Pervaporation membrane reactor water removal

Pervaporation Membrane for Water Removal The use of pervaporation membranes for water removal proposes a serious alternative which allows the water separation to operate at the same reaction temperature without any loss in selectivity. The Nb20s 3-10 %/Ce02 catalyst has been used in a flow reactor for several days coupled to a pervaporation membrane for water elimination [60] (Fig. 6.8). 

With pervaporation membranes the water can be removed during the condensation reaction. In this case, a tubular microporous ceramic membrane supplied by ECN [124] was used. The separating layer of this membrane consists of a less than 0.5 mm film of microporous amorphous silica on the outside of a multilayer alumina support. The average pore size of this layer is 0.3-0.4 nm. After addition of the reactants, the reactor is heated to the desired temperature, the recyde of the mixture over the outside of the membrane tubes is started and a vacuum is apphed at the permeate side. In some cases a sweep gas can also be used. The pressure inside the reactor is a function of the partial vapor pressures and the reaction mixture is non-boiling. Although it can be anticipated that concentration polarization will play an important role in these systems, computational fluid dynamics calculations have shown that the membrane surface is effectively refreshed as a result of buoyancy effects [125]. 

Separation of products from the reaction mixture In situ product removal from enzymatic reactor via a nanofiltration or ultrafiltration membrane Removal of selected enantiomer via a liquid membrane Removal of water in esterification reactions via a pervaporation membrane... 

A novel type of membrane reactor, emerging presently, is the pervaporation reactor. Conventional pervaporation processes only involve separation and most pervaporation set-ups are used in combination with distillation to break azeotropes or to remove trace impurities from product streams, but using membranes also products can be removed selectively from the reaction zone. Next to the polymer membranes, microporous silica membranes are currently under investigation, because they are more resistant to chemicals like Methyl Tertair Butyl Ether (MTBE) [23-24], Another application is the use of pervaporation with microporous silica membranes to remove water from polycondensation reactions [25], A general representation of such a reaction is ... 

Most of the research pertained on membrane reactors is carried out on gas phase reactions i using ceramic, metal or zeolite membranes. However, the concept can be used as well for liquid phase reactions. A verj specific class of reactions are the condensation or polycondensation reaction in which water is one of the products. Water is easily be removed by pervaporation (see section Vl.4.3 ) and therefore pervaporation can be applied if the reaction temperature is not too high. As example we will use here an esterification reaction [89,90]. This reaction may be carried out in a batch reactor coupled with a pervaporation unit in which water is removed constantly (see figure VI - 76). 

Pervaporation-assisted catalysis is a typical example of an operation eflide-ntly carried out in extractor-type catalytic membrane reactors. Esterification is by far the most studied reaction combined with pervaporation. " Esters are a class of compounds with wide industrial appUcation, from polymers to fragrance and flavour industries. Esterification, a reaction between a carboxylic acid and an alcohol with water as a by-product, is an equilibrium-limited reaction. So, this is a typical reaction that can be carried out advantageously in a extractor-type membrane reactor. By selectively removing the reaction product water, it is possible to achieve a conversion enhancement over the thermodynamic equilibrium value based on the feed conditions. 

Reaction cum pervaporation. This technology can be used for dewatering of organics, which is the removal of organics from waste water in place of the conventional distillation operation. A membrane is the heart of the operation. A combination of reaction and pervaporation, the latter of which occurs when placed in a loop around the reactor, replaces a condenser... 

The use of PIMRs in pervaporation has the advantage of the direct application of the well-established technology of the polymeric membranes used in solvent drying. For R2 type reactors in which the component to be removed is usually water, hydrophilic polymers are usually used, such as PVA or chitosan. On the other hand, for R1 type reactors, in which the extracted component is the desired product, usually less polar than water, the membrane material is a hydrophobic polymer (e.g., PDMS). ... 

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