METHOD FOR PREPARING A SORBENT

Abstract

A method is described for preparing a sorbent comprising the steps of: (i) forming agglomerates comprising a particulate support material, (ii) coating the agglomerates with a coating mixture powder comprising a particulate copper sulphide and a particulate calcined, rehydratable alumina to form a coated agglomerate, and (iii) drying the coated agglomerate to form a dried sorbent.

Claims

1. A method for preparing a sorbent 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 copper sulphide and a particulate calcined, rehydratable alumina to form coated agglomerates, and (iii) drying the coated agglomerates to form a dried sorbent.

2. A method according to claim 1, wherein the support material alumina, metal-aluminate, silicon carbide, silica, titania, zirconia, zinc oxide, an aluminosilicate, a 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, a cement binder, or an 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 agglomerates have a diameter in the range of 1-15 mm.

9. A method according to claim 1, wherein the particulate copper sulphide material is manufactured by roasting copper or a copper compound with elemental sulphur, precipitating copper sulphide from solution, sulphiding copper compounds using hydrogen sulphide, or a mechanochemical process comprising mixing powdered copper metal with elemental sulphur under conditions that cause the elemental copper and elemental sulphur to react to form one or more copper sulphides.

10. A method according to claim 1, wherein the copper sulphide comprises copper (II) sulphide and/or a substoichiometric copper sulphide of formula Cu.sub.2-xS where x is 0-1.

11. A method according to claim 1, wherein the particulate copper sulphide has a S:Cu atomic ratio of 0.8.

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

13. A method according to claim 1, wherein the copper sulphide content of the sorbent is in the range of 0.5-75% by weight expressed as CuS in the dried sorbent.

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

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

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

17. A method according to claim 1, wherein the sorbent comprises a mixture of a particulate copper sulphide 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.

18. (canceled)

19. A method according to claim 1, wherein the coating mixture is applied to the agglomerates under a non-oxidising atmosphere.

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

21. A method according to claim 1, wherein the sorbent is dried at a temperature up to 120 C. under a non-oxidising atmosphere.

22. A sorbent obtained by the method of claim 1.

23. A process for removing a heavy metal from a fluid stream comprising contacting the fluid stream with a sorbent prepared according to claim 22.

Description

EXAMPLE 1

[0046] 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.

[0047] 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

[0048] A coating mixture consisting of a copper sulphide powder and the same calcined, rehydratable alumina powder was then applied to the alumina agglomerates. The recipe for the coating mixture was as follows:

TABLE-US-00002 Component % Copper sulphide (99%) Eurolub 67 Calcined, rehydratable alumina (CP-5, BASF) 33

[0049] 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 adding the coating mixture to the alumina agglomerates in a rotating pan with further addition of water. Following coating, the material was aged at 45 C. before being dried in a fluid bed dryer at 105 C. The finished product was sieved to provide a sorbent particle size in the range 2.80-4.75 mm.

[0050] The physical properties were determined, and are shown below compared to a sulphided copper sorbent prepared using basic copper carbonate, cement and clay binders, and an alumina trihydrate (ATH) support material, according to the method described in WO2009/101429.

[0051] 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.

[0052] 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.

[0053] 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 time TBD DrTL MCS Example Description (h) (g cm.sup.3) (%) (kgF) 1(a) Agglomerate cores 1 0.86 0.00 3.82 1(b) Coated sorbent 1 0.91 0.00 5.46 material (5 minutes coating) 1(c) Coated sorbent 1 0.97 0.00 7.50 material (12 minutes coating) Comparative WO2009/101429 12 0.99 2.20 1.48

[0054] The use of a calcined, rehydratable alumina provided a much stronger product when compared to the prior art material produced using mixed binder 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 5 times higher following 1 h of ageing.