Engineering Solutions for CO2 Conversion. Группа авторов

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Engineering Solutions for CO2 Conversion - Группа авторов


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or separation factor of polymer membranes, it is defined as a product of mobility selectivity, (Di/Dj) the fraction of the diffusion coefficients of the two gases, the solubility coefficient ( Si/Sj), and the ratio of the solubility coefficients of the two gases.

      (3.2)alpha Subscript italic i j Baseline equals alpha Subscript upper D Baseline dot alpha Subscript upper S Baseline equals left-bracket StartFraction upper D Subscript i Baseline Over upper D Subscript j Baseline EndFraction right-bracket dot left-bracket StartFraction upper S Subscript i Baseline Over upper S Subscript j Baseline EndFraction right-bracket

      (3.3)v Subscript normal f Baseline equals StartFraction v minus v 0 Over v EndFraction

Graph depicts the diffusion and solubility coefficient for different polyimides.

      Source: Adapted from Baker and Tanaka et al. [16, 17].

      where v is the specific volume of the polymer (cm3 g−1), i.e. the correlative of the polymer density, and v0 is the volume occupied by the polymer molecules (cm3 g−1). In principle, FFV is the sum of all the spaces between the polymer chains.

      Nowadays, polymer membranes for CO2 capture are being intensively investigated, specifically regarding post‐combustion carbon capture (CO2/N2), hydrogen purification (CO2/H2), and natural gas sweetening (CO2/CH4) [19]. In terms of post‐combustion carbon capture, competing with chemical absorption, gas separation membranes appear as a more environmentally friendly solution. As an example, a simulation of two potential polymer membranes, Polyactive® and PVAm/polyvinyl alcohol membranes, was performed for a 600 MW (gross) reference power plant [20]. Other materials, such Pebax, were also investigated for similar purposes, regarding CO2 capture in post‐combustion processes [21].

      With regard to natural gas sweetening, or in other words, CO2 removal from natural gas, membrane systems show greater potential than conventional chemical absorption because they have main advantages such as low cost, environmentally friendly technologies, and process flexibility [25]. Several commercial membranes are available for CO2 elimination from natural gas. The most common representative materials for CO2 removal are cellulose acetate/triacetate and polyimide [25].

      In order to study the properties of different membrane materials, and to be able to compare different polymer materials, Robeson published several charts, the first time in 1991 and the latest in 2008, about membrane permeability as a function of selectivity. These charts are called upper bound correlation [26, 27]. These experimental data are obtained from single gas tests at 30 °C and 1 bar. This indicates that permeabilities were measured using pure gas tests, and selectivities were obtained from the ratio of the pure gas permeabilities. This gives ideal selectivities, despite the fact that industrial processes of gas separation membranes are commonly performed with gas mixtures. Nevertheless, it is possible to extrapolate to industrial applications, this is because, in principle, if gases do not interact with the membrane material, the difference between single gas selectivity and gas mixture selectivity will be small. Consequently, in gas mixtures, molecules that possess high‐solubility coefficients will be sorbed enough by the membrane material to affect the other gas permeabilities.

Schematic illustration of the upper bound correlation for (a) CO2/CH4 separation and (b) CO2/N2 separation in 2008.

      Source: Kim and Lee [28].

      The application of strategies for capturing the CO2 from combustion processes is of great importance for effectively implementing CO2 conversion approaches and thus reducing the impact of industrial activity regarding CO2 emissions. Oxyfuel technology is one of the most considered options for conducting the implementation of this capture and sequestration of CO2 from exhaust


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