GB1565231A - Ethylene glycol extraction process - Google Patents

Description

(54) ETHYLENE GLYCOL EXTRACTION PROCESS (54) ETHYL , (71) We, UNION CARBIDE COR PORATION, a corporation organized and existing under the laws - of the State of New York, United States of America, of 270 Park Avenue, New York, State of New York 10017, United States of America (assignee of DAVID ROBERT BRYANT), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the followihg statement: This invention relates to a process for the recovery of ethylene glycol from admixture with tetraglyme (i.e., dimethyl ether of tetra- ethylene glycol). More particularly, this invention is concerned with the extraction of ethylene glycol from admixture with tetraglyme containing rhodium.

There are described in U.S. Patent No.

3,833,634, patented September 3, 1974, and U.K. Patent No. 1,477,391, processes for making alkane polyols, particularly ethylene glycol, by the reaction of oxides of carbon (particularly carbon monoxide) and hydrogen in the presence of a rhodium catalyst in which rhodium is in complex combination with carbon monoxide, i.e., a rhodium carbonyl complex. A preferred method for effecting that process involves forming a homogeneous liquid phase mixture of the rhodium carbonyl com- plex in a solvent such as tetraglyme and feeding carbon monoxide and hydrogen to the mixture. By maintaining the mixture at a temperature and pressure sufficient to effect a reaction between the carbonyl species and hydrogen in the mixture one is able to proZ duce a mixture of ethylene glycol, glycerine, methanol, ethanol and methyl formate.

The disclosures of the above-mentioned patents establish the capability for produc ing a product mixture of ethylene glycol dis solved in tetraglyme which also contains the rhodium values derived from or in the form of the catalytic species. Both these patents state in a general way that the products of the reaction can be recovered by distillation or extraction. However, indiscriminate distillation or extraction can cause losses of rhodium values.

In U.K. Patent No. 1,520,475, there is described a process for separating the products of the aforementioned reaction which involves combining water and an extraction solvent with the homogeneous liquid phase mixture derived from the reaction. The products are concentrated in the resultant water phase and the rhodium values are concentrated into the extraction solvent phase.

U.K. Patent No. 1,520,475 points to the necessity of avoiding excessive losses of rhodium values. Rhodium is a costly metal. Small losses of rhodium in carrying out this homo generous liquid phase reaction process, either during the reaction or in the recovery of reaction products can make the process uneconomical for commercial purposes.

Though the process of U.K. Patent No.

1,520,475 is superior to simple distillation alone, and defines a unique extraction process, it is not without certain disadvantages. For example, it is most difficult to keep water from being introduced into the reaction solvent. Since the extraction solvent is a liquid which is different from the components of the homogeneous liquid phase reaction mixture, it is usually necessary to separate it from the tetraglyme solvent and the rhodium values being recycled to the reaction. This last separation provides another opportunity to lose some rhodium values.

There is described herein a process for recovering products from the homogeneous liquid phase reaction mixture obtained from the aforementioned reaction which avoids the extra separation steo of the process of U.K.

Patent No. 1,520,475 and avoids the use of extraction solvents which are alien to the comoonents of the reaction.

The process of this invention is predicated on the discovery that glycerine has limited solubility in tetraglyme and that ethylene glycol partitions favourably to it. It has also been discovered that this partitioning affect is adversely affected by the presence of other alcohols and water. It is believed that these other components increase the solubility of glycerine in tetraglyme and vice versa, thereby increasing the amount of glycerine which is required to achieve partitioning or reducing the capability to achieve a discriminating separation of ethylene glycol. As noted above, glycerine is a product formed in the aforedefined homogeneous liquid phase reaction.

The maximum amount of glycerine that can be dissolved in tetraglyme, determined at 250C, will form a solution containing 6.5 weight per cent of glycerine. The maximum amount of tetraglyme that can be dissolved in glycerine, determined at 250C., will form a solution containing 0.78 weight per cent of tetraglyme.

The process of this invention involves separating ethylene glycol from admixture with tetraglyme containing rhodium therein.

The ethylene glycol and rhodium are - provided by the homogeneous liquid phase reaction, in the presence of rhodium as a carbonyl complex, of oxides of carbon (especially carbon monoxide) wherein tetraglyme is the solvent. This separation is achieved by contacting such admixture with an amount of glycerine greater than that amount which is soluble in the admixture. This causes two liquid phases to be formed. At least a portion of the ethylene glycol enters the phase richer in glycerine. The greater portion of the rhodium is contained in the phase richer in tetra- glyme. The ethylene glycol is thereafter recovered from admixture with the phase richer in glycerine.

The homogeneous liquid phase reaction mixture obtained from the reaction may be treated directly with glycerine according to the process of this invention. However, there are reasons for subjecting the mixture to mild distillation to drive off the low boiling components present in the mixture, such as methanol, ethanol, methyl formate, and water. It is believed, based on the evidence obtained to date, that these lower boilers repress the partitioning affinity that ethylene glycol has for the glycerine over the tetraglyme phase. Thus the process of this invention envisions a conventional distillation, preferably at atmospheric pressure or higher pressures, to distill these lower boilers from the mixture.

In particular, the experiments to date suggest that the lower boilers and higher temperatures repress extraction efficiency. Con sequently, it will probably be desirable to strip the lower boilers from the mixture prior to the extraction and the extraction should be conducted at lower temperatures, e.g., room temperature.

It may be desirable to operate the extraction process under an atmosphere of carbon monoxide to help in maintaining the solubility of the rhodium values.

This extraction may be carried out in any of the conventional apparatus employed for effecting such types of extraction. Countercurrent or current flow, continuous extraction procedures are believed suitably employable to practice this invention.

The following example further illustrates the practice of this invention.

Example A 150 ml. capacity stainless steel reactor capable of withstanding pressures up to 7,000 atmospheres was charged with a premix of 38 cubic centimeters (cc) of tetraglyme, 38 cc of glycerine, 3.0 millimoles (mmols), .77 grams, of rhodium dicarbonyl - acetylacetonate, and 7.0 mmols of N - methylmorpholine. The reactor was sealed and charged with a gaseous mixture, containing equal molar amounts of carbon monoxide and hydrogen, to a pressure of 8,000 pounds per square inch (psig). Heat was applied to the reactor and its contents; when the temperature of the admixture inside the reactor reached 1900 C., as measured by -a suitably placed thermocouple, an additional adjustment of carbon monoxide and hydrogen (E2: CO 1: 1 mole ratio) was made to bring the pressure back to 8000 psig. The temperature was maintained at 2400 C. for 4 hours.

During this period of time additional carbon monoxide and hydrogen was added whenever the pressure inside the reactor dropped below about 7500 psig. With these added repressurizations the pressure inside the reactor was maintained at 8000 psig+400 psig over the entire 4 hour period.

After the 4 hour period, the vessel and its contents were cooled to room temperature, the excess gas vented and the reaction proW duct mixture was removed and was found to consist of two liquid phases. Analysis of each of the two liquid phases containing reaction product was made by gas chromatographic analysis using a Hewlett Packard FM (Trade Mark) model 810 Research Chromatograph.

Rhodium recovery was determined by atomic absorption analysis of each of the liquid phases after the venting of the unreacted gases at the end of the reaction.

The following is the analysis of each layer: Top Layer Bottom Layer gms wt. gms Wt.0/o Water 0.48 1.21 0.93 2.09 Methyl formate 0.07 0.17 - - Methanol 1.01 2.54 1.21 2.71 Ethanol 0.08 0.20 0.08 0.18 Ethylene glycol 0.73 1.85 1.51 3.39 Propylene glycol 0.13 0.33 0.21 0.46 Glycerine 9.44 23.8 28.9 64.9 Tetraglyme 24.09 60.8 9.29 20.9 Rh 1530 ppm 50 ppm Ethylene glycol was recovered from the bottom layer.

WHAT WE CLAIM IS:- 1. A process of separating ethylene glycol from admixture with tetraglyme containing rhodium therein which ethylene glycol and rhodium are provided by the homogeneous liquid phase reaction in the presence of rhodium as a carbonyl complex of oxides of car bon and hydrogen wherein the tetraglyme is a solvent therefor, which comprises contacting said admixture with an amount of glycerine greater than that amount which is soluble in said admixture thereby forming two liquid phases, one which is richer in glycerine and the other containing the greater concentration of tetraglym and causing at least a portion of said ethylene glycol to enter the phase richer in glycerine, maintain ing the greater portion of the rhodium with the phase containing the greater concentra tion of tetraglyme and recovering ethylene glycol from said phase which is richer in glycerine.

2. A process as claimed in claim 1 wherein the admixture also contains methanol.

3. A process as claimed in claim 1 or 2 wherein the admixture also contains water.

4. A process as claimed in claim 1, 2 or 3 wherein the admixture contains methyl formate.

5. A process as claimed in any one of claims 1 to 4 wherein the extraction is conducted at room temperature.

6. A process as claimed in claim 1 wherein the admixture is free of at least one of water, methanol, ethanol, and methyl formate.

7. A process as claimed in any one of claims 2 to 6 in which the admixture is subjected to a mild distillation to remove low boiling components before contact with glycerine.

8. A process as claimed in any one of claims 1 to 7 in which the extraction is carried out under an atmosphere of carbon monoxide.

9. A process as claimed in claim 1 and substantially as hereinbefore described with reference to the Example.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. Top Layer Bottom Layer gms wt. gms Wt.0/o Water 0.48 1.21 0.93 2.09 Methyl formate 0.07 0.17 - - Methanol 1.01 2.54 1.21 2.71 Ethanol 0.08 0.20 0.08 0.18 Ethylene glycol 0.73 1.85 1.51 3.39 Propylene glycol 0.13 0.33 0.21 0.46 Glycerine 9.44 23.8 28.9 64.9 Tetraglyme 24.09 60.8 9.29 20.9 Rh 1530 ppm 50 ppm Ethylene glycol was recovered from the bottom layer. WHAT WE CLAIM IS:-

1. A process of separating ethylene glycol from admixture with tetraglyme containing rhodium therein which ethylene glycol and rhodium are provided by the homogeneous liquid phase reaction in the presence of rhodium as a carbonyl complex of oxides of car bon and hydrogen wherein the tetraglyme is a solvent therefor, which comprises contacting said admixture with an amount of glycerine greater than that amount which is soluble in said admixture thereby forming two liquid phases, one which is richer in glycerine and the other containing the greater concentration of tetraglym and causing at least a portion of said ethylene glycol to enter the phase richer in glycerine, maintain ing the greater portion of the rhodium with the phase containing the greater concentra tion of tetraglyme and recovering ethylene glycol from said phase which is richer in glycerine.

2. A process as claimed in claim 1 wherein the admixture also contains methanol.

3. A process as claimed in claim 1 or 2 wherein the admixture also contains water.

4. A process as claimed in claim 1, 2 or 3 wherein the admixture contains methyl formate.

5. A process as claimed in any one of claims 1 to 4 wherein the extraction is conducted at room temperature.

6. A process as claimed in claim 1 wherein the admixture is free of at least one of water, methanol, ethanol, and methyl formate.

7. A process as claimed in any one of claims 2 to 6 in which the admixture is subjected to a mild distillation to remove low boiling components before contact with glycerine.

8. A process as claimed in any one of claims 1 to 7 in which the extraction is carried out under an atmosphere of carbon monoxide.

9. A process as claimed in claim 1 and substantially as hereinbefore described with reference to the Example.