The switchable solvent 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)/methanol can be used in transesterification with oil to produce biodiesel (fatty acid methyl ester). The reactants (methanol, oil and catalyst DBU) and the products (fatty acid methyl ester and glycerol) are partially soluble in the production process. The phase equilibrium of the product components is essential data for biodiesel separation and process operation. In this work, the effects of catalyst dosage and temperature were studied on the phase equilibrium of the product systems. The phase composition of the product systems and the distribution of components were measured. The results showed the distribution of methanol, DBU and glycerol in the biodiesel-rich phase increases with the increase of DBU dosage from 1 wt% of oil to 15 wt% of oil and temperature from 298.1 K 0.1 K to 333.1 K 0.1 K, and decreases accordingly in the glycerol-rich phase. The distribution of biodiesel in both phases varies little. Increasing the dosage of DBU and/or temperature enhances the distribution and solubility of methanol, DBU and glycerol in the biodiesel-rich phase. This phenomenon was explained by estimating and analyzing van der Waals forces and hydrogen bonds.
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