GB808101A - Process for obtaining pure trimethylolpropane - Google Patents

Abstract

Pure trimethylolpropane is obtained from the aqueous reaction mixture obtained by alkaline condensation of butyraldehyde with formaldehyde, by treating the reaction mixture with a partially water-miscible solvent consisting of a monohydric aliphatic, cycloaliphatic or araliphatic alcohol containing 4-8 carbon atoms thus forming an aqueous phase and an organic phase, organic impurities going into the organic phase and the trimethylolpropane being distributed between the aqueous and organic phases. If a minor amount of solvent is used the bulk of the trimethylolpropane remains in the aqueous phase and the organic impurities, together with a small amount of trimethylolpropane pass into the organic phase. The bulk of the trimethylolpropane can be obtained from the aqueous solution by treating it with a greater quantity of the same or a different solvent as defined above. The small quantity of trimethylol propane can be recovered from the organic phase by washing with water or with a trimethylolpropane-free raffinate obtained at the end of the working process. If a major amount of the solvent is used the trimethylolpropane and organic impurities go into the organic phase. The bulk of the solvent is distilled off and the remaining extract is treated with water or a trimethylolpropane-free raffinate so that the trimethylol propane goes into the aqueous phase and the organic impurities remain behind in the solvent. In the examples: (a) a solution of trimethylolpropane obtained by the alkaline condensation of butyraldehyde and formaldehyde is treated with a minor proportion of iso-octanol to give an extract layer containing small amounts of trimethylolpropane and iso-octanol and organic impurities and a raffinate containing the major part of the trimethylolpropane; the iso-octanol is reclaimed from the extract layer by distillation; the raffinate layer is treated with a large quantity of iso-octanol, thereby giving an extract containing the bulk of the trimethylolpropane, which is obtained by evaporating the extract solution and may be further purified by distillation; and (b) a solution of trimethylolpropane obtained by the alkaline condensation of butyraldehyde and formaldehyde is treated with a major quantity of cyclohexanol thus forming an extract layer containing most of the trimethylolpropane and cyclohexanol and a raffinate containing small amounts of trimethylolpropane and cyclohexanol; the extract layer is distilled to give cyclohexanol, trimethylolpropane and a residue containing a further quantity of trimethylolpropane; the residue is treated with a major portion of the raffinate from the first extraction and a minor amount of cyclohexanol is added; the raffinate so obtained may be treated with a further quantity of cyclohexanol or may be added to some fresh crude condensation solution.