Patent CA-2851175-A1 (CA)
Title: Process for preparing formic acid by reacting carbon dioxide with hydrogen
Inventor: SCHAUB THOMAS
IPC: C07C51/02
Filed: 2012-10-02
Abstract: The invention relates to a method for producing formic acid, comprising the following steps: (a) reacting, in a homogeneously catalyzed manner, a reaction mixture (Rg) containing carbon dioxide, hydrogen, at least one polar solvent and at least one tertiary amine in the presence of at least one coordination catalyst in a hydrogenation reactor in order to obtain a two-phase hydrogenation mixture (H) containing an upper phase (O1), which contains the at least one coordination catalyst and the at least one tertiary amine (A1), and a lower phase (U1), which contains the at least one polar solvent, residues of the at least one coordination catalyst, and at least one formic acid/amine adduct; (b) processing the hydrogenation mixture (H) obtained in step (a) according to one of the following steps: (b1) phase-separating the hydrogenation mixture (H) obtained in step (a) in a first phase-separating device into the upper phase (O1) and the lower phase (U1), or (b2) extracting the at least one coordination catalyst from the hydrogenation mixture (H) obtained in step (a) in an extraction unit with an extracting agent containing the at least one tertiary amine (A1) in order to obtain a raffinate (R1) containing the at least one formic acid/amine adduct (A2) and the at least one polar solvent and an extract (E1) containing the at least one tertiary amine (A1) and the at least one coordination catalyst, or (b3) phase-separating the hydrogenation mixture (H) obtained in step (a) in a first phase-separating device into the upper phase (O1) and the lower phase (U1) and extracting the residues of the at least one coordination catalyst from the lower phase (U1) in an extraction unit by means of an extracting agent containing the at least one tertiary amine (A1) in order to obtain a raffinate (R2) containing the at least one formic acid/amine adduct (A2) and the at least one polar solvent and an extract (E2) containing the at least one tertiary amine (A1) and the residues of the at least one coordination catalyst; (c) separating the at least one polar solvent from the lower phase (U1), from the raffinate (R1), or from the raffinate (R2) in a first distillation device in order to obtain a distillate (D1) containing the at least one polar solvent, which is fed back into the hydrogenation reactor in step (a), and a two-phase bottom mixture (S1) containing an upper phase (O2), which contains the at least one tertiary amine (A1), and a lower phase (U2), which contains the at least one formic acid/amine adduct (A2); (e) cleaving the at least one formic acid/amine adduct (A2) contained in the bottom mixture (S1) or optionally in the lower phase (U2) in a thermal cleaving unit in order to obtain the at least one tertiary amine (A1), which is fed back to the hydrogenation reactor in step (a), and formic acid, which is discharged from the thermal cleaving unit, wherein carbon monoxide is added to the lower phase (U1), the raffinate (R1), or the raffinate (R2) directly before and/or during step (c) and/or carbon monoxide is added to the bottom mixture (S1) or optionally the bottom phase (U2) directly before and/or during step (e).