GB653448A - Improvements in or relating to the distillation of furfural - Google Patents

Abstract

Furfural is separated from furfural-polymer in the absence of oxygen by feeding the mixture into the first of a series of connected evaporating zones maintained at successively-decreasing, non-polymerizing temperatures and introducing steam directly into the final zone, the zones being connected so that the furfural and water vapours from each zone (except the first) pass through the liquid in the preceding zone while the liquid accumulating in the base of each zone (except the last) passes into the succeeding zone; withdrawing a liquid mixture of polymer and water from the final zone, taking-off and condensing furfural vapours and steam from the first zone, and separating purified furfural containing about 5 per cent of dissolved water from the condensate. The process is particu <PICT:0653448/III/1> larly applicable to the purification of furfural which has been used as a solvent in the extraction of butadiene from hydrocarbon mixtures. It is preferable to operate at pressures in the range from atmospheric to about 30 pounds per square inch (gauge). In the apparatus shown, the zones 4, 5, 6 are arranged to form a tower, and are separated by perforated plates 34, 35. The feed-mixture is supplied through line 1 into the top section 4 which is maintained at about 295 DEG F. by coil 29 and pressure-control valve 10. Section 5 is maintained at about 280 DEG F. by coil 31; while live steam is introduced through line 24 into section 6 which is maintained at about 240 DEG F. Furfural vapours and steam rise through perforated plates 35, 34 and through the liquid thereon, but the liquid does not pass through the perforations-it flows from section 4 to section 5 through overflow pipe 7, and from section 5 to section 6 through overflow pipe 8. Polymer and water leave section 6 via line 25, and enter settling zone 26 from which the polymer is withdrawn from the system by line 27 while the water is passed to accumulator 17. The vapours withdrawn from the head of the tower are condensed in condenser 12; the condensate being passed to separator 14. Furfural is withdrawn from the system through line 16. The water which forms the upper layer in separator 14, is passed to accumulator 17. The water in accumulator 17 contains small amounts of dissolved furfural and, in order to prevent loss of furfural, this water is used as a source of live steam for injection into section 6, vaporizer 22 being employed for the purpose. Make-up steam is supplied through line 30. Another embodiment is described wherein the zones are separate but connected by liquid-pumps and flow-controllers.