## 3 Research Progress on Adsorption and Separation of Hydrocarbon Molecules
### n-Alkanes
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Item** & **Temperature/\({}^{\circ}\)C** & **nC\({}_{\mathbf{11}}\)** & **nC\({}_{\mathbf{12}}\)** & **nC\({}_{\mathbf{13}}\)** & **nC\({}_{\mathbf{14}}\)** & **nC\({}_{\mathbf{15}}\)** & **nC\({}_{\mathbf{16}}\)** \\ \hline \multirow{6}{*}{\(\Delta V_{R}/\)mL} & 120 & 9.56 & 10.28 & 7.84 & 4.83 & 4.45 & 3.88 \\  & 150 & 12.20 & 12.33 & 12.84 & 12.48 & 10.89 & 9.91 \\  & 180 & 11.74 & 11.19 & 10.65 & 10.25 & 9.77 & 9.62 \\  & 200 & 11.75 & 10.77 & 10.12 & 9.79 & 9.61 & 9.78 \\ \hline \multirow{6}{*}{\(W_{1/2}/\)mL} & 120 & 10.64 & 17.10 & 22.38 & 19.47 & 18.45 & 17.44 \\  & 150 & 9.67 & 14.41 & 18.50 & 18.98 & 16.67 & 15.65 \\  & 180 & 9.25 & 11.01 & 12.43 & 12.44 & 11.99 & 11.91 \\  & 200 & 10.22 & 10.91 & 11.48 & 11.67 & 11.61 & 11.73 \\ \hline \multirow{6}{*}{\(R\)} & 120 & 0.90 & 0.74 & 0.48 & 0.32 & 0.31 & 0.28 \\  & 150 & 1.29 & 1.04 & 0.93 & 0.88 & 0.84 & 0.80 \\ \cline{1-1}  & 180 & 1.31 & 1.14 & 1.01 & 0.98 & 0.95 & 0.94 \\ \cline{1-1}  & 200 & 1.21 & 1.07 & 0.98 & 0.94 & 0.92 & 0.94 \\ \hline \hline \end{tabular} \(\Delta V_{R}\): net retention volume; \(W_{1/2}\): half width; \(R\): degree of separation. \(W_{1/2}\): half peak width of envelope line in each group; a parameter characterizing the mass transfer rate; \(V_{R}\): the retention volume of the component in the adsorption column; \(\Delta V_{R}\): the difference between \(V_{R}\) and 0 point of an n-alkane component or the net retention volume of the component; The results show the adsorptive capacity of 5A molecular sieve for this component; \(R\): degree of separation.  
\end{table} 
Table 2: Pulse data of nC\({}_{11-16}\) at different adsorption temperatures [36]. Figure 6: Pulse parameters of nC\({}_{10-16}\) when n-alkanes with different carbon numbers are used as adsorbents [36] the values of (a) \(\Delta V_{R}\) (b) \(W_{1/2}\) (c) \(R\). The relationship between the \(\Delta V_{R}\), \(W_{1/2}\), \(R\) values of nC\({}_{10-16}\), and the water content of the adsorbent was shown in Figure 7. It could be seen from Figure 7a that the \(\Delta V_{R}\) of nC\({}_{10-16}\) decreased gradually with the increase of the water content of the adsorbent, indicating that the water content of the adsorbent may be unfavorable for the adsorption of n-alkanes. This was mainly due to the fact that water molecules occupied the micropores of molecular sieves, reducing the adsorption volume and active sites of the adsorbent. From Figure 7b, it was found that the \(W_{1/2}\) of nC\({}_{10-16}\) decreased firstly and then increased, and reached the minimum value when the adsorbent moisture content was 3.3%, especially for n-alkanes with carbon number larger than 12, indicating that the water content of adsorbent could improve the rate of adsorption and desorption to a certain extent. This may be due to the improved mass transfer of nC\({}_{10-16}\) in a 5A molecular sieve driven by water polarization [37]. As shown in Figure 7c, the \(R\)-value decreased with the increase of water content when the carbon number was 10-11, but only slightly decreased before 3.3%. When the carbon number is between 12 and 16, the \(R\)-value first increased and then decreased, reaching a maximum value of 3.3%. In conclusion, nC\({}_{10-16}\) exhibited the most excellent adsorption and separation performance with a water content of 3.3%. It has been confirmed that the Ca\({}^{2+}\) exchange degree of the adsorbent has an effect on the adsorption and desorption performance. Figure 8 showed the effect of the replacement percentage of Na\({}^{+}\) by Ca\({}^{2+}\) in the molecular sieve on the adsorption performance. As the ionic radius of Ca\({}^{2+}\) is larger than that of Na\({}^{+}\), the six-membered ring of the A-type molecular sieve will be partially replaced by an eight-membered ring when a substitution occurs [38]. When the exchange degree of Ca\({}^{2+}\) of the adsorbent was between 70.8% and 85.5%, the pulse spectrum showed no obvious difference.