Carbon adsorbent uses

Gunko, V.M. and Do, D.D. (2001). Characterisation of pore structure of carbon adsorbents using regularisation procedure. Colloid Surf., 193, 71—83. 

The activated carbon adsorbent used to produce these data is produced from coal. The common commercial adsorbents are activated carbon produced from either coal or coconut shell. 

Table 8.4. Characteristics of the four carbon adsorbents used for gold adsorption (Kononova et al., 2005).

It was not nndl the 1950s that detonation flame arresters made of crimped metal ribbon elements were developed and began to be used more freqnendy (Binks 1999). The major impetus for die use of crimped metal ribbon detonation flame arresters in the US was the enactment of clean air legislation (Clean Air Act of 1990) which inadvertently created a safety problem by requiring reductions in volatile organic compound (VOC) emissions. To do this, manifolded vent systems (vapor collection systems) were increasingly installed in many chemical process industry plants which captured VOC vapors and transported them to suitable recovery, recycle, or destruction systems. This emission control requirement has led to the introdnction of ignition risks, for example, from a flare or via spontaneous combustion of an activated carbon adsorber bed. Multiple... 

The rate of adsorption r, is proportional to the concentration in solution, [C], (at equilibrium in this case) and the amount of adsorption sites left vacant by the desorbing solutes. Now, let us determine these vacant adsorption sites. On a given trial of the experiment, the number of adsorption sites filled by the solute may be quantified by the ratio XIM, as mentioned previously. The greater the concentration of the solute in solution, the greater this ratio will be. For a given type of solute and type of carbon adsorbent, there will be a characteristic one maximum value for this ratio. Call this (Z/M) ,(. Now, we have two ratios XJM, which is the ratio at any time and (Z/M) ,p which is the greatest possible ratio. The difference of these two ratios is proportional to the number of adsorption sites left vacant consequently, the rate of adsorption r, is therefore equal to ks[C][(XIM) i, - (XIM)], where is a proportionality constant. 

In a recent study for the US Department of Energy [61], AGLARG have shown that suitable adsorbents for ANG can be produced from peach pit or coconut shell using KOH as the activating agent. These carbons, like all KOH produced carbons, were low in bulk density. Densities of greater than 0.6 g/ml were possible with compaction in small vessels (<50 ml) and deliveries of greater than 150 V/V methane could be obtained from 3.4 MPa at 298 K. 

Exepriments in the gas phase have supplied us with considerable knowledge on the state of adsorbed carbon monoxide on platinum. 

Figure 1 shows that decreasing temperature (250 K) results in a lower mobility of the adsorbed molecules. If the temperature is further decreased (200 K), the translational motion of the molecules is almost quenched, while the internal rotation of the methyl groups remains. Let us emphasize that in the linewidth and the relative intensity variations, there exists a greater ressem-blance between carbons 1,2 and 3, which denote a greater interaction of these carbons with the surface. 

The results of adsorption and desorption of CO mentioned above suggest that for the reaction at low temperature, the sites for relatively weakly chemisorbed CO are covered by the deposited carbon and the reaction occurs between molecularly adsorbed CO and oxygen on the carbon-free sites which are the sites for relatively strongly chemisorbed CO. Therefore, the definition of the turnover rate at 445 K remains as given in Equation 1. For the reaction at 518 K, however, this definition becomes inappropriate for the smaller particles. Indeed, to obtain the total number of Pd sites available for reaction, we now need to take into consideration the number Trp of CO molecules under the desorption peak. Furthermore, let us assume that disproportionation of CO takes place through reaction between two CO molecules adsorbed on two adjacent sites, and let us also assume that the coverage is unity for the CO molecules responsible for the LT desorption peak, since this was found to be approximately correct on 1.5 nm Pd on 1012 a-A O (1). Then, the number Np of palladium sites available for reaction at 518 K is given by HT/0 + NC0 LT s nce t ie co molecules under the LT desorption peak count only half of the available sites. Consequently, the turnover rate at 518 K should be defined as ... 

Clearly the molecular events with iron were complex even at 80 K and low NO pressure, and in order to unravel details we chose to study NO adsorption on copper (42), a metal known to be considerably less reactive in chemisorption than iron. It was anticipated, by analogy with carbon monoxide, that nitric oxide would be molecularly adsorbed on copper at 80 K. This, however, was shown to be incorrect (43), and by contrast it was established that the molecule not only dissociated at 80 K, but NjO was generated catalytically within the adlayer. On warming the adlayer formed at 80 K to 295 K, the surface consisted entirely of chemisorbed oxygen with no evidence for nitrogen adatoms. It was the absence of nitrogen adatoms [with their characteristic N(ls) value] at both 80 and 295 K that misled us (43) initially to suggest that adsorption was entirely molecular at 80 K. 

Metals which with adsorbed CO prefer to form metal-carbon bonds on the summits are Pt and Ir (Cu ) metals which promote binding in the valley are Pd > Ni > Rh, Re. Metals promoting multiple metal-carbon bonds (with hydrocarbons) are Ni, Ru, Rh Pt and Pd are much worse in this respect. Let us extrapolate and assume that what holds for CO also holds for hydrocarbon molecules, and that the characterization of the multiple-bond formation propensity is valid also at higher temperatures than were established experimentally by exchange reactions. Then we can attempt to rationalize the available information on the formation and the role of various hydrocarbon complexes. 

Next let us consider adsorption from solutions that are not infinitely dilute. Suppose, for example, that adsorption is studied over the full range of binary liquid concentrations. Figure 7.18 is an example of such results for the benzene-ethanol system adsorbed on carbon. At... 

That several model organic compounds were only partially or incompletely retained by the resins prompted us to investigate the use of Carbopack B as an alternative or complementary adsorbent. Test solutions without humic acids were used to verify the sorptive-desorptive behavior of several model compounds under the experimental conditions proposed by Bacaloni et al. (8), except that the compounds were desorbed with methylene chloride. The results of duplicate experiments are given in Table III. Isophorone and MIBK were not effectively retained by Carbopack B, whereas bis(2-ethylhexyl) phthalate was almost equally distributed between the aqueous phase and the carbon. The relatively poor recovery of 1-chlorododecane, 2,4 -dichlorobiphenyl, and 2,2, 5,5 -tetrachlorobiphenyl may be ascribed to sorptive losses onto reservoir glass wall, whereas furfural may be inefficiently... 

If two substances adsorb onto given active sites of the surface of the adsorbent, the removal of substance A from the solution is highly dependent on the adsorption characteristics of substance B on the adsorbent surface. For example, the efficacy of activated carbon against an overdose of an active drug is subject to the presence of adsorbable substances in the gastrointestinal tract. Let us consider that substance A and substance B adsorbed the fractions of the adsorbent surface aA and aB, respectively. The remaining fractions, which can be used for adsorption, are l-aA-aB. Then, the rates of adsorption of A and B (i.e., rA and rB, respectively) are given by ... 

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