3.5 Distributions of DESs at the interface
From the above experimental results, it is clear that the introduction of DESs can effectively increase the RON of alkylate, but the lifetime of H2SO4 catalyst was almost not promoted. It can be inferred that the better performance of alkylate is probably due to the intensification of acid/hydrocarbons interface, rather than the tunability of H2SO4microenvironment. However, the effect of DESs on the acid/hydrocarbons interface remains unclear to a great extent. Thus, the acid/hydrocarbons interfacial behaviors with the addition of ChCl-Pho (1:2), ChCl-TsOH (1:1), and ChCl-BOA (1:2), respectively, were further investigated using MD simulations in details.
Initially, the equilibrated snapshots of DES distributions at different concentrations were presented in Figure 6. For all the systems, ChCl molecules were clearly observed with a better dispersion in H2SO4 phase, while the phenyl molecules, such as Pho, TsOH, and BOA molecules, tend to aggregate in the interfacial regions. Quantitatively, the mass density profiles alongz axis with DESs at different concentrations were displayed in Figure 7 and Figure S3. For the density profiles of different moieties of DESs, the distinct difference is that the phenyl molecules present an obvious peak in the interfacial regions, and the intensity of the peak becomes much larger with the increased DES concentrations. Conversely, ChCl molecules show a uniform distribution in the H2SO4 phase along z axis. One can conclude that the phenyl molecules play the essentially important role in the tunability of acid/hydrocarbons interface. In addition, there is a larger peak intensity of TsOH molecules in the interfacial regions compared to Pho and BOA molecules at the same concentrations, suggesting the stronger aggregation of TsOH molecules at the interface. Moreover, the TsOH molecules stay closer to the H2SO4 phase than Pho and BOA molecules, probably due to the strong interaction between SO3H groups and H2SO4.