DD274810A1 - METHOD FOR OBTAINING CRYPTON AND XENONE FROM THE RESTOMASTS OF THE AMMONIA AND METHANOL SYNTHESIS IN WHICH U. A. HOEHER IS A METHANE OF VARIOUS HYDROCARBONS - Google Patents

Abstract

The invention relates to a process for the recovery of krypton and xenon from the residual gases of an ammonia or methanol synthesis, which essentially contain the components H2, N2, Ar, CH4, Kr, Xe and higher than methane boiling hydrocarbons. The invention is for the recovery of the noble gases krypton and xenon individually or in the mixture of synthesis residual gases containing higher than methane hydrocarbons, applicable. Krypton and xenon are concentrated together with the higher than methane boiling hydrocarbons, in a subsequent catalytic hydrogenation, the hydrocarbons boiling above methane are chemically converted to methane and thus the ratio krypton and xenon to higher than methane boiling hydrocarbons so improved that, depending on the technology the downstream final treatment plant pure krypton and xenon is recoverable. Fig. 1

Description

For this 3 pages drawings

Field of application of the invention

The invention finds application in the chemical industry. It is used to obtain pure krypton and pure xenon, 'singly or in a mixture, from residual gases of ammonia or methanol synthesis, if in the residual gases also higher than methane boiling hydrocarbons are present. With the method according to the invention, both already installed as well as newly constructed facilities can be equipped.

Characteristic of known technical solutions

Krypton and xenon or krypton / xenon mixtures are generally obtained from the residual gases of ammonia or methanol synthesis by cryogenic treatment. Known from DO-PS 204145 a method of cryogenic separation to obtain a high-boiling fraction from a gas mixture in dom the high-boiling components are present in only small concentrations and as the highest-boiling components in the mixture. According to the invention, a continuously operating Tioftemperaturrektifikation, a discontinuous cryogenic rectification and a Rekondensations- or storage device are combined and operated batchwise. In the exemplary embodiment of DD-PS 204145, the application of the method in the recovery of krypton and xenon from a mixture containing only krypton, xenon and methane will be described. Are in this mixture but also higher than methane boiling Kohlenwa. contained in the methane fraction together with krypton and xenon. The recovery of krypton and xenon from this high-boiling methane fraction is then feasible only with additional measures, for which no instructions for technical action are described in this patent.

From DE-OS 2828498 is a method for the decomposition of a gas mixture, the u. a. contains higher than methane boiling hydrocarbons known. This method has the task to provide a high quality, at higher than methane boiling hydrocarbons depleted fuel gas.

This is achieved by separating the higher than methane sledendone hydrocarbons by a multistage process consisting of condensation, rectification and absorption. This method is very expensive and therefore not suitable for the solution of the object according to the invention, because the required selectivity is not achievable. From DD-PS 239580 a process for the production of krypton and xenon is already known, can be produced with the 99% krypton and xenon. A prerequisite for this final processing of krypton and xenon recovery is a product containing only small amounts of higher than methane boiling hydrocarbons and a ratio of recoverable krypton and xenon to higher than methane boiling hydrocarbons of at least 1000: 2. How such a ratio of synthesis residual gases, which contain higher than methane-boiling hydrocarbons can be produced, has also remained unsolved. From the DR-PS 629297 and 658112 it is known. Krypton and xenon from air, which also contains hydrocarbons to win. First, an enrichment of the noble gases krypton and xenon and the hydrocarbons in the oxygen and the elimination of hydrocarbons by adsorption or catalytic combustion (oxidation) to carbon dioxide and water. The combustion leads to the complete removal of the hydrocarbons. The combustion products are removed by absorption. Thereafter, a further concentration of krypton and xenon is partially carried out by recycling in the 1st stage. Disadvantage of this solution is that the reaction products must be additionally separated and removed.

Object of the invention

It is an object of the invention to be able to continue to use the known work-up processes for the recovery of pure krypton and pure xenon even then, w-rv. the content of hydrocarbons boiling higher than methane reaches values in the synthesis residual gases at which the known work-up procedures become inoperative.

Explanation of the essence of the invention

The object of the invention is to minimize the accumulation of krypton and xenon simultaneously occurring enrichment of higher than methane boiling hydrocarbons m so far that a final treatment to pure krypton and xenon is possible.

This object is achieved in that the krypton and xenon, and the methane fraction containing more than methane boiling hydrocarbons of a catalytic hydrogenation to a hydrogenation catalyst under supply VQn hydrogen is subjected.

In this hydrogenation, the higher than methane boiling hydrocarbons are hydrogenated to stable methane and thus almost completely eliminated. The ratio of krypton and xenon to the higher than methane boiling hydrocarbons thereby improves to levels that allow recovery of krypton and xenon, singly or in admixture, according to known finishing methods. For this purpose, the hydrogenated mixture is fed to a known treatment process.

Depending on the ratio krypton and xenon to higher than Metjian boiling hydrocarbons in the synthesis gas, depending on the efficiency of the hydrogenation and depending on the final purification process selected, the entire hydrogenated mixture or only a subset of the hydrogenated mixture is fed to the final treatment stage. The other part of the hydrogenated mixture, which is depleted in hydrocarbons boiling higher than methane, is recycled to the methane fraction. This recycling of a portion of the hydrogenated mixture, which is almost free of higher than methane boiling hydrocarbons and has a better ratio of krypton and xenon to the higher than methane boiling hydrocarbons, thus again increases the quality of the methane fraction.

The reduction of the higher than methane boiling hydrocarbons in the methane fraction, which is necessary for ensuring high purity of the cryptone and xenon, is accomplished by altering the amount fed to the catalytic hydrogenation. That is, the concentration of the higher than methane boiling hydrocarbons in the methane fraction is adjusted in accordance with the amount supplied to the catalytic hydrogenation.

The change in the ratio of krypton and xenon to higher than methane boiling hydrocarbons in the methane fraction as the starting material for the hydrogenation process by the change in the recycled amount of hydrogenated mixture and / o ier by changing the Beiriebparameter in the accumulation of krypton and xenon and higher than

Methane boiling hydrocarbons in the methane fraction (precursor) possible. By the recycled hydrogenated mixture

The concentration of higher than methane boiling hydrocarbons in the methane fraction decreases, making it possible to significantly improve the accumulation of krypton and xenon in this methane reaction.

Particularly good operating conditions are set when the ratio of krypton and xenon in the Metrv.nfraktlon

higher than methane boiling hydrocarbons regulated to values greater than 1:50 and the enrichment of these two

Components in the bottom fraction except maxima! 50% by volume. In the hydrogenation reactor is a hydrogenation catalyst. This hydrogenation catalyst may be a pure nickel catalyst or a Be catalyst mixture with nickel catalyst content. Very good results are obtained with a catalyst mixture, besthe'id

of a de-cationized zeolite promoted with 2 mass% nickel and 0.25 mass% palladium and a nickel catalyst.

The hydrogenation reaction can be further optimized if the catalyst used is a catalyst mixture consisting of 50 to 90% by mass.

de-cationized zeolite and 50 to 10% by weight nickel catalyst, but in particular from 80% by weight zeolite and 20% by mass

Nickel catalyst is used. The hydrogenation is carried out at 550-670 K, preferably at 570 to 630K, the undesirable components being higher than Methane boiling hydrocarbons, almost completely converted to methane. As the main component of the Gas methane is methane and this is removed anyway in a subsequent final treatment stage, no results

additional expense for the methane produced by the hydrogenation.

The temperature of the methane fraction is countercurrent to the already hydrogenated mixture and by external energy supply

gradually, changing the state of aggregation, up to the reaction temperature of 570 to 630K increased. This cools the

Reverse flow from the hydrogenation reactor gradually and is partially acted after passage of a cooling water Heat exchanger with ambient temperature of the following finishing stage fed and partly for further Cooling in countercurrent to the dew point or below returned to the methane. If the hydrogenated mixture passed to the final treatment stage is already after cooling water Heat exchanger withdrawn from the hydrogenation, then the ^ um enrichment column and compressor is switched Heat exchanger operated with ambient air and the methane fraction with evaporation to ambient temperature

heated.

Depending on the technology of the final treatment stage, a gas mixture of the final treatment stage can also be used

which is withdrawn from the hydrogenation loop before the hydrogenation reactor and before hydrogen supply. In such a case, the concentration of higher than methane boiling hydrocarbons will be even higher than when the hydrogenated gas mixture is withdrawn after the hydrogenation reactor, but through the subsequent final treatment stage

Oxidation of all hydrocarbons (methane and higher than methane boiling hydrocarbons) still a recovery of

guaranteed pure krypton and pure xenon.

Before the hydrogenation reactor, the pressure in the system is reduced to max. 1.0MPa increases to overcome the

to ensure hydraulic resistance.

The hydrogen required for hydrogenation can also hydrogen from one of the enrichment of krypton and xenon, as well

be higher than methane boiling hydrocarbons upstream process stage, which can contain up to 60Vol .-% N ₂ , Ar and methane.

The hydrogen is the hydrogenation process in the molar ratio of hydrogen to higher than methane boiling hydrocarbons

between 1.0 and 1.5.

The advantages of this inventive solution are that it has succeeded for the first time, from synthesis residual gases, the higher than Methane boiling hydrocarbons contained in larger quantities to win the noble gases krypton and xenon. In addition, this solution according to the invention is procedurally elegant and economical, because it is the undesirable Ingredients (higher than methane boiling hydrocarbons) in a usable and already existing in the gas mixture Ingredient (methane) chemically converts anyway in the upstream enrichment process and / or the

subsequent finishing process is removed. This may indicate an otherwise necessary separation level for the higher than

Methane boiling hydrocarbons are dispensed with. The 9rfindungsgemäße solution thus provides a completely lossless Technology The noble gases krypton and xenon, which are valuable raw materials in economics, are of great importance. The cost of the additional hydrogenation step and the cost of operating the hydrogenation are compared to the total cost

the krypton and xenon recovery negligible. The hydrogenation works at low pressures. Special control loop / s not needed. The effort for dip measuring, control and regulation technology is low.

embodiment The invention will be explained in more detail with reference to a drawing. In the drawing show:

Fig. 1: a schematic representation of the inventive method for the removal of higher than methane boiling hydrocarbons from a krypton and xenon-containing methane fraction by hydrogenation with partial recycling of the hydrogenated mixture and partial removal of the hydrogenated mixture with the aim of obtaining pure krypton and xenon.

Fig. 2: a schematic representation of the method according to the invention as in Fig. 1 only with the difference that the

entire hydrogenated mixture (without recycle) is fed to a final treatment stage to recover pure krypton and xenon.

3: a compilation of the analysis values. example 1

This example starts from a synthesis residual gas of an ammonia synthesis, the synthesis gas of which is produced by a steam reforming process. As shown in Fig. 1, arrive about 12000 m ³ / h i. N. residual gas of an ammonia synthesis through line 1 in a process operating for the cryogenic separation process stage for hydrogen separation 2, from which a gaseous hydrogen fraction with more than 85% hydrogen is withdrawn via line 3 for further use. The resulting liquid fraction is fed via the line 4 of the methane column 5, whose top product is an argon / nitrogen mixture with low hydrogen content, which is withdrawn via line β and fed to an argon production. The bottom product of the methane column 5 with about 130OmVh i. N. has a methane content of more than 98 vol .-% and contains in addition to a small amount of argon all contained in the residual gas of the ammonia synthesis higher than methane boiling components, such as 0.08mVh i. N. krypton and xenon and about 1.1 mVh higher than methane boiling hydrocarbons. This bottom product is fed partly in gaseous form via line 7, partly liquid via line 8 to the enrichment column 9. The enrichment column 9 is associated with a methane heat pump cycle 10 through which the enrichment column 9 is heated and cooled. The only traces of krypton, xenon and higher than methane boiling hydrocarbons containing top product of the enrichment column 9 is discharged as a top fraction via line 11.

In the bottoms fraction of the enrichment column 9 (methane fraction), apart from methane, there are still about 0.08 m ³ / h in krypton and xenon and about 1.1 nrVh IN higher than methane-boiling hydrocarbons, a ratio of 1:14 to one another. For the purpose of eliminating the higher than methane boiling hydrocarbons from this methane fraction about 20m ³ / h i. N. withdrawn liquid 12 of the enrichment column 9, evaporated in the heat exchanger 13 ι nd heated to ambient temperature, fed via line 14 to the compressor 15 and compressed therein to about 1.0MPa for safely overcoming the hydraulic resistances.

Thereafter, the product stream is introduced through line 16 into the heat exchanger 17. Previously, a stream taken from line 3 and fed via line 32 before the heat exchanger 17 hydrogen is fed to this product stream. The amount of hydrogen is about 2.2mVh i. N. In the heat exchanger 17, the gas mixture thus obtained is heated to 570K, fed through line 18 to an electrically heated tip heater 19 where it is heated to about 600 K and fed via line 20 to the Hydrierrealaor 21. The hydrogenation reactor 21 contains about 0.075m ^{3 of} catalyst. This catalyst is a catalyst mixture consisting of 80% by volume of de-cationized zeolite and 20% by weight of nickel catalyst, the de-cationized zeolite being still promoted with 2% by weight of nickel and 0.2% by weight of palladium.

In the hydrogenation reactor 21, the almost complete hydrogenation of the higher than methane boiling Kohlenwas'.erstoffe to methane. The gas mixture contains about 2,9mVh krypton and xenon is about 1.1 m ^J / h higher than methane boiling hydrocarbons, about 16m ³ / h i at the entrance of the hydrogenation reactor 21st N. methane and about 2.2 m ³ / h i. N. hydrogen. After the hydrogenation reactor 21, the hydrogenated mixture contains 2.9 m ³ / h i. N. krypton and xenon, about 0.002 m ³ / h in higher pis methane boiling hydrocarbons, about 18.5 m "h i. N. methane and about 0.8 m ³ / h in hydrogen. This hydrogenated mixture is the heat exchanger 17 via line 22, the heat exchanger 24, which is supplied with cooling water from line 25 via line 26, heat exchanger 13, line 28, expansion valve 29 and line 30 in the bottom fraction of the enrichment column 9 (methane fraction ) in an amount of about 21.6m ³ / h iN recycled. In this product guide, the hydrogenated mixture is cooled in the heat exchanger 17 to about 310K, in the heat exchanger 24 to about 290 K and in the heat exchanger 13 to the dew point of about 120 K or partially liquefied. The hydrogenated mixture is added in a subset of about 0.6 mVh i. N. taken via line 27 or line 31 from the Krsislaufprozeß and processed in a downstream final stage (not shown) to pure krypton and pure xenon. Since the hydrogenated mixture, as the compilation of analytical data shows a ratio of krypton and xenon to higher than methane boiling hydrocarbons of 1450: 1, the final treatment stage, the rectification according to DD-PS 239580 is used. This produces krypton and xenon, each with 99.8% purity.

Example 2

This example starts from a synthesis residual gas of an ammonia synthesis whose synthesis gas is produced from coal with the supply of oxygen. The deep sintering treatment of these residual gases 1, the operation of the methane column 5 and the enrichment column 9 are carried out analogously to Example 1.

By way of derogation from Example 1 fall in accordance with FIG. 2 in the bottom of the enrichment column about 0.1 m ³ / h iN krypton / xenon and about 0.05 m ³ / h i. N. higher than methane boiling hydrocarbons to about 0.75 m ³ / h i. N. removed through line 12 from the bottom of the enrichment column 9 and introduced via heat exchanger 13, line 14, compressor 15 and line 16 into the heat exchanger 17. Through line 32 about 0.085m ³ / h iN hydrogen in line 16 are fed. The hydrogenation reactor 21 contains about 0.002 m ^{3 of} catalyst. This catalyst is a catalyst mixture consisting of 80% by volume of de-cationized zeolite and 20% by weight of nickel catalyst, the de-cationized zeolite being still promoted with 2% by weight of nickel and 0.2% by weight of palladium. The gas mixture contains at the entrance of the hydrogenation reactor 21 about 0.1 mVh i. N. krypton and xenon,

about 0.05m ³ / h i. N. higher than methane boiling hydrocarbons, about 0.6m ³ / h i. N. methane and otwa 0,085rn ³ / h i. N.

Hydrogen. .

The hydrogenated gas mixture contains at the outlet of the hydrogenation reactor 21 about 0.1 m ³ / h i. N. krypton and xenon, about 0.001 m ³ / h

i. N. higher than methane boiling hydrocarbons, about 0.71 m ³ / h i. N. methane and about 0.02m ³ i. N. hydrogen.

This hydrogenated mixture has a ratio of krypton and xenon to higher than methane boiling hydrocarbons of

The hydrogenated mixture leaving the hydrogenation reactor 21 is fed via line 22, heat exchanger 17, line 23, heat exchanger 24, line 26, heat exchanger 13 and line 28 to the final treatment stage to pure krypton and pure xenon.

The final treatment stage works on the adsorption principle.

Example 3 This Example 3 corresponds to Example 1 in the starting product and in the process engineering workup with two Differences.

1. Since the quality of the methane fraction by the circulation method of the hydrogenated mixture has a ratio of krypton and xenon to higher than methane boiling hydrocarbons of 2.6: 1, a part of this mixture before the hydrogenation and before the supply of hydrogen, ie from the line 14 before the compressor 15, removed from the circuit (not shown in the drawing) and fed to a final treatment stage.

2. This final treatment stage works on the principle of catalytic oxidation, after which also pure krypton and xenon is recovered.

Claims (13)

1. A process for the recovery of krypton and xenon from -Jen residual gases of ammonia or methanol synthesis, in which u. a. Higher than methane boiling hydrocarbons are present, in which initially krypton, xenon and the higher than methane boiling hydrocarbons are enriched in a methane fraction, characterized in that this methane fraction is subjected to a catalytic hydrogenation on a hydrogenation catalyst under the supply of hydrogen, while the higher than Methane-boiling hydrocarbons hydrogenated to methane and the hydrogenated mixture fed to a known end-preparation process to krypton and xenon and krypton and xenon are obtained in high purity. 2. The method according to claim 1, characterized in that the hydrogenated mixture is partially recycled to the methane fraction. 3. Process according to claims 1 and 2, characterized in that the concentration of hydrocarbons boiling higher than methane in the methane fraction, depending on the amount of the catalytic! Hydrogenuno supplied mixture is set: is. 4. The method according to claims 1 to 3, characterized in that the ratio of krypton and xenon to the higher than methane siedonden hydrocarbons by changing the recirculated to the methane fraction amount of hydrogenated mixture and / or by changing the operating parameters for the enrichment of krypton and Xenon and the higher than methane boiling hydrocarbons in the methane fraction is adjusted to values greater than 1:50 in the methane fraction. 5. Process according to claims 1 to 4, characterized in that the accumulation of the components krypton and xenon and the higher than methane boiling hydrocarbons in the methane fraction up to a maximum of 50Vol .-% takes place. 6. Process according to claims 1 to 5, characterized in that the hydrogenation of the higher than methane boiling hydrocarbons takes place on a nickel catalyst. 7. Process according to claims 1 to i>, characterized in that the hydrogenation is promoted on a catalyst mixture consisting of a dekationisiertem zeolite which is promoted with 2 wt .-% nickel and 0.25 wt .-% palladium, and a nickel catalyst is carried out. 8. Process according to claims 1 to 7, characterized in that the hydrogenation is carried out on a catalyst mixture consisting of 50 to 90Ma .-% dekationisiertem zeolite and 50 to 10Ma.-7 <nickel catalyst. 9. The method according to claims 1 to 8, characterized in that the hydrogenation is carried out on a catalyst mixture consisting of 80 wt .-% zeolite and 20 wt .-% nickel catalyst. 10. The method according to claims 1 to 9, characterized in that the hydrogenation of the higher than methane boiling hydrocarbons to methane at temperatures between 550 to 670K is performed. 11. The method according to claims 1 to 10, characterized in that the hydrogenation is carried out at temperatures between 570 and 630 K. 12. The method according to claims 1 to 11, characterized in that in the supply of hydrogen, a molar ratio of hydrogen to higher than methane boiling Kuhlenwasserstoff in the range between 1.0 and 1.5 is set. 13. The method according to claims 1 to 12, characterized in that the hydrogenation hydrogen from one of the enrichment of krypton and xenon and the higher than methane boiling hydrocarbons upstream process stage, which may contain up to 60Vol .-% N2, Ar and CHi, is used.