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Abstract
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Deep eutectic solvents (DESs) have gained considerable attentions as novel green solvents in the natural gas (NG)
sweetening processes Using molecular dynamics simulations, the performance of an amine-based DES composed
of a 6: 1 M ratio of methyl diethanolamine (MDEA) and choline chloride (ChCl) for NG sweetening process is
investigated. To this end, the effect of pressure on the performance of amine-based DESs for sweetening of the
NG, and the penetration of acid gasses from the NG to the DES are examined. The results of the H2S and CO2
solubility in the DES phase demonstrate that H2S and CO2 solubilities are proportional to the pressure, and the
maximum values of 0.225 and 0.04 are obtained for H2S and CO2 solubilities, respectively, at 2 MPa and 310 K.
Additionally, calculations of the solubility selectivity parameter at various pressures reveal monotonic behaviors
for the solubility selectivity of H2S over CH4. The solubility selectivity of H2S over CH4 has a larger value, by a
factor of 10 to 20, than the solubility selectivity of CO2 over CH4 at pressure range from 0.1 MPa to 2 MPa. It can
be concluded that the MDEA-based DES used here, have higher efficiency for H2S separation, and greater
selectivity towards CO2 and CH4 compared to aqueous MDEA-solvent. The structural and dynamical analyses are
computed to assist interpreting of the observed behavior at the molecular level. Moreover, diffusion coefficient of
H2S (102 Å2/n) and CO2 (302.3 Å2/ns) in MDEA-based DES at 2 MPa and 310 K have the lowest values among all
the considered pressures. Our findings indicate that MDEA-based DES can compete with the conventional amine
solvents in the NG sweetening processes.
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