# Experimental Setup and Graphical User Interface for Zero-Length Column Chromatography
## 6 Results and Discussion
### Binary Equilibrium in Zeolite 5A  
The system described in Figure 1 also provides information about the equilibrium of binary mixtures in the ZLC. This type of study begins by degassing the sample. To do this, FSV-4 must be placed in position B, ball valve P1 in position A, ball valve P2 in position A, FSV-6 in position B, the sample furnace must be heated to degassing temperature, and the MFC-4 must supply a controlled flow of He. For zeolite 5A, the He flow rate was 10 sccm, the degassing temperature 623.15 K, and the heating time 1 h. At the end of degassing, the sample is isolated in He atmosphere by placing valve P2 in OFF position and valve P1 in B position. Subsequently, the mixture is prepared by setting FSV-4 in position A and setting the desired flow rates on the mass controllers MFC-1, MFC-2, and MFC-4. These flows were in our case: 2 sccm, 2 sccm and 16 sccm, respectively. The mixture is flowed long enough for the lines to purge and the mixture to reach the desired composition. When this has been achieved, valves P1 and P2 are placed in positions A and B, respectively, and the FID-1 signal is recorded until it reaches a constant value. This means that equilibrium has been reached between the mixture and the adsorbent. From that point on, the flow is maintained for an additional time to ensure equilibrium. In the case of zeolite 5A and the methane/ethane mixture, this additional time was 30 min. Once equilibrium is reached, valve P2 is placed in position A and the line to FSV-6 is purged with the saturation mixture. Simultaneously, or some time before, He is flowed through the loop and SCSC to prepare them for analysis. Helium flow is controlled by the MFC-3 (4.6 sccm in this work). If necessary, the SCSC can be heated. With these steps, the system is ready to perform the binary equilibrium studies. The FID-2 detector must be properly calibrated following standard procedures prior to any analysis. Since these procedures have been extensively described in the literature, we will omit them. Before sampling the desorption curve it is convenient to measure the composition of the saturation mixture as a control measure. To do this, FSV-6 is simply placed in position A for a sufficient time to fill the loop (in this work the loop was 500 mL and 2 s of filling were sufficient) and then returned to position B. In the latter position, the carrier flows through the loop and injects its contents into the column. The retention time for methane using the above flow rate and at 298 K was about 140 s, while that for ethane was about 360 s (Figure 6). These retention times do not allow more than one sampling on the desorption curves without facing the risk of overlapping peaks at the SCSC output. It was for this reason that the binary equilibrium experiments were performed by sampling only  
Figure 5: Experimental ZLC desorption curves of methane and ethane on zeolite 5A at 298 K and flow rate of 5 sccm. once on each desorption curve. This has the disadvantage that the saturation procedure described above has to be repeated for each sampling. Consequently, the experiment is more time-consuming than when using mass spectrometry. However, it is less expensive and allows to test some simple theoretical models. Desorption is initiated with the FSV-6 in position B and changing the FSV-4 to position B so that the flow of He from the MFC-4, causes the desorption in the sample (Figure 1). Desorption curve sampling was performed switching the FSV-6 to position A and filling the loop for 2 s, before returning it to position B and FSV-6 in position B allows the carrier gas to flow through the loop and injects its contents into the column. Once the sampling is finished, the saturation process described above is restarted. Care must first be taken to isolate the sample by setting valve P2 to OFF and P1 to B to prevent the sample from hydrating while the mixture is being prepared and the lines are purged again. The number of experiments required to obtain bicomponent ZLC desorption curves rules out any kinetic study.