Patent ID: 8524945

Claim:
A process for preparing acrolein, which comprises the following steps: (a) dehydration of an aqueous glycerol phase G1 in an acrolein reaction region to give an aqueous acrolein reaction phase wherein the aqueous acrolein reaction phase comprises a liquid solvent selected from hydroxypiperidine, sulfolane, diglyme, tetraglyme, dioxane, trioxane or γ-butyrolactone, and wherein the acrolein reaction region is constructed with a first metal and the acrolein reaction region further comprises a different metal or metal compound which is immobilized in particulate form by means of sieves or filters present in the acrolein reaction region; (b) at least partial separation of the aqueous acrolein reaction phase into an acrolein-rich acrolein phase and a residue phase R1; wherein said residue phase R1 is low in acrolein compared to the acrolein phase, and wherein the residue phase R1 comprises glycerol, water and residual materials other than glycerol and water; and (c) recirculation of at least part of the residue phase R1 to step (a); wherein i) at least one of the residual materials present in a glycerol phase G2 comprising glycerol, water and residual materials other than glycerol and water is separated from the glycerol phase G2 and the purified glycerol phase G2 obtained in this way is fed directly to the acrolein reaction region or ii) at least one of the residual materials other than glycerol and water is separated off from a mixed phase M1 obtained by mixing said glycerol phase G2 comprising glycerol, water and residual materials other than glycerol and water with said low-acrolein residue phase R1 and the purified mixed phase M1 obtained in this way is fed to the acrolein reaction region, wherein a further glycerol phase G3 is fed in addition to the purified glycerol phase G2 or the purified mixed phase M1 into the acrolein reaction region, wherein the glycerol phase G3 is obtained as distillate in the distillation of crude glycerol obtained in the cleavage or transesterification of triglycerides, and wherein at least part of a bottom product obtained in the distillation of the crude glycerol goes through a salt separator and is subsequently fed back into the distillation of the crude glycerol.