METHOD AND APPARATUS FOR ALKANE OXIDATION

Abstract

The present invention provides a method for catalytic oxidation of alkanes, where the catalyst comprises a photoactive material that is activated when the catalyst is irradiated with UV light. In particular, the method is for the catalytic oxidation of a C1-C5 alkane using an oxidation catalyst comprising a photoactive material, said method comprising the steps of a) activating the photoactive material by irradiating the catalyst with UV light and b) contacting the activated catalyst with a gaseous feedstream comprising an amount of C1-C5 alkane at a temperature of from 150° C. to 600° C.

Claims

1. A method for the catalytic oxidation of a C1-C5 alkane using an oxidation catalyst comprising a photoactive material, said method comprising the steps of: a) activating the photoactive material by irradiating the catalyst with UV light; and b) contacting the activated catalyst with a gaseous feedstream comprising an amount of C1-C5 alkane at a temperature of from 150° C. to 600° C.

2. A method according to claim 1, wherein the photoactive material is activated in step a) in the absence of the gaseous feedstream comprising an amount of C1-C5 alkane, for example wherein activation is performed in the presence of air or under at least a partial vacuum.

3. A method according to claim 1, wherein the photoactive material is activated in step a) in the presence of the gaseous feedstream comprising an amount of C1-C5 alkane, and preferably at a temperature of from 150° C. to 600° C.

4. A method according to any one of claims 1 to 3, wherein the photoactive material is irradiated intermittently or continuously with UV light during contact with the gaseous feedstream comprising an amount of C1-C5 alkane in step b).

5. A method according to any one of the preceding claims, wherein the gaseous feedstream comprises from 0.01 to 20% by volume of C1-C5 alkane, preferably from 0.1 to 10.0% by volume, more preferably from 0.5 to 5.0% by volume of C1-C5 alkane.

6. A method according to any one of the preceding claims, wherein the C1-C5 alkane is selected from C1-C3 alkanes and combinations thereof, more preferably the C1-C5 alkane is selected from methane, propane or a combination thereof, even more preferably the C1-C5 alkane is methane.

7. A method according to any one of the preceding claims, wherein the feedstream comprises from 4.0% to 20.0% by volume of water vapour, preferably from 5.0 to 15.0% by volume of water vapour, more preferably from 5.0% to 10.0% by volume of water vapour.

8. A method according to any one of the preceding claims, wherein contacting step b) is conducted at a temperature of at least 175° C., preferably at least 200° C., more preferably at least 225° C., even more preferably at least 250° C.

9. A method according to any one of the preceding claims, wherein irradiation in step a) is with UV radiation having a wavelength of from 280 to 450 nm, preferably UV radiation having a wavelength of from 375 to 395 nm.

10. A method according to any one of the preceding claims, wherein the photoactive material comprises a photoactive material selected from TiO.sub.2, WO.sub.3 and CoO and combinations thereof, preferably wherein the photoactive material is TiO.sub.2.

11. A method according to any one of the preceding claims, wherein the oxidation catalyst comprises one or more metals selected from ruthenium, palladium, platinum, gold, silver, rhodium, iridium, rhenium, manganese, chromium, nickel, iron, molybdenum, tungsten, zirconium, gallium, thorium, lanthanum, cerium and mixtures thereof.

12. A method according to claim 11, wherein the oxidation catalyst comprises at least two different metals, preferably selected from palladium, platinum, gold, silver, rhodium, iridium and rhenium, more preferably wherein the at least two different dopant metals includes palladium and platinum.

13. A method according to any one of the preceding claims, wherein the oxidation catalyst is supported with a support material, wherein the support material is in the form of a powder, granulate, pellet, extrudate, or combinations thereof.

14. A method according to claim 13, wherein the catalyst is supported with a support material and the supported catalyst comprises from 10 to 40% of the photoactive material by weight of the supported photocatalyst, preferably from 15 to 35%, more preferably 20 to 30% of the photoactive material by weight of the supported catalyst.

15. A method according to claim 13 or claim 14, wherein the support material is selected from silica, alumina, aluminosilicate such as zeolite, silica-alumina, ceria, titania, gallia, zirconia, magnesia, zinc oxide, activated carbon, silicon carbide, titanium carbide, fluoropolymer resins and mixtures thereof, preferably where the support material is alumina or zeolite such as ZSM-5.

16. A method according to any one of the preceding claims wherein the gaseous feedstream is an exhaust gas stream, preferably wherein the exhaust gas stream is derived from: i) an engine, such as an engine powered by natural gas and/or propane; or ii) an electric power generator or combined heat and power (CHP) generator.

17. A method according to claim 16, wherein the engine is an internal combustion engine for an automotive vehicle, locomotive vehicle or marine vessel and steps a) and b) of the method are conducted adjacent to, or inside, the exhaust gas system of the automotive vehicle, locomotive vehicle or marine vessel.

18. A method according to any one of claims 1 to 15, wherein the gaseous feedstream is an exhaust stream from a hydrocarbon combustion process using a methane-based fuel.

19. An apparatus for use in catalytic oxidation of C1-C5 alkane present in an gaseous feedstream, said apparatus comprising: a) an oxidation catalyst configured for catalytic oxidation of C1-C5 alkane present in a gaseous feedstream at temperatures of up to 600° C., wherein the catalyst comprises a photoactive material; b) a UV light generating means configured for irradiation of the photoactive material; and c) a housing within which the oxidation catalyst is disposed and within which UV light from the UV light generating means may be transmitted, which housing is configured to receive a supply of the gaseous feedstream comprising C1-C5 alkane.

20. An apparatus according to claim 19, wherein the gaseous feedstream is an exhaust gas and the housing is configured for fluidic attachment to a means for conveying the exhaust gas from an exhaust gas supply, such as piping connected to an engine's exhaust system.

21. An apparatus according to claim 19 or claim 20, wherein the engine powers an automotive vehicle, locomotive vehicle or marine vessel and the apparatus is configured for integration adjacent to, or inside, the exhaust system of the automotive vehicle, locomotive vehicle or marine vessel.

22. An apparatus according to any one of claims 19 to 21, wherein the housing comprises a UV light reflective interior surface, such as a metal foil or ceramic.

23. An apparatus according to any one of claims 19 to 22, wherein the oxidation catalyst is as defined in any one of claims 10 to 15.

24. An apparatus according to claim 23, wherein the oxidation catalyst is applied on a monolithic structure disposed within the housing.

25. An apparatus according to any one of claims 19 to 24, wherein the UV light generating means is configured to provide pulsed and/or continuous UV light having a wavelength of from 280 to 450 nm, preferably having a wavelength of from 375 to 395 nm.

26. An exhaust system for an internal combustion engine for powering an automotive vehicle, locomotive vehicle or marine vessel comprising an apparatus as defined in any one of claims 19 to 25.

Description

[0089] The invention will now be further described by reference to the following Examples and with reference to the following figures, in which:

[0090] FIG. 1: shows a schematic of the lab-scale testing setup according to Examples 3 and 4;

[0091] FIG. 2: shows a schematic of the testing setup with the catalyst integrated into a vehicle exhaust according to Example 5;

[0092] FIG. 3: shows a different schematic of the testing set-up with the catalyst integrated into a vehicle exhaust according to Example 5;

[0093] FIG. 4: is a graph showing the effect of UV irradiation in accordance with Example 6;

[0094] FIG. 5: is a graph showing the effect of UV irradiation in accordance with Example 7;

[0095] FIG. 6: is a graph showing a comparison of catalyst pellets with a coated monolith in accordance with Example 8;

[0096] FIG. 7: is a graph showing methane oxidation at different temperatures in accordance with Example 9;

[0097] FIG. 8: is a graph showing conversion of water to hydrogen in accordance with Example 10;

[0098] FIG. 9: is a graph showing methane concentration in accordance with Example 11;

[0099] FIG. 10: is a graph showing methane conversion in accordance with Example 11;

[0100] FIG. 11: is a graph showing methane concentration in accordance with Example 12;

[0101] FIG. 12: is a graph showing methane conversion in accordance with Example 12; and

[0102] FIG. 13: is a graph showing methane conversion in accordance with Comparative Example 1.

EXAMPLES

Example 1

Preparation of powdered catalyst

[0103] The catalyst was prepared by a wet impregnation method with the aid of sonication. ZSM-5 zeolite was placed in a vial and the mass of metal precursor (palladium nitrate dihydrate or tetraammineplatinum (II) hydroxide) solution or slurry, required to give a 5 wt. % palladium and 2 wt. % platinum loading was added to the powder. Then the required amount of TiO.sub.2 to give 25 wt. % loading was added and the powder mixture dispersed in deionised water (5 ml). The mixture was sonicated at 80° C. (Crest ultrasonic bath model 200 HT), under a 45 kHz frequency for 3 h and resulted in a homogeneous paste. All mixtures were dried at 120° C. overnight in an oven before being calcined in air at 500° C. in a furnace for 4 h with a heating ramp of 2° C. min.sup.−1. The powder catalyst had a particle size in the range of 250 to 425 μm.

Example 2

Preparation of Catalyst Monolith

[0104] The catalyst prepared according to Example 1 was loaded onto a cordierite monolith (400 cpsi/62 cells per cm.sup.2, wall thickness 0.07 mm) as a washcoat, so as to give a catalyst loading of 18.6 wt. % on the monolith.

Example 3

General Procedure for Lab-Scale Tests

[0105] FIG. 1 shows a schematic representation of the lab-scale setup for catalyst testing. With reference to FIG. 1, a gaseous feedstream is supplied into a quartz sample tube (22 mm outer diameter) containing a packed bed of powdered catalyst 108 prepared according to the general procedure above or a coated monolith. The quartz sample tube containing the catalyst is disposed inside a stainless steel tube which in itself is disposed inside a tubular furnace 102 for heating the catalyst and feedstream, and UV light sources are arranged on both sides of the catalyst, inside the steel tube but outside the quartz tube, for irradiating the catalyst. The gaseous stream exiting the tube after passing over the catalyst is then sent to a mass spectrometer for analysis. Where a monolith is used, the packed bed of powdered catalyst is replaced with a monolith cut to fit the stainless steel tube with a monolith length of 20 mm.

[0106] The gaseous feedstream was 0.5% methane, 10% oxygen, 5% Neon, dry or 1 to 10% water, and the remaining balance of argon. Methane conversion was calculated by comparing against a baseline with no catalyst and a sample of the feed taken upstream of the catalyst.

Example 4

General Prcedure for Chassis Dyno Tests

[0107] The setup in FIG. 1 and described in Example 3, was used to analyse a feedstream sampled from the exhaust of an engine, just after the turbo. The engine was a DAF Truck 9 L, diesel/natural gas dual fuel engine, operated in dual fuel mode with an approximately 50:50 blend of diesel and natural gas.

Example 5

General Procedure/Setup for Monolith Testing Integrated in an Exhaust

[0108] FIG. 2 shows a schematic representation of the setup for testing where the photocatalyst is integrated into the exhaust train of a HGV (DAF truck with 9 L, diesel/natural gas dual fuel engine, operated in dual fuel mode with an approximately 50:50 blend of diesel and natural gas). An exhaust stream 2 is directed down a pipe 4 from the turbo of the engine into housing 12. UV lights 6 are disposed adjacent a catalyst monolith 8 prepared according to Example 2. The exhaust gases 2 pass through the catalyst monolith 8 and are passed to a conventional catalytic convertor 10. Exhaust gases were analysed using an exhaust gas analyser for real-time concentration measurements (Kane International Limited 4 gas analyser and mass spectrometry).

[0109] As shown in FIG. 3, the UV lights 6 are generally offset from the perimeter of the monolith inlet and are offset from each other so as to provide overlapping UV irradiation to the central area of the monolith.

Example 6

Effect of UV Light on Catalyst Activity

[0110] An experiment was conducted using the setup of Example 3, with a dry feedstream at a GHSV of 100,000 mLg.sup.−1h.sup.−1 and using the catalyst of Example 1. The conversion of methane, as measured by mass spectroscopy, is shown over time in FIG. 4.

[0111] After around 25 minutes, the catalyst was illuminated continuously with UV light. Following this, an improvement in methane conversion of around 5% was observed, demonstrating an increase in catalyst activity when UV irradiation of the catalyst is used.

Example 7

Effect of UV Light on Catalyst Stability

[0112] Two experiments were conducted using the setup of Example 3 using a feed containing water vapour (1 to 10%) and the powdered catalyst according to Example 1: (i) with continuous irradiation of the catalyst with UV light and (ii) without UV irradiation of the catalyst. As can be seen in FIG. 5, with UV irradiation of the catalyst, the catalyst performance does not substantially decrease on a timescale of over 50 hours. Meanwhile, when the same catalyst is not irradiated with UV light, the catalyst performance degrades over time to give around an 8% decrease in methane conversion after about 50 hours compared to where UV irradiation is used.

Example 8

Lab-Scale Comparison of Catalyst Pellets and Monolith

[0113] Two experiments were conducted using the setup of Example 3 and a dry feed, one using a packed bed of powder and the other using a coated monolith. UV irradiation of the catalyst was conducted continuously. The conversion of methane at different temperatures is shown in FIG. 6. As can be seen, while the catalyst powder appears to achieve slightly better conversion at lower temperatures, the performance of the catalyst in the case of both pellets in a packed bed and with the coated monolith are comparable.

Example 9

Effect of Temperature on Methane Conversion

[0114] An experiment was conducted by sampling exhaust gases according to Example 4, using the powdered catalyst according to Example 1 and continuous UV irradiation of the catalyst. The reaction temperature was maintained at around 275° C. for approximately 1 hour, after which the temperature was lowered to 168° C. over a period of about 15 minutes. The conversion of methane over time at the two temperatures is shown in FIG. 7. At 275° C. the conversion corresponds to around 82% methane conversion, and even as low as 168° C. a methane conversion of around 26% is maintained.

Example 10

Water Conversion to Hydrogen

[0115] An experiment was conducted according to Example 3, using a freshly prepared catalyst according to Example 1 and at a feed temperature of 400° C. The catalyst was irradiated with UV light, and hydrogen and water content after the catalyst were measured by mass spectroscopy. A slight exotherm from 400° C. to about 412° C. was observed along with conversion of water into hydrogen, as illustrated by the change in water and hydrogen content as measured by mass spectroscopy, and shown in FIG. 8. When this experiment is conducted without irradiation with UV light, hydrogen production is not observed.

Example 11

Testing in Exhaust of a HGV

[0116] An experiment was conducted according to Example 5 and the methane concentration was monitored before (raw emissions) and after the catalyst. Continuous UV irradiation of the catalyst was used. Methane concentration before and after the catalyst for an exhaust stream at 260° C. produced by running the engine with a lambda value of 3 over a period of time of 2 to 3 hours, is shown in FIG. 9 and the corresponding % conversion of methane is shown in FIG. 10. As can be seen, under these conditions, methane conversions of from around 60% to 70% can be achieved.

Example 12

Testing in Exhaust of a HGV

[0117] An experiment was conducted according to Example 5 and the methane concentration was monitored before (raw emissions) and after the catalyst. Continuous UV irradiation of the catalyst was used. Methane concentration before and after the catalyst for an exhaust stream at 325° C. produced by running the engine with a lambda value of 4 over a period of time of 2 to 3 hours, is shown in FIG. 11 and the corresponding % conversion of methane is shown in FIG. 12. As can be seen, under these conditions, methane conversions of more than 95% can be achieved.

Comparative Example 1

[0118] An experiment was conducted according to Example 5 and the methane concentration was monitored before (raw emissions) and after the catalyst. In this example no UV irradiation was used. For temperatures higher than 400° C., the engine was run with a lambda value of 1.5. The results are shown in FIG. 13. As can be seen, at 300° C. the conversion is significantly lower than at temperatures higher than 400° C., indicating that without UV irradiation, the water containing exhaust stream requires higher temperatures to reach the same conversion levels.