Activated carbon pellets

Once the heel has been established in the carbon bed, the adsorption of the fuel vapor is characterized by the adsorption of the dominant light hydrocarbons composing the majority of the hydrocarbon stream. Thus it is common in the study of evaporative emission adsorption to assume that the fuel vapor behaves as if it were a single light aliphatic hydrocarbon component. The predominant light hydrocarbon found in evaporative emission streams is n-butane [20,33]. Representative isotherms for the adsorption of n-butane on activated carbon pellets, at two different temperatures, are shown in Fig. 8. The pressure range covered in the Fig. 8, zero to 101 kPa, is representative of the partial pressures encountered in vehicle fuel vapor systems, which operate in the ambient pressure range. 

Due to this technology s stage of development, no cost information is available regarding product cost. Cost information regarding production cost, however, has been developed. The cost of producing BAC is 39% less than producing conventional activated carbon 227.00 per ton for BioBinder pellets compared with 375.00 per ton for activated carbon pellets made from wood char and wood tar in 1996 dollars (D137421, p. 2). 

In the third variation a mixture of moisturized green coffee beans and activated carbon is filled into the extractor, and the activated carbon pellets used are just big enough to fit between the beans. For 3 kg of coffee beans, 1 kg of activated carbon is needed. At 220 bar and 90°C the caffeine in the supercritical CO2 diffuses directly out of the beans into the activated carbon. A CO2 circulation is not necessary. The required degree of decaffeination is reached after 6 to 8 hours. After extraction, the beans and activated carbon are separated by a vibrating sieve. 

A differential permeation method was used to determine diffusion kinetics of strongly adsorbing vapors through an Ajax activated carbon (type 976) (whose physical properties [7] particle density of 733 kg/m micropore porosity 0.40, macropore porosity 0.31 and mean macropore radius 0.8 pm). An activated carbon pellet was carefully mounted in a copper block, separating two reservoirs. One reservoir is much larger in volume than the... 

With carbon adsorption, solvent vapors escaping from a degreaser are captured by a lip exhaust, filtered and blown through a bed of activated carbon pellets, granules or fibers. The carbon traps the solvent but allows the air to pass through. The solvent is recovered by steaming the bed and condensing the solvent and steam. Obviously, solvent vapors that are not collected by the exhaust cannot be recovered. Automated systems are common, but manually operated units are available. 

Faber et al. also report on a successful industrial installation using a steam dryer for activated carbon pellets (2000 kg/h, dry basis) from an initial moisture content of 50%-2% (dry basis) [6], The pellets are dried to 8% (dry basis) before they are fed to an evacuated chamber in which the final moisture content of 2% is achieved. The steam enters the dryer at 300°C and leaves at 150°C. The steam discharged is used to preheat the feed. The authors report smooth operation of the dryer since 1985. The installed cost of the steam drying steam was 40% lower than that for a conventional air dryer. The air dryer can operate at a maximum temperature of 125°C to avoid combustion in the dryer. The energy costs (1986 data) were estimated to be about 3.6 per ton of dry product in South Africa. 

Steam-fluidized beds with steam have been in successful operation in South Africa for nearly a decade (Faber et al., 1986). Faber et al. (1986) have shown that fluid-bed steam drying of activated carbon pellets saves energy (15%) as well as capital costs (14). 

Due to its predominantly hydrophobic surface properties, activated carbon preferentially adsorbs organic substances and other non-polar compounds from gas and liquid phases. Activated alumina, silica gel and molecular sieves will adsorb water preferentially from a gas-phase mixture of water vapor and an organic contaminant. In Europe cylindri-cally-shaped activated carbon pellets with a diameter of 3 or 4 mm are used for solvent recovery, because they assure a low pressure drop across the adsorber system. Physical and... 

Table 22.1.9. Activated carbon pellets for solvent recovery (After reference 13)...

Small particle size activated carbon will produce a high pressure drop through the activated-carbon bed. Figure 22.1.12 compares the pressure drop of cylindrically-shaped activated carbon pellets with activated-carbon granulates. The activated carbon particle diameter must not be excessively large, because the long diffusion distances would delay adsorption and desorption. Commercially, cylindrical pellets with a particle diameter of 3 to 4 mm have been most efficient. 

Faber et al. (1986) also reported on a successful industrial installation using a steam dryer for activated carbon pellets (2000 kg/h dry basis) from an initial moisture content of 50% to 2% (dry basis). The pellets were dried... 

Lavine and La Course and Sparks proposed placing a semipermeable membrane on the active carbon pellet surface. The thickness of the semipermeable membrane was about 50 nm, which ensured a good rate of diffusion of adsorbed... 

Rutherford, S.W. Nguyen, C., and Do, D.D., Characterisation of through-flowing pores in activated carbon pellets by the method of time-lag, Dev. Chem. Eng. Mineral Process., 3(3), 125-138(1995),... 

An example of this relation is given in Fig. 4.8 for gaseous phase adsorption of propane and butane on activated carbon pellets. A are well plotted in proportion to 9 d Inp/d In 9 determined from the isotherm relations. 

Suzuki and Kawazoe (197S) measured the effective surface diffusion coefficients of various volatile organics during aqueous phase adsorption on activated carbon pellets and correlated the data using the boiling... 

Figure 5.48. Adsorption isotherms of N2 at 77 K for sepiolite, activated carbons, P-thermal activation - steam C-chemical activation, SP-sepiolite-activated carbon pellets (Rodrfguez-Reinoso et al, 2001).

Inomata K, Kanazawa K, Urabe Y, Ozono H, Araki T. Natural gas storage in activated carbon pellets without binder. Carbon 2002 40(l) 87-93. 

---