Adsorbent activation procedures

These techniques are especially useful for studies of the adsorption of reactants, intermediates and products of electrode reactions. The simplest case corresponds to adsorption that is so strong that the electrode can be removed from the solution, rinsed and its activity measured without interference from desorption. When this procedure is impossible, the activity of the adsorbate can be measured by the electrode lowering method . The radioactive counter is placed under the bottom of the cell, which is made of a plastic foil. The electrode can be located at large distances from the bottom or can be placed so close to the bottom that only a thin layer of solution remains beneath it. The radioactivity values at the two electrode positions permit determination of the adsorbate activity. This procedure can be repeated many times, thus supplying data on the kinetics of the adsorption process. 

Pt/H-MCM-22 catalysts for methane combustion have been prepared by ion-exchange of a highly crystalline H-MCM-22 zeolite using [Pt(NH3)4](N03)2. The activation procedure of the catalyst precursor has been optimized and all steps monitored by HRTEM, SEM and FTIR of CO adsorbed. The preliminary decomposition/calcination of the ion exchanged sample is very crucial in that influence the final properties of platinum active species. 

One way to clarify the role of the adsorbate is the in situ investigation of platinum catalysts with electron spectroscopy, which is capable of quantitatively determining the abundance and chemical structure of the carbon species present. This has been done for a platinum black [66] material used after various activation procedures in n-hexane conversion reactions. It was... 

The quality of the adsorbent and binder, presence of impurities, and uniformity of thickness must be carefully maintained or batch to batch variations will occur. If the plates are to be activated, the procedure should be the same on each occasion. Plates should be stored over silica gel in a desiccator before use and the sample should be applied quickly so that the water vapour in the atmosphere is not adsorbed by the plate. Because of the difficulties associated with activation procedures it is far better to use plates stored at room temperature and not to activate them. The spots must be at least 2 cm from the side of the plate and the solvent used for applying the sample must be completely removed before the plate is run. 

The functional groups present in charcoal are phenols, carboxylic acids, quinones, ketones and lactones. They are essentially acidic supports. The nature and extent of the functionalities on the charcoal particle surface are a function of the material used in the carbonization and the type and duration of the activation procedure. In addition, treatment of these charcoals with oxidizing agents such as nitric acid or hydrogen peroxide increases the number of acid species present. A similar treatment will also functionalize the non-porous carbon blacks.25 Because of this it is difficult to draw any general conclusions concerning the adsorption capabilities of these charcoals other than to say that being acidic they will most readily adsorb cationic species. 

Studies of the influence of activation procedures on the characteristics of the resulting activated carbon employ synthetic solutions in which a single adsorbable solute is dissolved in water. Some recent studies indicate that a test solution containing two or more adsorbable solutes will reveal properties not disclosed when only a single solute is present. 

The precise standardization of thin-layer adsorbents by quantitative extensions of the Brockmann and Schodder procedure should be straightforward. values for a series of standard dyes or other compounds must be tabulated versus adsorbent activity or nominal water content. Figure... 

Activated carbon adsorbents generally show very little selectivity in the adsorption of molecules of different size. However, by special activation procedures it is possible to prepare carbon adsorbents with a very narrow distribution of micropore size and which therefore behave as molecular sieves. The earliest examples of carbon molecular sieves appear to have been prepared by decomposition of polyvinylidene dichloride (Saran) but more recently a wide variety of starting materials have been used. Most commercial carbon sieves are prepared from anthracite or hard coal by controlled oxidation and subsequent thermal treatment. The pore structure may be modified to some extent by subsequent treatment including controlled cracking of hydrocarbons within the micropore system and partial gasification under carefully regulated conditions. ... 

In order to prevent auto-ignition of activated carbon adsorbers activated carbons are tested in standardized procedures for their tendency to self-heating. These tests deliver parameters, which include a number of properties of the tested material, but important properties like the permeability for gasflow, etc. are neglected. The field of velocities in the adsorber plays an important role too. The calculation results discussed show that it is necessary to take not only the parameters of the material but of the whole system into account. On the other hand the calculaton results show that REBOS is a efficient tool... 

Pollard, S.J.T. Sollars, C.J., and Perry, R., A low cost adsorbent from spent bleaching earth The selection of an activation procedure, J. Chem. Technol. Biotechnol.. 50(2). 265-276 (1991). 

Figure 1.9. Helium adsorption at T = 298.15 K on molecular sieves (MS 5A) with different activation procedures. Full symbols ( , a) present the measured values of the reduced masses (fl), cp. Eq. (1.6). Open symbols (0, ) are masses of helium adsorbed on the samples calculated by Eq. (1.7). Data indicate saturated states of adsorption of helium at increasing pressures for both samples. However, the (specific) volumes (V ) of both samples seen by the helium molecules and calculated by Eq. (1.6) from steepnesses of the linearly correlated fl-data are quite different [1.48].

The purpose of this paper is to present such a model which can be regarded as a synthesis of fundamental considerations resulting from the activities in porous sorbents characterization and classical thermodynamics developments. This model is able to represent in a correct way adsorption data of oxygen, argon, nitrogen and methane on a given carbonaceous adsorbent using a unique pore size distribution function whatever the adsorbate. The procedure was applied on four different activated carbons and on a carbon molecular sieve. The adsorption isotherms were measured at 283 K, 303 K and 323 K and for pressures up to 2200 kPa. 

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