Removal of chlorinated hydrocarbons

Ceria was also proposed as a component of catalysts for the removal of chlorinated hydrocarbons [54]. The process is based on the destmctive adsorption of the chlorinated hydrocarbons on metal oxides [55]. It was demonstrated that CaO and MgO were able to convert CCI4, CHCI3 and C2CI4 to COj and COClj and the corresponding metal chlorides at temperature around 400-500°C in the absence of an oxidant, such as oxygen. Ceria has shown comparable properties CCI4 destruction started at around 450°C, and was accompanied by the reduction of Ce(IV) to Ce(III) and by the formation of CeOCl as intermediate product. 

Hayes, K.F., 1996. Sorption-desorption studies. In The Use of Surfactants to Enhance the Removed of Chlorinated Hydrocarbons from Aquifer Materials, Spring Progress Reports. The Great Lakes Mid-Atlantic Center for Hazardous Substance Research. Ann Arbor, MI The University of Michigan, pp. 13-16, 39-40. 

The unmodified and modified pillared clays, synthesized using amines or with mixed pillars, have an intermediate hydrophylic-hydrophobic character and thus have some potential for the removal of chlorinated hydrocarbons. In Figure 12, the adsorption isotherms of some hydrocarbons on different pillared clays are compared to the adsorption isotherm on Na-montmorillonite (79). In all cases, the adsorption capacity of the mixed Fe-/Zr-PILC is a factor 4 higher than that of the pure Fe-PILC. Besides the adsorption capacity, the isotherm type also changes. 

Berty J, Stenger Jr HG, Buzan GE, Hu K. Oxidation and Removal of Chlorinated Hydrocarbons. Stud Surf Sci Catal 1993 75 1571-1574. 

Much later (Marcinkowsky and Berty 1973) it was proven that ethane did indeed have an effect. In the study of the inhibitor action of chlorinated hydrocarbons it was discovered that these compounds chlorinate the silver catalyst and ethane removes the chlorine from the catalyst by forming ethyl chloride. Since the inhibitor was in the 10 ppm range and similar quantities were used from the ethane present in about one volume percent, the small difference could not be calculated from material balance. The effect of ethane was only noticed as significant by the statistics, which justifies the statement made by Aris (1966) that, The need for sophistications should not be rejected unsophisticatedly. ... 

The results of chain transfer studies with different polymer radicals are compared in Table XIV. Chain transfer constants with hydrocarbon solvents are consistently a little greater for methyl methacrylate radicals than for styrene radicals. The methyl methacrylate chain radical is far less effective in the removal of chlorine from chlorinated solvents, however. Vinyl acetate chains are much more susceptible to chain transfer than are either of the other two polymer radicals. As will appear later, the propagation constants kp for styrene, methyl methacrylate, and vinyl acetate are in the approximate ratio 1 2 20. It follows from the transfer constants with toluene, that the rate constants ktr,s for the removal of benzylic hydrogen by the respective chain radicals are in the ratio 1 3.5 6000. Chain transfer studies offer a convenient means for comparing radical reactivities, provided the absolute propagation constants also are known. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

IT thermal desorption has been used for several years to demonstrate removal of chlorinated phenols, pesticides, polycyclic aromatic hydrocarbons (PAHs), dioxins, polychlorinated biphenyls (PCBs), solvents and mercury from soils and sludges. 

The very extensive use and high consumption of chlorinated hydrocarbons in plant protection resulted in a contamination of the whole environment. DDT (l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane) is very dangerous on account of its toxic effects on all the living organisms. It is remarkably resistant, and its residence time in the atmosphere is considered to be several decades. Due to its method of its application, the atmosphere serves as its largest reservoir. Its vapour pressure at 273 K is 2 x 10 Pa, which represents about 3 fig m. This concentration would correspond to a total amount in the troposphere of roughly 10 t. The other estimate is lower by about one half. From the atmosphere, it is removed only by the rain and the great majority is then transported into the oceans. It is nearly insoluble in sea water but is soluble in fats and thus, it is accumu-... 

Chromium oxide is a well known catalyst for the complete oxidation of chlorinated hydrocarbons due to its high removal activity [1-5]. The commercial application of this catalytic system, however, has been limited by fear about the evaporation of Cr during the course of reaction, especially at high feed concentrations of chlorinated compounds in the feed gas system [3, 4]. Many studies have reported the irreversible deactivation caused by the loss of active Cr components by the formation of Cr02Cl2 from the catalyst surface. 

Reductive dehalogenation is a mechanism for the anaerobic biotransformation of chlorinated hydrocarbons such as hexachlorobenzene (HCB). In reductive dehalogenation, the halogenated compound serves as the electron acceptor rather than the donor that requires a separate carbon source. In a microbially catalyzed reaction, a halide ion is replaced by a hydrogen ion (Figure 13.7). The removal of halide ions results in compounds that are generally easier to degrade, and, in some instances, are completely mineralized. 

CNTs can be combined with various metal oxides for the degradation of some organic pollutants too. Carbon nanotubes/metal oxide (CNT/MO) composites can be prepared by various methods such as wet chemical, sol gel, physical and mechanical methods. To form nanocomposite, CNTs can be combined with various metal oxides like Ti Oj, ZnO, WO3, Fc203, and AI2O3. The produced nanocomposite can be used for the removal of various pollutants. Nanoscale Pd/Fe particles were combined with MWNTs and the resulted composite was used to remove 2,4-dichlorophenol (2,4-DCP). It was reported that the MB adsorption was pH-dependent and adsorption kinetics was best described by the pseudo-second-order model. Iron oxide/CNT composite was reported to be efficient adsorbent for remediation of chlorinated hydrocarbons. The efficiency of some other nanocomposites such as CNT/ alumina, CNT/titania and CNT/ZnO has also been reported [60-62]. 

Decantation alone is likely to be a sufficient method for cleaning up effluents contaminated with hydrocarbons with water solubilities of less than 0.2% and will, by removing the majority of chlorinated hydrocarbons and other sparingly water-soluble solvents at point-source, minimize their spread throughout the effluent system. However, decantation does nothing to remove materials in solution. Indeed, water-miscible solvents will help to take into solution otherwise immiscible components. 

These disinfection by-products, which may be present at levels of a few parts per million or less, include dichloromethane, chloroform, trichloroethylene, and chlorobenzene—all suspected carcinogens. The presence of chlorinated hydrocarbons can be prevented by more efficient removal of the organic matter that becomes chlorinated. 

Rey et al. ° removed chlorinated aromatic hydrocarbon from a pharmaceutical plant by stripping the chlorinated hydrocarbons with air and then adsorbing in activated carbon beds. The removal of chlorinated volatile organic compounds such as trichloroethane, cis, and trans dichloroethane from ground water contaminated with these nonaqueous liquids was carried out by Yu et al." using activated carbon fibers. All the halogenated compounds were adsorbed rapidly by the activated carbon... 

Solvent washing is the removal of organic contaminants from the surface to be cleaned by the use of chlorinated hydrocarbons or other suitable solvents. The solvents frequently used for solvent washing and ultrasonic cleaning are methylene chloride refrigerant 11 (trichlorofluoromethane) refrigerant 113 (trichlorotrifluoroethane) perchloroethylene 1,1,1 -trichlor oethane... 

Jones J, Ross J. The Development of Supported Vanadia Catalysts for the Combined Catalytic Removal of the Oxides of Nitrogen and of Chlorinated Hydrocarbons from Flue Gases. Catal Today 1997 35 97-105. 

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