Method for preparing a sorbent

Abstract

A method for preparing a sorbent precursor, which may be sulphided and used to remove heavy metals such as mercury from fluid streams, includes the steps of: (i) mixing together an inert particulate support material and one or more binders to form a support mixture, (ii) shaping the support mixture by granulation in a granulator to form agglomerates, (iii) coating the agglomerates with a coating mixture powder including a particulate copper compound and one or more binders to form a coated agglomerate, and (iv) drying the coated agglomerate to form a dried sorbent precursor.

Claims

1. A method for preparing a sorbent precursor comprising the steps of: (i) mixing together an inert particulate support material and one or more binders to form a support mixture, (ii) shaping the support mixture by granulation using a liquid in a granulator to form agglomerates, (iii) coating the agglomerates with a coating mixture powder comprising a particulate copper compound and one or more 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.

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

3. The method according to claim 1 wherein the inert particulate support material is an alumina or hydrated alumina.

4. The method according to 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 1-100 m.

5. The method according to claim 1 wherein the binder used to prepare the agglomerates is a clay binder, cement binder, organic polymer binder, or a mixture thereof.

6. The method according to claim 1 wherein the agglomerates have a diameter in the range of from 1-15 mm.

7. The method according to 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.

8. The method according to 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 5-100 m.

9. The method according to claim 1 wherein the copper content of the dried sorbent precursor is in the range of from 0.5-30% by weight (expressed as copper present in the dried material).

10. The method according to claim 1 wherein the 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 from 1 to 1000 m (micrometers).

11. The method according to claim 1 wherein the sorbent precursor comprises a mixture of a particulate basic copper carbonate and a clay 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 with a cement binder and a clay binder.

12. The method according to claim 1 wherein the coated agglomerates are dried at a temperature in a range of from 70-150 C.

13. The 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 copper compound to copper sulphide.

14. The method according to claim 13 wherein the sulphiding step is performed by reacting the copper compound with a sulphur compound that is hydrogen sulphide, an alkali metal sulphide, ammonium sulphide, elemental sulphur or a polysulphide.

15. The method according to claim 13 wherein the sulphiding step is performed using hydrogen sulphide at a concentration in the range of from 0.1 to 5% by volume in an inert gas.

16. The method according to claim 13 wherein the sulphiding step is performed on the dried sorbent precursor composition ex-situ in a sulphiding vessel through which a sulphiding agent is passed, or performed in situ, in which case the dried sorbent precursor composition is installed and undergoes sulphidation in the vessel in which it is used to absorb heavy metals.

Description

EXAMPLE 1

(1) Agglomerates were prepared according to the following recipe (all parts by weight). 100 parts aluminium trihydrate powder [D.sub.50 10 m] 7 parts Ciment Fondu (calcium aluminate) 7 parts Attagel 50 (attapulgite clay)

(2) 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.

(3) 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.

(4) 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.

(5) 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.

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

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

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

EXAMPLE 2

(9) Agglomerates of material A were prepared according to the method described in Example 1.

(10) 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.

(11) Sorbent precursor F was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and pressure to produce sorbent G.

EXAMPLE 3

(12) Agglomerates of material A were prepared according to the method described in Example 1.

(13) 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.

(14) Sorbent precursor H was sulphided using 1% vol hydrogen sulphide in nitrogen at ambient temperature and pressure to produce sorbent I.

EXAMPLE 4: COMPARATIVE

(15) A sorbent was prepared according to the method of WO2011/021024.

(16) 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.

(17) 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

(18) 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. Pressure: 10 barg Temperature 30 C. Gas flow 110.2 NL.Math.hr1 Contact time 8 seconds Test duration 690 hours

(19) 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.

(20) 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

(21) 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

(22) 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.

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

(24) 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.