3.7 Interfacial compositions and diffusion
To further study the effect of DESs on the interfacial behaviors of the
MixC4 reactants, the interfacial compositions and diffusion coefficients
of MixC4 reactants for different DES systems at different concentrations
were calculated, as listed in Table 2. In the interfacial regions, there
are almost no ChCl molecules, while the ratio of phenyl molecules
increases as the concentrations of DESs. This observation is in good
agreement with the finding from density profiles. Due to the higher
ratio of phenyl molecules at higher concentration of DESs, the ratio of
both isobutane and butene gradually declines as a function of
concentration. However, the key point factor for alkylation is the ratio
of isobutane to butene (I/O ratio) in the interfacial reaction zone.
Meaningfully, the I/O ratio of all the systems with DESs additives are
quite higher than that of pure H2SO4system (0.850)15. This strongly indicates that the
DESs additives can significantly improve the I/O ratio, which can
restrain the oligomerization of butene, promote the hydride transfer,
and thus lead to higher-quality of alkylate. For ChCl-Pho
(1:2)-containing systems, the I/O ratio rises with the concentrations,
while the opposite trend is found for ChCl-TsOH (1:1)- and ChCl-BOA
(1:2)-containing systems. For the dynamics, the diffusion coefficients
ratio of isobutane to butene is also generally larger than that in pure
H2SO4 system
(0.858)15. Thus, the introduction of DESs can promote
the diffusion of isobutane with respect to butene, which is also helpful
to restrain the oligomerization of butene, and promote the hydride
transfer, resulting in higher-quality of alkylate. For different DESs,
the diffusion coefficient ratio of isobutane to butene follows similar
trend as the I/O ratio as a function of concentrations. To sum up, one
can safely say that the DES additives can
efficiently promote the solubility
and diffusion of isobutane with respect to butene, and thus make
positively contributions to the quality of alkylate.
Table 2. The interfacial compositions and interfacial diffusion
coefficients of isobutane and butene, and the ratio of isobutane to
butene for different DES systems at different concentrations.