Patent ID: 8791297
Filing Date: 2014-07-29
Classification: C07C

Abstract:
1. 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 among methanol, ethanol, propanols and butanols and also water, 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 and two liquid phases are formed in the reaction in the hydrogenation reactor, namely a lower phase which comprises predominantly the polar solvent and in which the formic acid/amine adducts are present in enriched form and an upper phase which comprises predominantly the tertiary amine and in which the catalyst is present in enriched form, wherein the work-up of the output from the hydrogenation reactor is carried out by the following process steps: 1) separating the two liquid phases from the hydrogenation reactor 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 in which 2) extracting residues of catalyst with the same tertiary amine which was used in the hydrogenation and the catalyst-laden tertiary amine is 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 in which 3) separating off the polar solvent as overhead stream and recycling to the hydrogenation reactor to give a stream which 4) is separated in a phase separation vessel into an upper phase comprising predominantly the tertiary amine and a lower phase comprising predominantly the formic acid/amine adducts, where 5) the lower phase from the phase separation vessel is fed to a thermal dissociation unit and dissociated therein into a stream which comprises the tertiary amine and is recirculated to the phase separation vessel and pure formic acid and a stream comprising the tertiary amine is conveyed from the phase separation vessel into the extraction apparatus as selective solvent for the catalyst.