Membrane reactor

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A membrane reactor is a system for carrying out a chemical or biochemical reaction that contains a membrane-based separation stage as an integral component. However, there are also designs in which the membrane is located outside the chemical reactor. The use of membrane reactors leads in part to an improvement in the selectivity of a reaction and, due to the continuous decrease in product, to an increase in the yield in the case of reactions with equilibrium limits.

The increase in the yield of the reaction is based on the change in the concentration of a substance due to the continuous removal or supply from or into the reaction space. This is done selectively for the substance in question through a membrane that is permeable to this substance.

The membrane in such reactors can e.g. B. porous glasses or made of suitable polymer layers.

Applications

Membrane reactors can be used to increase the selectivity in the selective oxidation of hydrocarbons . Oxygen is added along the catalyst bed, so that its low local concentration prevents or suppresses the undesired total oxidation. Membrane reactor technology can also be used for dehydrogenation reactions of hydrocarbons (e.g. propane to propene ). In this case come palladium / silver -Kompositmembranen for the reaction and for hydrogen separation is used.

The immobilization of enzymes on a porous membrane can also be viewed as a membrane reactor system (enzyme membrane reactor, EMR ). Such systems are used in biotechnology and facilitate the separation of the products from the reaction mixture (catalyst, starting materials). There are several technical processes in which enzyme membrane reactors are used in industrial production, e.g. B. in the kinetic resolution ( enantioselective hydrolysis ) of DL - N -acetylamino acids. In a continuous process under the action of a suitable enzyme ( L - acylase ), a mixture of the L - amino acid , acetic acid and D - N - acetylamino acid is produced, which can be separated by fractional crystallization or ion exchange chromatography. Because of the relatively high molar mass of the enzyme remains in the membrane, which acts as a molecular filter, hang , while the amino acid, the N can pass -Acetylaminosäure and acetic acid. In some cases, enzyme derivatives with enlarged molecules are used in enzyme membrane reactors instead of pure enzymes. Also amidases , Hydantoinases , racemases are already longer used in membrane reactors with success.

Coenzyme-dependent biochemical conversions can also be carried out in the enzyme membrane reactors. Such methods allow e.g. B. the enantioselective continuous conversion of α- ketocarboxylic acids into enantiomerically pure α-amino acids and are used in technical pilot plants. Also hydrogenases have been used successfully.

Similar to enzymes, whose catalytic activity is closely linked to the macromolecular structure, chemical catalysts can also be modified so that they are retained by membranes. This concept is also known as chemzym .

Another application with increasing importance is wastewater treatment with membrane activated sludge reactors (MBR).

literature

  • T. Melin, R. Rautenbach: Membrane process - basics of module and plant design . VDI book, 2007, ISBN 978-3-540-34327-1 .

Individual evidence

  1. ↑ Wolfgang Leuchtenberger and Ulf Plöcker: Production of amino acids with biotechnological methods , Chemie-Ingenieur-Technik 60 (1988) 16-23.
  2. ^ AS Bommarius, K. Drauz, U. Groeger, C. Wandrey: Membrane Bioreactors for the Production of Enantiomerically Pure α-Amino Acids , in AN Collins, GN Sheldrake, J. Crosby (editors): Chirality in Industry , Wiley (1992 ), Pp. 371-397, ISBN 0-471-93595-6 .
  3. ↑ GM Rios, MP Belleville, D. Paolucci, J. Sanchez, Journal of Membrane Science, 242 (2004) 189.
  4. ↑ A. Bückmann, M.-R. Kula, R. Wichmann and C. Wandrey , Journal of Applied Biochemistry 3 (1981) 301.
  5. ↑ L. Greiner, DH Müller, ECD van den Ban, J. Wöltinger, C. Wandrey, A. Liese, Advanced Synthesis & Catalysis 342 (2003) 679.
  6. ↑ J. Wöltinger, K.-H. Drauz, AS Bommarius, Applied Catalysis A: General 221 (2001) 171.