PROCESS FOR REMOVING CARBON MONOXIDE AND/OR GASEOUS SULPHUR COMPOUNDS FROM HYDROGEN GAS AND/OR ALIPHATIC HYDROCARBONS

Abstract

The present invention concerns a process for removing carbon monoxide and/or gaseous sulphur compounds from hydrogen gas and/or aliphatic hydrocarbons, preferably at low temperatures, with the aid of complex metal aluminium hydrides.

Claims

1. A process for removing carbon monoxide and/or gaseous sulphur compounds from a gas containing carbon monoxide and/or gaseous sulphur compounds, the gas being selected from hydrogen gas and/or one or more gaseous aliphatic hydrocarbons or a mixture thereof, said process comprising bringing the gas into contact with a complex metal aluminium hydride in a reaction vessel, wherein the metal aluminium hydride is selected from the group which consists of one or more compounds of Formula I Me.sup.x+[AlH.sub.4].sup.−.sub.x with x=1-5, of Formula II Me.sub.y.sup.w+[AlH.sub.6].sup.3−.sub.z with w.Math.y=3z, and of Formula III Me.sub.p.sup.q+[AlH.sub.5].sup.2−.sub.r with p.Math.q=2r, wherein Me represents one or more alkalis or alkaline-earth metals.

2. The process as claimed in claim 1, in which one or more complex metal aluminium hydrides of Formulae I to III are used which are supplemented with one or more metals as metal compounds, or in the form of particles, wherein as the precious metal, one or more transition metals from groups 3, 4, 5, 6, 7, 8, 9, 10, or 11 are used, or alloys or mixtures of these metals with each other or with aluminium are used.

3. The process as claimed in claim 2, in which the metals or the compounds themselves are used in the form of very small particles with a high degree of distribution.

4. The process as claimed in claim 1, in which one or more complex metal aluminium hydrides of Formulae I to III which have been completely or partially dehydrogenated.

5. The process as claimed in claim 1, in which one or more complex metal aluminium hydrides of Formulae I to III are used to which one or more metals in the form of particles have been added and the mixture obtained has been ground to a particle size of 0.5 to 1000 nm, wherein the added metal or metals are selected from transition metals from groups 3, 4, 5, 6, 7, 8, 9, 10, or 11, or alloys or mixtures thereof with each other or with aluminium.

6. The process as claimed in claim 5, for which the metal or metals in the form of particles have been produced by in situ reduction with the complex metal aluminium hydride of Formulae I to III.

7. The process as claimed in claim 1, in which a complex metal aluminium hydride is used to which carbon particles selected from graphite, nodular carbon, activated carbon, or mixtures thereof have been added.

8. The process as claimed in claim 1, in which the reaction vessel is configured in the form of a perfusable filter unit which is filled with one or more complex metal aluminium hydrides of Formulae I to III as claimed in a process as used in claim 1, optionally in combination with one or more metals in the form of particles and/or in combination with carbon particles.

9. A filter unit which has a filling with one or more complex metal aluminium hydrides selected from the group which consists of one or more compounds of Formula I Me.sup.x+[AlH.sub.4].sup.−.sub.x with x=1-5, of Formula II Me.sub.y.sup.w+[AlH.sub.6].sup.3−.sub.z with w.Math.y=3z, and of Formula III Me.sub.p.sup.q+[AlH.sub.5].sup.2−.sub.r with p.Math.q=2r, wherein Me represents one or more alkalis or alkaline-earth metals, wherein said one or more complex metal aluminium hydrides of Formulae I to III are optionally in combination with one or more metals in the form of particles and/or in combination with particles of carbon.

10. A fuel cell with at least one filter unit as claimed in claim 9.

11. The process as claimed in claim 2, wherein the metal compounds are metal salts.

12. The process as claimed in claim 2, wherein the metal salts are metal halides.

13. The process as claimed in claim 2, wherein the transition metals are selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Pr and Nd.

14. The process as claimed in claim 3, wherein the particles have particle sizes of approximately 0.5 to 1000 nm and/or specific surface areas of 50 to 1000 m.sup.2.

15. The process as claimed in claim 5, wherein the metals are selected from Ti, Zr, Sc, Y, and rare earth metals.

Description

[0019] The invention will now be explained in more detail with the aid of the accompanying FIGS. 1 to 5 and the examples of production.

[0020] In this regard, FIGS. 1 to 4 show plots for experiments with the process in accordance with the invention compared with a process which is not in accordance with the invention.

[0021] In this regard, FIG. 4 illustrates the reusability of a flow tube filled with a complex metal aluminium hydride used in the process in accordance with the invention which has undergone a step for removal of the absorbed carbon monoxide, for example by the action of ambient air on the complex metal aluminium hydride.

[0022] FIG. 5 shows the test apparatus and serves to explain the test procedure. As can be seen in FIG. 5, the test apparatus consists of an absorption tube 4 filled with a complex aluminium hydride, the reservoir 5 for the gas mixture employed, a mass flow controller 6, a vacuum pump 7 and an IR spectrometer 8 for monitoring the CO concentration in the gas mixture. The individual operational procedures can be carried out under inert conditions by means of the valves 1, 2 and 3.

[0023] Before starting the measurement, the entire apparatus is evacuated via the valve 2 with valves 1 and 3 closed. Next, the valve 2 is closed and the apparatus is filled with an inert gas via the valve 3. The gas mixture is supplied with the valves 1 and 3 open, wherein the gas flow is adjusted to the required quantity of gas with the aid of the mass flow controller 6. After the gas mixture has flowed through the absorption tube 4, the CO concentration is determined with the aid of the IR spectrometer 8.

[0024] A reduction in the absorption capacity of the complex aluminium hydrides upon the removal of contaminants from hydrogen gas can be made visible in a simple manner by means of a colour reaction in the window of a cartridge which is downstream in the flow direction of the absorption tube 4 and upstream of the valve 1, and thus be monitored in this manner. An example is the reaction of CO with iodine pentoxide deposited on a support in the cartridge with a window, wherein oxidation of CO occurs and iodine is formed in accordance with the following reaction:

5CO+I.sub.2O.sub.5.fwdarw.5CO.sub.2+I.sub.2

[0025] The support material on which the colour reaction occurs is coloured by the iodine that is released. In this manner, optical observation and monitoring of a diminishing absorption capacity is possible, and an exchange of the absorption tube can be carried out in a timely manner. Preferably, two or more absorption tubes 4 are disposed in parallel in the flow direction and when the absorption capacity diminishes, the gas flow can be switched from one absorption tube 4 to another.

[0026] FIG. 4 illustrates the reusability of a flow tube filled with a complex metal aluminium hydride used in the process in accordance with the invention, which has undergone a step for removing the adsorbed carbon monoxide, for example under the action of ambient air on the complex metal aluminium hydride.

[0027] Methods and Apparatus

[0028] A URAS 26 NDIR spectrometer (non-dispersive infrared spectrometer) from ABB was used to determine the CO concentration. The gas concentration was determined with the aid of a gas-filled optopneumatic detector. The particle sizes were determined either by laser diffraction, or in the case of very small particles with the aid of TEM analyses (transmission electron microscopy).

[0029] Example of Production

[0030] In a typical process, Na.sub.3AlH.sub.6 was ground with TiCl.sub.3 (2-4 mol %) and optional other additives in a ball mill. The material obtained in this manner was used to remove CO from hydrogen gas. Similarly, other contaminants such as CO.sub.2, H.sub.2O and S compounds could be eliminated from hydrogen gas using this process.

[0031] Example 1

[0032] In a flow tube, 2.0 g of a mixture of partially dehydrogenated Na.sub.3AlH.sub.6(composition: (1−x)Na.sub.3AlH.sub.6+3xNaH+xAl), TiCl.sub.3 (4 mol %), activated carbon (8 mol %) and Al powder (8 mol %), which had been produced by grinding in a ball mill, was perfused with hydrogen gas containing 10 ppm CO at a flow rate of 50 ml/min. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture, whereupon initially, no CO could be detected. After 75 h, the CO concentration had grown to 3 ppm.

[0033] Example 2

[0034] In a flow tube, 2.0 g of a mixture of Na.sub.3AlH.sub.6, TiCl.sub.3 (4 mol %), activated carbon (8 mol %) and Al powder (8 mol %), which had been produced by grinding in a ball mill, was perfused with hydrogen gas containing 10 ppm CO at a flow rate of 3 l/h. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture, whereupon initially, no CO could be detected. After 46 h, the CO concentration had grown to 1.6 ppm.

[0035] Example 3

[0036] In a flow tube, 2.0 g of a mixture of Na.sub.3AlH.sub.6 and TiCl.sub.3 (4 mol %), which had been produced by grinding in a ball mill, was perfused with hydrogen gas containing 100 ppm CO at a flow rate of 50 ml/min. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture. Over a time period of 60 min, no CO could be detected. In the following 50 min the CO content grew to 50 ppm.

[0037] Example 4

[0038] In a flow tube, 2.0 g of a mixture of NaAlH.sub.4 and TiCl.sub.3 (4 mol %), which had been produced by grinding in a ball mill, was perfused with hydrogen gas containing 100 ppm CO at a flow rate of 50 ml/min. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture. Over a time period of 35 min, no CO could be detected. In the following 25 min, the CO content had grown to 75 ppm.

[0039] Example 5

[0040] In a flow tube, 2.0 g of pure NaAlH.sub.4 was perfused with hydrogen gas containing 100 ppm CO at a flow rate of 50 ml/min. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture. After 3 min, the CO content had grown to 100 ppm.

[0041] Example 6

[0042] In a flow tube, 2.0 g of a mixture of Na.sub.3AlH.sub.6, TiCl.sub.3 (4 mol %), activated carbon (8 mol %) and Al powder (8 mol %), which had been produced by grinding in a ball mill, was perfused with hydrogen gas containing 100 ppm CO at 30° C. and a flow rate of 3 l/h. After it had been perfused, IR spectroscopy was used to monitor for CO in the gas mixture. Up to 30 min following the start of the experiment, no CO was detected. In the following 3 h, the CO content increased to 90 ppm. The flow tube was then separated from the gas flow and exposed to the ambient air for 10 minutes. After this time, hydrogen gas containing 100 ppm CO was conducted through the flow tube once again. The mixture again exhibited a high absorption capacity for CO and no CO could be detected for 15 min. After that, the CO content in the hydrogen gas once again increased continuously.