Robeson upper bound

Figure 8.4 The compression power used and membrane area required for nitrogen membrane production as a function of membrane selectivity. The membrane permeability used for each selectivity is taken from the Robeson upper-bound trade-offline shown in Figure 8.3. All numbers are shown relative to a membrane with a selectivity of 6 and an oxygen permeability of 0.8 Barren...

Figure 15.1 Comparing the CO2/CH4 Robeson upper bound for dense and thermally rearranged (TR) polymer membranes to the carbon membranes/ and the region for industrial applicability was suggested by Hillock et alf (Data for CMS membranes and industrial applicability region added to the original Robeson plot.)...

In order to compare the performance for polymeric and carbon membranes, Figure 15.13 shows a CO2/CH4 trade-offline for P84 and Matrimid precursors and their carbon membranes as reported by Tin et al It is clear that carbon membranes possess excellent permeation properties, where both of the permeability and ideal selectivity access the Robeson upper-bound curve. Moreover, some researchers have also investigated the influence of temperature on the gas permeability.They concluded that the gas permeability values increased with the increase of temperature due to the activated process for the CMS membranes. They also found that the apparent activation energies for CO2 calculated from the Arrhenius equation Pe = Peo Qxp(-EJRT)) was much smaller than the other gas species of O2, N2 and CH4, thereby indicating that CO2 has much higher permeability. 

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.

Figure 2.4 Double logarithmic plots of selectivity against permeability for the gas pairs (a) O2/N2, (b) CO2/CH4 and (c) CO2/N2, showing the 1991 Robeson upper bound (solid line), [23] the 2008 Robeson upper bound (dashed line), [24] literature data [16] for various polymers measured since 1991 ( j, and measurements for PlM-1 in state 1 (x), state 2 (O) and state 3 (%)...

The latter was recently further elaborated by Rowe et al. in order to correlate permeability directly to o-Ps lifetime from PALS analysis [44]. Freeman discussed the physical basis for the Robeson upper bound, closely related to the fractional free volume and to penetrant size ratio [45]. 

Robeson upper bound 10 Robeson upper bound... 

Han et al. investigated the gas separation behavior of the PBOs (Figure 5.57) prepared from thermal rearrangement of the fluorinated o-HPAs [80]. The thermal rearrangement occurred at a comparatively low temperature (350 °C) than the precursor poly-imides. The cavity sizes and distribution of FFV elements were tuned to obtain a higher combination of permeability (Phj = 206 Barrer) and selectivity by changing the precursor HPA structure and thermal treatment. The reduction of CO2 solubility for PBO in comparison to the precursor HPAs improved the H2/CO2 selectivity (a = 6.2 at 210 °C, in which Ph2 > 200 Barrer) and moved the membrane performance to polymeric upper bound (Robeson upper bound). 

Figure 4 Schematic presentation of the trade-off between permeability and selectivity with the 1991 and 2008 Robeson upper bounds.In most cases, the technologically attractive region lies around or above the Robeson upper bound...

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. 

Hj/COj separation performance of pure PBI and ZIF-7/polybenzimidazole (PBI) nano-composite membranes compared to the Robeson upper bound (open symbols pure gas separation performance closed symbols mixed-gas separation performance). From YangT, Xiao Y, ChungTS. Poly-/metal-benzimidazole nano-composite membranes for hydrogen purification, Ener f Environ Sci... 

State of the Art A desirable gas membrane has high separating power (ot) and high permeability to the fast gas, in addition to critical requirements discussed below. The search for an ideal membrane produced copious data on many polymers, neatly summarized by Robeson [J. Membrane ScL, 62, 165 (1991)]. Plotting log permeability versus log selectivity (ot), an upper bound is found (see Fig. 22-73) which all the many hundreds of data points fit. The data were taken between 20-50°C, generally at 25 or 35°C. 

Robeson []. Membrane ScL, 62, 165 (1991) Polymer, 35, 4970 (1994)] has determined upper-bound hnes for many permeant pairs in hundreds of polymers. These hnes may be drawn from Eq. (22-109) and the data included in Table 22-28. These values will give in Barrers a is dimensionless. Robeson [op.cit., (1991) op. cit., (1994)] hsts high-performance polymers for most of these gas pairs, hke Table 22-28. 

Figure 8.29 Cost of oxygen-enriched air produced by membrane separation on an EP02 basis as a function of the oxygen permeability and oxygen/nitrogen selectivity of the membrane. The performance of today s best membranes is represented by the upper bound performance line from Robeson s plot (Figure 8.24) [35,47]. Reprinted from J. Membr. Sci. 62, B.O. Bhide and S.A. Stem, A New Evaluation of Membrane Processes for the Oxygen-enrichment of Air, p. 87. Copyright 1991, with permission from Elsevier...

The above-mentioned inverse selectivity/permeability relationship of polymers has been summarized by Robeson by means of log-log plots of the overall selectivity versus the permeability coefficient, where A is considered to be the more rapidly permeating gas. These plots were made for a variety of binary gas mixtures from the list He, H2, O2, N2, C02, and CH4, and for a large number of rubbery and glassy polymer membranes. Such representations, shown in Fig. 8 and Fig. 9 are often referred to as upper bound plots (Robeson, 1991). The upper bound lines clearly show the inverse selectivity/permeability relationship of polymer membranes. While these plots were prepared in 1991, only small advances have been made to push the upper bound higher since that time. 

Attempts to circumvent an apparent upper bound on gas permeability and selectivity through polymeric membranes [Robeson, 1991]... 

Although these rules can lead to increased permeability and selectivity, an extensive compilation of the data in the literature by Robeson suggests an upper bound exists on transport properties - increases in permeability eventually lead to a decrease in selectivity and vice versa [38]. Figure 10 illustrates the upper bounds that exist for a number of gas pairs such plots of selectivity versus permeability are referred as Robeson plots . As one might expect, a similar upper bound exists for pervaporation membranes used to separate benzene-cyclohexane mixtures [39]. 

Mehta and Zydney [41] show a similar relationship exists for ultrafiltration membranes where transport through the membrane occurs by convective pore flow. A Robeson plot was created by taking the selectivity of an ultrafiltration membrane as the reciprocal of the protein sieving coefficient (the ratio of protein concentration in the permeate to that in the fluid adjacent to the membrane surface) and the permeability as the solvent hydraulic permeability. A plot of literature data for bovine serum albumin separation shows the existence of an upper bound. The location of the upper bound was predicted assuming the... 

---