Carbon dioxide self-diffusion

In biphasic reactors or two-phase partitioning bioreactors (TPPB), the substrate is located mostly in the immiscible phase and diffuses to the aqueous phase. The enzyme catalyzes conversion of the substrate at the interface and/or in the aqueous phase. The product/s of the reaction then may partition to the organic phase. The system is self-regulated, as the substrate delivery to the aqueous phase is only directed by the partitioning ratio between the two phases and the enzymatic reaction rate [53]. The use of ionic liquid/supercritical carbon dioxide for enzyme-catalyzed transformation is gaining attention [69]. 

The self-diffusion of carbon dioxide in single pellets of commercial type 5A molecular sieve has been studied using C 02 as a tracer. Experiments were carried out at atmospheric pressure between - -25° and —2S°C. Using a simple model of the pellet structure, it was possible to deduce effective diffusivities for both pore and crystal diffusion. Ordinary gas diffusion occurs in the pores crystal diffusivities have values of the order of 10 cm /sec. 

E. B Winn, The Temperature Dependence of the Self-Diffusion Coefficients of Argon, Neon, Nitrogen, Oxygen, Carbon Dioxide, and Methane, Phys. Rev., 80 1024,1950. 

Anderson TF (1969) Self-diffusion of carbon and oxygen in calcite by isotope exchange with carbon dioxide. J Geophys Res 74 3918-3932... 

Figure 2. Isothermal change in the density (p), viscosity (rj), and self-diffusivity ( ll) of Carbon Dioxide(adaptedfrom Subramaniam and McHugh (38)).

SELF-DIFFUSION IN LIQUID CARBON DIOXIDE AND PROPANE. 

Figure 3. Density p [22], viscosity 77 [26], and self-diffusion coefficient D [27] of pure carbon dioxide as a function of pressure p at 313 K (for Du at 323 K).

Care mustbe used in applying such arguments when estimating practical diffusion coefficients, however, since increases in infinite-dilution hmit can cause significant changes in the effective mobility of the penetrant. Moreover, the (9 In oa/9 In o>a) term can deviate from unity at weight fractions as small as 10-20%, as was indicated in the case of carbon dioxide and ethylene earher. In the case of o-xylene diffusion in polyethylene at 150°C, both the effects of plasticization and of the (9 In oa/9 In self-diffusion coefficient have been analyzed and are shown in Figure 13 (34). 

By means of the isotopic exchange reaction between uranium dioxide powders with a normal content, and carbon dioxide gas enriched in 1 0, the self-diffusion of oxygen in the stoichiometric and non-stoichiometric dioxide was measured. For essentially stoichiometric UO2, the diffusion of oxygen at 550 to 780C was... 

P Etesse, JA Zega, R Kobayashi. High pressure nuclear magnetic resonance measurement of spin-lattice relaxation and self-diffusion in carbon dioxide. J Chem Phys 97 2022-2029, 1992. 

T Gross, J Buchhauser, H-D LUdemann. Self-diffusion in fluid carbon dioxide at high pressures. J Chem Phys 109 4518-4522, 1998. 

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