# Experimental Setup and Graphical User Interface for Zero-Length Column Chromatography
## 6 Results and Discussion  
### Case Study I: Methane and Ethane Adsorption on Zeolite 5A and Basolite(r) C300  
The aim of this case study is to evaluate the dimensionless Henry law constant in zeolite 5A for methane (CH4) and ethane (C2H6). In addition, the adsorption capacities of zeolite 5A and Basolite(r) C300 will be compared by using the desorption curves. We measured ZLC desorption curves for 10 % methane and ethane on each adsorbent. All experiments were conducted at small volumetric flow rates (5 sccm) to ensure low \(L\) values (Table 1). Under these conditions the solid is effectively at equilibrium with the fluid. Figure 4a,b shows the C/C\({}_{0}\) vs. \(Ft/M\) curves for each material in this study, where \(F\) is the purge flow rate, \(t\) the time, \(M\) is the mass of the sample, and C/C\({}_{0}\) is the concentration in the gas phase normalized by the initial concentration \(C_{0}\). Figure 4a shows that the area under the relative ZLC curve for methane is smaller than the area under curve for \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Adsorbate** & \(T\) **(K)** & \(L\) & \(K\) & **Reference** \\ \hline \multirow{4}{*}{CH4} & 298 & 1.22 & 726 & This work \\  & & – & 817 & [26] \\ \cline{2-5}  & 308 & 1.68 & 522 & This work \\  & & – & 658 & [26] \\ \hline \multirow{4}{*}{C2H6} & 298 & 2.27 & 1223 & This work \\  & 308 & 1.27 & 1044 & This work \\  & 248 to 358 & – & 4000 to 75 & [27] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental temperature (\(T\)), time constant ratio (\(L\)) and dimensionless Henry law constant (\(K\)) for equilibrium measurements of methane and ethane on zeolite 5A. ethane (Figure 4b) for both zeolite 5A and Basolite(r) C300. This suggests a lower methane adsorption capacity. For ethane, there is a greater difference in the areas under the curve, being higher in Basolite(r) C300 than zeolite 5A (Figure 4b). According to the experimental data, zeolite 5A and Basolite(r) C300 exhibit similar adsorption preferences, showing a higher affinity for ethane. Both adsorbates have similar kinetic diameters (3.988 A) [28]. Therefore, steric hindrance cannot explain the affinity for ethane of both adsorbates. However, the electrical characteristics of the adsorbates and adsorbent surfaces can shed light on the understanding of the observed behavior. Ethane has a quadrupole moment of 0.27 A\({}^{3}\)[29] while the moment of methane is negligible. For this reason, cation in the zeolite framework are expected to interact stronger with ethane than with methane due to the quadrupole-field gradient interaction that exists between ethane and framework. [PERSON] et al. observed similar behavior in zeolite 5A [30]. Basolite(r) C300 also exhibits these interactions mainly due to the existence of open metal sites. After removal of the host molecules, the partial positive charges on the metal sites are available to interact electrostatically with molecule quadrupole, improving the adsorption capacity [31]. The areas under the curve shows that the adsorption capacity of methane and ethane is higher in Basolite(r) C300 than in zeolite 5A, which is consistent with previous reports [32; 33], validating the methodology used in the ZLC setup. This is due to the difference in porosity between the two frameworks. In zeolite, the free aperture of the pore is 4.4 A, which causes strong interactions of the adsorbed molecules with the surface. This produces strong confinement effects and hinders the diffusion of methane and ethane within the micropores [34], preventing access to the active sites of the zeolite [35]. On the other hand, the Basolite(r) C300 has a microporous structure formed by two types of cavities. One of them are large cavities, connected by 9 A windows, which can adsorb large molecules. The other cavity type is small side pockets connected to the large one through 4.6 A windows. This type of porosity improves the diffusivity of the adsorbates allowing access to the metal sites in the Basolite(r) C300.