Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US10596517B2

This analysis identifies combinations of prior art references that would render the independent claims of US patent 10596517 obvious to a person having ordinary skill in the art (PHOSITA) at the time of the invention (priority date August 30, 2004).

Independent Claim 1: Promoted Carbon Sorbent

Claim 1: A promoted carbon sorbent comprising a base activated carbon that has reacted with a promoter selected from the group consisting of halides, halogens, and combinations thereof, such that the reaction product is effective for the removal of mercury from a gas stream.

Combination of References: U.S. Pat. No. 5,891,324 (Nelson) in combination with the general knowledge in the art regarding the use of activated carbon for gas-phase mercury removal.

Reasoning for Obviousness:
Nelson (U.S. Pat. No. 5,891,324) describes an activated carbon containing an acid (specifically listing HCl, a hydrohalide) for the removal of mercury, albeit from a liquid phase [cite: U.S. Pat. No. 5,891,324 describes an activated carbon containing an acid (HCl, H 2 SO 4 , or H 3 PO 4 ) for the removal of mercury contained in a liquid phase, such as would occur in a process steam in the oil industry.]. A PHOSITA would be aware that activated carbon is a well-established sorbent for removing mercury from gas streams, such as flue gas, as broadly acknowledged in the background of US10596517 itself [cite: Fine-particle injection sorbents include activated carbon, metal oxide sorbent, sodium sulfide particles, and basic silicate or oxide sorbents.].

A PHOSITA, motivated to enhance the efficiency of mercury removal from gas streams using activated carbon, would find it obvious to apply a known mercury-capturing additive (a halide, like HCl, as taught by Nelson) that is effective with activated carbon in one application (liquid phase) to another analogous application (gas phase) where activated carbon is also used for the same target pollutant (mercury). The patent acknowledges that "Reactions of halogens and acidic species with the basic binding sites on the activated carbon sorbent create sites for oxidizing mercury," [cite: Reactions of halogens and acidic species with the basic binding sites on the activated carbon sorbent create sites for oxidizing mercury.] suggesting a known underlying chemical principle that would guide a PHOSITA. Although Nelson focused on liquid-phase applications and lacked certain features of the claimed invention (e.g., in-flight treatment, regeneration, larger particle size), the core concept of a halide-containing activated carbon sorbent for mercury removal is present. The chemical distinction of forming a "carbon bromide compound" versus simply containing an acid, as highlighted by the applicant, represents a mechanistic difference or optimization rather than rendering the initial concept of a halide-promoted carbon sorbent non-obvious.

Independent Claim 10: Method of Preparation

Claim 10: A method comprising providing a granular activated carbon; reacting the activated carbon with a promoter selected from the group consisting of halogens, halides, and combinations thereof, such that the reaction product comprises a promoted carbon sorbent effective for removal of mercury from a gas stream.

Combination of References: U.S. Pat. No. 5,891,324 (Nelson) in combination with conventional methods for impregnating or reacting activated carbon.

Reasoning for Obviousness:
As discussed for Claim 1, Nelson (U.S. Pat. No. 5,891,324) teaches an activated carbon containing an acid, such as HCl, for mercury removal [cite: U.S. Pat. No. 5,891,324 describes an activated carbon containing an acid (HCl, H 2 SO 4 , or H 3 PO 4 ) for the removal of mercury contained in a liquid phase, such as would occur in a process steam in the oil industry.]. For activated carbon to "contain" such an acid, it necessarily implies a method of preparation where the acid is introduced to the carbon. Methods for treating activated carbon with various chemical agents, including impregnation from liquid solutions or reaction with gases, were well-known and conventional in the chemical and materials arts at the time of the invention. Indeed, US10596517 itself describes various preparation methods, including reacting halogens/halides in vapor phase, in organic solvents, and "in-flight," demonstrating the array of known techniques [cite: Sorbent treatment and/or preparation methods are also described. New methods for in-flight preparation, introduction, and control of the active sorbent into the mercury contaminated gas stream are described.]. The use of "granular activated carbon" is a routine choice among different forms of activated carbon available for treatment.

A PHOSITA, desiring to create the halide-containing activated carbon sorbent taught by Nelson, would be motivated to employ any of these routine and well-known techniques to achieve the "reacting" or "impregnating" step. The specific parameters of the reaction (e.g., precise concentration, temperature, contact time) would be considered within the skill of the art for optimizing the desired outcome of mercury removal.

Independent Claim 18: Method for Reducing Mercury in Flue Gas

Claim 18: A method for reducing mercury in flue gas comprising providing a sorbent, injecting the sorbent into a mercury-containing flue gas stream, collecting greater than 70 wt-% of the mercury in the flue gas on the sorbent to produce a cleaned flue gas, and substantially recovering the sorbent from the cleaned flue gas.

Combination of References: General knowledge of sorbent injection and particulate collection for mercury removal in flue gas, combined with the disclosure of the GE-Mitsui-BF system (Tsuji et al.) regarding carbon sorbent recovery and regeneration.

Reasoning for Obviousness:
The steps of "injecting the sorbent into a mercury-containing flue gas stream" and "collecting ... the sorbent from the cleaned flue gas" were common practices in the field of mercury emissions control. The patent itself notes that "Fine-particle injection sorbents include activated carbon...When particle injection is employed, the mercury captured on the sorbent particles is removed from the gas stream in a bag house or electrostatic precipitator (ESP) and collected along with ash particulate." [cite: Fine-particle injection sorbents include activated carbon, metal oxide sorbent, sodium sulfide particles, and basic silicate or oxide sorbents., When particle injection is employed, the mercury captured on the sorbent particles is removed from the gas stream in a bag house or electrostatic precipitator (ESP) and collected along with ash particulate.].

The GE-Mitsui-BF system (Tsuji et al., 1993, as cited in the patent) explicitly discloses a "recirculating carbon bed" used for mercury removal, where the carbon is "regenerated at high temperatures" [cite: the GE-Mitsui-BF system (Tsuji, K.; Shiraishi, I.; Dague, R. F. Proceedings, Sixth International Symposium, Air & Water Management Assoc., New Orleans, La., Mar. 10-12, 1993) employs a recirculating carbon bed, where mercury is removed along with acid gases (as ammonium salts) and the carbon is regenerated at high temperatures where ammonium sulfate is decomposed to SO 2 and N 2 and mercury is converted to the elemental form, which desorbs from the sorbent.]. This system clearly teaches the concept of recovering and regenerating carbon sorbent for reuse in mercury control applications.

A PHOSITA, confronted with the known problems of high sorbent consumption and waste disposal associated with single-pass sorbent injection systems, would be motivated to seek solutions to reduce costs and environmental impact. The GE-Mitsui-BF system provides a clear example of carbon sorbent recovery and regeneration in the context of mercury removal. It would be obvious to a PHOSITA to adapt the principle of "substantially recovering the sorbent" from a recirculating bed system, like GE-Mitsui-BF, to an injected sorbent system where the collection of sorbent along with ash is already a standard practice (e.g., via ESP or baghouse). The motivation would be to improve the economics and sustainability of injected sorbent processes by enabling reuse. The "greater than 70 wt-%" removal efficiency, while a desirable outcome, is dependent on the specific sorbent used. If the chosen sorbent (whether a conventional activated carbon or an enhanced version) achieved this, the method steps of injection, collection, and recovery would be obvious.

Independent Claim 22: Method for Mercury & Ash Reduction with Recycle (Large Particle Size)

Claim 22: A method for reducing the mercury content of a mercury and ash containing gas stream wherein particulate activated carbon sorbent with a mass mean size greater than 40 μm is injected into the gas stream, mercury is removed from the gas by the sorbent particles, the sorbent particles are separated from the ash particles on the basis of size, and the sorbent particles are re-injected to the gas stream.

Combination of References: General knowledge of activated carbon injection for mercury removal, the GE-Mitsui-BF system, and the acknowledged problem in the art regarding separating fine activated carbon from fly ash.

Reasoning for Obviousness:
The practice of injecting activated carbon for mercury removal into gas streams containing ash is well-known. The GE-Mitsui-BF system, as noted above, teaches the desirability and method of recycling carbon sorbent in a mercury removal process [cite: the GE-Mitsui-BF system (Tsuji, K.; Shiraishi, I.; Dague, R. F. Proceedings, Sixth International Symposium, Air & Water Management Assoc., New Orleans, La., Mar. 10-12, 1993) employs a recirculating carbon bed, where mercury is removed along with acid gases (as ammonium salts) and the carbon is regenerated at high temperatures where ammonium sulfate is decomposed to SO 2 and N 2 and mercury is converted to the elemental form, which desorbs from the sorbent.].

Critically, the background of US10596517 explicitly identifies a key problem that Claim 22 aims to solve: "Standard AC sorbents generally are of fine size with a mean particle diameter of less than 20 micrometers, which is also typical of the flyash that is generated from pulverized coal combustion. Consequently, because the sizes of standard AC and flyash are similar, separation of the two is difficult." [cite: Standard AC sorbents generally are of fine size with a mean particle diameter of less than 20 micrometers, which is also typical of the flyash that is generated from pulverized coal combustion. Consequently, because the sizes of standard AC and flyash are similar, separation of the two is difficult.]. The patent then directly articulates the motivation for using larger particles for separation: "In a scheme to recycle the injected carbon, the carbon is separated from the flyash. A separation based on size fractionation requires a treated larger particle sorbent." [cite: In a scheme to recycle the injected carbon, the carbon is separated from the flyash. A separation based on size fractionation requires a treated larger particle sorbent. To test this concept, a treated larger sized (>60 μm) sorbent was developed, prepared, and tested.].

A PHOSITA, motivated to implement a sorbent recycling system (as suggested by the GE-Mitsui-BF system and the economic/environmental advantages of reuse), and fully aware of the documented difficulty in separating fine activated carbon from fly ash due to similar particle sizes, would find it an obvious design choice to use larger-sized activated carbon particles to enable separation by size. While the patent states that "Injection of larger sized AC is generally not considered because the sorbent effectiveness decreases with size," [cite: Injection of larger sized AC is generally not considered because the sorbent effectiveness decreases with size.] this teaching away identifies a problem that the promoted sorbent (as in Claim 1) aims to overcome. However, the method steps of using larger particles for separation and re-injection to enable recycling, given the clear motivation and the known problem, would be obvious. The subsequent mercury removal by these particles and their re-injection would logically follow from the goal of a recycle system.