Adsorption design example

Data collected during the batch adsorption study will be used in the determination of coefficients for the adsorption isotherms. The procedures are shown in the design examples in the following section. 

Fructose—Dextrose Separation. Emctose—dextrose separation is an example of the appHcation of adsorption to nonhydrocarbon systems. An aqueous solution of the isomeric monosaccharide sugars, C H 2Dg, fmctose and dextrose (glucose), accompanied by minor quantities of polysaccharides, is produced commercially under the designation of "high" fmctose com symp by the enzymatic conversion of cornstarch. Because fmctose has about double the sweetness index of dextrose, the separation of fmctose from this mixture and the recycling of dextrose for further enzymatic conversion to fmctose is of commercial interest (see Sugar Sweeteners). 

The elution of such gels is an example not of size exclusion but rather of hydrodynamic fractionation (HDF). However, it must be remembered that merely being able to physically fit an insoluble material through the column interstices is not the only criterion for whether the GPC/HDF analysis of an insoluble material will be successful. A well-designed HDF packing and eluant combination will often elute up to the estimated radius in Eq. (5), but adsorption can drastically limit this upper analysis radius. For example, work in our laboratory using an 8-mm-bead-diameter Polymer Laboratories aqueous GPC column for HDF found that that column could not elute 204 nM pSty particles, even though Eq. (5) estimates a critical radius of —1.5 jam. 

Evaluation of design options. Costs are required to evaluate process design options for example, should a membrane or an adsorption process be used for purification ... 

Data used for the design of adsorption processes are normally derived from experimental measurements. The capacity of an adsorbent to adsorb an adsorbate depends on the compound being adsorbed, the type and preparation of the adsorbate, inlet concentration, temperature and pressure. In addition, adsorption can be a competitive process in which different molecules can compete for the adsorption sites. For example, if a mixture of toluene and acetone vapor is being adsorbed from a gas stream onto activated carbon, then toluene will adsorbed preferentially, relative to acetone and will displace the acetone that has already been adsorbed. 

Several examples have already been pointed out in which the properties of the solute itself can impact on the results obtained from a transport experiment. Metabolic instability and propensity for nonspecific adsorption are problems which can frequently be encountered and must be considered any time a new solute is to be studied. In addition to these problems, there are several other solute-related factors which must be considered in the design and interpretation of transport studies. 

These and other data (10) show that hydrogen chemisorption is operationally of two types Type I chemisorption which is removed by evacuation for 15 min at room temperature, and type II chemisorption which is not removed by evacuation at room temperature even after several hours. The type I chemisorption appears to be independent of the amount of type II chemisorption (compare runs 3 and 5). Figure 2 show s an isotherm for type I adsorption, as defined. This is a typical curve for chemisorption and suggests that type I chemisorption occurs on sites corresponding to roughly 5% of the BET Vm value. (The designation type I and type II chemisorption was chosen in preference to fast and slow because not all of the type II chemisorption is slow. For example, the amount of adsorption in curve 1 of Fig. 1 is 0.154 cm3/gm after 2 min. We would estimate at least one-third of this adsorption is type II. Thus, some type II irreversible chemisorption is quite rapid.)... 

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