A WIRE FOR MANUFACTURING CATALYST GAUZES

Abstract

Wire for weaving or knitting a catalyst gauze, said wire being characterized in that it is a stranded wire comprising an assembly of n intertwined filaments, n being an integer with 2n8, wherein each of said filaments comprises Pt or a Pt alloy constituted of at least 50% by 5 weight of Pt, said filaments being twisted together over their length so that each of the filaments is wound to at least one other filament.

Claims

1. A wire for weaving or knitting a catalyst gauze, wherein said wire is a twisted wire comprising an assembly of n intertwined filaments, n being an integer with 2n8, wherein each of said filaments comprises at least 50% by weight of Pt, said filaments being twisted together over their length so that each of the filaments is wound to at least one other filament.

2. Wire according to claim 1, wherein 3n8.

3. Wire according to claim 1, wherein each of said filaments have its own reference diameter dr inferior or equal to 0.100 mm and superior or equal to 0.010 mm, each first reference diameter d.sub.f being defined as the diameter of a circle having the same area as the cross sectional area of the corresponding filament.

4. Wire according to claim 3, wherein 0.010 mmd.sub.f0.075 mm.

5. Wire according to claim 1, wherein said wire has a reference diameter d.sub.w being defined as the diameter of a circle having the same area as the cross sectional area of the wire, with 0.040 mmd.sub.w0.300 mm.

6. Wire according to claim 1, wherein it comprises at least four filaments

7. Wire according to claim 1, wherein each of said filaments comprise at least 90% by weight of Pt.

8. Wire according to claim 1, wherein each of said filaments comprise at least 5% by weight of Rh.

9. Wire according to claim 3, wherein d.sub.f=0.060 mm.

10. A catalyst gauze made of the wire according to claim 1.

11. Use of the gauze according to claim 10 in an installation for the catalytic oxidation of ammonia into NO.

12. Installation for the catalytic oxidation of ammonia to NO, comprising at least one catalyst gauze according to claim 10.

13. Wire according to claim 3, wherein 0.010 mmd.sub.f0.070 mm.

14. Wire according to claim 3, wherein 0.010 mmd.sub.f0.065 mm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0117] In order to explain the invention a non-limiting example of a specific embodiment of a catalyst gauze according to the invention and its use is given below, with reference to the following figures:

[0118] FIGS. 2a and 2b, which show two magnified microscopic images (a-left and b-right), acquired from two different views, of a twisted wire according to the invention comprising four filaments which are twisted together over their length so that each of the filaments is wound to at least one other filament, resulting into a yarn wire. Each of the filaments is a cord and has a diameter of 0.060 mm. The composition of each of the filaments is PtRh5 [95.0 wt % Pt+5.0 wt % Rh], and

[0119] FIGS. 3i and 3ii, which depict: i)-left: a 2D structure of a catalyst gauze made of the twisted wire of FIG. 1; and ii)-right: a 2D structure of a catalyst gauze made of two single-filament wires, each of the wires having a diameter of 0.076 mm and a composition that is similar to the composition of the filaments constituting the wire of FIG. 1 (PtRh5). Gauzes i) and ii) have been knitted with the same pattern (identical knitting types).

DETAILED DESCRIPTION

[0120] The twisted wire according to the invention which is depicted in FIGS. 2a and 2b is a yarn wire comprising four filaments, these filaments are preferably tubular.

[0121] Each of these filament is a cord (tubular-shaped) characterized by a first reference diameter d.sub.f of +/0.060 mm0.003 mm. These filaments are twisted so as to provide a twisted wire having a second reference diameter d.sub.f of +/0.140 mm0.003 mm.

[0122] Diameter where measured with conventional LAZER-based technology inspired of the well-known Modular Laser Measuring Head for Diameter, Width, Height principle.

[0123] In the context of the present invention, d.sub.w and d.sub.f are expressed in mm, and values of d.sub.w and d.sub.f expressed as 0,(0).sub.m X.sub.[i1,il], where X.sub.[i1, ii]=X.sub.i1X.sub.i2 . . . X.sub.ii, with m and X being an integer; and X>0, which is equivalent to a following alternative expression: X 10.sup.(m+(ii)); where 10.sup.(m+(ii)) is a factor for designating a m+(il) decimal multiples (and submultiples) of X.(il)=I. For instance if X=15, X.sub.i1=1; and X.sub.i2=5, and (il)=(i2)=2

[0124] Alternatively, a value expressed as 0,(0).sub.m X.sub.[i1,il] is equivalent to a value expressed as 0.(0).sub.m X.sub.[i1,ii].

[0125] For instance, a value of 0.010 is equivalent to 0.010.

[0126] In said value of 0.010; m=1 and: X.sub.i1=1; so that (il)=1, and is further equivalent to 1 10.sup.(1+1)=1 10.sup.2.

[0127] In another example, a value of 0.015 is equivalent to 0.015.

[0128] In said value of 0.015; m=1 and: X.sub.i1=1; and X.sub.i2=5; so that (il)=(i2)=1+1=2. Therefore, 0.015=15 10.sup.(1+2)=15 10.sup.3.

[0129] In another example, a value of 0.150 is equivalent to 0.150.

[0130] In said value of 0.150; m=0 and: X.sub.i1=1; X.sub.i2=5; so that (il)=(i2)=2, and is further equivalent to 1 10.sup.(0+1+1)=1 10.sup.2.

[0131] In the assembly of FIGS. 2a and 2b, each of the filaments has its outer surface contacting at least partially at least one other neighboring filament outer surface, so that shadowing regions are created in the wire.

[0132] An outer surface of filament is defined in the context of this invention by the following formula: [0133] 2Ld.sub.f;

[0134] with L being a predetermined length of the filament and d.sub.f the reference diameter of the filament.

[0135] These shadowing regions correspond to parts of the outer surface of each filament that are unavailable for the catalysis reaction. These shadowed regions are not free and cannot be accessed by the ammonia gas when the wire is used in a gauze. On the opposite, an available (or free; or catalytic) outer surface of a filament is an outer surface that will be available for reacting with the ammonia gas.

[0136] As depicted in FIGS. 2a and 2b, each of the free outer surfaces (also considered here as the catalytic surface) of the filaments defines the catalytic surface of the wire according to the invention.

[0137] The catalyst gauzes 3i of FIG. 3i results from the knitting of the 4-filaments wire of FIG. 2a.

[0138] This wire was knitted on a flat-bed knitting machine into gauze 3i with a weight per square meter (m.sup.2) of 800 g/m.sup.2. Gauze 3i type is called here Twisted type 01.

[0139] The catalyst gauze 3ii of FIG. 3ii was knitted under the same condition than for gauze 3i, but with two single-filament wires (see FIG. 2b) having a diameter of 0.076 mm.

[0140] Compositions of the two single-filament wires used for the gauze catalyst 3ii are the same than for the wire of gauze catalyst 3i. Gauze 3ii type is called here Platinit type 01.

[0141] Comparative Tests

[0142] The catalyst gauzes 3i and 3ii were tested for their catalytic properties as follows:

[0143] A test reactor was used with an effective diameter of 10.0 cm. In this test reactor, the following catalyst gauzes were installed (per test), in order:

[0144] Test 1: Measurement of the Twisted Type 01 Catalytic Gauze Properties

[0145] Bed of: [0146] 4 superimposed Twisted type 01 gauzes which have been superimposed; [0147] 4 superimposed standard knitted catalyst gauzes [Platinit type 01] made of 2 single-filament wires of 0.076 mm diameter of Pt+5 wt % Rh alloy with total weight of 800 g/m.sup.2.

[0148] Test 2: Measurement of the Reference Platinit Type 01 Catalytic Gauze Properties

[0149] Bed of: [0150] 8 superimposed standard knitted catalyst gauzes [Platinit type 01] made of 2 single-filament wires of 0.076 mm diameter of Pt+5.0 wt % Rh alloy with total weight of 800 g/m.sup.2;

[0151] In test 2, the Platinit type 01 gauze is made of 2 single-filament wires. As illustrated in FIG. 3ii, the two filaments are not brought into intimate contact and are therefore present in a loose and isolated form. On the contrary, in test 1, the Twisted type 01 comprises filaments which are secured together and are not single-filaments like in the Platinit type 01 gauze.

[0152] Results

[0153] For tests 1 and 2, the bed of catalyst gauzes was heated to a temperature range: 870 C.-890 C. The reactor was operated at 3.6 or 5.0 bar absolute pressure.

[0154] A feed of approx. 4.76 kg/h NH.sub.3 in the form of a 10.7 vol.-% (equals 6.7% w/w) NH.sub.3 mixture in air was supplied to the bed of catalyst gauzes. The N.sub.2O content was determined each day and after maximum 13 days on stream, and was as follows:

TABLE-US-00001 TABLE 1 Output results data from tests 1 and 2; including test parameters (pressure (bar), temperature temp [ C.], load (in days), weight of ammonia (wt %); and post-ammonia oxidation results: N.sub.2O content (in ppm) in mixture and corresponding NO selectivity. The nitrous oxide concentration in nitrous gases was determined by gas chromatography method. Type 01 twisted Type 01 standard load pressure temp w_NH3 Sel. [%] N2O [ppm] Sel. [%] N2O [ppm] 12 5 890 6.78 95.5 941 95.4 1048 12 5 890 6.72 95.6 935 95.2 1040 12 5 890 6.71 95.3 999 95.5 1091 12 5 890 6.72 95.9 1004 95.6 1099 8 5 870 6.75 95.6 1047 95.3 1057 8 5 890 6.7 95.4 814 95.2 849 8 5 890 6.74 95.3 861 95.3 909 8 5 890 6.72 95.7 858 95.4 889 8 5 870 6.77 95.4 1116 95.3 1150 8 5 870 6.76 95.4 1142 95.1 1167 15 5 890 6.7 95.9 1152 95.3 1255 15 5 890 6.67 95.6 1156 95.2 1184 15 5 890 6.71 95.8 1150 95.3 1268 15 5 890 6.65 95.8 1158 95.3 1274 12 3.6 870 6.66 95.5 1050 95.5 1160 12 3.6 870 6.73 95.7 1047 95.5 1147 12 5 870 6.65 95.7 1305 95.3 1411 12 5 870 6.66 95.7 1285 95.2 1387 12 5 890 6.68 96.1 1092 95.9 1170 12 3.6 870 6.72 96.1 1116 95.6 1188 mean value 95.65 1061.40 95.37 1137.15 , where, w_NH3 = % w/w (NH3). , where reactors loads' indications [t N/(m.sup.2d)] a tolerance of +/ 0.05 t N/(m.sup.2d), where t is ton; N is Nitrogen (equivalent to ammonia: mol. N = 14/17 mol. NH.sub.3); m.sup.2 is a surface unit parameter (surface of a cross section (perpendicular to the flow gas direction) of the reactor [for instance in FIG. 1, section .fwdarw.2 4]; and d is 24 hours (a day). indicates data missing or illegible when filed

[0155] Pressure was stable during the operation time and was on the level of 5.0+/0.02 bar absolute and 3.6+/0.02 bar absolute, according to the test schedule.

[0156] The selectivity to NO of the oxidation reaction, determined as mean value after 13 days, was 0.28% [confidence interval=+/0.097] higher by using a gauze made of the wire according to the invention; the N.sub.2O level being decreased by 6.7%.

[0157] NO selectivity (S.sub.NO) is provided by the following formula:

S.sub.NO(in %)=(X2/X1)*100%;

[0158] where X1=ammonia concentration in ammonia-air mixture; and

[0159] where X2=concentration of oxidized ammonia (NO+NO.sub.2), % w/w.

[0160] Although Table 1 provides 20 measurements, it must be understood that for some day of the 13-days measurement period, more than one load has been performed during this test period.

[0161] It is understood that the present invention is by no means limited to the forms of the above detailed description and that many modifications can be made without departing from the scope of the appended claims.

[0162] For instance, it must be understood that if the description discloses a wires made of 4 twisted or spun filaments, the scope of the present invention also covers a wire which may be made of n filaments, with n being an integer varying from 2 to 8, including these two values.