RU2099278C1 - Method of producing hydrogen peroxide, catalyst, and method of preparation thereof - Google Patents

Abstract

FIELD: hydrogen peroxide production. SUBSTANCE: hydrogen peroxide is prepared via direct catalytic oxidation of hydrogen by oxygen in acidic aqueous medium in presence of Na⁺,F^-,Cl^- provided by adding NaCl and NaF in quantities 3-30 and 2-10% based on catalyst weight, respectively. Catalyst contains at least one VIII group metal, preferably 0.1-10 wt % Pd, applied on carbon-containing carrier: fluoridated carbon with fluoridation rate 10-65% or partly wettable carbon. Process is carried out in autoclave under stirring at temperature from freezing point of aqueous medium to 60 C, pressure 2.5-20 MPa, and partial pressure of hydrogen below detonation limit. Catalyst is prepared by adding sodium citrate solution to VIII group metal chloride, e.g. PdCl₂, heating resulting mixture, adding metal and fluoridated or partly wettable carbon, evaporation, and reducing solid residue in hydrogen atmosphere at elevated temperature to produce 5-6% hydrogen peroxide. Selectivity of reaction is close to 100% and productivity of catalytic oxidation 5 to 11 g/l-g H₂O₂. EFFECT: improved efficiency of process. 11 cl, 4 tbl

Description

 The present invention relates to a method for producing hydrogen peroxide by direct catalytic oxidation of hydrogen by oxygen. The invention also relates to a catalyst for such a method and a method for producing a catalyst.

 Hydrogen peroxide is commercially prepared using the known Riedl-Pfleiderer process. According to this two-step process, anthraquinone in a carrier solvent called a “working solution” is circulated between the oxidation reactor and the hydrogenation reactor to convert hydrogen and oxygen to hydrogen peroxide. All changes to this method were concentrated on changing the type of anthraquinone, the composition of the working solution, and the type of catalyst used.

 A common catalyst is palladium, a skeletal nickel hydrogenation catalyst or an inert support of nickel boride. The catalyst may be in the form of a suspension or a fixed bed. The presence of hydrogen in this reaction at high partial pressures contributes to the explosion. The method is characterized as complex and requiring large capital expenditures.

 Methods for the direct oxidation of hydrogen and oxygen to hydrogen peroxide provide an opportunity to create a less expensive method. Methods of this kind have been proposed before, but they did not turn the knowledge of inventors into a source of profit. Difficulties encountered in the previously proposed methods include a low concentration of the product, low selectivity (which leads to a large consumption of hydrogen), low reaction rate, dangerous working conditions (especially the requirements for the partial pressure of hydrogen in the explosion region) and a high acid content.

A known method of producing hydrogen peroxide by direct oxidation of hydrogen by oxygen in an acidic aqueous medium in the presence of Cl ^- ions and a catalyst containing at least one group YIII metal supported on a carbon-containing support in an autoclave with stirring [1]
The disadvantages of this method are the low concentration of the resulting hydrogen peroxide, the low selectivity of the process and the reaction rate, which does not allow the process to be carried out at low acid concentrations and below the hydrogen explosion region.

A known catalyst for producing hydrogen peroxide, comprising a carbon-containing carrier and a Group VIII metal deposited on it [1]
The disadvantages of the known catalyst are the inability to ensure with it a high selectivity of the process and a high reaction rate, which leads to a low concentration of the resulting hydrogen peroxide.

A known method of producing a catalyst for the process of producing hydrogen peroxide, comprising evaporating a suspension containing a chloride of a metal of group VIII and a solid carbon-containing catalyst carrier, followed by obtaining a solid precipitate in an atmosphere of hydrogen at elevated temperature [2]
The disadvantage of this method is the inability to obtain a catalyst free from the above disadvantages.

 The invention solves the problem of developing a method for producing hydrogen peroxide by direct catalytic oxidation of hydrogen by oxygen, which provides a significant concentration of the resulting hydrogen peroxide with high selectivity and reaction rate, as well as a catalyst for this process and a method for producing such a catalyst.

 The present invention is based on many surprising discoveries made by studying the direct catalytic oxidation of hydrogen by oxygen in an acidic aqueous medium and using a catalyst containing a Group VIII metal on a support. First, the inventors have found that the nature of the catalytic support used is important. Typically, the carriers used in the known methods were either highly hydrophobic or highly hydrophilic. The inventors have found that hydrophilic-hydrophobic equilibrium in a catalytic support (and thus in the resulting catalyst) is desired. The catalyst (and catalyst support) must be partially hydrophobic so that gaseous reactants (hydrogen and oxygen) come into contact with the catalytic surface. However, the catalyst (and the catalyst support) must also be partially hydrophilic or partially wettable so that hydrogen peroxide formed on the surface of the catalyst diffuses into the liquid phase. If hydrogen peroxide remains bound to the surface of the catalyst for some time, water is formed.

 The inventors have found that hydrophobic-hydrophilic equilibrium is preferably achieved using fluorinated or partially wettable carbon. The degree of fluorination is preferably 10-65%, more preferably 20-50% F.

 The second surprising discovery was that the selectivity of the reaction for hydrogen peroxide can be increased by adding a source containing sodium ions and chloride ions. This can be achieved at the stage of preparation of the catalyst, as will be described later, or by adding a source of these ions to the aqueous acidic reaction medium. In fact, since these soluble ions are constantly removed from the aqueous reaction medium during the process, it is preferable to supply these ions to the reaction medium during the entire process, or at least when a decrease in catalytic activity is noted.

 The most economical source of these ions is NaCl. A quantity of 3 to 30 wt.% Is desirable. relative to the catalyst.

 The inventors have noticed that the catalytic activity of the catalyst (Pd on a fluorinated carbon support) decreases as it is used. Having discovered that the degree of fluorination is important for the catalyst, the inventors tried to add a fluoride ion source to the reaction medium. This led to an important third discovery, consisting in the fact that a source of fluoride ions in an aqueous medium stabilized the catalyst against a decrease in catalytic activity. A suitable source of fluoride ions is NaF, which can be included in an amount of from 2 to 10 wt. relative to the catalyst.

Upon receipt of the supported catalyst, the inventors made a fourth important discovery. The inventors have found that it is preferable to suspend together with a metal of group VIII (preferably Pd) sodium citrate in a solution, for example in aqueous. It is believed that this leads to the formation of a sodium Pd citrate or colloid complex, and two important conclusions have been made. When the catalyst support is impregnated with the sodium Pd-citrate complex, the metal is firmly attached to the support and is well distributed on the surface of the support. In a preferred embodiment of the invention, this catalyst preparation method also provides the desired sodium ions and chloride ions in the catalyst, with sodium ions being supplied from sodium citrate and chloride ions from group VIII metal chloride (e.g., PdCl ₂ ), which is initially suspended with sodium citrate.

The combination of the above findings led to a method for producing hydrogen peroxide, which can be carried out to obtain significant concentrations of H ₂ O ₂ (5-6%) with high selectivity (up to 100%) and a good reaction rate (5-11 g / h H ₂ O ₂ ), which makes it possible to work at hydrogen pressures below the detonation limit and at moderate acidity (for example, 6 g / l H ₂ SO ₄ ).

Generally speaking, the invention provides a method for producing hydrogen peroxide by direct oxidation of hydrogen by oxygen in an acidic aqueous medium in the presence of Cl ^- ions and a catalyst containing at least one Group VIII metal supported on a carbon-containing support in an autoclave with stirring, and as a support catalyst use fluorinated or partially wettable carbon and the process is carried out at a temperature from the freezing point of the aqueous medium to 60 ^o C, a pressure in the reactor of 2.5-20 MPa and a partial pressure of hydrogen n below the knock limit.

The process is conducted in the presence of Na ⁺ , F ^- and is provided with the addition of NaCl and NaF in an amount of 3-30% and 2-10% by weight of the catalyst, respectively.

 NaCl and NaF are introduced into the autoclave simultaneously with the catalyst or after a decrease in its catalytic activity.

 Fluorinated carbon is used with a fluorination degree of 10-65% and Pd is used as a group VIII metal.

 The invention also provides a catalyst for producing hydrogen peroxide, comprising a carbon-containing support and a Group VIII metal deposited thereon, moreover, it contains fluorinated carbon with a fluorination degree of preferably 10-65% or partially wettable carbon as a carbon-containing support, and preferably a Group VIII metal Pd in an amount of 0.1-10 wt.

 The invention also provides a method for producing a catalyst, comprising evaporating a suspension containing a Group VIII metal chloride and a solid carbon-containing carrier, followed by reduction of the obtained solid precipitate in a hydrogen atmosphere at an elevated temperature, and a sodium citrate solution is first added to the Group VIII metal chloride solution, then the resulting solution is heated the mixture and methanol and a catalyst support are introduced into it, in which case fluorinated or partially wettable carbon is used.

As the metal chloride, PdCl _{2 is} preferably used in an amount sufficient to provide 0.1-10 wt. in the catalyst, and fluorinated carbon is used preferably with a degree of fluorination of 10-65%
Group VIII metal is used in a catalytically effective amount in the catalyst of this invention. Although metals such as Pt, Ru, Rh, Ir are catalytically active to produce hydrogen peroxide, Pd is the preferred metal. Mixtures of Group VIII metals may also be used. The metal is usually used in the form of a salt, preferably chloride, for example PdCl ₂ .

 Group VIII metal is used in the form of a supported catalyst, the catalyst support being partially hydrophobic and partially hydrophilic, as will be described later.

The carrier must have a surface area in the range of 50 m ² / g to 1500 m ² / g. A surface area of about 130 m ² / g was found to be suitable. Preferably, the carrier is used in the form of individual particles or granules (a particle size of less than 1 μm is suitable), but it can also be deposited on a carrier of another material, for example ceramic granules or rings, which is known in the art.

As described above, the catalyst carrier (and the formed catalyst) must have a hydrophobic-hydrophilic equilibrium, which provides access of reagents (H ₂ + O ₂ ) to the surface of the catalyst (in the aquatic environment), which ensures the release of the formed H ₂ O ₂ into the aqueous . Highly hydrophobic catalyst supports that are known in the art are unsuitable. Hydrophobicity is often determined by the "corner angle" in accordance with Young's theory. Generally acceptable is a catalyst support having a contact angle of 90 ^° , which is a hydrophobic catalyst support. The catalyst carriers in accordance with the present invention have a contact angle of less than 90 ^o .

 Two preferred catalyst supports of the present invention are partially wettable pre-fluorinated carbon and Vulcan carbon. As for the first material, it must be borne in mind that the degree of fluorination affects the hydrophobic-hydrophilic nature of the catalysts. A degree of fluorination of 10-65% F is preferred. A degree of fluorination of 20-50% F is more preferred, and a degree of fluorination of 28% F is found to be sufficient. Partially Wettable Carbon Vulcan is a specially treated activated carbon available from Cabot, USA .

 The catalyst is preferably prepared by first preparing a complex or colloid of a Group VIII metal with sodium nitrate. This provides a stronger attachment of the metal to the catalyst carrier and contributes to a better distribution of the metal on the surface of the catalyst.

 To this end, sodium citrate and a Group VIII metal are suspended in a solution, for example aqueous, and heated to form a colloid. Heating is carried out to the boiling point for at least 6 hours. The amount of metal of group VIII used must be sufficient to ensure its content of 0.1-10 wt. in the final catalyst. As for Pd, its amount in the catalyst is 0.7 wt. is sufficient.

The catalyst carrier is impregnated with a metal-colloidal solution. Preferably, a reagent is added to reduce the density of the suspension and reduce the tendency of the catalyst to surface on the surface of the metal-colloidal suspension of the catalyst carrier. Methanol is suitable for this purpose. After suspension, the solution was evaporated and the catalyst was reduced under a hydrogen atmosphere (preferably for 14 hours at 300 ^° C).

According to the preferred embodiment described above, the catalyst inherently contains the desired sodium ions and chloride ions, which have been found to improve the subsequent production of H ₂ O ₂ . Sodium ions are provided via sodium citrate, while chloride ions are provided via the PdCl ₂ salt. When the catalyst is prepared in this way, it can initially be used without adding NaCl to the reaction medium.

The method of producing hydrogen peroxide is preferably carried out in an autoclave with a stirrer, for example a flowing slurry autoclave, at temperatures between the freezing point of the liquid medium and 60 ^o C, preferably in the range 0-25 ^o C. Since the reaction is highly exothermic, cooling to these temperatures is usually necessary .

 The reactor is preferably charged with catalyst and additives (if desired NaCl and NaF) before adding an acidic aqueous solution. As previously indicated, these additives can be added later during the reaction as soon as the catalytic activity begins to decrease. Additive NaCl is preferably administered in an amount of 3-30 wt. (relative to the catalyst), and the NaF additive is preferably added in an amount of 2-5 wt. relative to the catalyst.

The acidic solution is preferably a slightly acidic solution. An economical solution is H ₂ SO ₄ . Suitable is a concentration of sulfuric acid of 0.5-1 wt.

 It was found that higher concentrations of acid do not contribute to the improvement of the method.

 Then, gaseous oxygen and hydrogen are fed into the reactor. The main advantage of the method of this invention is that it can be carried out at a partial pressure of hydrogen below the knock limit. By such a limit is meant the highest percentage of hydrogen in the reaction atmosphere, which will indicate the range of detonation, which is measured using a standard MSA device.

Usually use a partial pressure of H ₂ below 4 vol. The total pressure in the reactor will be in the range of 500 lbs / ⁱⁿ² (3.5 MPa) to 3000 lb / ⁱⁿ² (20 MPa), preferred is the range from 1000 lbs / ⁱⁿ² (6,7MPa) to 1500 lb / inch ² (10 MPa). Oxygen can be supplied in pure form or, more preferably, in combination with nitrogen. Can be used such a low oxygen content, which is present in the air. The preferred feed gas to the reactor consists of 3.2% H ₂ , 10% Na ₂ and 86.8% O ₂ .

 The reaction can be carried out continuously or intermittently. Since the additives NaCl and NaF are water soluble, these additives should be added continuously since they are washed out of the system.

 Catalyst Preparation

Example 1. Sodium citrate (8.07 g) was dissolved in 807 ml of water, to which 56 ml of 6.7 x 10 ^-7 M PdCl _{2 was} added. Then this mixture was diluted with 403 ml of water. The mixture was heated to boiling for 10 hours to form a colloidal solution of sodium Pd-citrate. To it was added 2 g of fluorinated carbon (fluorine content 28% average particle size less than one micrometer, surface area 130 m ² / g) together with 100 ml of methanol. The solution was evaporated and the solid residue was reduced in hydrogen for 14 hours at 300 ^° C. The resulting catalyst contained approximately 0.7% Pd. The catalyst was a partially wettable, black, slightly sticky powder.

Example 2. Other catalysts were obtained in accordance with the procedure described in example 1, using fluorinated carbon carriers, similar in all other respects, but with fluorine content of 10 and 65%, respectively
Example 3. Another catalyst was prepared in accordance with the procedure described in example 1, but using a partially wettable carbon carrier Vulcan, available from Cabot, USA (Vulcan 9A32CS-329).

 Obtaining hydrogen peroxide.

Example 4. 450 ml flowing slurry autoclave with a stirrer was loaded as follows: 0.3 g of catalyst (example 1), 0.03 g of Pd, 50 ml of 0.6 wt. H ₂ SO ₄ .

The autoclave is inserted in an ice bath, maintained at 0 ^o C. To the autoclave was fed hydrogen and oxygen, and the pressure increased to 1000 lbs / in ² at a total gas flow rate was 300 ml / min (about 3.2. H _2, 10 vol. N ₂ and 86.8 vol. O ₂ ) and vigorous stirring. The degree of product conversion and selectivity were analyzed after 1, 3, 6, and 10 hours. The gas phase was analyzed by gas chromatography using a thermal conductivity detector. In the analysis, argon was used as the carrier gas. H ₂ , N ₂ and O ₂ in the feed gas were separated using a 10 ft x 1/8 inch diameter stainless steel column filled with a Porapak QS 80-100 mesh.

The liquid product was titrated with potassium permanganate to quantify the formed H ₂ O ₂ . The equation for titration is as follows:
5H ₂ O ₂ + 2KMnO ₄ + 3H ₂ SO ₂ -> 2MnSO ₄ + K ₂ SO ₄ + 8H ₂ O + 5O ₂ .

.The concentration of H ₂ O _{2 was} measured directly by titration and confirmed by ultraviolet spectroscopy. The degree of conversion of H _{2 was} calculated as the ratio
Initial hydrogen content measured content

.

где

где F поток газа,
t время реакции.The selectivity of H ₂ O _{2 was} calculated on the basis that if all of the reacted H ₂ turned into H ₂ O ₂ , the selectivity would be 100%. Thus

Where

where F is the gas flow,
t reaction time.

 The results are presented in table 1.

Example 5. This example is included in order to show the results of obtaining H ₂ O ₂ without the addition of NaCl. The catalyst obtained after several experiments in accordance with example 4 was thoroughly washed and filtered to remove NaCl. When the washed catalyst was then used in the preparation of H ₂ O ₂ (the same conditions as in Example 4, without the addition of NaCl), the following results were obtained after 10 hours: 1.32 wt. H ₂ O ₂ , degree of conversion of H ₂ 25.5% selectivity of H ₂ O ₂ 30%
Example 6. This example illustrates the stabilizing effect of NaF. To obtain H ₂ O _{2, the} procedure described in Example 4 was repeated. After the reaction within 8 days without adding NaF, the degree of hydrogen conversion dropped to 33%. When NaF was added to the aqueous medium in an amount of 0.01 g, the degree of hydrogen conversion after 8 days was 44%
Example 7. This example illustrates the importance of hydrophobic-hydrophilic equilibrium in a catalyst support. The catalysts of example 2 (fluorine content of 10 and 65%) was subjected to reaction conditions similar to the conditions of example 4, and after 10 hours the results are shown in table.2.

Example 8. This example illustrates the effect of various amounts of NaCl added to the reaction medium. The catalyst of example 1 (0.7 wt. Pd on a fluorinated carbon support) reacted under conditions similar to the conditions of example 4 (0.3 g of catalyst, 50 ml wt. H ₂ SO ₄ , various amounts of NaCl, 3.2 vol. H ₂ , 10 vol. N ₂ balanced with oxygen, 0 ^o C, 1000 pounds / inch ² , the gas velocity of 300 ml / min, reaction time 10 h). The results are presented in table.3.

Example 9. This example illustrates the effect of various amounts of NaF added to the reaction medium. The procedure of Example 4 was repeated, but using 0.0261 g of NaCl and 0.0054 g of NaF. After 6 hours, 4 wt. H ₂ O ₂ , the degree of hydrogen conversion was 61% and the selectivity of H ₂ O ₂ 63%. This procedure was repeated using 0.0328 g of NaCl and 0.078 g of NaF. After 6 hours, 3.32 wt. H ₂ O ₂ , the degree of hydrogen conversion was 58% and the selectivity of H ₂ O ₂ 60%. This procedure was repeated using 0.03 g of NaCl and 0.0290 g of NaF. After 10 hours, the concentration of H ₂ O ₂ was 2.16 wt. the degree of conversion was 52% and the selectivity of H ₂ O ₂ 23.6%
Example 10. In this example, it is illustrated that NaBr and KBr do not provide the same benefits that the NaCl or NaF additives of this invention provide. The procedure of Example 4 was repeated using, instead of NaCl, 0.0361 g of KBr (the acidic solution was 1% H ₂ SO ₄ ). After 10 hours, 1.1% wt. H ₂ O ₂ , the degree of hydrogen conversion was about 4% and the selectivity of H ₂ O ₂ 100%
This procedure was repeated using, instead of NaCl, 0.0308 g of NaBr. After 10 hours of reaction time, 1.1 wt. H ₂ O ₂ , the degree of conversion was 3% (below the threshold sensitivity C), and the selectivity of H ₂ O ₂ was about 100%
Example 11. This example illustrates the preparation of H ₂ O ₂ using a variable catalyst carrier, partially wettable carbon Vulcan. The catalyst of example 3 was reacted under the conditions of example 4, and the results presented in table 4 were obtained.

 From the presented examples and tables it follows that the invention allows to obtain hydrogen peroxide with a concentration of 5-6% by direct catalytic oxidation of hydrogen with oxygen at high selectivity of the reaction close to 100%, as well as a catalyst for this process and a method for producing such a catalyst.

Claims (9)

1. A method of producing hydrogen peroxide by direct oxidation of hydrogen by oxygen in an acidic aqueous medium in the presence of Cl ^- ions and a catalyst containing at least one Group VIII metal supported on a carbon-containing support in an autoclave with stirring, characterized in that the support of said catalyst is use fluorinated or partially wettable carbon, and the process is conducted at a temperature of from the freezing point of the aqueous medium to 60 ^o C, a reactor pressure of 20.0 2.5 MPa and a hydrogen partial pressure lower limit Detoni ii. 2. The method according to claim 1, characterized in that the process is carried out in the presence of Na ⁺ , F ^- and provide it with the addition of NaCl and NaF in the amount of 3 30% and 2 10% by weight of the catalyst, respectively.  3. The method according to claim 2, characterized in that NaCl and NaF are introduced into the autoclave simultaneously with the catalyst or after reducing its catalytic activity. 4. The method according to claim 1, characterized in that the use of fluorinated carbon with a degree of fluorination of 10 65%
5. The method according to claim 1, characterized in that Pd is used as the metal of group YIII.  6. A catalyst for producing hydrogen peroxide, comprising a carbon-containing support and a Group VIII metal deposited on it, characterized in that it contains fluorinated or partially wettable carbon as a carbon-containing support. 7. The catalyst according to claim 6, characterized in that it contains fluorinated carbon with a degree of fluorination of 10 65%
8. The catalyst according to claim 6, characterized in that as the metal of group VIII it contains Pd in an amount of 0.1 to 10.0 wt.  9. A method of producing a catalyst for a hydrogen peroxide production process, comprising evaporating a suspension containing a Group VIII metal chloride and a solid carbon-containing catalyst carrier, followed by reducing the resulting solid precipitate in a hydrogen atmosphere at elevated temperature, characterized in that the Group VIII metal chloride solution is first added a solution of sodium citrate, then the resulting mixture is heated and methanol and a catalyst support are introduced into it, using fluorinated or partially o wettable carbon. 10. The method according to claim 1, characterized in that as the chloride of the metal of group VIII use PdCl ₂ in an amount sufficient to provide 0.1 to 10.0 wt. Pd in the catalyst.  11. The method according to claim 9, characterized in that the use of fluorinated carbon with a degree of fluorination of 10 65%

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