CA2245904A1 - Compounds for the sorption of gases - Google Patents
Compounds for the sorption of gases Download PDFInfo
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- CA2245904A1 CA2245904A1 CA 2245904 CA2245904A CA2245904A1 CA 2245904 A1 CA2245904 A1 CA 2245904A1 CA 2245904 CA2245904 CA 2245904 CA 2245904 A CA2245904 A CA 2245904A CA 2245904 A1 CA2245904 A1 CA 2245904A1
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Abstract
Compounds having the formula: A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1; a method for preparing the compounds; a method for producing composite materials on various matrices and thin or thick films deposited on various substrates which contain the compounds; their use; and a method for eliminating certain gases from a mixture that includes them by using the compounds.
Description
CA 0224~904 1998-08-07 CO~n~DUNDS FOR THE SORPl~ON OF GASES
Technical Field The present invention relates to a new class of compounds having a gas-fixing activity, to a method for preparing said compounds, to methods for producing composite materials on various matrices and thin or thick 5 films deposited on various substrates and containing said compounds, and to their use, as well as to a method for eliminating certain gases from a mixture that comprises them by using said compounds.
Background Art Various classes of materials with gas-fixing lo capabilities are currently known. They can be divided into two categories, depending on whether a) the fixing properties depend on actual chemical reactions, which entail the decomposition of the fixing material or b) the fixing properties depend on the adsorption characteristics 15 at the physical surface of the fixer and, in general, on the size of the molecules to be fixed. Some typical examples of type a) mate~ials are compounds capable of eliminating water vapor from a mixture of gases, for example calcium sulfate, phosphorus pentoxide, magnesium 20 chloride, or carbon dioxide from a mixture of gases, for example sodium and potassium hydroxides and calcium, strontium, and barium oxides. ~lassic examples o~ type b) fixing materials are materials having an activated surface, such as activated charcoal or the various types of zeolite s 25 or some kinds of clay.
The fixing properties of type a) materials are selective, in that a compound is capable of fixing a single CA 0224~904 1998-08-07 type of gas. The range of usa~le spontaneous reactions is rather limited and does not include gases which are highly harmful to the health and to the environment, such as nitrogen monoxide No and carbon monoxide CO. Moreover, the involved reactions may be irreversible, so that the fixer loses all activity after a given utilization cycle.
On the other hand, type b~ materials are not selective and fix gas molecules according to their size, degree of polarity, and relative molecular mass. These materials are unable to fix light molecules, such as the combustion products that are most harmful to the health and to the environment, such as mixtures of nitrogen oxides NO and N02 and carbon oxides, particularly the monoxide CO.
Disclosure of the Invention A principal aim of the present invention is to eliminate the drawbac~s of conventional materials having gas-fixing capabilities, with particular interest for the removal of noxious components from combustion products and more generally from gas mixtures.
This.aim as well as other ob~ects which will become apparent ~rom the following detailed description of the invention are achieved by a class of compounds according to the invention, which is represented by a compound having the formula A2B306+d, wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide or a solid solution thereof; B is a transition metal, an element of group III, or a solid solution thereof; and d has a value between O
and 1.
Advantageously, A is chosen from the group constituted by barium, cesium, potassium, strontium, a lanthanide, or CA 0224~904 1998-08-07 W O 97/Z8884 PCT~EP97/00598 solid solutions thereo~.
Conveniently, B is chosen from the group constituted b by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
Examples of compounds according to the invention, wherein A is a solid solution of the above-mentioned cations, are those having the formula (Ba2_xSrx)Cu306 produced with values of x up to 0 75.
Other examples of compounds according to the invention, wherein B is a solid solution of the above-mentioned cations, have the formula Ba2(Cu3_yPdy)Od produced with y up to 0.33;
Ba2(Cu3_yNiy)~d produced with y up to 1Ø
A compound having the formula Ba2Cu305+x has been identified and partially described in the literature (see for example w. Wong-Ng and L.P. Cook, Powder Dif~raction, 9 (1994), p. 280-289 and the references listed therein).
However, the researchers who preceded the inventors of the 20 present invention did not realize that they were in the presence of a new class of compounds having particular chemical activity characteristics.
In the compounds of the class to which this description relates, several phenomena which are 25 intermediate between the behavior observed in type a) and type b) fixing compounds have been observed for the first time. The fixed gas molecules in fact react with the fixing material, in that they are truly bonded to the structure of the solid in the form of anions, as in type a) materials.
30 However, the chemical reaction, within wide limits in terms CA 0224~904 1998-08-07 of fixed gas amount, does not produce the decomposition of the fixing compound, the structural characteristics whereof vary to a very limited extent and in any case continuously and reversibly as a function of the amount of gas removed 5 from the reaction atmosphere, similarly to the behavior observed in type b) fixers. Moreover, the fixing properties of the compounds according to the invention are not selective as in type a) materials and occur with a relatively wide variety of gases, such as gaseous halogens 10 and oxides.
Compounds having the formula A2B306+d according to the present invention can be prepared by direct reaction starting from mixtures containing oxide, peroxide, and nitrate precursors. These compounds lead to a 15 characteris~ic X-ray powder dif~raction profile, a typical example whereof, related to a sample of Ba2Cu306+d, is shown in figure 1 (CuK~ radiation was used). The spectrum in the figure can be indexed on the basis of an orthorhombic cell with a = 4.316(1), b = 6.889(2), and c =
20 11.442(3) A; the cell parameters, however, undergo significant variations as a function o~ d.
The formation temperatures of the compounds according to the present invention are typically within the range of 300 to 950~C. The optimum values of course vary as a 25 function of the cations being used.
The method for preparing the compounds having the formula A2B306~d according to the present invention comprises a stage for the heat treatment of mixtures of oxides, peroxides, or salts of the required cations in 30 highly oxidizing conditions. For example, heating occurs in CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/0~598 _ ~ _ a controlled atmosphere that contains only o~ygen, nitrogen, and inert gases.
of course, the higher the content of oxidizing compounds (for example peroxides or nitrates) in the 5 initial mixture, the lower the partial pressure of oxygen in the atmosphere required to prepare the chosen compound.
Vice versa, the higher the pressure of the o~ygen in the reaction atmosphere, the lesser the role of the oxidizing component in the mixture of precursors.
lo The compounds according to the present invention can be prepared as polycrystalline aggregates, as components in composite materials having various matrices, and in the form of thin or thick layers on various substrates.
Advantageously, the compounds according to the present 15 invention can be prepared starting from a mixture comprising one or more oxygenated compounds of an alkaline or alkaline-earth metal and one or more oxides of transition metals or elements of group III.
Moreover, the compounds according to the present 20 invention can be prepared starting from a mixture comprising one or more nitrates of an alkaline-earth or alkaline metal and one or more nitrates of transition metals or of elements of group III.
The following procedures illustrate the methods for 25 preparing the compound A2B306+d.
The following examp7es of a preparation method for the compounds according to the present invention are given only by w~y of non-limitative example.
In all the procedures presented hereafter, the 30 cationic molar ratio for producing the indicated solutions CA 0224~904 1998-08-07 and mixtures is given. For the sake of greater precision, the corresponding weight ratios are specified hereafter for each procedure.
Procedure A
A1) A mixture of fine powders of barium peroxide and copper oxide in a 2:3 molar ratio [0.704 grams of copper oxide (CuO) for every gram of ~arium peroxide (BaO2)~ is produced;
A2) The mixture is homogenized by milling with a mechanical mill or manually with a mortar and pestle of agate or with another method for dry mixing or for mixing in the presence of appropriate liquids;
A3) The homogenized mixture is placed in an inert refractory container (alumina or the like) and is heated in a furnace under a stream of oxygen and inert gas (the partial pressure of the oxygen is typically 2 0.2 bar, 1 cc/sec) at 580.650~C.
A4) The compound is kept at the same temperature for 12 hours.
A5) Steps A2, A3, and A4 are repeated until a compound is obtained which provides the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2Cu306+d phase.
Procedure B
Bl) A mixture of fine powders of barium nitrate and copper oxide in a 2:3 molar ratio [0.457 grams of copper oxide (CuO) for every gram of barium nitrate (Ba(N03)2)] is produced;
CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 B2) Same as A2.
B3) Same as A3.
B4) The compound is kept at the same temperature until the solution o~ No2 gas generated by the decomposition of the nitrate salts is depleted. At the end of the process, the compound is obtained which gives the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2CU3~6+d phase, B5) With this procedure, the dimensions of the resulting granules are in the millimeter range and allow the use of sing~e-crystal characterization techniques.
Procedure C
C1) A mixture of fine powders of barium nitrate and copper nitrate in a 2:3 molar ratio [1.335 grams of hemipentahydrate copper nitrate (Cu(N03)2+2.520) or 1.077 grams of anhydrous copper nitrate (Cu(N03)2) for every gram of barium nitrate] is produced;
C2) Same as A2.
C3) S.ame as A3.
C4) Same as B4.
C5) Same as B5.
Procedure D
D1) A mixture of fine powders of barium oxide and copper oxide in a 2:3 molar ratio ~0.778 grams of copper 2~ oxide (CuO) for every gram of barium oxide (BaO)] is produced;
D2) Same as A2;
D3) The homogenized mixture is placed in an inert CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 8 _ refractory container ~alumina or the li~e) and is heated in a pressurized furnace with a partial oxygen pressure in excess of 1 bar at 580.650~C;
D4) Same as A4;
D5) Steps D2, D3, and D4 are repeated until a compound is obtained which has the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2Cu306+d phase.
Procedure E
El) A solution of barium nitrate and copper nitrate in 10 a 2:3 molar ratio is prepared in distilled water up to the solubility limit for barium nitrate [1.335 grams of hemipentahydrate copper nitrate (Cu(N03)2+2.520) or 1.077 grams of anhydrous copper nitrate (Cu(N03)2) for every gram of barium nitrate];
E2) An inert, temperature-resistant, porous medium (for example neutral activated Brockman alumina) is impregnated with the solution thus prepared;
E3) The water is eliminated with a drying treatment at 150~C for 2 hours.
E4) Same as B4, but the reflections of the porous substrate, if crystalline, are also found in the X-ray diffractogram.
E5) The final product is a composite material wherein the compound Ba2Cu306+d fills the microcavities o~ the 25 porous substrate.
Procedure F.
Fl) Same as El;
F2) The solution is used to wet the surface of a CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 _ g _ :
substrate of temperature-resistant, non-porous, inert material, constituted by polycrystalline A1203 with a relative density of 99.9% (other examples of usable non-porous inert materials are quartz, porcelain, Inconel, 5 oxidation-resistant alloys and metals, etcetera);
F3) The deposited water is quickly evaporated ~y electrical heating to approximately 230~C;
F4) Steps F2 and F3 are repeated until a thin deposition of nitrates of the desired thickness, for lo example approximately 10 ~, is o~tained;
F5) Same as B4.
F6) The final product is a film of Ba2Cu306+d having a presettable thickness.
In another aspect, the present invention relates to a 15 method for eliminating certain gases from a gaseous mixture including them. The ability of the compounds according to the present invention to fix molecules of various gases directly from the gaseous state has been verified by direct measurements, such as thermogravimetry, analysis of the gases in the reaction atmosphere, or by indirect measurements, such as Raman and infrared spectroscopy. The compounds according to the present invention are particularly adapted for fixing oxides and halogens in the gaseous phase.
Fxamples of such gases are N02, C02, S02, N0, C0, F2, and C12.
The way of fixing the gas depends on the type of gas and on the temperature and composition of the atmosphere in which the reaction occurs.
The inventors of the present invention have observed CA 0224~904 l998-08-07 W O 97/28884 PCT~EP97/00598 for the first time in the compounds of the class to which the present invention relates ~ixing phenomena which are intermediate between the behavior observed in conventional fixing compounds of types a) and b) described above. The 5 gas molecules are in fact fixed by reacting chemically with the fixing material, in that they are bonded to the structure of the solid in the form of anions. However, the chemical reactions related to the fixing processes, although continuously modifying the composition of the lo fixer, do not cause, over a broad range in terms of amount of fixed gas, the destruction of the structure of the fixing solid, the structural parameters whereof vary to a very small extent and in any case continuously as a function of the amount of gas removed from the reaction 15 atmosphere. If the process is continued beyond these limits, absorption can continue but it entails the destruction of the fixer structure and the formation of oxides or of the salts corresponding to the anions that form.
The gases fixed by means of the mechanisms that are active in the first stages of the process, regardless of their nature, enter the compounds according to the invention in the form of oxyanions or halide ions. The structural characteristics of the fixing compounds vary 25 continuously during this first part of the process, in the same way in which the structural characteristics of a solid solution vary as one of its components varies. During this stage, the fi~ing process is reversible for many of the fixable gases; by varying the partial pressures and the 30 temperature it is possible to d-esorb them fully or ~ CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/OOS98 partially. Gaseous oxides with a low oxidation state (NO
and CO, for example) can be desorbed in a higher oxidation state (N02 and C02, for example) if the atmosphere in which release occurs is sufficiently oxidizing. Once a first 5 limit concentration of oxyanions or halides, which depends on the type of gas and on the temperature, has been reached, reversibility is lost except in the case of nitrogen oxides. In this particular case, reversibility of the fixing process is complete, since the final product 10 corresponds to the initial material for the production of the compounds at issue, as described in preparation procedure B) or C), depending on whether the process occurs above or below the temperature at which the copper nitrate decomposes to copper oxide.
The chemical reactions related to the fixing processes occur by virtue of the presence of an excess of oxygen in the structure. By way of example, in the case of the compound in which A = Ba and B = Cu, the oxygen composition produced by the normal state of oxidation of the cations 20 (Ba2+ and Cu2+) would be 5 atoms per unit of the formula (Ba2Cu305), whilst accurate determinations of the oxygen content in samples prepared according to the previously described procedures show an oxygen content that is typically in the range of 5.5 to 6.1 atoms per unit of the 25 formula. Accordingly, the fixing processes do not require r the addition of external oxygen; however, their yield is increased by the presence o~ oxygen in the gas mixtures placed in contact with the fixing materials.
The method according to the present invention for 30 eliminating certain gases from a gaseous mixture that CA 0224~904 l998-08-07 includes them consists in placing the gas mixture in contact with a compound having the formula A2B306+d in pure form or as a component of composite materials, in which A
is an al~aline-earth metal, an alkaline metal, a 5 lanthanide, or a solid solution thereof; B is a transitiOn metal, an element of group III, or a solid solution thereof; and d has a value between 0 and 1, at a temperature between the melting temperature of the compound to be fixed and 650~C. Preferably, A is chosen from the 10 group constituted by barium, cesium, potassium, strontium, or solid solutions thereof, and B is chosen from the group constituted by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
The method is described in greater detail hereinafter with two examples referring to situations that produce different yields:
1) fixing of N02 at room temperature from an oxygen-containing atmosphere;
2) hot fixing o~ N0 ~rom an o~ygen-free atmosphere.
The following examples of gas fi~ing methods using compounds according to the present invention are given merely by way of non-limitative example.
Example 1) N02 fixing 3 grams of ~a2Cu306+d produced according to procedure B) are placed in a U-shaped tube wherein a stream of No2 (50%) and air is made to flow (90 cc/min flow, 20~C
temperature). The gas fixing activity is clearly shown in figure 2, which shows a first U-shaped tube (1) and a 30 second U-shaped tube (2) which are parallel-connected with CA 0224~904 l998-08-07 _ ~3 respect to the stream of N02 and air; a layer of Ba2Cu30~+d is present in the base of tube (1), whilst a layer of white material (for example cotton) is present in the base of tube (2). It is o~served that in tube (1) the gas changes 5 color from orange (represented by stippling) to colorless as a consequence o~ its passage through the layer of sa2cu306+d, whilst in tube (2) it remains of the same orange color after passing through the white layer. In these conditions, the ~ixing activity persists for lo approximately 300 minutes. At the end of the process, a weight increase was found which corresponded, within the measurement errors (5%), to the total conversion of the initial compound into copper and barium nitrate salts and to the fixing of 10 moles of gas per mole of fixer.
15 Example 2) NO fixing Figure 3 shows the result of an N0 concentration analysis by mass spectrometry on two gas streams (112 cc/min) originating ~rom a common source o~ a mixture of He+0.4%N0, one of which passes through a reactor brought to 20 350~C which contains 1 gram of Ba2Cu306+d compound produced according to procedure A). This measurement points out different fixing processes with separate kinetics. The amount of gas fixed at saturation (2 hours) is 0.28 moles per mole of fixer.
Another aspect of the present invention relates to an electric sensor for gas concentration, which comprises a compound having the formula A2B306+d. The inventors have in fact found that for the compounds according to the present invention, during the gas fixing process, the value CA 0224~904 1998-08-07 O 97/28884 PCT~gP97/00598 14 -of electrical resistivity increases in proportion to the amount of gas that is incorporated. For example, the compound Ba2Cu306+d is a semiconductor with typical values of electrical resistance at room temperature on the order of 10-100 ohm/cm. In the case of the fixing of nitrogen or carbon oxides, this value is up to 4 orders of magnitude higher. Figure 4 plots the electrical resistance of a film produced according to procedure E) and exposed to a stream of No2 (50~) and air at room temperature.
Moreover, in another aspect the present invention relates to optical gas concentration sensors which comprise a compound having the formula A2B306+d.
The inventors of the present invention have found that the compounds having the formula A2B3~6+d show considerable variations in their optical properties during the gas incorporation process. These variations become apparent as variations in the intensities of the characteristic modes in infrared and Raman spectra, with the appearance of new optical modes caused by the characteristic vibrations of the incorporated anions and with the appearance of characteristics which cannot be ascribed to the initial material or to the guest anions, such as ~or example a plurality of highly intense luminescence peaks which appear as a consequence of the incorporation of small amounts of carbon oxides. In addition to the variations in the measured spectra, macroscopic changes in color are observed as a consequence of the incorporation of small amounts of carbon oxides. For example, the color of the Ba2Cu306+d changes from the initial dark blue to black, whilst a color change is CA 02245904 l998-08-07 observed towards greenish pale blue as a consequence of the incorporation of large amounts of nitrogen oxides below 70~C .
s ~ h ~i
Technical Field The present invention relates to a new class of compounds having a gas-fixing activity, to a method for preparing said compounds, to methods for producing composite materials on various matrices and thin or thick 5 films deposited on various substrates and containing said compounds, and to their use, as well as to a method for eliminating certain gases from a mixture that comprises them by using said compounds.
Background Art Various classes of materials with gas-fixing lo capabilities are currently known. They can be divided into two categories, depending on whether a) the fixing properties depend on actual chemical reactions, which entail the decomposition of the fixing material or b) the fixing properties depend on the adsorption characteristics 15 at the physical surface of the fixer and, in general, on the size of the molecules to be fixed. Some typical examples of type a) mate~ials are compounds capable of eliminating water vapor from a mixture of gases, for example calcium sulfate, phosphorus pentoxide, magnesium 20 chloride, or carbon dioxide from a mixture of gases, for example sodium and potassium hydroxides and calcium, strontium, and barium oxides. ~lassic examples o~ type b) fixing materials are materials having an activated surface, such as activated charcoal or the various types of zeolite s 25 or some kinds of clay.
The fixing properties of type a) materials are selective, in that a compound is capable of fixing a single CA 0224~904 1998-08-07 type of gas. The range of usa~le spontaneous reactions is rather limited and does not include gases which are highly harmful to the health and to the environment, such as nitrogen monoxide No and carbon monoxide CO. Moreover, the involved reactions may be irreversible, so that the fixer loses all activity after a given utilization cycle.
On the other hand, type b~ materials are not selective and fix gas molecules according to their size, degree of polarity, and relative molecular mass. These materials are unable to fix light molecules, such as the combustion products that are most harmful to the health and to the environment, such as mixtures of nitrogen oxides NO and N02 and carbon oxides, particularly the monoxide CO.
Disclosure of the Invention A principal aim of the present invention is to eliminate the drawbac~s of conventional materials having gas-fixing capabilities, with particular interest for the removal of noxious components from combustion products and more generally from gas mixtures.
This.aim as well as other ob~ects which will become apparent ~rom the following detailed description of the invention are achieved by a class of compounds according to the invention, which is represented by a compound having the formula A2B306+d, wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide or a solid solution thereof; B is a transition metal, an element of group III, or a solid solution thereof; and d has a value between O
and 1.
Advantageously, A is chosen from the group constituted by barium, cesium, potassium, strontium, a lanthanide, or CA 0224~904 1998-08-07 W O 97/Z8884 PCT~EP97/00598 solid solutions thereo~.
Conveniently, B is chosen from the group constituted b by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
Examples of compounds according to the invention, wherein A is a solid solution of the above-mentioned cations, are those having the formula (Ba2_xSrx)Cu306 produced with values of x up to 0 75.
Other examples of compounds according to the invention, wherein B is a solid solution of the above-mentioned cations, have the formula Ba2(Cu3_yPdy)Od produced with y up to 0.33;
Ba2(Cu3_yNiy)~d produced with y up to 1Ø
A compound having the formula Ba2Cu305+x has been identified and partially described in the literature (see for example w. Wong-Ng and L.P. Cook, Powder Dif~raction, 9 (1994), p. 280-289 and the references listed therein).
However, the researchers who preceded the inventors of the 20 present invention did not realize that they were in the presence of a new class of compounds having particular chemical activity characteristics.
In the compounds of the class to which this description relates, several phenomena which are 25 intermediate between the behavior observed in type a) and type b) fixing compounds have been observed for the first time. The fixed gas molecules in fact react with the fixing material, in that they are truly bonded to the structure of the solid in the form of anions, as in type a) materials.
30 However, the chemical reaction, within wide limits in terms CA 0224~904 1998-08-07 of fixed gas amount, does not produce the decomposition of the fixing compound, the structural characteristics whereof vary to a very limited extent and in any case continuously and reversibly as a function of the amount of gas removed 5 from the reaction atmosphere, similarly to the behavior observed in type b) fixers. Moreover, the fixing properties of the compounds according to the invention are not selective as in type a) materials and occur with a relatively wide variety of gases, such as gaseous halogens 10 and oxides.
Compounds having the formula A2B306+d according to the present invention can be prepared by direct reaction starting from mixtures containing oxide, peroxide, and nitrate precursors. These compounds lead to a 15 characteris~ic X-ray powder dif~raction profile, a typical example whereof, related to a sample of Ba2Cu306+d, is shown in figure 1 (CuK~ radiation was used). The spectrum in the figure can be indexed on the basis of an orthorhombic cell with a = 4.316(1), b = 6.889(2), and c =
20 11.442(3) A; the cell parameters, however, undergo significant variations as a function o~ d.
The formation temperatures of the compounds according to the present invention are typically within the range of 300 to 950~C. The optimum values of course vary as a 25 function of the cations being used.
The method for preparing the compounds having the formula A2B306~d according to the present invention comprises a stage for the heat treatment of mixtures of oxides, peroxides, or salts of the required cations in 30 highly oxidizing conditions. For example, heating occurs in CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/0~598 _ ~ _ a controlled atmosphere that contains only o~ygen, nitrogen, and inert gases.
of course, the higher the content of oxidizing compounds (for example peroxides or nitrates) in the 5 initial mixture, the lower the partial pressure of oxygen in the atmosphere required to prepare the chosen compound.
Vice versa, the higher the pressure of the o~ygen in the reaction atmosphere, the lesser the role of the oxidizing component in the mixture of precursors.
lo The compounds according to the present invention can be prepared as polycrystalline aggregates, as components in composite materials having various matrices, and in the form of thin or thick layers on various substrates.
Advantageously, the compounds according to the present 15 invention can be prepared starting from a mixture comprising one or more oxygenated compounds of an alkaline or alkaline-earth metal and one or more oxides of transition metals or elements of group III.
Moreover, the compounds according to the present 20 invention can be prepared starting from a mixture comprising one or more nitrates of an alkaline-earth or alkaline metal and one or more nitrates of transition metals or of elements of group III.
The following procedures illustrate the methods for 25 preparing the compound A2B306+d.
The following examp7es of a preparation method for the compounds according to the present invention are given only by w~y of non-limitative example.
In all the procedures presented hereafter, the 30 cationic molar ratio for producing the indicated solutions CA 0224~904 1998-08-07 and mixtures is given. For the sake of greater precision, the corresponding weight ratios are specified hereafter for each procedure.
Procedure A
A1) A mixture of fine powders of barium peroxide and copper oxide in a 2:3 molar ratio [0.704 grams of copper oxide (CuO) for every gram of ~arium peroxide (BaO2)~ is produced;
A2) The mixture is homogenized by milling with a mechanical mill or manually with a mortar and pestle of agate or with another method for dry mixing or for mixing in the presence of appropriate liquids;
A3) The homogenized mixture is placed in an inert refractory container (alumina or the like) and is heated in a furnace under a stream of oxygen and inert gas (the partial pressure of the oxygen is typically 2 0.2 bar, 1 cc/sec) at 580.650~C.
A4) The compound is kept at the same temperature for 12 hours.
A5) Steps A2, A3, and A4 are repeated until a compound is obtained which provides the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2Cu306+d phase.
Procedure B
Bl) A mixture of fine powders of barium nitrate and copper oxide in a 2:3 molar ratio [0.457 grams of copper oxide (CuO) for every gram of barium nitrate (Ba(N03)2)] is produced;
CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 B2) Same as A2.
B3) Same as A3.
B4) The compound is kept at the same temperature until the solution o~ No2 gas generated by the decomposition of the nitrate salts is depleted. At the end of the process, the compound is obtained which gives the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2CU3~6+d phase, B5) With this procedure, the dimensions of the resulting granules are in the millimeter range and allow the use of sing~e-crystal characterization techniques.
Procedure C
C1) A mixture of fine powders of barium nitrate and copper nitrate in a 2:3 molar ratio [1.335 grams of hemipentahydrate copper nitrate (Cu(N03)2+2.520) or 1.077 grams of anhydrous copper nitrate (Cu(N03)2) for every gram of barium nitrate] is produced;
C2) Same as A2.
C3) S.ame as A3.
C4) Same as B4.
C5) Same as B5.
Procedure D
D1) A mixture of fine powders of barium oxide and copper oxide in a 2:3 molar ratio ~0.778 grams of copper 2~ oxide (CuO) for every gram of barium oxide (BaO)] is produced;
D2) Same as A2;
D3) The homogenized mixture is placed in an inert CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 8 _ refractory container ~alumina or the li~e) and is heated in a pressurized furnace with a partial oxygen pressure in excess of 1 bar at 580.650~C;
D4) Same as A4;
D5) Steps D2, D3, and D4 are repeated until a compound is obtained which has the X-ray diffraction pattern shown in figure 1, which characterizes the Ba2Cu306+d phase.
Procedure E
El) A solution of barium nitrate and copper nitrate in 10 a 2:3 molar ratio is prepared in distilled water up to the solubility limit for barium nitrate [1.335 grams of hemipentahydrate copper nitrate (Cu(N03)2+2.520) or 1.077 grams of anhydrous copper nitrate (Cu(N03)2) for every gram of barium nitrate];
E2) An inert, temperature-resistant, porous medium (for example neutral activated Brockman alumina) is impregnated with the solution thus prepared;
E3) The water is eliminated with a drying treatment at 150~C for 2 hours.
E4) Same as B4, but the reflections of the porous substrate, if crystalline, are also found in the X-ray diffractogram.
E5) The final product is a composite material wherein the compound Ba2Cu306+d fills the microcavities o~ the 25 porous substrate.
Procedure F.
Fl) Same as El;
F2) The solution is used to wet the surface of a CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/00598 _ g _ :
substrate of temperature-resistant, non-porous, inert material, constituted by polycrystalline A1203 with a relative density of 99.9% (other examples of usable non-porous inert materials are quartz, porcelain, Inconel, 5 oxidation-resistant alloys and metals, etcetera);
F3) The deposited water is quickly evaporated ~y electrical heating to approximately 230~C;
F4) Steps F2 and F3 are repeated until a thin deposition of nitrates of the desired thickness, for lo example approximately 10 ~, is o~tained;
F5) Same as B4.
F6) The final product is a film of Ba2Cu306+d having a presettable thickness.
In another aspect, the present invention relates to a 15 method for eliminating certain gases from a gaseous mixture including them. The ability of the compounds according to the present invention to fix molecules of various gases directly from the gaseous state has been verified by direct measurements, such as thermogravimetry, analysis of the gases in the reaction atmosphere, or by indirect measurements, such as Raman and infrared spectroscopy. The compounds according to the present invention are particularly adapted for fixing oxides and halogens in the gaseous phase.
Fxamples of such gases are N02, C02, S02, N0, C0, F2, and C12.
The way of fixing the gas depends on the type of gas and on the temperature and composition of the atmosphere in which the reaction occurs.
The inventors of the present invention have observed CA 0224~904 l998-08-07 W O 97/28884 PCT~EP97/00598 for the first time in the compounds of the class to which the present invention relates ~ixing phenomena which are intermediate between the behavior observed in conventional fixing compounds of types a) and b) described above. The 5 gas molecules are in fact fixed by reacting chemically with the fixing material, in that they are bonded to the structure of the solid in the form of anions. However, the chemical reactions related to the fixing processes, although continuously modifying the composition of the lo fixer, do not cause, over a broad range in terms of amount of fixed gas, the destruction of the structure of the fixing solid, the structural parameters whereof vary to a very small extent and in any case continuously as a function of the amount of gas removed from the reaction 15 atmosphere. If the process is continued beyond these limits, absorption can continue but it entails the destruction of the fixer structure and the formation of oxides or of the salts corresponding to the anions that form.
The gases fixed by means of the mechanisms that are active in the first stages of the process, regardless of their nature, enter the compounds according to the invention in the form of oxyanions or halide ions. The structural characteristics of the fixing compounds vary 25 continuously during this first part of the process, in the same way in which the structural characteristics of a solid solution vary as one of its components varies. During this stage, the fi~ing process is reversible for many of the fixable gases; by varying the partial pressures and the 30 temperature it is possible to d-esorb them fully or ~ CA 0224~904 1998-08-07 W O 97/28884 PCT~EP97/OOS98 partially. Gaseous oxides with a low oxidation state (NO
and CO, for example) can be desorbed in a higher oxidation state (N02 and C02, for example) if the atmosphere in which release occurs is sufficiently oxidizing. Once a first 5 limit concentration of oxyanions or halides, which depends on the type of gas and on the temperature, has been reached, reversibility is lost except in the case of nitrogen oxides. In this particular case, reversibility of the fixing process is complete, since the final product 10 corresponds to the initial material for the production of the compounds at issue, as described in preparation procedure B) or C), depending on whether the process occurs above or below the temperature at which the copper nitrate decomposes to copper oxide.
The chemical reactions related to the fixing processes occur by virtue of the presence of an excess of oxygen in the structure. By way of example, in the case of the compound in which A = Ba and B = Cu, the oxygen composition produced by the normal state of oxidation of the cations 20 (Ba2+ and Cu2+) would be 5 atoms per unit of the formula (Ba2Cu305), whilst accurate determinations of the oxygen content in samples prepared according to the previously described procedures show an oxygen content that is typically in the range of 5.5 to 6.1 atoms per unit of the 25 formula. Accordingly, the fixing processes do not require r the addition of external oxygen; however, their yield is increased by the presence o~ oxygen in the gas mixtures placed in contact with the fixing materials.
The method according to the present invention for 30 eliminating certain gases from a gaseous mixture that CA 0224~904 l998-08-07 includes them consists in placing the gas mixture in contact with a compound having the formula A2B306+d in pure form or as a component of composite materials, in which A
is an al~aline-earth metal, an alkaline metal, a 5 lanthanide, or a solid solution thereof; B is a transitiOn metal, an element of group III, or a solid solution thereof; and d has a value between 0 and 1, at a temperature between the melting temperature of the compound to be fixed and 650~C. Preferably, A is chosen from the 10 group constituted by barium, cesium, potassium, strontium, or solid solutions thereof, and B is chosen from the group constituted by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
The method is described in greater detail hereinafter with two examples referring to situations that produce different yields:
1) fixing of N02 at room temperature from an oxygen-containing atmosphere;
2) hot fixing o~ N0 ~rom an o~ygen-free atmosphere.
The following examples of gas fi~ing methods using compounds according to the present invention are given merely by way of non-limitative example.
Example 1) N02 fixing 3 grams of ~a2Cu306+d produced according to procedure B) are placed in a U-shaped tube wherein a stream of No2 (50%) and air is made to flow (90 cc/min flow, 20~C
temperature). The gas fixing activity is clearly shown in figure 2, which shows a first U-shaped tube (1) and a 30 second U-shaped tube (2) which are parallel-connected with CA 0224~904 l998-08-07 _ ~3 respect to the stream of N02 and air; a layer of Ba2Cu30~+d is present in the base of tube (1), whilst a layer of white material (for example cotton) is present in the base of tube (2). It is o~served that in tube (1) the gas changes 5 color from orange (represented by stippling) to colorless as a consequence o~ its passage through the layer of sa2cu306+d, whilst in tube (2) it remains of the same orange color after passing through the white layer. In these conditions, the ~ixing activity persists for lo approximately 300 minutes. At the end of the process, a weight increase was found which corresponded, within the measurement errors (5%), to the total conversion of the initial compound into copper and barium nitrate salts and to the fixing of 10 moles of gas per mole of fixer.
15 Example 2) NO fixing Figure 3 shows the result of an N0 concentration analysis by mass spectrometry on two gas streams (112 cc/min) originating ~rom a common source o~ a mixture of He+0.4%N0, one of which passes through a reactor brought to 20 350~C which contains 1 gram of Ba2Cu306+d compound produced according to procedure A). This measurement points out different fixing processes with separate kinetics. The amount of gas fixed at saturation (2 hours) is 0.28 moles per mole of fixer.
Another aspect of the present invention relates to an electric sensor for gas concentration, which comprises a compound having the formula A2B306+d. The inventors have in fact found that for the compounds according to the present invention, during the gas fixing process, the value CA 0224~904 1998-08-07 O 97/28884 PCT~gP97/00598 14 -of electrical resistivity increases in proportion to the amount of gas that is incorporated. For example, the compound Ba2Cu306+d is a semiconductor with typical values of electrical resistance at room temperature on the order of 10-100 ohm/cm. In the case of the fixing of nitrogen or carbon oxides, this value is up to 4 orders of magnitude higher. Figure 4 plots the electrical resistance of a film produced according to procedure E) and exposed to a stream of No2 (50~) and air at room temperature.
Moreover, in another aspect the present invention relates to optical gas concentration sensors which comprise a compound having the formula A2B306+d.
The inventors of the present invention have found that the compounds having the formula A2B3~6+d show considerable variations in their optical properties during the gas incorporation process. These variations become apparent as variations in the intensities of the characteristic modes in infrared and Raman spectra, with the appearance of new optical modes caused by the characteristic vibrations of the incorporated anions and with the appearance of characteristics which cannot be ascribed to the initial material or to the guest anions, such as ~or example a plurality of highly intense luminescence peaks which appear as a consequence of the incorporation of small amounts of carbon oxides. In addition to the variations in the measured spectra, macroscopic changes in color are observed as a consequence of the incorporation of small amounts of carbon oxides. For example, the color of the Ba2Cu306+d changes from the initial dark blue to black, whilst a color change is CA 02245904 l998-08-07 observed towards greenish pale blue as a consequence of the incorporation of large amounts of nitrogen oxides below 70~C .
s ~ h ~i
Claims (35)
1. Use of a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1, for fixing gases.
2. Use of a compound according to claim 1, characterized in that A is chosen from the group constituted by barium, cesium, potassium, strontium, a lanthanide, or solid solutions thereof.
3. Use of a compound according to claim 1, characterized in that B is chosen from the group constituted by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
4. Use of a compound according to claim 1, characterized in that said compound has the formula Ba2Cu3O6~d.
5. Use of a compound according to claim 1, characterized in that said compound has the formula (Ba2-x A x)Cu3O6~d wherein A is an alkaline metal, an alkaline-earth metal, or a lanthanide.
6. Use of a compound according to claim 1, characterized in that said compound has the formula (Ba2-x Sr x)Cu3O6~d, 0 < x < 0.75
7. Use of a compound according to claim 1, characterized in that said compound has the formula Ba2(Cu3-y B y)O6~d, 0 < y < 1, wherein B is a transition metal or an element of group III.
8. Use of a compound according to claim 1, characterized in that said compound has the formula Ba2(Cu3-y Ni y)O6~d, 0 < y < 1
9. Use of a compound according to claim 1, characterized in that said compound has the formula Ba2(Cu3-y Pd y)O6~d, 0 < y < 0.33
10. Use of a compound according to claim 1, characterized in that said gas is an oxide or a gaseous halogen.
11. Use of a compound according to claim 10, characterized in that said gas is chosen from the group constituted by NO, NO2, CO2, CO, SO2, F2, and C1 2.
12. A method for eliminating one or more gaseous oxides or halogens from a mixture of gases that contains them, comprising the stage of placing said gas mixture in contact with a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1, at a temperature between -196°C and 650°C.
13. A method according to claim 12, characterized in that said gas to be eliminated is chosen from the group constituted by NO, NO2, CO2, CO, SO2, F2, and C1 2.
14. A method according to claim 13, characterized in that the gas to be eliminated is NO2 and said temperature is preferably between -20°C and 300°C.
15. A method according to claim 13, characterized in that the gas to be eliminated is NO and said temperature is between -20°C and 500°C.
16. A method according to claim 12, characterized in that it comprises a subsequent step for the regeneration of said compound by heating to a temperature between 550 and 750°C.
17. A method according to claim 16, characterized in that said regeneration step occurs in an oxidizing atmosphere.
18. A compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1, and its oxyanionic derivatives, provided that said compound is different from Ba2Cu3O6~d, Na2Ti3O7 and LA2Ti3O7.
19. A compound according to claim 18, characterized in that A is chosen from the group constituted by barium, cesium, potassium, strontium, a lanthanide, or solid solutions thereof.
20. A compound according to claim 18, characterized in that B is chosen from the group constituted by copper, nickel, manganese, iron, palladium, titanium, aluminum, gallium, zinc, cobalt, or solid solutions thereof.
21. A compound according to claim 18, characterized in that said compound has the formula (Ba2-x A x)Cu3O6~d, 0 < x < 1, wherein A is an alkaline metal or an alkaline-earth metal or a lanthanide.
22. A compound according to claim 18, characterized in that said compound has the formula Ba2(Cu3-y B y)O6~d, 0 < y < 1, wherein B is a transition metal or an element of group III.
23. A compound according to claim 18, characterized in that said compound has the formula ( Ba2-x Sr x)Cu3O6~d, 0 < x < 0.75.
24. A compound according to claim 18, characterized in that said compound has the formula Ba2(Cu3-yNi y)O6~d, 0 < y < 1.
25. A compound according to claim 18, characterized in that said compound has the formula Ba2(Cu3-yPd y)O6~d, 0 < y < 0.33.
26. A method for preparing a compound as defined in any one of claims 18-25, comprising the heat treatment of a mixture of one or more compounds chosen from the group constituted by oxides, peroxides, and nitrates of alkaline or alkaline-earth metals or lanthanides, and one or more compounds chosen from the group constituted by oxides, peroxides, and nitrates of transition metals or of elements of group III, said heat treatment being performed in a controlled atmosphere which contains only oxygen, nitrogen, and inert gases.
27. A method according to claim 26, characterized in that said mixture comprises an oxide of an alkaline-earth or alkaline metal or lanthanide and an oxide of a transition metal or of an element of group III.
28. A method according to claim 26, characterized in that said mixture comprises a nitrate of an alkaline-earth or alkaline metal or lanthanide and a nitrate of a transition metal or of an element of group III.
29. A method for preparing a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1, comprising the heat treatment of a mixture of one or more compounds chosen from the group constituted by nitrates of alkaline or alkaline-earth metals or lanthanides, and one or more compounds chosen from the group constituted by nitrates of transition metals or of elements of group III, said heat treatment being performed in a controlled atmosphere which contains only oxygen, nitrogen, and inert gases, said method comprising the stages of a -- impregnating a porous substrate with an aqueous solution of said mixture of nitrates, b -- heating said support impregnated with said solution in order to eliminate the water, c -- maintaining heating until the evolution of NO2 produced by the decomposition of the nitrates ends, thus obtaining a composite material wherein said compound fills the microcavities of the porous substrate.
30. A method for preparing a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition 20a metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1, comprising the heat treatment of a mixture of one or more compounds chosen from the group constituted by nitrates of alkaline or alkaline-earth metals or lanthanides, and one or more compounds chosen from the group constituted by nitrates of transition metals or of elements of group III, said heat treatment being performed in a controlled atmosphere which contains only oxygen, nitrogen, and inert gases, said method comprising the stages of a -- wetting a substrate of non-porous inert material with an aqueous solution of said nitrates, b -- heating said wetted substrate to evaporate the water, c -- repeating stages a and b until a deposition of nitrates having a preset thickness is obtained, d -- maintaining heating until the evolution of NO2 produced by the decomposition of the nitrates ends, thus obtaining a film constituted by said compound.
31. A composite material comprising a compound as defined in any one of claims 18-25.
32. A film constituted by a material comprising a compound as defined in any one of claims 18-25.
33. A gas fixing device, comprising a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1.
20b
20b
34. An electrical gas concentration sensor, comprising a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1.
35. An optical gas concentration sensor, comprising a compound having the formula A2B3O6~d wherein A is an alkaline-earth metal, an alkaline metal, a lanthanide, or a solid solution thereof, B is a transition metal, an element of group III, or a solid solution thereof, and d has a value between 0 and 1.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ITBO96A000063 | 1996-02-12 | ||
| IT96BO000063A IT1285562B1 (en) | 1996-02-12 | 1996-02-12 | COMPOUNDS WITH GAS FIXING ACTIVITIES |
| PCT/EP1997/000598 WO1997028884A2 (en) | 1996-02-12 | 1997-02-10 | Compounds for the sorption of gases |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2245904A1 true CA2245904A1 (en) | 1997-08-14 |
Family
ID=29421801
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2245904 Abandoned CA2245904A1 (en) | 1996-02-12 | 1997-02-10 | Compounds for the sorption of gases |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2245904A1 (en) |
-
1997
- 1997-02-10 CA CA 2245904 patent/CA2245904A1/en not_active Abandoned
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