UV/visible absorption spectroscopy was applied to measure the microscopic solvent dipolarity/polarizability, π*, and hydrogen-bond-acceptor basicity, β, parameters of supercritical CO2/n-alcohol mixtures. Experiments were conducted at 45°C by varying the pressure between 86 and 230 bar, the type of n-alcohol from methanol to n-hexanol, and the n-alcohol mole fraction, x2, from 0 to 0.05. The effect of our experimental conditions on maximum Δπ* changes can be represented in the following order: system pressure (Δπ* ≈ 0.4) > n-alcohol mole fraction (Δπ* ≈ 0.3) > type of n-alcohol (Δπ* ≈ 0.1). However, the corresponding order for Δβ changes was as follows: n-alcohol mole fraction (Δβ ≈ 0.6) > type of n-alcohol (Δβ ≈0.3) > system pressure (Δβ ≈ -0.1). Under our experimental conditions, the π* parameters of the mixtures were below the corresponding value for liquid cyclohexane, whereas β parameters at x2 = 0.05 approached the values for liquid alcohols under ambient conditions. Because the solvent strength for CO2/methanol mixtures can be varied over the widest range by changing the methanol mole fraction and system pressure, methanol is the best cosolvent among the n-alcohols studied here.
|Number of pages||8|
|Journal||Industrial and Engineering Chemistry Research|
|Publication status||Published - 1 May 2002|