Recovery of propylene glycol from dilute aqueous solutions via reversible reaction with aldehydes
- Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering
A means is proposed for separating propylene glycol and other compounds bearing multiple hydroxyl groups by reversible chemical reaction. Glycols react with aldehydes in cyclic acetalization reactions to form substituted dioxolanes. Propylene glycol reacts with formaldehyde and acetaldehyde to form 4-methyl-1,3-dioxolane and 2,4-dimethyl-1,3-dioxolane. The reaction is catalyzed homogeneously by strong mineral acids or heterogeneously by cation exchange resins in the acid form. Separation processes utilizing this reaction would include an acetalization step, several distillative separation steps and finally a hydrolysis step in which the reaction is reversed. Both reaction steps must be forced to completion by removing the reaction product simultaneously. The equilibrium and kinetics of the reaction with formaldehyde were studied experimentally in systems catalyzed by Amberlite IR-120 ion exchange resin. A number of solvents were screened for their ability to extract 2,4-dimethyl-1,3-dioxolane from aqueous solution. Aromatic hydrocarbons exhibited the highest distribution into the organic phase. To achieve an effective separation of propylene glycol from aqueous solution by combined reaction with formaldehyde and distillation, formaldehyde would have to be present in excess and would be difficult and costly to separate from the aqueous solution. In reactive distillation using acetaldehyde as a reactant this is not a problem. A large flow of acetaldehyde would be necessary to recover the propylene glycol sufficiently in a distillative process. In a process combining reaction and extraction into an organic solvent this problem is avoided. Process simulation indicates the energy input of such a process is less than half of the energy required in a triple-effect evaporation process. This benefit is offset by higher capital costs and increased complexity in the reaction/extraction process.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 10129183
- Report Number(s):
- LBL-35155; ON: DE94007499; TRN: 94:003228
- Resource Relation:
- Other Information: PBD: Dec 1993
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
GLYCOLS
MATERIALS RECOVERY
AQUEOUS SOLUTIONS
SEPARATION PROCESSES
ALDEHYDES
CHEMICAL REACTIONS
CHEMICAL REACTION KINETICS
HETEROGENEOUS CATALYSIS
HOMOGENEOUS CATALYSIS
DISTILLATION
ION EXCHANGE MATERIALS
ACTIVATION ENERGY
EVAPORATION
400105
400201
SEPARATION PROCEDURES
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES