Catalytically enhanced compositions for efficient removal of contaminants in flue gas streams

Abstract

A sorbent composition that is useful for injection into a flue gas stream of a coal burning furnace to efficiently remove mercury from the flue gas stream. The sorbent composition may include a sorbent with an associated ancillary catalyst component that is a catalytic metal, a precursor to a catalytic metal, a catalytic metal compound or a precursor to a catalytic metal compound. Alternatively, a catalytic metal or metal compound, or their precursors, may be admixed with the coal feedstock prior to or during combustion in the furnace, or may be independently injected into a flue gas stream. A catalytic promoter may also be used to enhance the performance of the catalytic metal or metal compound.

Claims

1. A sorbent composition comprising: a powdered activated carbon sorbent having a mean particle diameter (D50) of not greater than about 25 μm, a surface area of at least about 350 m.sup.2/g, and a total pore volume of at least about 0.20 cc/g; and an ancillary catalyst component selected from the group consisting of: (i) a catalytic metal selected from the group consisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, and combinations thereof, (ii) a precursor to the catalytic metal, wherein the precursor to the catalytic metal comprises the catalytic metal and is selected from the group consisting of a metal oxide, a metal halide, a metal hydroxide, a metal sulfate, a metal nitrate, a metal carbonate, and combinations thereof, and (iii) combinations of the catalytic metal and the precursor to the catalytic metal, wherein the ancillary catalyst component is coated on a surface of the powdered activated carbon sorbent, and wherein the amount of the ancillary catalyst component is at least 0.001 wt. % and not greater than about 20 wt. % of the sorbent composition.

2. The sorbent composition of claim 1, wherein the precursor to the catalytic metal is selected from the group consisting of copper (II) oxide (CuO), copper (II) chloride (CuCl.sub.2), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), iron (III) oxide (Fe.sub.2O.sub.3), iron (III) chloride (FeCl.sub.3), iron (III) nitrate (Fe(NO.sub.3).sub.3), iron (III) sulfate Fe.sub.2(SO.sub.4).sub.3, cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), zinc (II) oxide (ZnO), zinc sulfate (ZnSO.sub.4), and combinations thereof.

3. The sorbent composition of claim 1, further comprising a catalytic promoter dispersed on the powdered activated carbon sorbent, wherein the catalytic promoter comprises a promoter metal compound selected from the group consisting of alkali metal compounds, alkaline earth metal compounds, and combinations thereof.

4. The sorbent composition of claim 3, wherein the catalytic promoter comprises a metal in elemental form or in the form of a metal oxide, a metal hydroxide, or a metal salt, the metal being selected from the group consisting of Li, Na, K, Be, Ca, Sr, Ba, Mg, and combinations thereof.

5. The sorbent composition of claim 1, wherein the sorbent composition comprises not greater than about 1 wt. % of the ancillary catalyst component.

6. The sorbent composition of claim 1, wherein the sorbent composition comprises not greater than about 5 wt. % of the ancillary catalyst component.

7. The sorbent composition of claim 1, wherein the sorbent composition comprises not greater than about 10 wt. % of the ancillary catalyst component.

8. The sorbent composition of claim 1, wherein the powdered activated carbon sorbent has a mean particle diameter (D50) of not greater than about 20 μm.

9. The sorbent composition of claim 1, wherein the powdered activated carbon sorbent has a mean particle diameter (D50) of not greater than about 15 μm.

10. The sorbent composition of claim 1, wherein the sorbent composition further comprises less than about 15 wt. % of a halogen.

11. The sorbent composition of claim 1, wherein the sorbent composition further comprises less than about 6 wt. % of a halogen.

12. The sorbent composition of claim 1, wherein the sorbent composition further comprises less than about 3 wt. % of a halogen.

13. The sorbent composition of claim 1, wherein the sorbent composition comprises substantially no halogens.

14. The sorbent composition of claim 1, wherein the sorbent composition further comprises an aqueous solubilizing medium in an amount that is at least about 2 wt. % and not greater than about 12 wt. %.

15. A sorbent composition comprising: a powdered activated carbon sorbent having a mean particle diameter (D50) of not greater than about 25 μm, a surface area of at least about 350 m.sup.2/g, and a total pore volume of at least about 0.20 cc/g; and an ancillary catalyst component comprising one or more of: (i) a catalytic metal selected from the group consisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, and combinations thereof, (ii) a precursor to the catalytic metal, wherein the precursor to the catalytic metal comprises the catalytic metal and is selected from the group consisting essentially of a metal oxide, a metal halide, a metal hydroxide, a metal sulfate, a metal nitrate, a metal carbonate, and combinations thereof, and (iii) combinations of the catalytic metal and the precursor to the catalytic metal, wherein the ancillary catalyst component is bound to a surface of the powdered activated carbon sorbent, and wherein the amount of the ancillary catalyst component is at least 0.001 wt. % and not greater than about 20 wt. % of the sorbent composition.

16. The sorbent composition of claim 15, wherein the precursor to the catalytic metal is selected from the group consisting of copper (II) oxide (CuO), copper (II) chloride (CuCl.sub.2), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), iron (III) oxide (Fe.sub.2O.sub.3), iron (III) chloride (FeCl.sub.3), iron (III) nitrate (Fe(NO.sub.3).sub.3), iron (III) sulfate Fe.sub.2(SO.sub.4).sub.3, cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), zinc (II) oxide (ZnO), zinc sulfate (ZnSO.sub.4), and combinations thereof.

17. The sorbent composition of claim 15, further comprising a catalytic promoter dispersed on the powdered activated carbon sorbent, wherein the catalytic promoter comprises a metal in elemental form or in the form of a metal oxide, a metal hydroxide, or a metal salt, the metal being selected from the group consisting of Al, Li, Na, K, Be, Ca, Sr, Ba, Sc, Y, Mg, and combinations thereof.

18. The sorbent composition of claim 15, wherein the sorbent composition comprises not greater than about 1 wt. % of the ancillary catalyst component.

19. The sorbent composition of claim 15, wherein the sorbent composition comprises not greater than about 5 wt. % of the ancillary catalyst component.

20. The sorbent composition of claim 15, wherein the sorbent composition comprises not greater than about 10 wt. % of the ancillary catalyst component.

21. The sorbent composition of claim 15, wherein the sorbent composition further comprises less than about 15 wt. % of a halogen.

22. The sorbent composition of claim 15, wherein the sorbent composition comprises substantially no halogens.

23. The sorbent composition of claim 15, wherein the sorbent composition further comprises an aqueous solubilizing medium in an amount that is at least about 2 wt. % and not greater than about 12 wt. %.

24. A sorbent composition comprising: a powdered activated carbon sorbent having a mean particle diameter (D50) of not greater than about 25 μm, a surface area of at least about 350 m.sup.2/g, and a total pore volume of at least about 0.20 cc/g; and an ancillary catalyst component selected from the group comprising one or more of: (i) a catalytic metal selected from the group consisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, and Ce, and (ii) a precursor to the catalytic metal, wherein the precursor to the catalytic metal comprises the catalytic metal and is selected from the group comprising one or more of a metal oxide, a metal halide, a metal hydroxide, a metal sulfate, a metal nitrate, and a metal carbonate, wherein the amount of the ancillary catalyst component is at least 0.001 wt. % and not greater than about 20 wt. % of the sorbent composition and wherein the sorbent composition comprises substantially no halogens.

25. The sorbent composition of claim 24, wherein the precursor to the catalytic metal is selected from the group consisting of copper (II) oxide (CuO), copper (II) chloride (CuCl.sub.2), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), iron (III) oxide (Fe.sub.2O.sub.3), iron (III) chloride (FeCl.sub.3), iron (III) nitrate (Fe(NO.sub.3).sub.3), iron (III) sulfate Fe.sub.2(SO.sub.4).sub.3, cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), zinc (II) oxide (ZnO), zinc sulfate (ZnSO.sub.4), and combinations thereof.

26. The sorbent composition of claim 24, further comprising a catalytic promoter dispersed on the powdered activated carbon sorbent, wherein the catalytic promoter comprises a metal in elemental form or in the form of a metal oxide, a metal hydroxide, or a metal salt, the metal being selected from the group consisting of Al, Li, Na, K, Be, Ca, Sr, Ba, Sc, Y, Mg, and combinations thereof.

27. The sorbent composition of claim 24, wherein the sorbent composition comprises not greater than about 1 wt. % of the ancillary catalyst component.

28. The sorbent composition of claim 24, wherein the sorbent composition comprises not greater than about 5 wt. % of the ancillary catalyst component.

29. The sorbent composition of claim 24, wherein the sorbent composition comprises not greater than about 10 wt. % of the ancillary catalyst component.

30. The sorbent composition of claim 24, wherein the sorbent composition further comprises an aqueous solubilizing medium in an amount that is at least about 2 wt. % and not greater than about 12 wt. %.

31. The sorbent composition of claim 15, wherein the ancillary catalyst component is bound to a surface of the powdered activated carbon sorbent through covalent bonding, ionic bonding, or intramolecular forces.

32. A sorbent composition comprising: a powdered activated carbon sorbent having a mean particle diameter (D50) of not greater than about 25 μm, a surface area of at least about 350 m.sup.2/g, and a total pore volume of at least about 0.20 cc/g; and an ancillary catalyst component associated with a surface of the powdered activated carbon sorbent and comprising one or more of: (i) a catalytic metal selected from the group consisting of Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, and combinations thereof, (ii) a precursor to the catalytic metal, wherein the precursor to the catalytic metal comprises the catalytic metal and is selected from the group consisting essentially of a metal oxide, a metal halide, a metal hydroxide, a metal sulfate, a metal nitrate, a metal carbonate, and combinations thereof, and (iii) combinations of the catalytic metal and the precursor to the catalytic metal, wherein the ancillary catalyst component is bonded to a surface of the powdered activated carbon sorbent through covalent bonding, ionic bonding, or intramolecular bonding, and wherein the amount of the ancillary catalyst component is at least 0.001 wt. % and not greater than about 20 wt. % of the sorbent composition.

33. The sorbent composition of claim 32, wherein the precursor to the catalytic metal is selected from the group consisting of copper (II) oxide (CuO), copper (II) chloride (CuCl.sub.2), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), zinc (II) oxide (ZnO), zinc sulfate (ZnSO.sub.4), and combinations thereof.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a flow sheet for the manufacture of the sorbent composition.

(2) FIG. 2 illustrates a plant configuration and method for the capture and sequestration of contaminants from a flue gas stream.

(3) FIGS. 3A and 3B illustrate a method of mercury capture by a sorbent composition disclosed herein.

DETAILED DESCRIPTION

(4) It would be advantageous to provide a novel sorbent composition with little or no added halogen, that can act as efficiently as highly halogenated PAC sorbents to remove mercury from a flue gas stream, e.g., to meet governmental regulations for mercury emissions even in the presence of increased concentrations of acid gases. In this regard, disclosed herein are compositions of matter that are particularly useful for injection into a flue gas stream emanating from a boiler (e.g., a coal burning and/or biomass burning boiler) to remove mercury from the flue gas stream. These compositions may be used to replace a halogen oxidant, or may be used in conjunction with halogen oxidants thus allowing reduced amounts of corrosive halogens such as bromine to be used as compared to other mercury oxidizing compositions and may be efficient mercury oxidizers and capture agents in flue gas streams, even those flue gas streams with increased levels of acid gases. The compositions may include an ancillary catalyst component that is selected to oxidize mercury and/or catalyze the oxidation of mercury, making the mercury more available for capture by the sorbent, thereby enhancing the removal of mercury from the flue gas stream.

(5) Various examples of a sorbent composition are provided that are particularly useful to rapidly and efficiently capture and remove contaminants, including but not limited to mercury, from the flue gas stream. In this regard, the sorbent composition may include a sorbent, such as powdered activated carbon (PAC), in combination with one or more components that synergistically may increase the probability of the sorbent contacting mercury species in the flue gas, and may decrease the time required for mercury oxidation and capture (e.g., as a result of enhanced oxidation reaction kinetics and/or mass diffusional kinetics).

(6) In a particular embodiment, the sorbent is a carbonaceous sorbent such as PAC, and may have various beneficial physical attributes such as a relatively small particle size, a high surface area and a well-controlled pore size distribution. For example, the sorbent composition (i.e., the solid sorbent) may have a median particle size of not greater than about 25 μm, a sum of micropore volume, mesopore volume and macropore volume (e.g., a total volume) of at least about 0.2 cc/g, such as at least about 0.25 cc/g, and a ratio of micropore volume to mesopore volume of at least about 0.7 and not greater than about 1.5.

(7) In one characterization, the sorbent is a particulate solid sorbent (e.g., PAC) that has a high pore volume and a well-controlled distribution of pores, particularly among the mesopores (i.e., from 20 Å to 500 Å width) and the micropores (i.e., not greater than 20 Å width). A well-controlled distribution of micropores and mesopores is desirable for effective removal of mercury from the flue gas stream. While not wishing to be bound by any theory, it is believed that the mesopores are the predominant structures for capture and transport of the oxidized mercury species to the micropores, whereas micropores are the predominate structures for sequestration of the oxidized mercury species.

(8) In this regard, the sum of micropore volume plus mesopore volume and macropore volume of the sorbent (e.g., PAC) may be at least about 0.10 cc/g, such as at least 0.20 cc/g, at least about 0.25 cc/g or even at least about 0.30 cc/g. The micropore volume of the sorbent may be at least about 0.10 cc/g, such as at least about 0.15 cc/g. Further, the mesopore volume of the sorbent may be at least about 0.10 cc/g, such as at least about 0.15 cc/g. In one characterization, the ratio of micropore volume to mesopore volume may be at least about 0.7, such as 0.9, and may be not greater than about 1.5. Such levels of micropore volume relative to mesopore volume advantageously enable efficient capture and sequestration of oxidized mercury species by the sorbent. Pore volumes may be measured using gas adsorption techniques (e.g., N.sub.2 adsorption) using instruments such as a TriStar II Surface Area Analyzer (Micromeritics Instruments Corporation, Norcross, Ga., USA).

(9) In another characterization, the sorbent is a particulate solid sorbent that has a relatively high surface area. For example, the solid sorbent may have a surface area of at least about 350 m.sup.2/g, such as at least about 400 m.sup.2/g or even at least about 500 m.sup.2/g. Surface area may be calculated using the Brunauer-Emmett-Teller (BET) theory that models the physical adsorption of a monolayer of nitrogen gas molecules on a solid surface and serves as the basis for an analysis technique for the measurement of the specific surface area of a material. BET surface area may be measured using the Micromeritics TriStar II 3020 (Micromeritics Instrument Corporation, Norcross, Ga.).

(10) In another characterization, the sorbent may have a median particle size of not greater than about 30 μm, such as not greater than about 25 μm, such as not greater than about 15 μm. Characterized in another way, the median particle size may be at least about 5 μm, such as at least about 6 μm, or even at least about 8 μm. The D50 median particle size may be measured using techniques such as light scattering techniques (e.g., using a Saturn DigiSizer II, available from Micromeritics Instrument Corporation, Norcross, Ga.). A relatively small median particle size, such as not greater than about 15 μm, means greater external surface area per volume of the same sorbent. The increased surface area may result in many benefits, including, but not limited to, increased exposure of the mercury to chemical species (e.g., elements or compounds) disposed on the sorbent surface, increased area available for reactions to occur, and thus overall improved reaction kinetics.

(11) The sorbent may comprise a porous carbonaceous sorbent material (e.g., fixed carbon) that is adapted to provide a large surface area in the appropriate pore size to sequester contaminant species such as mercury, bromine, selenium, etc. The sorbent may include at least about 10 weight percent of fixed carbon, such as at least about 15 weight percent or even at least about 20 weight percent fixed carbon. In some characterizations, the fixed carbon content of the sorbent may not exceed about 95 weight percent, such as not greater than about 85 weight percent, such as not greater than about 75 weight percent, such as not greater than about 60 weight percent, or such as not greater than about 55 weight percent fixed carbon. Due to a well-controlled pore structure and the presence of the other components in the sorbent (e.g., in addition to fixed carbon), a relatively low amount of fixed carbon may be required for sequestration of contaminants.

(12) In addition to a sorbent, such as powdered activated carbon, the sorbent composition may comprise an ancillary catalyst component that includes one or more of a catalytic metal, a precursor to a catalytic metal, a catalytic metal compound or a precursor to a catalytic metal compound. The catalytic metal(s) or metal compounds are selected to catalyze the oxidation of a contaminant such as mercury to a contaminant species that is more easily captured by the sorbent due to the charge (e.g., ionic charge) of the oxidized form, and/or due to the size of the oxidized form. If the ancillary catalyst component comprises a precursor to a metal or a precursor to a metal compound, the precursor should be capable of rapidly converting to the catalytic metal or the catalytic metal compound at the temperatures typically encountered in a flue gas stream, such as at least about 250° F. (about 120° C.) and not greater than about 700° F. (about 370° C.). The catalytic metal or catalytic metal compound may be associated with the sorbent in that it may be covalently bound to the sorbent, it may be associated with the sorbent via ionic binding, and/or it may be associated with the sorbent through intramolecular forces.

(13) The ancillary catalyst component may comprise a catalytic metal that is selected from metals that are categorized as transition metals, e.g., Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn and Ti. The ancillary catalyst component may also include other metals such as Sn and Ce. In one characterization, the catalytic metal may be selected from the group consisting of Fe, Cu, Mn, Zn and combinations thereof. The catalytic metal(s) may be present as elemental metals (e.g., in the zero valent state), or as an ionic species, or in the form of catalytic metal compounds including oxides, hydroxides, or salts such as sulfates, carbonates, nitrates, and halides, of the catalytic metals. Examples of such catalytic metal compounds may include, but are not limited to, copper (II) oxide (CuO), copper (II) chloride (CuCl.sub.2), copper (II) sulfate (CuSO.sub.4), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), iron (III) oxide (Fe.sub.2O.sub.3), iron (III) chloride (FeCl.sub.3), iron (III) nitrate (Fe(NO.sub.3).sub.3), iron (III) sulfate (Fe.sub.2(SO.sub.4).sub.3), iron (II) chloride (FeCl.sub.2), cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), zinc oxide (ZnO), or zinc sulfate (ZnSO.sub.4).

(14) The sorbent composition may include the ancillary catalyst component (e.g., the catalytic metal, catalytic metal compound or precursors thereto) in a concentration that is sufficient to enhance the oxidation of mercury in the flue gas stream. In some examples, as little as about 10 ppm by weight (0.001 wt. %) of the ancillary catalyst component may be sufficient. Thus, in one characterization, the sorbent composition may comprise at least about 10 ppm (0.001 wt. %) of the ancillary catalyst component, at least about 20 ppm (0.002 wt. %), at least about 40 ppm (0.004 wt. %), at least about 100 ppm (0.010 wt. %) at least about 200 ppm (0.020) wt. % of the ancillary catalyst component, or at least about 5000 ppm (0.5 wt. %). In another characterization, the sorbent composition may include not greater than about 20 wt. %, such as not greater than about 10 wt. %, not greater than about 5 wt. %, not greater than about 1 wt. %, not greater than about 0.5 wt. %, not greater than about 500 ppm (0.050 wt. %), or even not greater than about 200 ppm (0.020 wt. %) of the ancillary catalyst component. In one particular characterization, the sorbent composition comprises at least about 0.5 wt. % and not greater than about 5 wt. % of the ancillary catalyst component.

(15) Optionally, the sorbent composition may also include a catalytic promoter, e.g., dispersed on the sorbent, e.g., dispersed on the powdered activated carbon. The catalytic promoter may comprise, for example, a metal species (e.g., compound) selected from Group 1 metals (i.e., alkali metals), Group 2 metals (i.e., alkaline earth metals), or Group 3 metals, their ionic species, salts, oxides, halides, or combinations thereof. For example, the catalytic promoter may comprise a metal in elemental form or in the form of a metal oxide, hydroxide, or salt, the metal being selected from the group consisting of Al, Li, Na, K, Be, Ca, Sr, Ba, Sc, Y, Mg and combinations thereof.

(16) The ancillary catalyst component may be present in the composition alone or with other additions, such as a halogen, to a sorbent. However, reduced amounts of halogens such as Br may be enabled by the addition of the ancillary catalyst component. As such, the sorbent composition may advantageously comprise not greater than about 20 wt. % of a halogen, such as not greater than about 15 wt. %, not greater than about 6 wt. %, not greater than about 3 wt. %, or even not greater than about 1 wt. % of a halogen. In one characterization, the sorbent composition comprises substantially no halogens, i.e., from 0 to not greater than about 0.1 wt. % halogens.

(17) In various characterizations, the sorbent may be selected from the group consisting of activated carbon, reactivated carbon, carbonaceous char, zeolite, silica, silica gel, alumina, clay or combinations thereof. In a particular characterization, the particulate sorbent comprises a porous carbonaceous material, for example powdered activated carbon.

(18) One component of the sorbent may be inherent minerals, being native to the sorbent. These inherent minerals may also catalyze the oxidation of the elemental mercury in the flue gas stream but may be limited in availability for interaction with flue gas stream compounds and elements. These minerals may include, but not limited to, aluminum-containing minerals, calcium-containing minerals, iron-containing minerals, silicon-containing minerals (e.g., silicates), sodium-containing minerals, potassium-containing minerals, zinc-containing minerals, tin-containing minerals, magnesium-containing minerals, and combinations thereof. The minerals may predominantly be oxide-based minerals, such as metal oxide minerals (e.g., CaO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, FeO, Al.sub.2O.sub.3), and silicates (e.g. Al.sub.2SiO.sub.5). In one characterization, the minerals predominantly include metal oxides, particularly aluminum oxides and iron oxides. In another characterization, the minerals include calcium-containing minerals, iron-containing minerals and aluminosilicates. The inherent minerals, being disposed within the sorbent framework, may have less surface functionality compared to the ancillary catalyst component, and thereby may be less active for mercury oxidation.

(19) Moreover, the sorbent composition may also include an amount of aqueous-based solubilizing medium such as water. Such aqueous-based solubilizing medium can combat the acidity of the flue gas, enhance the mass diffusional kinetics of mercury oxidation and sequestration reactions by solubilizing oxidized mercury species within the pore structure, and prevent captured mercury from re-solubilizing and reentering the flue gas. In this regard, the sorbent composition may include at least about 2 wt. % of the solubilizing medium, such as at least about 3 wt. % or at least about 6 wt. %. However, the amount of solubilizing medium in the sorbent composition should be not greater than about 12 wt. %, such as not greater than about 10 wt. %, such as to avoid interfering with the mercury oxidation reaction(s), particle flow, and consuming carbon adsorption capacity.

(20) In one example, a method for manufacture of a sorbent composition is provided. FIG. 1 is a flow sheet that illustrates an exemplary method for the manufacture of a sorbent composition in accordance with one example. The manufacturing process begins with a carbonaceous feedstock 101 such as low-rank lignite coal with a relatively high content of natural deposits of native minerals. In the manufacturing process, the feedstock is subjected to an elevated temperature and one or more oxidizing gases under exothermic conditions for a period of time to sufficiently increase surface area, create porosity, alter surface chemistry, and expose and exfoliate native minerals previously contained within feedstock. The specific steps in the process include: (1) dehydration 102, where the feedstock is heated to remove the free and bound water, typically occurring at temperatures ranging from 100° C. to 150° C.; (2) devolatilization 103, where free and weakly bound volatile organic constituents are removed, typically occurring at temperatures above 150° C.; (3) carbonization 104, where non-carbon elements continue to be removed and elemental carbon is concentrated and transformed into random amorphous structures, typically occurring at temperatures of from about 350° C. to about 800° C.; and (4) activation 105, where steam, air or other oxidizing agent(s) is added and pores are developed, typically occurring at temperatures above 800° C.

(21) The manufacturing process may be carried out, for example, in a multi-hearth or rotary furnace. The manufacturing process is not discrete and steps can overlap and use various temperatures, gases and residence times within the ranges of each step to promote desired surface chemistry and physical characteristics of the manufactured product. After activation 105, the product may be subjected to a comminution step 106 to reduce the particle size (e.g., reduce the median particle size) of the activated product. Comminution 106 may occur, for example, in a mill such as a roll mill, jet mill or other like process. Comminution 106 may be carried out for a time sufficient to reduce the median particle size of the thermally treated product to not greater than about 30 μm, such as not greater than about 25 μm, or even 15 μm, 12 μm or less. Following comminution, classification 107 may take place wherein particles of a given size are selected.

(22) In the event that manufacturing conditions result in a greater number of carbonaceous particles that have a very fine size than is desired, classification 107 may be carried out to remove such very fine particles from the larger carbonaceous particles. For example, classification 107 may be carried out using an air classifier, screen/mesh classification (e.g., vibrating screens) or centrifugation. Smaller particles may also be agglomerated to reduce the concentration of fine particles. The potential benefits of such a classification step are described in U.S. Pat. No. 9,314,767 to McMurray et al., which is incorporated herein by reference in its entirety.

(23) Addition of the ancillary catalyst component, and optionally a catalytic promoter, may take place before (106A) or after comminution (106B), and in one characterization occurs after comminution of the sorbent to maximize the available surface area for attachment of the additional components. This may be accomplished by dry admixing, impregnation, or by coating the sorbent with the ancillary catalyst component or the catalytic promoter. For example, the catalytic promoter may be added in an optional subsequent step following addition of the ancillary catalyst component. Coating of the sorbent with the ancillary catalyst component may be accomplished by first making an aqueous solution or slurry of the ancillary catalyst component and then applying the solution directly to the sorbent either by mixing with or spraying onto the sorbent such as in a fluidized bed coater, as an example. Additional additives may be combined with the ancillary catalyst component, for example a halogen or a catalytic promoter.

(24) The sorbent compositions disclosed herein are particularly useful for removal of metal contaminants, especially mercury, from flue gas streams. The ability to capture mercury may be measured by a dynamic mercury index (DMI) test that measures mercury (Hg) captured in micro-grams of Hg per gram of sorbent composition (μg Hg/g sorbent composition). An increase in, or higher DMI, or μg Hg/g carbon (μg/g) captured, is an indication of a higher mercury capture efficiency of a sorbent. The DMI test simulates conditions in a coal burning facility's flue gas stream. The test system includes a preheater, sorbent feed, mercury feed, and reaction chamber. The mercury is fed into a reactor chamber along with the sorbent composition, wherein they are entrained. Uncaptured mercury is analyzed and DMI calculated. Temperature of the entrained mercury and sorbent is kept at about 325° F. (163° C.). Air entrainment and injection rates of between about 1 and about 5 lb./MMacf (pounds sorbent per one million actual cubic feet) are maintained such that residence time of the sorbent in the reaction chamber is about one second to simulate electrical generation unit (EGU) facility conditions. The mercury concentration in the system is approximately 10 μg/m.sup.3.

(25) In one example, the DMI of the sorbent compositions disclosed herein is at least about 100 μg/g, such as at least about 150 μg/g, at least about 300 μg/g, at least about 400 μg/g, at least about 500 μg/g, at least about 550 μg/g, or even at least about 590 μg/g.

(26) In another embodiment, a method for the treatment of the flue gas stream to remove contaminants such as mercury therefrom is provided that includes the step of contacting the flue gas stream with a sorbent composition as described herein, e.g., including a powdered activated carbon sorbent and an ancillary catalyst component comprising at least one constituent selected from the group consisting of a catalytic metal, a precursor to a catalytic metal, a catalytic metal compound, and a precursor to a catalytic metal compound. One exemplary method is illustrated in FIG. 2. A feedstock (e.g., a fuel) such as coal 201 is added to a boiler 202 where the coal is combusted and produces a flue gas stream 203. As illustrated in FIG. 2, the flue gas stream 203 may then proceed to an air heater unit 203 where the temperature of the flue gas stream 203 is reduced. Thereafter, the flue gas stream 203 may be introduced to a separation unit 205 such as an electrostatic precipitator or a fabric filter baghouse which removes particulate matter from the flue gas, before exiting out a stack 206. For example, a cold-side 204 (i.e., after the air heater unit) electrostatic precipitator (ESP) can be used to remove particulate matter from the flue gas. It will be appreciated by those skilled in the art that the plant may include other devices not illustrated in FIG. 2, such as a selective catalytic reduction unit (SCR), a wet or dry scrubber and the like, and may have numerous other configurations. In order to capture contaminants from the flue gas stream, the sorbent compositions disclosed herein, including the sorbent and the ancillary catalyst component, and optionally the catalytic promoter, may be introduced to (e.g., injected into) the flue gas stream 203 either before 203A or after 203B the air heater unit 204, but before the separation unit 205 which will remove the sorbent composition from the flue gas.

(27) Alternatively or in addition to the introduction of the sorbent compositions disclosed herein to the flue gas stream, the ancillary catalyst component may be added to the fuel (e.g., the coal 201) before or during combustion in the boiler 202. Such an addition may be made in lieu of or in addition to the injection of a sorbent composition including a solid sorbent and an ancillary catalyst component to the flue gas stream.

(28) In another embodiment, the ancillary catalyst component may also be added directly to the flue gas stream separate from the solid sorbent, such as by injecting the ancillary catalyst component into the flue gas stream prior to addition of the sorbent 203C to the flue gas stream. The ancillary catalyst component may also be co-injected 203A into the flue gas stream with the sorbent. As is noted above, if the ancillary catalyst component comprises a precursor to a catalytic metal or a precursor to a catalytic metal compound, then the ancillary catalyst component should be injected at a point that will permit sufficient time for conversion of the precursor to the catalytic metal or the catalytic metal compound in the flue gas stream.

(29) A method for capture of a contaminant such as mercury is schematically illustrated in FIGS. 3A and 3B. The sorbent composition may have a surface 301 with mesopores 302 and micropores 303. An ancillary catalyst component 304, being a catalytic metal or a catalytic metal compound, such as copper (II) oxide (CuO), for example, may be dispersed thereon as shown in FIG. 3A. As shown in FIG. 3B, when a contaminant mercury species 305 such as Hg.sup.0 contacts the surface 301, the ancillary catalyst component 304, may catalyze the oxidation of the Hg.sup.0 species to Hg.sup.+/2+, e.g., to an oxidized mercury species. The Hg.sup.+/2+ species subsequently may be more easily captured (e.g., sequestered) by the sorbent surface 301.

(30) In one example a sorbent composition as described herein is formed using a powdered activated carbon sorbent such as PowerPAC® or FastPAC (ADA Carbon Solutions, LLC, Littleton, Colo.). An ancillary catalyst component metal or metal compound, such as those metals or metal compounds disclosed herein, may be coated onto the sorbent, e.g., from a solution as described in FIG. 1 step 106A or 106B. The ancillary catalyst component metal compounds may be in the form of substantially insoluble metal or metal compounds, or precursors thereto, such as particulate oxides having a median size (diameter) of not greater than about 10 μm, or even not greater than about 1 μm, or even not greater than about 100 nm, or even not greater than about 50 nm, or even not greater than about 25 nm, or not greater than about 10 nm. Examples of these ancillary catalyst component metal compounds may include copper (II) oxide (CuO), iron (III) oxide (Fe.sub.2O.sub.3), cerium (IV) oxide (CeO.sub.2), manganese (IV) oxide (MnO.sub.2), vanadium (V) oxide (V.sub.2O.sub.5), and zinc (II) oxide (ZnO). Alternately, the metal compounds, or metal precursors such as salts, that may be chlorides, sulfates, nitrates, or hydroxides, for example, may be soluble in a liquid phase (e.g., water) used for application to the powdered activated carbon sorbent. Examples of these salts may include copper (II) chloride (CuCl.sub.2), copper (II) sulfate (CuSO.sub.4), copper (II) nitrate (Cu(NO.sub.3).sub.2), copper (II) hydroxide (Cu(OH).sub.2), copper (II) carbonate (CuCO.sub.3), iron (III) chloride (FeCl.sub.3), iron (III) nitrate (Fe(NO.sub.3).sub.3), iron (III) sulfate (Fe.sub.2(SO.sub.4).sub.3), iron (II) chloride (FeCl.sub.2), and zinc sulfate (ZnSO.sub.4). A metal species that is small in size, and therefore exhibits a high surface area to volume ratio, may have increased effectiveness as a catalyst. The ancillary catalyst component also may be dry admixed with the sorbent. Alternately, the ancillary catalyst component in a solution may be added to the sorbent such as by coating the sorbent with a solution or slurry, the solution or slurry possibly also including one or more halogens. Halogens may for example include halogen-containing compounds such as sodium, calcium, and ammonium salts of chloride, bromide, magnesium, phosphorous, potassium, and/or iodide, or combinations thereof. In one example, no added halogen is required to meet mercury capture standards. In yet another example, a lower amount of halogen may be needed when an ancillary catalyst component is used.

(31) In addition, the optional catalytic promoter discussed above may be used to enhance the catalytic potential of the ancillary catalyst component. Such catalytic promoters may include Group 1 metals (alkali metals), Group 2 metals (alkaline earth metals), and Group 3 metals. Particular examples include Li, Na, K, Mg, Ca, Ba, and Al.

(32) In some embodiments, the catalytic metal precursor or catalytic metal compound precursor may be capable of converting to the catalytic metal or catalytic metal compound in-situ, i.e., upon injection of the precursor into the flue gas stream. In another embodiment, the composition may be post-treated, e.g., in the absence of a catalytic promoter, to convert the catalytic metal precursor or catalytic metal compound precursor on the surface of the sorbent to form the active form of the metal or metal compound. This post-treatment may include a variety of treatments to convert the precursor to a species of higher catalytic activity, such as the application of a chemical treatment such as a reducing agent, oxidizing agent, or sulfiding agent, and/or the application of heat such as in a heated reducing or oxidizing environment.

(33) In another example, the ancillary catalyst component may be directly added to the coal feed that is used to manufacture an activated carbon sorbent, e.g., at the point that the coal enters the activation furnace, to enrich the activated sorbent with the catalytic species. Examples include copper species such as aqueous solutions/slurries of: CuCl.sub.2, Cu(NO.sub.3).sub.2, Cu(OH).sub.2, or CuCO.sub.3. At the high furnace temperatures these additives (e.g., precursors) convert to the metal oxide which may then be adsorbed on the sorbent surface.

(34) In yet another example, the catalytic metal or metal compound may be added to the coal feed prior to incineration at an EGU or boiler facility thereby enhancing oxidation of mercury.

EXAMPLES

Example 1

(35) A comparative sample, Sample A, comprised of a PAC, derived from a lignite coal feedstock, and an oxidizing agent is prepared. The PAC is characterized as having a median particle size (D50) of about 12 μm, a surface area of at least about 350 m.sup.2/g, a particle density of at least about 0.3 g/cc, and a total pore volume of at least about 0.3 cc/g. Sample A also contains about 5.5 wt. % Br as the oxidizing agent. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 2

(36) To test for enhanced mercury capture performance, a catalytic metal compound, here being copper (II) chloride, is added to comparative Sample A to form Sample B. For preparation of Sample B, a copper (II) chloride solution is made by dissolving 36.25 g of copper (II) chloride in 50 g of deionized water. 5.03 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed PAC is dried at approximately 150° C. for 2 hours to yield Sample B, a sorbent composition comprising PAC as a sorbent, about 1 wt. % Cu (as CuCl.sub.2) as an ancillary catalyst component and about 5.5 wt. % Br. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 3

(37) To test for enhanced mercury capture performance, a catalytic metal compound, here being copper (II) sulfate, is added to comparative Sample A to form Sample C. For preparation of Sample C, a copper (II) sulfate solution is made by dissolving 25 g of copper (II) sulfate in 100 g of deionized water. 25.12 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed PAC is dried at approximately 150° C. for 2 hours to yield Sample C a sorbent composition including PAC as a sorbent, having about 2 wt. % Cu (as CuSO.sub.4) and about 5.5 wt. % Br. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 4

(38) To test for enhanced mercury capture performance, a catalytic metal compound, here being iron (II) chloride, is added to comparative Sample A to form Sample D. For preparation of Sample D, an iron (II) chloride solution is made by dissolving 20 g of iron (II) chloride in 70 g of deionized water. 16.02 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed sample is dried at approximately 150° C. for 2 hours to yield a sorbent composition including PAC as a sorbent with about 1 wt. % Fe (as FeCl.sub.2) and about 5.5 wt. % Br. Approximately 4.196 g of deionized water is added to form Sample D having about 10 wt. % moisture. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 5

(39) To test for enhanced mercury capture performance, a catalytic metal compound, here being iron (III) sulfate, is added to comparative Sample A to form Sample E. For preparation of Sample E, an iron (III) sulfate solution is made by dissolving 60 g of iron (III) sulfate in 50 g of deionized water. 9.22 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed sample is dried at approximately 150° C. for 2 hours to yield a sorbent composition including PAC as a sorbent with about 1 wt. % Fe (as Fe.sub.2(SO.sub.4).sub.3) and about 5.5 wt. % Br. Approximately 4.196 g of deionized water is added to form Sample E with about 10 wt. % moisture. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 6

(40) To test for enhanced mercury capture performance, a catalytic metal compound, here being iron (III) chloride, is added to comparative Sample A to form Sample F. For preparation of Sample F, an iron (III) chloride solution is made by dissolving 200 g of iron (III) chloride in 100 g of deionized water. 14.51 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed sample is dried at approximately 150° C. for 2 hours to yield a sorbent composition including PAC as a sorbent with about 2 wt. % Fe (as FeCl.sub.3) and about 5.5 wt. % Br. Approximately 3.884 g of deionized water is added to form Sample F with about 11 wt. % moisture. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

Example 7

(41) To test for enhanced mercury capture performance, a catalytic metal compound, here being zinc sulfate, is added to comparative Sample A to form Sample G. For preparation of Sample G, a zinc sulfate solution is made by dissolving 37.1 g of zinc sulfate in 100 g of deionized water. 15.85 g of this solution is sprayed onto 100 g of Sample A while fluidizing the PAC in a mixer for 10 minutes. The sprayed sample is dried at approximately 150° C. for 2 hours to yield a sorbent composition including PAC as a sorbent with about 2 wt. % Zn (as ZnSO.sub.4) and about 5.5 wt. % Br. Approximately 3.348 g of deionized water is added to form Sample G with about 8 wt. % moisture. The ability to capture mercury is assessed using the DMI test, and this result is provided in Table 1.

(42) TABLE-US-00001 TABLE 1 DMI results for compositions of matter Ancillary catalyst DMI Sample component Wt. % metal (μg/g) A none N/A 174 B Copper (II) chloride 1 wt. % Cu 597 C Copper (II) sulfate 2 wt. % Cu 401 D Iron (II) chloride 1 wt. % Fe 303 E Iron (III) sulfate 1 wt. % Fe 579 F Iron (III) chloride 2 wt. % Fe 436 G zinc sulfate 2 wt. % Zn 555

(43) The example sorbent compositions disclosed herein having ancillary catalyst component metal compounds demonstrate an increased ability to capture mercury as evidenced by the DMI results indicated in Table 1. The addition of the ancillary catalytic metals Fe, Cu, Mn, Zn and combinations thereof to the Sample A sorbent increased mercury capture ability by as much as two- to three-fold when compared to the sorbent composition comprising the NaBr oxidizing agent alone.

(44) While various examples of a sorbent composition have been described in detail, it is apparent that modifications and adaptations of those examples will occur to those skilled in the art. However, is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.