Pollutant treatment process and apparatus

Abstract

A process for removing hydrocarbons from a feed stream containing hydrocarbons includes introducing ozone to the feed stream to produce an ozone doped stream containing ozone and hydrocarbons, and contacting the ozone doped stream with a supported metal catalyst at a temperature of from 100° C. to 300° C. to produce a treated stream, wherein the supported metal catalyst comprises iron supported on a support selected from aluminosilicates, silica-aluminas, silicates and aluminas. A process for removing NOx from a feed stream containing NOx, and an apparatus for removing hydrocarbons and/or NOx from a feed stream containing hydrocarbons and/or NOx are also provided.

Claims

1. An apparatus for removing hydrocarbons and/or NO.sub.x from a feed stream containing hydrocarbons and/or NO.sub.x, the apparatus comprising: a source of ozone arranged to introduce ozone to the feed stream to produce an ozone doped stream containing ozone and hydrocarbons and/or NO.sub.x; a supported metal catalyst comprising iron supported on a support selected from aluminosilicates, silica-aluminas, silicates and aluminas; wherein the apparatus is arranged to contact the ozone doped stream with the supported metal catalyst at a temperature of from 100° C. to 300° C.

2. The apparatus of claim 1, wherein the support of the supported metal catalyst comprises beta zeolite.

3. The apparatus of claim 1, wherein the apparatus is arranged to receive an exhaust stream from a hydrocarbon combustion process or a waste gas stream from an industrial process as at least a portion of the feed stream.

4. The apparatus of claim 3, further comprising means for carrying out hydrocarbon combustion and feeding an exhaust stream to the apparatus as at least a portion of the feed stream.

5. The apparatus of claim 4, wherein the means for carrying out hydrocarbon combustion comprises a natural gas engine.

6. The apparatus of claim 1, wherein the apparatus is configured so that the ozone doped stream is contacted with the supported metal catalyst at a temperature of from 130° C. to 280° C.

7. The apparatus of claim 1, wherein the apparatus is configured to provide a flow of the ozone doped stream over the supported metal catalyst continuously for greater than 1 minute.

8. The apparatus of claim 1, wherein the apparatus is configured to contact the ozone doped stream with the supported metal catalyst at a pressure of 10 bar absolute or less.

9. The apparatus of claim 1, wherein the source of ozone comprises an ozone generator configured to generate ozone in situ.

10. The apparatus of claim 9, wherein the ozone generator comprises a corona discharge ozone generator, a cold plasma ozone generator or a UV ozone generator.

11. An industrial processing plant comprising the apparatus of claim 1 for reducing emissions of hydrocarbons and/or NO.sub.x.

12. A vehicle comprising the apparatus of claim 1 for reducing emissions of hydrocarbons and/or NO.sub.x.

13. A process for removing methane from a feed stream containing methane using the apparatus of claim 1, the process comprising: using a source of ozone to generate ozone and introducing the ozone to a feed stream containing methane to produce an ozone doped stream containing ozone and methane; and contacting the ozone doped stream with a supported metal catalyst at a temperature of from 100° C. to 300° C. produce a treated stream; wherein the supported metal catalyst comprises iron supported on a support selected from aluminosilicates, silica-aluminas, silicates and aluminas.

14. The process of claim 13, wherein the ozone doped stream is contacted with the supported metal catalyst at a temperature of from 130° C. to 280° C.

15. The process of claim 13, wherein the support of the supported metal catalyst comprises a zeolite support.

16. The process of claim 13, wherein the contacting step comprises providing a flow of the ozone doped stream over the supported metal catalyst continuously for greater than 1 minute.

17. The process of claim 13, wherein the contacting step is conducted at a pressure of 10 bar absolute or less.

18. The process of claim 13, wherein the feed stream comprises an exhaust stream from a natural gas engine.

19. The process of claim 13, wherein the ozone introduced to the feed stream is generated by an ozone generator in situ.

20. The process of claim 13, wherein water is present in the feed stream or the ozone doped stream in an amount of up to 15% v/v.

Description

(1) The present invention will now be illustrated by way of the following examples and with reference to the following figures in which:

(2) FIG. 1 is a graph showing methane conversion and NO outlet concentration against temperature in accordance with Example 1;

(3) FIG. 2 is a graph showing methane conversion against temperature in accordance with Example 2;

(4) FIG. 3 is a graph showing methane conversion against water concentration in accordance with Example 2;

(5) FIG. 4 is a graph showing propane conversion against temperature in accordance with Example 3;

(6) FIG. 5 is a graph showing methane conversion against temperature with and without water in accordance with Example 4;

(7) FIG. 6 is a graph showing CO selectivity against temperature in accordance with Example 4;

(8) FIG. 7 is a graph showing NO.sub.x conversion against temperature in accordance with Example 5;

(9) FIG. 8 is a graph showing methane and NO.sub.x conversion against temperature in accordance with Example 6;

(10) FIG. 9 is a graph showing methane and NO.sub.x conversion against temperature in accordance with Comparative Example 1;

(11) FIG. 10 is a graph showing methane conversion against temperature in accordance with Comparative Example 2;

(12) FIG. 11 is a graph showing methane and NO.sub.x conversion against temperature in accordance with Comparative Example 3;

(13) FIG. 12 is a graph showing methane and NO.sub.x conversion against temperature in accordance with Comparative Example 4;

(14) FIG. 13 is a graph showing methane conversion against temperature in accordance with Comparative Example 5;

(15) FIG. 14 is a graph showing NO.sub.x conversion against temperature in accordance with Example 5 and Comparative Examples 3, 4 and 6;

(16) FIG. 15 is a graph showing CO and CO.sub.2 selectivity against temperature in accordance with Example 4; and

(17) FIG. 16 is an X-Ray diffraction spectrum of an iron on beta zeolite catalyst on cordierite as used in Examples 1 to 7 and Comparative Example 1.

EXAMPLES

(18) General Procedure for Catalyst Preparation

(19) Catalysts were either obtained commercially or synthesised by wet impregnation of the support with an aqueous solution of a metal nitrate, followed by drying in air at 150° C. for 2 hours and thermal decomposition in air at 550° C. for 8 hours.

(20) Catalysts were loaded into cordierite cores of 1 inch diameter and 3 inch long with a 300 CPSI cell density and a volume of 38.6 ml. The catalyst slurry was coated onto the cordierite by a dipping process and then dried.

(21) A powder X-Ray diffraction spectrum for the iron on beta zeolite catalyst on cordierite, as used in Examples 1 to 7 and Comparative Example 1 is shown in FIG. 15.

(22) General Procedure for Reactor Experiments

(23) All experiments were conducted in a bench scale continuous flow reactor comprising an in-line heater, gas injection ports, water injector and vaporizer, in-line mixer, sample ports, sample holder, and exhaust. Gases were mixed by a helicoidal stainless steel in-line static mixer directly upstream of the catalyst sample. The ozone was generated by an air-cooled, corona discharge ozone generator. The ozone generator was fed with dry air unless otherwise specified. The 5 SLPM ozone containing outlet stream of the ozone generator was fed to the reactor directly upstream of the static mixer. Ozone concentration in the feed to the reactor is estimated to be around 500 ppm. Unless otherwise specified, the feed contained 10% oxygen and the balance of the feed was nitrogen. The flow rate through the reactor was 25 to 30 SLPM with a space velocity of from 40,000 h.sup.−1 to 50,000 h.sup.−1. Outlet gas samples were analysed continuously by a FTIR gas analyser capable of simultaneous quantitative analysis of more than 30 gases. Sample gas temperature was maintained at 150° C. or 191° C. Specifically, gases were monitored continuously in the exhaust gas and logged at 1 hertz. Catalyst sample temperature was controlled by an in-line gas heater and monitored by five Type-K thermocouples inserted in the catalyst sample channels. Catalyst temperature was either maintained constant or ramped up or down at a controlled rate between 0° C. and 25° C. per minute, generally around 5° C. to 10° C. per minute. Inlet gas blend composition was controlled by mass flow controllers and a high precision liquid water pump. The outlet of the catalyst sample was maintained at atmospheric pressure.

(24) In each case the observed products were largely CO, CO.sub.2 and water. For a propane feed (Example 3), some formation of formaldehyde was observed in addition to CO and CO.sub.2.

Example 1

(25) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (150 ppm) and less than 0.1% water. Temperature was ramped up from around 80° C. to 400° C. The catalyst used was a catalyst comprising iron on beta zeolite. The methane conversion with varying temperature is shown in FIG. 1.

(26) FIG. 1 shows that by using the iron catalyst in combination with ozone, very good methane conversion efficiency can be obtained at temperatures of from 100° C. to 300° C.

Example 2

(27) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (156 ppm) and water (2.5%). Temperature was ramped up from around 110° C. to 360° C. The catalyst used was a catalyst comprising iron on beta zeolite. The methane conversion with varying temperature is shown in FIG. 2.

(28) The temperature was then held constant at around 225° C. and the water content of the stream was varied from around 5% to 0%. The methane conversion with varying water concentration is shown in FIG. 3.

(29) The results in FIGS. 2 and 3 show that good methane conversion may be obtained in the presence of water at low temperatures and that the conversion may be improved by reducing the level of water in the feed.

Example 3

(30) A reactor experiment was conducted according to the general procedure above with a feed stream comprising propane (223 ppm) and water (2.5%). Temperature was ramped up from around 120° C. to 400° C. The catalyst used was a catalyst comprising iron on beta zeolite. The propane conversion with varying temperature is shown in FIG. 4.

(31) The results in FIG. 4 show very good conversion of propane at temperatures below 300° C., showing that the combination of the iron catalyst and ozone is also effective for longer chain hydrocarbons.

Example 4

(32) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (155 ppm). Temperature was ramped down from around 430° C. to 100° C. The catalyst used was a catalyst comprising iron on beta zeolite. The same experiment was conducted with a feed comprising 155 ppm methane and 2.7% water. The methane conversion with varying temperature for the two experiments is shown in FIG. 5. The selectivity for conversion to CO is shown in FIG. 6.

(33) The results in FIGS. 5 and 6 show that at low temperatures, there is increased selectivity CO. It will be appreciated that as a result of the reactions shown in Equations 2 and 3 previously, the presence of CO may be used to infer the production of hydrogen from the methane in the feed stream.

(34) This experiment was repeated with a feed comprising 180 ppm methane and without water and CO and CO.sub.2 selectivity was monitored. The CO and CO.sub.2 selectivity is shown in FIG. 15, which demonstrates that CO and CO.sub.2 are the major carbon containing products formed in the process.

Example 5

(35) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (180 ppm), NO (150 ppm) and water (2.7%). Temperature was ramped up from around 120° C. to 400° C. The catalyst used was a catalyst comprising iron on beta zeolite. The methane and NO.sub.x conversions with varying temperature are shown in FIG. 7.

(36) The data in FIG. 7 shows that NOx may be effectively removed at low temperatures by using ozone and the iron catalyst below 300° C., whilst also simultaneously removing methane from the feed.

Example 6

(37) A reactor experiment was conducted according to the general procedure above with a feed stream comprising NO (157 ppm) and water (2.5%). Temperature was ramped up from around 210° C. to 420° C. The catalyst used was a catalyst comprising iron on beta zeolite. The same experiment was then repeated by ramping down the temperature instead of ramping up. The NO.sub.x conversion with varying temperature is shown in FIG. 8.

(38) The data in FIG. 8 shows that NO.sub.x may be effectively removed at low temperatures by using ozone and the iron catalyst below 300° C. in the absence of hydrocarbons. It was also found that when water was absent from the feed, temporary adsorption of NO.sub.x was observed rather than conversion.

Example 7

(39) The procedure of Example 5 was modified so that oxygen is fed to the ozone generator instead of air, which gave an improvement to the observed methane conversion.

Comparative Example 1

(40) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (180 ppm), NO (150 ppm) and water (2.7%) and without the addition of ozone to the feed. Temperature was ramped down from around 425° C. to 150° C. The catalyst used was a catalyst comprising iron on beta zeolite. The methane and NO.sub.x conversions with varying temperature are shown in FIG. 9.

(41) The data in FIG. 9 indicates that the addition of ozone to the feed plays a crucial role in the low temperature removal of hydrocarbons and NO.sub.x from the feed stream.

Comparative Example 2

(42) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (195 ppm). Temperature was ramped down from around 435° C. to 100° C. The catalyst used was a copper zeolite catalyst obtained commercially. The methane conversion with varying temperature is shown in FIG. 10.

(43) The data in FIG. 10 shows that the copper catalyst performs poorly and does not show the same low temperature activity for removal of hydrocarbons. In this way there is a certain synergy between the use of the supported iron catalyst and the introduction of ozone to the feed.

Comparative Example 3

(44) A reactor experiment was conducted according to Comparative Example 2, except with a feed comprising methane (204 ppm) and NO (195 ppm). The methane and NO.sub.x conversions with varying temperature are shown in FIG. 11.

(45) FIG. 11 similarly shows very poor methane conversion at low temperature. The copper catalyst does facilitate conversion of NO.sub.x at low temperatures, however the temperature range where the copper catalyst is effective is narrower than for the iron catalyst.

Comparative Example 4

(46) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (178 ppm) and NO (195 ppm). Temperature was ramped down from around 390° C. to 70° C. The catalyst used was a magnesium oxide (MgO) catalyst (300 mg). This experiment was repeated with water 3%, without NO.sub.x, and with water and without NO.sub.x. The methane and NO.sub.x conversions with varying temperature are shown in FIG. 12.

(47) The data in FIG. 12 shows that the MgO based catalyst performs poorly and does not show the same low temperature activity for removal of hydrocarbons. In this way there is a certain synergy between the use of the supported iron catalyst and the introduction of ozone to the feed.

(48) This experiment was repeated with 1200 mg MgO and no increase in methane conversion was observed.

Comparative Example 5

(49) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (179 ppm). Temperature was ramped down from around 440° C. to 125° C. The catalyst used was iron (3 wt. %) supported on magnesium oxide (MgO). The methane conversion with varying temperature is shown in FIG. 13.

(50) The data in FIG. 13 shows that the iron supported on MgO performs poorly and does not show the same low temperature activity for removal of hydrocarbons as the iron supported on zeolite. In this way there is a certain synergy between the use of an iron catalyst supported on aluminosilicates, silica-aluminas, silicates and/or aluminas and the introduction of ozone to the feed.

Comparative Example 6

(51) A reactor experiment was conducted according to the general procedure above with a feed stream comprising methane (196 ppm) and NO (197 ppm). Temperature was ramped down from around 225° C. to 125° C. No catalyst was used and the reactor was empty with no cordierite core. No methane conversion was observed.

(52) Some conversion of NO.sub.x was observed at low temperature without the catalyst, however the effective temperature range was much narrower than for the iron zeolite catalyst. A comparison of NO.sub.x conversions with temperature for the experiments of Example 5 and Comparative Examples 3, 4 and 6 is shown in FIG. 14.