Glycerol distillation process

Claim 1

A process for the purification of crude glycerol derived from the transesterification, hydrolysis, and saponification of naturally occurring fats and oils, comprising (a) alkalizing crude glycerol containing up to 10% by weight of water without predrying and chemical prepurificaton by mixing with an aqueous alkali hydroxide solution for about 1 hour at about 90°-100° C., followed by the addition of about 10 N/m 3 of air per cubic meter of said crude glycerol; (b) distilling the alkalized mixture at about 165°-180° C. and about 10-20 mbar and discharging high boiling constituents for additional distillation; (c) passing the vapors generated by said distillation into a lower part of a packing column and flowing said vapors upward through said column, said column containing low-pressure-loss plates having a pressure loss of at most 1 mbar/theoretical separation stage at an air velocity of 2 m/s and having at least seven theoretical separation stages; (d) partially first condensing the vapors from said column at about 80°-90° C. under a head pressure of about 5-10 mbars, and second condensing the remaining vapors at about 20°-30° C., so that the second condensate corresponds to approximately 1% of the quantity of crude glycerol; (e) cooling the first condensate by about 30°-50° C. and returning same to the head of said column; (f) continuously removing a main product from said column as a liquid sidestream at a point approximately 1/3 of the height of said column, and returning a partial stream thereof to said column beneath the point of removal; (g) cooling the remaining non-returned portion of said main product to about 80°-90° C.; (h) adding about 0.1 to 0.3% by weight of activated charcoal to the said non-returned portion as a bleaching agent and stirring under nitrogen for about 15 to 30 mintures while at about 80°-90° C.; and then removing said bleaching agent; (i) drawing off bottom product from the column sump, evaporating said bottom product at temperatures of about 150°-180° C., and returning vapor generated thereby to said sump, (j) continuously removing a partial stream of about 1% of the quantity of glycerol being processed from said bottom product before it is evaporated.