## 3 Results
### Separation of \(n\)-Paraffins C5-C9 by IGC  
From the results of N\({}_{2}\) adsorption seen above, we can infer that: (i) larger molecules than N\({}_{2}\), as is the case of \(n\)-paraffins (9C9), can be adsorbed and diffused into the material mesoporosity and (ii) the differences in dispersion interactions between these molecules and the solid surface must be due to the quantity of -CH\({}_{2}\)- groups in the \(n\)-paraffins chain. An important experimental feature is the low column temperature necessary to separate \(n\)-paraffins (C5-C9). As reported in previous studies, the separation of \(n\)-C3-\(n\)-C7 mixtures in hexacyanocobaltates [18], \(n\)-C3-\(n\)-C9 mixtures in clinoptilolite [19] and \(n\)-paraffins and aromatics in zeolites, elution temperatures above 127 \({}^{\circ}\)C were required [40]. Instead, the separation of \(n\)-C5-\(n\)-C9 mixtures in a larger boehmite column (90 cm) was achieved at elution temperatures below 77 \({}^{\circ}\)C. These data were a first indication that the non-specific interactions between \(n\)-paraffins and boehmite were lower than those present in the other two adsorbents. Therefore, in the present study it was evaluated the separation of \(n\)-C5-\(n\)-C9 mixtures on synthetic pseudoboehmite. For the five studied \(n\)-paraffins, it was observed that the chromatographic peaks were sufficiently symmetric to verify that the experiments were performed to infinite dilution (Henry Zone), (Figure 7). Moreover, all the paraffins eluted at temperatures lower than 70 \({}^{\circ}\)C.  
In all cases, the graphs of lnKs vs. 1000/Tc were about straight lines with R \(>\) 0.99 (Figure 8) which allow determination of the differential adsorption heats Qd from the slopes of these lines (Table 1). The Qd dependence as a function of carbon atom number of the studied \(n\)-paraffins was also a straight line (Figure 9) whose slope corresponds to the contribution of each -CH\({}_{2}\)- group being 3.22 kJ/mol. By comparing the obtained differential adsorption heat (Qd) values of the \(n\)-paraffins in boehmite with those obtained with the same \(n\)-paraffins (\(n\)-C5-C9) and other adsorbents, the values obtained in the present research are lower. Thus, in dealuminated clinoptilolite, Qd were in the range 33-53 kJ/mol [19] and in hexacyanocobaltates greater than 40 kJ/mol [18]. It is believed that the path followed by the molecules of \(n\)-paraffins during diffusion in these adsorbents is the cause of this great change in adsorption heats values. The molecules are diffused into the channels and cavities of dealuminated clinoptilolite and hexacyanocobaltates interacting in all directions, while in boehmite, the \(n\)-paraffins can only follow the outside of the particles, interacting with the outer surface, due to the layered structure of boehmite, where each layer consists of double chains of AlO(OH) octahedra linked by OH groups inside. The space between the layers of octahedra in boehmite has been reported to vary between 2.71 A [41] and 2.50 A [42]. The differences in size might be caused by water adsorbed between the layers [43]. However, there is a consensus that the spacing between layers is very small, due to the -OH groups that form strong hydrogen bonds holding together the layers, thus preventing the passage of molecules of \(n\)-paraffins C5-C9. Moreover, considering the cross-sectional area of analytical -CH\({}_{2}\)-group (assuming the circular area) is about 6 A\({}^{2}\), the \(n\)-paraffins C5-C9 can only diffuse through the mesopores and the exterior of the particles and interact with those surfaces and their -OH groups. In this way, it becomes known that in spite of the relatively low Qd values, the differences between them are sufficient according to the Bering-Sierpinski (K\({}_{\text{BS}}\)) separation criterion to perform the separation of the mixture \(n\)-C5-\(n\)-C9 satisfactorily (Figure 9), indicating that to achieve a proper separation of compounds, the Qd values are not as important as the differences between them.