Measurement of Diffusion Coefficient of Solute in Porous Material in the Presence of High Pressure Fluid

测定了超临界二氧化碳存在下，苯、甲苯和丙酮在BPL和高比表面积两种吸附剂上的吸附平衡负荷。测定了纯吸附物、二氧化碳、苯、甲苯和丙酮在这些活性碳上的负载量，在一定的吸附分压下，所有的吸附负载量在纯状态下都有一个最大值，并随着压力的增加而减小。在相同的吸附剂上，苯和甲苯的负载量几乎相同，而丙酮的负载量要低于苯和甲苯的负载量。高比表面积活性碳的吸附负荷大于BPL活性碳。但是，压力依赖性与BPL活性碳的变化趋势基本一致。这可能意味着二氧化碳的吸附对二氧化碳在液体相中的吸附量和溶剂力的影响。采用Prausnitz等人提出的理想吸附溶液理论(IAST)。IAST预测值与实验值吻合较好。通过分析吸附等温线非线性区域的穿透曲线，研究了苯在超临界二氧化碳中的吸附动力学。表面扩散是吸附颗粒内部的主要输运机制。表面扩散系数与其他研究人员在较低压力下报告的值相似。

The adsorption equilibrium loadings of benzene, toluene, and acetone on two adsorbents, a BPL activated carbon and a high surface area activated carbon in the presence of supercritical carbon dioxide were measured at temperature of 313 K and pressures from 1 to 12 MPa. Loading of the pure adsorbates, carbon dioxide, benzene, toluene, and acetone on these activated carbons were also measured.At a constant partial pressure of the adsorbates, all adsorption loadings showed a maximum value at pure state and decreased with increasing pressure. On the same adsorbent benzene and toluene loadings shwed almost the same amount absorbed, while the loadings of acetone were lower than those of benzene and toluene. The adsorption loadings on the high surface area activated carbon were larger than those on the BPL activated carbon. However, pressure dependence was almost the same trend as that of BPL activated carbon. This may imply the effect of carbon dioxide adsorption over the amount of adsorbates and solvent power of carbon dioxide in fluid phase.Prediction method of adsorption amounts in the presence of supercritical fluid was examined in this work. An ideal adsorption solution theory (IAST) reported by Prausnitz et al.was used. Prediction values of IAST were in good agreement with experimental ones.Dynamics of adsorption of benzene dissolved in supercritical carbon dioxide on activated carbon were studied by analysis of breakthrough curves in the nonlinear region of the adsorption isotherm. Surface diffusion was found to be a main transport mechanism inside the adsorbent particles. Surface diffusion coefficients were similar to values reported by other investigators under lower pressures.