Gas separation: processes – Solid sorption – And liquid contact
Reexamination Certificate
2000-11-22
2002-03-12
Smith, Duane S. (Department: 1724)
Gas separation: processes
Solid sorption
And liquid contact
C095S116000, C095S135000, C423S242700, C423S244010
Reexamination Certificate
active
06355094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a porous, preferably dimensionally stable material for the removal of gaseous impurities from a gas mixture, such as H
2
S, COS, CS
2
, and SO
2
, into the pores of which there is incorporated a secondary amine which chemically bonds with the constituents to be removed and a method for such removal.
2. Description of Related Art
The use of porous material incorporating a secondary amine for the removal of gaseous impurities from a gas mixture has earlier been described in GB-A-2 049 468. The porous material described in that document includes mineral carriers which are inert towards secondary amines. Examples of suitable mineral carriers mentioned are pumice, kieselguhr, bauxite, alumina, carbon, and silicates. The particle size preferably is in the range of from 0.1 mm to 5 cm. Further, preference is given to particles having an internal porosity of at least 0.1, for example from 0.1 to 0.8. Internal porosity is defined as the ratio of the volume of internal empty space to the actual volume of the particles of solid; internal porosity is measured for example by means of mercury porosimetry.
In actual practice, using such known materials is attended with a wide range of problems connected with, on the one hand, the presence of minerals in the carrier material and, on the other, the hydrophilic nature of both the carrier material and the employed amines. The presence of traces of certain metals in carrier material of mineral origin may catalyze the conversion of CS
2
and COS into sulphur. A drawback to the use of hydrophilic amines is that it leads also to the bonding of CO
2
. A further drawback consists in that regeneration by means of, e.g, steam stripping, is not readily workable in the case of every gas, for instance in that of CS
2
.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a porous, preferably dimensionally stable material for the removal of gaseous impurities from a gas mixture, such as H
2
S, COS, CS
2
, and SO
2
, including a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 &mgr;m into the pores of which there is incorporated a secondary amine having hydrophobic properties which chemically bonds with the constituents to be removed.
In accordance with another aspect of the present invention, there is provided a method for the removal of gaseous impurities from a gas mixture including contacting the gas mixture with a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 &mgr;m, wherein in the pores thereof there is incorporated a secondary amine having hydrophobic properties which chemically bonds with the constituents to be removed and which optionally is incorporated into a hydrophobic liquid.
These and other objects of the present invention will become apparent upon a review of the following detailed description and the claims appended thereto.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a porous material incorporating in its pores a secondary amine which chemically bonds with the constituents to be removed, which material is easy to regenerate on a commercial scale.
More particularly, the present invention provides a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 &mgr;m which contain a secondary amine having hydrophobic properties, which optionally is incorporated into a hydrophobic liquid.
The average pore diameter is determined with advantage using mercury porosimetry in accordance with ASTM D 4284-83.
It is regarded as extremely surprising that the use of a porous material having both a hydrophobic surface area and an average pore diameter in the indicated range provides a system which can be regenerated by means of, e.g., steam stripping and is so effective as to now render industrial scale use possible.
According to the present invention, favorable results are generally obtained when use is made of a porous material where at least 15% of the pores are filled with a liquid composed of secondary amine or a secondary amine-containing liquid.
More preferable results are commonly obtained when use is made of a material where at least 60% of the pores are filled with a liquid composed of secondary amine or a secondary amine-containing liquid.
It has been found that, as a rule, preferable results can be obtained when use is made of a material having an average pore diameter in the range of from 0.2 to 15 &mgr;m.
The secondary amines suitable for use according to the invention generally have a low vapor pressure, preference being given to amines having a boiling point of at least 250° C. As a rule, favorable results can be obtained when the secondary amine corresponds to the formula R
1
—NH—R
2
, wherein R
1
represents a functionalized or unfunctionalized (ar)aliphatic group with at least 7 carbon atoms and R
2
represents a functionalized or unfunctionalized (ar)alkyl group with at least 3 carbon atoms. Preference is given in this case to secondary amines having a total number of carbon atoms of at least 14. Examples of secondary amines according to the aforementioned formula include dibenzyl amine and ditridecyl amine. Very favorable results are obtained also when use is made of a secondary amine of the formula R
3
—NH—R
4
—NH—C(O)O—R
5
, wherein R
3
represents a functionalized or unfunctionalized (ar)aliphatic group with at least 7 carbon atoms, R
4
represents a functionalized or unfunctionalized alkylene group with at least 2 carbon atoms, and R
5
represents a substituted or unsubstituted alkyl group with at least 2 carbon atoms. These compounds can be obtained by blocking the primary amino group of a compound having a primary as well as a secondary amino group. As examples of suitable blocking agents may be mentioned ethylene carbonate and propylene carbonate. In the above formula R
3
preferably is a coco- or C
12
to C
14
-alkyl group, R
4
is an alkylene group with 2 to 6, preferably with 2 or 3 carbon atoms, and R
5
is a hydroxyalkyl group with 2 or 3 carbon atoms. Alternatively, it is possible to achieve favorable results by using a secondary amine obtained by converting an alkyl amine with an alkyl(meth)acrylate. As an example of such a compound is the reaction product of oleyl amine and butyl acrylate.
While the hydrophobic secondary amine may be incorporated into the pores of the hydrophobic polymer as such, preference is given to material where the secondary amine is dissolved in a hydrophobic liquid. If a regeneratable absorption system is required, the secondary amine and the hydrophobic liquid preferably both have high thermal, hydrolytic, oxidative, and chemical stability. The glycerol esters of one or more, preferably unsaturated fatty acids may be indicated as examples of a hydrophobic liquid suitable for use according to the present invention, with preference being given to an oil, e.g., palm oil, olive oil, groundnut oil, paraffin oil, fish oil such as herring oil, linseed oil, and, more particularly, soybean oil and/or castor oil. In general, the use of a hydrophobic liquid having one or more tertiary amino groups will be preferred, favorable results are obtained using an alkyl dialkanol amine, more particularly an alkyl diethanol amine, even more particularly a C
12
to C
14
-alkyl diethanol amine. Preferably, the equivalency ratio of secondary amino groups to tertiary amino groups is ≦1.
The process of preparing from hydrophobic polymers a porous, preferably dimensionally stable material suitable for use according to the present invention has been described, int.al., in U.S. Pat. No. 4,247,498, which is incorporated herein by reference in its entirety. Examples of suitable polymers include: low density polyethylene, high density polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene terpolymers, styreneacrylonitrile copolymers, styrene-butadiene copolymers, polybutene, and poly(4-methyl-pentene-1).
Most preferable results were
Bos Johannes
Schomaker Elwin
Akzo Nobel N.V.
Smith Duane S.
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