Liquid purification or separation – Processes – Chemical treatment
Patent
1994-06-20
1996-06-04
McCarthy, Neil
Liquid purification or separation
Processes
Chemical treatment
261104, 261107, C02F 170
Patent
active
055230032
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of introducing hydrogen through a membrane into aqueous liquids without forming bubbles.
In a number of chemical, biological, biochemical and other technical processes, it is necessary to charge hydrogen into aqueous liquids, for example, during the biological reduction of substances with hydrogen or the reduction of substances with hydrogen promoted by catalysts, such as the biological or catalyzed reduction of oxygen, nitrite or nitrate in water.
Generally, the introduction of hydrogen may take place in the form of bubbles or without forming bubbles. Although the charging of gas in the form of bubbles is very simple to implement, it is inefficient. In contrast, the charging of gas without the formation of bubbles permits a better utilization of the gas to be introduced. The charging of hydrogen without the formation of bubbles through a membrane in water which contains nitrite and/or nitrate for the purpose of catalytically removing these harmful substances while selectively forming nitrogen is known from European Patent Document EP-A 359 074. The charging of gas without the formation of bubbles which was recognized to be advantageous takes place by way of non-porous unreinforced or fabric-reinforced silicone hoses or flat silicone membranes. Despite their large wall thicknesses, these silicone hoses can withstand little mechanical stress.
Published German Patent Application DE-OS 35 44 382 describes a process for supplying bioreactors with oxygen and an apparatus which can be used for this purpose. The oxygen is introduced into the aqueous phase without the formation of bubbles through a non-porous silicon membrane with a fabric-reinforcement. The silicone hoses which were described there as "thin-walled" have a wall thickness of from 0.2 to 0.5 mm. The transport rate for gases is low. Although the gas charging rate is improved when very high pressures are used, the risk of the formation of bubbles is increased. The discharge of gases dissolved in the water is also low. European Patent Application No. EP 0 448 973 describes a spiral-form, wound membrane for introducing a gas into water. The gas to be introduced with that membrane is not particularly limited; oxygen and carbon dioxide are preferred. The membrane comprises a carrier structure of porous polymer with a homogenous layer, which is in contact with the water.
The invention is based on the object of providing an improved method for introducing hydrogen into aqueous liquids without the formation of bubbles. This object is achieved by means of the process according to the invention indicated in the claims.
The method according to the invention for the introduction of hydrogen into aqueous liquids without the formation of bubbles, whereby the hydrogen is charged into the aqueous liquid through a membrane, is characterized in that a membrane is used which comprises a) a carrier structure formed of a porous polymer, and b) at least one layer of a non-porous polymer, the aqueous liquid on the side of the layer made of non-porous polymer being in contact with the membrane.
Composite membranes having an integral-asymmetrical construction are particularly suitable. They comprises a carrier structure which is formed of a porous polymer and has a microporous layer and a non-porous coating. Membranes of this type and their manufacture are described in European Patent Application EP-A 291 679 (U.S. Pat. No. 4,933,085).
The carrier structure with the microporous layer is normally manufactured in a single step and is preferably formed from hydrophobic water-resistant polymers, such as polysulfones, for example, polyethersulfones, polyamides, polyimides, or particularly polyetherimide.
The integral-asymmetrical composite membranes used according to the method of the invention have the following construction:
One side of the membrane is formed by a non-porous layer of a hydrophobic polymer. A microporous skin will then normally follow in the direction toward the other side of the membrane. This microporous skin will be adjoined
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patent: 3520416 (1970-07-01), Keedwell
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patent: 4355636 (1982-10-01), Oetjen et al.
patent: 4933085 (1990-06-01), Kneifel et al.
patent: 5190627 (1993-03-01), Saito et al.
patent: 5348691 (1994-09-01), McElroy et al.
Behling Rolf-Dieter
Bischoff Michael
Kneifel Klemens
Mann Andreas
Peinemann Klaus-Viktor
McCarthy Neil
Solvay Unmeltchemie GmbH
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