Process for removing heavy metals from hydrocarbons

Abstract

This invention provides a process for removing mercury, from a mercury-containing hydrocarbon fluid. More specifically, the invention relates to a process for the removal of mercury from a mercury-containing hydrocarbon fluid feed comprising the steps of: (i) contacting the mercury-containing hydrocarbon fluid feed with a metal perhalide having the following formula: [M].sup.+[X].sup. wherein: [M].sup.+ represents one or more metal cations wherein the metal has an atomic number greater than 36; an atomic radius of at least 50 pm and a 1st ionization energy of less than 750 kJmol.sup.1; [X].sup. represents one or more perhalide anions; and (ii) obtaining a hydrocarbon fluid product having a reduced mercury content compared to mercury-containing hydrocarbon fluid feed.

Claims

1. A process for the removal of mercury from a mercury-containing hydrocarbon fluid feed comprising the steps of: contacting the mercury-containing hydrocarbon fluid feed with a metal perhalide having the following formula:
[M].sup.+[X].sup. wherein: [M].sup.+ represents one or more metal cations wherein the metal has an atomic number greater than 36; an atomic radius of at least 150 pm and a 1.sup.st ionization energy of less than 750 kJmol.sup.1; [X].sup. represents one or more perhalide anions; and obtaining a hydrocarbon fluid product having a reduced mercury content compared to mercury-containing hydrocarbon fluid feed.

2. A process according to claim 1, wherein [M].sup.+ is selected from an alkali metal or a post-transition metal cation.

3. A process according to claim 1, wherein [M].sup.+ is selected from rubidium, caesium, thallium or bismuth cations.

4. A process according to any of claim 1, wherein [M].sup.+ is a caesium cation.

5. A process according to any of claim 1, wherein [X].sup. comprises at least one perhalide anion selected from [I.sub.3].sup., [BrI.sub.2].sup., [Br.sub.2I].sup., [ClI.sub.2].sup., [Br.sub.3].sup., [ClBr.sub.2].sup., [BrCl.sub.2].sup., [ICl.sub.2].sup., or [Cl.sub.3].sup..

6. A process according to claim 5, wherein [X.sup.] comprises at least one perhalide anion selected from [BrI.sub.2].sup., [Br.sub.2I].sup., [ClI.sub.2].sup., [ClBr.sub.2].sup., [BrCl.sub.2].sup., or [ICl.sub.2].sup..

7. A process according to claim 5, wherein [X.sup.] comprises at least one perhalide anion selected from [I.sub.3].sup., [Br.sub.3].sup., or [Cl.sub.3].sup..

8. A process according to any of claim 1, wherein the metal perhalide is caesium periodide, or rubidium periodide.

9. A process according to claim 1, wherein the mercury is in elemental, particulate, or organic form.

10. A process according to claim 1, wherein the mercury concentration in the mercury-containing hydrocarbon fluid feed is in the range of from 1 to 50,000 parts per billion.

11. A process according to claim 1, wherein the mercury-containing hydrocarbon fluid feed is a liquid.

12. A process according to claim 11, wherein the mercury-containing hydrocarbon fluid feed comprises one or more of: a liquefied natural gas; a light distillate comprising at least one member of a group consisting of: liquid petroleum gas, gasoline, and naphtha; a natural gas condensate; a middle distillate comprising at least one member of a group consisting of: kerosene and diesel; a heavy distillate; and a crude oil.

13. A process according to claim 1, wherein the mercury-containing hydrocarbon fluid feed is a gas.

14. A process according to claim 13, wherein the mercury-containing hydrocarbon fluid feed comprises at least one member of a group consisting of natural gas and refinery gas.

15. A process according to claim 1, wherein the metal perhalide is in the form of a neat salt.

16. A process according to claim 1, wherein the metal perhalide is supported by a solid carrier material.

17. A process according to claim 16 wherein the solid carrier material is a porous material.

18. A process for the removal of a toxic heavy metal selected from cadmium, mercury, indium, thallium, germanium, tin, lead, arsenic, antimony, bismuth, selenium, tellurium and polonium from a heavy metal-containing hydrocarbon fluid feed comprising the steps of: contacting the heavy metal-containing hydrocarbon fluid feed with a metal perhalide having the following formula:
[M].sup.+[X].sup. wherein: [M].sup.+ represents one or more metal cations wherein the metal has an atomic number greater than 36; an atomic radius of at least 150 pm and a 1.sup.th ionization energy of less than 750 kJmol.sup.1; [X].sup. represents one or more perhalide anions; and obtaining a hydrocarbon fluid product having a reduced toxic heavy metal content compared to the heavy metal-containing hydrocarbon fluid feed.

19. A process according to claim 18, wherein [M].sup.+ is selected from an alkali metal or a post-transition metal cation.

20. A process according to claim 18, wherein [X].sup. comprises at least one perhalide anion selected from [I.sub.3].sup., [BrI.sub.2].sup., [Br.sub.2I].sup., [ClI.sub.2].sup., [Br.sub.3].sup., [ClBr.sub.2].sup., [BrCl.sub.2].sup., [ICl.sub.2].sup., or [Cl.sub.3].sup..

Description

(1) The present invention will now be illustrated by way of the following examples and with reference to the following figures:

(2) FIG. 1: Graphical representation for the results of mercury extraction experiments with a gaseous feed using caesium periodide and commercial mercury absorbants; and

(3) FIG. 2: Graphical representation for the results of mercury extraction experiments with a liquid hydrocarbon feed using caesium periodide and commercial mercury absorbants.

EXAMPLES

Example 1

Synthesis of Metal Perhalide

(4) Caesium triiodide (CsI.sub.3) can be purchased directly from Sigma Aldrich with 99.9% purity. The following method was also employed for preparation of caesium triiodide (CsI.sub.3). Caesium iodide (0.06 g) and iodine (0.06 g) were dissolved in methanol at 25 C. and the mixture stirred for 30 minutes in a fumehood, whereupon a homogenous solution was obtained. Thereafter, the solvent was subsequently evaporated off at 70 C. to afford caesium triiodide (0.11 g) as a solid.

Example 2

Preparation of a Supported Metal Perhalide

(5) Caesium triiodide (CsI.sub.3) (1.2 g) was dissolved in methanol (7 ml) before granular virgin activated carbon (ATLAS 1, of Atlas Chemical Industries, Inc) (12 g) was added to the solution. The resulting mixture was dried at 70 C. for 12 hours to evaporate the solvent, thereby forming a solid-supported CsI.sub.3 material (10 wt % on activated carbon).

Example 3

Removal of Mercury from a Gas Phase Fluid

(6) The supported CsI.sub.3 material from Example 2 was milled to afford granules of between 0.30 and 0.425 mm diameter before 0.1 g of material was introduced into a sealed reactor vessel. The reactor was supplied with a mercury-containing nitrogen gas stream at a flow rate of 60 ml/min and an inlet mercury concentration of 20 to 30 ppmv, and operated at ambient temperature and a pressure of 1 to 2 bar (100 to 200 kPa).

(7) Commercially available, conventional sulfur-impregnated activated carbon Absorbents A, B and C (each having 8 to 12 wt. % active concentration) were also independently used in separate mercury extractions using the same experimental protocol. Breakthrough time, which is defined as the time required from the start of the extraction process to the point in time where the mercury concentration in the outlet stream of the reactor reached up to 5% of the mercury concentration of the inlet stream, was measured in each case. The results of the experiments are provided in Table 2 below, as well as graphically in FIG. 1.

(8) TABLE-US-00002 TABLE 2 Experiment Breakthrough Number Type of Adsorbent Time (hr) 1 10 wt % CsI.sub.3 on Activated Carbon 96 2 Commercial Adsorbent A 20 3 Commercial Adsorbent B 17 4 Commercial Adsorbent C 28

(9) As can be seen from both Table 2 and FIG. 1, the breakthrough time observed in respect of a metal perhalide according to the present invention, supported on activated carbon, substantially out-performed the commercially available Absorbents A to C (not of the invention) in terms of mercury extraction over time.

Example 4

Removal of Mercury from a Gas Phase Fluid

(10) The experiment described in Example 3 was repeated apart from unsupported CsI.sub.3 was used in place of the supported material. In this example, unsupported CsI.sub.3 was able to substantially remove elemental mercury from the gaseous nitrogen stream; reducing the mercury concentration of the stream from 30 mg/m.sup.3 (inlet) to below 0.1 g/m.sup.3 (outlet).

Example 5

Removal of Mercury from a Liquid Phase Hydrocarbon Fluid

(11) A supported CsI.sub.3 material was prepared in a similar manner to that described in Example 2, apart from alumina (A8) was added to the solution such that a supported CsI.sub.3 (10 wt % on alumina) was formed on evaporation of the solvent. The supported material was milled to a mesh size of between from 20 to 30 and subsequently used in a sealed reactor vessel supplied with a mercury-containing liquid hydrocarbon stream at a flow rate of 1 ml/min.

(12) A commercially available, conventional metal halide on activated carbonAbsorbent D, and a conventional metal sulfide on activated carbonAbsorbent E, (both having 8 to 12 wt. % active concentration) were also independently used in separate mercury extractions using the same experimental protocol. Breakthrough time, which is defined as the time required from the start of the extraction process to the point in time where the mercury concentration in the outlet stream of the reactor reached up to 30% of the mercury concentration of the inlet stream, was measured in each case. The results of the experiments are provided in Table 3 below, as well as graphically in FIG. 2.

(13) TABLE-US-00003 TABLE 3 Experiment Breakthrough Number Type of Adsorbent Time (hr) 5 10 wt % CsI.sub.3 on Alumina 9.5 6 Commercial Adsorbent D 4.5 7 Commercial Adsorbent E <1

(14) As can be seen from both Table 3 and FIG. 2, the breakthrough time observed in respect of a metal perhalide according to the present invention, which is supported on alumina, substantially out-performed the commercially available Absorbents D and E (not of the invention) in terms of mercury extraction over time.