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.