Patent ID: 7112707

Claim:
A process for isolating trimethylolpropane from a reaction mixture which has been obtained by reaction of n-butyraldehyde with formaldehyde in the presence of a base and, if appropriate, hydrogenation by distillation, wherein i) the mixture is introduced into a feed column having an enrichment section located above the feed point and a stripping section located below the feed point, ii) an upper combining column which has a condenser at the upper end of the column and communicates with the upper end of the enrichment section and a lower combining column which has a heater at the lower end of the column and communicates with the lower end of the stripping section are provided, iii) an offtake column which communicates with the upper combining column and the lower combining column is provided, iv) pure trimethylolpropane is taken off from the offtake column at a side offtake, and compounds having boiling points lower than that of trimethylolpropane are taken off at the top or in the upper region of the upper combining column and compounds which have boiling points higher than that of trimethylolpropane are taken off at the bottom or in the lower region of the lower combining column.