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Membrane for the selective separation of fatty acids from aqueous media

A method for separating fatty acids from an aqueous medium by means of open-pored membranes has not previously existed. A method was developed to dissolve fatty acids in aqueous media using a biomolecule. A membrane was developed for the separation of dissolved fatty acids from aqueous media, with which a selective electrophoretic transport of fatty acdes is made possible. The established membrane technology for the separation of carboxylic acids can be used in various life science areas (e.g. medicine, chemistry or environmental technology).

Fatty acids are one of the most common organic compounds that are found as intermediates or educts in almost all organic media. Fatty acids with a carbon chain length of more than 6 are hydrophobic and form micelles in an aqueous medium. Such fatty acids can be emulsified in an aqueous medium by means of various biomolecules. In preliminary investigations it was found that the amino acid arginine is particularly suitable for this, since the guanidine group of the arginine can bind the carboxyl group of the fatty acid via hydrogen bonds in a 1:1 ratio. This can bring about nanoemulsification of the fatty acids in an aqueous medium. It could be shown that fatty acids that are bound to biomolecules, such as albumin, are detached by arginine and bound to it. It was also found that fatty acids that are bound to arginine in an aqueous solution can be separated from one another by means of an electrical gradient. Thus, in principle, an electrophoretic separation of fatty acids from an aqueous medium in which they are nanoemulsified by arginine is possible. Since most aqueous media in which free fatty acids are present also contain other compounds that would be transported and separated electrophoretically together with the fatty acids, a selective separation of the fatty acids should be aimed for. In principle, the electrodialysis process using a membrane that enables selective substance transport is suitable for this purpose. Fundamental studies have shown that it is not possible to transport fatty acids through anion-selective membranes that are available in the prior art. It has also been found that when using membranes which have transmembrane channels, fatty acids adhere to the channel surfaces which leads to an electro-osmotic flow which hinders the transport and causes further disadvantageous effects.

The aim of the development work was therefore to produce a membrane that enables selective electrokinetic transport of fatty acids with the highest possible transport rate. Based on the principle of nanofluidic material separation, nano- and microporous inorganic separation membranes were functionalized with amino acid polymers. It has been found that coating of the channel surfaces is not sufficient to ensure selectivity of the material transport. The aim was achieved by creating a room-spanning network of amino acid polymers within the channels, which have a high surface hydrophobicity.  The process for the production of hydrophobic, room-spanning polymer structures that form nanoscaled gaps could be transferred to mesoporous ceramic membranes.

It has also been found that the formation of an electro-osmotic flow can also be prevented by coating the open-pore membranes with a hydrophobized polycation. Furthermore, it has been found that the combination of an open-pore membrane with a hydrophobic, room-spanning polymer network and a coating with a hydrophobized polycation is particularly suitable for enabling the selective transport of fatty acids from an aqueous medium with a high transport capacity, whereby there is no electro -osmotic flow.

Thus, the task could be solved and a method for the production of membranes for the electrophoretic separation of fatty acids from aqueous media could be provided.

Patent applications have been filed for the process for the production of room-spanning polymer networks in open-pore membranes as well as the membranes obtainable through this (Patent WO2018042060A1).

The development work was funded by the BMBF (FKZ: 13N11392 as well as 13XP5027A