IMPROVING THE CAPACITY OF COSMO-SAC IN PREDICTING THE ACTIVITY COEFFICIENT OF IONIC LIQUIDS AT INFINITE DILUTION
IMPROVING THE CAPACITY OF COSMO-SAC IN PREDICTING THE ACTIVITY COEFFICIENT OF IONIC LIQUIDS AT INFINITE DILUTION
No Thumbnail Available
Date
2023-05
Authors
AKPAN, DANNY JAMES
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A new approach for improving the accuracy of infinite dilution activity coefficient (IDAC) of organic solutes in ionic liquids using COSMO-SAC was investigated in this research. The accuracy of Infinite Dilution Activity Coefficient of solutes in ionic liquids determined by the original COSMO-SAC model has been improved by modifying the model and fitting the adjustable parameters with experimental data from the National Institute of Standards and Technology (NIST). To carry out the fitting, sigma profile of ionic liquid cations and anions were first created using Dmol3 module in 2017 Accelrys Materials Studio and Sigma Averaging program. The sigma profile of the solutes was obtained from the VT-Database. The exchange energy expression was modified by including segment interaction parameters C1 and C2 to account for the charges on cations and anions, as well as the non-electrostatic contribution Cne to ascertain its effect on the systems. The standard segment surface area, aeff, standard surface area in Staverman–
Guggenheim equation, q, standard volume in Staverman–Guggenheim equation, r, segment interaction parameters C1 and C2, and the non-electrostatic contribution, Cne, were fitted to 414 experimental data points using least square curve fitting program in Matlab. The data points were composed of 38 solutes, 10 cations and 11 anions in a temperature range from 288.15 to 395. 95K. The optimal values for the parameters aeff, q, and r in the modified model from this work are 7.649 Å2, 236.61Å2 and 3.111 Å3, respectively. Values for the hydrogen bond interaction coefficient CHB
and hydrogen bonding interaction cutoff charge σHB still remain 85580 and 8.4 × 10-3 respectively, as in the original model. The parameters C1, C2 and Cne introduced to the model have been determined to be 3.415 × 10-14, 1.278 and 5.06 × 10-2, respectively. The calculated results agree with the experimental data within the Average Relative Deviation (ARD) deviation of 20.71%. The model from this work performs best for solutes with low polarity. Among the solutes used in this work, the model performed best for Alkynes, with ARD of 5.91%, while the poorest result was recorded for Water with ARD of 98.75%.
The ARD of IDAC from 29 data points which were not included in the parameter optimization was computed using the modified model to be 18.07%. In terms of Henry’s law constant calculation for CO2 in ionic liquids, the ARD of COSMO-SAC model from this work is 24.2% for 17 data points, as against that from COSMO-SAC 2010 which is 21.5%. Henry’s law constant for CO2 in 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-amide [BMIM][TF2N] and in 1-ethyl-
3-methyl-imidazolium bis(trifluoromethylsulfonyl)-amide [EMIM][TF2N] was also in good agreement with the experimental values at temperatures below the critical temperature of CO2.
The IDAC of benzene in ionic liquid of the type 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide at 313.15K varied with chain length of the alkyl group as follows: IDACmethyl > IDACethyl > IDACbutyl > IDAChexyl while the IDAC of benzene in 1-ethyl-3-
methylimidazolium-anion at 323.15K and 333.15K varied with anion size as follows: IDAC of Benzene: IDACTF2N > IDACEtSO4 > IDACMeSO3
Description
A DESSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA. IN PARTIAL FULFILLMET OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE IN CHEMICAL ENGINEERING, DEPARTMENT OF CHEMICL ENGINEERING, FACULTY OF ENGINEERING, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA