Oxychlorination of benzene

A second example is the gas-phase oxychlorination of benzene in presence of Cu—Fe catalyst (Raschig process to phenol)248 and the liquid-phase equivalent catalyzed by nitrogen oxides249 alone or combined with metals250 developed by Gulf. 

Raschig process (refs.9,10,11) which was essentially a regenerative route introduced prior to World War II. Chlorobenzene, obtained by the oxychlorination of benzene with an air/chlorine mixture at 200-230°C in the presence of a catalyst containing cupric chloride, ferric chloride and alumina, was hydrolysed with steam under pressure at 400-450°C over a calcium phosphate catalyst. Alternatively a copper-promoted calcium phosphate/silica catalyst has been employed. 

In the early 1930 s a process was developed by Raschig for the synt esis o p e-nol, the principle of which had already been found in England days of aromatic chemistry, namely, oxychlorination of benzene wit m sequen alkaline hydrolysis. This route had been originally discovered by usart an Ch. Bardy in 1872. 

Unlike the Raschig process (see Chapter 5.3.2), in which chlorobenzene is obtained by the oxychlorination of benzene at 240 °C with benzene conversion of 10 to 15%, the process operates with satisfactory selectivity and high conversions, even at relatively low temperatures (60 to 150 °C). 

Only minor catalytic activity of CuCl2 in oxychlorination of arenes is, however, observed in the liquid phase at 80 °C251. Aqueous HBr brominates benzene at 325 °C in presence of air and Fe/silica-alumina catalyst252. 

Thus, in ammonia synthesis, mixed oxide base catalysts allowed new progress towards operating conditions (lower pressure) approaching optimal thermodynamic conditions. Catalytic systems of the same type, with high weight productivity, achieved a decrease of up to 35 per cent in the size of the reactor for the synthesis of acrylonitrile by ammoxidation. Also worth mentioning is the vast development enjoyed as catalysis by artificial zeolites (molecular sieves). Their use as a precious metal support, or as a substitute for conventional silico-aluminaies. led to catalytic systems with much higher activity and selectivity in aromatic hydrocarbon conversion processes (xylene isomerization, toluene dismutation), in benzene alkylation, and even in the oxychlorination of ethane to vinyl chloride. 

Chlorination of benzene and catalytic saponification by Cu in the steam hydrolysis of the chlorobenzene (Raschig process, Raschig-Hooker, Gulf oxychlorination). 

This process involves four main steps. The first,1 conducted at elevated temperature (230 to 270 Q concerns tbe action of benzene on a mixture of hydrochloric acid gas and air in the presence of an oxychlorination catalyst, consisting of copper and iron chlorides on an inert support Once-through conversion is limited to between 10 and 15 per cent to prevent the excessive formation of polychlorobenzenes (10 to 12 molar per cent) This conversion is as high as 98 per oent in relation to the hydrochloric acid. Since the reaction is exothermic, the catalyst is distributed in several beds, between which benzene injections at a lower temperature than those of the reaction streams serve to control the overall temperature. 

This step is followed by the purification of monochlorobenzene by distillation. In its initial version, this operation first involves the partial condensation of the oxychlorination products, followed by their introduction into a brick-lined column, with separation of the water/benzene azeotrope at the top. which is recycled to the reactor after settling. The 1/1 mixture of benzene and chlorobenzenes obtained at the bottom is neutralized with caustic soda, washed with water, and distilled in two columns to separate the dichlorobenzenes, monochlorobenzene and benzene. 

For the same systems haloperoxidase activity has been reported with H2O2 / O2 as oxidant and HC1 / HBr as halogen source [22]. In this way oxychlorination / oxybromination of benzene, toluene, phenol, aniline, anisolc and resorcinol could be achieved. 

In addition to Friedel-Crafts chlorination of benzene, chlorobenzene can also be produced by oxychlorination, using hydrogen chloride in the process developed by Gulf, phenol is obtained as the end product. 

The first step is a vapour phase oxychlorination (cf.. Section 4.2.2.2) of benzene. A mixture of benzene, hydrogen chloride and air is passed over a catalyst (e.g., cupric chloride-lithium chloride) at 200-300°C. About 10% of the benzene is converted per pass. The unreacted benzene is removed to leave a mixture consisting mainly of chlorobenzene, dichlorobenzenes and water. In the second step, this mixture is passed over a complex catalyst at about 500 C this treatment converts both chlorobenzene and dichlorobenzenes (via chlorobenzene) to phenol. The reaction mixture is separated into its various components by passage through a single series of distillation columns. 

Chlorine and sodium hydroxide are the main products of the industrial chlor-alkali electrolysis that is described as a process example in Section 6.19. Hydrochloric acid is produced by reaction from the elements H2 and CI2 or by the reaction of chloride salts such as, for example, NaCl or CaCl2, with sulfuric acid. Other important sources of HCl are industrial chlorination processes using CI2 as chlorination agent (e.g., chlorination of benzene to form chlorobenzene and HCl or the chlorination of methane to give chloromethane and HCl) or industrial dehydrochlorination processes (e.g., production of vinyl chloride and HCl from 1,2-dichloroethane). The main uses of hydrochloric acid are addition reactions to unsaturated compounds (by hydrochlorination or oxychlorination), formation of chlorine in the Deacon process, production of chloride salts from amines and other organic bases, dissolution of metals, regeneration of ion exchange resins, and the neutralization of alkaline products. 

Benzene Oxychlorin tion. In the benzene oxychlorination process, also known as the Raschig Hooker process, benzene is oxychlorinated with hydrogen chloride, air, and with the presence of iron and copper chloride catalyst to form chlorobenzene. The reaction occurs at 200—260°C and atmospheric pressure. The chlorobenzene is hydrolyzed at 480°C in the presence of a suitable catalyst to produce phenol and chloride. The yield of phenol is - 90 mol% of theoretical. These plants have been shut down for environmental and economic reasons. 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

Benzene oxychlorination process, of phenol manufacture, 18 751 Benzeneperoxyseleninic acid, 13 466 Benzene rings, in liquid crystalline materials, 15 103-104 Benzene sulfonation process, of phenol manufacture, 18 751 Benzenesulfonic acid, 3 602 Benzene-toluene fraction, in styrene manufacture, 23 341-342 Benzene-toluene-xylene (BTX), 10 782 ... 

Direct chlorination of vinyl chloride generates 1,1,2-tnchloroethane [79-00-5] from which vinylidene chloride required for vinylidene polymers is produced. Hydrochlorination of vinylidene chloride produces 1,1,1-trichloroethane [71-55-6], which is a commercially important solvent. Trichloroethylene and perchloroethylene are manufactured by chlorination, hydrochlorination, or oxychlorination reactions involving ethylene. Aromatic solvents or pesticides such as monochlorobenzene, dichlorobenzene, and hexachlorobenzene are produced by reaction of chlorine with benzene. Monochlorobenzene is an intermediate in the manufacture of phenol, insecticide DDT, aniline, and dyes (see Chlorocarbons a>td Chlorohydrocarbons.)... 

These processes perform the oxidation of hydrochloric add in situ. Their principle is similar to the one implemented to produce phenol from benzene by the Hooker/Raschig process (see Section 10.1.3). The first industrial ethylene oxychlorination plant was built by Dow in the United States in 1955. 

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