂。例如，10bar下Zeolite 13X可吸附15 mmol/g 的CO₂. 在本次穿透曲线研究中，陡峭的曲线表明系统中不存在压降和传质问题。