Activated carbon to recover

The effects of adsorption and desorption on the performance of fluidized beds are discussed elsewhere. Adsorption of carbon disulfide vapors from air streams as great as 300 nr/s (540,000 ft3/min) in a 17-m- (53-ft-) diameter unit has been reported by Avery and Tracey ( The Application of Fluidized Beds of Activated Carbon to Recover Solvent from Air or Gas Streams, Tripartate Chemical Engineering Conference, Montreal, Sept. 24, 1968). 

The basis of the process is to use activated carbon to recover SO2 in a salable form. The process flowsheet and chemistry are summarized in Figure 1. All steps of this dry, cyclic process are performed in continuous, countercurrent, multi-stage fiuidized-bed equipment. In the S02-removal step the carbon catalyzes the reaction of the SO2 with oxygen in the flue gas to form SO3, which is hydrolyzed to sulfuric acid that remains sorbed... 

As in the hydrogenation step, several unique oxidizer designs are employed commercially, including cocurrent and countercurrent flow oxidations in single or serial column arrangements. Oxidizer off-gas is passed over beds of activated carbon to recover solvent vapor and for purification. 

In the thermal desorption technique excavated soil is heated to around 200 to 1000°F (93 to 538°C). Volatile and some semivolatile contaminants are vaporized and carried off by air, combustion gas, or inert gas. Off-gas is typically processed to remove particulates. Volatiles in the off-gas may be burned in an afterburner, collected on activated carbon, or recovered in condensation equipment. Thermal desorption systems are physical separation processes that are not designed to provide high levels of organic destruction, although some systems will result in localized oxidation or pyrolysis. 

A mixed-valent polymolybdate on active carbon was prepared from molybdenum metal and H202, followed by the addition of active carbon to the aqueous solution [114,115], This catalyzed the epoxidation of several alkenes in 2-propanol using H202 as an oxidant, while the efficiency of H202 utilization was very low (< 25%). The epoxidation likely proceeded mainly on the surface of the catalyst because the recovered catalyst showed almost similar catalytic activity. 

The crude product is dissolved in 800 ml. of hot 95% ethanol, 15.5 g. of activated carbon (Note 7) is added, and the mixture is swirled periodically while it is allowed to cool for 1 hour. The activated carbon is recovered by filtration with suction through a bed of filter aid (Note 4), the filter cake is washed with 50 ml. of 95% ethanol, and the combined filtrates are evaporated under vacuum with a rotary evaporator. The residue is dissolved in 225 ml. of boiling water, and the hot solution is decanted through glass wool placed in a filter funnel. The filtrate is cooled to 0° and the product is collected by filtration with suction, washed with a small amount of cold water, and dried in a vacuum oven at 50°. The yield of p-formylbenzenesulfon-amide is 25.6-28.0 g. (62.9-68.8%), m.p. 117-118° (Note 8). 

Whether the previously described process is economically optimized depends, of course, on many factors. Whether to recover the CO2, how much to recover, how much downtime can be endured, and similar considerations are a strong function of the amount of activated carbon to be processed, the operating conditions, the cost of the activated carbon, the cost of the equipment, and similar items. For the case of activated carbon regeneration, recovery of CO2 should probably be considered, and the additional capital expense of the second vessel may be justified. 

Tests aiming at recovering the phenols by carbon extraction have so far been unsuccessful. It is generally possible, however, by treating the condensate with activated carbon, to bring down the COD to a lower level than this would be possible by liquid-liquid extraction. Economic factors limit the application of this process to relatively small waste water quantities with high phenol concentrations. 

The dephenolated gas liquor is first treated in a combined Phenosolvan/CLL unit (Sect. 5.1) to expel the acid gas and then recover 99.99% pure liquid ammonia as illustrated in Fig. 5.5. The water leaving the total stripper goes to a biological treatment stage and is then aftertreated by means of activated carbon to serve as make-up water for the cooling loop and possibly also for the BFW loop. 

The difference between disposal and treatment of waste components lies in the fate of those components. When one uses a bed of activated carbon to capture waste components by absorption (Chapter 4.2), the saturated bed is usually discarded and either put to landfill or incineration. That s disposal. Treatment would be if those components were recovered from the bed and recycled or converted for another type of reuse (Chapter 4.16). 

Given that the thmst of environmental r ulations over the last half-century is toward more and not less restriction of pollution, use of activated carbon to treat exhaust air, and possibly recover the solvent from it, is likely to become much more common — whether the treated solvents are characterized as being halogenated, or VOC. 

Carbon absorption utilizes activated carbon to physically absorb bioisoprene from the fermentor ofF-gas. As moisture would affect the absorption capacity of activated carbon, a dehumidifier unit is needed before the contact of the steam with activated carbon (Figure 16.5). The method is useful to recover the low concentration of bioisoprene at the laboratory level. Pioneering studies have shown that the method could absorb more than 80% of bioisoprene from the ofF-steam of 14-1 scale fermentation [52]. A preUminary study in our laboratory also confirmed that the absorption unit (filled with activated carbon fiber cloth) could effectively absorb gas-phase bioisoprene of low concentrations (1000-10 000 ppm, Zou et al., unpublished data). After the absorption step, an offline desorption/condensation step is needed to recover isoprene from activated carbon. Steam is utilized in the regeneration of the activated carbon and desorption of the isoprene. Then a series of condensers and cold traps follow to recover the liquid-phase isoprene. 

The solvent used to form the dope is evaporated during the extrusion process and must be recovered. This is usually done by adsorption on activated carbon or condensation by refrigeration. For final purification, the solvent is distilled. Approximately 3 kg of acetone, over 99%, is recovered per kg of acetate yam produced. Recovery of solvent from triacetate extmsion is similar, but ca 4 kg of methylene chloride solvent is needed per kg of triacetate yam extmded. 

Sodium thiosulfate is a by-product of the manufacture of Sulfur Black and other sulfur dyes (qv), where organic nitro compounds are treated with a solution of sodium polysulfide to give thiosulfate. The dyes ate insoluble and ate recovered by fUtration. The fUtrate is treated with activated carbon and filteted to obtain a sodium thiosulfate solution. After concentration and crystallization, the final product assays ca 96% Na2S202 5H20 (34) (see Dyes AND... 

Other types of regenerators designed for specific adsorption systems may use solvents and chemicals to remove susceptible adsorbates (51), steam or heated inert gas to recover volatile organic solvents (52), and biological systems in which organics adsorbed on the activated carbon during water treatment are continuously degraded (53). 

Process Stream Separations. Differences in adsorptivity between gases provides a means for separating components in industrial process gas streams. Activated carbon in fixed beds has been used to separate aromatic compounds from lighter vapors in petroleum refining process streams (105) and to recover gasoline components from natural and manufactured gas (106,107). 

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