Internal Adsorption

Is decisive. Adsorption of positively charged Ions of the admixture can occur on a neutral or even on an also positively charged surface [155), however. In any event, a direct dependence between the amount of admixture adsorbed and the specific surface of crystals has been found. 

The term Internal adsorption Is also used for the adsorption occurring on the internal crystal surface, closely connected with various defects in crystal structure like breaches or mlcrocavitles formed In the block 

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Giorgio Carta, Ph.D., Professor, Department of Chemical Engineering, University of Virginia Member, American Institute of Chemical Engineers, American Chemical Society, International Adsorption Society (Section 16, Adsorption and Ion Exchange)... 

The relationship between adsorption capacity and surface area under conditions of optimum pore sizes is concentration dependent. It is very important that any evaluation of adsorption capacity be performed under actual concentration conditions. The dimensions and shape of particles affect both the pressure drop through the adsorbent bed and the rate of diffusion into the particles. Pressure drop is lowest when the adsorbent particles are spherical and uniform in size. External mass transfer increases inversely with d (where, d is particle diameter), and the internal adsorption rate varies inversely with d Pressure drop varies with the Reynolds number, and is roughly proportional to the gas velocity through the bed, and inversely proportional to the particle diameter. Assuming all other parameters being constant, adsorbent beds comprised of small particles tend to provide higher adsorption efficiencies, but at the sacrifice of higher pressure drop. This means that sharper and smaller mass-transfer zones will be achieved. 

He refrigerators fall into two categories (1) refrigerators with external adsorption pump and (2) refrigerators with internal adsorption pump. Hereafter, we will describe a refrigerator of the second type. 

They are defined in complete analogy to the integral molar energy. The difference between the energy and the enthalpy of adsorption is usually small. If we treat the free gas as being ideal, the difference is AadU = AadHm1 + RT. At 25°C RT is only 2.4 kJ/mol. For this reason we do not need to worry too much about whether a heat of adsorption is the adsorption enthalpy or the internal adsorption energy, if we only want to estimate is. 

E. Hoinkis, B. Rohl-Kuhn, in Proc. Conf. Fundamentals of Adsorption FOA7, Nagasaki, Japan, 2001, p.601. Intern. Adsorption Soc.,K. Kaneko, H. Kanoh, Y. Hanzawa (eds.). 

Day Chr. and Hauer V., Pore characterisation of cryosorbent carbon materials. In K. KANEKO (ed.) Fundamentals of Adsorption 7 (International Adsorption Society, 2002)pp.1093-1100... 

International Adsorption Society. (2002). Adsorption. Available http //ias.vub.ac.be/ General/Adsorption. 

Comparing n-hexane adsorption on US-69 and modified zeolites is possible to mark, that internal adsorption volume of a sample prepared by impregnation by a solution of acids (BP-US-69 (2)) has decreased insignificantly, and its share has made 0.91-0.95 in relation to starting zeolite. On data of n-hexane adsorption available volume for molecules has made 0.8 from the value for US-69 for BP-US-69 (1) modified by reagent vapors. 

Internal adsorption energy, AC/ads, is calculated by a Boltzmann weight of (t)tot summed at constant temperature, T ... 

The mechanism of transfer to the sohd includes diffusion through the fluid film around the particle and diffusion through the pores to internal adsorption sites. The actual process of physical adsorption is practically instantaneous, and equilibrium is assumed to exist between the surface and the fluid at each point inside the particle. The transfer process is approximated using an overall volumetric coefficient and an overall driving force ... 

However, the two-sink model as well as other existing adsorption (sink) models do not seem to be able to describe the strong asymmetry between the adsorption/desorption of VOCs on/from indoor surface materials (the desorption process is much slower than the adsorption process). Diffusion combined with internal adsorption is assumed to be capable of explaining the observed asymmetry. Diffusion mechanisms have been considered to play a role in interactions of VOCs with indoor sinks. Dunn and Chen (1993) proposed and tested three unified, diffusion-limited mathematical models to account for such interactions. The phrase unified relates to the ability of the model to predict both the ad/absorption and desorption phases. This is a very important aspect of modeling test chamber kinetics because in actual applications of chamber studies to indoor air quality (lAQ), we will never be able to predict when we will be in an accumulation or decay phase, so that the same model must apply to both. Development of such models is underway by different research groups. An excellent reference, in which the theoretical bases of most of the recently developed sorption models are reviewed, is the paper by Axley and Lorenzetti (1993). The authors proposed four generic families of models formulated as mass transport modules that can be combined with existing lAQ models. These models include processes such as equilibrium adsorption, boundary layer diffusion, porous adsorbent diffusion transport, and conveetion-diffusion transport. In their paper, the authors present applications of these models and propose criteria for selection of models that are based on the boundary layer/conduction heat transfer problem. 

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