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Direct Measurements of the Enthalpy of Solution of Solid Solute in Supercritical Fluids: Study on the CO 2 –Naphthalene System
Author(s) -
Zhang Xiaogang,
Han Buxing,
Zhang Jianling,
Li Hongping,
He Jun,
Yan Haike
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011001)7:19<4237::aid-chem4237>3.0.co;2-8
Subject(s) - supercritical fluid , enthalpy , enthalpy change of solution , thermodynamics , dissolution , chemistry , solubility , naphthalene , solvent , organic chemistry , physics
A setup for a calorimeter for simultaneously measuring the solubility and the solution enthalpy of solid solutes in supercritical fluids (SCFs) has been established. The enthalpy of solution of naphthalene in supercritical CO 2 was measured at 308.15 K in the pressure range from 8.0–11.0 MPa. It was found that the enthalpy of solution (Δ H ) was negative in the pressure range from 8.0 to 9.5 MPa, and the absolute value decreased with increasing pressure. In this pressure range, the dissolution of the solute was enthalpy driven. However, the Δ H became positive at pressures higher than 9.5 MPa, and the dissolution was entropy driven. Monte Carlo simulation was performed to analyze the local structural environment of the solvated naphthalene molecules in supercritical CO 2 under the experimental conditions for the calorimetric measurements. By combining the enthalpy data and the simulation results, it can be deduced that the energy level of CO 2 in the high compressible region is higher than that at higher pressures, which results in the large negative enthalpy of solution and the larger degree of solvent–solute clustering in the high compressible region.