Dissolution of Gaseous Methyl Iodide into Aqueous Sodium Hydroxide Solutions

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Absorption process of gaseous methyl iodide by water or sodium hydroxide solutions was investigated using a semi-flow type experimental apparatus by measuring the concentration of all measurable chemical species in both the gas and the liquid phase.The experimental temperature ranged from 288 to 311 K and the gaseous methyl iodide and aqueous sodium hydroxide concentrations were approximately 0.6 × 10^-3 to 7 × 10^-3 and O to 0.2 mol/dm³, respectively. It is estimated that the dissolution of methyl iodide into the sodium hydroxide solution proceeds according to the following steps.
Step (1) Methyl iodide in air dissolves physically into the aqueous phase. Physical dissolution process obeys Henry's law.
Step (2) Methyl iodide dissolved into the aqueous phase is decomposed by a base catalytic hydrolysis and produces methyl alcohol and iodide ion.
The equilibrium constants of physical dissolution were obtained from the steady concentration in both the gas and the liquid phases in the semi-flow type experiment because the hydrolysis reaction rate of methyl iodide is very slow in comparison with the physical dissolution in this experimental conditions. The obtained value of the standard heat of solution of methyl iodide into water was 7.2 kcal/mol.
Salting-out effect was, observed when the concentration of sodium hydroxide in the absorbent was over 0.01 mol/dm³.