Adsorption sequential

Ramsden J J 1993 Review of new experimental methods for investigating random sequential adsorption J. Stat. Phys. 73 853-77... 

Evans J W 1993 Random and cooperative sequential adsorption 1993 REv. Mod. Phys.65 1281-1329... 

The appHcations of adsorbents are many and varied and may be classified as nonregenerative uses, in which the adsorbent is used once and discarded, and regenerative appHcations, in which the adsorbent is used repeatedly in a cycHc manner involving sequential adsorption and regeneration steps. 

There are seven commercial processes in operation six operate in the vapor phase. The Universal Oil Products process operates in the Hquid phase and is unique in the simulation of a moving bed. The adsorption unit consists of one vessel segmented into sections with multiple inlet and oudet ports. Flow to the various segments is accompHshed by means of a rotary valve which allows each bed segment to proceed sequentially through all the adsorption/desorption steps. 

Despite the recent efforts for settling operational conditions for metal and metalloid fractionation, conventional batch sequential extraction schemes lack automation and are rather time consuming and laborious. Two additional main problems are the phase overlapping and possible re-adsorption of released elements. 

Fig. 5.10. Series of sequential in-situ AFM images of the growth of ODS on silicon. The numbers indicate the adsorption time in minutes.

The sticking coefficient of H2 on a metal has been determined through an adsorption experiment. The metal surface is assumed to have No = 1.5 x 10 sites m and each adsorption site is assumed to be occupied by one hydrogen atom when the surface is saturated. The experiment was performed by exposing the surface to a known pressure of hydrogen over a well-defined period of time (dosis) and then sequentially determining how much was adsorbed by, for example, TPD. All adsorption experiments where performed at such low temperatures that desorption could be neglected. 

A sequential analysis protocol includes three steps (1) extraction in water or other appropriate solvent for the colorant, (2) purification or concentration of the colorant, and (3) separation coupled with detection of the target molecule. Different methods of extracting synthetic colorants from foods have been developed using organic solvents followed by SPE protocols using as adsorption support RP-C18, amino materials, or Amberlite XAD-2. Eor qualitative evaluations, the easiest option for separating colorant molecules from unwanted ingredients found in an extract is SPE on polyamide or wool. 

Usually, physisorption is carried out using nitrogen as an adsorbate at 77.3 K, the boiling point of liquid nitrogen. The solid material is called the adsorbent. Adsorption can be measured in many different ways. So-called volumetric adsorption, in which volumes of gas are introduced. sequentially while simultaneously measuring the pressure, is a commonly used technique. Fig. 3.41 shows a schematic of the equipment used (referred to as barometric equipment ). 

The reaction sequence of formaldehyde formation and subsequent COad formation can proceed either as sequential reactions of adsorbed species, or it can involve formation and desorption of formaldehyde into the electrol5d e and subsequent re-adsorption and further decomposition of formaldehyde to COad. Considering the significant transport and catalyst loading effects discussed above, it is clear that desorption and subsequent re-adsorption plus dehydrogenation of formaldehyde will play an important role also for COad formation, although a direct reaction of adsorbed RIad species can not be ruled out. 

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