Recovery desorption and

A rough prediction of desorption and recovery can be made by extrapolation from similar compounds however, until we know more about the factors involved, this practice can lead to difficulties as illustrated in Table II. The recovery of naphthalene and biphenyl from charcoal are much lower than one would predict from the recoveries of other aromatic compounds, and this stronger attraction may be related to bond angles or steric effects. The order of recovery, ortho (84%) > meta (81%) > para (76%) methyl biphenyl, supports this theory. One may predict from this information that the recovery of benzene would be very poor, which is not the case. 

Apparently, 1 is adsorbed only at the pore mouths of the ZSM-5 zeolite, so that desorption and recovery of the cyclized products remain possible. The high selectivity for 2a points to a highly selective interaction between the zeolite outer surface and the organic reactant, resulting in excellent stereoselectivity. 

Thermal treatment is used to destroy, break down, or aid in the desorption of contaminants in gases, vapors, Hquids, sludges, and soHds. There are a variety of thermal processes that destroy contaminants, most of which are classified as incineration. Incineration HteraHy means to become ash (from Medieval Latin, incinerare in or into ashes). With respect to the incineration of hazardous wastes regulated in the United States, however, there is a strict legal definition of what constitutes an incinerator. The Resource Conservation and Recovery Act (RCRA) definition of incinerator at 40 CFR 260.10 is... 

Purge-and-trap methods have also been used to analyze biological fluids for the presence of trichloroethylene. Breast milk and blood were analyzed for trichloroethylene by purging onto a Tenax gas chromatograph to concentrate the volatiles, followed by thermal desorption and analysis by GC/MS (Antoine et al. 1986 Pellizzari et al. 1982). However, the breast milk analysis was only qualitative, and recoveries appeared to be low for those chemicals analyzed (Pellizzari et al. 1982). Precision (Antoine et al. 1986) and sensitivity (Pellizzari et al. 1982) were comparable to headspace analysis. 

Sampling on Tenax TA followed by thermal desorption and GC affords a simple method for the determination of nitrobenzene in the workplace air. Recoveries were quantitative in the mass range 0.04-10 i-g452. 

Industrial examples of adsorbent separations shown above are examples of bulk separation into two products. The basic principles behind trace impurity removal or purification by liquid phase adsorption are similar to the principles of bulk liquid phase adsorption in that both systems involve the interaction between the adsorbate (removed species) and the adsorbent. However, the interaction for bulk liquid separation involves more physical adsorption, while the trace impurity removal often involves chemical adsorption. The formation and breakages of the bonds between the adsorbate and adsorbent in bulk liquid adsorption is weak and reversible. This is indicated by the heat of adsorption which is <2-3 times the latent heat of evaporahon. This allows desorption or recovery of the adsorbate from the adsorbent after the adsorption step. The adsorbent selectivity between the two adsorbates to be separated can be as low as 1.2 for bulk Uquid adsorptive separation. In contrast, with trace impurity removal, the formation and breakages of the bonds between the adsorbate and the adsorbent is strong and occasionally irreversible because the heat of adsorption is >2-3 times the latent heat of evaporation. The adsorbent selectivity between the impurities to be removed and the bulk components in the feed is usually several times higher than the adsorbent selectivity for bulk Uquid adsorptive separation. 

Since the Sorbex process is a liquid-phase fixed-bed process, the selection of particle size is an important consideration for pressure drop and process hydraulics. The exact particle size is optimized for each particular Molex process to balance the liquid phase diffusion rates and adsorbent bed frictional pressure drop. The Sorbex process consists of a finite number of interconnected adsorbent beds. These beds are allocated between the following four Sorbex zones zone 1 is identified as the adsorption zone, zone 2 is identified as the purification zone, zone 3 is identified as the desorption and zone 4 is identified as the buffer zone. The total number of beds and their allocation between the different Sorbex zones is dependent on the desired performance of the particular Molex process. Molex process performance is defined by two parameters extract normal paraffin purity and degree of normal paraffin recovery from the corresponding feedstock. Details about the zone and the bed allocations for each Molex process are covered in subsequent discussions about each process. 

Gas-adsorption processes Involve the selective concentration (adsorption) of one or more components (adsorbates) of a gas (or vapor) at the surface of a microporous solid (adsorbent) The attractive forces causing the adsorption are generally weaker than those of chemical bonds and are such that, by Increasing the temperature of the adsorbent or reducing an adsorbate s partial pressure, the adsorbate can be desorbed The desorption step Is quite Important in the overall process First, desorption allows recovery of adsorbates In those separations where they are valuable, and second, It permits reuse of the adsorbent for further cycles ... 

Displacement desorption Good for strongly held species avoids risk of cracking reactions during regeneration avoids thermal aging of adsorbent Product separation and recovery needed (choice of desorbent is crucial)... 

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