Sorbents

Abstract

A sorbent is described, suitable for removing heavy metals, particularly mercury, from fluid streams including 20-75% by weight of copper (expressed as copper (II) oxide) in the form of one or more copper sulphides, the sorbent having a sulphur to copper atomic ratio in the range 0.7 to 0.95:1.

Claims

1. A sorbent suitable for removing mercury from fluid streams comprising 20-75% by weight of copper (expressed as copper (II) oxide) in the form of granules comprising one or more copper sulphide, a support and a binder, said sorbent having a sulphur to copper atomic ratio in the range 0.7 to 0.95:1, wherein the sorbent is formed by: (i) combining a copper oxide or copper hydroxycarbonate with one or more binders and a support material in a granulator to form a granulated sorbent precursor, (ii) sulphiding the sorbent precursor with a gas mixture comprising 0.5-5% by volume hydrogen sulphide at a temperature in the range of 1-150 C. to form a sulphided copper material, and (iii) partially reducing the sulphided copper material to a lower oxidation state with a hydrogen gas mixture containing 20-80% H.sub.2 by volume at a temperature in the range 150-350 C. for 5-24 hours to form the sorbent.

2. A sorbent according to claim 1, wherein the copper content of the sorbent is in the range of 20-40% by weight.

3. A sorbent according to claim 1, wherein the S:Cu atomic ratio of the sorbent is in the range of 0.8-0.95.

4. A sorbent according to claim 1, wherein the binder is a clay, cement or organic polymer binder, or a mixture thereof.

5. A sorbent according to claim 1, wherein the support material is alumina, hydrated alumina, metal-aluminate, silica, titania, zirconia, zinc oxide, an aluminosilicate, a zeolite, metal carbonate, or carbon, or a mixture thereof.

6. A sorbent according to claim 1 further comprising one or more zinc compounds.

7. A method for the production of a sorbent comprising 20-75% by weight of copper (expressed as copper (II) oxide) in the form of granules comprising one or more copper sulphides, a support and a binder, said sorbent having a sulphur to copper atomic ratio in the range 0.7 to 0.95:1, comprising the steps of: (i) making a sorbent precursor comprising an oxide or hydroxycarbonate of copper by either applying a layer of a copper compound on the surface of a shaped support material by dipping or spraying the shaped support material with a slurry of copper compound, and drying the coated support material; or by combining an oxide or hydroxycarbonate of copper, with one or more binders and a support material (ii) sulphiding the sorbent precursor with a gas mixture comprising 0.5-5% by volume hydrogen sulphide at a temperature in the range 1-150 C. to form a sulphided copper material, and (iii) partially reducing the sulphided copper material to a lower oxidation state with a hydrogen gas mixture containing 20-80% H2 by volume at a temperature in the range 150-350 C. for 5-24 hrs to form the sorbent, wherein the sorbent precursor or sorbent is shaped.

8. A method according to claim 7 wherein the sulphiding stage is carried out with hydrogen sulphide in an inert gas at a H.sub.2S concentration in the range 0.5 to 5% by volume.

9. A method according to claim 7 wherein the reduction temperature is in the range 175-300 C.

10. A process for the removal of mercury from a process fluid stream by contacting the fluid stream with the sorbent according to claim 1.

11. A process for the removal of mercury from a process fluid stream by contacting the fluid stream with the sorbent prepared according to the method of claim 7.

12. A sorbent according to claim 2 wherein the S:Cu atomic ratio of the sorbent is in the range 0.8-0.9.

13. A method according to claim 9 wherein the reduction temperature is in the range 200-250 C.

Description

EXAMPLE 1: MATERIAL PREPARATION

(1) A sorbent precursor was prepared using a granulation technique wherein basic copper carbonate (35 parts by weight), alumina trihydrate (51 parts by weight), calcium aluminate (14 parts by weight) and attapulgite clay (14 parts by weight) were combined with a little water and mixed to form granules in a Hobart mixer. The recovered granulated material was dried and then sulphided using 1% H.sub.2S in N.sub.2 at ambient temperature and pressure (Sorbent A). The copper content of the dried un-sulphided precursor was 22.1% wt (expressed as copper (II) oxide).

(2) A partially reduced sorbent (Sorbent B) was prepared by the partial reduction of sorbent A in a gas flow of 50% hydrogen/50% nitrogen v/v at 210 C. for 8 hours (GHSV=700 hr.sup.1, reactor ID=30 mm, bed volume=30 ml, flow rate=21 NL.hr.sup.1).

(3) For comparison a fully reduced sorbent (Sorbent C) was prepared by the complete reduction of sorbent A in a gas flow of 100% hydrogen at 210 C. for 24 hours (all other conditions as with sorbent B).

(4) Further partially reduced sorbents were prepared by reducing portions of Sorbent A in a gas flow of 50% hydrogen/50% nitrogen v/v at 210 C. for 5, 8 and 24 hours (GHSV=700 hr.sup.1, reactor ID=30 mm, bed volume=30 ml, flow rate=21 NL.hr.sup.1) to prepare sorbents D, E & F respectively.

(5) The sulphur to copper atomic ratios in the sorbents were determined by combustion of a sample at 1300 C. and subsequent IR analysis to quantify the amount of SO.sub.2 evolved using a LECO SC632. The copper content of the sorbents was determined using quantitative X-Ray Fluoresecence spectroscopy (XRF). The results are given in table 1.

(6) TABLE-US-00001 TABLE 1 Sorbent Measured S:Cu atomic ratio Comparative A 0.98 B 0.84 Comparative C 0.57 D 0.94 E 0.89 F 0.72

EXAMPLE 2: GAS PHASE TESTING

(7) Sorbents A, B and C were individually charged (15 ml) to a glass reactor (19 mm ID). A flow of 100% % nitrogen was passed through a bubbler containing elemental mercury to allow the gas to pick up the mercury. The mercury-laden gas was then passed downflow through the reactor under the following conditions.

(8) TABLE-US-00002 Pressure: 3 psig Temperature ambient Gas flow 6.8 NL .Math. hr.sup.1 Contact time 8 seconds Test duration 1175 hours (A & C) or 550 hours (B)

(9) Samples from the reactor inlet and exit were periodically analysed for mercury content by atomic fluorescence detection. The inlet gas was saturated at ambient temperature giving a mercury concentration at the inlet of about 13,000 m/m.sup.3. The sorbents A & B reduced the mercury content of the exit gas to below detectable limits throughout the test. The results are given in Table 2.

(10) TABLE-US-00003 TABLE 2 Comparative Comparative Sorbent A Sorbent B Sorbent C Bulk S:Cu atomic ratio 0.98 0.84 0.57 Mercury Bed 1 5.64 2.04 0.67 loading, Bed 2 0.60 0.09 0.69 wt. % Bed 3 0.06 <0.01 0.63 Bed 4 <0.01 <0.01 0.76 Bed 5 <0.01 <0.01 0.65

(11) The un-reduced Sorbent A is an effective mercury sorbent. The fully reduced sorbent C is poor in comparison due to its lower capacity. The partially reduced sorbent according to the present invention (sorbent B) despite the shorter run, clearly provides improved mercury capture.

EXAMPLE 3: LIQUID PHASE ACTIVITY TESTING

(12) Sorbents A, C & D, E, F were tested for mercury removal activity in the liquid phase by contact with a solution of elemental mercury in n-hexane, which contained ca. 500 p.p.b. w/v. The materials were stirred in the solution, with regular samples taken over 20 minutes to determine the mercury concentration using atomic fluorescence spectroscopy. The first order rate constants, k (min.sup.1), were determined as the gradient of a plot of In(Hg.sub.o/Hg.sub.x) against reaction time. The results are given in table 3.

(13) TABLE-US-00004 TABLE 3 Sorbent Bulk S:Cu atomic ratio Rate constant, k, min.sup.1 Comparative A 0.98 0.09 D 0.94 0.20 E 0.89 0.28 F 0.72 0.16 Comparative C 0.57 0.14

(14) The rate constants for sorbents D, E and F are surprisingly better than those for sorbents A and C.