Adsorption Size Effects for Langmuir Systems in Process Simulators: Case Study Comparing Explicit Langmuir-Based Models and FASTIAS

Adsorption processes are typically designed with the aid of process simulators. Here, the extended Langmuir model and derivates are frequently used when dealing with type I isotherms (Langmuirian). The extended Langmuir model captures competition effects based on low-coverage Henry selectivity. However, it does not account for adsorbate size effects, where smaller adsorbates can be preferred at a higher pressure. Still, in simulators, the extended Langmuir model is predominantly used over the implicit ideal adsorbed solution theory (IAST), which does predict a size effect. In this work, we define and explore two models, having an explicit form and aimed at introducing an adsorbate size effect. The aim is twofold: First, the extended Langmuir and new model predictions are compared to IAST to demonstrate the adsorbate size effect. Second, all models are tested in a process simulator case study where the performance results as well as execution time are considered. A temperature swing adsorption (TSA) process simulation case study with a 10-component mixture was performed at high loading: the extended Langmuir model shows large recovery differences over the models which do incorporate a size effect. Explicit models can be executed quicker than IAST (FASTIAS), although the manner of implementation in the process simulator is important. The new models may improve the extended Langmuir predictions with respect to (IAST) size effects and also have their limitations.