Activated carbon saturation

The preparation of chlorinated organic compounds involves reactions that seldom go to completion and some free chlorine is present in the end products. The free chlorine may be removed by passing the product through a bed of activated carbon saturated with water. The carbon acts as a catalyst to promote the reaction between chlorine and water, and the hydrochloric acid that is formed drains away with the water at the base of the bed. 

A simple method of regeneration consists in reactivating the spent material in a reactivation oven at the producers. A temperature between 900 and 1,200 °C is required with the presence of an oxidant such as steam or COi. The method is applied to activated carbons saturated with organic volatile compounds. This operation gives a loss of carbon estimated at 5 to 20 %. 

Regeneration with steam is the most common technique applied to activated carbon saturated with solvents. The steam, at temperatures ranging between 105 and 140 °C, flows through the packing material and cleans the activated carbon. The desorbate is then condensed. Of come, the solvent has to be non-miscible in water. The steam consumption is between 3 and 14 kg kg of recuperated VOC. Table 11 gives the steam consumption for different VOC and activated carbons of different origins. 

Ferro-Garcia, M.A., et al., Chemical and thermal regeneration of an activated carbon saturated with chlorophenols, J. Chem. Technol. Biotechnol., 67(2), 183-189 (1996). 

Wang L, Balasubramanian N (2009) Electrochemical regeneration of granular activated carbon saturated with organic compounds. Chem Eng J 155 763-768... 

Slavinskii AS, Velikaya LP, Karimova AM, Baturin AP (1984) Electrochemical regeneration of activated carbon saturated with p-nitrotoluene. Sov J Water Chem Technol 6(6) 40-43... 

Many simple systems that could be expected to form ideal Hquid mixtures are reasonably predicted by extending pure-species adsorption equiUbrium data to a multicomponent equation. The potential theory has been extended to binary mixtures of several hydrocarbons on activated carbon by assuming an ideal mixture (99) and to hydrocarbons on activated carbon and carbon molecular sieves, and to O2 and N2 on 5A and lOX zeoHtes (100). Mixture isotherms predicted by lAST agree with experimental data for methane + ethane and for ethylene + CO2 on activated carbon, and for CO + O2 and for propane + propylene on siUca gel (36). A statistical thermodynamic model has been successfully appHed to equiUbrium isotherms of several nonpolar species on 5A zeoHte, to predict multicomponent sorption equiUbria from the Henry constants for the pure components (26). A set of equations that incorporate surface heterogeneity into the lAST model provides a means for predicting multicomponent equiUbria, but the agreement is only good up to 50% surface saturation (9). 

The overhead temperatures of both the absorber and stripper are kept as low as possible to minimise solvent carryover. A temperature of about 311 K is typically used ia the high pressure absorber. The overhead temperature ia the stripper is set by the boiling poiat of the saturated complex solution and by the operating pressure of the stripper. At a stripping pressure of 0.166 MPa (1.7 atm), a temperature of 378 Kis used. The solvent-rich gas from the stripper is cooled to recover as much solvent as possible by condensation prior to the final aromatics-recovery section. Fiaal solvent recovery is accomphshed by adsorption on activated carbon (95). 

An initially clean activated carbon Led at 320 K is fed a vapor of benzene in nitrogen at a total pressure of 1 MPa. The concentration of benzene in the feed is 6 mol/m. After the Led is uniformly saturated with feed, it is regenerated using benzene-free nitrogen at 400 K and 1 MPa. Solve for Loth steps. For sim-phcity, neglect fluid-phase acciimiilation terms and assume constant mean heat capacities for stationary and fluid phases and a constant velocity. The system is described by... 

The adsorbers are usually built of steel, and may be lagged or left unlagged the horizontal type is shown in Figure 28. The vapor-laden air is fed by the blower into one adsorber which contains a bed of 6- to 8-mesh activated carbon granules 12 to 30 inches thick. The air velocity through the bed is 40 to 90 feet per minute. The carbon particles retain the vapor only the denuded air reaches the exit, and then the exhaust line. The adsorption is allowed to continue until the carbon is saturated, when the vapor-laden air is diverted to the second adsorber, while the first adsorber receives low-pressure steam fed in below the carbon bed. The vapor is reformed and carried out by the steam. The two are condensed and if the solvent is not miscible with water, it may be decanted continuously while the water is run off similarly. After a period which may be approximately 30 or 60 minutes, all the vapor has been removed, the adsorbing power of the charcoal has been restored, and the adsorber is ready to function again, while adsorber No. 2 is steamed in turn. 

We wUl now touch upon some of these factors. First, let s look at what we mean by system isotherm. Freundlich liquid phase isotherm studies can be used to establish the adsorptive capacity of activated carbon over a range of different concentrations. Under standard conditions, the adsorptive capacity of activated carbon increases as the concentration increases, until we reach a point of maximum saturation capacity. An example of an isotherm for phenol is shown in Figure 8. 

Cost estimation and screening external MSAs To determine which external MSA should be used to remove this load, it is necessary to determine the supply and target compositions as well as unit cost data for each MSA. Towards this end, one ought to consider the various processes undergone by each MSA. For instance, activated carbon, S3, has an equilibrium relation (adsorption isotherm) for adsorbing phenol that is linear up to a lean-phase mass fraction of 0.11, after which activated carbon is quickly saturated and the adsorption isotherm levels off. Hence, JC3 is taken as 0.11. It is also necessary to check the thermodynamic feasibility of this composition. Equation (3.5a) can be used to calculate the corresponding... 

The elimination of HCHO by gas adsorption using activated carbon having high specific surface area is one of the effective removal methods. However, in this method, periodical replacement of carbon adsorbents, regeneration, and combustion after saturation with HCHO are required. An ideal method is the catalytic oxidation of HCHO to CO2 at room temperature, using molecular oxygen in ambient atmosphere. 

Fig 18. Experimental trickle-bed system A, tube bundle for liquid flow distribution B, flow distribution packing of glass helices C, activated carbon trickle bed 1, mass flow controllers 2, gas or liquid rotameters, 3, reactor (indicating point of gas phase introduction) 4, overflow tank for the liquid phase feed 5, liquid phase hold-up tank 6, absorber pump 7, packed absorption column for saturation of the liquid phase 8, gas-liquid disengager in the liquid phase saturation circuit. (Figure from Haure et ai, 1989, with permission, 1989 American Institute of Chemical Engineers.)... 

Once the micropore surfaces of activated carbon are saturated with target material, the spent carbon must be replaced or regenerated. Granular activated carbon (GAC) is favored over powder activated carbon (PAC) in most cases, because the former is considered to be capable of regeneration and sustainable to flow, although the costs of both carbons and the cost of regeneration are high. 

Interaction of chlorine with methane is explosive at ambient temperature over yellow mercury oxide [1], and mixtures containing above 20 vol% of chlorine are explosive [2], Mixtures of acetylene and chlorine may explode on initiation by sunlight, other UV source, or high temperatures, sometimes very violently [3], Mixtures with ethylene explode on initiation by sunlight, etc., or over mercury, mercury oxide or silver oxide at ambient temperature, or over lead oxide at 100°C [1,4], Interaction with ethane over activated carbon at 350°C has caused explosions, but added carbon dioxide reduces the risk [5], Accidental introduction of gasoline into a cylinder of liquid chlorine caused a slow exothermic reaction which accelerated to detonation. This effect was verified [6], Injection of liquid chlorine into a naphtha-sodium hydroxide mixture (to generate hypochlorite in situ) caused a violent explosion. Several other incidents involving violent reactions of saturated hydrocarbons with chlorine were noted [7],... 

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