Ethylene glycol recovery process
AssigneeMobile Process Technology, Co.
InventorsFrank S. Craft, Sr., Michael D. Kelly
Life of this patent
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Abstract
The present invention is an improved process for the recovery of ethylene glycol from spent glycol generated in the manufacture of polyethylene terephthalate. The spent glycol typically consists of metal oxide catalyst residues, low molecular weight terephthalate oligomers, diethylene glycol and other trace impurities. The improved process of the present invention is based on the principle that elevating the temperature of the spent glycol increases the solubility of the low molecular weight oligomers so that the low molecular weight oligomers can be dissolved in the ethylene glycol and further that the spent glycol at an elevated temperature may be passed through an ion exchange bed to remove metal oxide catalysts, color forming impurities and other trace impurities.
Claims31
A process for the recovery of ethylene glycol from spent glycol formed in the manufacture of polyethylene terephthalate wherein terephthalic acid or dimethyl terephthalate is reacted with an excess of ethylene glycol to form dihydroxyethyl terephthalate and said dihydroxyethyl terephthalate is polymerized in the presence of a metal oxide catalyst to form polyethlene terephthalate and spent glycol containing metal oxide catalysts, cation impurities and anion impurities, low molecular weight terephthalate oligomers, ethylene glycol and diethylene glycol, comprising the steps of:
- (a) raising the temperature of said spent glycol sufficiently to solubilize said low molecular weight terephthalate oligomers;
- (b) passing said spent glycol at said raised temperature through an ion exchange medium capable of removing said metal oxide catalysts;
- and
- (c) distilling said spent glycol to recover ethylene glycol, diethylene glycol and terephthalate oligomers.
A process for the recovery of ethylene glycol from spent glycol formed in the manufacture of polyethylene terephthalate wherein terephthalic acid or dimethyl terephthalate is reacted with an excess of ethylene glycol to form dihydroxyethyl terephthalate, and said dihydroxyethyl terephthalate is polymerized in the presence of a metal oxide catalyst to polyethylene terephthalate and spent glycol containing metal oxide catalysts, cation and anion impurities, color forming impurities, trace impurities, low molecular weight terephthalate oligomers, ethylene glycol and diethylene glycol, comprising the steps of:
- (a) raising the temperature of said spent glycol to a temperature of from about 50.degree. C. to about 160.degree. C. to solubilize said low molecular weight terephthalate oligomers;
- (b) passing said spent glycol through activated carbon at a temperature of from about 50.degree. C. to about 160.degree. C. to remove said color forming impurities;
- (c) passing said spent glycol through a cation exchange resin at a temperature of from about 50.degree. C. to a maximum temperature tolerable by said cation exchange resin to remove said metal oxide catalyst and said cation impurities;
- (d) passing said spent glycol through an anion exchange resin at a temperature of from about 50.degree. C. to a maximum temperature tolerable by said anion exchange resin to remove said metal oxide catalyst and said anion impurities;
- (e) passing said spent glycol through a mixed bed ion exchange resin at a temperature of from about 50.degree. C. to a maximum temperature tolerable by said mixed bed resins;
- and
- (f) distilling said spent glycol to recover ethylene glycol, diethylene glycol and terephthalate oligomers.
A process for the recovery of ethylene glycol, diethylene glycol, metal oxide catalysts and polyethylene terephthalate from still bottoms formed from the distillation of spent glycol formed in the manufacture of polyethylene terephthalate wherein terephthalic acid or dimethyl terephthalate and ethylene glycol are reacted to form dihydroxyethyl terephthalate, said dihydroxyethyl terephthalate is polymerized in the presence of a metal oxide catalyst to form polyethylene terephthalate, and spent glycol containing ethylene glycol, diethylene glycol, low molecular weight terephthalate oligomers and metal oxide catalysts, and ethylene glycol is recovered by distillation from the spent glycol producing still bottoms containing ethylene glycol, diethylene glycol, low molecular weight terephthalate oligomers and metal oxide catalysts, comprising the steps of:
- (a) adding ethylene glycol to said still bottoms in an amount sufficient to depolymerize said low molecular weight oligomers upon raising the temperature of said still bottoms;
- (b) raising the temperature of said still bottoms sufficiently to depolymerize said low molecular weight terephthalate oligomers;
- (c) passing said still bottoms at said raised temperature through an ion exchange medium capable of removing metal oxide catalysts from said still bottoms;
- and
- (d) distilling said still bottoms to recover ethylene glycol, diethylene glycol and low molecular weight terephalate oligomers.
Dependencies are inferred from the claim text.