Patent ID: 8426641

Claim:
A process for preparing formic acid by hydrogenation of carbon dioxide in the presence of a homogenous catalyst comprising an element of group 8, 9 or 10 of the Periodic Table, a tertiary amine (I) and a polar solvent (III) at a pressure of from 0.2 to 30 MPa abs and a temperature of from 20 to 200° C. to form two liquid phases, separation of the one liquid phase (A) enriched with the formic acid/amine adduct (II) from the other liquid phase (B) enriched with the homogenous catalyst together with the tertiary amine (I), and recirculation of the liquid phase (B) to the hydrogenation reactor, wherein (a) an amine which at a pressure of 1013 hPa abs has a boiling point which is at least 5° C. higher than that of formic acid and is present in enriched form in the liquid phase (B) is used as tertiary amine (I); (b) a solvent whose electrostatic factor is ≧200·10 −30 Cm and which at a pressure of 1013 hPa abs has a boiling point which is at least 5° C. higher than that of formic acid and is present in enriched form in the liquid phase (A) is used as polar solvent (III); (c) the formic acid/amine adduct (II) of the liquid phase (A) which has been separated off is thermally dissociated into free formic acid and free tertiary amine (I) in a distillation unit; (d) the free formic acid is removed by distillation; and (e) the free tertiary amine (I) comprised in the bottoms from the distillation unit and the polar solvent (III) are recirculated to the hydrogenation reactor.