METHOD FOR PREPARING A SORBENT

Abstract

A method is described for preparing a sorbent precursor comprising the steps of: (i) forming agglomerates comprising a particulate support material, (ii) coating the agglomerates with a coating mixture powder comprising a particulate sulphidable copper compound and a particulate calcined, rehydratable alumina to form a coated agglomerate, and (iii) drying the coated agglomerate to form a dried sorbent precursor. The sorbent precursor may be sulphided and used to remove heavy metals such as mercury from fluid streams.

Claims

1. A method for preparing a sorbent precursor comprising the steps of: (i) forming agglomerates comprising a particulate support material in a granulator with a liquid, and ageing the agglomerates to form aged agglomerates, (ii) adding a coating mixture powder to the aged agglomerates in the granulator, wherein the coating mixture powder comprises a particulate sulphidable copper compound and a particulate calcined, rehydratable alumina, to form coated agglomerates, and (iii) drying the coated agglomerates to form a dried sorbent precursor.

2. A method according to claim 1 wherein the support material is alumina, metal-aluminate, silicon carbide, silica, titania, zirconia, zinc oxide, aluminosilicate, zeolite, metal carbonate, carbon, or a mixture thereof.

3. A method according to claim 1, wherein the support material is a particulate calcined, rehydratable alumina.

4. A method according to claim 1, wherein the calcined rehydratable alumina comprises a calcined amorphous alumina or a transition alumina that is one or more of rho-alumina, chi-alumina, or pseudo gamma-alumina.

5. A method according to claim 1 wherein the support material is in the form of a powder with a D.sub.50 particle size in the range of 1-100 m.

6. A method according to claim 1, wherein a binder that is a clay binder, cement binder or organic polymer binder is combined with the support material to form the agglomerates.

7. A method according to claim 6 wherein the binder combined with the support material is a combination of a cement binder and a clay binder.

8. A method according to claim 1, wherein the agglomerates have a diameter in the range 1-15 mm.

9. A method according to claim 1, wherein the particulate sulphidable copper compound is one or more compounds that is copper oxide, basic copper carbonate, or a precipitated material comprising copper basic carbonate and zinc basic carbonate.

10. A method according to claim 1, wherein the particulate sulphidable copper compound is in the form of a powder with an average particle size, [D.sub.50], in the range of 5-100 m.

11. A method according to claim 1, wherein the copper content of the dried sorbent precursor is in the range of 0.5-35% by weight expressed as copper present in the dried material.

12. A method according to claim 1, wherein the particulate sulphidable copper compound content in the coating mixture is in the range of 50-95% by weight.

13. A method according to claim 1, wherein the coating mixture consists of a particulate sulphidable copper compound and a particulate calcined, rehydratable alumina.

14. A method according to claim 1, wherein the sulphidable copper compound is present as a layer on the surface of the agglomerate and the thickness of the layer in the dried sorbent precursor is in the range of 1 to 2000 micrometres.

15. A method according to claim 1, wherein the sorbent precursor comprises a mixture of a particulate basic copper carbonate and a particulate calcined, rehydratable alumina, coated as a surface layer of 1 to 2000 m thickness on the surface of 1-15 mm agglomerates formed from a particulate calcined, rehydratable alumina support material.

16. (canceled)

17. A method according to claim 1, wherein the coated agglomerates are aged for 0.5-8 hours before drying.

18. A method according to claim 1, wherein the coated agglomerates are dried at 70-150 C.

19. A method for preparing a sorbent comprising preparing a sorbent precursor according to claim 1 and subjecting the dried sorbent precursor to a sulphiding step to convert the sulphidable copper compound to copper sulphide.

20. A method according to claim 19, wherein the sulphiding step is performed by reacting the copper compound with a sulphur compound that is hydrogen sulphide, alkali metal sulphide, ammonium sulphide, elemental sulphur or a polysulphide.

21. A method according to claim 19, wherein the sulphiding step is performed using hydrogen sulphide at a concentration in the range of 0.1 to 5% by volume in an inert gas.

22. A method according to claim 19, wherein the sulphiding step is performed (i) ex-situ in a sulphiding vessel and a sulphiding agent is passed through the sulphiding vessel, or (ii) in situ in the vessel in which it is used to absorb heavy metals.

23. A sorbent precursor obtained by the method of claim 1.

24. A sorbent obtained by the method of claim 19.

25. A process for removing a heavy metal from a fluid stream comprising contacting the fluid stream with a sorbent of claim 24.

Description

[0050] The invention is further described by reference to the following Examples.

EXAMPLE 1

[0051] Agglomerates were formed by tumbling a calcined, rehydratable alumina powder in a rotating pan and adding water sprayed via a fine mist onto the alumina. The water content of the freshly granulated agglomerates before drying was found to be 29.7 wt %. Following granulation, the material was aged at 45 C. for 1 hour.

[0052] The properties of the calcined, rehydratable alumina powder were as follows:

TABLE-US-00001 (wt %) Chemical composition Residual Moisture (dried a 250 C. for 30 minutes) 2 Total loss on ignition (250-1100 C.) 7 SiO.sub.2 <0.02 Fe.sub.2O.sub.3 <0.01 Na.sub.2O <0.4 Physical Properties Surface area 270 m.sup.2/g Packed bulk density 38 lb/ft.sup.3 Particle size distribution (average size) 5 m Particle size distribution (90 wt % <) 12 m XRD Phase Amorphous

[0053] A coating mixture consisting of basic copper carbonate and the same calcined, rehydratable alumina was then applied to the alumina agglomerates. The recipe for the coating mixture was as follows:

TABLE-US-00002 Component % Basic copper carbonate (100%), Adchem 67 Calcined, rehydratable alumina CP-5, BASF 33

[0054] The amount of coating mixture was adjusted to produce a copper loading in the finished dried product of 18% wt (expressed as Cu). A coating layer (thickness about 1000 m) was formed by was formed by adding the coating mixture to the alumina agglomerates in a rotating pan with further addition of water. Following coating, the material was aged at 65 C. before being dried in a fluid bed dryer at 105 C. The dried sorbent precursor product was sieved to provide the sorbent in two size ranges, 1.00-2.80 mm and 2.80-4.75 mm.

[0055] The physical properties of the sorbent precursor were determined, and are shown below compared to a sorbent precursor comprising basic copper carbonate, cement and clay binders, and an alumina trihydrate (ATH) support material, prepared according to the method described in WO2009/101429.

[0056] The tapped bulk density (TBD) was measured by pouring approximately 500 mls of sorbent granules into a 500 ml plastic measuring cylinder and tapping it until a constant volume was achieved. The TBD was calculated by dividing the mass of sorbent by the tapped volume.

[0057] The drum tumbling loss (DrTL) was measured by rotating 100 g of sorbent through 1800 total revolutions at 60 rpm for 30 minutes according to the ASTM method D4058-96. The DrTL is reported as a percentage of the original mass.

[0058] The mean crush strength (MCS) was determined by crushing 25 granules of each sorbent using an Engineering Systems C53 machine to calculate mean crush strength based on a normal distribution.

TABLE-US-00003 Ageing TBD DrTL MCS Example Description time (h) (g cm.sup.3) (%) (kgF) 1(a) Coated sorbent 4 0.99 0.00 8.06 precursor 1.00-2.80 mm 1(b) Coated sorbent 4 0.99 0.00 10.38 precursor 2.80-4.75 mm Comparative W02009/101429 4 1.03 2.8 2.7 2.80-4 mm

[0059] The use of a calcined, rehydratable alumina provided a much stronger product when compared to the prior art material produced using mixed binders and aluminium trihydrate. The rate at which strength develops also occurs much more rapidly in the calcined rehydratable alumina product when compared to the mixed binder product with strength achieved almost 4 times higher for the same ageing time.