GB1560480A - Production of ethylene oxide - Google Patents

Description

(54) PRODUCTION OF ETHYLENE OXIDE (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SWIP 3JF, a British Company, 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 following statement:- This invention relates to the production of ethylene oxide.

Ethylene oxide is normally produced by the catalytic oxidation of ethylene with oxygen (which may be supplied in the form of air). Part of the ethylene is oxidised to oxides of carbon and water, and it is desirable that the proportion of ethylene consumed in this way should be as small as possible; that is, that the reaction should be as selective as possible in forming the desired product, namely ethylene oxide.

Catalysts should, therefore be employed which make this possible, but they should be sufficiently active to make an acceptable rate of production possible. Thus, an important feature of a catalyst is that it should show a good combination of activity and selectivity under its intended reaction conditions.

In our co-pending British Patent No.

1,491,447 we have disclosed catalysts for the production of ethylene oxide by the oxidation of ethylene with oxygen, which comprise silver supported on and introduced by impregnation of a decomposable silver compound to a preformed porous heat resisting support, the catalysts comprising various promoters.

Optionally an alkali metal could be used in conjunction with various other promoters.

We have found that if the support is an alpha-alumina support and a high concentration of sodium is present, it is not necessary to incorporate any other promoter.

This invention comprises a process for producing ethylene oxide by contacting ethylene and oxygen with a catalyst which comprises silver supported on and introduced by impregnation with a solution of decomposable silver compound to a preformed porous alpha-alumina support which catalyst comprises at least 300 preferably at least 700 and more preferably at least 1000 atoms of sodium in excess of any present as impurities or cements in the support per thousand atoms of silver and is substantially free from any other promoter.

The catalyst may contain for example up to 50,000 and preferably up to 30,000 atoms of sodium as aforesaid per thousand atoms of silver. Preferably the catalyst contains 1.5 to 30% and more preferably 2 to 100o by weight of sodium per sq. metre/gram of support surface area as determined by the Brunaeur Emmett and Teller method.

It is preferred that the catalyst should contain sodium in a form which when extracted with water gives an alkaline reaction to the resulting solution.

The alpha-alumina preferably has a specific surface area in the range 0.04 to 10 m2/g preferably 0.05 to 3 m2/g, more preferably 0.1 to 1.5 m2/g, and especially 0.2 to 0.6 m2/g as measured by the Brunauer, Emmett and Teller method, an apparent porosity as measured by the mercury absorption method of at least 20%, preferably 30 to 65%, and more preferably 40 to 60%, for example 45 to 55% and median pore diameters of 0.3 to 15 microns, preferably 1 to 15 microns as measured by the mercury porosimetry method.

The solution of the decomposable silver compound may be alkaline, i.e. it may be a solution which, when added to ten times its own volume of water, produces an alkaline reaction. The solution may comprise silver oxide or hydroxide or a silver salt, and a nitrogen-containing base which acts as a ligand, for example pyridine, acetonitrile, an amine, especially a primary or secondary amine, having 1 to 6 carbon atoms, acrylonitrile, hydroxylamine, an alkanolamine, for example ethanolamine, a vicinal alkylene diamine of from 24 carbon atoms (e.g. ethylene diamine) optionally together with a vicinal alkanolamine having 24 carbon atoms, ammonia and a vicinal alkanolamine, or preferably ammonia; the silver dissolves in such solutions by complex formation. The solutions are suitably aqueous solutions and may contain 3 to 50 Ó of silver by weight.

The sodium may be introduced before during or after impregnation with the solution of the decomposable silver compound. It may be introduced as an aqueous solution of a sodium compound.

The nature of the compound is not critical, sulphates, nitrates, nitriles, carboxylates and many other compounds may be employed.

It is desirable that silver should be deposited às discrete particles throughout substantially all of the available surface (inter alia within the pores) of the support rather than being -deposited on the external surface of the support. It is preferred that the total amount of solution used should be such that it is substantially entirely absorbed into the support rather than an excess being left in contact with it. Any surplus solution may alternatively be drained off prior to drying the solid. The silver compound may be decomposed by heating the impregnated support to a temperature of 200--4000C, preferably 200--3500C.

The conversion of ethylene to ethylene oxide using the catalysts of the invention may be carried out in a conventional manner. Pressures of from 1 to 35 bars absolute may be employed. The temperature is suitably in the range 190 to 270"C, and preferably 210 to 245 C. In general a diluent, for example methane, is present in proportions of, for example 10 to 50 Mn by weight. Generally 5 to 70, for example 50 to 70% of ethylene is recycled.

Oxygen may be supplied for example in the form of air or as commercial oxygen.

Carbon dioxide is generally also present. A reaction modifier, for example ethylene dichloride, may be used to supress the formation of hot spots in the catalyst.

Example 1 An alpha-alumina support composite in the form of pellets sold by Norton Co. under the Registered trademark 'Alundun' was crushed and sieved to give particles of diameters of between 0.42 and 1.00 mm.

The apparent porosity of the support was 40 to 44%, the water porosity was 0.24 cc/g and the specific surface area was 0.36 m2/g. The bulk (950/,) of the pore volume was contained in pores with diameters within the range 1 to 15 y; the mean pore diameter was 2.7 ,u.

The support (100 g) was impregnated with a solution comprising sodium acetate (14.4 g) dissolved in water (24 cc). The resulting moist solid was heated in an air atmosphere at 300"C for 30 minutes then in an atmosphere of carbon dioxide at 3000C for 60 minutes.

Silver acetate (15 g) was dissolved in a mixture of aqueous ammonia (S.G. 0.880; 21 cc) and ethanolamine (3 cc). The resulting solution was impregnated into the support containing the pyrolised sodium acetate to provide a damp solid which was heated in a forced draught (air) oven for four hours whilst the temperature was raised from 1000C to 3000C at 0.8"C per minute.

This procedure provides a dry catalyst containing about 8% by weight of silver together with about 2.2% by weight of sodium. The catalyst contained 1200 atoms of sodium per 1000 atoms of silver, and 7 5An Na gm-2.

20 g of catalyst were loaded into a glass reactor (internal diameter 13 mm) contained within an air circulated thermostatically controlled oven. A gas mixture containing 30% ethylene 8 ' 02, 62,in N2 and 4 ppm ethylene dichloride was passed over the catalyst at 1 bar pressure and a gas hourly space velocity of 200 hours-'. The selectivity to ethylene oxide (S) conversion of oxygen (C) and catalyst activity (A) were determined at 2400 C.

S=yield of olefine oxide (moles per 100 moles of olefine consumed).

C=% oxygen conversion.

A=rate of olefine consumption (moles of olefine consumption per kilogram of catalyst per hour).

T=Time taken for S to fall from 94% to 85%.

The result of the catalyst test was S=94% C=22% A=0.21 M kg-lhr- T=30 days.

Example 2 An alpha-alumina support composite in the form of pellets sold by Norton Co. under the Registered trademark 'Alundum' was crushed and sieved to give particles of diameters of between 0.42 and 1.00 mm.

The apparent porosity of the support was 40 to 44%, the water porosity was 0.24 cc/g of and the specific surface area was 0.36 cc/g.

The bulk (95%) of the pore volume was contained in pores with diameters within the range I to 15 y; the mean pore diameter was 2.7 ,a.

The support (100 g) was impregnated with a solution comprising sodium acetate (9.6 g) dissolved in water (24 cc). The resulting moist solid was heated in an air atmosphere at 300"C for 30 minutes and then in an atmosphere of carbon dioxide at 300"C for 60 minutes.

Silver acetate (15 g) was dissolved in a mixture of aqueous ammonia(S.G. 0.880; 21 cc) and ethanolamine (3 cc). The resulting solution was impregnated into the support containing the pyrolysed sodium acetate to provide a damp solid which was heated in a forced draught (air) oven for four hours whilst the temperature was raised from 100"C to 300"C at 0.8"C per minute.

This procedure provides a dry catalyst containing about 8 ', by weight of silver together with about 1.5% by weight of sodium per 1000 atoms of silver and 5", Nag m-2.

20 g of catalyst were loaded into a glass reactor (internal diameter 12 mm) contained within an air circulated thermostatically controlled oven. A gas mixture containing 30 / > ethylene 8 n 02, 620/, N2 and 4 ppm ethylene dichloride was passed over the catalyst at 1 bar pressure and at a gas hourly spaced velocity of 200 hrs-'. The selectivity to ethylene oxide (S), conversion of oxygen (C) and catalyst activity (A) were determined at 240"C.

S= yield of olefine oxide (mole per 100 moles of olefine consumed).

C='0 oxygen conversion.

A=rate of olefine consumption (moles of olefine consumed per kilograme of catalyst per hour).

T=time taken for S to fall to 85%.

The result of the catalyst test was s=91 C=210/, A=0.20 M kg-1hr-' T=19 days.

Example 3 A catalyst was made up to contain silver and sodium supported on an alpha-alumina support as described in Example 1.

The support (100 g) was impregnated with a solution comprising sodium acetate (2.4 g) dissolved in water (24 cc). The resulting moist solid was heated in an air atmosphere at 300"C for 30 minutes and then in an atmosphere of carbon dioxide at 3000C for 60 mins. The solid was then impregnated with silver as described in Example 1 and heat treated as in that Example.

This procedure provides a dry catalyst containing about 8% by weight of silver together with about 0.50,,, bv weight of sodium equivalent to 300 atoms of sodium per 1000 atoms of silver and 1.7in Nag m-2.

20 g of catalyst were loaded into a glass reactor (internal diameter 13 mm) contained within an air circulated thermostatically controlled oven. A gas mixture containing 30" ethylene 8% 2 62 " N2 and 4 ppm ethylene dichloride was passed over the catalyst at 1 bar pressure and a gas hourly spaced velocity of 200 hrs-'. The selectivity to ethylene oxide (S), conversion of oxygen (C) and catalyst activity (A) were determined at 240 C.

S=yield olefine oxide (moles per 100 moles of olefine consumed).

C= n oxygen conversion.

A=rate of olefine consumption (moles of olefine consumer per kilogram of catalyst per hour).

T=time taken for S to fall to 85',.

The result of the catalyst test was S=90 " C=30U A=0.23 M Kg hr-' T=12 days.

WHAT WE CLAIM IS: 1. A process for producing ethylene oxide by contacting ethylene and oxygen with a catalyst which comprises silver supported on and introduced by impregnation with a solution of a decomposable silver compound to a preformed porous alphaalumina support which catalyst comprises at least 300 atoms of sodium in excess of any present as impurities of cements in the support per 1000 atoms of silver and is substantially free from any other promoter.

2. A process as claimed in Claim 1 in which the catalyst comprises at least 700 atoms of sodium in excess of any present as impurities or cements in the support per 1000 atoms of silver.

3. A process as claimed in Claim 2 in which the catalyst comprises at least 1000 atoms of sodium in excess of any present as impurities or cements in the support per 1000 atoms of silver.

4. A process as claimed in any preceding claim in which the catalyst contains at most 50,000 atoms of sodium as aforesaid per 1000 atoms of silver.

5. A process as claimed in Claim 4 in which the catalyst contains at most 30,000 atoms of sodium as aforesaid per 1000 atoms of silver.

6. A process as claimed in any preceding claim in which the catalyst contains 1.5 to 30% by weight of sodium per sq metre/g of support surface area as determined by the Brunaeur, Emmett and Teller method.

7. A process as claimed in any preceding claim in which the catalyst contains sodium in a form which when extracted with water, gives an alkaline reaction to the resulting solution.

8. A process as claimed in any preceding claim in which the alpha-alumina support has a specific surface area in the range 0.04 to 10 sq metres/g as measured by the Brunaeur, Emmett and Teller method, an apparent porosity as measured by the mercury absorption method of 30--650/, and median pore diameters of 0.3 to 15 microns as measured by the mercury porosimetry method.

9. A process as claimed in any preceding

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

Claims (1)

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

   containing the pyrolysed sodium acetate to provide a damp solid which was heated in a forced draught (air) oven for four hours whilst the temperature was raised from 100"C to 300"C at 0.8"C per minute.

   This procedure provides a dry catalyst containing about 8 ', by weight of silver together with about 1.5% by weight of sodium per 1000 atoms of silver and 5", Nag m-2.

   20 g of catalyst were loaded into a glass reactor (internal diameter 12 mm) contained within an air circulated thermostatically controlled oven. A gas mixture containing 30 / > ethylene 8 n 02, 620/, N2 and 4 ppm ethylene dichloride was passed over the catalyst at 1 bar pressure and at a gas hourly spaced velocity of 200 hrs-'. The selectivity to ethylene oxide (S), conversion of oxygen (C) and catalyst activity (A) were determined at 240"C.

   S= yield of olefine oxide (mole per 100 moles of olefine consumed).

   C='0 oxygen conversion.

   A=rate of olefine consumption (moles of olefine consumed per kilograme of catalyst per hour).

   T=time taken for S to fall to 85%.

   The result of the catalyst test was s=91 C=210/, A=0.20 M kg-1hr-' T=19 days.

   Example 3 A catalyst was made up to contain silver and sodium supported on an alpha-alumina support as described in Example 1.

   The support (100 g) was impregnated with a solution comprising sodium acetate (2.4 g) dissolved in water (24 cc). The resulting moist solid was heated in an air atmosphere at 300"C for 30 minutes and then in an atmosphere of carbon dioxide at 3000C for 60 mins. The solid was then impregnated with silver as described in Example 1 and heat treated as in that Example.

   This procedure provides a dry catalyst containing about 8% by weight of silver together with about 0.50,,, bv weight of sodium equivalent to 300 atoms of sodium per 1000 atoms of silver and 1.7in Nag m-2.

   20 g of catalyst were loaded into a glass reactor (internal diameter 13 mm) contained within an air circulated thermostatically controlled oven. A gas mixture containing 30" ethylene 8% 2 62 " N2 and 4 ppm ethylene dichloride was passed over the catalyst at 1 bar pressure and a gas hourly spaced velocity of 200 hrs-'. The selectivity to ethylene oxide (S), conversion of oxygen (C) and catalyst activity (A) were determined at 240 C.

   S=yield olefine oxide (moles per 100 moles of olefine consumed).

   C= n oxygen conversion.

   A=rate of olefine consumption (moles of olefine consumer per kilogram of catalyst per hour).

   T=time taken for S to fall to 85',.

   The result of the catalyst test was S=90 " C=30U A=0.23 M Kg hr-' T=12 days.

   WHAT WE CLAIM IS: 1. A process for producing ethylene oxide by contacting ethylene and oxygen with a catalyst which comprises silver supported on and introduced by impregnation with a solution of a decomposable silver compound to a preformed porous alphaalumina support which catalyst comprises at least 300 atoms of sodium in excess of any present as impurities of cements in the support per 1000 atoms of silver and is substantially free from any other promoter.

   2. A process as claimed in Claim 1 in which the catalyst comprises at least 700 atoms of sodium in excess of any present as impurities or cements in the support per 1000 atoms of silver.

   3. A process as claimed in Claim 2 in which the catalyst comprises at least 1000 atoms of sodium in excess of any present as impurities or cements in the support per 1000 atoms of silver.

   4. A process as claimed in any preceding claim in which the catalyst contains at most 50,000 atoms of sodium as aforesaid per 1000 atoms of silver.

   5. A process as claimed in Claim 4 in which the catalyst contains at most 30,000 atoms of sodium as aforesaid per 1000 atoms of silver.

   6. A process as claimed in any preceding claim in which the catalyst contains 1.5 to 30% by weight of sodium per sq metre/g of support surface area as determined by the Brunaeur, Emmett and Teller method.

   7. A process as claimed in any preceding claim in which the catalyst contains sodium in a form which when extracted with water, gives an alkaline reaction to the resulting solution.

   8. A process as claimed in any preceding claim in which the alpha-alumina support has a specific surface area in the range 0.04 to 10 sq metres/g as measured by the Brunaeur, Emmett and Teller method, an apparent porosity as measured by the mercury absorption method of 30--650/, and median pore diameters of 0.3 to 15 microns as measured by the mercury porosimetry method.

   9. A process as claimed in any preceding

   claim in which the solution of the decomposable silver compound is an alkaline solution as hereinbefore defined.

   10. A process as claimed in Claim 9 in which the solution comprises a nitrogen containing base which acts as a ligand.

   11. A process as claimed in Claim 10 in which the nitrogen containing base is ammonia.

   12. A process as claimed in any preceding claim in which the solution of a decomposable silver compound comprises 30--500/, of silver by weight.

   13. A process as claimed in any preceding claim in which the total amount of the solution of the decomposable silver compound which is used is substantially entirely absorbed into the support before the silver compound is decomposed.

   14. A process as claimed in any preceding claim in which the impregnated support is heated to decompose the silver compound to a temperature of 200400 C.

   15. A process as claimed in any preceding claim in which the production of ethylene oxide by contacting ethylene and oxygen with the catalyst is carried out at a pressure of from 1--35 bars absolute and a temperature in the range of 190-270'C.

   16. A process as claimed in Claim 15 in which a diluent is present in proportions of 1050 g by weight.

   17. A process as claimed in Claim 15 or 16 in which 5 to 70% of the ethylene fed to the reaction is recycled.

   18. A process as claimed in Claim 15, 16 or 17 in which a reaction modifier is used to suppress the formation of hot spots in the catalyst.

   19. A process as claimed in any preceding claim whenever carried out substantially as described in any of the Examples.

   20. Ethylene oxide whenever produced by a process as claimed in any preceding claim.