Chlorination using Solid Catalysts

Chloromethane is an important industrial chemical. Olah et al. [56] have reported the selective catalytic monochlorination of methane to chloromethane over superacidic sulfated zirconia solid catalysts, for example 804 /Zr02, Pt/ S04 7Zr02, and Fe/Mn/S04 7Zr02- The reactions were conducted in a continuous-flow reactor under atmospheric pressure. At 200 °C with 30 % chlorine the selectivity to chloromethane was 90 %.The selectivity could be enhanced by adding platinum. The only by-product was CH2CI2. The latter is formed by the subsequent chlorination of chloromethane. No chloroform or carbon tetrachloride was formed. The authors postulated that chlorination occurs by an electrophilic insertion of an electron-deficient, metal coordinated, chlorine molecule into the C-H bond of methane. One drawback of the process was that above 225 °C, part of the metal was removed as the metal chloride [56]. Formation and subsequent loss of volatile metal chlorides is a major pitfall that should be avoided during vapor-phase chlorination over solid catalysts. 

The gas-phase oxychlorination of ethylene with HCl to 1,2-dichloroethane (ethylene dichloride or EDC) catalyzed by CUCI2 supported on alumina, followed 

In a recent study of the CUCI2-AI2O3 catalyst system, Finocchio et al. [42] discovered that at 250 °C, whereas the oxychloiination reaction occurs on copper sites, the alumina surface converts the desired product, EDC, to by-products such as vinyl chloride, trichloroethane, and dichloroethylene. The superiority of copper chloride over copper nitrate as the catalyst precursor is probably because metal chlorides are more highly dispersed than metal nitrates on impregnated alumina surfaces and, hence, expose less of the uncovered alumina surface. CuCT is also more effective than copper nitrate in poisoning the nucleophilic sites (exposed oxide anions) on alumina. 

An extensive literature exists on the characterization and structure—activity correlation of industrial copper-alumina oxychlorination catalysts [95-120]. At least two different major copper species have been identified. At low concentrations of copper (below ca 5 %), a well-dispersed copper species in intimate interaction with the alumina surface is formed. This species has a very low oxychlorination activity. At higher concentrations, a second species, probably formed by the de-position/precipitation of the copper chloro complexes, is observed. The latter gives rise to the active sites during the oxychlorination reaction. On the basis of an FTIR study of the oxychlorination reaction Finocchio et al. [42] postulated the formation of surface copper chloride-ethylene r-complex intermediates (which lead eventually to EDC) and weakly adsorbed HCl during oxychlorination. Formate species associated with copper and probable precursors for formation of the oxides of carbon by combustion were also identified. 

More progress has been reported on the halogenation of aromatic compounds over zeolite catalysts. Jang et al. [55] studied the vapor phase catalytic chlorination of chlorobenzene using solid-acid catalysts such as silica-alumina, alumina, zeolites and modified clay (bentonite) impregnated with FeClj Dichlorobenzene selectivity was higher over the zeolite catalysts. 

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XRF analysis was used for the determination of ruthenium, tin, sodium and chlorine content. Solid catalysts samples were examined by automatic sequence RTG spectrometer (ARE 9400 XP). Elements loadings were evaluated by UNIQUANT analyzer. The program used a universal calibration method. 

Reaction of dialkylmagnesium compounds with selected chlorinated compounds produces finely divided MgCl that can be used as a support for polyethylene catalysts. Other reagents may be used to produce different inorganic magnesium compounds, also suitable as supports. Examples are shown in Figure 4.1. Treatment of these products with transition metal compounds results in a supported "precatalyst." Typically, the transition metal is subsequently reduced by reaction with an aluminum alkyl and the solid catalyst isolated. The solid catalyst and cocatalyst (usually TEAL) may then be introduced to the polymerization reactor. 

Why are solid, unmodified alumina, silicas, and zeolites able to be used as catalysts (77) Are lanthanide catalysts really environmentally friendly 18) What are solid acids and solid bases and how can they be used for catalysis 19) Why is catalysis a foundational pillar of green chemistry 20) What are the advantages of a totally chlorine free bleaching process (27)... 

Diamond has long been regarded as an inert material for chemical reactions. Recently, one of the present authors elucidated that the surface of diamond can be modified by chemical reactions, such as hydrogenation, oxidation, chlorination, etc. [1]. Activated carbon, composed of sp carbon atoms, has been utilized as a support material for catalyst. However, no carbon materials consisting of sp carbon atoms have been used as catalyst supports. Silicon oxide (or silica) is also a very popular support material to catalysts. Carbon belongs to the same group of elements as silicone, but no carbon oxide solid phase exists. 

Most of the industrial chlorinations of organic compounds are, at present, performed by free CI2 either in the absence of catalysts or in the presence of Lewis acid catalysts such as the halides of aluminium and iron. The major handicap of the Lewis acid catalysts like FeCb or AICI3, is the difficulty of their disposal, after use in the chlorination reaction, in an environmentally friendly manner. The use of zeolite catalysts in the chlorination processes will avoid corrosion and disposal problems. Work-up procedures to isolate and recover the desired product will also be easier leading to simpler and cleeiner process routes. In addition, if zeolites are used as solid catalysts, one may anticipate that desired changes in selectivity (enhanced para-selectivity in nuclear chlorination of aromatics, for example) may be achieved. Zeolite catalysts are well known to catalyze various synthetic transformations, however, relatively a few reports are available on the selective chlorination of aromatics using zeolite catalysts [1-4],... 

E-J Shin, MA Keane. Detoxifying chlorine rich gas streams using solid supported nickel catalysts. J. Hazard. Mater. B 66 265-278, 1999. 

Dangerous materials may require special equipment. Chlorination with gaseous chlorine requires quite expensive storage facilities. Chlorination with chlorine, thionyl chloride, sulphuryl chloride, phosphorus oxychloride, phosphorus trichloride, or phosphorus pentachloride, all of which are fairly hazardous, requires off-gas treatment. Some of these reactants can be recycled. Pyrophoric solids such as hydrogenation catalysts, anhydrous aluminium trichloride for Friedel-Crafts reactions, or hydrides used as reducing agents should usually be handled using special facilities. Therefore, all of the above proce.sses are usually carried out in dedicated plants. 

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

In SL-PC, a catalyst is supported on a solid matrix in the form of the film of a nonvolatile liquid phase adsorbed on the solid. The catalytic film can be, for example, a molten salt or a molten oxide (e.g., Deacon s catalyst (CUCI2/KCI) used to oxidize HCl with oxygen for the chlorination of ethylene in the synthesis of vinyl chloride. Figure 6.1 V2O5 for the oxidation of sulphurous to sulphuric anhydride). Alternately, it can be a liquid phase (e.g., ethylene glycol, PPh3, butyl benzyl phthalate, etc.) that contains a soluble catalytic species such as a metal complex. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

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