Process for the continuous preparation of pure glycerol from crude glycerol containing potassium sulfate

摘要

Continuous production of pure glycerin from potassium sulfate containing crude glycerin derived from the transesterification of fats or fatty oils, where the crude glycerin contains glycerin, water, potassium sulfate, matter organic non-glycerol (MONG) and methanol or ethanol, comprises saponifying the crude glycerin by the addition of alkaline solution of the MONG, subsequently evaporating water and methanol or ethanol in a forced circulation evaporator, and crystallizing potassium sulfate, removing the glycerin-rich phase on a separator, under restraint of potassium sulfate crystals. Continuous production of pure glycerin from potassium sulfate containing crude glycerin derived from the transesterification of fats or fatty oils, where the crude glycerin contains at least 80 wt.% of glycerin and 5-15 wt.% of water, 0.5-5 wt.% of potassium sulfate, 0.5-5 wt.% of matter organic non-glycerol (MONG) and 0.2-2 wt.% of methanol or ethanol, comprises saponifying the crude glycerin by the addition of alkaline solution of the MONG and adjusting a pH-value to 7.5-9.5, preferably 8-9, subsequently evaporating water and methanol or ethanol in a forced circulation evaporator, and crystallizing potassium sulfate, where the desired average crystal size in the forced circulation evaporator is adjusted by adjusting the density of the surrounding suspension, removing the glycerin-rich phase on a separator installed in the circulation of the evaporator, under restraint of potassium sulfate crystals, from the evaporator, and concentrating in a rectification column (4) at least to 99.5 wt.% and subsequently liberating by adsorption of color- and odor-substances, liberating the bottom product of the rectification column and the turbid consisting of glycerin and potassium sulfate removed from the forced circulation evaporator, together in a complete metal screw centrifuge (9) from the potassium sulfate crystals, and the organic residues consisting of MONG, removed from the complete metal screw centrifuge, contain less than 4 wt.%, preferably less than 3 wt.%, of potassium sulfate.