Biporous adsorbent pellets

FIGURE 4 Schematic diagram of a biporous adsorbent pellet showing the three resistances to mass transfer (external fluid film, macropore diffusion, and micropore diffusion). R9 pellet radius rc crystal radius. 

This technique may also be used to measure effective macropore diffusivities in biporous adsorbent pellets [13,14]. For such a system with a linear equilibrium isotherm and assuming rapid intracrystalhne diffusion, the governing diffusion equation is of the same form as for micropore control. The solution is identical to Eq. 1 except that R now refers to the particle radius and the diffusivity D is replaced by the effective diffusivity De = Dp p/(ep + (1 - p)fC). Since the equilibrium constant (K) is generally large and varies with temperature according to the van t Hoff equation (K = it is clear that a macropore-controlled system will gener-... 

Physical adsorption at a surface is extremely rapid, and the kinetics of physical adsorption are invariably controlled by mass or heat transfer rather than by the intrinsic rate of the surface process. Biporous adsorbents such as pelleted zeolites or carbon molecular sieves offer three distinct resistances to mass transfer the external resistance of the... 

The definitions of the moments and their relationship to the system parameters for a biporous (macropore-micropore) adsorbent such as a commercial pelleted molecular sieve are given by the following equations(15,16) ... 

Liquid chromatography is a technique widely used for the determination of adsorption and diffusion parameters in microporous materials such as zeolites [6], in meso- and macroporous materiels such as aluminas [7], as well as in biporous pelletized materials [8]. This technique enables also the development of suitable adsorbent for a given separation, for example the separation of isomers of xylenes on X or Y zeolites [9,10]. 

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