Recovery by activated carbon

Cost for Hydrogen Recovery by Activated-Carbon Adsorption Process 833... 

Hydrocarbon Recovery. Toluene is typically recovered from the oxidizer vent gases through the use of refrigeration followed by activated carbon adsorption. 

One of the major uses of activated carbon is in the recovery of solvents from industrial process effluents. Dry cleaning, paints, adhesives, polymer manufacturing, and printing are some examples. Since, as a result of the highly volatile character of many solvents, they cannot be emitted directly into the atmosphere. Typical solvents recovered by active carbon are acetone, benzene, ethanol, ethyl ether, pentane, methylene chloride, tetrahydrofuran, toluene, xylene, chlorinated hydrocarbons, and other aromatic compounds [78], Besides, automotive emissions make a large contribution to urban and global air pollution. Some VOCs and other air contaminants are emitted by automobiles through the exhaust system and also by the fuel system, and activated carbons are used to control these emissions [77,78],... 

A hydrogen-recovery method based on selective adsorption by activated carbon will be used. 

M. Lordgooei, K. Carmichael, T. Kelly, M. Rood, and S. Larson, Separation and concentration of volatile organic contaminants by activated carbon cloth for cryogenic recovery, American Chemical Society, Division of Fuel Chemistry Preprints, New Orleans, LA, 1996, pp. 369-373. 

In contrast to the situation of a decade ago [3.1). a substantial literature has now accumulated on copper removal by activated carbons. This is not only because of metal recovery from acid mine wastes [176] and acidic corrosion of pipes [33] but also because of increasing industrial contamination of water streams [177-182]. In particular.many wastewaters contain complexing ions such as ethylenedi-aminetetraacetate (EDTA) and the removal of EDTA-chelated copper (and other) ions has been a special focus of attention [45,173,183-186]. 

Many wastes can be effectively purified by activated carbon,1 but the cost is generally higher than with other methods. The use of carbon often can be justified, however, when the process involves the simultaneous recovery of useful ingredients. Depending on the nature of the adsorbed substances, they may be extracted from the carbon by steam distillation, by elution with a suitable solvent, or by a combination of both. The desorption restores some adsorptive power to the carbon, but the regeneration is seldom complete because many impurities adsorbed from waste liquors cannot be removed either by steam or by a solvent. 

Indirect effects of carbon are sometimes confused with direct catalytic activity, e.g., some reactions are accelerated by activated carbon as a result of the adsorption of inhibitors. An example is found in the recovery of iodine from iodides present in petroleum salt brines. Nitrous acid is employed to oxidize the iodides to iodine —a reaction that may be retarded by the presence of inhibitors in the brine. Treatment of the brine with an activated carbon removes the inhibitors and enables the oxidation reaction to proceed. 

The principle of solvent recovery of activated carbon adsorption has been known for almost a century a process was patented in 1905, but in practice the method was used in 1916 when vapors of volatile substances were recovered by using on activated carbon prepared by using chemical activation with zinc chloride. The solvent recovery became very important during World War 1, due to the shortage of solvents because the war industries needed them in large quantities. 

Activated carbon is applied in the first place as adsorbent for water purification and for gas/air purification. Production streams in the chemical, pharmaceutical and food industry are purified for decolorization and deodorization etc. Recovery of the adsorbates by desorption brings a number of other applications. Known examples are the recovery of solvents in solvent recovery installations and the recovery of gold in mines. Activated carbon is not only applied as an adsorbent. It is also used as a catalyst for a limited number of reactions and as a catalyst carrier. As catalyst carrier activated carbon is among others applied as support for precious metals. These catalysts are mainly applied in the fine chemical and in the pharmaceutical industry. Nevertheless a limited number of precious metal catalyst applications for the bulk chemical industry is known. Not only precious metal catalysts based on activated carbons are produced. A hmited number of other catalytic active compounds are supported by activated carbon. 

The removal of volatile organic compounds (VOC) from air is most often accompHshed by TSA. Air streams needing treatment can be found in most chemical and manufacturing plants, especially those using solvents. At concentrations from 500 to 15,000 ppm, recovery of the VOC from steam used to regenerate activated carbon adsorbent thermally is economically justified. Concentrations above 15,000 ppm ate typically in the explosive range and... 

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. 

Other recovery methods have been used (10). These include leaching ores and concentrates using sodium sulfide [1313-82-2] and sodium hydroxide [1310-73-2] and subsequentiy precipitating with aluminum [7429-90-3], or by electrolysis (11). In another process, the mercury in the ore is dissolved by a sodium hypochlorite [7681-52-9] solution, the mercury-laden solution is then passed through activated carbon [7440-44-0] to absorb the mercury, and the activated carbon heated to produce mercury metal. Mercury can be extracted from cinnabar by electrooxidation (12,13). 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Other techniques include oxidative, steam atmosphere (33), and molten salt (34) pyrolyses. In a partial-air atmosphere, mbber pyrolysis is an exothermic reaction. The reaction rate and ratio of pyrolytic filler to ok products are controlled by the oxygen flow rate. Pyrolysis in a steam atmosphere gives a cleaner char with a greater surface area than char pyroly2ed in an inert atmosphere however, the physical properties of the cured compounded mbber are inferior. Because of the greater surface area, this pyrolytic filler could be used as activated carbon, but production costs are prohibitive. Molten salt baths produce pyroly2ed char and ok products from tine chips. The product characteristics and quantities depend on the salt used. Recovery of char from the molten salt is difficult. 

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