Preparation of primary diamines
Primary diamines are prepared by hydrogenation of a dinitrile compound in the presence of a catalyst, in particular hexamethylenediamine is prepared by hydrogenation of adiponitrile; the product diamines are recovered by distillation in several distillation columns mounted in series and the heavy impurities are separated from the second distillation.
1. A process for the preparation of a primary diamine by hydrogenation of a dinitrile compound in the presence of a hydrogenation catalyst, comprising:
hydrogenating the dinitrile compound with hydrogen or a hydrogen-containing gas;
subjecting the stream E 0 resulting from the hydrogenation medium to a first distillation and recovering a top fraction E 1 which comprises water and the imines present and a bottom fraction Q 1 which comprises the hydrogenated compounds;
subjecting the stream Q 1 to a second distillation and recovering a top fraction E 2 which comprises the hydrogenated compounds and a bottom fraction Q 2 which comprises compounds having a higher boiling point than the primary diamine;
subjecting the top fraction E 2 to a third distillation and recovering a bottom fraction Q 3 which comprises the hydrogenated compounds and a top fraction E 3 which comprises the compounds having a lower boiling point than that of the diamine compound formed; and
subjecting the bottom fraction Q 3 to a fourth distillation and recovering a top fraction E 4 which comprises the pure diamine, and a bottom fraction Q 4 which comprises compounds having a higher boiling point than the primary diamine.
2. The process as defined by claim 1 , wherein the catalyst comprises Raney nickel or Raney cobalt.
3. The process as defined by claim 1 , wherein the hydrogenation is carried out in the presence of a strong inorganic base selected from the group consisting of sodium hydroxide and potassium hydroxide.
4. The process as defined by claim 1 , wherein the distillation stages are carried out in distillation columns selected from the group consisting of perforated plate columns, plate columns, packed columns, valve tray columns and structured packed columns.
5. The process as defined by claim 1 , wherein the fractions comprising heavy impurities, Q 2 and Q 4 , are treated in a distillation column to recover the diamine and such recovered diamine is recycled to the second or fourth distillation.
6. The process as defined by claim 1 , wherein the diamine is hexamethylenediamine and the dinitrile compound is adiponitrile.