CO2 permeance

The experimental results are summarized in Table 2. CO2 permeance (Rco2), selectivity (oicx)2/N2) and CO2 recovery (Y) increased with decreasing CO2 mole fraction in feed gas. CO2 in the feed gas was successfully concentrated to 97-99 % by the single-stage operation. CO2... 

Other promising separation data. Porous BaTiOs membranes have been prepared on alpha-alumina supports. A CO2 to N2 separation factor of 1.2 at 500 C which is higher than the Knudsen diffusion prediction of 0.8 has been obtained. If there had not been pinholes on the order of 100 nm in the membranes, the separation factor would have been higher [Kusakabe and Morooka, 1994]. The maximum CO2 permeance through the BaTiOs membranes is very high at 1.1x10 cm (STP)/s-cm -cm Hg. 

A polycrystalline Y-type zeolite membrane was formed by hydrothermal synthesis on the outer surface of a porous a-alumina support tube, which was polished with a finely powdered X-type zeolite for use as seeds. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 permeance was nearly equal to that for the singlecomponent system, and the N2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. At 30"C, the permeance of CO2 was higher than 10- mol m-2 s- Pa-, and the permselectivity of CO2 to N2 was 20-100. 

In order to determine the reproducibility of membrane formation, nine membranes of 3 cm length were formed under the same conditions except for reaction time. One membrane was accidentally fractured during the setup procedure. The others obeyed the same relationship between selectivity and permeance as indicated in Figures 3 (a) and (b). The CO2/N2 selectivity was decreased when the CO2 permeance exceeded 10" mol m s->Pa-. ... 

CO2 from O2 [27]. An aqueous solution of cesium bicarbonate (6.4 M) was immobilized in a porous cellulose acetate film. For a 5% CO2 feed gas at 1 atm and sweep side of CO2 partial pressure at 0.005-0.026 atm the CO2 permeance was about 8.9 x barter/cm and the separation factor... 

Recently, Bao et al. [68] compared the efficiency of facilitated transport of CO2 across a liquid membrane by different carriers (diethanolamine (DEA) and carbonic anhydrase (CA) + bicarbonate (NaHCO3) in a polypropylene HFCLM configuration. The hollow fibers used are made of polypropylene, pore size 0.04 pm. In all the experiments, the measured CO2 permeance and selectivity (CO2/O2) using CA bicarbonate as carrier was higher than in the case of DEA. The separation factor (CO2/O2) using DEA was about 152 which are 65% lower than the selectivity calculated with CA bicarbonate. 

In another work [51], glycerol carbonate was studied as a new physical solvent with and without carriers (poly(amidoamine) dendrimer and Na-glycinate) for carbon dioxide separation from CO2/N2 mixtures. The performance of pure glycerol carbonate appears to be independent of the CO2 partial pressure difference and the selectivity remains constant (80-100) for any value of the feed side moisture. Addition of the carriers significantly helps CO2 facilitation at low CO2 partial pressures. In particular, at 0.66 kPa the presence of the dendrimer and Na-glycinate increased the selectivity (CO2/N2) to 1000 and 480, respectively. It was also proved that the decrease of membrane thickness did not affect the selectivity (90-100), which was similar either for 25 and 250 pm thickness membranes, but slightly increased the CO2 permeance. 

We have developed a one-dimensional non-isothermal model for the countercurrent WGS membrane reactor with a C02-selective membrane in the hollow-fiber configuration using air as the sweep gas. Figure 1 shows the schematic of each hollow-fiber membrane with catalyst particles in the reactor. The modeling study of the membrane reactor is based on (1) the CO2 / H2 selectivity and CO2 permeance reported by Ho [1, 2] and (2) low-temperature WGS reaction kinetics for the commercial catalyst copper oxide, zinc oxide, aluminum oxide (CuO/ZnO/ AI2O3) reported by Moe [3] and others [4]. In this modeling study, the model that we have developed has taken into account critical system parameters including temperature, pressure, feed gas flow rate, sweep gas (air) flow rate, CO2 permeance, CO2 /H2 selectivity, CO concentration, CO conversion, H2 purity, H2 recovery, CO2 concentration, membrane area, water (H20)/C0 ratio, and reaction equilibrium. 

Thickness of selective silica layer Length of membrane Outer diameter of ceramic membrane Volume of membrane reactor CO2 permeance (200 bar, 353 K)... 

H2/CO2 stream without MDBS vapour. The second modification of the membrane resulted in a further increase in the H2 separation factor from 57 to a stable value of 123 under the feed containing MDBS vapour, with only a small decrease in H2 permeance to 2.2 x 10 mol/m s Pa. After the termination of feeding MDBS, the H2 separation factor stabilized at 108 in about 24 h with a virtually unchanged H2 permeance and a slightly increased CO2 permeance. 

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... 

Besides the experimental investigation, the theoretical researches on the CO2 capture over CNT were also reported. For example, Liu et al. [155] have shown, from molecular dynamics simulations, that the windowed CNTs are able to separate CO2 from the CO2/CH4 mixture with a CO2 permeance several orders of magnitude higher than the conventional analogs (Fig. 2.26). 

Fig. 7.10 CO2 permeance as a function of temperature and composition for modified silica membrane. Reprinted from Ref [48], Copyright 2011, with permission from Elsevier...

AU these factors combined result in increasing CO2 permeances with increasing temperature at a given partial pressure. 

Figures 7.13 and 7.14 show the data for the CO2/N2 separation factor and the CO2 permeance for the ALD-APTS-modified manbrane along with results for APTS membrane (without ALD the modification was done on a 5 nm Vycor substrate). As can be seen from these Figs, there is no hysteresis between the three conditions with respect to the separation factor. As far as the permeance is concerned, there is a bit of hysteresis between condition (a) and conditions (b) and (c). Also overaU, the separation characteristics of the ALD-APTS manbrane are better by about 30 % than those of APTS membrane, which is probably due to the smaller starting pore size of the substrate. Thus, we can conclude that a reduction in the pore size of the starting material can gready influence the separation characteristics.

Gas testing of these membranes for carbon capture applications showed an enhanced CO2 permeance up to 1830 GPU, without a significant drop in CO2/N2 selectivity at 35°C and 350 kPa, relative to a pure PEBAX upper layer. The impacts of temperature and pressiue on membrane performance were investigated for temperatures from 25°C to 55°C and pressures from 100 kPa to 500 kPa. 

Theoretical calculations indicated that in the absence of a gutter layer, the upper layer could achieve a CO2 permeance of over 3000 GPU with a CO2/N2 selectivity of 22. These results represent a significant increase in the gas permeance (72). 

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