GB2050376A

GB2050376A - Production of glycols

Info

Publication number: GB2050376A
Application number: GB8015675A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1979-05-24
Filing date: 1980-05-12
Publication date: 1981-01-07
Also published as: GB2050376B

Abstract

Polyols are produced by contacting olefins or hydroxyolefins with oxygen and an aqueous solution which comprises copper and/or iron ions, bromide and/or iodide ions and a substantial amount of dissolved carbon dioxide.

Description

SPECIFICATION Production of glycols This invention relates to the production of glycols. It is known, for example from US Patent 4,008,286, to oxidise olefines to glycols by contacting them with oxygen and an aqueous solution which comprises copper or iron bromide. This reaction is usually accompanied by a certain amount of complete oxidation of the olefine to water and carbon dioxide.

The resulting carbon dioxide concentration is low and it is important that any carbon dioxide production by this mechanism should be kept low because of the waste of olefine involved.

We have found that the presence of substantial amounts of dissolved CO2 improves the selectivity with which the olefine is converted to diols and other useful products, for example, bromo-hydrins and di-and poly-glycols, including, in the case of ethylene, dioxan.

According to the invention a polyol, for example a diol, is produced by contacting an olefin or hydroxy olefin, especially ethylene or propylene with oxygen and an aqueous solution which comprises as catalyst (i) copper and/or iron ions and (ii) bromide ions and/or iodide ions preferably both iodide and bromide ions being present, the ratio of iodide ions to bromide ions being preferably in the range 1:1000 to 1:5 and more preferably 1:100 to 1:10 in the presence of a substantial amount of dissolved 002.

The pH of solution is preferably at most 5 and is more preferably in the range 0 to 4.5.

The aqueous solution preferably comprises at least 0.05 moles per litre and more preferably at least 0.15 moles per litre of 002. Suitably the CO2 concentration may be for example 0.15 to 5 moles per litre.

The process may be carried out at a total pressure in the range 1-100 bars and preferably 1-150 bars, the partial pressure of CO2 being for example 0.2 to 50 and preferably 0.5 to 25 bars.

The temperature is suitably 100-225 C and is preferably 110-180"C.

The total concentration of copper and iron ions in the solution may be at least 0.02 gram atoms and is preferably in the range 0.02 to 3 gram atoms per litre and is more preferably 0.1 to 2 gram atoms per litre.

The total concentration of iodide and bromide ions is suitably equivalent to the copper and/or iron ions in their highest valency state; however if desired free hydrobromic and/or hydroiodic acid may be present or other anions - for example nitrate, sulphate or acetates may be present. It is preferred that the total iodide and bromide ion concentration in the solution should be at least 0.02, for example 0.02 to 3 gram atoms, and preferably 0.1 to 2 gram atoms per litre.

The molar ratio of olefine to oxygen fed to the reaction may be 1:1 to 20:1 and is preferably in the range 2:1 to 15:1. The combined partial pressure of the olefine and oxygen is preferably 0.5 to 99 and preferably 1 to 45 bars. If desired an inert gas for example nitrogen may be present. It is necessary to avoid flammable conditions in the process.

The process may be carried out in the presence of an additional solvent for example a carboxylic acid having for example 2-6 carbon atoms.

A liquid which boils at a higher temperature than the glycol product is preferably present in an amount of 2-80% by weight of the total reaction medium.

This allows the glycol product to be distilled from the high boiling liquid whilst catalyst components remain in solution or suspension in the high boiling liquid. This solution or suspension may be recycled to the process. Suitable liquids are high boiling polyols for example higher boiling by-products of the reaction e.g. diethylene glycol, dipropylene glycol, triethylene glycol or tripropylene glycol or lower esters or ethers of these polyols or of the lower glycols for example ethylene or propylene glycol e.g. the acetates or C1 to C4 alkyl ethers, or other polyol acetates, e.g. triacetin, ethers, inert nitriles e.g. adiponitrile or sulphoxides for example dimethyl sulphoxide. The higher boiling solvent may if desired form a single phase in the aqueous solution during the production of the glycol.When such a liquid is present any precipitated catalyst components may be removed from the initial reaction product, e.g. by filtering or centrifuging it, and then water preferably together with any dioxan or dimethyl dioxan which may be produced may be distilled in a first distillation under reduced pressure, glycol may be distilled from the bottoms product of the first distillation in a second distillation under reduced pressure, and a bottoms product from the second distillation (which contains catalyst components) may be recycled to the reaction.

An alternative method of separating the glycol product may be used. This involves separating the catalyst from the reaction mixture by adsorbing it onto one or more ion exchange resins. The remaining mixture is then distilled under reduced pressure.

The catalyst is recovered from the ion exchange resin and returned to the reaction. The catalyst may alternatively be adsorbed onto carbon to facilitate its removal and the catalyst may either be separated from the carbon and returned to the reaction or the catalyst returned to the reaction adsorbed on the carbon. Unconverted materials may be recycled.

Example 1 An aqueous solution (2 litres) containing 0.3 moles/litre of cupric bromide and 0.5 moles/litre potassium iodide was charged to a 4 litre titanium pressure vessel equipped with stirrer and condenser. The pressure was raised to 300 psig with nitrogen and the temperature raised to 1400C.

Ethylene (150 1/h) and oxygen (50 1/h) and nitrogen (500 1/h) were then passed through. The rate of oxidation was followed by the uptake of oxygen. The residual ethylene and by-product carbon oxides and acetaldehydes were monitored in the exit gas. The build up of intermediates, products and by-products in the liquid phase (e.g. bromohydrin, 1-bromo, 1-hydroxy diethyl ether, glycol, diglycol, dioxan) was followed by withdrawing small samples at frequent intervals from the reactor.

The rate of oxidation under the above conditions was 16.8 litres 02/litre of solution/hour. After 5 hours the following components were found in the reaction mixture; ethylene glycol 12.8% by weight, diethylene glycol 1.7% by weight, bromohydrin 1.5% by weight, dioxan 0.8% by weight. The rate of CO2 production production during this period was 3.8 litres C02/litre of solution/hour. The overall yield of ethylene glycol and its derivatives on oxygen consumed was 40% of theoretical.

Example 2 Example 1 was repeated with the exception that carbon dioxide was used in place of nitrogen.

The rate of oxidation under these conditions was 10.3 litres 02/litre/hour. After 4 hours 50 minutes the following components were found in the reaction mixture; ethylene glycol 12.8% by weight, diethylene glycol 2.3% by weight, bromohydrin 1.4% by weight, dioxan 0.64% by weight. The overall yield of ethylene glycol and its derivatives on oxygen consumed was 70% of theoretical.

Claims

1. A process in which a polyol is produced by contacting an olefine or hydroxy olefin with oxygen and an aqueous solution which comprises as catalyst (i) copper and/or iron ions and (ii) bromide ions and/or iodide ions in the presence of a substantial amount of dissolved carbon dioxide.

2. A process as claimed in Claim 1 in which both iodide and bromide ions are present, the ratio of iodide ions to bromide ions being in the range 1:1000 to 1:5.

3. A process claimed in Claim 1 or2 in which the pH of the solution is at most 5.

4. A process as claimed in claim 1,2 or 3 in which the aqueous solution comprises at least 0.15 moles per litre of carbon dioxide.

5. A process as claimed in claim 4 in which the aqueous solution comprises 0.15 to 5 moles per litre of carbon dioxide.

6. A process as claimed in any preceding claim which is carried out at a total pressure of 1 to 50 bars and a partial pressure of carbon dioxide of 0.5 to 25 bars.

7. A process as claimed in any preceding claim whenever carried out at a temperature in the range 110-180"C.

8. A process as claimed in any preceding claim in which the total concentration of copper and iron ions in the solution is in the range 0.02 to 3 gram atoms per litre.

9. A process as claimed in any preceding claim in which the total concentration of iodide and bromide ions is at least equivalent to the copper and/or iron ions in their highest valency state.

10. A process as claimed in any preceding claim in which the total iodide and bromide ion concentration in the solution is 0.02 to 3 gram atoms per litre.

11. A process as claimed in any preceding claim in which the molar ratio of olefine to oxygen fed to the reaction is in the range 2:1 to 15:1.

12. A process as claimed in any preceding claim in which the combined partial pressure of the olefine and oxygen is 1 to 45 bars.

13. A process in which ethylene glycol is pro duced substantially as described in Example 2.

14. Polyols whenever produced bya process as claimed in any preceding claim.