Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through immobilized liquid
Patent
1996-09-17
1998-05-12
Spitzer, Robert
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through immobilized liquid
95 49, 95 51, 96 5, 96 8, B01D 5322, B01D 5314
Patent
active
057499411
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the absorption of one or more gaseous components from a gas phase, in that the gas phase with the component(s) to be absorbed present therein is brought into contact with a liquid phase, wherein the gas phase and the liquid phase are separated by a hydrophobic membrane of a material other than polytetrafluoroethene, and wherein the liquid phase comprises water and a water-miscible and/or water-soluble absorbent.
BACKGROUND OF THE INVENTION
A method of this type was disclosed in the now withdrawn European patent application 0 451 715 (H. Matsumoto et al.) in the name of Mitsubishi, claiming a Japanese priority from 1990. The reference describes an apparatus for separating polar gases from a gas source, in which said gas source containing the polar gas(es) is led through an encased module of porous hollow membrane filaments made of hydrophobic material and having innumerable micropores penetrating through the wall of the hollow filament and distributed over the wall of the hollow filament for effecting gas/liquid mass transfer to an absorption liquid flowing on the other side of the hollow filaments of the module. Although this reference is preferably directed to an apparatus for carrying out said method, it is also described that as the absorption liquid "diethanolamine, aqueous solutions of K.sub.2 CO.sub.3 and KHCO.sub.3.H.sub.2 O and mixtures thereof" can be used. However, this reference is silent with respect to the parameters for carrying out this process, including the concentrations of the components in the absorption liquor, and the surface tension of the final solution.
In a 1994 article from the inventors of EP-A-0 415 715 entitled "Fundamental Study on CO.sub.2 Removal from the Flue Gas of Thermal Power Plant by Hollow-Fibre Gas Liquid Contactor", Mitsubishi Heavy Industries Ltd and Tokyo Electric Power Company, presented at CO.sub.2 Chemistry Workshop, Hemavan, Sweden, 19-23 Sep. 1993, results are given for the absorption from carbon dioxide from the flue gas from power stations with the aid of hollow fibre membranes, the liquid phase used being a solution of monoethanol amine in water.
In this article, a comparison is given of polypropene (PP), polyethene (PE) and polytetrafluoroethene (PTFE) hollow fibres, from which it can be seen that with polypropene and polyethene membranes the mass transfer coefficient decreases after some time in the case of continuous use. Consequently, using these membranes it is not possible to operate gas/liquid absorption under stable conditions over a prolonged period. Therefore, in this article preference is given to PTFE hollow fibre membranes.
However, the PTFE membranes used have an appreciably lower mass transfer coefficient than the polypropene and polyethene membranes. Moreover, PTFE is very difficult to process. For example, hollow fibres with small external diameters (<0.72 mm) which are desirable for use in compact equipment for, for example, the `offshore` industry and aerospace, cannot be produced from PTFE.
As it can be seen from the above two citations, the inventors/authors thereof, despite the four years lying between these references, were unable to satisfactorily perform gas/liquid absorption with polypropene or polyethene hollow fibres, concentrating instead on PTFE fibres, which however have practical disadvantages.
The first aim of the invention is, therefore, to improve the abovementioned gas/liquid absorption methodology, more particularly to provide a method for membrane gas absorption which can be operated under stable conditions over a prolonged period in a system of small dimensions.
A compact system of this type could be provided by the use of, for example, polypropene or polyethene hollow fibres in place of PTFE hollow fibres, in combination with an aqueous solution of a conventional absorbent, such as monoethanolamine.
However, research by the Applicant has now revealed that when an aqueous solution of an organic absorbent customary in the prior art, (such as monoethan
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Feron Paul Hubert Maria
Jansen Albert Edward
Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk On
Spitzer Robert
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