The carbonation of vegetable oils was studied by using tetra-n-butylammonium bromide (TBAB) as catalyst. Thermal stability of TBAB was studied by differential scanning calorimetry and thermogravimetric analysis, and it was demonstrated that the maximum reaction temperature should not exceed 130 °C. Reaction conditions were optimum at 130 °C, 50 bar, with 3.5% mol of catalyst. The gas–liquid mass-transfer coefficient and solubility of CO2 were determined by taking into account the nonideality of the gas phase using Peng–Robinson state equations. At 130 °C, the CO2 solubility was found to be independent from epoxide conversion and equal to 0.57 mol·L–1, and the gas–liquid mass-transfer coefficient (kLa) decreases with the epoxide conversion, i.e., at 0% of conversion kLa = 0.0249 s–1 and at 94% of conversion kLa = 0.0021 s–1.