The
density, viscosity, and surface tension of aqueous solutions
containing three imidazolium bromine ionic liquids (ILs) [C
n
MIM]Br with different alkyl chain lengths (n = 2, 3, 4) are determined within the temperature ranging
from 283.15 to 343.15 K and at ambient pressure, respectively. The
effect of the alkyl chain length of the imidazolium cation on the
properties of the solutions is investigated. The experimental density
and viscosity are satisfactorily described with the linear model and
the Vogel–Tammann–Fulcher type equation, respectively.
On the basis of the experimental data, the energy barrier and the
surface entropy/enthalpy are calculated. The results show that the
density and surface tension of aqueous ILs solution decrease and the
viscosity increases with the increase of carbon atom number in imidazole
ring carbon chain under the same conditions. The surface ordering
in each aqueous solution follows [C2MIM]Br > [C3MIM]Br > [C4MIM]Br. The calculation of the molecular/ionic
cluster interaction energy shows that there is a strong interaction
between IL and water molecules, and the strong interaction between
water and bromine ions is the main factor determining the properties
of the solution. The data and results can provide a reliable support
for the design and process calculation of chemical absorption cycle
with water/IL working pairs.
Experimental
measurements for the vapor–liquid
equilibria
(VLE) of benzene + 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([EMIM][NTf2]), benzene + 1-ethyl-3-methylimidazolium ethylsulfate
([EMIM][EtSO4]), and benzene + mixed ionic liquids (ILs)
(equimolar [EMIM][NTf2] + [EMIM][EtSO4] mixture)
are performed. The non-random two liquid (NRTL) model binary interaction
parameters are then obtained by fitting the new VLE data and the liquid–liquid
equilibrium data previously reported. The interactions between chemical
species are analyzed using quantum chemical calculations and the COSMO-SAC
method, and it is found that the interactions between benzene and
ILs are strongly attractive. Taking as a reference the industrial
process that uses sulfolane as the entrainer, several novel industrial
processes are proposed, which involve either pure ionic liquids [EMIM][NTf2] and [EMIM][EtSO4] or their mixtures as the extractant
for separating aromatic hydrocarbons (benzene) and paraffins (n-hexane). The optimal operating parameters, such as the
number of theoretical stages, the extractant-to-hydrocarbon feed ratio,
the reflux ratio, and the feed stage, are determined for the different
processes. Steady-state process simulations are performed to evaluate
the total annual cost (TAC) and the environmental impact (carbon dioxide
emissions). It is shown that significant savings in energy consumption
(reduction of 19.6–48.7%), TAC (reduction of 6.3–27.1%),
and CO2 emissions (reduction of 17.8–47.6%) can
be achieved for the processes that use IL extractants, compared to
the process based on sulfolane extractant. The proposed IL extractant
and the corresponding process are promising alternatives to conventional
solvents and processes for aromatic extraction.
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