Membrane reactor
A membrane reactor is a device for carrying out a chemical or biochemical reaction which comprises a membrane-based separation step as an integral part. However, there are also embodiments in which the membrane is outside of the chemical reactor. The use of membrane reactors leads partly to improve the selectivity of a reaction and by the continuous removal of product for increasing the yield in equilibrium-limited reactions.
Increase the yield of the reaction is based on the change in the concentration of a substance by the continuous removal and supplying from or into the reaction chamber. This is selective for the substance concerned by a permeable membrane for this substance.
The membrane in such reactors, for example, porous glasses or consist of suitable polymer layers.
Applications
Membrane reactors may be used to increase the selectivity in the selective oxidation of hydrocarbons. In this case, through the catalyst bed of oxygen is added, so that by the local low concentration prevents the undesirable total oxidation, or is suppressed. Also for dehydrogenation reactions of hydrocarbons (eg propane to propene ), the membrane reactor technology to be used. This palladium / silver composite membranes come for the reaction and for hydrogen separation for use.
The immobilization of enzymes on a porous membrane can be considered as a membrane reactor system ( enzyme membrane reactor EMR). Such systems are used in the biotechnology and facilitate the separation of the products from the reaction mixture (catalyst, reactants ). There are several technical methods where the enzyme membrane reactors are used in industrial production, for example, in the kinetic resolution ( enantioselective hydrolysis) of DL- N- acetyl amino acid. This produces a continuous process under the action of a suitable enzyme (L- acylase ), a mixture of the L-amino acid, acetic acid and DN- acetylamino acid, which can be separated by fractional crystallization or ion exchange chromatography. Because of the relatively high molar mass of the enzyme to the membrane which acts as a molecular filter remains hanging, whilst the amino acid of N- acetylamino acid and the acetic acid can pass. Partly are molekülvergrößerte enzyme derivatives, used instead of pure enzymes in enzyme membrane reactors. Also amidases hydantoinases Racemases are already used longer in Menbranreaktoren with success.
In the enzyme membrane reactors can also be realized coenzyme -dependent biochemical transformations. Such methods allow, for example, the enantioselective continuous conversion of α -ketocarboxylic acids in enantiomerically pure α -amino acids and are used in industrial pilot facilities. Also hydrogenases have been used successfully.
Analogous to enzymes whose catalytic activity is closely linked to the macromolecular structure, also chemical catalysts can be modified so that they are retained by the membranes. This concept is also referred to as chemzyme.
A further application of increasing importance is the wastewater treatment with membrane bioreactors (MBR).