RU2248323C2 - Method for selective oxidation of carbon monoxide in hydrogen- containing stream - Google Patents

Abstract

FIELD: selective oxidation of carbon monoxide in hydrogen-containing stream.

SUBSTANCE: invention relates to method for selective oxidation of carbon monoxide to carbon dioxide in raw material containing hydrogen and carbon monoxide in presence of catalyst comprising platinum and iron. Catalyst may be treated with acid. Certain amount of free oxygen is blended with mixture containing hydrogen and carbon monoxide to provide second gaseous mixture having elevated ratio of oxygen/carbon monoxide. Second gaseous mixture is brought into contact with catalyst, containing substrate impregnated with platinum and iron. Carbon monoxide in the second gaseous mixture is almost fully converted to carbon dioxide, i.e. amount of carbon monoxide in product stream introduced into combustion cell is enough small and doesn't impact on catalyst operation characteristics.

EFFECT: production of hydrogen fuel for combustion cell with industrial advantages.

13 cl, 1 tbl, 4 ex

Description

Field of Invention

The invention relates to the catalytic oxidation of carbon monoxide. In accordance with other aspects of the invention, the invention relates to the selective oxidation of carbon monoxide in the presence of hydrogen. In accordance with another aspect, the invention relates to catalytic compositions effective in the oxidation of carbon monoxide. In accordance with another aspect, the invention relates to the removal of the maximum possible amount of carbon monoxide, preferably all carbon monoxide, from a stream containing carbon monoxide and hydrogen, in particular to provide hydrogen feed for fuel cells.

BACKGROUND OF THE INVENTION

Selective oxidation of carbon monoxide in hydrogen-rich streams is of considerable technical interest for the purification of hydrogen obtained in the reforming process used in the feed gas in the synthesis of ammonia.

Recently, the said selective oxidation process, which is sometimes referred to as the preferred oxidation, has attracted interest due to the possibility of using this technology to provide suitable hydrogen fuel for fuel cells. Since carbon monoxide is also oxidized to produce carbon dioxide used in carbon dioxide lasers, it has previously been found that a catalyst that is suitable for oxidizing carbon monoxide for use in carbon dioxide lasers can be adapted for use in providing hydrogen free carbon monoxide intended for use as a feedstock for fuel cells.

A fuel cell is an electrochemical device that provides the ability to convert the chemical energy of fuels directly into electricity. The exhaust pipe of a fuel cell with a polyelectrolyte membrane (PEM) for the hydrogen-air system is currently considered the best way to adapt this technology to most applications. A PEM fuel cell is most effective when using hydrogen gas as a fuel. Using a fuel processor to generate hydrogen enriched feedstocks at the point of use eliminates the problems associated with the storage and distribution of hydrogen fuel.

A fuel processor can convert fuels, such as alcohol, gasoline, liquefied petroleum gas or natural gas, into a hydrogen-rich stream. Using a steam reforming process, a stream consisting mainly of hydrogen, carbon dioxide and carbon monoxide can be obtained, but the product is usually saturated with water. When this stream is processed in a conversion reactor, the carbon monoxide content is reduced, while a relatively greater amount of hydrogen is provided through the well-known water gas conversion reaction. This reaction provides a product that contains from 0.2 to 2 vol.% Carbon monoxide, which is sufficient to poison the platinum-based catalyst on the PEM anode. It has now been found that to provide hydrogen feed for fuel cells containing carbon monoxide at a commercially suitable level, in addition to other possible ways to remove carbon monoxide to the level necessary to prevent poisoning of the PEM catalyst, the same catalyst can be used that is used to recombination of carbon monoxide and oxygen in carbon dioxide lasers. The operating conditions for the methods are essentially different. Compared to the conditions used to recombine carbon monoxide and oxygen in carbon dioxide lasers, the removal of carbon monoxide by selective oxidation of a stream containing both carbon monoxide and hydrogen can be carried out using the same catalyst used in carbon dioxide lasers by controlling the increased oxygen flow supplied to the oxidation process, increasing the operating temperature of the oxidation process and avoiding the reaction between oxygen and hydrogen.

SUMMARY OF THE INVENTION

There is a need to provide a process that is effective for the catalytic oxidation of carbon monoxide with free oxygen. Another objective of the present invention is to provide a method for converting carbon monoxide (CO) to carbon dioxide CO ₂ in the presence of hydrogen. It is also desirable to provide a method for producing hydrogen fuel for a fuel cell in which carbon monoxide (CO) is converted to carbon dioxide (CO ₂ ) in the presence of hydrogen on a scale that is commercially suitable.

In accordance with this invention, a method for the selective oxidation of carbon monoxide to carbon dioxide in a gaseous mixture containing hydrogen and carbon monoxide is provided. In this method, a certain amount of free oxygen is mixed with a gaseous mixture containing hydrogen and carbon monoxide to obtain a second gaseous mixture having an increased molar ratio of oxygen to carbon monoxide. The second gaseous mixture is contacted with a catalyst containing platinum and iron impregnated on the support material. Carbon monoxide in the second gaseous mixture is thereby substantially completely converted to carbon dioxide. Used in this description, the expression "essentially complete conversion of carbon monoxide to carbon dioxide" or a similar expression means that the amount of carbon monoxide present in the flow of material entering the fuel cell is small enough, so that there is no significant effect on the operation of the PEM catalyst .

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, a method for oxidizing carbon monoxide in a feed stream that also contains hydrogen can be carried out in such a way that CO rather than hydrogen is selectively oxidized, thereby providing means for delivering a high-purity hydrogen stream for operating a fuel cell in which the oxidation of carbon monoxide in hydrogen fuel can be combined to generate hydrogen-enriched feedstocks at the point of use.

The gas entering the oxidation process can be formed by any suitable method, such as mixing before contacting with a hydrogen catalyst that contains a carbon monoxide pollutant with oxygen-containing air anywhere.

The method of oxidizing a feed containing carbon monoxide and hydrogen gas can be carried out at any pressure, for any period of time, at any average hourly gas supply rate and any volumetric ratio of O ₂ to CO, which are suitable for the selective oxidation of CO in the presence of hydrogen in the temperature a range of from about 0 to about 300 ° C., preferably in a range of from about 25 to about 250 ° C., and most preferably in a range of from about 50 to about 200 ° C.

The pressure during the oxidation process generally is in the range of from about 68.9 to about 6890 kPa (about 10 to about 1000 pounds / ^in2), preferably from about 96.4 to about 1378 kPa (about 14 to about 200 lbs / inch ² ).

The ratio of the number of moles of O ₂ in the incoming gas to the number of moles of CO in the incoming gas will usually be in the range from about 0.5 to 8.0 mol O ₂ / mol CO, preferably from 0.5 to 4.0 mol O ₂ / mol CO, most preferably from 0.5 to 1.5 mol O ₂ / mol CO.

The hourly average gas flow rate (cubic cm of incoming gas per cubic cm of catalyst per hour) may range from about 100 to about 200,000, preferably from about 5,000 to about 50,000.

The amount of hydrogen will usually be in the range of about 50-90 vol.%, And the amount of CO at the inlet will usually be in the range of from about 0.1 to about 5 vol.%.

The preparation of the catalyst suitable in this invention can be carried out by the method disclosed in US patent No. 5017357 and US patent No. 4943550, in these patents disclosed methods in which the catalyst is used for the recombination of carbon monoxide and oxygen for carbon dioxide lasers.

As the carrier material for the composition of the substance used as a catalyst in the method of the present invention, any of the well-known carrier materials containing metal oxide can be used. Preferred at present are essentially pure alumina (alumina) titanium dioxide and / or magnesia spinel. More preferably, the support material may comprise at least 95% by weight of Al ₂ O ₃ or magnesium aluminate. These materials are commercially readily available.

The specific surface area of the carrier material, which can be determined by the BET / N ₂ method (ASTM D3037), is usually in the range from about 10 to about 350 m ² / g. The carrier may be spherical, cylindrical, triangular, quadrangular, annular, or it may have an irregular shape. The material of the spherical support typically has a diameter in the range of from about 0.2 to about 20 mm, preferably from about 1 to about 5 mm.

The carrier may also be an inert porous ceramic material having any of the above forms, while it may be coated with alumina and / or magnesia spinel.

Impregnation of the support material with platinum and iron can be accomplished by any suitable method. Typically, platinum compounds and iron compounds are dissolved in a suitable solvent, preferably water, to obtain a solution of the appropriate concentration, usually containing from about 0.005 to about 5.0 g of platinum per cm ³ solution and from about 0.005 to about 5.0 g iron per cm ³ solutions. Suitable compounds of both platinum and iron are, but are not limited to, nitrates, carboxylates and acetylacetonates, with acetylacetonates being preferred. In accordance with this invention, organic solvents such as methanol, ethanol, acetone, ethyl acetate, toluene and the like solvents can be used as solvents for platinum or iron. In practice, acetone is preferred.

The carrier material may be impregnated in a solution containing platinum compounds and / or iron compounds, or it may be sprayed with such a solution to impregnate the carrier. The ratio of the impregnating solution to the carrier material is usually such that the final catalyst composition contains from 0.05 to about 10 wt.% Platinum, preferably from about 0.1 to about 5 wt.% Platinum and from about 0.05 to about 20 weight wt.% iron, preferably from about 0.1 to about 4 wt.% iron. It is also within the scope of this invention to use any weight percent of platinum and iron in which they act as co-promoters of CO oxidation with oxygen. It is currently preferred to spray the solution containing the compounds of both metals onto the carrier, but the metal compounds may also be added individually in any order.

After impregnation, the material of the impregnated carrier is heated to a temperature sufficient to remove the solvent used in the impregnation. An inert gas stream supplied through the surface of the carrier material may be used. For this purpose, a temperature in the range of up to about 250 ° C. is usually sufficient for about one hour.

The dried catalyst is treated by heating in an oxidizing atmosphere, preferably in an atmosphere containing free oxygen (such as air), typically at a temperature in the range of about 80 to about 700 ° C. for a time in the range of about 0.5 hours to about 10 hours. The heat treatment is preferably carried out with a stepwise increase in temperature. Heat treatment is generally carried out at 150 ° C for 1 hour, at 200 ° C for 2 hours and at 400 ° C for 3 hours. Any combination of heating at a temperature for a time sufficient to calcine the impregnated support material to produce at least one platinum oxide, optionally mixed with platinum metal, and at least one iron oxide, satisfies the requirements of the present invention.

After oxidation, the calcined, platinum / iron-impregnated support is subjected to a reduction reaction that can be carried out by any suitable method, preferably at a temperature in the range of from about 20 to about 650 ° C, more preferably from about 200 to about 500 ° C. Any reducing gas, such as a gas containing hydrogen, CO, gaseous hydrocarbons such as methane, mixtures of the above substances and the like, can be used. Preferably, a gas containing free hydrogen is used, more preferably a gas stream of substantially pure hydrogen. The recovery step can be carried out over a suitable period of time from about 1 minute to about 20 hours, preferably from about 1 hour to about 5 hours.

The reconstituted platinum / iron impregnated support may be further treated by contacting with any suitable organic or inorganic acid having a pH of less than about 7. An aqueous solution of nitric acid or carboxylic acid (preferably acetic acid) is preferably used. The pre-reduced platinum / iron-impregnated carrier is preferably soaked in (impregnated) in about 0.01-16 mol / L HNO _3, typically at a temperature of from about 10 to about 80 ° C. for a period of time from about 0.01 to about 1 hour, but enough to get the initial hydration.

After acid treatment, the impregnated support material is heated to a temperature sufficient to remove the solvent used in the acid treatment. An inert gas stream supplied to the carrier material may be used. For this purpose, a temperature in the range of up to about 250 ° C. is usually sufficient for about an hour.

The dried, acid-treated catalyst is subjected to heat treatment in an oxidizing atmosphere, preferably in an atmosphere containing free oxygen (such as air), typically at a temperature in the range of about 80 to about 700 ° C. for a time in the range of about 0.5 hours to about 10 hours. The heat treatment is preferably carried out with a stepwise increase in temperature. Heat treatment is generally carried out at 150 ° C for 1 hour, at 200 ° C for 2 hours and at 400 ° C for 3 hours. Any combination of heating at a temperature for a time sufficient to calcine the impregnated support material to produce at least one platinum oxide, optionally mixed with platinum metal, and at least one iron oxide, satisfies the requirements of the present invention.

Prior to use in the carbon monoxide oxidation process, an oxidized, acid-treated, supported platinum / iron catalyst can be activated by a reduction step, which can be carried out by any suitable method, preferably at a temperature of from about 20 to about 650 ° C, more preferably from about 200 to about 500 ° C for a time of from about 0.5 hours to about 20 hours, preferably from about 1 hour to about 5 hours, to increase the activity of the catalytic composition for the catalysis of low-temperature oxidation of CO ki oxygen in the presence of hydrogen. Any reducing gas may be used: hydrogen, CO, paraffins and the like, and mixtures thereof.

The following examples are provided to further illustrate the invention, and should not be construed as limiting the scope of the invention.

Example I

The catalyst precursor was obtained by weighing about 500 g of 1/8 inch (0.32 cm) alumina spheres (Alcoa S-100 activated alumina) in two medium-sized porcelain bowls and calcined at 800 ° C. for 16 hours in an air-blown muffle ovens. 400 grams of dry calcined alumina was placed in a large porcelain bowl and, using a conventional plastic bottle for manual spraying, were sprayed with an impregnating solution obtained by dissolving 8.07 g of platinum (II) acetylacetonate (platinum (II) 2.4 pentanedionate) and 10.13 g iron (III) acetylacetonate in about 650 cm ^{3 of} acetone. The carrier was often mixed to ensure uniform distribution of the solution. When approximately 1/4 of the impregnating solution was applied to the support, the catalyst was placed in an exhaust furnace and heated at 175 ° C. for a period of 45 minutes to an hour, with the removal of acetone and partial decomposition of metal acetylacetonates. The processes of spraying, mixing and heating were repeated more than three times. When the entire impregnating solution was used, the catalyst was divided into equal portions, each weighing about 202 grams, and placed in an air-blown muffle furnace heated at 150 ° C for 1 hour, at 200 ° C for 2 hours and at 400 ° C within 3 hours. As a result of this heat treatment, two 202 gram portions of oxidized 1.0 wt.% Platinum / 0.4 wt.% Iron on alumina were obtained as a catalyst precursor.

Example II

A 202 g portion of the catalyst precursor was transferred to a 2 inch (5.08 cm) diameter quartz reactor, which was then installed in a vertical tube furnace. The catalyst was activated by reduction for three hours at 300 ° C and atmospheric pressure using a downward flow of hydrogen gas flowing at a speed of about 200 cm ³ / min. The catalyst and reactor were cooled in a stream of hydrogen, then purged with nitrogen, resulting in an activated catalyst. The resulting catalyst is a catalyst A.

Example III

Another 202 g portion of the catalyst precursor was transferred to a 2-inch (5.08 cm) diameter quartz reactor and mounted in a vertical tube furnace. The catalyst was reduced for three hours at 300 ° C and atmospheric pressure using a downward flow of hydrogen gas flowing at a speed of about 200 cm ³ / min. The catalyst and reactor were cooled in a stream of hydrogen, then purged with nitrogen. The freshly reduced catalyst was poured into a large bowl and soaked in a fume hood with approximately 60 cm ^{3 of} concentrated nitric acid. The acid impregnation was carried out dropwise with stirring. To minimize oxidation under the influence of atmospheric oxygen, the impregnation was carried out as quickly as possible. The acid-treated catalyst was dried and calcined in an air-blown muffle furnace heated at 150 ° C for 1 hour, at 200 ° C for 2 hours, and at 400 ° C for 3 hours. The catalyst was transferred to a 2 inch diameter quartz reactor, which was then mounted in a vertical tube furnace. The catalyst was activated by reduction for three hours at 300 ° C and atmospheric pressure using a downward flow of hydrogen gas flowing at a speed of about 200 cm ³ / min. The catalyst and reactor were cooled in a stream of hydrogen, then purged with nitrogen, resulting in an activated acid-treated catalyst. The resulting catalyst is a catalyst B.

Example IV

When conducting experiments on conversion used the following equipment. There were two separate Brooks 5850 E mass flow controllers, one for the stock mixture containing CO, and the other for air flow. The CO-containing mixture was kept under high pressure in a 30 liter aluminum cylinder. The CO-containing mixture usually had a CO content of 1%, the rest until the balance was hydrogen. Air was supplied from the air supply system. Streams of CO-containing mixture and air were combined at the inlet of a jacketed glass tube, while the outer jacket was designed to circulate the cooling medium. The glass tube was cooled in a bath with electrolyte circulation and a controlled temperature, which could regulate the temperature to the required temperature, selected in the range from 5 to about 100 ° C. The catalyst was charged inside a glass tube.

The catalyst was prepared as described in Examples I-III. The treated catalyst in an amount of 2.0 g was loaded into a glass tube with granular crushed quartz stuffed into an empty space. Each catalyst was pretreated for one hour with a stream of hydrogen flowing through the catalytic bed at a speed of 100 cm ³ / min, while heating to 97 ° C. The experiments were carried out under the conditions shown below in the table. All experiments were carried out at ambient pressure, GHSV (hourly average gas flow rate) of 10,000 cm ^{3 of} incoming gas per cm ^{3 of} catalyst per hour, while the feedstock, which was 1% CO in hydrogen, was used. Data was recorded every 15 minutes, with results obtained after 30 minutes being recorded as test results.

Table 1 Pt / Fe and Pt / Fe (acid treated) in the presence of hydrogen Catalyst Reaction temperature ° C Target molar ratio O: CO Actual molar ratio O: CO The degree of conversion of O ₂ % The degree of conversion of CO,% Unreacted CO (vol.%) Selectivity for CO ₂ ,% A 80 1 0.8 100.1 59.3 0.4270 75.0 A 80 2 1,6 99.9 94.9 0,0519 61.1 A 80 2,5 1.9 99.8 99.9 0,0006 51.6 A 80 2.75 2.1 99.6 100.0 0.0000 47.2 A 80 3 2,3 99,4 100.0 0.0000 43.3 IN 80 1 0.8 100.0 59.5 0.4290 76.6 IN 80 2 1,5 100.0 97.0 0,0314 62.7 IN 80 2,5 1.9 100.0 100.0 0.0000 51.7 IN 80 2.75 2.1 100.0 100.0 0.0000 47.0 IN 80 3 2,3 99.9 100.0 0.0000 43.1 A 25 1 0.8 90.3 85.0 0.1570 119.2 A 25 1,5 1,2 87.6 96.5 0,0359 93.1 A 25 2 1,6 84.7 98.0 0,0202 74,4 A 25 3 2,3 80.5 98.9 0.0114 52.9 A 25 4 3,1 78.3 99.0 0.0093 41.1 IN 25 1 0.8 94.6 88.7 0,1200 120.7 IN 25 1,5 1,2 91.5 98.9 0.0116 91.4 IN 25 1.75 1.4 88.3 99.1 0.0089 82.3 IN 25 2 1,5 85.5 99.3 0.0072 75.1 IN 25 2,5 1.9 82.6 99.6 0.0045 62.3 IN 25 3 2,3 77.1 99,4 0.0057 55.6

The data show that both Pt / Fe and Pt / Fe (treated with acid) were effective as a catalyst in the conversion of CO to CO ₂ . Oxygen conversion data show that the acid-treated catalyst had a higher activity than the catalyst that was not treated with an acid.

The resulting higher activity was present under all conditions, including very high hourly average gas flow rates. At 80 ° C and GHSV 10000, the acid-treated catalyst provided a slightly higher degree of CO conversion, resulting in a lower amount of unreacted CO and a higher selectivity for CO ₂ . At 25 ° C and GHSV 10000, the acid-treated catalyst provided a higher degree of CO conversion than the untreated catalyst, resulting in a much smaller amount of unreacted CO and increased CO ₂ selectivity.

Reasonable changes, modifications and alterations can be made within the scope of this description and the appended claims, designed for various conditions and applications.

Claims (13)

1. The method of selective oxidation of carbon monoxide to carbon dioxide in a gaseous mixture containing hydrogen and carbon monoxide, including (A) mixing the amount of free oxygen with said gaseous mixture containing hydrogen and carbon monoxide, providing a molar ratio of oxygen to carbon monoxide in the range of about 0.5-8.0 mol O ₂ / mol CO and forming a second gaseous mixture; (B) contacting the second gaseous mixture at a temperature in the range of about 0 ° C-300 ° C with an acid-treated catalyst containing platinum and iron impregnated on the support material, resulting in essentially complete conversion of carbon monoxide in the second gaseous mixture in carbon dioxide. 2. The method according to claim 1, in which the carrier material is selected from the group consisting of aluminum oxide, magnesium aluminate and mixtures thereof. 3. The method according to claim 2, in which the carrier material is alumina. 4. The method according to claim 1, in which the acid-treated catalyst is obtained by a method comprising (1) impregnating the support material with a solution containing a platinum compound and a solution containing an iron compound, thereby providing an impregnated mixture comprising an impregnated support material, a platinum impregnating compound, an iron containing impregnating compound, and a solvent; (2) heating the impregnated mixture at a temperature and for a time sufficient to at least partially remove the solvent, thereby providing a dried catalyst mixture; (3) optionally repeating steps (1) and (2) at least once; (4) heating the dried catalyst mixture in the presence of an oxygen-containing gas under oxidizing conditions to obtain an oxidized catalyst mixture; (5) heating the oxidized catalyst mixture in the presence of a reducing atmosphere under reducing conditions to obtain a reduced catalyst mixture; (6) contacting the reduced catalyst mixture with an acid to obtain an acid-treated catalyst mixture and (7) contacting the acid-treated catalyst mixture with an atmosphere containing free oxygen at a temperature and for a time sufficient to provide an oxidized, acid-treated catalyst mixture. 5. The method according to claim 4, in which the oxidized catalytic mixture is contacted with an atmosphere containing hydrogen at a temperature and for a time sufficient to provide a reduced, oxidized catalytic mixture. 6. The method according to claim 5, in which the carrier material is selected from the group consisting of aluminum oxide, magnesium aluminate and mixtures thereof. 7. The method according to claim 6, in which the carrier material is alumina. 8. The method according to claim 5, in which the temperature at which the impregnated mixture is heated is in the range of about 125-225 ° C and the time during which the impregnated mixture is heated is in the range of about 0.5-1.5 hours 9. The method according to claim 8, in which the temperature at which the dried catalytic mixture is in contact with an atmosphere containing free oxygen is in the range of about 100-600 ° C and the time during which the impregnated mixture is heated is in the range of about 0, 5-1.5 hours 10. The method according to claim 4, in which the acid used in the acid treatment is nitric acid. 11. The method according to claim 5, in which the temperature at which the oxidized catalytic mixture is in contact with an atmosphere containing hydrogen is in the range of about 200-400 ° C and the time during which the oxidized catalytic mixture is in contact with an atmosphere containing hydrogen is in the range of about 2-4 hours 12. A method for the selective oxidation of carbon monoxide to carbon dioxide in a gaseous mixture containing hydrogen and carbon monoxide, including: (A) mixing the amount of free oxygen with said gaseous mixture containing hydrogen and carbon monoxide, providing a molar ratio of oxygen to carbon monoxide in the range of about 0.5-8.0 mol O ₂ / mol CO and forming a second gaseous mixture; (B) contacting the second gaseous mixture at a temperature in the range of about 0-300 ° C. with a catalyst containing platinum and iron impregnated on the support material, resulting in the substantially complete conversion of carbon monoxide in the second gaseous mixture to carbon dioxide, where the catalyst is obtained by a method including: (1) impregnating the support material with a solution containing a platinum compound and a solution containing an iron compound, thereby providing an impregnated mixture comprising an impregnated support material, a platinum impregnating compound, an iron containing impregnating compound, and a solvent; (2) heating the impregnated mixture at a temperature and for a time sufficient to at least partially remove the solvent, thereby providing a dried catalyst mixture; (3) optionally repeating steps (1) and (2) at least once; (4) heating the dried catalyst mixture in the presence of an oxygen-containing gas under oxidizing conditions to obtain an oxidized catalyst mixture; (5) heating the oxidized catalyst mixture in the presence of a reducing atmosphere under reducing conditions to obtain a reduced catalyst mixture; (6) contacting the reduced catalyst mixture with an acid to obtain an acid-treated catalyst mixture and (7) contacting the acid-treated catalyst mixture with an atmosphere containing free oxygen at a temperature and for a time sufficient to provide an oxidized, acid-treated catalyst mixture. 13. The method according to item 12, in which the process for producing a catalyst includes an additional step: (8) contacting the oxidized, acid-treated catalyst mixture with an atmosphere containing hydrogen at a temperature and for a time sufficient to provide a reduced, oxidized, acid-treated catalyst mixture.