Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
2001-07-02
2003-02-04
Simmons, David A. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C423S239100
Reexamination Certificate
active
06514320
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for absorbing nitrogen oxides from gas mixtures containing said oxides. The process according to the present invention is particularly, but not exclusively, useful for removing nitrogen oxides contained in gases produced by combustion processes such as, for example, the gas emissions of thermoelectric power stations, kilns and furnaces for producing cement and ceramic materials, motor vehicle exhausts, and domestic heating system exhausts. These gases are also produced by various specific industrial processes, such as the production of semiconducting materials.
Absorption of nitrogen oxides by Ba—Cu—O mixed oxides has been described in the literature (Masato Machida et al., “NO Removal by Absorption into BaO—CuO Binary Oxides”, J Chem Soc Chem Commun, 1990, p. 1165; M. Machida et al., “Catalytically Accelerated Solid Gas Reaction Between NO and Ba—Cu—O for Efficient NO Removal”, Proceedings of the 10th International Congress on Catalysts, Jul. 9-24 1992, Budapest, Hungary).
In particular, the activity of reversible absorption of NO of two phases of mixed oxide, BaCuO
2.1
and BaCuO
2.5
, has been noted.
The main drawback in using BaCuO
x
compounds where x=2.1 and x=2.5 is the reactivity of these compounds in the presence of CO
2
and H
2
O, which are unavoidable components of combustion exhaust gases; this reactivity leads to the rapid and irreversible passivation of the nitrogen oxide absorption activity.
Absorption of NO
x
by materials based on BaCuO
2
, such as for example MnO
2
BaCuO
2
, is also known (EP 540280 and EP 580389).
The addition of MnO
2
, reported as a solution to the above described drawback, has proved itself ineffective, contrary to what has been claimed, as demonstrated by our experiments.
Moreover, WO97/28884 describes the NO and NO
2
absorption activity of compounds having the formula Ba
2
Cu
3
O
6±d
, where d has a value between 0 and 1, for example (Ba
2−x
A
x
)Cu
3
O
6±d
; the same document describes the absorption of nitrogen oxides by (Ba
2−x
A
x
)Cu
3
O
6±d
where A is an alkaline or alkaline-earth metal or a lanthanide, for example a compound having the formula e (Ba
2−x
Sr
x
)Cu
3
O
6±d
.
Ba
2
Cu
3
O
6±d
compounds absorb nitrogen oxides reversibly and, if synthesized appropriately, are resistant to the action of CO
2
and H
2
O; however, the regeneration temperature is no less than 650° C. and the optimum absorption temperature is close to 300° C. These values can constitute a considerable technological complication in using said materials. Furthermore, the high relative density of the compound, caused by the presence of a relatively heavy ion such as Ba, reduces the effectiveness of the absorbent, which can be expressed as the mass of NO
x
, absorbed to saturation per gram of absorbent.
SUMMARY OF THE INVENTION
The aim of the present invention is to eliminate the above-mentioned drawbacks in various known processes for absorbing nitrogen oxides from gas mixtures which comprise said oxides by devising a process which allows to absorb nitrogen oxides at lower temperatures with equal efficiency.
An object of the present invention is to provide a nitrogen oxide absorption process in which the regeneration temperature of the absorbent is lower, accordingly ensuring an important technological advantage.
Another object of the present invention is to provide a process for absorbing nitrogen oxides at ambient temperature, albeit with reduced kinetics.
Another object of the present invention is to provide a process for absorbing nitrogen oxides which uses absorbent materials which are resistant to carbonatation if exposed to atmospheres similar to those of flue gas ducts (10% CO
2
, 10% H
2
O).
This aim, these objects and others are achieved by the process according to the present invention, which comprises the step of placing a gas mixture containing nitrogen oxides in contact with absorbent compounds comprising or constituted by mixed copper oxides chosen among CaCuO
2
, Sr
14
Cu
24
O
41
derivatives thereof obtained by isovalent and/or heterovalent substitutions, and mixtures thereof. Advantageously, the CaCuO
2
and Sr
14
Cu
24
O
41
derivatives are derived by isovalent and/or heterovalent substitutions both on the sites occupied by the metals of the second group (for example Sr or Mg on Ca in CaCuO
2
and Ca, La, Na on Sr in Sr
14
Cu
24
O
41
) and on the sites occupied by copper (for example fourth-period transition metals such as Ni).
Selective NO and NO
2
absorption properties have been found unexpectedly in CaCuO
2
and Sr
14
Cu
24
O
41
compounds and in compounds derived therefrom by isovalent and heterovalent substitutions on the sites occupied by metals of the second group.
Both compounds and their derivatives obtained by substitution are known in the literature (for CaCuO
2
, Roth et al., J Am Ceram Soc, Vol. 72, p. 1545 (1989), JCPDS card no. 46-0054; for Sr
14
Cu
24
O
41
, McCarron et al., Mat Res Bull, Vol. 23, p. 1355 (1988), JCPDS card no. 43-0025); in particular, for the Sr
14
Cu
24
O
41
compound there is a considerable body of literature associated with its unusual magnetic properties.
Hereinafter, when referring to the CaCuO
2
and Sr
14
Cu
24
O
41
compounds, such reference is to be understood as a reference to compounds which produce powder diffraction spectra corresponding to JCPDS card no. 46-0054 for CaCuO
2
and, JCPDS card no. 43-0025for Sr
14
Cu
24
O
41
, respectively.
However, no reference to the absorption properties of these materials or to their use in any application thereof has been noted.
REFERENCES:
patent: 5312607 (1994-05-01), Schiabel et al.
patent: 6066590 (2000-05-01), Horii et al.
patent: 6334987 (2002-01-01), Matacotta et al.
patent: 6379432 (2002-04-01), Matacotta et al.
patent: A-97 02886 (1997-01-01), None
patent: A-97 28884 (1997-08-01), None
patent: WO 99/04881 (1999-02-01), None
Calestani Gianluca
Dionigi Chiara
Matacotta Francesco Cino
Nozar Petr
Consiglio Nazional Delle Ricerche
Lawrence Frank M.
Simmons David A.
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