Carbon activation molecular sieve

Amorphous siHca gel, activated alumina, activated carbon, and molecular sieve carbons. 

Ethylenediamine (en) [15] Among the impurities are water, carbon dioxide, ammonia and polyethylene amines (e.g. diethylenetriamine and triethylenetetra-mine). In the recommended purification method, commercial product (98%) is shaken for about 12h with activated molecular sieves (5A, 70 gl-1), the supernatant is decanted and shaken for about 12 h with a mixture of CaO (50 gl-1) and... 

Abstract. Activated carbon Norit R 08 Extra, and molecular sieve type 4A, were investigated using dynamic (tert-butylbenzene (TBB), cyclohexane (CHX) and water vapour) adsorption methods. The TBB, CHX and water breakthrough plots for fixed activated carbon - molecular sieve beds were analyzed. It was found that the type of bed composition with mechanically mixed activated carbon with molecular sieve, or separated activated carbon and molecular sieve layers, affects the dynamic adsorption characteristics. 

Dry air, spiked with required amounts of cyclohexane vapour, was supplied through a glass tube (internal section 20 cm2) filled with the tested carbon and molecular sieve. An initial concentration of cyclohexane was Co = 3.6 0.1 mg dm-3 (0.1% V/V). The experiments were carried out with two bed configurations 1) a separated (layer of molecular sieve type 4A 2 cm in height, and a layer of activated carbon 2 cm) and 2) mechanically mixed activated carbon with molecular sieve in equal volumetric amounts. 

Figure 1. Log-scaled TBB breakthrough plots vs. time for mixed M and separated S beds of activated carbon and molecular sieve without water vapour (RH = 0 %).

Comparing the log-scaled TBB breakthrough plots vs time for mixed M and separated S beds of activated carbon and molecular sieve without or with water vapour, it can be affirmed that separated activated carbon/molecular sieve bed ( S ) is more effective than mixed ( M ). In the case of cyclohexane breakthrough a negative effect caused by mixing of activated carbon with molecular sieve is observed. This effect is probably caused by the different linear flow rates for TBB and CHX on the breakthrough experiments. 

The use of dry adsorbents like activated carbon and molecular sieves has received considerable attention in removing final traces of objectional gaseous pollutants. Adsorption is generally carried out in large, horizontal fixed beds often equipped with blowers, condensers, separators, and controls. A typical installation usually consists of two beds one is onstream while the other is being regenerated. 

Air samples were collected on 11.5 cm x 6 mm OD x4mm ID three-phase Carbotrap 300 thermal desorption tubes (Supelco) or four-phase Carbotrap 400 tubes. These sorbent tubes house a sequence of graphitized carbon and molecular sieves of increasing activity that sorb volatile and semi-volatile organic compounds over a molecular size range from Q to C30. 

Nearly the total area accessible for adsorptive molecules is provided by the micro-pores with diameters below 2 nm. This is trae for activated carbons and molecular sieves. Macropores with diameters larger than 50 mn are decisive for the adsorption kinetics or the mass transfer, see later. Adsorbents like aluminium oxides and molecular sieves with electrical charges are hydrophilic and can be highly loaded with polar adsorptive molecules such as water, ammonia, and methanol, see Chap. 3. Adsorption isotherms of water are a good tool to characterize the capacity of these adsorbents. 

The Nitta et al. s equation (5.7-4) works satisfactorily for activated carbon and molecular sieving carbon with adsorbates of similar physical and chemical nature such as lower order paraffin hydrocarbons. This is exemplified with the experimental data of Nakahara et al. (1974) using methane, ethane, propane and n-butane on molecular sieving carbon 5A. The following table shows some typical parameters obtained using the Nitta et al. equation (5.7-1) assuming the interaction energy to be zero. 

Ad Adsorption De Desorption AC Active carbon AA Active alumina ACO Active coke C Carbon MS Molecular sieve SG Silica gel PSA Pressure swing adsorption... 

The use of carbons as sorbents for preconcentration of pollutants, an application that has much in common with the preceding one, was recently reviewed by Matisova and Skrabakova [23], who investigated the applicability of carbon sorbents (active carbon, graphitized carbon black, molecular sieves, and porous carbon) for preconcentration of organic pollutants in environmental samples and their analysis by GC and HPLC. Another example of an application of carbonaceous materials in which surface chemistry is involved is the reduction of pollutant emissions from aqueous and gaseous media [24]. 

The second mechanism appears to be adsorption onto porous solids (Urushizaki, 1987 Kader et al., 1989). Examples include sachets containing activated carbon or molecular sieves, and plastic films containing dispersed Ohya stone, crystobalite, coral sand, silica gel and synthetic zeolite (Abe, 1990). 

One may use D/R technology with both activated carbon and molecular sieves (Chapter 3, Footnote 94) based on carbon substrates. Per the reference of Footnote 15, the values of p are essentially the same. 

Purification adsorption of nitrogen trifluoride is NOT recommended. Purification process using dry media such as activated charcoal (carbon) or molecular sieve may be subject to rapid exotherms from sudden exposure of the media to large quantities of nitrogen trifluoride. 

The main applications of activated carbon with molecular sieving ability are separation of nitrogen and oxygen in air on the basis of difference of diffusion rates of these gases in small micropores, and adjustment of fragrance of winery products where only small molecules are removed by adsorption in liquid phase. 

Char Utilization. Char produced in the pyrolysis process can have a range of applications to offset the cost of producing liquid fuels. One obvious application is on-site combustion to generate heat for the pyrolysis process itself. Alternatively, chars can be used for combustion in electric power plants. Char can also be gasified to produce hydrogen for use in the pyrolysis plant if the process requires hydrotreatment (e.g., tar upgrading or hydropyrolysis). Other applications include production of activated carbon and molecular sieves. 

In smaller SOFC systems, sulphur can be removed by adsorption methods, most frequently using activated carbon or molecular sieves [3]. The ability of activated carbon to adsorb H2S can be enhanced by chemically impregnating it. Such adsorbent systems can be reactivated by thermal treatment. However, their use becomes impractical for larger scale SOFC systems because of the large quantities of adsorbent required and the subsequent problems associated with adsorbent reactivation and disposal of the desorbed sulphur [3]. 

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