Membrane reactors approaches

Hollow-fiber microporous silica membrane Plug-flow reactor 55% increase in cyclohexane conversion (the conversion in the membrane reactor approaches 100% whereas it is 45% in the conventional one) Koutsonikolas, Kaldis, ZaspaUs, and SakeUaropoulos (2012)... 

Several hundred tons of L-methionine per year are produced by enzymatic conversion in an enzyme membrane reactor. An alternative approach is dynamic resolution, where the unconverted enantiomer is racemized in situ. Starting from racemic /V-acetyl-amino acid, the enantioselective L-acylase is used in combination with an TV-acyl-amino acid racemase to enable nearly total conversion of the substrate. 

Cox et al. (1995) portray a new approach to thermochemical gasification of biomass to hydrogen. The process is based on catalytic steam gasification of biomass with concurrent separation of hydrogen in a membrane reactor that employs a permselective membrane to separate the hydrogen as it is produced. The process is particularly well-suited for wet biomass and may be conducted at temperatures as low as 575 K. 

Using an approach involving a tubular membrane reactor in which the biocatalysts were retained, Nasufi et al. [59] reported the production of ascorbic acid by a... 

The present study investigates a different approach. The membrane is used to allow the desired intermediate product to escape from the reaction zone before it is consumed by further reaction. This use of a membrane reactor was first suggested by Michaels [15]. The partial oxidation of methane, which is a challenging reaction of the type propos for this application of membrane reactors, has been analyzed herein. There is no thermodynamic limitation for the production of carbon dioxide and water, actually these products are favored. It is desired to remove any partial oxidation product, for example formaldehyde, before it has a chance to be further oxidized. 

In all cases studied, the membrane reactor offered a lower yield of formaldehyde than a plug flow reactor if all species were constrained to Knudsen diffusivities. Thus the conclusion reached by Agarwalla and Lund for a series reaction network appears to be true for series-parallel networks, too. That is, the membrane reactor will outperform a plug flow reactor only when the membrane offers enhanced permeability of the desired intermediate product. Therefore, the relative permeability of HCHO was varied to determine how much enhancement of permeability is needed. From Figure 2 it is evident that a large permselectivity is not needed, usually on the order of two to four times as permeable as the methane. An asymptotically approached upper limit of... 

An asset of the Aachen/Jiilich bioorganic synthesis approach is technology transfer, which is testified by no less than five start-up companies. Scale-up requires stable and highly efficient enzymes as well as appropriate reaction technology. The development of membrane reactors has been a key to success. Reaction technology is outlined by C. Wandrey and co-workers in the final article. 

All peptide-catalyzed enone epoxidations described so far were performed using insoluble, statistically polymerized materials (neat or on solid supports). One can, on the other hand, envisage (i) generation of solubilized poly-amino acids by attachment to polyethylene glycols (PEG) and (ii) selective construction of amino acid oligomers by standard peptide synthesis-linked to a solid support, to a soluble PEG, or neat as a well-defined oligopeptide. Both approaches have been used. The former affords synthetically useful and soluble catalysts with the interesting feature that the materials can be kept in membrane reactors for continuously oper-... 

Arylpropionic acids are important class of non-steroidal anti-inflammatory drugs (NSAID). Their pharmacological activity is mainly in one of both enantiomers. Thus, efforts had been made to access to the enantiomerically pure substance. The kinetic resolution of racemic 2-(2-fluoro-4-biphenyl) propanoic acid 56 and 2(4-isobutylphenyl) propanoic acid 59 (Ibuprofen) was performed via enzymatic esterification and transesterification using an alcohol and vinyl acetate, respectively in a membrane reactor. The unreacted acid is obtained in highly enantiomerically enriched form. A consecutive approach consisting of the enzymatic hydrolysis of the resulted esters is needed to achieve the alcohol in optically pure form.77... 

The Van Koten group has developed an interesting approach to the assessment of the permeability of nanofiltration membranes for the application of metallodendrimer catalysts in membrane reactors. They have selectively grafted dendrons to organometallic pincers with sensory properties and have used these as dyes in a colorimetric monitoring procedure. 

To illustrate this approach, we will consider a new example the case of a simple tubular membrane reactor for which we wish to show the dependence between the conversion (rij of the main reactant and other variables which influence the process. 

As mentioned earlier, most membrane reactor models are based on isothermal macroscopic balances in the axial direction and do not solve the transport equations for the membrane/support matrix. They all account for the effects of membrane permeation through the use of some common relevant parameters (as a permeation term) in the transport equations for both the feed and permeate sides. Those parameters are to be determined experimentally. The above approach, of course, is feasible only when the membrane (or membrane/support) is not catalytic. 

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