Process for the purification of gases

Details Process for the purification of gases Process for the purification of gases

1999-11-23

2001-08-21

Griffin, Steven P. (Department: 1754)

Chemistry of inorganic compounds

Modifying or removing component of normally gaseous mixture

C423S220000, C423S228000, C423S229000, C423S236000, C423S242700, C423S245300, C048S127500, C048S198300, C252S182120

Reexamination Certificate

active

06277345

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the use of alkanolamines for freeing gases of acid-forming impurities, and also to a suitable absorption liquid.
DESCRIPTION OF THE RELATED ART
Gases of widely varying origins, for example natural gas or synthesis gas, contain gaseous, acid-forming impurities such as CO
2
, H
2
S, SO
2
, CS
2
, HCN, COS or mercaptans. The removal of the impurities mentioned is generally necessary because of the further use to which the gases are put. If the gases are burnt, regulations which limit sulfur emissions have to be observed. High CO
2
contents reduce the calorific value. Mercaptans have to be removed because of their odor and their toxicity. If the gases are used for chemical processes, the impurities are often troublesome catalyst poisons. In addition, the acidic impurities cause corrosion of components which come into contact with the gases.
Processes for removing such impurities are described in the prior art.
U.S. Pat. No. 3,716,620 discloses a process for removing mercaptans by bringing the gases into contact with a solution of iodine and amines.
WO-A-95/13128 discloses a process for freeing gases of acidic impurities by bringing the gases into contact with a solution comprising from 10 to 98% by weight of a polyethylene glycol alkyl ether, from 1 to 20% by weight of secondary monoalkanolamine and, if desired, from 10 to 60% by weight of a dialkanolamine.
The processes of the prior art require large amounts of basic alkanolamines. It is an object of the present invention to provide a process for freeing gases of acidic impurities which makes do with small amounts of alkanolamines.
It has now surprisingly been found that dialkanolamines dissolved in polyalkylene glycol alkyl ethers in the presence of small amounts of water in very low concentrations effectively remove the acidic impurities, in particular hydrogen sulfide, from gases. The increased effectiveness of the absorption liquid of the invention makes it possible to operate gas scrubbing plants using smaller amounts of absorption liquid or to increase the gas throughput.
SUMMARY OF THE INVENTION
The invention provides for the use of an absorption liquid for freeing gases of gaseous, acidic impurities, wherein the absorption liquid comprises
A) from 0.01 to 4% by weight of at least one compound of the formula
B) from 0.001 to 8.0% by weight of water, and
C) at least one polyalkylene glycol alkyl ether of the formula
R
1
—O—(R
2
—O)
x
—R
3
to 100% by weight,
where
R
1
is C
1
-C
4
-alkyl,
R
2
is ethylene or 2-methylethylene,
R
3
is hydrogen or C
1
-C
4
-alkyl,
R
4
is hydrogen or C
1
-C
4
-alkyl,
R
5
is C
1
-C
4
-alkylene and
X is an integer from 1 to 10.
The gases to be purified can be any gases which contain such impurities and which themselves do not react with the absorption liquid. The absorption liquid is particularly suitable for the purification of natural gas and synthesis gas.
The impurities which are to be removed by the process of the invention are acid-forming and in the form of a gas of vapor. In particular, they are CO
2
, H
2
S, SO
2
, CS
2
, HCN, COS or lower mercaptans having C
1
-C
8
-hydrocarbon radicals.
The present invention is described in the German priority application No. 198 54 353.0, filed Nov. 25, 1998, which is hereby incorporated by reference as is fully disclosed herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The absorption liquid comprises at least one polyalkylene glycol alkyl ether and at least one dialkanolamine, plus water. In a preferred embodiment of the invention, R
1
and R
3
are methyl or butyl or R
1
is methyl or butyl and R
3
is hydrogen. R
2
is preferably an ethylene radical. X is preferably from 2 to 8.
In a preferred embodiment, R
4
is methyl. R
5
is preferably methylene or ethylene, in particular ethylene. A particularly preferred dialkanolamine is N-methyidiethanolamine. The dialkanolamine content of the absorption liquid is preferably from 0.1 to 2% by weight, in particular from 0.2 to 0.99% by weight, especially from 0.25 to 0.7% by weight and particularly preferably from 0.3 to 0.6% by weight. In a further preferred embodiment of the invention, the absorption liquid contains from 0.005 to 5% by weight, in particular from 0.01 to 1% by weight, of water.
The scrubbing of the gas can be carried out at atmospheric or superatmospheric pressure. If the scrubbing of the gas is carried out under superatmospheric pressure, preference is given to pressures up to 100 atmospheres.
The scrubbing of the gas can be carried out at temperatures above the solidification point of the absorption liquid. Preference is given to the temperature range from 20 to 100° C.
The invention further provides an absorption liquid for acidic impurities in the form of gas or vapor, comprising
A) from 0.01 to 4% by weight of at least one compound of the formula
B) from 0.001 to 8.0% by weight of water, and
C) at least one polyalkylene glycol alkyl ether of the formula
R
1
—O—(R
2
—O)
x
—R
3
to 100% by weight,
where
R
1
is C
1
-C
4
-alkyl,
R
2
is ethylene or 2-methylethylene,
R
3
is hydrogen or C
1
-C
4
-alkyl,
R
4
is hydrogen or C
1
-C
4
-alkyl,
R
5
is C
1
-C
4
-alkylene and
X is an integer from 1 to 10.
The preferred embodiments of the absorption liquid of the invention have already been described.
The invention also provides a process for the purification of gases, which comprises bringing the gases into contact with the absorption liquid of the invention at temperatures of from 20 to 100° C. and pressures of from 1 to 100 atmospheres.


REFERENCES:
patent: 3622267 (1971-11-01), Bartholome et al.
patent: 3716620 (1973-02-01), Deschamps et al.
patent: 4551158 (1985-11-01), Wagner et al.
patent: 4705673 (1987-11-01), Capobianco et al.
patent: 5589149 (1996-12-01), Garland et al.
patent: 5705090 (1998-01-01), Garland et al.
patent: 5877386 (1999-03-01), Schubert
patent: 39 22 904 A1 (1991-01-01), None
patent: 0 452 694 A2 (1991-10-01), None
patent: WO 95/13128 (1995-05-01), None
EPO Search Report.
Derwent Patent Family Abstract for DE 39 22 904.

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