MFI zeolite membrane reactors

S., Fiaty, K., and Dalmon, J.-A. (2000) Experimental smdy and numerical simulation of hydrogen/isobutane permeation and separation using MFI-zeolite membrane reactor. Catal. Today, 56 (1-3), 253-264. 

Lin s group [49] synthesized bilayer MFI zeolite membrane reactor for WGS reaction. They investigated the membrane reactor for long-term... 

Illgen U et al (2001) Membrane supported catalytic dehydrogenation of iso-butane using an MFI zeolite membrane reactor. Catal Commun 2 339-345... 

Separation factor of MFI membranes for H2 i-C4Hio mixture. Reprinted from U. Illigen, R. Schafer, M. Noack, P. Kolsch, A. Kuhnle and J. Caro, Membrane supported catalytic dehydrogenation of isobutane using an MFI zeolite membrane reactor . Catalysis Communications, 2, 339-345, 2001, with permission from Elsevier. 

Improved selectivity in the liquid-phase oligomerization of i-butene by extraction of a primary product (i-octene C8) in a zeolite membrane reactor (acid resin catalyst bed located on the membrane tube side) with respect to a conventional fixed-bed reactor has been reported [35]. The MFI (silicalite) membrane selectively removes the C8 product from the reaction environment, thus reducing the formation of other unwanted byproducts. Another interesting example is the isobutane (iC4) dehydrogenation carried out in an extractor-type zeolite CMR (including a Pt-based fixed-bed catalyst) in which the removal of the hydrogen allows the equilibrium limitations to be overcome [36],... 

MFI zeolite membranes (silicalite-1, ZSM-5), on either flat or tubular porous supports, have been the most investigated for gas separation, catalytic reactors, and pervaporation applications. The structural porosity of MFI zeolite consists of channels of about 5.5 A, in diameter, the sihca-rich compositions induce... 

MFI zeolite membranes at 450 500°C. confirming the possible application of an MFI zeolite membrane for use in a catalytic membrane reactor. 

Similarly, Mota et al. [297] carried out the selective oxidation of butane to maleic anhydride over VPO mixed oxides-based catalysts enclosed in an MFI membrane. Different feed configurations of the zeolite-membrane reactor were tested in order to outperform the conventional co-feed configuration. The results achieved were rather similar however, the authors pointed out the possibility to take advantage of the O2 distribution, which limits the flammability problems and allows operation with higher butane concentrations than those used in conventional processes. 

Another way to control the residence time of valuable intermediate products within the reactor is to use a selective membrane to remove them from the reaction environment as they are produced before they can react further in consecutive reactions. Therefore, it is a classical example of an IMR in which a considerable increase in the yield to the desired product can be obtained, provided that the membrane is sufficiently selective to the intermediate product under reaction conditions. Regarding this approach, Piera et al. [311] solved the selectivity problem already discussed in the oligomerization of i-butene by removing selectively the i-octene formed using an MFI zeolite membrane surrounding a fixed bed of... 

Pd-based alloy and modified MFI zeolite membranes are the best candidates to be used as membrane reactors for simultaneous WGS reaction and H2 separation in the coal gasification process. For Pd-based membranes, thermodynamic calculations... 

Zeolite membranes show high thermal stability and chemical resistance compared with those of polymeric membranes. They are able to separate mixtures continuously on the basis of differences in the molecular size and shape [18], and/or on the basis of different adsorption properties [19], since their separation ability depends on the interplay of the mixture adsorption equilibrium and the mixture. Different types of zeolites have been studied (e.g. MFI, LTA, MOR, FAU) for the membrane separation. They are used still at laboratory level, also as catalytic membranes in membrane reactors (e.g. CO clean-up, water gas shift, methane reforming, etc.) [20,21]. The first commercial application is that of LTA zeolite membranes for solvent dehydration by pervaporation [22], Some other pervaporation plants have been installed since 2001, but no industrial applications use zeolite membranes in the GS field [23]. The reason for this limited application in industry might be due to economical feasibility (development of higher flux membranes should reduce both costs of membranes and modules) and poor reproducibility. 

Synthesis of membranes with high permeability and selectivity, that is, oriented and thin zeolite membranes. Optimal MR operation requires the membrane flux to be in balance with the reaction rate. A large number of factors - such as the support, organic additives, temperature, and profile - have a significant influence on the microstructure and overall quality of the membrane. However, the precise correlation between the synthesis procedure and conditions and the properties of the resultant zeolite membranes is not clear. In contrast, the majority of membranes synthesized so far are MFI-type zeolite membranes that have pore diameters 5 A, which are still too big to separate selectively small gaseous molecules. Zeolite membranes with pores in the 3 A range should be developed for membrane reactors, to separate small gas molecules on the basis of size exclusion. In addition, a method to produce zeolite membranes without non-zeolite pores or defects has to be found. 

Daramola M O, Burger A J and Giroir-Fendler A (2011), Modelling and sensitivity analysis of a nanocomposite MFI-alumina based extractor-type zeolite catalytic membrane reactor for m-Xylene isomerization over Pt-HZSM-5 catalyst , Chem Eng J, 171,618-627. 

---