Chemical treatment with activated

Fig. 3.68. Analytical HPLC chromatograms with detection of diode array of 4.7 x 10"5mol/l of R3R dye curve (1) before and curve (2) after 180 min of photoelectrocatalysis on the Ti02 thin-film electrode biased at +1.0 V in NajSCT, 0.025 mol/l. Curve (4) before and curve (3) after photoelectrocatalysis in NaCl 0.022 mol/l and curve (5) after bleaching of 4.7 X 10-5 mol/l of R3R dye submitted to a chemical treatment by active chlorine addition. The mobile phase was methanol-water 80 20 per cent with a flow rate of 1 ml/min and controlled temperature at 30°C. The column was a Shimpack (Shimadzu) CLC-ODS, 5 /an (250 mm X 4.6 mm). Reprinted with permission from P. A. Cameiro el al. [138].

The activated carbons have been prepared by carbonization of precursors, i.e., raw materials with subsequent activation by physical treatment and/or chemical treatment. The activation procedure is conducted in order to enlarge the volume and size of the pores which were already created during the carbonization process and to create some new porosity. Most commonly employed activation methods are divided into physical and chemical activations.14"16,18"35... 

Sulfolene (butadiene cyclic sulfone), m.p. 64-66°, from Shell Chemical Co., or from Aldrich Chemical Co., was found satisfactory for use as received. One lot purchased from another source required solution in hot methanol and treatment with activated carbon (250 ml. of methanol and 2 g. of Norit per 100 g. of material), filtration, and crystallization to free it of color, odor, and particulate matter. 

Anaerobic sediments frequently contain large amounts of elementary sulfur (S8) which may cause serious interference during GC analysis. The traditional method that is applicable to chemically stable analytes is treatment with activated copper, but an elegant and milder procedure in which elementary sulfur is converted into water-soluble thiosulfate by reaction with tetrabutyl ammonium sulfite has been developed 0ensen et al. 1977). This method cannot, however, be applied to samples containing sensitive compounds such as phenols in such cases, the sulfur may be removed from the phenol acetates by silica gel chromatography and elution with cyclohexane (Allard et al. 1991). 

An attempt was made to correct the copper corrosion problem by different types of fuel treatments (25). JP-5 samples were subjected to clay or silica gel filtration, or treatment with activated charcoal to remove the corrosive compounds. None of these treatments was successful. Samples were also treated with barium nitrate (to precipitate out sulfonates), sodium hydroxide (to extract mercaptans), and air bubbling to oxidize the corrosive compounds. These chemical treatments also were unsuccessful. However, JP-5 fuel (which failed the copper corrosion test) passed if benzotriazole, sometimes used to passivate copper surfaces, was added to the fuel in low concentrations (2 ppm) using FSII as a solvent. This technique is effective for reducing jet fuel attack on copper-nickel pipes used aboard aircraft carriers (26). 

Pretreatment with carbon of a material to be purified often enables a chemical agent to function more effectively (Table 4 13). 2,3 In a process to reclaim iodides from petroleum brine, the initial step consisted of oxidizing the iodides to elemental iodine, and this reaction had been prevented by impurities in the brine that acted as inhibitors of oxidation. It became necessary to remove these inhibitors by pretreating the brine with a special type of activated carbon, after which the oxidation proceeded without difficulty. A similar type of behavior probably explains why hydrogen peroxide is a more effective bleaching agent for certain waxes after they have been given prior treatment with activated carbon. 

The first step in the treatment process usually is the chlorination of the solution to ensure oxidation of all the mercury. This may be carried out at pH 3 to avoid the precipitation of iron. After filtration to remove undissolved mercury and hydroxides of other metals, the effluent goes on to final treatment. In order to protect the easily oxidized thiol groups, reduction of free chlorine is necessary. This is usually done in two steps, chemical treatment with a reducing agent and chemisorption on activated carbon (both in Section 7.S.9.3). The reducing agent in mercury-removal plants is commonly an -based species. 

HjS. This change may result in potential SSC and other cracking mechanisms. Sulfate-reducing bacteria (SRB) activity in the water phase is the primary cause of the H2S increase. As a result, chemical treatment with a biocide may be required. 

When the efficiency of the activated carbon is diminished by coating the snrface of the activated carbon with adsorbed material, reactivation is reqnired.This is accomplished by oxidizing the adsorbed material in regeneration furnaces at temperatnres aronnd 1470°F (800°C), or chemical treatment with phosphoric acid, potassinm hydroxide, or zinc chloride. 

The water that evaporates from the dechlorinated brine is condensed in a cooler. The condensate, which may be chemically dechlorinated, is returned to the brine circulation system if necessary to maintain the volume of the brine circuit. If necessary, the remaining chlorine content can be further reduced by blowing with compressed air, by a second vacuum treatment, by treatment with activated carbon (63], or by chemical treatment with hydrogen sulfite, thiosulfate, sulfur dioxide, or sodium hydrogensulfide. 

The conducting polymers can make a transition from an initial insulating/seniiconducting state to an electrically conducting state after the chemical treatment with redox active agents and have been increasingly used for optical and bio/gas sensors. However, the problem of stability and its reaction with moieties present in the environment limits the appH-cation of most of the organic materials (Kaushika et al., 2013). 

The surface of an activated carbon adsorbent is essentially non-polar but surface oxidation may cause some slight polarity to occur. Surface oxidation can be created, if required, by heating in air at around 300°C or by chemical treatment with nitric acid or hydrogen peroxide. This can create some hydrophilic character which can be used to advantage in the adsorption of polar molecules but can cause difficulties in other applications such as the... 

The cobalt catalyst can be introduced into the reactor in any convenient form, such as the hydrocarbon-soluble cobalt naphthenate [61789-51 -3] as it is converted in the reaction to dicobalt octacarbonyl [15226-74-17, Co2(CO)g, the precursor to cobalt hydrocarbonyl [16842-03-8] HCo(CO)4, the active catalyst species. Some of the methods used to recover cobalt values for reuse are (11) conversion to an inorganic salt soluble ia water conversion to an organic salt soluble ia water or an organic solvent treatment with aqueous acid or alkah to recover part or all of the HCo(CO)4 ia the aqueous phase and conversion to metallic cobalt by thermal or chemical means. 

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