Microporous silica membranes membrane reactor

Kurungot, S., Yamaguchi, T., Nakao, S.-L, Rh/y-AljOj catalytic layer integrated with sol-gel synthesized microporous silica membrane for combact membrane reactor applications, Catal. Lett. 2003, 86, 273-278. 

The results obtained for microporous silica membranes in the membrane steam-reforming project, described in this thesis, provide favourable perspectives to realise a Th-permselective membrane reactor for the dehydrogenation of H2S. Realisation of such a reactor, however, imposes significant scientific and technical challenges. 

Apart from esterifications, dehydrations, condensations, oxidations, Diels-Alder alkylation, and hydrogenations also have been coupled to PV. In the production of alkyl coating resins at temperatures as high as 150-300° C, the use of microporous silica PV-membranes has been successfully investigated. A mixture of acids, acid anhydrides, and alcohols reacts to form a resin and water. In a kilogram-scale unit, energy savings turned out to be 40% and reactor efficiency increased by 30%. 

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)... 

Koutsonikolas, D., Kaldis, S., Zaspalis, V. T., Sakellaropoulos, G. P. (2012). Potential application of a microporous silica membrane reactor for cyclohexane dehydrogenation. International Journal of Hydrogen Energy, 37, 16302—16307. 

Microporous silica membranes fundamentals and applications in membrane reactors for... 

Key words microporous silica, membrane reactors, water-gas shift reaction, autothermal reforming, steam reforming. 

Microporous silica membranes operate on a molecular sieving principle and are usually tailored to separate H2 from other, larger, gases. Hence their incorporation into membrane reactor technology is most suited to those reactions that either consume or produce H2 and especially, given their thermal stability, for those reactions involving H2 that occur at temperatures up to 800°C. This section explores the membrane reactor performance of several of the catalytic reactions where silica-based membranes have been effectively demonstrated at the research level. 

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 ... 

The insertion of catalytically active guests, such as transition metal ions, is an example of the potentialities of zeolite membranes for applications in catalytic membrane reactors. The well-known catalytic properties of supported vanadium oxides for selective oxidations have recently prompted a number of studies on the possibility of inserting vanadium in the framework of crystalline microporous silica and aluminosilicate powders. " ... 

Ref. 192) The setup of the continuous flow membrane reactor is shown in Figure 4.6. A microporous silica membrane with an average pore size of 0.6 nm was used in the reactor. The characteristics of the reactor are summarized in Table 4.4. First, the active catalyst was generated in situ in a high-pressure reactor from [RhCl(COD)]2 and P(C6H4-/t-SiMe2CH2CH2C8Fiv)3, which were introduced into the system by... 

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]. 

Table 2.7 summarizes some of the dehydrogenation reactions studied in the literature using porous MRs. As can be seen, the membranes for dehydrogenation reactions are primarily microporous silica due to it high hydrogen perm-selectivity. Meso- or macroporous membranes are not suitable for dehydrogenation reactions because their low perm-selectivity may lead to much loss of the reactants. The catalysts for dehydrogenation may be packed in the reactor or loaded inside the membrane wall. All the studies demonstrate enhanced conversions or even beyond-equilibrium values. 

The dimerization of isobutene carried out in a forced-flow polymeric catalytic membrane reactor was reported by D. Fritsch and co-workers. The authors prepared composite porous membranes consisting of a catalytic layer made of solid add catalysts, such as siUca supported Naflon , Nafion NR50, Amberlyst 15 and silica supported tungstophosphoric add dispersed in polymeric binders such as Teflon AF, Hyflon AD, polytrim-ethylsilylpropyne, or polydimethylsiloxane (PDMS), cast on microporous support membranes made of polyacrylonitrile (PAN) or Torlon . The membranes were assembled in the membrane reactor into which isobutene was fed in the retentate side with a build-up pressure of 4 bar. The liquid product was collected on the permeate side. 

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