Sorbents bulk density

In Table 4.16 we summarize the heavy oil sorption performance of the three carbon sorbents used by listing their sorption capacity, sorptivity as a measure of sorption rate, and the cycling processes that can be applied. Both sorption capacity and sorptivity K, depend strongly on sorbent bulk density, as shown in Figure 4.43. 

With the purpose of a choice of the most suitable sorbent of hydrogen, isotherms (Fig. 7) of studied materials were compared at a level of pressure 3.5-6 MPa, representing practical interest for development of onboard storage system. It is obvious, that the best sorbent in the field of nitrogen temperature - the activated fiber "Busofit-M8", having major effective porosity (0.78), bulk density of 500 kg/m3 and an advanced surface area (2985 m2/g). 

Figure 27.8 Dependences of sorption capacity of exfoliated graphite and carbonized fir fibers for the C- and B-grade heavy oils on bulk density of carbon sorbents.

Figure 27.13 Sorption curves of carbon sorbents with different bulk densities for the A-grade heavy oil.

Figure 27.14 Dependences of sorptivity fQ on the bulk density of sorbents.

For the viscous C-grade heavy oil, the value of sorptivity was so small, about 0.2kg/m s, that its slight dependence on the bulk density of the two carbon sorbents — carbonized fir fibers and carbon fiber felts — was observed. 

Prior to the introduction of a liquid into the adsorbent bed, there must be suflflcient time for any gas or vapor that may be trapped in the pores of the sorbent to outgas. Otherwise the gas or vapor may contaminate a product during operation. In the case of upflow adsorption, the effective bulk density may be lowered enough to cause excessive bed expansion or flow channeling. 

In this expression, C is the contaminant concentration in the sorbed phase and is a function of S through the adsorption process, s is the porosity of the particle, is the surface diffusion coefficient within the sorbent particle, p is the oxide bulk density, is the pore diffusion coefficient within the sorbent, and r is the radial position within the sphere measured from the center. In aqueous environments, where contaminant concentrations are dilute, diffusivities are constant [23]. Also, the reaction is rapid or instantaneous for adsorption to amorphous oxides the balance reduces to... 

Fibrous components of several plants, such as milkweed, kenaf, cotton, and sugi (don), have been applied for recovery of spilled heavy oils [15-21,70]. In Section III.B, carbonized fir fibers were described as useful sorbents for heavy oils. The hydrophobic (oleophilic) nature of most carbon materials is expected to be advantageous for oil sorption. It seemed interesting from the viewpoint of global environment to apply as oil sorbents porous charcoals with a low bulk density prepared from quickly growing woods and plants. 

The capacity of carbon sorbents for heavy oils was found to depend mainly on their bulk density, rapidly decreasing with increasing bulk density, because the macropores in the sorbent in the range of 1 to 600 pm are primarily responsible for heavy oil sorption. As both exfoliated graphite and carbonized fir fibers can have very low bulk density, for example, 6 to 7 kg/m, they have a very high sorption capacity of about 80 kg/kg. The sorption capacity of exfoliated graphite was also found to depend on the viscosity of the oil. Carbon fiber felts, however, do not have such low bulk density, and so their sorption capacity is correspondingly low. 

FIGURE 4.19 Plots of versus f 2 o" carbon sorbents with different bulk densities, (a) Exfoliated graphite, (b) carbonized fir fibers, and (c) carbon fiber felt. 

FIGURE 4.20 Dependence of sorptivity on bulk density of the three carbon sorbents. 

Dependence of effective sorbent porosity e on bulk density of carbon... 

A quantitative comparison of values of the average pore radius is also difficult, for the same reason. As shown in Figure 4.22, the pore size distribution of carbon sorbents is quite complicated and broad, particularly for exfoliated graphite and carbonized fir fibers of low bulk density. With increasing bulk density, it tends to become simpler and shifts to smaller pore sizes. 

For the carbon fiber felt, s is almost independent of bulk density and has a rather high value in comparison with the other two sorbents, and its X is expected... 

FIGURE 4.43 Dependence of heavy oil sorption parameters on bulk density of three carbon sorbents, (a) Sorption capacity and (b) sorptivity K. ... 

The most common approach to chromatographic stationary-phase characterization is in terms of bulk-phase properties, such as percent carbon loading onto the silica substrate. This property together with the surface area of the substrate and the molecular characteristics of the bonded silane can be used to calculate the bonding density (A) of the chromatographic sorbent [60] ... 

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