Production of formamides

A process for production of formamides of formula Ia

• where R1 and R2 are each independently selected from the group consisting of hydrogen, linear or branched radicals having from 1 to 15 carbon atoms, cycloaliphatic radicals having from 5 to 10 carbon atoms, a substituted or unsubstituted phenyl radical and a phenylalkyl radical, or R1 and R2 are combined to form a five- or six-membered ring comprising an oxygen atom, an N—H radical or an N—R1 radical, where R1 is as defined above,
• by reacting carbon dioxide with hydrogen in a hydrogenation reactor I in the presence of
• a catalyst comprising an element from group 8, 9 or 10 of the periodic table,
• a tertiary amine of the formula NR3R4R5 (IVa), where R3 to R5 are the same or different and each is independently selected from the group consisting of a branched or unbranched, cyclic or acyclic, aliphatic, araliphatic or aromatic radical having in each case from 1 to 16 carbon atoms, where individual carbon atoms are optionally independently substituted by a hetero group selected from the group consisting of —O— and >N—, and also two or all three radicals may be linked together to form a chain comprising at least four atoms in each case, with the proviso that the total number of carbon atoms is at least 6, and also
• a polar solvent
• to form formic acid-amine adducts as intermediates of formula IIa
• NR3R4R5.xiHCOOH (IIa),
• (xi=0.4 to 5)
• wherein two liquid phases form in said hydrogenation reactor I in the course of the reaction, viz., a bottom phase comprising predominantly the polar solvent, in which the formic acid-amine adducts are enriched, and also a top phase comprising predominantly the tertiary amine, in which the homogeneous catalyst is enriched, and wherein
• the effluent from said hydrogenation reactor I is worked up in accordance with the following process steps:
• separating the two liquid phases from said hydrogenation reactor I in a phase separation vessel II,
• returning said top phase from said phase separation vessel II into said hydrogenation reactor I, and
• forwarding said bottom phase from said phase separation vessel (II) into an extraction unit III, in which
• residues of catalysts are extracted with the same tertiary amine as used in the hydrogenation and the tertiary amine laden with catalyst is recycled into said hydrogenation reactor I,
• which comprises
• (i) forwarding the catalyst-free stream comprising the formic acid-amine adducts of formula (Ha) and polar solvent into a reactor IV, and therein reacting the formic acid-amine adducts of formula (IIa) at temperatures of 0 to 200° C. with ammonia or amines of formula (Ia),
• where R1 and R2 are each as defined under formula (Ia),
• to obtain via the interstage having formula (Va) of the corresponding adduct of formic acid with ammonia or an amine of formula (IIIa)
• NHR1R2.xHCOOH (Va)
• the corresponding formamide of formula (Ia), and
• (ii) separating the two-phase liquid reaction effluent from said reactor IV (stream 9) in a phase separation vessel V into a liquid phase (stream 10) enriched with formamides of formula (Ia) and a second liquid phase (stream 12) enriched with tertiary amine and wholly or partly returning the liquid phase (stream 12) enriched with tertiary amine into said extraction unit III, and
• (iii) separating stream 10 in a distillation unit VI by distillation to recover said formamide of formula (Ia), remove water from the system, return the polar solvent (stream 8) into said hydrogenation reactor I and return the unconverted ammonia or amine of formula (IIIa) into said reactor IV (stream 11).