PROCESS FOR PRODUCING OLEFIN OXIDE Technical Field

The present invention relates to a process for producing an olefin oxide.

Background Art

WO 98/58921 Al and US 7319156 B2 disclose a process for producing an olefin oxide comprising reacting an olefin with oxygen in the presence of a silver catalyst.

Summary of Invention

The present invention provides a process for producing an olefin oxide related to the following:

[ 1 ] A process for producing an olefin oxide comprising reacting an olefin with oxygen in the presence of a catalyst, wherein the catalyst comprises particles consisting of silver metal and gold metal, and a ratio of gold metal to silver metal of the particles ( [Au/Ag(bulk) ] ) and a ratio of gold metal to silver metal of the surfaces of the particles ( [Au/Ag (surface) ] ) satisfy the following formula (1) :

0<[Au/Ag (surface) ]/ [Au/Ag (bulk)]<0.9 (1);

[2] The process according to [1], wherein the catalyst is supported on a carrier;

[3] The process according to [1] or [2], wherein the olefin is propylene and the olefin oxide is propylene oxide;

[4] A catalyst for producing an olefin oxide which comprises particles consisting of silver metal and gold metal wherein a ratio of goldmetal to silver metal of the particles ( [Au/Ag (bulk) ] ) and a ratio of gold metal to silver metal of the surfaces of the particles ( [Au/Ag (surface) ] ) satisfy the following formula (1):

0<[Au/Ag (surface) ]/ [Au/Ag (bulk)]<0.9 (1) Description of Embodiments

The present invention is a process for producing an olefin oxide comprising reacting an olefin with oxygen in the presence of a catalyst, wherein the catalyst comprises particles consisting of silver metal and gold metal, and a ratio of gold metal to silver metal of the particles ( [Au/Ag (bulk) ] ) and a ratio of gold metal to silver metal of the surfaces of the particles ( [Au/Ag (surface) ] ) satisfy the following formula (1) :

0<[Au/Ag (surface) ] / [Au/Ag (bulk) ] <0.9 (1)

The catalyst can be prepared according to the process described in Chem. Mater. 2009, 21, 410-418.

Specifically, the catalyst can be produced, for example, by the following steps (a) and (b) :

(a) a step of contacting gold particles with a silver salt to obtain a catalyst precursor,

(b) a step of reducing the catalyst precursor with a reducing agent .

After, step (b) , the catalyst obtained may be heated under an atmosphere free from oxygen.

The contacting temperature in the step (a) is usually 0 to 100°C.

Examples of the silver salt include silver nitrate. Examples of the reducing agent include sodium borohydride . The temperature of the reduction is usually 0 to 100°C.

The ratio of gold metal to silver metal of the particles ( [Au/Ag (bulk) ] ) can be calculated based on the used amount of gold particles and the used amount of the silver salt. Therefore, [Au/Ag (bulk) ] can be controlled by changing the used amount of gold particles and/or the used amount of the silver salt. In the catalyst, [Au/Ag (bulk) ] is preferably 1 or more, and more preferably 3 or more.

[Au/Ag (surface) ]/ [Au/Ag (bulk) ] is 0.9 or less, and preferably 0.7 or less. The ratio of gold metal to silver metal of the surfaces of the particles ( [Au/Ag (surface) ] ) can be controlled by changing the temperature of heating after the step (b) . The higher the temperature of the heating is, the more silver metal of the surfaces of the particles are diffused into the inside of the particles, and therefore, [Au/Ag (surface) ] becomes bigger. Therefore, the temperature of the heating is usually 0°C to 200°C, preferably 0°C to 150°C, and more preferably 0°C to 100°C.

The particle size of the catalyst is usually 500 nm or less, preferably 100 nm or less and more preferably 50 nm or less.

From the viewpoint of ease of the preparation of the catalyst having a small particle size, the catalyst supported on a carrier is preferably prepared. The catalyst supported on the carrier can be produced by the following steps (c) to (f) :

(c) a step of contacting chloroauric acid with a carrier functionalized by amino groups to obtain a gold precursor,

(d) a step of reducing the gold precursor with a reducing agent to obtain gold supported on the carrier,

(e) a step of contacting gold supported on the carrier with a silver salt to obtain a catalyst precursor,

(f) a step of reducing the catalyst precursor. The contacting temperature in the step (c) is usually 0 to 50°C. The contact in the step (c) is usually conducted in water. After, contacting chloroauric acid with the carrier, the gold precursor obtained may be washed and/or dried before the step (d) .

Examples of the reducing agent used in the steps (d) and (f) include the same as described in the above step (b) . The temperature of the reduction is usually 0 to 100°C.

The contacting temperature in the step (e) is usually 0 to 50°C. The contact in the step (e) is usually conducted in water.

The temperature of the reduction in the step (f) is usually 0 to 100°C. After the step (f) , the reaction mixture obtained is usually filtrated to obtain the catalyst. The catalyst obtained can be washed with water.

As described above, the catalyst obtained may be heated under an atmosphere free from oxygen in order to control [Au/Ag (surface) ] .

[Au/Ag (surface) ] in the catalyst can be measured with XPS (X-ray photoelectron spectroscopy) analysis. The catalyst usually has a core-shell structure in which the core consists of gold particle and the shell consists of silver particle .

The carrier is preferably one on which the catalyst can be supported and which does not change in property under the condition of the process of the present invention. Examples of the carrier include a metal carbonate, a metal oxide and carbon.

Preferable examples of the metal carbonate include an alkali metal carbonate, an alkaline earth metal carbonate and a transition metal carbonate, and the alkaline earth metal carbonate is preferable .

Examples of the alkali metal carbonate include sodium carbonate and potassium carbonate . Examples of the alkaline earth metal carbonate include magnesium carbonate, calcium carbonate, strontium carbonate and barium carbonate, and calcium carbonate, strontium carbonate and barium carbonate are preferable. The alkaline earth metal carbonate having a specific surface area of 1 to 70 m ² /g measured by nitrogen adsorption of the BET method is preferable.

As the carrier, the metal carbonate may be used as it is or after fixing particles of the metal carbonate each other using a suitable binder. The metal carbonate may be mixed with a molding agent and molded by extrusion molding, press molding or the like to use the obtained product as the carrier. It is preferred that the metal carbonate is used as it is as the carrier. A metal oxide having a crystal form of a rock salt structure, a corundum structure, a spinel-type structure, a fluorite-type structure, a wurtzite-type structure, a rutile-type structure, a bixbite-type structure, an ilmenite-type structure, a pseudobrookite-type structure or a perovskite-type structure can be used.

Examples of the metal oxide having a rock salt structure include TiO, VO, MnO and NiO.

Examples of the metal oxide having a corundum structure include α-Α1 ₂ 0 ₃ and a-Fe ₂ 0 ₃ .

Examples of the metal oxide having a spinel-type structure include ZnAl ₂ 0 ₄ , y-Fe ₂ 0 ₃ and SnZn ₂ 0 ₄ .

Examples of the metal oxide having a fluorite-type structure include Zr0 ₂ and Ce0 ₂ .

Examples of the metal oxide having a wurtzite-type structure include ZnO.

Examples of the metal oxide having a rutile-type structure include Sn0 ₂ , Ti0 ₂ and Ru0 ₂ .

Examples of the metal oxide having a bixbite-type structure include p-Fe ₂ 0 ₃ .

Examples of the metal oxide having an ilmenite-type structure include FeTi0 ₃ .

Examples of the metal oxide having a pseudobrookite-type structure include FeTiOs.

Examples of the metal oxide having a perovskite-type structure include CaTi0 ₃ , SrTi0 ₃ , BaTi0 ₃ , CaZr0 ₃ , SrZr0 ₃ , BaZr0 ₃ and LaA10 ₃ .

Examples of the carbon include activated carbon, carbon black, graphite and carbon nanotubes, and graphite is preferred.

As the carrier, a silicon compound can be also used, and examples thereof include a water-soluble silicate such as sodium metasilicate and potassium metasilicate, and a porous silicate having silica as a main component such as silica gel, zeolite and mesoporous silicate.

A commercially available carrier may be used as it is, and such a commercially available carrier may also be used after purifying and molding by a well-known method.

The used amount of the carrier is preferably 0.1 to 200 parts by mass per 1 part by mass of the catalyst.

The catalyst is preferably activated before using for the process of the present invention. The activation of the catalyst is usually conductedby heating the catalyst prepared in the absence of oxygen. The heating temperature of the activation is usually 150 to 300°C.

Next, the process for producing an olefin oxide of the present invention will be illustrated. The process of the present invention comprises reacting an olefin and oxygen in the presence of the above-mentioned catalyst.

The process of the present invention can be performed in a batch-wise reactor or a continuous reactor. From the viewpoint of an industrial process, it is preferably performed in a continuous reactor .

The amount of the. catalyst is preferably 0.00005 mole or more relative to 1 mole of the olefin, and more preferably 0.0001 mole or more in a silver metal equivalent . The upper limit thereof is not limited, and while a larger amount of the olefin oxide can be produced if increasing the amount of the catalyst, the upper limit of the amount of the catalyst is usually adjusted by taking an economic efficiency such as the cost of catalyst into consideration.

Oxygen can be used in combination with an inert gas such as nitrogen and carbon dioxide. Air can be used as oxygen. The amount of oxygen can be appropriately adjusted according to the reaction mode (continuous type or batch type) . The amount of oxygen is preferably in the range of 0.01 to 100 moles relative to 1 mole of the olefin, and more preferably in the range of 0.03 to 30 moles.

The reaction temperature is preferably in the range of 100°C 400°C, and more preferably in the range of 120°C to 300°C. In this specification, "olefin" means a hydrocarbon having one carbon-carbon double bond, and examples thereof include ethylene, propylene, butene, pentene and hexene, and propylene is preferable.

The olefin can be used in combination with an inert organic gas such as a lower alkane such as methane and ethane. Olefin and oxygen gases can be fed in the form of their mixed gas. Olefin and oxygen gases may be fed with diluent gases . Examples of diluent gases include nitrogen, methane, ethane, propane, carbon dioxide and rare gases such as argon and helium.

The reaction of the olefin and oxygen can be conducted in the presence of a halogen compound, particularly an organic halogenated compound. Examples of the halogen compound include the halogen compounds disclosed in Japanese Unexamined Patent Application Publication No. 2008-184456, and it is preferably an organic chlorinated compound. Examples of the organic chlorinated compound include chloroethane , 1 , 2-dichloroethane , chloromethane and vinyl chloride. The halogen compound is preferably a compound existing in the form of a gas at the temperature and pressure condition in the reaction system of the reaction.

The amount of the halogen compound is preferably 1 to 1000 ppm by volume, and more preferably 1 to 500 ppm by volume based on a total volume of the mixed gas other than steam, i.e. a mixed gas composed of oxygen, the olefin and a dilution gas added as necessary.

The reaction pressure is not limited, and may be selected from those in reducedpressure conditions topressurized conditions . The pressure under pressurized conditions is preferable from the viewpoint of allowing sufficient contact of oxygen and the olefin with the catalyst, it may be a reaction pressure selected from the range of 0.01 to 3 MPa. in absolute pressure, and is more preferably selected from the range of 0.02 to 2 MPa. The reaction pressure is determined by also taking into consideration the pressure resistibility of the reaction device used in the present productionmethod. The reducedpressure condition means apressure lower than the atmospheric pressure. The pressurized condition means a pressure higher than the atmospheric pressure.

The reaction can be carried out in the presence of water. When the reaction is carried out in the presence of water, water is preferably changed into steam by heating to use, and a mixed gas obtained by mixing steam, oxygen and the olefin is preferably contacted with the catalyst. It is preferable to use water as steam.

The amount of water is preferably in the range of about 0.1 to about 20 moles relative to 1 mole of the olefin, more preferably in the range of 0.2 to 10 moles, and still more preferably in the range of 0.3 to 8 moles. The above-mentioned "amount of water" indicates an amount of water supplied separately from water contained in air in a case of supplying air as oxygen.

Hereinafter, an embodiment of the present production method of a continuous type, which is a favored reaction mode, will be explained .

First, the catalyst in a predetermined amount is filled into a reaction tower equipped with a gas supply port and a gas exhaust port. Suitable heating means may be provided in the reaction tower, and the inside of the reaction tower may be raised in temperature up to a predetermined reaction temperature by such heating means. Subsequently, using a compressor or the like, a source gas containing the olefin and oxygen is supplied from the gas supply port into the reaction tower. By contacting this source gas with the catalyst in the reaction tower, the olefin and oxygen reacts in the presence of the catalyst, and the olefin oxide is generated. Furthermore, the product gas containing the olefin oxide thus generated is exhausted from the gas exhaust port .

The linear velocity of the source gas that is passed through the inside of a reaction tower is determined so as to make a residence time that allows the source gas and the catalyst to sufficiently generate the olefin oxide.

Although a case of heating means being provided in the reaction tower has been described in the above embodiment, it may be a mode in which the reaction tower may be maintained at ambient temperature, and the source gas may be supplied and then heated up to a predetermined reaction temperature by appropriate heating means, and then supplied into the reaction tower. It may be a mode in which suitable stirring means is provided in the reaction tower, and a source gas is supplied while stirring the catalyst that is present inside the reaction tower.

The olefin oxide thus generated, unreacted olefin and oxygen, and byproducts such as carbon dioxide may be contained in the product gas passing through the reaction tower. In addition, in a case of using the olefin and oxygen after dilution, an inert gas used for dilution may be incorporated. After having collected this product gas, the olefin oxide, which is the objective, can be removed by separation means such as distillation.

Examples of the olefin oxide include ethylene oxide, propylene oxide, butene oxide, pentene oxide and hexene oxide.

Examples

Hereinafter, Examples of the present invention will be described, but the present invention is not to be limited thereto.

[Au/Ag (surface) ] in the catalyst prepared was measured with XPS analysis: The XPS analysis was carried out under the following conditions; The spectra were energy calibrated by taking Si2p peak at 103 eV.

Producer: SPECS

Analyser: PHOIBOS 150MCD-9

X ray source: For BE determination: Al non-monocromatic, lOkV, 50W

Take off angle 0° versus normal

Diameter of the X ray beam 1 cm No flood gun

Energy resolution: Ag3d5/2 at 368,14eV, FWHM l,22eV at 704Kcps with Pass Energy 20eV; for non monochromatic Al X ray source Vacuum pressure 1*10 ^~9 mbar during spectra acquisition

Preparation Example

A catalyst was prepared according to the method described in Chem. Mater. 2009, 21, 410-418. One (1) g of a commercial silica carrier (Scharlau, 500m ² /gr) was added to a 50 mL of ethanol solution containing 2.5 g of APTES (H ₂ N (CH ₂ ) 3S1 (OE ^' t) 3 ) . Themixture obtained was refluxed for 24 hours to graft APTES on the silica surface. After being washed with ethanol and dried at 60°C, the solid was dispersed in 16 g of water at room temperature, to which 4 mL of 1.88% by weight HAuCl ₄ solution was added under stirring during 1.5 hours. After filtration and washing, the recovered solid was added into 10 g of water, to which 10 mL of 0.2 M NaBH ₄ solution was added under vigorous stirring for reduction of AuCl ₄ ^" . After 20 minutes, the solid was recovered by filtration and thoroughly washed with water to remove CI ^" for the subsequent Ag deposition. After dried at 60°C, the solid was dispersed in 16 g of H ₂ 0 at room temperature, to which _. 4 mL of 0.277% by weight AgN0 ₃ solution was added under stirring. After filtration and washing, the recovered solid was added into 10 g of water, to which 10 mL of 0.2 MNaBH ₄ solution was added under vigorous stirring . After 20 minutes, the solid was recovered by filtration and thoroughly washed with water and dried under vacuum (10 ^~3 mbar) .

The obtained catalyst is called as "CAT-1". "CAT-1" was aged for 1 month to obtain a catalyst. This catalyst is called as "CAT-2" . "CAT-1" was calcined at 500°C in air to obtain a catalyst. This catalyst is called as "CAT-3". The nominal total metal loadings were 5% by weight. The results .are shown in Table 1. Table 1

Examples 1 to 2 and Comparative Example 1

The reaction of propylene and oxygen was conducted using a microreactor connected to a mass spectrometer . The mass analysis was carried out under the following conditions:

MODEL: QMG 220 Ml (Telstar)

Filament current: 1.20 mA

Vacuum pressure: 1*10 ^~6 mbar during acquisition

The reactant mixture was 5 ml/min. of propylene (C ₃ H ₆ ) , 2.5 ml/min. of oxygen (O ₂ ) , and 22.5 ml/min. of argon (Ar) , which represent a molar ratio C ₃ H ₆ :0 ₂ = 2:1. The catalysts weight was around 150 mg, diluted in CSi in a 1 : 1 weight ratio . The activation of the catalyst was conducted prior to the reaction.

In order to determine the onset temperature of reaction, product distribution and their evolution with the temperature, we performed temperature programmed surface reaction (TPSR) at a rate of 2°C/min. The activation of the catalyst was done under several conditions (argon or O ₂ at different temperatures) .

The results are shown in Table 2. In Table 2, "Ar" means argon, "PO" means propylene oxide, "C0 ₂ " means carbon dioxide, and CO ₂ and PO are increment values measured relative to reference values of the reactant mixture. Table 2

Industrial Applicability

According to the present invention, propylene oxide, which is useful as an intermediate material of manufactured products, can be produced from propylene and oxygen with superior propylene oxide selectivity (PO/C0 ₂ ) .