Catalyst and process for the direct synthesis of hydrogen peroxide

Process for the direct synthesis of hydrogen peroxide

Full description

Background of the invention

The present invention relates to a bimetallic catalyst and a process for the direct synthesis of hydrogen peroxide from hydrogen and oxygen in which said catalyst is used.

Hydrogen peroxide is a commercially important compound that is widely used as a bleach in the textile and paper industries, as a biocide in the environmental field, and in oxidation processes in the chemical industry. Examples of such processes include those in which titanium silicalite is used as catalysts, such as the introduction of epoxidation to olefins (European Patent No. 100-EP 119), the introduction of ammoximation to carbonyl compounds (US Patent No. 198 794 4), and the oxidation of ammonia to Hydroxylamine (US Patent No. 819,320,5) and hydroxylation of aromatic hydrocarbons

(US Patent No. 783,3694).

The industrial production of aqueous solutions of H2O2 is known by a complex two-step process. In this process, a solution of an anthraquinone, such as butylanthraquinone or ethylantbraquinone, is hydrogenated in an organic medium that is not soluble in water, and then oxidized with air to produce H2O2, which is subsequently extracted into an aqueous phase.

This procedure is considered economically expensive due to the high investment costs required for the complex production unit involved and the necessity of separating and conditioning the by-products generated during the oxidation phase and preserving and reintegrating the anthraquinone solution before its reuse.

Processes for the direct synthesis of hydrogen peroxide from H2 and O2 have been demonstrated in the field to overcome these drawbacks. These processes generally use a catalytic system consisting of a precious metal, specifically platinum or its alloys, in the form of salts or loaded metals.

For example, US Patents Nos. 4,772,458 and 4,832,938 describe a process for synthesizing aqueous solutions of H2O2 using a palladium-based and/or platinum-based catalyst loaded on carbon, in the presence of hydrogen ions and bromide ions. Amounts of acids ranging from 2.5 to 10 g/L are generally needed to obtain concentrations

H2O2

The use of large quantities of acids creates serious problems associated with dissolution of the active phase (metal) of the catalyst in the reaction medium, with subsequent instability of both the catalyst and the resulting hydrogen peroxide solution.

In addition, under these conditions the resulting H2O2 solutions are difficult to use due to the high acid content. These processes are also carried out under critical conditions, such that H2 concentrations higher than 5% (17% or more) are used as an additive to the reaction mixture and therefore fall within the explosive limits of H2/O2 mixtures.

European Patent No. 492064-EP describes a process for the synthesis of hydrogen peroxide from hydrogen and oxygen using a platinum-based catalyst loaded on a halogenated resin, specifically brominated styrene/divinylbenzene resin.

The reaction is carried out in water, in the presence of an acid chosen from sulfuric, phosphoric, or nitric acid. This process works despite the H2O2 concentrations

Which amounts to about 0.58%.

European Patent No. EP-504741 describes a process for the synthesis of H2O2 from hydrogen and oxygen, in which an acid- or superacid-based catalyst is used as a carrier material made from oxides of molybdenum, zirconium, or tungsten.

Working according to this process, hydrogen peroxide is obtained in concentrations not exceeding 1%. US Patent No. 921,320 5 describes a process for the synthesis of H2O2 from hydrogen and oxygen, in which a palladium- or platinum-based catalyst loaded on a water-insoluble heterogeneous polyacid is used. The reaction is carried out in water in the presence of bromide ions (0.5 mmol/L of sodium bromide). H2O2 concentrations equal to approximately 1.1% are obtained.

Therefore, these processes known in the prior art are characterized by low productivity, weak reaction selectivity, and the production of H2O2 solutions that are too diluted to be suitable for industrial and economic use.

Italian patent application No. 01843-98 MI, filed by the applicant, relates to the direct synthesis of hydrogen peroxide using a platinum and/or platinum-based catalyst that is impregnated in combination with a sulfonate-infused activated carbon.

General description of the invention

It has now been found that by conducting the reaction between hydrogen and oxygen in the presence of a bimetallic catalyst prepared by successively and alternately dispersing the materials producing the individual metallic components of the catalyst onto a carrier, the defects of the known art described above can be overcome. The mentioned preparation method also allows adjustment of the catalyst activity and selectivity, hydrogen peroxide concentration or hydrogen consumption, in relation to the process requirements and the availability of raw materials, for example low-cost hydrogen.

Specifically, the use of these catalysts gives the following advantages: - The possibility of using very low quantities of halides (less than 10-4 moles/l) and free acids (H+ less than 10-2 moles/l) in the reaction medium. This has beneficial effects on the stability of the catalytic system and the H2O2 solutions obtained, thus allowing the possibility of direct use of the previous solutions in oxidation processes. The presence of small quantities of halides and acids is not considered a shortcoming in direct use in previous reactions, such as the possible introduction of salts or acids in subsequent processes in smaller quantities than possible.

Producing hydrogen peroxide solutions in concentrations suitable for direct use and economic suitability in oxidation processes, generally ranging from 2% to 10% by weight.

Possibility of performing the reaction under high safety conditions. In fact, less than 4% by volume hydrogen means good operation outside the detonation range of chemically inactive H2O2 mixtures.

Detailed description

Accordingly, the present invention relates to a bimetallic catalyst obtained by successively and alternately dispersing materials producing the individual metallic components of the catalyst on the carrier, and to a process for the synthesis of hydrogen peroxide by direct reaction of hydrogen with oxygen, in a solvent medium containing a halogen-introduced promoter and an acidic promoter, in The presence of the aforementioned catalyst. Specifically, the catalyst used for the purposes of the present invention is obtained by:

(a) Preparation of solutions or suspensions of materials producing individual metallic components in the catalytic system,

(b) successively dispersing the solutions or suspensions obtained in step (a) onto a carrier,

(c) Treating the catalyst using a metal reducing agent and drying at 120-140 °C between each dispersion process.

In preparing the aforementioned catalyst, steps (b) and (c) may be repeated once or several times. The metal components of the catalyst are selected from platinum group components. Platinum and palladium are preferably used.

In these catalysts, palladium is naturally present in an amount ranging from 0.01 to 5% by weight, and platinum is present in an amount ranging from 0.01 to 1% by weight, with an atomic ratio between platinum and palladium.

Ranging from 0.1/99.5 to 50/50.

It is preferable for palladium to be present in an amount ranging from 0.4 to 2% by weight, and platinum to be present in an amount

It ranges from 0.05 to 0.5% by weight, with an atomic ratio between palladium and platinum ranging from 99/1 to 70/30.

The active ingredients may be dispersed onto the carrier material by precipitation, impregnation or absorption starting from solutions of their salts or soluble complexes selected from acetates, halides and nitrates. Reduction of catalyst components to the metallic state can be accomplished by thermal and/or chemical treatment with reducing agents such as hydrogen, sodium formiate, and sodium citrate, using preparation methods well known in the art. The inert carrier material can be activated carbon, silica, alumina, silica-alumina, zeolite and other materials well known in the art. Activated carbon is preferred for preparing catalysts useful for the invention.

The activated carbon that can be used for the purposes of the present invention is one that has a low ash content and a surface area of at least 100 m2/g, and specifically one that has a surface area greater than 300 m2/g.

A sulfonated activated carbon described in Italian Patent Application No. 01843-98 MI may also be used for the purposes of the invention.

The carrier materials can be in the form of powder, granules, pellets, etc.

Before loading individual metal-producing materials, the activated carbon may be subjected to treatment such as washing with distilled water or treatment with dilute acids, bases or oxidizing agents, for example acetic acid, hydrochloric acid, sodium carbonate and hydrogen peroxide.

Specifically, it was observed that the catalyst resulting from dispersing palladium first and then platinum on the carrier material is the most active, while that resulting from dispersing platinum first and then platinum in sequence is more selective.

The catalyst of the present invention is specifically characterized in a process for the direct synthesis of hydrogen peroxide from...

Hydrogen and oxygen in a solvent in the presence of a halogen-incorporated promoter and an acidic promoter.

The catalyst is used in a catalytic amount that generally ranges from 10-6 to 10-3 moles of total metals contained in the catalyst per liter of reaction medium.

Distinctive results are obtained using quantities of catalyst ranging from 10-4 to 10-3 moles in relation to the total metals contained in the catalyst per liter of reaction medium. The reaction solvent can consist of water, C1-C3 alcohol, or mixtures thereof. Among the C1-C3 alcohols, methanol is preferred for the purposes of the present invention. Among the mixtures, it is preferable to use a mixture of methanol and water with a weight ratio ranging from 50/50 to

0.1/99.9, and more preferably from 10/90 to 9 9/1.

An acid promoter can be any substance capable of generating H+ ions in a liquid reaction medium and is generally made from inorganic acids such as sulfonic acids. It is preferable to use sulfuric acid and phosphoric acid. The acid concentration generally ranges from 20 to 1000 mg per kg of solution and more preferably 50 to 500 mg per kg of solution.

A halogenated promoter can be any substance capable of generating hydrogen ions in the liquid reaction medium. It is preferable to use materials capable of generating bromide ions. These materials are generally chosen from hydrobromic acid and its salts that are soluble in the reaction medium, for example sodium bromide, potassium bromide, sodium bromate, or ammonium bromate. Hydrochloric acid, sodium bromide, and potassium bromide are particularly preferred. The concentration of the halogenated booster generally ranges from 0.1 to 50 mg per kg of solution and preferably from 1 to 10 mg per kg of solution.

The process of producing hydrogen peroxide is carried out by the reaction of oxygen and hydrogen in the reaction medium in the presence of the catalyst and promoters and in the presence or absence of an inert gas chosen from nitrogen, helium and argoir. The gas is preferably nitrogen. The molecular ratio of H2/O2 in the feedstock ranges from 1 to 2, and from 1 to 3, and the hydrogen concentration in the gas phase, which is in contact with the liquid reaction medium, is traditionally maintained at a value less than 4.5% molar, outside the explosion limits of the inert gas mixture /H2/O2. .

According to one embodiment of the process of the present invention, the reaction can be performed using air instead of oxygen.

The reaction is typically carried out at temperatures ranging from -5°C to 90°C, preferably from 2°C to 50°C, and at a total pressure higher than atmospheric pressure, preferably from 50 to

300 Pressure .

The process according to the present invention may be performed in batches, or preferably, by continuous use of a suitable-for-purpose reactor selected from those described in the art. When operating under the above conditions, hydrogen peroxide can be produced under safe conditions with

Production yield normally ranges between 30 and 200 g of H2O2 (expressed as b

100% H2O2) per liter of reaction medium per hour and with a selectivity of molecular ratios towards the formation of H2O2, with reference to the hydrogen used, in the range from 60% to 90%. Hydrogen peroxide solutions produced in this way can be used directly in oxidation processes involving the use of H2O2 without the need for costly intermediate treatments such as deacids and solvents.

The process of the present invention enables the transfer of chemical agents to H2O2 with high conversion ratios and high selectivities and to obtain H2O2 solutions that are not acidic or contain acidic residues and/or minor salts.

The following examples, which are intended to describe the present invention in greater detail, should not be considered as limiting the scope of the invention.

Example No. (1):

Catalyst preparation:

(a) 8 g of Martim Ben activated charcoal in powder form (Ceca 2S/E) was packed in a 0.5 L glass bottle, containing 90 ml demineralized water and 0.28 g of NaCO3. The suspension remains at room temperature (20-25°C), under stirring, for 10 minutes. Then add 0.101 g of H2PtCl6 solution (8% by weight of Pt) diluted dropwise in 10 ml of water.

The suspension was kept at room temperature for 10 minutes and then heated in a water bath for 10 minutes at 90°C. Then a solution containing 0.76 g of sodium formiate in 10 ml of water was added and stirring was continued at 90 C for two hours. After cooling at room temperature, the suspension is filtered and the extracted charcoal is washed with distilled water until the chlorides disappear, then dried in an oven at 120°C for two hours.

(b) The carbon resulting from this process is resuspended in a solution containing 0.4 g Na2C03 in 90 ml water and then treated following the same procedure as described in step (a), but using a solution of 0.8 g Na2PdCl4 at 10%. Pd, instead of the solution H2PdCl6. After drying at 120 C, a catalyst containing 1%' of Pd and 0.1%' Pt on activated carbon is obtained.

Example No. (2):

The same procedure as described in Example (1) is followed, but the arrangement of the Pt-Pd precipitate is reversed. In step (a) the solution Na2PdCl4 is used, and in step (b) the solution HPdCl6 remains at the same quantities. A catalyst containing 0.1% Pt and 1% Pd is obtained on activated carbon.

Example No. (3): Comparative:

Preparation of co-impregnated catalyst:

8 g activated maritime pine powder (Ceca 2S/E) is packed in a 0.5 liter glass bottle, containing 90 ml demineralized water and 0.28 g Na2CO3. The suspension remains at room temperature (20-25°C) under stirring for 10 minutes.

Successively add 0.101 g of H2PdCl6 solution (8% by weight Pt) and 0.8 g of Pd (10% Na2PdCl4) diluted in 10 ml of water, drop by drop, under stirring. The suspension was kept at room temperature for 10 minutes and then heated in a water bath for 10 minutes at 90°C. Then a solution containing 0.76 g of sodium formate in 10 ml of water is added and stirring is continued at 90 C for two hours.

After cooling at room temperature, the suspension is filtered and the extracted charcoal is washed with distilled water until the chloride salts disappear, then dried in an oven at 120°C for two hours.

The final catalyst contains 1% Pd and 0.1% Pt, and the active phase is obtained by co-impregnation of Pd and Pt.

Example No. (4) comparative:

The same procedure is followed as described in Example (3) using only the Pd salt in the preparation. A catalyst containing 1% Pd is obtained on activated carbon.

Example No. (5) comparative:

The same procedure is followed as described in Example (3) using only the Pt salt in the preparation. A catalyst containing 0.1% Pt activated carbon is obtained.

Example No. (6): H2O2 synthesis:

An industrial unit is used for semi-industrial production, which consists of a Hastelloy C autoclave equipped with a thermostatic control system, a magnetic stirrer, a pressure adjustment and control system during the reaction, a filter for continuous removal of the liquid phase containing the reaction products, a feeding system with the solvent mixture in which the reaction takes place, and a set of devices. To adjust and control mortal feed materials. The reaction is then subjected to continuous analysis of hydrogen and oxygen in the feedstock and at the reactor outlet.

Selectivity to the converted hydrogen is calculated based on the concentration of H2O2 in the reaction filament stream and on the analysis of H2 leaving the reactor. The concentration of H2O2 formed is determined by titration with potassium permanganate.

0.6 g of catalyst prepared as described in Example 8 and 200 g of a methanol:water solution (5/95 by weight) containing 6 ppm HBr and 300 ppm H2SO4 are filled into the reactor.

The reactor pressure is equalized, without stirring, at 0 1 bar using a gas mixture containing 3.6% H2, 10% O2 and 86.4% N2. Stirring then begins at 800 rpm, and the pressure is maintained with the introduction of a constant stream, 700 liters (Nl), of the same gaseous mixture and 300 g/h of a methanol:water solution of the same composition as defined before, into the same the time. The temperature inside the reactor is maintained at 6°C. The results are presented in Table (1).

<img file="SA1475B1_D0001.tif" />

Example No. (7):

Example (6) is repeated using the catalyst prepared in Example (2).

The results obtained are listed in Table No. (2).

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Example No. (8):

Example No. (6) is repeated using the catalyst that was prepared in Example No. (2), but using carbon with sulfonate additives as a carrier material, which was prepared according to what was described in Example No. (1) in Italian Patent No. 1843 MI 98-AO.

The results obtained are listed in Table (3).

<img file="SA1475B1_D0003.tif" />

Example No. (9) comparative:

Example No. (6) is repeated using the catalyst prepared in Example No. (3), and the results obtained are listed in Table No. (4):

<img file="SA1475B1_D0004.tif" />

Example No. (10):

Example No. (6) is repeated using the catalyst prepared in Example No. (4). The results obtained are listed in Table (5).

<img file="SA1475B1_D0005.tif" />

Example No. (11):

Example No. (6) is repeated using the catalyst prepared in Example No. (5). The results obtained are listed in Table (6).

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