SAPO-34 membranes

Zhang LX, Jia MD, and Min EZ. Synthesis of SAPO-34/ceramic composite membranes. Stud Surf Sci Catal 1997 105 2211-2216. Poshusta JC, Noble RD, and Falconer JL. Characterization of SAPO-34 membranes by water adsorption. 7 Membr Sci 2001 186 25 10. Li SG, Falconer JL, and Noble RD. SAPO-34 membranes for CO2/CH4 separation. J Membr Sci 2004 241 121-135. 

Among the numerous strategies which have been adopted to produce zeolite membranes with either a reduced number of defects or with specific properties, a series of modification techniques have been tested. Most of them are listed in [491. One can namely mention isomorphous substitutions of e.g. Al, Fe, B, or Ge in the structure, ion exchange, silylation, atomic layer deposition (ALD), chemical vapor deposition (CVD), coking, catalytic cracking, and reactions with adsorption sites in the zeolite structure. Silylation is very attractive for increasing the selectivity of zeolite membrane to H2 [122], MFI and SAPO-34 membranes have been recently modified by silylation and atomic layer deposition (ALD) to create H2 selective membranes [123],... 

Li et al. [54] increased the length of their tubular SAPO-34 membranes by a factor of 5 by controlling thoroughly the synthesis conditions. Sato et al. [55] have developed industrial size (40 cm long) chabazite (CHA)-type zeolite membranes by controlling the synthesis conditions and used them in pervaporation showing that continuous research is devoted in this field to be able to compete with polymeric membranes. 

Poshusta JC, Noble RD, Falconer JL. Characterization of SAPO-34 membranes by water adsorption. J Membr Sci 2001 186 25-40. 

Avila AM, Funke HH, Yanfeng Z, Falconer JL, Noble RD. Concentration polarization in SAPO-34 membranes at high pressures. J Membr Sci 2009 335(1-2) 32-36. 

SAPO 34 zeolite has pores similar to the kinetic diameter of the CH4 (3.8 A) but larger than that of CO2 (3.3 A) and for this reason exhibited also a good CO2/CH4 separation factor. SAPO-34 membranes, prepared by the one step method, present a maximum in CO2 permeance at 2 °C for both single and binary systems. Moreover, the CO2/CH4 selectivity decreases with the temperature in the range from 2 to 200 °C. The highest selectivity value (67) was found at 25... 

Figure 17.12 Revised Robeson upper bound for CO2/N2. Reprinted from The upper bound revisited , Journal of Membrane Science, 320, 390-400,2008, with permission from Elsevier. Data point of SAPO-34 membrane is also shown for comparison. Reprinted from S. Li and C. Q. Fan, High flux SAPO-34 membrane for CO2/N2 separation. Industrial and Engineering Chemistry Research, 49, 4399-4404, 2010, with permission from ACS.

With SAPO-34 membrane Noble and co-workers separated H2 from CH4 since this latter gas has its kinetic diameter close to the membrane pore size. 

CO2/H2 selectivity versus the temperature, (b) (CO2-H2 mixture 54-46 (S) single and (M) mixture). Reprinted from M. Hong, S. Li, J. L. Falconer and R. D. Noble, Hydrogen purification using a SAPO-34 membrane, Journal of Membrane Science, 307, 277-283, 2008, with permission from Elsevier. 

In 2001, Masuda et al. (2001) developed a catalytic cracking deposition (CCD) technique for zeolitic pore size reduction to enhance the H2 separation factor of MFI zeolite membranes. After the CCD modification, the zeolite pore size was reduced to about 0.36—0.47 nm, and the H2/CO2 separation factor of MFI zeolite membranes was enhanced from 1.5—4.5 to more than 100. However, the H2 permeance of the modified membrane was only about one-tenth of the fresh membrane. Using the method developed by Masuda et al., Falconer and co-workers modified B-ZSM-5 and SAPO-34 membranes for the enhancement of H2/CO2 separation factor (Hong, Falconer, Noble, 2005). Similarly, the H2/CO2 separation factor of the modified membrane was increased to 48, while the H2 permeance of the B-ZSM-5 membrane was decreased by more than one order of magnitude. 

A similar situation is observed for the separation of CO2/CH4 on a SAPO-34 membrane [6,7] (i.e. mutual diffusion leads to higher separation)factors than those predicted from the simplified Habgood model. 

Figure 6. Permeance and selectivity for CO2/ (50/50 mixture) in a SAPO-34 membrane as a function of temperature. Note the mixture selectivity is greater than the ideal selectivity predicted from single component permeances [6].

A supported SAPO-34 membrane has been developed using the seeding technology which can separate a COj/CH mixture with a selectivity of 115 and a reasonable CO permeance of 4x1 0 mol m s Pa at the feed pressure of 70 bar [3]. Also a supported DD3R zeolite membrane can separate CO from CH with a selectivity of over 4000 at 225 K and 1 bar of the equimolar feed [4,5], The Robeson upper bound showing the limit of polymer membrane performance is from 1991. From Van den Bergh J, Zhu W, Kapteijn F, Moulijn JA, Yajima K, Nakayama K, etal. Separation ofCO and CH by a DDR membrane. Res Chem Intermediates 2008 34 467-74, with permission. 

Li SG, Falconer JL, Noble RD. Improved SAPO-34 membranes for CO /CH separations. Adv Mater... 

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