Process for removing carbon monoxide and / or gaseous sulfur compounds from hydrogen gas and / or aliphatic hydrocarbons - Patent Application 20070122999

Abstract

The present invention relates to a method for removing carbon monoxide and / or gaseous sulfur compounds from hydrogen gas and / or aliphatic hydrocarbons, preferably at low temperatures, using a complex metal aluminum hydride.

Description

[Technical Field]

[0001] The present invention relates to a method for removing carbon monoxide and / or gaseous sulfur compounds from hydrogen gas and / or aliphatic hydrocarbons, preferably at low temperatures, using a complex metal aluminum hydride. [Background technology]

[0002] Hydrogen is the most important energy carrier for fuel cells. Among the six types of fuel cells, polymer electrolyte fuel cells (PEFCs), commonly referred to as PEMs, have recently gained importance as low-temperature fuel cells. Polymer electrolyte fuel cells (PEFCs), commonly referred to as PEMs, operate at operating temperatures below 100°C.

[0003] Polymer electrolyte fuel cells are characterized by a thin, gas-tight, proton-conducting, solid polymer membrane as the electrolyte. This plastic membrane incorporates acid groups, and protons, as in all acid cells, diffuse through the membrane from the anode to the cathode, where they recombine with oxygen ions to form water. Currently available perfluoropolymer membranes (e.g., made from NAFION®) contain the water necessary for conduction, meaning their operating temperature is limited to a maximum of 100°C. Electrical contact from the electrodes to the bipolar plates is made through current collectors containing metal or carbon. These current collectors must be permeable to gases and liquids to allow reactant gases to be transported into the membrane and reactant water to be transported away.

[0004] To ensure a sufficient reaction rate of the electrochemical reaction, a catalyst is required at low temperatures. In terms of materials, the membrane's high acidity (comparable to sulfuric acid) necessitates the use of a precious metal catalyst such as platinum or a platinum alloy.

[0005] The precious metal catalysts and electrolytes used require a relatively high fuel gas purity. H2 is the only possible fuel gas. The oxidant is O2, but in contrast to other fuel cells, PEFCs can be operated with air, which significantly expands the range of applications. According to the ISO 14687-2 standard, carbon monoxide (CO) is only permitted in trace amounts of <0.2 ppm, as it acts as a catalyst poison, similar to sulfur compounds.

[0006] Hydrogen is rarely found in pure form on Earth and must therefore be produced at the expense of energy. A production method often used in industry is steam reforming of natural gas or hydrocarbons from other sources. Hydrogen is extracted stepwise from the hydrocarbon-hydrogen chain through various reforming processes. By-products include carbon monoxide, nitrogen oxides, and sulfur dioxide. Summary of the Invention [Problem to be solved by the invention]

[0007] If the gas generated during reforming is to be fed to a low-temperature fuel cell, carbon monoxide must first be separated. For thermodynamic reasons, carbon monoxide is also produced during reforming and, like sulfur compounds, is a catalyst poison in fuel cells. In prior art processes, purification is carried out in so-called water-gas shift reactors or in reactors for preferential oxidation. However, these processes are quite expensive, and a simplified process is needed to produce hydrogen gas or gaseous aliphatic hydrocarbons free from catalyst poisons such as CO or sulfur compounds. [Means for solving the problem]

[0008] The inventors have surprisingly found that carbon monoxide and / or gaseous sulfur compounds can be removed from hydrogen gas and / or aliphatic hydrocarbons by complex metal aluminum hydrides. Where the present invention refers to the removal of carbon monoxide from hydrogen gas, these statements are correspondingly applicable to the removal of gaseous sulfur compounds that are present in hydrogen gas and / or aliphatic hydrocarbons in admixture with a few ppm of CO and that can be contacted with complex metal hydrides.

[0009] More particularly, the present invention relates to a method for removing carbon monoxide and / or gaseous sulfur compounds from a gas containing carbon monoxide and / or gaseous sulfur compounds, A gas selected from hydrogen gas and / or one or more gaseous aliphatic hydrocarbons or a mixture thereof is mixed with a composite metal aluminum in a reaction vessel. hydrides and contacting it with metallic aluminum. hydrides is a compound of formula I, Me x+ [AlH4] - x (wherein x=1-5), one or more compounds of formula II, Me y w+ [AlH6] 3- z (Where y =3z), and one or more compounds of formula III, Me p q+ [AlH5] 2- r (where p·q=2r), where Me represents one or more metals from the periodic table of the elements.

[0010] The reaction can be carried out in a vessel configured as a reactor for batch reactions, or preferably in a vessel configured as a reactor for continuous reactions, in which the gas to be purified is introduced, contacted with the composite metal aluminum hydride, and then discharged from the reactor after the reaction. In this way, it is possible to maintain residual amounts of CO and sulfur-containing compounds below 0.2 ppm for extended periods. This makes it possible to design the reactor in the form of a flow-through filter unit filled with one or more composite metal aluminum hydrides of formulas I to III. Such a flow-through filter unit can be advantageously used as a filter cartridge, particularly upstream of a fuel cell, to protect the catalyst from catalyst poisons in the hydrogen gas used.

[0011] The flow-through filter unit can also have an indicator that indicates the degree of load of the filter unit and allows for timely replacement. Therefore, a fuel cell having at least one such flow-through filter unit according to the present invention is also a subject of the present invention. When the fuel cell is operated, depending on the degree of load of the first filter unit, the gas flow can be diverted to at least one second filter unit arranged "in parallel" with the gas flow, thereby enabling continuous operation of the fuel cell. At the same time, the first filter unit can be subjected to a step for recycling the complex metal hydride.

[0012] According to the invention, the metal-aluminum hydrides of the following formulae I to III are preferred as complex hydrides: Me x+ [AlH4] - x (where x=1~5), Me y x+ [AlH6] 3- z (where x·z=3z), and Me y x+ [AlH5] 2- r(where x y = 2r). Me represents one or more alkali or alkaline earth metals from the periodic table of elements. The complex hydride may be fully dehydrogenated or partially dehydrogenated. According to the present invention, dehydrogenation means that the metal-bound hydrogen has been removed from the metal hydride by dehydrogenation means, for example, by heating to decomposition temperatures.

[0013] The above composite hydrides can be supplemented with one or more metals, such as metal salts, metal compounds such as metal halides, or particulate metal compounds, to increase the reactivity of the metal hydrides. Preferred metals are transition metals from groups 3, 4, 5, 6, 7, 8, 9, 10, and 11, in particular Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Pr, and Nd, or alloys or mixtures of these metals with each other or with aluminum, or compounds of these metals, for example as metal salts such as metal halides, with particle sizes of about 10 nm to 1000 nm and / or specific surface areas of, for example, 50 to 1000 m. 2 / g) are provided in the form of very small particles with a high degree of distribution. For this purpose, metals are preferably used, such as the transition metals preferred above, as well as Ti, Zr, Sc, Y, and rare earth metals. The metals can be produced by a wide variety of reduction processes, either directly by in-situ reduction with complex metal hydrides, or ex-situ by the most widely different reduction processes. In this respect, in-situ production is preferred.

[0014] To ensure good distribution of the catalyst and complex hydride on the particle surface, additives such as carbon (graphite, spherical carbon, activated carbon) with particle diameters of 10 nm to 1000 nm or metal powder such as Al powder with particle diameters of 10 nm to 1000 nm can be added to the complex hydride or the mixture of metal and complex hydride. Partially oxidized complex hydrides can also be used. Oxidation is achieved simply by contact with oxygen (air), as in air.

[0015] The inventors hypothesized that when CO comes into contact with the metal hydride powder, a reaction occurs in which CO is at least partially reduced to CH4 and / or complexed, resulting in the absence of carbon monoxide in the gas after gas transfer / contact until the capacity of the complex metal hydride is exhausted.

[0016] According to the present invention, CO2-containing hydrogen gas is passed over and thus contacted with a metal hydride powder consisting of a composite hydride and a catalyst in a reactor, either in continuous or batch mode. The contacting can also be carried out in a closed reaction vessel such as a fluidized bed reactor or an autoclave. In continuous operation, the flow rate of the CO2-containing hydrogen gas is selected to ensure complete reaction and absorption (adsorption) on the composite metal hydride, and is typically 1.5 L / hg (complex metal hydride).

[0017] The pressure inside the reaction vessel is not critical as long as it is within the range of normal pressure to about 0.1 to 15 MPa. According to the present invention, the reaction temperature is, in principle, -20°C to 250°C.

[0018] Next, the present invention will be described in more detail with reference to the accompanying Figures 1 to 5 and manufacturing examples. [Brief explanation of the drawings]

[0019] In this regard, Figures 1 to 4 show plots for experiments comparing a method according to the invention with a method not according to the invention, and Figure 5 shows the test setup. DETAILED DESCRIPTION OF THE INVENTION

[0020] In this regard, FIG. 4 shows the reusability of a flow tube filled with complex metal aluminum hydride used in a method according to the invention, which has undergone a step to remove absorbed carbon monoxide, for example by the action of ambient air on the complex metal aluminum hydride.

[0021] Figure 5 shows the test equipment and explains the test method. As shown in Figure 5, the test equipment consists of an absorption tube 4 filled with composite aluminum hydride, a storage container 5 for the gas mixture used, a mass flow controller (mass flow meter) 6, a vacuum pump 7, and an IR spectrometer (IR spectrometer 8) for monitoring the CO concentration in the gas mixture. The individual work steps can be carried out under inert conditions via valves 1, 2, and 3.

[0022] Before starting the measurement, the entire apparatus is evacuated via valve 2 with valves 1 and 3 closed. Next, valve 2 is closed and the apparatus is filled with inert gas via valve 3. The mixed gas is supplied while valves 1 and 3 are open, and the gas flow rate is adjusted to the required amount by mass flow controller 6. After the gas mixture flows through absorption tube 4, the CO concentration is measured by IR spectrometer 8.

[0023] The decrease in the absorption capacity of the composite aluminum hydride during the removal of impurities from hydrogen gas can be seen in a simple manner by a color reaction in the window cartridge in the direction of flow downstream of the absorption tube 4 before the valve 1 and can therefore be monitored in this way. An example is the reaction of CO with iodine pentoxide deposited on the support of the window cartridge, which leads to the oxidation of CO to produce iodine according to the following reaction:

[0024] 5CO+I2O5 → 5CO2+I2

[0025] The released iodine discolors the support, where a color-forming reaction occurs. As a result, the decrease in absorption capacity can be optically observed and monitored, allowing the absorption tube to be replaced in good time. Two or more absorption tubes 4 are preferably arranged in parallel in the direction of flow, so that the gas flow can be switched from one absorption tube 4 to another in the event of a decrease in absorption capacity.

[0026] FIG. 4 shows the reusability of a flow tube filled with composite metal aluminium hydride for use in the method according to the invention, which can be reused after undergoing a step of removing absorbed carbon monoxide, for example by acting on the composite metal aluminium hydride with ambient air.

[0027] material and method CO concentrations were measured using an ABB URAS 26 NDIR spectrometer (non-dispersive infrared spectrometer). Gas concentrations were measured using a gas-filled opto-pneumatic detector. Particle size was determined by laser diffraction or, for very small particles, by TEM analysis (transmission electron microscopy).

[0028] Manufacturing example In a typical process, Na3AlH6 was ball-milled with TiCl3 (2-4 mol%) and optional other additives. The resulting material was used to remove CO from hydrogen gas. Similarly, this method could be used to remove other contaminants from hydrogen gas, such as CO2, HO, and sulfur compounds.

[0029] Example 1 In a flow tube, 2.0 g of a mixture of partially dehydrogenated Na3AlH6 (composition: (1-x)Na3AlH6 + 3xNaH + xAl) prepared by ball milling, TiCl3 (4 mol%), activated carbon (8 mol%), and Al powder (8 mol%) was passed through with hydrogen gas containing 10 ppm CO at a flow rate of 50 ml / min. After the gas mixture was passed through, CO was analyzed using IR spectroscopy; initially, no CO was detected. After 75 h, the CO concentration increased to 3 ppm.

[0030] Example 2 In a flow tube, 2.0 g of a ball-milled mixture of Na3AlH6, TiCl3 (4 mol%), activated carbon (8 mol%), and Al powder (8 mol%) was mixed with hydrogen gas and 10 ppm CO at a flow rate of 3 L / h. After the gas mixture was flowed, CO was analyzed using IR spectroscopy; initially, no CO was detected. After 46 hours, the CO concentration increased to 1.6 ppm.

[0031] Example 3 In a flow tube, 2.0 g of a ball-milled mixture of Na3AlH6 and TiCl3 (4 mol%) was flushed with hydrogen gas containing 100 ppm CO at a flow rate of 50 ml / min. After the flush, the gas mixture was analyzed for CO using IR spectroscopy. No CO was detectable for 60 minutes. Over the next 50 minutes, the CO content increased to 50 ppm.

[0032] Example 4 In a flow tube, 2.0 g of a ball-milled mixture of NaAlH4 and TiCl3 (4 mol%) was flushed with hydrogen gas containing 100 ppm CO at a flow rate of 50 ml / min. After the flush, the gas mixture was analyzed for CO using IR spectroscopy. No CO was detectable for 35 minutes. Over the next 25 minutes, the CO content increased to 75 ppm.

[0033] Example 5 In a flow tube, 2.0 g of pure NaAlH4 was flowed through hydrogen gas containing 100 ppm CO at a flow rate of 50 ml / min. After flowing, the gas mixture was examined for CO by IR spectroscopy. After 3 minutes, the CO content increased to 100 ppm.

[0034] Example 6 A 2.0 g mixture of ball-milled Na3AlH6, TiCl3 (4 mol%), activated carbon (8 mol%), and Al powder (8 mol%) was passed through a flow tube with 100 ppm hydrogen gas containing 100 ppm CO at a flow rate of 3 L / h at 30 °C. After the flow, the gas mixture was examined for CO by IR spectroscopy. No CO was detected until 30 minutes after the start of the test. Over the next 3 hours, the CO content increased to 90 ppm. The flow tube was then disconnected from the gas flow and exposed to ambient air for 10 minutes. After this, hydrogen gas containing 100 ppm CO was again passed through the flow tube. This mixture again exhibited a high absorption capacity for CO, with no CO detected for 15 minutes. After this, the mixture was washed with water. The CO content in the raw gas increased continuously again. Furthermore, the present invention includes the following items. [Item 1] 1. A method for removing carbon monoxide and / or gaseous sulfur compounds from a gas containing carbon monoxide and / or gaseous sulfur compounds, comprising: contacting a gas selected from hydrogen gas and / or one or more gaseous aliphatic hydrocarbons or mixtures thereof with a complex metal aluminum hydride in a reaction vessel; The metal aluminum hydride has the formula I, Me x+ [AlH 4 ] - x (wherein x=1-5), one or more compounds of formula II, Me y w+ [AlH 6 ] 3- z (wherein w·z=3z), and one or more compounds of formula III, Me p q+ [AlH 5 ] 2- r (where p·q=2r), and Me represents one or more alkali metals and / or alkaline earth metals. [Item 2] 2. A method for removing carbon monoxide and / or gaseous sulfur compounds from a gas containing carbon monoxide and / or gaseous sulfur compounds according to item 1, wherein a complex metal aluminum hydride of formula I-III is used, supplemented with one or more metals, as a metal compound such as a metal salt, e.g. a metal halide, or preferably in particulate form, and the metals used are one or more transition metals of groups 3, 4, 5, 6, 7, 8, 9, 10, 11, in particular Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Pr, and Nd, in particular Ti, Zr, Sc, or alloys or mixtures of these metals with each other or with aluminum. [Item 3] The metal or its compound has, for example, a particle size of about 10 nm to 1000 nm and / or a specific surface area of, for example, 50 to 1000 m 2 3. The method for removing carbon monoxide and / or gaseous sulfur compounds from a gas containing carbon monoxide and / or gaseous sulfur compounds according to Item 2, wherein a highly distributed, very small particle form having a particle size of 1 / 2 s / g is used. [Item 4] 4. The method according to any one of items 1 to 3, wherein one or more fully or partially dehydrogenated complex metal aluminum hydrides of formulae I to III are used. [Item 5] 5. The method according to any one of items 1 to 4, wherein one or more composite metal aluminum hydrides of formulae I to III are used, to which one or more metals in the form of particles are added, and the resulting mixture is preferably 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, and 11, preferably Ti, Zr, Sc, Y, and rare earth metals, or alloys or mixtures of these metals with each other or with aluminum. [Item 6] Item 6. The method according to item 5, wherein the metal or metals in the form of particles are produced by in situ reduction with a composite aluminum metal hydride of formula I-III. [Item 7] 7. The method according to any one of items 1 to 6, wherein a composite metal aluminum hydride to which carbon particles selected from graphite, spherical carbon, activated carbon or a mixture thereof are added is used. [Item 8] 8. The method according to any one of the preceding items, wherein the reaction vessel is configured in the form of a flow-through filter unit filled with one or more composite metal aluminum hydrides of formulae I to III as claimed in the method according to any one of the preceding items, optionally in combination with one or more metals in the form of particles and / or in combination with carbon particles. [Item 9] 1. A filter unit packed with one or more composite metal aluminum hydrides of formulae I to III, as used in the method according to one of items 1 to 6, optionally in combination with one or more metals in particulate form and / or in combination with particles of carbon. [Item 10] 10. A fuel cell having one or more filter units according to item 9.

Claims

1. 1. A method for removing carbon monoxide from a gas containing carbon monoxide, comprising: contacting the carbon monoxide-containing gas selected from hydrogen gas and / or one or more gaseous aliphatic hydrocarbons or mixtures thereof with a complex metal aluminum hydride in a reaction vessel; The metal aluminum hydride has the formula I, Me ｘ＋ [AlH ４ ] － ｘ (wherein x=1-5), and one or more compounds of formula II, Me ｙ ｗ＋ [AlH ６ ] ３－ ｚ where w y = 3z, and Me represents one or more alkali metals and / or alkaline earth metals; A composite metal aluminum hydride of formula I-II is used to which one or more metals in the form of metal particles as metal halides are added, The metal is one or more transition metals selected from Ti, Zr, Sc, or The above method, wherein an alloy or mixture of these metals with each other or with aluminum is used.

2. The metal or its compound has a particle size of about 10 nm to 1000 nm and / or a specific surface area of ​​50 to 1000 m ２ 2. The method for removing carbon monoxide from a gas containing carbon monoxide according to claim 1, wherein a form in which the carbon monoxide content is 1 / g is used.

3. 3. The process according to claim 1, wherein one or more partially dehydrogenated complex metal aluminum hydrides of formulae I-II are used.

4. 4. The method according to any one of claims 1 to 3, wherein one or more composite metal aluminium hydrides of formula I-II are used to which one or more metals in particulate form are added, and the resulting mixture is ground to a particle size of 0.5 to 1000 nm, wherein the metal or metals added are selected from Ti, Zr, Sc, or alloys or mixtures of these metals with each other or with aluminium.

5. 5. The method of claim 4, wherein the metal or metals in particulate form are produced by in situ reduction of a metal halide with a complex metal aluminum hydride of formula I-II.

6. 6. The method according to claim 1, wherein a composite aluminum metal hydride is used to which carbon particles selected from graphite, spherical carbon, activated carbon or mixtures thereof are added.

7. The composite metal aluminum hydride is Na ３ AlH ６ or NaAlH ４ The method according to any one of claims 1 to 6, wherein

8. 8. The method according to any one of claims 1 to 7, wherein the reaction vessel is configured in the form of a flow-through filter unit filled with one or more composite metal aluminium hydrides of formulae I to II as defined in the method according to any one of claims 1 to 6, in combination with one or more metals in the form of particles and / or in combination with carbon particles.

9. 7. A filter unit packed with one or more composite metal aluminum hydrides of formula I-II as defined by the method according to any one of claims 1 to 6 in combination with one or more metals in particle form and / or in combination with particles of carbon.

10. A fuel cell comprising one or more filter units according to claim 9.

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