Process for the recovery of a polyol from an aqueous solution

#None

#(1) Field of the Invention

#The present invention relates to a process for the separation of a polyol from an aqueous solution. The process involves reactive distillation of the polyol as a cyclic acetal from an aqueous reaction mixture containing other organic compounds, particularly other polyols. In particular, the cyclic acetal is prepared by reaction of a ketone or aldehyde with the polyol along with distillation of cyclic acetal as it is formed from the reaction mixture.

#FIG. 1 is a schematic front view of a polyol recovery system 10 with a single reactive distillation column 11 for forming the cyclic acetal(s). EG is ethylene glycol, PG is propylene glycol, and Gly is glycerol.

#FIG. 2 is a schematic front view of the polyol recovery system 10 including reactive distillation column 11 and acetal hydrolysis and polyol recovery columns 18 and 19. MD is 2-methyl-1,3-dioxolane (acetal of EG), DMD is 2,4-dimethyl-1,3-dioxolane (acetal of PG).

#FIG. 3 is a schematic view of reactive distillation column 21 and acetal hydrolysis and polyol recovery columns 25 and 26 as an alternative to the process of FIG. 2 for the recovery of EG and PG.

#The present invention relates to a process involving acetalization and reactive distillation of a polyol that takes advantage of the reversible reaction of the acetal which is formed and facilitates the separation and recovery of the polyol from an aqueous solution. The focus of the invention is on recovering ethylene and propylene glycols from aqueous solutions containing higher polyols, but the method has broader applications to recovery of a wide range of polyols from water. Boiling points of some acetals of interest for this process are given in Table 1.

#TABLE 1 Boiling points of some acetals and aldehydes Glycol Aldehyde Acetal b.p., ° C. EG Formaldehyde 1,3-dioxolane 74-75 PG Formaldehyde 4-methyl-1,3- 84 dioxolane Glycerol Formaldehyde Glycerol formal 191-195 EG Acetaldehyde 2-methyl-1,3- 82-83 dioxolane PG Acetaldehyde 2,4-dimethyl-1,3- 91-93 dioxolane EG Acetone 2,2-dimethyl-1,3- 92-93 dioxolane PG Acetone 2,2,4-trimethyl- 98-99 1,3-dioxolane Glycerol Acetone 188 Formaldehyde 101 Acetaldehyde 21 Isobutyr- 64 aldehyde Acetone 56

#The reactive distillation process involves several distillation columns where the acetals are formed, separated from water, and subsequently hydrolyzed back to the desired polyol. The acetalization/reactive distillation scheme facilitates polyol recovery and purification at lower cost than conventional distillation or extraction methods. For the recovery of ethylene glycol and propylene glycol, acetals formed with formaldehyde or acetaldehyde have lower boiling points than water, so they can be removed once formed without having to boil off all the water present. This offers a large cost savings over conventional distillation. Further, these acetals have much lower boiling points than acetals of higher polyols such as glycerol, sorbitol and xylitol, which can be in potential feedstocks for EG/PG production, and acetals of process byproducts such as C4 and C5 polyols, so they are easily separated from the higher polyols and their acetals in solution. This aspect of the invention distinguishes it from the work of Broekhuis et al (1994) and Chopade and Sharma (1997), who did not consider recovery of EG and PG from mixed polyols. Further, the acetals of EG and PG can be separated from each other at much lower temperatures and potentially more easily than EG and PG themselves, so the cost of the polyol separation is substantially lower as well. Overall, the integration of the acetalization scheme into a biomass-based polyols process enhances the commercial usefulness of the process.