Understanding competitive adsorption between propylene (CH) and propane (CH) in mixtures is essential for the development of an adsorptive separation process, a promising alternative to energy-intensive distillation, to produce polymer-grade propylene. This work investigated the selective adsorption of CH over CH on zeolite 5A using a pulse injection method, followed by temperature-programmed desorption (TPD) to investigate desorption kinetics. In mixture adsorption on uncoated 5A, CH/CH selectivity increased markedly with cumulative gas exposure, such that it reached ∼26 from an equimolar mixture at high exposures; in contrast, the ideal selectivity measured from single-gas adsorption was only ∼1.6. TPD experiments indicated that mixture selectivity was higher than ideal selectivity because CH, having a stronger affinity for the zeolite, hindered CH adsorption and displaced pre-adsorbed CH. To gain further insights into the roles of pore diffusion versus surface penetration in the separation mechanism, zeolite 5A was also modified with -butylphosphonic acid (TBPA) or -octadecylphosphonic acid (ODPA). These coatings imposed an additional diffusion barrier that hindered CH transport more substantially than CH, with highly dense ODPA having more effect than sterically bulky TBPA. While the coatings were selective to CH transport, their effect on overall selectivity in mixture adsorption was complex: initial selectivity was higher than on uncoated 5A, but the selectivity on PA-coated zeolites did not improve as rapidly with exposure time. Thus, design of optimal composite materials for selective adsorption must account for both barriers to gas diffusion and competition for adsorption sites between adsorbates.

中文翻译：

---

丙烯和丙烷在5A沸石上的竞争吸附及有机膦酸涂层的影响

了解混合物中丙烯 (CH) 和丙烷 (CH) 之间的竞争吸附对于开发吸附分离工艺至关重要，吸附分离工艺是生产聚合物级丙烯的能源密集型蒸馏的一种有前景的替代方案。这项工作使用脉冲注入方法研究了 CH 在 5A 沸石上的选择性吸附，然后通过程序升温解吸 (TPD) 来研究解吸动力学。在未涂层 5A 上的混合物吸附中，CH/CH 选择性随着气体暴露的累积而显着增加，使得在高暴露下等摩尔混合物达到~26；相比之下，单一气体吸附测得的理想选择性仅为~1.6。 TPD实验表明，混合物选择性高于理想选择性，因为CH对沸石具有更强的亲和力，阻碍了CH吸附并取代了预吸附的CH。为了进一步了解孔扩散与表面渗透在分离机制中的作用，还用-丁基膦酸（TBPA）或-十八烷基膦酸（ODPA）对5A沸石进行了改性。这些涂层施加了额外的扩散屏障，比 CH 更显着地阻碍 CH 传输，高密度 ODPA 比空间庞大的 TBPA 更有效。虽然涂层对 CH 传输具有选择性，但它们对混合物吸附中整体选择性的影响很复杂：初始选择性高于未涂层的 5A，但 PA 涂层沸石的选择性并没有随着暴露时间的推移而迅速提高。因此，用于选择性吸附的最佳复合材料的设计必须考虑气体扩散的障碍和吸附物之间吸附位点的竞争。