Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-11-09
2002-03-12
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S049000, C095S051000, C095S052000, C095S231000, C095S234000, C095S235000, C095S236000, C096S004000, C096S008000
Reexamination Certificate
active
06355092
ABSTRACT:
The present application relates to an apparatus and method for performing membrane gas/liquid absorption at elevated pressure.
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
Methods for membrane gas/liquid absorption are known, for example from Applicant's patent applications mentioned below. These processes generally comprise the absorption of one or more gaseous components from a gas phase, the gas phase containing the components to be absorbed being brought into contact with a liquid phase, the gas phase and the liquid phase being kept separate by a membrane.
Membrane gas/liquid absorption is a very flexible and versatile technique, which can be used for specific absorption of diverse compounds from a gas phase, depending on, inter alia, the membrane used, the liquid phase used, and the gas stream to be cleaned. For example, membrane gas/liquid absorption can be used for specifically absorbing carbon dioxide and H
2
S (European application 0,751,815), oxidizable and reducible constituents such as mercury vapour (PCT application NL 96/00279), and also for removing water vapour (European application 0,524,242 by Applicant).
The known techniques have the drawback, however, that they cannot be applied to/with gas streams at elevated pressure, in particular pressures of more than 4 bar. Nevertheless it would be highly advantageous to be able to carry out membrane gas/liquid absorption at elevated pressure from the gas phase, particularly in those cases where the gas phase is provided at elevated pressure and where it is not possible/desirable, for technical and/or economical reasons, to reduce the gas stream pressure prior to the absorption process. An example of this is refining of natural gas which, as a rule, is produced, and has to be processed, at a pressure of more than 50 bar and sometimes 100 to 200 bar.
Existing membrane gas/liquid absorption techniques cannot, however, be applied to gas streams having such a high pressure, notably because:
existing equipment for gas/liquid membrane absorption is not designed for such high pressures;
existing membranes, particularly porous membranes, cannot be used if there is a pressure drop across the membrane;
if “closed” membranes that can withstand a high(er) pressure drop (i.e. having a suitable thickness) are used, the mass transfer and consequently the capacity may become too low.
SUMMARY OF THE INVENTION
The invention therefore relates to an apparatus for performing membrane gas/liquid absorption at elevated pressure, comprising:
a pressure vessel (
1
) which encloses an essentially closed chamber (
2
);
means for supplying (
3
a
) and discharging (
4
a
) a gas phase to/from chamber (
2
);
a membrane unit (
5
) disposed in chamber (
2
), comprising at least one membrane element (
6
) which defines a feed-through channel (
7
);
means for supplying (
8
a
) or discharging (
9
a
) a liquid phase to the membrane unit (
5
), such that the liquid phase can be passed from inlet (
8
a
) through feed-through channel (
7
) to outlet (
9
a
);
wherein pressure vessel (
1
), inlet (
3
a
) and outlet (
4
a
) and membrane unit (
5
) are provided in such a way in chamber (
2
) that the gas phase can be directed past membrane element (
6
) in a flow direction essentially perpendicular to the flow direction of the liquid phase through membrane element (
6
), exchange of components to be absorbed being able to take place between the gas phase and the liquid phase through (the wall of) membrane element (
6
).
The invention further relates to a method for performing membrane gas/liquid absorption at elevated pressure for absorbing one or more components from a gas phase, employing the above-described apparatus, comprising
feed-through of the gas phase comprising the one or more components to be absorbed, via inlet (
3
a
) and outlet (
4
a
) through chamber (
2
) past the one or more membrane elements (
6
), the gas phase having a pressure of more than 4 bar, preferably more than 10 bar, more preferably 50-200 bar;
feed-through of a liquid phase suitable for absorbing the one or more components, via inlet (
8
a
) and outlet (
9
a
) through feed-through channel (
7
), the liquid phase having a pressure which differs from the gas phase pressure by not more than 5 bar, preferably not more than 0.5 bar;
in such a way that the one or more components to be absorbed are absorbed from the gas phase into the liquid phase through (the wall of) the one or more membrane elements (
6
), the gas phase and the liquid phase being kept separate by the membrane elements (
6
).
According to the invention, the membrane gas/liquid absorption is performed with so-called “cross-flow”, i.e. the direction of the gas phase containing the one or more components to be absorbed is perpendicular to the plane of flow of the liquid phase.
Pressure vessel (
1
) is preferably essentially cylindrical or encloses an essentially cylindrical chamber (
2
). Whilst, in the operating position shown, the longitudinal axis of pressure vessel (
1
) is arranged essentially vertically, other setups are also possible, since membrane absorption is essentially independent of the orientation of the pressure vessel. These additional degrees of freedom regarding the set-up of the membrane absorber are an important advantage of membrane gas absorption compared with (for example) the use of packed columns which operate under the influence of gravity and therefore always have to be operated essentially vertically to achieve the desired counterflow.
Pressure vessel (
1
) may comprise guide means for controlling the flow of the gas phase through chamber (
2
).
Membrane element (
6
) has such a shape that it defines at least a feed-through channel (
7
). As such, membrane element (
6
) may consist of one membrane or of an assembly of a plurality of membranes, which form/enclose the feed-through channel; for example, membrane unit (
5
) may consist of planar membranes having transport channels, membranes that form a so-called “plate-and-frame” module or are in the form of spirally coiled membranes. Membrane element (
6
) is preferably in the form of a hollow fibre.
The membranes can be made of any suitable material which is at least permeable for the one or more gaseous constituents to be absorbed, but not for the gas phase and the liquid phase.
The membranes are preferably inert and able to withstand the gas phase and liquid phase used and the constituents to be absorbed, and are further selected on the basis of the intended use and further factors such as the desired mass transfer. In this context it is also possible to employ selective membranes.
The membranes can be either porous and nonporous, and can be asymmetric and/or coated membranes. It will be evident to those skilled in the art that, to achieve high mass transfer, porous membranes are to be preferred as a rule; these, however, are most sensitive to a pressure drop across the membrane.
Suitable membrane materials are known from the prior art, such as the abovementioned applications by Applicant, and comprise porous membranes such as polypropylene (PP), polyethylene (PE), poly(vinylidene fluoride) (PVDF), poly(tetrafluoroethylene) (PTFE) and polysulphone (PSU); nonporous membrane materials, asymmetric and/or coated membranes such as plasma membranes, membranes coated with siloxane rubbers (PDMS), membranes treated with fluorine, paraffin waxes and the like. Other suitable materials are, for example, ceramic membranes (Al
2
O
3
, TiO
2
, ZrO
2
), cellulose acetate (CA), butadiene rubber, EPDM (ethylene/propylene terpolymer); metallic membranes (e.g. Pd), poly(phenylene oxide) (PPO), polyimide (PI) and the like. Other materials will be obvious to those skilled in the art.
The membrane unit (
5
) comprises at least the one or more membrane elements (
6
) and possibly further means, such as guide elements for guiding the gas stream past the membrane elements (
6
), for example wall elements which enclose the membrane unit parallel to the gas flow direction; and/or connecting and distributing elements for distributing the (stream of the) liqu
Feron Paul Hubert Maria
Hanemaaijer Jan Hendrik
Huisjes Piet
Jansen Albert Edward
Browdy and Neimark PLLC
Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk On
Spitzer Robert H.
LandOfFree
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