USE OF CATALYST AND METHOD OF REMOVING ALDEHYDES

Abstract

A method for removing one or more aldehydes from a carrier fluid, using a catalyst including manganese oxide. The method is particularly effective at removing longer chain aldehydes from a carrier fluid. Also provided is a method of regenerating a catalyst including manganese oxide.

Claims

1. A method of removing one or more aldehydes from a carrier fluid comprising ambient air, the method comprising the step of: contacting the carrier fluid comprising one or more aldehydes with a catalyst comprising manganese oxide.

2. The method of claim 1 wherein the catalyst comprises manganese IV oxide and/or cryptomelane.

3. The method of claim 1 wherein at least one aldehyde comprises at least two carbon atoms.

4-5. (canceled)

6. The method of claim 1 wherein the catalyst comprises a support on or in which the manganese IV oxide and/or cryptomelane is supported.

7. The method of claim 6 wherein the support comprises a foam and/or a metal support and/or a ceramic support.

8. The method according to claim 6 wherein the catalyst comprises at least 10 wt % support, and up to 90 wt % support.

9. The method according to claim 1 wherein the catalyst comprises a binder.

10. The method according to claim 9 wherein the catalyst comprises up to 60 wt % binder.

11. The method of claim 1 wherein the carrier fluid consists essentially of ambient air.

12. The method of claim 1 comprising contacting the carrier fluid with the catalyst at a temperature of at least 10 C.

13-16. (canceled)

17. The method of claim 1 comprising contacting a flow of the carrier fluid with the catalyst, the flow rate of the carrier fluid being configured to provide a reduction in the aldehyde content of the carrier fluid of at least 30%.

18. The method of claim 1 wherein the carrier fluid comprises at least 1 ppb one or more aldehydes.

19. The method of claim 1 comprising contacting the carrier fluid with the catalyst at a pressure less than ambient pressure.

20. The method of claim 1 further comprising the step of: facilitating removal from the carrier fluid of one or more impurities before the step of contacting with the catalyst.

21. The method of claim 20 wherein the step of facilitating removal from the carrier fluid of one or more impurities comprises filtering the carrier fluid.

22. The method of claim 1 claim further comprising the step of: heating the catalyst to a regeneration temperature of at least 90 C. in the presence of a source of oxygen.

23. The method of claim 22, wherein the step of heating the catalyst to the regeneration temperature is before the step of contacting with the catalyst.

24-26. (canceled)

27. The method of claim 22 wherein the step of heating the catalyst to the regeneration temperature is carried out for at least 15 minutes.

28.-31. (canceled)

32. The method of claim 22 wherein the length of time of carrying out the step of contacting with the catalyst is at most 30 times the length of time of the step of heating the catalyst to the regeneration temperature.

33.-36. (canceled)

37. A method comprising removing one or more aldehydes from a carrier fluid comprising ambient air using a catalyst comprising manganese oxide.

38. The method of claim 37 wherein the catalyst comprises manganese IV oxide and/or cryptomelane.

39. The method of claim 37 wherein at least one aldehyde comprises at least two carbon atoms.

Description

SUMMARY OF THE FIGURES

[0086] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures.

[0087] FIG. 1. Graph showing single pass efficiency (SPE) over time from test data obtained during extended Continuous Injection Analysis (CIA) testing.

[0088] FIG. 2. Graph showing the decrease in SPE over the course of extended SPE tests and different temperatures.

[0089] FIG. 3. Graph showing SPE against cumulative test time for different catalyst temperatures during CIA testing.

[0090] FIG. 4. Graph showing the change in SPE for cryptomelane on aluminium as measured in an SPE test for different acetaldehyde concentrations.

[0091] FIG. 5. Graphs showing initial SPE (graph A) and SPE after exposure to approximately 36 hours of airflow (graph B) of 7 cryptomelane on aluminium samples.

[0092] FIG. 6. Graph showing the concentration of acetaldehyde measured downstream from a catalyst over time after purging with clean air.

[0093] FIG. 7. Graph showing the decrease in SPE over cumulative test time and subsequent recovery in SPE following regeneration.

[0094] FIG. 8. Graph showing the SPE measured before regeneration, and the SPE following regeneration at various temperatures.

[0095] FIG. 9. Graph showing the relationship between total catalyst performance recovery and regeneration temperature.

[0096] FIG. 10. Graph showing the relationship between total catalyst performance recovery and regeneration time.

[0097] FIG. 11. Graph showing the difference in SPE between initial and post-deactivation and subsequent regeneration, over cumulative regeneration time.

[0098] FIG. 12. Graph showing the relationship between SPE and space velocity.

DETAILED DESCRIPTION

[0099] Embodiments of the present invention will now be described by way of example only, with reference to the accompanying figures.

Examples 1-3 and Comparative Examples 1-3

[0100] The ability of cryptomelane to remove aldehydes from a stream of air was investigated. A gas comprising acetaldehyde, propanal, butanal, crotonaldehyde, isopropyl alcohol, acetone and methyl acetate in air was passed through 50 g of catalyst (BASF SE) comprising cryptomelane mounted on a metal support. The estimated cryptomelane content is 5-20 wt % of the weight of the catalyst. Samples of gas having passed through the cryptomelane were analysed as a function of time using a gas chromatography mass spectrometer, and the results are shown in Table 1. The temperature was 90 C., and the concentration of each of acetaldehyde, propanal, butanal, crotonaldehyde, isopropyl alcohol, acetone and methyl acetate was 0.5 ppm. The flow rate was 7.5 litres/second, with 39.1/s GHSV (gas hourly space velocity).

TABLE-US-00001 TABLE 1 challenge agents passing through cryptomelane catalyst Height of GCMS peak (% passing through catalyst, 3%) Comparative Comparative Example 1 Comparative Example 3 Time Example 1 Example 2 Example 3 Isopropyl Example 2 Methyl (mins) Propanal Butanal Crotanaldehyde alcohol Acetone acetate 0 18 60 55 12 90 90 15 6 12 12 20 100 90 30 2 3 2 8 60 90 45 1 0 2 3 50 90

[0101] The data of Table 1 show that, surprisingly, cryptomelane is particularly effective at removing aldehydes from a carrier gas (in this case, aldehydes comprising three and four carbon atoms) at relatively low temperatures, but was far less effective at removing a variety of other challenges, such as alcohols (e.g. isopropyl alcohol), ketones (e.g. acetone) and esters (methyl acetate).

Example 4

[0102] The ability of manganese IV oxide to remove aldehydes from a stream of air at about 100 C. was also investigated. A flow of air (251/min) comprising 0.5 ppm acetaldehyde was passed over 0.5 g of 60-mesh manganese IV oxide (Sigma Aldrich) at about 100 C. initial temperature, and the concentration of acetaldehyde in the air was measured. It is estimated that the temperature of the catalyst during measurement. In the absence of the catalyst, the concentration of acetaldehyde was determined to be 0.53 ppm. Immediately after insertion of the catalyst, the concentration of acetaldehyde in the air that had been passed through the catalyst was 0.20 ppm, rising slightly over a period of about 1 hour to a steady level of about 0.30 ppm. After removal of the catalyst, the concentration of the acetaldehyde in the airflow was determined to be about 0.48 ppm.

[0103] This demonstrates that manganese IV oxide is particularly effective at removing aldehydes (in particular, acetaldehyde) from a stream of air at relatively low temperatures.

Comparative Examples 4-9

[0104] The method of Example 4 was repeated using different prospective catalysts, in this case manganese II oxide (Comparative Example 4), manganese II, III oxide (Comparative Example 5) Li.sub.2Mn.sub.2O.sub.4 (Comparative Example 6) and Fe.sub.2O.sub.3 (Comparative Example 7). None of the catalysts of Comparative Examples 4-7 worked effectively under the conditions of Example 4. The method of Example 4 was also repeated using manganese III oxide (Comparative Example 8), at a lower temperature of 60 C., but this showed limited to no removal of acetaldehyde. Catalysts comprising Pd or Pt (Comparative Example 9) were also investigated for their ability to remove acetaldehyde, but temperatures much higher than 100 C. were needed for effective removal of acetaldehyde and did not yield high single pass efficiencies, gram-for-gram.

Examples 5-8

[0105] Single pass efficiency (SPE) is a performance metric that indicates the amount of challenge pollutant removed from the treated fluid in a single pass through the catalyst. SPE testing is a type of testing that involves passing a constant concentration of pollutant through a catalyst sample and measuring the difference in pollutant concentration upstream and downstream of the catalyst.

[0106] The ability of cryptomelane to remove various concentrations of acetaldehyde from an air flow was investigated as a function of temperature. 15 g of catalyst comprising cryptomelane supported on aluminium (BASF SE) was subjected to a challenge of acetaldehyde at 0.2 ppm (Example 5), 0.3 ppm (Example 6), 0.4 ppm (Example 7) and 0.5 ppm (Example 8) (flow rate was 25 litres/minute, 33.9/s space velocity). The single pass efficiency (SPE) was measured as a function of temperature at each stated concentration of acetaldehyde, and it was found that cryptomelane is a surprisingly effective catalyst for removing aldehydes (in this case, acetaldehyde), even at very low temperatures (e.g. 30 C.). Moreover, at slightly elevated temperatures (e.g. 70 C.), cryptomelane is a very efficient catalyst for removing aldehydes from an airflow. Furthermore, for these conditions at least, it was found that the efficiency of the catalyst was independent of the concentration of the challenge.

Examples 9-11

[0107] The ability of cryptomelane to remove acetaldehyde, propanal and crotanaldehyde from an air flow was investigated as a function of temperature. 33.6 g of a catalyst comprising cryptomelane supported on aluminium was subjected to a challenge of acetaldehyde at 0.5 ppm (Example 11), propanal at 0.5 ppm (Example 9) and crotanaldehyde at 0.5 ppm (Example 10) (flow rate of 7.5 litres/second, 39.1/s GHSV). The single pass efficiency for acetaldehyde was 14% at 50 C. and 28% at 70 C. The single pass efficiency for propanal was 14% at 50 C. and 28% at 70 C. The single pass efficiency for crotanaldehyde was 25% at 50 C. and 29% at 70 C. Examples 9 and 10 demonstrate that cryptomelane is surprisingly effective at removing longer chain aldehydes, such as propanal and crotanaldehyde, from an air flow, even at relatively low temperatures.

Example 12

[0108] FIG. 1 displays Example 12, namely test data obtained during extended Continuous Injection Analysis (CIA) testing. CIA testing is a type of testing that involves continuously dosing a chamber with pollutant at a set mass dosage rate whilst a catalyst sample is used to clean the chamber. The chamber is continuously mixed and the concentration of pollutant in the chamber is logged. From the concentration measurements, flow rate through the catalyst and the pollutant mass dosage rate, the SPE can be determined.

[0109] In Example 12, the CIA testing was conducted within a 30 m 3 chamber, using acetaldehyde as the pollutant with cryptomelane on an aluminium support (BASF SE, as is the case in all examples using this catalyst). The catalyst had a pore diameter of 2 mm. The mass dosage rate of the pollutant was 3.9-7.9 mg/h (the initial mass dosage rate was 7.9 mg/h, which was reduced for subsequent tests to ensure that the concentration within the chamber did not increase excessively due to the reduction in SPE). The airflow was heated to 50 C. The space velocity was 11.2 s.sup.1. FIG. 1 shows multiple tests combined with the x-axis being the cumulative test time. The data showed a decrease in SPE over the exposure time, from approximately between 86% and 70% within the first hour to about 5% after 42 hours. This demonstrated that the performance of the catalyst decreases as the cumulative exposure time to both the aldehyde and airflow increases.

Examples 13-16

[0110] The temperature dependency of catalyst deactivation was also investigated. FIG. 2 displays the change in SPE over time for cryptomelane on aluminium catalyst samples (having a pore diameter of 1 mm), which were exposed to 0.5 ppm of acetaldehyde at 50 C. (Example 13) and 85 C. (Example 14) in otherwise identical SPE tests, in which the space velocity was 14.7 s.sup.1. The heating took place in an oven, such that both the airflow and the catalyst were heated to the respective temperature. Over 15 hours, at 50 C. the SPE decreased by 20.1%, while at 85 C. the SPE decreased by 6.5%.

[0111] FIG. 3 displays SPE against cumulative test time for different catalyst temperatures during CIA testing. The CIA tests used acetaldehyde as the pollutant and cryptomelane on aluminium catalyst samples (having a pore diameter of 2 mm), and these tests were identical other than the airflow temperature. The space velocity was 11.2 s.sup.1. At 50 C. (Example 15), the rate of deactivation was found to be approximately 5.4 times greater than at 70 C. (Example 16).

[0112] Therefore Examples 13 to 16 demonstrated that the rate of deactivation of the catalyst decreases as the temperature of the catalyst increases.

Examples 17-20

[0113] The variation in catalyst deactivation for different aldehydes was investigated. Table 2 displays the results from a set of CIA tests, which were identical other than the identity of the challenge pollutant. Initial SPE values and SPE decay rates are shown for the different aldehydes, where k refers to the exponential decay rate constant fitted through the measured SPE data with time from CIA tests at approximately 3.7 mg/h injection rate.

TABLE-US-00002 TABLE 2 Initial SPE values and SPE decay rates for different aldehydes by CIA testing Example 17 Example 18 Example 19 Example 20 Crotonaldehyde Butanal Propanal Acetaldehyde SPE decay 0.0123 h.sup.1 0.0094 h.sup.1 0.0212 h.sup.1 0.032 h.sup.1 rate (k) Initial SPE 100% 100% 90% 80%

[0114] It was observed that the rate of catalyst deactivation varies with different aldehyde functionality, where the variation is in line with initial performance. Generally, lower aldehyde molecular weight leads to an increased rate of deactivation (although it is expected that formaldehyde would not follow this trend under these conditions).

Examples 21-23

[0115] The effect of aldehyde concentration on deactivation rate was investigated. FIG. 4 shows the change in SPE for cryptomelane on aluminium as measured in an SPE test for different acetaldehyde concentrations, where the data are offset to show the change in SPE from the initial value. The acetaldehyde concentrations tested were 1.0 ppm (Example 21), 0.5 ppm (Example 22) and 0.2 ppm (Example 23). These tests were conducted on the same sample at 50 C. with regenerations conducted between each test. It was observed that there was a decrease in SPE from the initial SPE over time, and that the rate of deactivation increases with increased concentration of the aldehyde challenge pollutant.

Example 24

[0116] Seven samples of cryptomelane on aluminium (sample numbers 1 to 7) were deactivated using separate airflows for approximately 36 hours. The SPE was measured before and after deactivation at a temperature of 57 C. FIG. 5 displays the observations of Example 24, where graph A shows the initial SPE and graph B shows the SPE after exposure to the approx. 36 hours of airflow, for each of sample numbers 1 to 7.

[0117] A negative SPE in this case indicates that off-gassing/desorption is occurring, i.e. a higher sensor signal is measured downstream from the catalyst than upstream whilst the challenge pollutant is passed through the entire test system. The off-gassing concentration is shown on the right axis of graph B, which is based on a calibration using acetaldehyde. For all SPE tests an Alphasense PID sensor was used. As the response factor of PID sensors can vary significantly for different VOCs, the concentration shown is an approximation.

[0118] The results showed that deactivation also occurs due to exposure to VOCs in the air. Heating catalyst samples, which have been exposed to airflow for an extended period, results in VOCs being off-gassed from the catalyst. The off-gassing measured shows that deactivation due to airflow and other VOCs is due to physisorption. As such, removing VOCs by a method such as pre-filtering (e.g. carbon filtering) would reduce deactivation effects.

Example 25

[0119] Catalyst samples were exposed to 0.5 ppm acetaldehyde for approximately 16 hours at 60 C. in an SPE test, during which the SPE was continuously measured. The total mass of acetaldehyde that was removed by the catalyst was then calculated. The catalyst sample was subsequently regenerated within a sealed chamber. This chamber was then purged with clean air whilst the concentration was measured downstream. From this, the mass of any off-gassed/desorbed acetaldehyde was calculated (see FIG. 6, which shows the concentration of acetaldehyde measured downstream from a cryptomelane on aluminium catalyst after purging with clean air). Table 3 shows the percentage of acetaldehyde that was destroyed for different catalysts. Deactivation due to aldehydes is related to a saturated catalytic cycle.

TABLE-US-00003 TABLE 3 Percentage of acetaldehyde destroyed Post- Post- Mass Mass Initial deactivation regeneration removed in desorbed in Percentage Material SPE SPE SPE regeneration regeneration destroyed MnO.sub.2 60% 4% 57% 1.39 mg 0.01 mg >99% powder Cryptomelane 77% 64% 84% 6.37 mg 0.02 mg >99% on Al

Examples 26-30

[0120] It has been discovered that initial catalyst performance can be fully recovered through a regeneration process, involving heating the catalyst to an elevated temperature in the presence of a source of oxygen. In the following examples and associated figures, regeneration can also be referred to as reactivation.

[0121] In Example 26, a test chamber was repeatedly dosed with a set mass of pollutant (crotonaldehyde), while a catalyst sample (cryptomelane on aluminium) was used to clean the chamber at a temperature of 60 C. The catalyst had a pore diameter of 1 mm, and the space velocity was 10.15 s.sup.1. The effect of heating the catalyst to 130 C. for 1 hour was observed. The rate of change of pollutant concentration in the chamber was used to calculate the removal efficiency of the catalyst, accounting for the flow rate of the test. FIG. 7 shows the results of Example 26. Each data point represents the performance measured from each dose of the pollutant. With each successive test, the cumulative test time increases as the catalyst processes more pollutant. A representative illustration of the effect of heating a catalyst is displayed in FIG. 7, which shows the decrease in SPE over cumulative test time and a subsequent recovery in SPE following regeneration.

[0122] In Example 27, a single sample of cryptomelane on aluminium was deactivated (by 16 hours of airflow within a laboratory environment) and subsequently regeneration was attempted by heating for 60 minutes. The heating was performed at various temperatures between 70 C. and 110 C. The SPE was measured before and after heating. The results are shown in FIG. 8.

[0123] In Example 28, the relationship between the total catalyst performance recovery and regeneration temperature was observed. The same test set-up as that in Example 27 was used except that, in Example 28, each regeneration was conducted on the same sample for 15 minutes at various temperatures between 110 C. and 150 C. The results are shown in FIG. 9, in which a value of 1 on the axis of Fraction reactivated would be equal to complete recovery of performance. The rate of performance recovery was found to increase with regeneration temperature.

[0124] In Example 29, the relationship between the total catalyst performance recovery and regeneration time was observed. The same test set-up as that in Example 27 was used except that, in Example 29, regeneration was conducted on the same sample at 110 C. for varying lengths of time. The results are shown in FIG. 10, in which a value of 1 on the axis of Fraction reactivated would be equal to complete recovery of performance. The total amount of catalyst performance recovered was found to increase with regeneration time (i.e. the time of heating the catalyst to the regeneration temperature), up to a maximum efficiency.

[0125] The relationship between the total catalyst performance recovery and regeneration time was also observed in Example 30. This used a similar set-up to that in Example 24, in which a sample of cryptomelane on aluminium was deactivated using airflow for approximately 36 hours in a home. The SPE was measured before and after deactivation at a temperature of 57 C. Subsequently, regeneration was attempted by heating at 130 C. for 1 hour, a further 2 hours, and a further 2 hours again, with SPE tests conducted between each regeneration. The results are shown in FIG. 11, which shows the difference in SPE between initial and post-deactivation and subsequent regeneration, over cumulative regeneration time. It can be seen that a significantly longer period of time was required to regenerate this sample, compared with Example 27 (FIG. 8) which involved a shorter deactivation time. Therefore the total time required to recover initial catalyst performance is dependent on the total performance loss.

[0126] In further experiments, it has also been observed that SPE is related to residence time and space velocity. Residence time is the total time for which treated fluid is in contact with the catalyst, which is calculated as the total volume of catalyst divided by the flow rate of the treated fluid. Space velocity is the inverse of residence time. Data showing the relationship between SPE and space velocity are shown in FIG. 12. FIG. 12 shows four separate SPE experiments conducted on a single catalyst sample (having a pore diameter of 2 mm and a volume of 20 cm.sup.3). The sample was regenerated between tests and the flow rate was varied to achieve the different space velocities. The SPE tests were all conducted at 50 C.

Comparative Example 10

[0127] The effect of an absence of oxygen during attempted regeneration on the total catalyst performance recovery was observed. A cryptomelane on aluminium catalyst was exposed to zero air and 2.73 ppm acetaldehyde for about 16 hours, and then regenerated at 130 C. in a sealed chamber filled with nitrogen for 2 hours. The SPE was measured before and after deactivation and then again after regeneration in nitrogen. The results are shown in Table 4. It can be seen that there was no appreciable regeneration observed in the nitrogen atmosphere, demonstrating a need for a source of oxygen in the regeneration process.

TABLE-US-00004 TABLE 4 Regeneration of deactivation caused by aldehydes requires a source of oxygen Test Single pass efficiency (SPE) Before deactivation 84% After deactivation in zero air 72% and 2.73 ppm acetaldehyde After 2 hours at 130 C. in N.sub.2 73%

[0128] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0129] The examples above demonstrate the use of one particular type of manganese IV oxide. Those skilled in the art will realise that other manganese IV oxides (i.e. other oxides of manganese (IV)) may be used.

[0130] The examples above demonstrate the use of unsupported manganese IV oxide. Those skilled in the art will realise that it is possible for the manganese IV oxide to be on a support.

[0131] The examples above demonstrate the use of cryptomelane on a support, such as on a foam or metal support. Those skilled in the art will realise that other supports are possible, and that cryptomelane may be used unsupported.

[0132] The examples above demonstrate how manganese IV oxide and cryptomelane may be used to remove aldehydes having up to four carbon atoms. Those skilled in the art will realise that manganese IV oxide and cryptomelane may be used to remove aldehydes with more than four carbon atoms.

[0133] The examples above show how manganese IV oxide and cryptomelane may be used by themselves to remove aldehydes from a carrier fluid. Those skilled in the art will realise that it would be possible to use manganese IV oxide and cryptomelane with other catalyst components. For example, manganese IV oxide and cryptomelane may be used together, for example, with both manganese IV oxide and cryptomelane on the same support. Alternatively or additionally, manganese IV oxide may be used sequentially with cryptomelane, for example, by first contacting carrier fluid with, say, manganese IV oxide, and then contacting the carrier fluid with cryptomelane.

[0134] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[0135] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0136] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0137] Any section headings used herein are for organisational purposes only and are not to be construed as limiting the subject matter described.

[0138] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word comprise and include, and variations such as comprises, comprising and including, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0139] It must be noted that, as used in the specification and the appended claims, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent about, it will be understood that the particular value forms another embodiment. The term about in relation to a numerical value is optional and means for example +/ 10%.