Carbon capture membrane processes

The combination of a less-constrained ASU for oxygen production and a carbon capture process using membranes instead of amine solvents can conduce to a minimal energy requirement associated with an oxygen purity ranging between 0.5 and 0.6 molar fraction. 

The following example illustrates the potential of membrane-separation processes for precombustion carbon capture in an IGCC. This approach avoids using an expensive air-separation unit (asu) or a difficult-to-implement high-temperature mixed-ion conducting membrane process however, it still enables capture of C02 at purities suitable for commercial use or sequestration. 

Bounaceur R., Lape N., Roizard D., Vafiieres C., Favre E. 2006. Membrane processes for post-combustion carbon dioxide capture A parametric study. Energy 31 2556-2570. 

Favre, E., Membrane processes and postcombustion carbon dioxide capture Challenges and prospects. Chemical Engineering Journal, 2011. 171(3) 782-793. 

Sulfur dioxide has also been reported to plasticize polymeric membranes, which produces a more rubbery material and increases the diffusivity of penetrant gases [26-28]. Plasticization also reduces the mechanical integrity of the membrane, meaning it is more likely the membrane will rupture. However, plasticization is a strongly pressure dependent phenomenon, for example it has been reported in polyvinylidene membranes to occur at SO2 pressures greater than 10 psi [29]. For many of the processes in carbon capture, such high partial pressures of SO2 are not observed (Table 11.1), and therefore only minor plasticization by SO2 is likely to occur. 

R. Bounaceur, N. Lape, D. Roizard, C. Vallieres, E. Favre, Membrane processes for postcombustion carbon dioxide capture A parametric study, Energy, 31, 2556-2570 (2006). 

Figure 2.8 Example of carbon dioxide separation from power plant flue gas using a two-step membrane process with two options for managing the permeate from the second membrane step. In Option 1 purple double-dotted lines), air is used directly in the burner while a vacuum pump creates partial pressure driving force in the second membrane step with return of the second step permeate to front of membrane process. In Option 2 blue dashed lines), the combustion air is used as a countercurrent permeate sweep gas in the second membrane step. Adapted from Figs. 11 and 12 in Merkel TC, Lin H, Wei X, Baker R. Power plant post-combustion carbon dioxide capture an opportunity for membranes. J Membr Sci 2010 359(1—2) 126—139.

Li X-S, Xia Z-M, Chen Z-Y, Wu H-J (2011) Precombustion capture of carbon dioxide and hydrogen with a one-stage hydrate/membrane process in the presence of tetra-n-butylammonium bromide (TBAB). Energy Fuels 25(3) 1302-1309... 

Carbon membranes are still in their infancy as a technology, yet the promise they hold is enormous. Already we know that nanoporous (0.5-1.0 nm average pore size) carbon membranes show an especially high affinity for carbon dioxide transport, a property that will undoubtedly be of utility in carbon capture and sequestration. They are robust enough to withstand use in aqueous media and at either high or low pH. When engineered with mesopores (1.0-3.0 nm), they can be used to provide ultrafiltration of water and other process flttids. In combination with catalysts, they are able to combine reaction and separation, thereby providing a viable means to... 

Table 2.1 Carbon capture strategies, currently best available capture technologies, and tentative breakthrough membrane separation processes...

Carbon capture strategy Gas mixture Currently best available separation process Possible breakthrough membrane process... 

A general sketch of the inlet-outlet boundary conditions which will be defined for the carbon dioxide capture process, according to the previous analysis, is presented on Figure 2.1. The membrane process simulation framework will be presented in the next paragraph, based on a binary feed mixture in a first step, as explained above. 

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