Patent ID: 8877965

Claim:
A process for preparing formic acid which comprises reacting carbon dioxide with hydrogen in a hydrogenation reactor in the presence of a catalyst comprising an element of group 8, 9 or 10 of the Periodic Table, a tertiary amine comprising at least 12 carbon atoms per molecule and a polar solvent comprising one or more monoalcohols selected from the group consisting of methanol, ethanol, propanol and butanol, to form formic acid/amine adducts as intermediates which are subsequently thermally dissociated, where a tertiary amine which has a boiling point at least 5° C. higher than that of formic acid is used and a reaction mixture comprising the polar solvent, the formic acid/amine adducts, the tertiary amine and the catalyst carried from the reactor is formed in the reaction in the hydrogenation reactor, wherein the work-up of the output from the hydrogenation reactor is carried out by the following process steps: 1) adding water to the output from the hydrogenation reactor to give two liquid phases, 2) separating the two liquid phases in a phase separation vessel, recirculation of the upper phase from the phase separation vessel to the hydrogenation reactor and passing-on of the lower phase from the phase separation vessel to an extraction apparatus, 3) extracting residues of catalyst with the same tertiary amine which was used in the hydrogenation in the extraction apparatus, wherein a catalyst comprising tertiary amine is formed and then recycled to the hydrogenation reactor and the catalyst-free stream of polar solvent loaded with the formic acid/amine adducts is passed on to a distillation unit, 4) carrying out a fractional distillation in the distillation unit to give a first fraction which comprises the polar solvent and is recycled to the hydrogenation reactor, a second fraction which comprises water and is recycled to the output ( 3 ) from the hydrogenation reactor or is discarded and also a third fraction containing the tertiary amine and the formic acid/amine adducts, 5) separating the third fraction in a phase separation vessel into an upper phase comprising the tertiary amine and a lower phase comprising the formic acid/amine adducts, and 6) feeding the lower phase from the phase separation vessel to a thermal dissociation unit that is dissociated therein into a first stream which comprises the tertiary amine and is recirculated to the phase separation vessel and pure formic acid and a second stream comprising the tertiary amine that is conveyed from the phase separation vessel into the extraction apparatus as selective solvent for the catalyst.