Method For Preparing A Sorbent

Abstract

A sorbent precursor is described comprising agglomerates of an inert particulate support material, the agglomerates being bound together with a binder comprising cement and/or clay, said binder being characterized as an agglomerate binder, wherein (a) the agglomerates are coated with a surface layer coating comprising a particulate copper compound and one or more coating binders, and (b) the surface layer has a thickness in a range of from 1 to 1000 m. The sorbent precursor may be sulphided to prepare a sorbent for removing heavy metals from fluid streams.

Claims

1. A sorbent precursor comprising agglomerates of an inert particulate support material, the agglomerates being bound together with a binder comprising cement and/or clay, said binder being characterized as an agglomerate binder, wherein: (a) the agglomerates are coated with a surface layer coating comprising a particulate copper compound and one or more binders, said one or more binders being characterized as coating binders; and (b) the surface layer has a thickness in a range of from 1 to 1000 m.

2. The sorbent precursor of claim 1 wherein the inert particulate support material is alumina, metal-aluminate, silicon carbide, silica, titania, zirconia, zinc oxide, aluminosilicates, zeolites, metal carbonate, carbon, or a mixture thereof.

3. The sorbent precursor of claim 1, wherein the inert particulate support material is an alumina or hydrated alumina.

4. The sorbent precursor of claim 1, wherein the inert particulate support material is in the form of a powder with a D.sub.50 particle size in the range of from 1 to 100 m.

5. The sorbent precursor of claim 1, wherein the inert particulate support material is in the form of a powder with a D.sub.50 particle size in the range of from 5 to 20 m.

6. The sorbent precursor of claim 1, wherein the agglomerate binder used to prepare the agglomerates is a combination of a cement and a clay.

7. The sorbent precursor of claim 6, wherein the relative weights of the cement agglomerate binder and clay agglomerate binder is in the range 1:1 to 3:1 (first to second binder).

8. The sorbent precursor of claim 1, wherein the total amount of the agglomerate binder in the agglomerate is in the range of from 5 to 30% by weight.

9. The sorbent precursor of claim 1 wherein the agglomerates have a diameter in the range of from 1 to 15 mm.

10. The sorbent precursor of claim 1, wherein the particulate copper compound is one or more of copper oxide, basic copper carbonate, or a precipitated material comprising copper basic carbonate and zinc basic carbonate.

11. The sorbent precursor of claim 1, wherein the particulate copper compound is in the form of a powder with an average particle size, [D.sub.50], in the range of from 5 to 100 m.

12. The sorbent precursor of claim 1, wherein the particulate copper compound is in the form of a powder with an average particle size, [D.sub.50], in the range of from 10 to 50 m.

13. The sorbent precursor of claim 1, wherein the copper content of the sorbent precursor is in the range of from 0.5 to 30% by weight, based on the total weight of the sorbent precursor.

14. The sorbent precursor of claim 1, wherein the total coating binder content of the surface layer coating is in the range of from 5 to 20% by weight.

15. The sorbent precursor of claim 1, wherein the surface layer coating comprises a particulate copper compound and a clay binder as the sole coating binder.

16. The sorbent precursor of claim 1, wherein the thickness of the surface layer coating of particulate copper compound in the sorbent precursor is in the range of from 1 to 500 m.

17. The sorbent precursor of claim 1, wherein the sorbent precursor comprises a mixture of a particulate basic copper carbonate and a clay coating binder, as a surface layer of 1 to 1000 m thickness coated on the surface of agglomerates formed from a particulate hydrated alumina support material, which is bound together in the agglomerates with an agglomerate binder comprising cement and a clay.

18. The sorbent of claim 1, wherein the sorbent precursor comprises granulated agglomerates.

19. A method for preparing the sorbent precursor of claim 1, comprising the steps of: (i) mixing together the inert particulate support material and the one or more agglomerate binders to form a support mixture, (ii) shaping the support mixture by granulation using a liquid in a granulator to form the agglomerates, (iii) coating the agglomerates with a coating mixture powder comprising the particulate copper compound and the one or more coating binders to form a coated agglomerate, and (iv) drying the coated agglomerate to form a dried sorbent precursor; wherein the agglomerates are coated in step (iii) by adding the coating mixture powder to the agglomerates in the granulator.

20. The method of claim 19, wherein the sorbent precursor comprises granulated agglomerates.

21. A sorbent prepared from the sorbent precursor of claim 1, wherein the sorbent precursor has been subjected to a sulphiding step to convert the particulate copper compound to copper sulphide.

22. A process for removing a heavy metal from a fluid stream comprising contacting the fluid stream with a sorbent according to claim 21.

Description

EXAMPLE 1

[0045] Agglomerates were prepared according to the following recipe (all parts by weight).

[0046] 100 parts aluminium trihydrate powder [D.sub.50 10 m]

[0047] 7 parts Ciment Fondu (calcium aluminate)

[0048] 7 parts Attagel 50 (attapulgite clay)

[0049] The dry powders were mixed to ensure homogeneity before employing a granulation technique where the mixed powder placed in the granulator and combined with water (0.2 ml/g mixture) and mixed to form agglomerates in an Eirich granulator. The resulting agglomerates were designated material A.

[0050] A mixture of basic copper carbonate powder (100 parts by weight) (D.sub.50 10-20 m) and attapulgite clay (10 parts by weight) was applied directly onto the agglomerated material A in the granulator with a little water (0.1 ml/g mixture) to and then dried at 105 C. to give dried sorbent precursor B loaded with 10% wt copper. The granules were sieved to provide a size fraction in the range 2.80-3.35 mm.

[0051] Sorbent precursor B was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature (20 C.) and at atmospheric pressure to produce sorbent C.

[0052] The method was repeated using a larger amount of the coating mixture on agglomerate material A to produce dried sorbent precursor D loaded with 18% wt copper.

[0053] Sorbent precursor D was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and atmospheric pressure to produce sorbent E.

[0054] The method was repeated using a coating mixture on agglomerate material A to produce dried sorbent precursor J loaded with 10% wt copper.

[0055] Sorbent precursor J was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and atmospheric pressure to produce sorbent K.

EXAMPLE 2

[0056] Agglomerates of material A were prepared according to the method described in Example 1.

[0057] A precipitated composition (100 parts by weight) comprising copper basic carbonate, zinc basic carbonate and alumina was mixed with attapulgite clay (10 parts by weight) and the mixture applied directly onto material A in the granulator with a little water (0.1 ml/g mixture) and then dried immediately in a laboratory fluid bed dried at 105 C. to give dried sorbent precursor F loaded with 10% wt copper.

[0058] Sorbent precursor F was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and pressure to produce sorbent G.

EXAMPLE 3

[0059] Agglomerates of material A were prepared according to the method described in Example 1.

[0060] A precipitated composition (100 parts by weight) comprising copper basic carbonate and zinc basic carbonate was mixed with attapulgite clay (10 parts by weight) and the mixture applied directly onto material A in the granulator with a little water (0.1 ml/g mixture) and then dried immediately in a laboratory fluid bed dried at 105 C. to give dried sorbent precursor H loaded with 10% wt copper.

[0061] Sorbent precursor H was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and pressure to produce sorbent I.

EXAMPLE 4: COMPARATIVE

[0062] A sorbent was prepared according to the method of WO2011/021024.

[0063] Washcoat preparation. 547 ml of demineralised water was heated with stirring to 52 C. 128 g of basic copper carbonate was added gradually followed by a mixture of 28 g Disperal P2 and 4 g Attagel 50. The mixture was stirred for 30 minutes and then milled using a bead mill to a particle size of 0.2-5.2 m. The solids content of the final slurry was determined to be 19 wt % and the pH was 6.44.

[0064] Sorbent preparation. 500 g of theta/delta alumina spheres were sprayed with the above slurry to achieve an even coating. The coated spheres were dried by applying hot air (at 50 C.) during the coating process to give sorbent precursor L loaded with 10% wt copper. Precursor L was then sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and atmospheric pressure to produce sorbent M.

EXAMPLE 5: TESTING

[0065] Sorbents C, E, G and I were individually charged (2.80-3.35 mm size fraction, volume 25 ml) to a stainless steel reactor (21 mm ID). A flow of 100% vol natural gas was passed through a bubbler containing elemental mercury to allow the gas to pick up the mercury. The mercury-laden gas was then passed downwards through the reactor under the following conditions.

[0066] Pressure: 10 barg

[0067] Temperature 30 C.

[0068] Gas flow 110.2 NL.Math.hr-1

[0069] Contact time 8 seconds

[0070] Test duration 690 hours

[0071] Samples from the reactor inlet and exit were periodically analysed for mercury content by atomic fluorescence detection. The inlet gas had a mercury concentration of about 1,100 g/m.sup.3. The sorbents C, E, G and I reduced the mercury content of the exit gas to below detectable limits throughout the test. At the end of each test the 25 ml sorbent bed was discharged as 9 discrete sub-beds which were ground to a fine powder and analysed by acid digestion/ICP-OES to determine total mercury content. The amount of mercury captured by each sorbent bed is shown in Table 1.

TABLE-US-00001 TABLE 1 Sorbent C Sorbent E Sorbent G Sorbent I Mercury Bed 1 (inlet) 2.04 2.24 1.97 2.23 Loading, Bed 2 1.10 0.97 1.01 1.11 wt % Bed 3 0.54 0.53 0.51 0.71 Bed 4 0.19 0.17 0.24 0.20 Bed 5 0.03 0.06 0.12 0.13 Bed 6 0.01 0.02 0.08 0.03 Bed 7 <0.01 <0.01 0.02 <0.01 Bed 8 <0.01 <0.01 <0.01 <0.01 Bed 9 (exit) <0.01 <0.01 <0.01 <0.01

[0072] All of the sorbents were effective for the removal of mercury with sorbents C and E providing the sharpest profiles.

EXAMPLE 6: MEASUREMENT OF PORE DIMENSIONS

[0073] Sorbent precursor J and sorbent K, along with comparative sorbent precursor L and sorbent M, were dried overnight at 115 C. and analysed using mercury porosimetry in order to probe their pore dimensions. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Corrected Median intrusion pore volume Entrapment diameter Pore volume (cm.sup.3/g) (% v/v) () (cm.sup.3/g) Sorbent precursor J 0.170 45 1583 0.181 Sorbent K 0.215 54 1641 0.247 Sorbent precursor L 0.303 33 68 0.394 Sorbent M 0.336 37 71 0.452

[0074] The granulated core-shell materials have a smaller pore volume than the wash-coated materials but a larger pore diameter. This suggests that they contain fewer bigger pores than the wash-coated materials which contain more pores of a smaller size. The entrapment value for the core-shell materials is larger, suggesting a more complex pore network.