Liquid-phase oxychlorination

Liquid-Phase Oxychlorination of Ethylene To Produce Vinyl Chloride... 

Two important examples of this scheme are the liquid-phase oxychlorination of ethylene to ethylene dichloride ... 

The catalytic oxychlorination of ethylene with HC1 and 02 to vinyl chloride can be catalyzed in the liquid phase by a PdCl2-CuCl2 mixture, or in the vapor phase over supported palladium... 

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. 

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. 

Description EDC is produced in both the addition chlorination (1) and oxychlorination (9) sections of the process. In addition chlorination, ethylene and chlorine are reacted in the liquid phase to produce EDC ... 

Feedstocks for the chlorination process are ethylene and chlorine. The chlorination of ethylene takes place in the liquid phase at 50-100°C (120-212°F) and slightly above atmospheric pressure. Ferric chloride is the homogeneous catalyst for this process. It is very efficient and highly selective. Selectivity to ethylene dichloride is better than 99%. Compared to oxychlo-rination, the chlorination step is more economical and efficient. However, oxychlorination is necessary to consume the hydrochloric acid formed in the EDC pyrolysis step. 

Differences in the processes used by individual VCM producers are due mainly to the different technologies applied in direct chlorination these include high- or low-temperature direct chlorination (both processes are operated in the homogeneous liquid phase in the presence of oxygen as substitution inhibitor), and oxychlorination (fixed- or fluidized-bed process in the heterogeneous gas phase). Differences in these... 

The direct chlorination of ethylene usually is run in the liquid phase and is catalyzed with ferric chloride. High-purity ethylene normally is used to avoid product purification problems. The cracking (pyrolysis) of EDC to vinyl chloride typically is carried out at temperatures of 430 to 530°C over a catalyst. The hot gases are quenched and distilled to remove HCl and then VCM. The unconverted EDC is returned to the EDC purification train. The oxychlorination step is the heart of the process and has two major variables, the type of reactor and the oxidant. The reactor may be either a fixed bed or a fluidized bed, and the oxidant is either air or oxygen. The temperature is in the range of 225 to 275" C with a copper chloride-impregnated catalyst. 

Halogenation—Hydrohalogenation. The most important intermediate is ethylene dichloride [107-06-2] (EDC) which is produced from ethylene either by direct chlorination or by oxychlorination. Direct chlorination is carried out in the liquid or vapor phase over catalysts of iron, aluminum, copper, or antimony chlorides, and at conditions of 60°C. Oxychlorination is carried out in a fixed or fluidized bed at 220°C with a suitable solid chloride... 

Reactor effluent gases are quenched with water in a prestressed brick-lined, packed tower. The liquid leaving the tower is cooled further and separated into aqueous and DCE phases. The aqueous phase is split, part being recycled to the tower as quench liquid and the remainder recycled to the reactor, except for a purge equal to the water produced in the oxychlorination reaction. The water recycled to the reactor is first used to absorb part of the HCl feed and enters the reactor as an aqueous HCl solution. DCE product is cooled further and flashed to separate out more water (purged) and dissolved ethylene (recycled). 

Bubble columns, in which the liquid is the continuous phase, are used for slow reactions. Drawbacks with respect to packed columns are the higher pressure drop and the important degree of axial and radial mixing of both the gas and the liquid, which may be detrimental for the selectivity in complex reactions. On the other hand, they may be used when the fluids carry solid impurities that would plug packed columns. In fact, many bubble column processes involve a finely divided solid catalyst that is kept in suspension, such as the Rheinpreussen Fischer-Tropsch synthesis, described by Kolbel [1971], or the former LG. Farben coal hydrogenation process or vegetable oil hardening processes. Several oxidations are carried out in bubble columns the production of acetaldehyde from ethylene, of acetic acid from C4 fractions, of vinyl chloride from ethylene by oxychlorination, and of cyclohexanone from cyclohexanol. 

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