Vapor phase carbon adsorption system

For effective volatilization using an enclosed mechanical aeration system, contaminated soil is mixed in a pug mill or rotary drum. The gasoline components are released from the soil matrix by the churning action of the air/soil contact. The induced airflow within the chamber captures the gasoline emissions and passes them through an air pollution control device (e.g., a water scrubber or vapor-phase carbon adsorption system) before they are discharged through a properly sized stack. 

Fuertes and Nevskaia [139] developed a vapor deposition polymerization (VDP) method to prepare OMCs. Carbon precursor FA was infiltrated into the pores via vapor-phase adsorption at room temperature. When ordered SBA-15 silica was used as a template, the resultant carbon possessed a unimodal pore structure similar to that of CMK-3. However, when a disordered mesoporous silica was used as a template, mesoporous carbon with a well-defined bimodal pore system (mesopores centered at 3 and 12 nm) was obtained, as can be seen from Figure 2.19. A mechanism responsible for the formation of such carbons was subsequently proposed [140] based on the degree of carbon infiltration, which can be controlled with the VDP method. Kruk et al. [141] described a polymerization method for carbon infiltration, which was believed to ensure uniform filling [142] and avoid the formation of nontemplated carbon. 

The use of active carbon to control VOC emissions is of increasing importance. Over 700 plant locations employing adsorption systems are listed in a 1983 EPA report (Troxler et al., 1983). This report covers full-scale activated-carbon vapor-phase adsorption applications and gives specific flow rates, chemicals adsorbed, and sources of emissions. A more recent report (EPA, 1988) presents detailed test data from 12 different sites that remove a wide variety of organic compounds. The report concludes that continuous removal efficiencies over 95% are achievable with the process. 

Special applications The environmental control and life support system on a spacecraft maintains a safe and comfortable environment, in which the crew can live and work, by supplying oxygen and water and by removing carbon dioxide, water vapor, and trace contaminants from cabin air. It is apparent that the processes aimed at the recycling of air and water are vital for supporting life in the cabin. These recycling processes include separation and reduction of carbon dioxide, removal of trace gas-phase contaminants, recovery and purification of humidity condensate, purification and polishing of wastewater streams, and are performed totally or in part by adsorption equipment (Dabrowski, 2001). ... 

In the first step, in which the molecules of the fluid come in contact with the adsorbent, an equilibrium is established between the adsorbed fluid and the fluid remaining in the fluid phase. Figures 22-8 through 22-10 show several experimental equilibrium adsorption isotherms for a number of components adsorbed on various adsorbents. Consider Fig. 22-8, in which the concentration of adsorbed gas on the solid is plotted against the equilibrium partial pressure p° of the vapor or gas at constant temperature. At 40°C, for example, pure propane vapor at a pressure of 550 mm Hg is in equilibrium with an adsorbate concentration at point P of 0.04 lb adsorbed propane per pound of silica gel. Increasing the pressure of the propane will cause more propane to Be adsorbed, while decreasing the pressure of the system at P will cause propane to be desorbed from the carbon. 

First results on n-complexation sorbents for desulfurization with Ag-Y and Cu(I)-Y zeolites have been reported recently [3,4]. In this work, we included the known commercial sorbents such as Na-Y, Na-ZSMS, H-USY, activated carbon and activated alumina (Alcoa Selexsorb) and made a direct comparison with Cu(l)-Y and Ag-Y which were the sorbents with n-complexation capability. Thiophene and benzene vapors were used as the model system for desulfurization. Although most of these studies can be applied directly to liquid phase problems, Cu-Y (auto-reduced) and Ag-Y zeolites were also used to separate liquid mixtures of thiophene/benzene, thiophene/n-octane, and thiophene/benzene/n-octane at room temperature and atmospheric pressure using fixed-bed adsorption/breakthrough techniques. These mixtures were chosen to understand the adsorption behavior of sulfur compounds present in hydrocarbon liquid mixtures and to study the performance of the adsorbents in the desulfurization of transportation fuels. Moreover, a technique for regeneration of the adsorbents was developed in this study [4]. 

One example (out of many) to illustrate the complexity of adsorption from solution (as compared with gas-phase adsorptions), is the removal of mercury, an unacceptable toxic pollutant in aqueous systems. It is found in wastewaters (before treatment) from such manufacturing industries as chloroalkali, paper and pulp, oil refining, plastic and batteries, and can exist as free metal, as Hg(I) and Hg(II). Mercury adsorption capacity, on AC, increases as the pH of the aqueous systems decreases. Carbons with different activation methods have widely different capacities. Sulfurization of the carbon, loading the carbon with zirconium, as well as the dispersion of FeOOH species over the carbon, enhanced Hg(II) uptake. Mercury vapor can be taken up using AC which have been pre-treated with sulfur, the effect of chemisorbed oxygen being to retard (not prevent) the uptake of mercury, Lopez-Gonzalez et al. (1982). 

In many solvent recovery systems, adsorption represents only one step in a complex series of chemical engineering operations. The design of a eomplete system for recovering methylene chloride and methanol from air emitted from a dryer in a resin processing plant has been described by Drew (1975). The overall solvent recovery system includes a water scrubber to remove resins and cool the air to 100°-110°F a standard 2-bed carbon adsorber unit designed for 95% solvent removal efficiency a condenser and decanter to handle the vapors that are stripped from the carbon by steam an extraction column in which water is used to remove the water soluble methanol from the methylene chloride phase a stripping column to remove dissolved methanol and methylene chloride from the waste water and a drying column to remove water from the recovered methylene chloride. These items of equipment and operations are representative of those required for complete solvent recovery systems however, each system must, of course, be tailored to the profierties of the specific solvent involved. 

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