METHOD OF REDUCING THE AMMONIA EMISSION FROM SECONDARY ALUMINUM OXIDE

Abstract

A method of reducing the ammonia emission from an aluminium oxide comprises the step of contacting secondary aluminium oxide with a zeolite. Preferably the zeolite is a used or unused fluid catalytic cracking (FCC) catalyst such as zeolite Y. The invention also relates to a mixture comprising secondary aluminium oxide and a zeolite, wherein the zeolite is a used or unused fluid catalytic cracking (FCC) catalyst and that the composition has a gaseous ammonia emission of 1 mg NH.sub.3 per gram of composition and hour. Lastly, the invention is directed towards the use of a zeolite for reducing the ammonia emission from secondary aluminium oxide.

Claims

1. A method of reducing the ammonia emission from an aluminium oxide composition, wherein the aluminium oxide composition has an Al.sub.2O.sub.3 content of 50 weight-% of dry matter and a metal nitride content of 0.01 weight-% of dry matter, wherein the method comprises the step of contacting the aluminium oxide composition aluminium with a zeolite, thereby obtaining a mixture of the aluminium oxide composition and a zeolite.

2. The method according to claim 1, wherein the aluminium oxide composition is a particulate solid with a d.sub.80 value of the particle size distribution of 500 m and/or the aluminium oxide composition has a content of metallic aluminium of 5 weight-% of dry matter.

3. The method according to claim 1, wherein the zeolite is distributed within the aluminium oxide composition.

4. The method according to claim 1, wherein the weight ratio of aluminium oxide composition to the zeolite is 1:1 to 10000:1.

5. The method according to claim 1, wherein the zeolite is a used or unused fluid catalytic cracking catalyst.

6. The method according to claim 1, wherein the zeolite is zeolite Y.

7. A mixture comprising an aluminium oxide composition and a zeolite, wherein the aluminium oxide composition has an Al.sub.2O.sub.3 content of 50 weight-% of dry matter and a metal nitride content of 0.01 weight-% of dry matter, wherein the zeolite is a used or unused fluid catalytic cracking catalyst and that the composition has a gaseous ammonia emission of 5 mg NH.sub.3 per gram of composition and hour.

8. The mixture according to claim 7, wherein the aluminium oxide composition is a particulate solid with a d.sub.80 value of the particle size distribution of 500 m and/or the aluminium oxide composition has a content of metallic aluminium of 5 weight-% of dry matter.

9. The mixture according to claim 7, wherein the zeolite is zeolite Y.

10.-15. (canceled)

16. The method according to claim 2, wherein the zeolite is distributed within the aluminium oxide composition.

17. The method according to claim 2, wherein the weight ratio of aluminium oxide composition to the zeolite is 1:1 to 10000:1.

18. The method according to claim 3, wherein the weight ratio of aluminium oxide composition to the zeolite is 1:1 to 10000:1.

19. The method according to claim 2, wherein the zeolite is a used or unused fluid catalytic cracking catalyst.

20. The method according to claim 3, wherein the zeolite is a used or unused fluid catalytic cracking catalyst.

21. The method according to claim 4, wherein the zeolite is a used or unused fluid catalytic cracking catalyst.

22. The method according to claim 2, wherein the zeolite is zeolite Y.

23. The method according to claim 3, wherein the zeolite is zeolite Y.

24. The method according to claim 4, wherein the zeolite is zeolite Y.

25. The method according to claim 5, wherein the zeolite is zeolite Y.

26. The mixture according to claim 8, wherein the zeolite is zeolite Y.

Description

[0023] The present invention has the object of providing a way to use or at least safely handle secondary aluminium oxide or other aluminium oxide-containing compositions which additionally contain metal nitrides as a raw material in manufacturing while avoiding the associated drawbacks of the reaction of the compositions with water.

[0024] This object is achieved by a method according to claim 1, a mixture according to claim 7 and a use according to claim 10. Advantageous embodiments are described in the dependent claims. They may be combined freely unless the context clearly indicates otherwise.

[0025] A method of reducing the ammonia emission from an aluminium oxide composition, wherein the aluminium oxide composition has an Al.sub.2O.sub.3 content of 50 weight-% of dry matter and a metal nitride content of 0.01 weight-% of dry matter, comprises the step of contacting the aluminium oxide composition aluminium with a zeolite, thereby obtaining a mixture of the aluminium oxide composition and the zeolite.

[0026] Examples for zeolites in the method, composition and use according to the present invention include zeolite beta, zeolite Y, zeolite omega, ZSM-5, ZSM-12, MCM-22, MCM-36, MCM-49, MCM-56, MCM-58, MCM-68, Faujasite and Mordenite. The zeolite is preferably an acidic zeolite, i.e. a zeolite with a pH (DN EN ISO 10523) of <7. Particularly preferred are zeolites with a pH (DIN EN ISO 10523) of 6, even more preferred 5. Furthermore, it is preferred that the d.sub.80 value (DIN EN 933) of the particle size distribution of the zeolite is 100 m, more preferred 1 m to 10 m. The zeolite may contain rare earth elements as dopants, such as La and/or Ce. They may serve to enhance the acidity of the zeolite.

[0027] Examples for preferred zeolites include acidic zeolites such as the aluminosilicate zeolites having a relatively high silica and low alumina content with the aluminium sites being acidic. The acidity is believed to be due to substitution of Al.sup.3+ in place of the tetrahedral Si.sup.4+ in the structure. Preferred silica to alumina molar ratios (SiO.sub.2/Al.sub.2O.sub.3) of the zeolite are 5 moles (i.e., 5 SiO.sub.2 per mole Al.sub.2O.sub.3) to 280 moles SiO.sub.2 per mole Al.sub.2O.sub.3. Within this range, a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of greater than or equal to 30 is preferred, with a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of greater than or equal to 50 being more preferred. Examples of especially suitable acidic zeolites include ZSM-5, zeolite Y, beta zeolite beta and the like, and combinations comprising one or more of the foregoing zeolites.

[0028] The method according to the invention has several additional advantages. By mixing the aluminium oxide composition with the zeolite the moisture of the mixture can be held below the transport moisture limit (TML). Ammonia dissolved in the interstitial water of the aluminium oxide can be absorbed. Customer specifications for elements such as Cl, F, alkalines (Na.sub.2O, K.sub.2O) and heavy metals can be met and the product specification under regulatory aspects can be retained. Lastly, zeolites are widely available and make the method economically attractive.

[0029] The aluminium oxide composition used in the method, composition and use according to the invention may be obtained by: [0030] separating aluminium metal from aluminium salt slag, thereby obtaining a metal-depleted salt slag; and [0031] treating the metal-depleted salt slag with water and separating a liquid phase and a water-insoluble residue obtained thereby.

[0032] The water-insoluble residue may be described as a secondary aluminium oxide product. This has the advantage that a substance already certified for numerous applications such as a cement additive is used and regulatory issues are simplified.

[0033] In an embodiment of the method according to the invention the aluminium oxide composition is a particulate solid with a d.sub.80 value of the particle size distribution of 500 m and/or the aluminium oxide composition has a content of metallic aluminium of 5 weight-% of dry matter.

[0034] The aluminium oxide composition used in the method, mixture and use according to the invention is preferably a particulate solid with a d.sub.80 value of the particle size distribution of 500 m, an Al.sub.2O.sub.3 content of 50 weight-% of dry matter, a metal nitride content of 0.01 weight-% of dry matter and a content of metallic aluminium of 5 weight-% of dry matter.

[0035] The particle size distribution may be determined in accordance with the norm DIN EN 933. It is preferred that the d.sub.80 value is 100 m to 500 m, more preferred 200 m to 400 m.

[0036] In the context of the present invention the Al.sub.2O.sub.3 content of a component represents a sum parameter from the contents of aluminium oxide and hydroxide species such as amorphous aluminium oxide, corundum, bayerite, boehmite, gibbsite, nordstrandite and spinel. The total content can be determined in an X-ray fluorescence spectroscopy measurement. Dry matter may be obtained by heating the samples to 105 C. until no further weight loss is observed. Preferably this Al.sub.2O.sub.3 content is 60 to 80 weight-% of dry matter, more preferred 65 to 75 weight-% of dry matter.

[0037] The aluminium oxide composition used in the method, mixture and use according to the invention also comprises metal nitride such as aluminium nitride and/or silicon nitride, a fact which is expressed by a minimum content for the metal nitrides of 0.01 weight-% of dry matter. The nitride content can be determined from the nitrogen content according to DIN 51732. Preferably, the nitrogen content is used to calculate a metal nitride content as aluminium nitride. A further example for a metal nitride content is 0.01 weight-% to 5 weight-% of dry matter.

[0038] The aluminium oxide composition preferably used in the method, mixture and use according to the invention may comprise metallic aluminium, however preferably only up to 5 weight-% of dry matter as most aluminium should have been recovered in preceding treatment steps. The metallic aluminium content may be determined according to DIN EN ISO 11885. Preferably the content is 0 to 5 weight-% of dry matter, more preferred 0 to 3 weight-% of dry matter.

[0039] The aluminium oxide composition preferably used in the method, mixture and use according to the invention may have the following properties with respect to dry matter, the sum of the weight percentages stated being 100 weight-%:

TABLE-US-00001 Al.sub.2O.sub.3 content 60 to 80 weight-% of dry matter SiO.sub.2 content 3 to 10 weight-% of dry matter CaO content 1 to 10 weight-% of dry matter MgO content 3 to 10 weight-% of dry matter
and/or the moisture content of the aluminium oxide composition is 20 to 30 weight-%.

[0040] The moisture content may be determined by the weight difference before and after heating the samples to 105 C. until no further weight loss is observed. SiO.sub.2, CaO and MgO content may be determined by X-ray fluorescence spectroscopy.

[0041] Preferred are:

TABLE-US-00002 Al.sub.2O.sub.3 content 65 to 75 weight-% of dry matter SiO.sub.2 content 4 to 9 weight-% of dry matter CaO content 2 to 9 weight-% of dry matter MgO content 4 to 9 weight-% of dry matter

[0042] More preferred are:

TABLE-US-00003 Al.sub.2O.sub.3 content 67 to 73 weight-% of dry matter SiO.sub.2 content 5 to 8 weight-% of dry matter CaO content 3 to 8 weight-% of dry matter MgO content 5 to 8 weight-% of dry matter

[0043] The method according to the invention may be performed until the resulting mixture has a pH (DIN EN ISO 10523) of 7 to 10, preferably 8 to 9.

[0044] In another embodiment of the method according to the invention the obtained mixture is stored for a time of 1 hour. After this time the mixture may be processed further, for example in the production of cement or mineral wool. As the method according to the invention leads to a storage-stable mixture, this storage time may also be 1 day or 30 days.

[0045] In another embodiment of the method according to the invention the obtained mixture has a moisture content of 1 weight-%. Preferably the moisture content is 10 to 20 weight-%.

[0046] In another embodiment of the method according to the invention the zeolite is distributed within the aluminium oxide composition. This may be achieved by mixing the materials thoroughly. Particularly preferred is an intensive mixing, the energy transfer of which into the composition being beneficial in breaking up aluminium oxide aggregates present after autogenic drying.

[0047] In another embodiment of the method according to the invention the weight ratio of aluminium oxide composition to the zeolite is 1:1 to 10000:1. Preferred is a weight ratio of aluminium oxide composition to the zeolite of 1:1 to 100:1, more preferred 1:1 to 5:1, even more preferred 1:1 to 2:1.

[0048] In another embodiment of the method according to the invention the zeolite is a used or unused fluid catalytic cracking (FCC) catalyst. FCC catalysts are widely available. Even used catalysts which otherwise would be discarded may be used in the present invention. Without wishing to be bound by theory it is believed that hydrocarbon residues present in the used FCC catalyst additionally serve to shield AlN regions in the particles of the aluminium oxide composition from moisture.

[0049] In another embodiment of the method according to the invention the zeolite is zeolite Y.

[0050] Another aspect of the present invention is a mixture comprising an aluminium oxide composition, and a zeolite, wherein the aluminium oxide composition has an Al.sub.2O.sub.3 content of 50 weight-% of dry matter and a metal nitride content of 0.01 weight-% of dry matter and wherein the zeolite is a used or unused fluid catalytic cracking catalyst and the composition has a gaseous ammonia emission of 5 mg (preferably 1 mg, more preferred 0.1 mg, even more preferred 0.01 mg) NH.sub.3 per gram of composition and hour. The ammonia emission may be determined by placing a sample in a gas collecting tube for 24 h and photometrically measuring the ammonia present according to the method VDI 3878 (VDI: Verein Deutscher Ingenieure, Association of German Engineers). The weight ratio of aluminium oxide composition to the zeolite may be 1:1 to 10000:1. Preferred is a weight ratio of aluminium oxide composition to the zeolite of 1:1 to 100:1, more preferred 1:1 to 5:1, even more preferred 1:1 to 2:1.

[0051] In an embodiment of the mixture according to the invention the aluminium oxide composition is a particulate solid with a d.sub.80 value of the particle size distribution of 500 m and/or the aluminium oxide composition has a content of metallic aluminium of 5 weight-% of dry matter.

[0052] In another embodiment of the mixture according to the invention the zeolite is zeolite Y.

[0053] In another embodiment of the mixture according to the invention the mixture has the following properties:

TABLE-US-00004 Moisture 10 to 20 weight-% Al.sub.2O.sub.3 content (dry matter) 40 to 60 weight-% Chloride content (dry matter) 0.5 weight-% Fluoride content (dry matter) 0.8 weight-% Alkaline content (dry matter) 2 weight-%

[0054] The chloride and fluoride content can be determined according to DIN EN ISO 10304-1. Such low chloride and fluoride contents have the advantage that caking of the composition in machinery parts when the composition is used in the production of cement is reduced or avoided and that gas purification systems in this process are not burdened with fluorine. Alkaline content (as K.sub.2O and Na.sub.2O) can be determined from dried samples via X-ray fluorescence spectroscopy.

[0055] Preferably the properties are:

TABLE-US-00005 Moisture 11 to 18 weight-% Al.sub.2O.sub.3 content (dry matter) 42 to 55 weight-% Chloride content (dry matter) 0.4 weight-% Fluoride content (dry matter) 0.8 weight-% Alkaline content (dry matter) 1.8 weight-%

[0056] The mixture according to the invention may have a pH (DIN EN ISO 10523) of 7 to 10, preferably 8 to 9.

[0057] The mixture according to the invention may be used as a starting material in a process which employs an aluminium oxide-containing starting material. Preferred processes are the production of cement or the production of mineral wool. Examples for cement types are Portland cement and calcium sulfoaluminate cement.

[0058] The present invention is furthermore directed towards the use of a zeolite for reducing the ammonia emission from an aluminium oxide composition, wherein the aluminium oxide composition has an Al.sub.2O.sub.3 content of 50 weight-% of dry matter and a metal nitride content of 0.01 weight-% of dry matter.

[0059] In an embodiment of the use according to the invention the aluminium oxide composition is a particulate solid with a d.sub.80 value of the particle size distribution of 500 m and/or the aluminium oxide composition has a content of metallic aluminium of 5 weight-% of dry matter.

[0060] In another embodiment of the use according to the invention the aluminium oxide composition has a moisture content of 1 weight-%. Preferably the moisture content is 10 to 20 weight-%.

[0061] In another embodiment of the use according to the invention the zeolite is distributed within the aluminium oxide composition. This may be achieved by mixing the materials thoroughly. Particularly preferred is an intensive mixing, the energy transfer of which into the composition being beneficial in breaking up aluminium oxide aggregates present after autogenic drying.

[0062] In another embodiment of the use according to the invention the weight ratio of aluminium oxide composition to the zeolite is 1:1 to 10000:1. Preferred is a weight ratio of aluminium oxide composition to the zeolite is 1:1 to 100:1, more preferred 1:1 to 5:1, even more preferred 1:1 to 2:1.

[0063] In another embodiment of the use according to the invention the zeolite is a used or unused fluid catalytic cracking catalyst. FCC catalysts are widely available. Even used catalysts which otherwise would be discarded may be used in the present invention. Without wishing to be bound by theory it is believed that hydrocarbon residues present in the used FCC catalyst additionally serve to shield AlN regions in the particles of the aluminium oxide composition from moisture.

[0064] In another embodiment of the use according to the invention the zeolite is zeolite Y.

[0065] The present invention will be further described with reference to the following examples without wishing to be limited by them.

[0066] As a zeolite a used fluid catalytic cracking catalyst was used. This was a zeolite Y with a pH (DIN EN ISO 10523) of 4.1 and a chemical composition according to the following analysis:

TABLE-US-00006 SiO.sub.2 39.50% Na.sub.2O 0.50% CaO 0.40% K.sub.2O 0.10% MgO 0.40% C free 0.15% Al.sub.2O.sub.3 41.90% CO.sub.2 0.20% TiO.sub.2 0.80% C total 0.20% Fe.sub.2O.sub.3 0.90% S total 0.95% MnO.sub.2 0.01% H.sub.2O 105 C. 3.33% P.sub.2O.sub.5 1.10% H.sub.2O 950 C. 6.92%

[0067] The particle size distribution according to a sieve analysis was:

TABLE-US-00007 smaller 32.60% >32 m 67.40% >45 m 50.70% >63 m 34.00% >90 m 16.50% >125 m 4.70% >250 m 0.00% Sum of sieve fractions 100.0%

[0068] The aluminium oxide composition, obtained by recycling aluminium salt slag, had a pH (DIN EN ISO 10523) of 9.7 composition according to the following specification in its data sheet (dry material):

TABLE-US-00008 Min. Max. Al.sub.2O.sub.3 58.00% 76.00% SiO.sub.2 2.00% 14.00% CaO 1.30% 3.80% MgO 6.50% 10.20% Fe.sub.2O.sub.3 0.90% 2.80% TiO.sub.2 0.50% 1.00% K.sub.2O 0.40% 1.20% Na.sub.2O 0.40% 1.20%

[0069] The zeolite and the aluminium oxide composition were mixed in a weight ratio of zeolite:aluminium oxide composition of 2:1. The resulting mixture had a pH (DIN EN ISO 10523) of 8.2 and a composition according to the following analysis:

TABLE-US-00009 Moisture at 105 C. % 13.85 Ammonia (calc.) ppm 1791.50 Ammonium (IC) ppm 1691.40 N (CHN-Analyser) % n.d. TOC (RC612) % 0.67 Chloride (potentiometry) % 0.31 Fluoride (Seel) % 0.78 Sulphur (CS-Analyser) % 0.30 BET m.sup.2/g 38.07 Blaine cm.sup.2/g 11750.00 Density g/cm.sup.3 2.80 Without L.o.I. L.o.I. 1050 C. % 15.56 SiO.sub.2 % 17.85 21.33 Al.sub.2O.sub.3 % 53.86 64.35 TiO.sub.2 % 0.74 0.88 MnO % 0.10 0.12 Fe.sub.2O.sub.3 % 3.04 3.63 CaO % 1.25 1.49 MgO % 5.28 6.31 K.sub.2O % 0.43 0.51 Na.sub.2O % 0.71 0.85 SO.sub.3 % 0.00 0.00 P.sub.2O.sub.5 % 0.44 0.53 Sum RFA (1050 C.) % 99.26 100

[0070] The following observations were made with respect to this mixture: [0071] Ammonia production ceased within 10 seconds of mixing, as determined by olfactory analysis [0072] Exothermic reactions ceased immediately after mixing [0073] Immediately after mixing, ammonia could be stripped out of the mixture by raising the pH; after 2 weeks of storing the mixture this was significantly decreased (at least by 90%) [0074] Aqueous extraction of a mixture which had been stored for over 2 weeks followed by evaporating the water did not lead to detectable ammonia emissions [0075] Raising the pH to >12 by adding lime did not lead to ammonia emission from a mixture stored for a considerable amount of time [0076] Even after storing a mixture with ca. 15-20% moisture for 6 months no ammonia emissions could be detected

[0077] All of the experiments above would have led to ammonia emissions of over 1000 ppm in the original aluminium oxide composition.