Catalytic adsorbents for mercury removal from flue gas and methods of manufacture therefor

a technology of catalytic adsorbent and flue gas, which is applied in the direction of separation process, dispersed particle separation, chemistry apparatus and processes, etc., can solve the problems of mercury toxicity to humans and the environment, neurological damage in humans, wide spread neurological damage among the local population, etc., to promote the formation of mercury halide, increase the adsorbent capacity, and accelerate the adsorption rate

Inactive Publication Date: 2006-09-14
PRAXAIR TECH INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0016] The present invention provides catalytic adsorbents in which a halide salt is dispersed on activated carbon and the oxidation catalytic activity of the activated carbon promotes the formation of mercury halide. At the same time, the adsorbent qualities of activated carbon retain the mercury halides thus formed. The present invention recognizes that while the halide salts are stable and harmless at room temperature, these doped activated carbon c...

Problems solved by technology

The toxicity of mercury to humans and the environment has long been known.
It is known for example that mercury exposure can cause neurological damage in humans.
A particularly devastating example of the harmful effects of mercury occurred in Minamata, Japan in the 1950's where organic mercury byproducts of acetaldehyde production were discharged into the local bay.
By consuming fish in the bay, wide spread neurological damage and birth defects among the local population were reported.
Through chemical and biological processes, this mercury can become concentrated in fish by many thousand fold, thereby entering human food supplies at harmful levels.
The effort to remove trace mercury from air, water, natural gas, and other industrial streams has a long history, however; removing mercury from coal burning flue gas streams is a very different problem.
Prior art techniques for removing mercury from air or hydrocarbons at room temperature generally have limi...

Method used

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  • Catalytic adsorbents for mercury removal from flue gas and methods of manufacture therefor
  • Catalytic adsorbents for mercury removal from flue gas and methods of manufacture therefor
  • Catalytic adsorbents for mercury removal from flue gas and methods of manufacture therefor

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0066] This example demonstrates that at room temperature, undoped PAC is a good adsorbent for elemental mercury and a promoter would appear to provide no additional benefit. At 270° F., however, physical adsorption is overwhelmed by kinetic energy and adsorption by undoped PAC and without a promoter was inadequate.

[0067] Fixed bed tests were conducted on four samples in a stream which contained nitrogen and about 13 μg / m3 of elemental mercury. The tests conditions and results are summarized in Table 1 and FIGS. 3-6. The undoped FGD carbon sample was tested at room temperature and achieved 100% mercury removal for more than 15 hours with no sign of mercury breakthrough. For samples tested at 270° F., all three types of activated carbon reached almost 100% breakthrough immediately (0% removal).

TABLE 1Test gasesSampleSampleTestcomposition andComments on TestSample #NametreatmentTempsequenceResultsFGDAs received 72 F.N2 + Hg100% Hg removal forcarbon15 hrs; no any signof breakthrough...

example 2

[0069] This example demonstrates how halide salts as a dopant alter the flue gas, mercury and carbon interaction so as to promote mercury adsorption from the flue gas stream. In this Example, thin fixed beds of PAC samples were exposed to different gas mixtures in sequence. All experiments started with nitrogen and mercury (about 13μ gm / cubic meter). Other components of the flue were added into the stream sequentially or in sequential combination toward a composition of synthetic flue gas, which is typified as: 6% O2, 12% CO2, 8% H2O, 1600 ppm SO2, 400 ppm NO, 20 ppm NO2, 50 ppm HCl, 12-14 μg / m3 Hg, with the balance being N2.

[0070] Two type of PAC (ashless and FGD) and three dopants (KBr, NaBr, and NaCl) were used in the experiments. Detail of the experiments are summarized in Table 2. The breakthrough curves are given in FIGS. 7-12.

TABLE 2Test gasesSampleSamplecomposition andComments onSample #NameDescriptionsequenceTest Results17297-99Ashless6 N HCl extraction1. N2 + Hg;Removed...

example 3

[0071] This example demonstrates that a physical adsorbent such as silica gel, doped with KBr, did not remove mercury from the flue gas.

[0072] The same thin fixed bed method as in Examples 1 and 2 was used in this Example. The details of sample preparation, test conditions and results are given in Table 3 and FIG. 13.

TABLE 3Test gasesCommentsSampleSamplecomposition andon TestSample #NameDescriptionsequenceResults17297-69KBrThe weight1. O2 6% + CO2The con-dopedratio of12% + H2O 8% + SO2centration ofsilicaKBr:Silica1600 ppm + NOHg reductiongelgel =400 ppm + HClwas less15:10050 ppm + NO2than 10%.20 ppm + Hg14 micro gram +N2 (fullsynthetic flue)

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Abstract

The present invention provides catalytic adsorbents formed from doping activated carbon with a dispersed halide salt. The catalytic adsorbents provided herein are stable and harmless at room temperature, yet allow for chemical adsorption at elevated temperatures typical of those for flue gas streams. The present invention also provides methods of manufacturing the doped activated carbon adsorbents.

Description

TECHNICAL FIELD [0001] The present invention relates generally to catalytic adsorbents for use in the removal of mercury from flue gas streams and methods of manufacturing such catalytic adsorbents. BACKGROUND OF THE INVENTION [0002] The toxicity of mercury to humans and the environment has long been known. It is known for example that mercury exposure can cause neurological damage in humans. A particularly devastating example of the harmful effects of mercury occurred in Minamata, Japan in the 1950's where organic mercury byproducts of acetaldehyde production were discharged into the local bay. The byproducts were consumed and metabolized by fish. By consuming fish in the bay, wide spread neurological damage and birth defects among the local population were reported. [0003] Coals used for generating electric power often contain about 0.1 ppm mercury. In the United States alone, about 50 tons of mercury are discharged as vapor in stack gas every year. Through chemical and biological...

Claims

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Application Information

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IPC IPC(8): C01B31/08
CPCB01D53/64B01D53/8665B01D2251/60B01D2253/102B01J20/3204B01J20/046B01J20/20B01J20/3236B01D2257/602
Inventor CHAO, CHIEN-CHUNGPONTONIO, STEVE J.
Owner PRAXAIR TECH INC
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