Patent ID: 8889905

Claim:
A process for obtaining formic acid by thermal separation of a stream comprising formic acid and a tertiary amine (I) which, at a pressure of 1013 hPa abs, has a boiling point which is at least 5° C. higher than that of formic acid, which comprises (a) producing a liquid stream comprising formic acid and tertiary amine (I) and having a molar ratio of formic acid to tertiary amine (I) of from 0.5 to 5 by combining tertiary amine (I) and a formic acid source; (b) separating off from 10 to 100% by weight of secondary components comprised therein from the liquid stream obtained from step (a); (c) removing formic acid by distillation from the liquid stream comprising formic acid and tertiary amine (I) obtained from step (b) in a distillation apparatus at a temperature at the bottom of from 100 to 300° C. and a pressure of from 30 to 3000 hPa abs, wherein the tertiary amine (I) to be used in step (a) and the degree of separation in the distillation apparatus are selected so that two liquid phases are formed in the bottom output; (d) separating the bottom output from the distillation apparatus of step (c) into two liquid phases, wherein the upper liquid phase has a molar ratio of formic acid to tertiary amine (I) of from 0 to 0.5 and the lower liquid phase has a molar ratio of formic acid to tertiary amine (I) of from 0.5 to 4; (e) recirculating the upper liquid phase from the phase separation in step (d) to step (a); (f) recirculating the lower liquid phase from the phase separation in step (d) to step (b) and/or (c); and (g) separating off low boilers which, at a pressure of 1013 hPa abs, have a boiling point which is at least 5° C. lower than that of the tertiary amine (I) by distillation from the upper liquid phase from the phase separation in step (d) in a distillation apparatus at a temperature at the bottom of from 100 to 300° C. and a pressure of from 1 to 1000 hPa abs, and the stream depleted in low boilers is recirculated to one of the abovementioned steps (a) to (f).