WO2000017142A1

WO2000017142A1 - Process for decontaminating ethanediol

Info

Publication number: WO2000017142A1
Application number: PCT/AU1999/000788
Authority: WO
Inventors: Simon Michael West
Original assignee: Swig Pty Ltd.
Priority date: 1998-09-17
Filing date: 1999-09-17
Publication date: 2000-03-30
Also published as: AUPP598098A0

Abstract

According to one form of the invention, there is provided a process for improving the quality of ethanediol to render it suitable for use in polymer production comprising the step of contacting the ethanediol with active carbon wherein the ethanediol is at a temperature in the range from room temperature to at or about the boiling point of ethanediol. According to a second aspect of the invention, there is provided a process for removing iron from ethanediol containing iron comprising the steps of (a) contacting the ethanediol containing iron with active clay to adsorb the iron; and (b) at the same time or thereafter, contacting the ethanediol with active carbon. According to a third aspect of the invention, there is provided a process for removing conjugated coloured substances and carbonyl compounds from ethanediol containing conjugated coloured substances and carbonyl compounds comprising the step of contacting the ethanediol containing conjugated coloured substances and carbonyl compounds with hydrogen peroxide(s) or acyl peroxide(s).

Description

PROCESS FOR DECONTAMINATING ETHANEDIOL

Field of the Invention

This present invention relates to a process for decontaminating ethanediol. More particularly, the present invention relates to a process for decontaminating ethanediol to give the degree of purity required for polyethylene terephthalate production.

Background to the Invention

Polyethylene terephthalate ("PET") is a thermoplastic polyester that can be formed from 1 ,2-dihydroxyethane ("ethanediol") and terephthalic acid by direct esterification to form bis (hydroxy ethyl) terephthalate ester which is then polymerised by catalysed ester exchange to useful polymers.

Traditionally, PET has been used extensively because it can be offered as an oriented film or fibre, has high tenacity, good electrical resistance and low moisture absorption together with a melting point of approximately 265°C.

For these reasons, its uses have been very diverse extending from being blended with cotton for wash and wear fabrics, blended with wool for worsteds and suitings, packaging films and recording tapes and containers including soft drink containers.

It is also possible to recycle PET after it has been used. For example, international patent application WO 93/23456 discloses a method which may be used to recycle post consumer PET which will remove the contaminants present such as paper, dyes, glue, container contents and other plastics. This method enables recovery of the ethanediol and terephthalic acid which can then be reformed into PET.

It is very important in the manufacture of PET that the starting material have a high degree of purity. Contaminants can cause discoloration of the PET produced. Therefore, in clear PET applications, contaminants are the indicator of whether there will be sale or no sale and therefore business or bankruptcy.

The ethanediol which is recovered in the recycling process is impure and needs to be further refined before it can be used to reform PET. Further, there are other sources of impure ethanediol available which if easily purified would provide an economical source of one of the main components of PET.

Accordingly, investigations were made into processes for decontaminating ethanediol.

It is known art that ethanediol must meet standards of low iron content and low adsorption of ultraviolet light if it is to be used for polymer production. If these standards are not met then the product will be discoloured and thus not commercially useful if it is a clear PET application. Currently, polymer manufacturers have to purchase "polymer grade" ethanediol in order to have ethanediol of the appropriate standard and such "polymer grade" ethanediol is expensive.

The known method of refining ethanediol requires distillation of the ethanediol. This is an expensive process. Further, there is a side reaction in which ethanediol ether oligimers are formed and thus contaminates the ethanediol and reduces the efficacy of the process. Investigations revealed no other methods which are used in the polymer industry or contained in published literature.

Summary of the Invention

It was found that the main ultraviolet light adsorbing molecule is dioxane-2:3-dione produced by oxidation of ethanediol to oxalic acid, and then esterification to the ring ester by excess ethanediol during distillation.

Surprisingly, it has been found that dioxane-2:3-dione will adsorb on active carbon where at sufficient temperature, the oxalate group rearranges to carbon monoxide and carbon dioxide and are removed. Further, it has been found that active clay will adsorb iron from ethanediol solutions. Contaminated ethanediol may contain aldehydes such as acetaldehyde and it has been found that these may be inactivated by peroxides without the generation of undesirable by-products.

According to one form of the invention, there is provided a process for improving the quality of ethanediol to render it suitable for use in polymer production comprising the step of contacting the ethanediol with active carbon wherein the ethanediol is at a temperature in the range from room temperature to at or about the boiling point of ethanediol. Preferably, the ethanediol is at a temperature in the range from 100°C to the boiling point of ethanediol. More preferably, the active carbon is added to ethanediol having a temperature at or about the boiling point of ethanediol.

Where active carbon is being added as opposed to contact with a carbon bed, the amount of active carbon added may be 0.1 to 0.3% by weight of the total composition. It is also possible in a continuous process to use a carbon bed with a short retention time (eg 30 seconds).

Preferably, during the step of contacting the ethanediol with active carbon, the active carbon adsorbs ultra violet adsorbing compounds. More preferably, the ultraviolet adsorbing compound is dioxane-2:3-dione. Typically, there is 10-50mg of dioxane-2:3- dione per kg of ethanediol.

Preferably, if dioxane-2:3-dione is being removed, the ethanediol is at a temperature in the range from 100°C to the boiling point of ethanediol. Dioxane-2:3-dione is unstable, in the presence of active carbon at this temperature (especially when adsorbed). It is believed that compound is degraded to products such as carbon monoxide, carbon dioxide and ethanediol at these temperatures.

The active carbon should be wetted by the ethanediol to facilitate the adsorption and reaction. Accordingly, it is preferred to select the active carbon from carbon which has been oxidised to have free carboxyls on the surface. Various types of active carbon are commercially available and may be used in this process. The active carbon acts as a true catalyst with a long lifetime. At the expiry of this lifetime, the active carbon may be reactivated using known processes.

According to a second aspect of the invention, there is provided a process for removing iron from ethanediol containing iron comprising the steps of

(a) contacting the ethanediol containing iron with active clay to adsorb the iron; and

(b) at the same time or thereafter, contacting the ethanediol with active carbon.

wherein the ethanediol containing iron is at a temperature in the range from room temperature to at or about the boiling point of ethanediol. Any form of clay can be used. For example, it has been found that good quality china clay will work. Preferably, the clay used is a montmorillonite clay as they have a higher capacity for the adsorption of cations. More preferably, "Fuller's earth" is used which has a very high affinity for Fe ⁺ and other triple charged ions.

Preferably, the active clay is added to ethanediol having a temperature in the range from 100° to at or about the boiling point of ethanediol. More preferably, the ethanediol is at a temperature at or about the boiling point of ethanediol.

Preferably, the ratio of clay to soluble iron is kept below 1 OOmg/kg. If the iron is in the form of insoluble ferric oxide/hydroxide then preferably, there should be less than 0.03:1 ratio of iron to clay.

Preferably, this iron removal process further comprises the step of adding a small amount of phosphoric acid in step (a). Typically, the concentration of phosphoric acid (H₃PO₄) used is in the range of 100 to 1000 mg per kg of clay. Usually, the only major contaminant in H₃PO₄ is arsenic and this does not adversely effect the process.

It was also found that ethanediol will not react readily or rapidly with hydrogen peroxides and other acyl peroxides and that this group of substances may be useful when the ethanediol contains dyes or coloured substances because the peroxides react with such conjugated coloured substances.

According to a third aspect of the invention, there is provided a process for removing conjugated coloured substances and carbonyl compounds from ethanediol containing conjugated coloured substances and carbonyl compounds comprising the step of treating the ethanediol containing conjugated coloured substances and carbonyl compounds with hydrogen peroxide(s) or acyl peroxide(s) wherein the ethanediol containing conjugated coloured substances and carbonyl compounds is at a temperature in the range from room temperature to at or about the boiling point of ethanediol and wherein the amount of the hydrogen peroxide(s) or acyl peroxide(s) added is ten times the molar carbonyl groups together with the moles of carbon-carbon double bonds. In particular, this process is useful for removing acetaldehyde from ethanediol by oxidising the acetaldehyde to volatile acetic acid. This process would be useful for treating heavily contaminated feedstock such as is found at an ethanediol reclaimer's factory.

The present invention is not pressure sensitive and can be performed at atmospheric pressure or under higher pressures as deemed appropriate by those skilled in the art.

The present invention it permits the purchase of low grades of ethanediol that would normally be used for antifreeze applications and enables them to be used as more expensive polymer grade ethanediol. Further, expensive distillation processes are avoided and there is no formation of ethanediol ether oligomers.

Examples

The invention will now be further explained and illustrated by the following non-limiting examples.

Materials

The materials used in the examples are described below.

The contaminated ethanediol used in the examples is called antifreeze grade and was obtained from Orica at Botany, NSW. This grade of ethanediol would be available at polymer plants as a by-product which would otherwise be sent to a reclaimer for purification.

The active carbon used in the examples is called Picazine which is supplied by Pica. It has also been found that Calgon Decolorising Carbon is effective.

The active clay used was Tonsil FF.

The phosphoric acid used was an Albright and Wilson product.

The hydrogen peroxide used was an Orica product of 30% H₂O₂.

The acyl peroxide was a terephthalic acid product, benzene di peroxy carboxylic acid, which was synthesised by the inventor. Another product which has been used is monoperoxyphthalic acid magnesium salt hexahydrate which was supplied by Aldrich. Example 1

20 kg of antifreeze grade ethanediol was heated to 180°C in a jacketed stirred tank and then 20g of Picazine carbon was added. After 30 seconds the ethanediol, as a clear liquid, was recovered by passing the mixture through a diatomite coated filter. The ultraviolet adsorption spectrum of the product showed less than 0.01 adsorbance between 300 and 280 nanometers compared with 0.025 in the feedstock ethanediol.

Example 2

20 kg of antifreeze grade ethanediol was heated to 180°C in a jacketed stirred tank. Then 20g of Picazine carbon and lOg of Tonsil FF clay (which had been dispersed in 50 ml of ethanediol with 1ml of phosphoric acid carefully mixed in and allowed to react for one hour) were added. After 30 seconds the ethanediol, as a clear liquid, was recovered by passing the mixture through a diatomite coated filter. The ultraviolet adsorption spectrum of the product showed less than 0.01 adsorbance between 300 and 280 nanometers compared with 0.025 in the feedstock ethanediol. The iron content was determined by atomic adsoφtion spectrophotometry to be less than 0.1 mg/kg compared with 0.6 mg/kg in the feedstock ethanediol.

Example 3

20 kg of antifreeze grade ethanediol were transferred to a jacketed stirred tank and contaminated with 200mg of acetaldehyde. 10 ml of 30% hydrogen peroxide was added and the mixture heated to 180°C in a jacketed stirred tank. Then 20g of Picazine carbon and lOg of Tonsil FF clay (which had been dispersed in 50 ml of ethanediol with 1ml of phosphoric acid carefully mixed in and allowed to react for one hour) were added. After 30 seconds the ethanediol, as a clear liquid, was recovered by passing the mixture through a diatomite coated filter. The ultraviolet adsoφtion spectrum of the product showed less than 0.01 adsorbance between 300 and 280 nanometers compared with 0.025 in the feedstock ethanediol. The iron content was determined by atomic adsoφtion spectrophotometry to be less than 0.1 mg/kg compared with 0.6 mg/kg in the feedstock. The concentration of acetaldehyde was determined by chromatography and was found to be less than 0.5 mg/kg. Example 4

20 kg of antifreeze grade ethanediol was transferred to a jacketed stirred tank and contaminated with 200mg of acetaldehyde. Then 500mg of benzene 1 :3 peroxy dicarboxylic acid was added and the mixture heated to 180°C in a jacketed stirred tank. 20g of Picazine carbon and lOg of Tonsil FF clay (which had been dispersed in 50 ml of ethanediol with 1 ml of phosphoric acid carefully mixed in and allowed to react for one hour) were added. After 30 seconds the ethanediol, as a clear liquid, was recovered by passing the mixture through a diatomite coated filter. The ultraviolet adsoφtion spectrum of the product showed less than 0.01 adsorbance between 300 and 280 nanometers compared with 0.025 in the feedstock ethanediol. The iron content was determined by atomic adsoφtion spectrophotometry to be less than 0.1 mg/kg compared with 0.6 mg/kg in the feedstock. The concentration of acetaldehyde was determined by chromatography and was found to be less than 0.5 mg/kg.

It will be understood by those skilled in this art that the invention is be applicable to any product containing significant concentrations of ethanediol and that the art of filtration may be performed using devices such as pressure leaf filters.

The word 'comprising' and forms of the word 'comprising' as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.

Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A process for improving the quality of ethanediol to render it suitable for use in polymer production comprising the step of contacting the ethanediol with active carbon wherein the ethanediol is at a temperature in the range from room temperature to at or about the boiling point of ethanediol.

2. A process according to claim 1 wherein the ethanediol is at a temperature in the range from 100┬░C to at or about the boiling point of ethanediol.

3. A process according to either claim 1 or 2 wherein the ethanediol is at a temperature at or about the boiling point of ethanediol.

4. A process according to any one of claims 1 to 3 wherein the amount of active carbon used is 0.1 to 0.3% by weight of the total composition.

5. A process according to any one of claims 1 to 3 wherein the active carbon used is in the form of a carbon bed.

6. A process according to any one of claims 1 to 5 wherein the ethanediol is contacted with the active carbon for 30 seconds.

7. A process according to any one of claims 1 to 7 wherein during the step of contacting the ethanediol with active carbon, the active carbon adsorbs ultra violet adsorbing compounds.

8. A process according to claim 7 wherein the ultraviolet adsorbing compound is dioxane-2:3-dione.

9. A process for removing iron from ethanediol containing iron comprising the steps of:

wherein the ethanediol containing iron is at a temperature in the range from room temperature to at or about the boiling point of ethanediol.

10. A process according to claim 9 wherein step (a) occurs in the presence of phosphoric acid.

11. A process according to claim 10 wherein the concentration of phosphoric acid used is in the range of 100 to 1000 mg per kg of clay.

12. A process according to any one of claims 9 to 11 wherein the active clay is added to ethanediol containing iron having a temperature in range from 100┬░C to at or about the boiling point of ethanediol.

13. A process according to any one of claims 9 to 12 wherein the active clay is added to ethanediol containing iron having a temperature at or about the boiling point of ethanediol.

14. A process according to any one of claims 9 to 13 wherein the active clay is a montmorillonite clay.

15. A process according to any one of claims 9 to 14 wherein the active clay is a "Fuller's earth" clay.

16. A process according to any one of claims 9 to 15 wherein the ratio of soluble iron to clay is kept below 100 mg/kg.

17. A process according to any one of claims 9 to 16 wherein the ratio of insoluble ferric oxide/hydroxide to clay is less than 0.03:1.

18. A process for removing conjugated coloured substances and carbonyl compounds from ethanediol containing conjugated coloured substances and carbonyl compounds comprising the step of treating the ethanediol containing conjugated coloured substances and carbonyl compounds with hydrogen peroxide(s) or acyl peroxide(s); wherein the ethanediol containing conjugated coloured substances and carbonyl compounds is at a temperature in the range from room temperature to at or about the boiling point of ethanediol; and wherein the amount of the hydrogen peroxide(s) or acyl peroxide(s) added is ten times the molar carbonyl groups together with the moles of carbon-carbon double bonds.

19. A process according to claim 18 wherein the ethanediol containing conjugated coloured substances and carbonyl compounds is at a temperature at or about the boiling point of ethanediol.

20. A process according to either of claims 18 or 19 wherein the conjugated coloured compound is acetaldehyde.

21. A process for improving the quality of ethanediol to render it suitable for use in polymer production comprising the steps of:

(a) treating the ethanediol with hydrogen peroxide(s) or acyl peroxide(s); and

(b) contacting the ethanediol with active clay and, at the same time or thereafter, contacting the ethanediol with active carbon wherein the ethanediol is at a temperature in the range from 100┬░C to at or about the boiling point of ethanediol.