DE2521924A1 - CATALYST FOR DEUTERIUM ENRICHMENT AND ITS PRODUCTION AND APPLICATION - Google Patents

Description

Ing.Walter Abitz

Dr. Dieter F, Morf ¹⁶ * ^{May 1975}

Dr. Hans-A P-το ^B - ¹¹³⁷

ENGELHARD MINERALS & CHEMICALS CORPORATION 430 Mountain Avenue, Murray Hill, New Jersey 07974, V.St.A.

Deuterium enrichment catalyst and its manufacture and use

Deuterium, the persistent hydrogen isotope with mass 2, occurs in naturally occurring hydrogen, in water, and in other hydrogen-containing compounds with an average of 0.015 mol%. Deuterium is of interest for research for marking in biological processes and chemical reactions, but there is by far the greatest need for deuterium in the form of heavy water, D2O, as a moderator for nuclear reactors.

In older methods of producing heavy water, there was a chemical exchange between hydrogen and water vapor or vacuum distillation of water for initial separation, followed by electrolysis for final concentration. Then there is a more efficient process with double temperature exchange of deuterium between hydrogen sulfide and water has been used extensively.

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When choosing a specific isotope separation process, one must choose between the enrichment of a few grams of an unusual isotope and the production of an isotope for technical purposes in the Order of magnitude of many tons can be distinguished. In the former Case, the main emphasis should be placed on the choice of a process that allows the greatest possible separation in one Single apparatus results, with economic considerations or energy consumption being secondary. With the large-scale For the production of deuterium, however, an extensive enrichment per unit of equipment is only of secondary importance. from The efficiency and reversibility of the process are of paramount importance here; H. the labor costs related to the Energy demand as well as capital investment. A typical process for the first procedure is electrolysis of water, a process that can be costly when used to generate large quantities of heavy water and when cheap hydroelectric energy is not available. For the second procedure, the one is reversible Process of chemical E ^ S / HpO exchange exemplified in which not only is the separation factor relatively small, but the one intentionally applied to one by applying a double temperature arrangement Even smaller enrichment factor is designed to result in a less costly method of material reflux within of the process.

In the above-mentioned electrolysis process, the pre-enrichment takes place 'under a water vapor / hydrogen exchange. These The way of working has not been economically attractive for the industrial scale, since only the catalysts are successful Have allowed work that worked in the vapor phase. The separation factor increases with decreasing temperature to, so that one works preferably at the lowest possible temperature, which thus favors the liquid phase. If those If catalysts are used together with liquid water, they are subject to large-scale poisoning in the process or inactivation. Considerable effort has therefore been devoted to a liquid phase exchange catalyst

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of deuterium to evolve with water.

An example of an approach to the problem of the enrichment of water with deuterium is to use the catalyst a closure means that is permeable to water vapor and hydrogen gas is to make the effect waterproof (CA-PS 907 292). As described in that patent specification, the catalyst sealed with a hydrophobic polymer, such as a polyalkyl silicone, polytetrafluoroethylene, polyethylene, Polypropylene or like polymers, with a siloxane polymer being preferred. There are two for this development Characterizing main points: 1. Becomes the hydrophobic polymer sealant applied directly to a catalyst carrier to which a catalytic material has already been applied, 2. The particles of the hydrophobic polymer sealing agent enter the pores of a catalyst and are deposited the pore surface. As has been shown, the efficiency or the relative specific activity of these catalysts is not high enough for large-scale, economical work.

The present invention provides an improved catalyst for effecting the enrichment of water with deuterium And also provides an improved method of making a catalyst for the production of deuterium. These and other advantages and details of the invention will become apparent from the following description.

The invention is directed to a catalyst for promoting deuterium enrichment of the water directed. The catalyst contains a noble metal from group VIII of the periodic table as an active element, like platinum. The platinum is deposited on carbon as a suitable mold for use in this process. The platinum carbon is supported on an inert support material such as alumina. As has been shown an effective catalyst can be made by using a hydrophobic polymer such as polytetrafluoroethylene

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det, which is applied directly to the inert support, whereupon the platinum-carbon, in an emulsion of hydrophobic polymer mixed in, like in a polytetrafluoroethylene emulsion, will be added. The inert carrier and the platinum carbon are coated by this procedure to add water thereto prevent getting into the pores of the carrier or the carbon.

As has been further shown, is a particularly effective catalyst obtainable by strongly controlling the amount and manner of distribution of the platinum in the catalyst.

In the method according to the invention, an inert one is used first Catalyst support with a hydrophobic polymer, such as polytetrafluoroethylene, coated, whereupon it is dried and calcined. Next is a precious metal, like platinum, on carbon distributed or dispersed, which you then with a polytetrafluoroethylene suspension slurries. The inert support is then coated with the suspension and then dried and calcined. The polytetrafluoroethylene is used in this mode of operation as a binder for the platinum-carbon particles as well as a closure or sealing agent, the one Liquid water prevents contact with the catalytic platinum-carbon surface. The relative sizes of the carbon pores and the second polytetrafluoroethylene emulsion are selected so that the polytetrafluoroethylene emulsion does not occur into the pores of the carbon particles, but rather coating of carbon is obtained.

An advantage of the invention is that the size of the inert carrier by using pellets, beads, or any other shape, and by maximizing it of the size and shape of the carrier in the sense of minimizing flooding in the deuterium exchange column can be varied.

Another advantage of the invention is that it optimizes both the platinum to carbon ratio

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as well as the amount of carbon-platinum in relation to that of the inert support for directing the catalyst activity. For example, if a catalyst with a platinum loading of 1 % is desired, one could disperse 1 g of platinum on 1 g of carbon and then apply this mixture to 98 g of inert support. However, since the ratio of platinum to carbon is so high, the platinum dispersion becomes very poor and the catalyst activity becomes poor. On the other hand, 1 g of platinum can be dispersed on 10 g of carbon and then this mixture can be applied to 89 g of inert support. In this case, the significantly reduced platinum loading on the carbon improves the dispersion and the final catalytic activity is far superior to that obtained in the previous example.

When using the platinum-carbon catalyst according to the Invention you can put this on an appropriate carrier, for. B. made of porous, sintered glass or metal, in a column or arrange column in a layer. Liquid water and hydrogen gas then flow through the column in countercurrent to one another passed so that the liquid water and hydrogen gas are brought into contact with each other and with the catalyst.

The catalyst is preferably supported on a relatively inert support in the form of at least one material selected from the group Aluminum oxide, magnesium oxide, silicon dioxide, silica gel, chromium oxide, molybdenum oxide, oxide of higher quality tungsten (Tungstic Oxide), Nickel oxide and diatomaceous earth are formed. The preferred carrier is alpha-alumina, which comes in a wide variety of shapes, sizes and structures is available.

The inert carriers are conveniently in the form of pelletized, granular ones or extruded form or in the form of bodies shaped in some other way, such as Berl saddle bodies. The inert catalyst carrier has a surface area of less than 5 m / g »preferably below 2 m / g in order to avoid undue absorption of water on the catalyst surface.

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The inert carrier, as in spherical form, is coated with a polytetrafluoroethylene emulsion mixed or soaked in this, allowed to drain, dried in a stream of air at conditions which keep the spheroids constantly in motion, and then calcined at a temperature of about 350 ° C. The used Polytetrafluoroethylene amount is about 2 to 20 wt.%, preferably 5 to 15% by weight of the spheroids; this quantity is enough to cover the surface with a continuous film.

The catalytic material is at least one metal from group VIII of the periodic table, in particular platinum, palladium, nickel, iridium and rhodium. Platinum is the preferred catalyst because of its high activity. The platinum is deposited on finely divided carbon using conventional techniques, e.g. B. by formate reduction of chloroplatinic acid. The amount of platinum, based on the weight of carbon, is about 1 to 25 %, with a range of 3 to 12% being preferred.

The platinum-on-carbon material is then coated with a polytetrafluoroethylene emulsion mixed, preferably in the presence of a plasticizer such as methyl cellulose. The particle size the polytetrafluoroethylene emulsion is larger than the pore size of the carbon particles. The carbon particles have a pore size of about 15 to 300 S. diameter. The polytetrafluoroethylene is used in an amount necessary for training a coherent film over the surface of the inert support is sufficient. A smaller amount has proven to be of value Plasticizers proven, d. H. 3 to 10% by weight of polytetrafluoroethylene; the plasticizer results a more coherent polytetrafluoroethylene catalyst film the coated carrier.

The calcined spheroids are then mixed with the metal-on-carbon catalyst / polytetrafluoroethylene mixture mixed and in air at about 90 ° C and then in a vacuum oven '

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about 250 ⁰ C. The calcined spheroids are washed and then dried in air at 90 ° C. The catalyst-polytetrafluoroethylene mixture is used on the spheroids in sufficient quantity to obtain a final platinum content of 0.02 to 5%, preferably 0.02 to 2%.

Polytetrafluoroethylene is preferred as the hydrophobic polymer for the purposes of the invention. But you can also work with others hydrophobic polymers or resins that are permeable to water vapor, such as a polyalkyl silicone, polyethylene, Medium to high molecular weight polypropylene or similar hydrophobic hydrocarbon polymers.

Examples

A catalyst according to the invention was prepared as follows:

1. 200 g spheroids ("Norton" SA 5218) were in a polytetrafluoroethylene emulsion ("T-30 Teflon" from E. I. du Pont & Co.) soaked, drained and allowed to air at 90 to Dried at 110 ° C. The dried spheroids were calcined at 350 ° C. in air.

2. 4 g of 25% Pt-on-carbon material ("Regal 53OR" of the Cabot Corp.) were diluted with a solution of 6 ml polytetrafluoroethylene emulsion ("T-30"; diluted to 150 mg / ml) plus 20 ml of methyl cellulose solution containing 0.3% by weight of methyl cellulose stirred.

3 «The mixed mixture from stage 2 was applied with stirring to the calcined spheroids from stage 1, whereupon the coated spheroids were dried in air at 90.degree. After drying, the beads were heated in a vacuum oven for 2 hours at I5O ⁰ C and then in the furnace for a further 2 hours at 250 ° C.

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4-. The calcined spheroids were washed with water to the metbyl (

dried,

remove the methyl cellulose, and then in air at 90 ° C

In all drying stages the spheroids were during the Drying kept in motion. The drying and calcining temperatures can be adjusted within conventional Change areas that are high enough to result in a permanent, coherent film, but below temperatures, which would lead to the degradation of the polytetrafluoroethylene.

The activity of the catalysts was measured in a column 2.5 cm in diameter at 1 atm. Pressure and at a water flow velocity of 10 cm ^ min. "^ or 1230 Pound.Foot"" ^2nd hour" ¹ measured. The columns were operated intermittently for a long time. They were only operated during the day using trickle mode; at night the gas and water flow were switched off. Before resuming measurements, the layers were removed by closing the water outlet valve and maintaining the flow of hydrogen at 5 to 10 cm. Sec. briefly flooded, after which the columns were allowed to drain and operated under Eiesel bed conditions. The purpose of the flooding was to try to restore an even flow of water through the hydrophobic catalyst bed after it had not been in operation overnight. In a few cases, the columns were operated continuously for periods of about 35 hours. A liquid phase enriched in deuterium was obtained from the columns. The activity values of these catalysts at 25 ° C. and physical properties of the same are shown in the table. The catalyst is prepared according to the procedure described above with variation of the proportions according to the table.

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B-1137

Catalyst Pt end Pt on carbon used In stage 2 Relative weight, fuel, Pt carbon used Activi no. % +) % fabric quantity, tes poly- tat, ++)

g tetrafluoroethylene good, cm3

1 0.37 25th 20th 6th 1.00 2 0.39 25th 20th 3 1.36 3 0.06 25th 5 3 1.66 4- 0.07 6.25 20th 3 8.1

+) based on the weight of the end product (including

inert carrier)

++) Activity per unit weight Pt, based on deuterium enrichment in the water phase

In another experiment, platinum was applied directly to the inert support (0.35% by weight) with polytetrafluoroethylene ("Teflon"; 6 cnr) coated and dried and calcined, using the above procedure. The relative activity of this catalyst was 0.05.

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Claims (11)

Sponsorship claims Catalyst for the deuterium enrichment of water with an inert carrier, a first coherent film of a hydrophobic polymer located on the carrier and one located on the first film; ,,. second coherent Film of a hydrophobic polymer, the second film. a catalyst in the form of finely divided metal of the group VIII of the periodic table contains carbon in itself. 2. Process for the preparation of a catalytic composition of matter to promote the deuterium enrichment of water, characterized in that one inert Support coated with a hydrophobic polymer, the coated support dries on the coated support a mixture of finely divided metal from Group VIII of the Periodic Table on carbon and one hydrophobic Applies polymers and the resulting composition of matter dries. 3 · The method according to claim 2, characterized in that polytetrafluoroethylene is used as the hydrophobic polymer. 4. The method according to claim 3 »characterized in that one as. Carrier alumina used. 5. The method according to claim 3> characterized in that platinum is used as the precious metal. 6. The method according to claim 3 »characterized in that the platinum is applied to finely divided carbon with a pore size of about 15 to 300 Å * in diameter. 7. The method according to claim 3> characterized in that drying of the heat-resistant, polytetrafluoroethylene-coated Carries out carrier with calcining in air. - 10 50984 9/0983 8. The method according to claim 3 »characterized in that the resulting product is dried with calcination in air. 9- The method according to claim 5 »characterized in that the platinum in an amount of 0.02 to 5% by weight of the catalyst begins. 10. The method according to claim 9 »characterized in that the platinum in an amount of 1 to 25% by weight of carbon begins. 11. A method for promoting the deuterium enrichment of water, characterized in that one has water and hydrogen gas passes over a catalyst which has an inert carrier, a first located on the carrier coherent film of a hydrophobic polymer and a second coherent film located on the first film of a hydrophobic polymer, the second film being a catalyst in the form of finely divided metal from group VIII of the Periodic Table contains carbon, and deuterium-enriched water is obtained. - 11 - 509849/0983