CO2/CH4 separation

The well-adhered interface resulted in defect-free mixed-matrix membranes with some improved performance for CO2/CH4 separation. 

M. Anson, J. Marchese, E. Garis, N. Ochoa, and C. Pagliero, ABS copolymer-activated carbon mixed matrix membranes for CO2/CH4 separation,. Membr. Sci., 243(l-2) 19-28, November 2004. 

D.Q. Vu, W.J. Koros and S.J. Miller, High Pressure CO2/CH4 Separations Using Carbon Molecular Sieve Hollow Fiber Membranes, Ind. Eng. Chem. Res. 41, 367 (2002). 

FIGURE 8 Literature data for CO2/CH4 separation factor vs CO2 permeability. 

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. 

If blending could raise the solubility selectivity from two to four without a serious loss in CO2 permeability, the resultant material would be quite attractive as a membrane for CO2/CH4 separations. 

The SAPO-34 structure is three-dimensional, with a pore diameter of 0.38 nm, and H—SAPO-34 has mild-to-moderate acidity. The separation of gases, such as CO2 and CH4, can be achieved by using H—SAPO-34 zeolite membranes modified with Li+, Na+, K+, NH4+, and Cu + as ion exchangers [6]. It was verified that the presence of the cations on the zeolite increases the CO2—CH4 separation selectivities up to 60%. 

M. Pourafshari Chenar, M. Soltanieh, T. Matsuura, A. Tabe-Mohammadi, and K. C. Khulbe. The effect of water vapor on the performance of commercial polyphenylene oxide and cardo-type polyimide hollow fiber membranes in CO2/CH4 separation applications. J. Membr. ScL, 285(l-2) 265-271, November 2006. 

Uddin MW, Hagg MB. Natural gas sweetening—The effect on CO2-CH4 separation after exposing a facilitated transport membrane to hydrogen sulfide and higher hydrocarbons. J Membr Sci 2012 423-124 143-149. 

Small-pore DDR membranes have been used [81] showing CO2/CH4 separation factors as high as 220 at 301 K. Again, DDR membranes have pores (0.36 x 0.44 mn) that are similar in size to CH4, and therefore, a configurational impediment to the flux of methane takes place in addition to the preferential adsorption of CO2. DD3R zeolite manbranes have also excellent separation performance for CO2/CH4 mixtures (selectivity 100-3000) and exhibit good selectivity for N2/CH4 (20-45), CO2 and NO/air (20 100), and air/BCr (5-10) and only a modest selectivity for O2/N2 (similar to 2) separation [120]. 

New materials with improved CO2/CH4 separation selectivity and membrane stability under realistic NG conditions have been developed however, even after three decades of development, only three membrane material types have been commercialized cellulose acetate-based Separex (Honeywell s UOP), Cynara (Cameron) membranes, polyimide-based membranes from Medal (Air Liquide) and Ube, and per-fluoropolymer-based Z-top membranes from Membrane Technology and Research, Inc. (MTR). The key reasons for the selection of the desired polymer for commercialization are the cost of material, ease of fabrication into commercially viable form, effect of impurities on membrane performance, and gas selectivity under realistic feed conditions. 

Staudt-Bickel, C. and W.J. Koros, Improvement of CO2/CH4 separation characteristics of polyimides by chemical crosslinking. Journal of Membrane Science, 1999. 155(1) 145-154. 

Vu, D.Q., Koros, W.J. and Miller, S.J. (2002) High pressure CO2/CH4 separation using carbon molecular sieve hollow fiber membranes. Industrial Engineering Chemistry Research, 41 (3), 367-380. 

Palomino, M., Corma, A., Jorda, J.L., Rey, F., Valencia, S. Zeolite Rho a highly selective adsorbent for CO2/CH4 separation induced by a structural phase modifieation. Chem. Commun. 48, 215-217 (2012)... 

Zeolite membranes with different topology were studied for CO2 separation from light gases. Table 17.5 reports some of the different results present in the open literature about CO2/N2 and CO2/CH4 separations. 

Table 17.5 Comparison of CO2/N2 and CO2/CH4 separations with zeolite membranes...

Figure 17.8 CO2/CH4 separation factor (a) as function of the total feed pressure at 303 K and (b) as a function of the temperature at a total feed pressure of 101.3 kPa. (Open symbols are the ideal selectivity). Reprinted from W. Zhu, P. Hrabanek, L. Gora, F. Kapteijn and J. Moulijn, Role of adsorption in the permeation of CH4 and CO2 through a silicalite-1 membrane, Industrial and Engineering Chemistry Research, 45, 937-944, 2006, with permission from ACS.

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... 

In summary, porous carbon-based materials for CO2 capture have experienced rapid development in the last several decades and will continue to blossom. The requirements of CO2 captures vary a lot depending on different processes, namely post-combustion (low pressure, predominantly CO2/N2 separation), pre-combustion (high pressure, predominantly CO2/H2 separation) capture and natural gas sweetening (predominantly CO2/CH4 separation). Thus, various kinds of new carbon materials with defined textural properties as well as tailored surface chemistry have been synthesized for a specific CO2 capture process. Another advantage lies... 

Polybutadiene/polycarbonate membranes with a pp-ethylenediamine layer had an increased gas permeability (in comparison with the unmodified one) due to surface etching. Their selectivity was closely connected with the chemical composition of the top layer. A high nitrogen content was required for high O2 selectivity (Ruaan et al. 1998). The presence of the amine groups on the membrane surface also enhanced the capacity for CO2/CH4 separation. The plasma-polymerized diisopropylamine on the surface of the composite membrane—porous polyimide (support)/ silicone (skin)— made the separation coefficient as high as 17 for a permeation rate of 4.5 X cmVcm sec cmHg (Matsuyama et al. 1994). 

Hosseini, S.S. and Chung, T-S. 2009. Carbon membranes from blends of PBI and polyimides for N2/CH4 and CO2/CH4 separation and hydrogen purification, 328 ... 

A. Bos, High pressure CO2/CH4 separation with glassy polymer membranes, PhD Thesis, Twente, 1996. 

The properties of Hyflon AD 60X are clearly improved by the presence of silicalite-1. As can be seen in Figure 6.5a the CO2/CH4 separation factor gets closer to the Robeson s upper bound. Although other polymers have higher separation factors, the resistance to plasticization of medium free-volume perfluorinated polymers [4,9] makes this polymer/... 

For CO2/CH4 separation, more attractive behaviour is observed (Figure 8.7). The values of a(C02/CH4) of the hybrid membranes prepared solely with TMOS increase with increasing sihca content in connection with increased CO2 permeability. The remarkable CO2/CH4 separation behaviour of the HBPI-sihca hybrid membranes prepared with TMOS is considered to be due to the characteristic distribution and interconnectivity of free volume elements created by the incorporation of sihca, which provides a size-selective CO2/CH4 separation ability [11]. On the other hand, 0 (CO2/CH4) values of the... 

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