Reactor direct chlorination

Figure 10.5 The direct chlorination step of the vinyl chloride process using a liquid phase reactor. (From McNaughton, Chem. Engg., December 12, 1983, pp. 54-58 reproduced by permission.)...

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

Direct chlorination usually produces EDC with a purity greater than 99.5 wt %, so that, except for removal of the FeCl, Httle further purification is necessary. Ferric chloride can be removed by adsorption of a sofld, or the EDC can be distilled from the FeCl in a boiling reactor, as noted above. Alternatively, the FeCl can be removed by washing with water, usually in conjunction with EDC from the oxychlorination process. 

Other Routes. A unique process that produces vinyl chloride, trichloroethylene, dichloroethane, and trichloroethane simultaneously has been developed by Produits Chemiques Pechiney-Saint-Gobain in France (31). Dichloroethylene is chlorinated directly at low temperature to tetrachloroethane, which is then thermally cracked to give trichloroethylene and hydrochloric acid. The dichloroethylene feed is coproduced with vinyl chloride in a hot chlorination reactor, using chlorine and ethylene as feedstocks. 

The low-temperature process, as its name implies, operates at a relatively low temperature where the exothermic heat of the direct chlorination reaction is removed by cooling water. The natural circulation is driven by the gas lift effect of the gaseous feeds before solution and the density differences of a cooler leg that has a relatively higher liquid density than the reactor leg. 

The high temperature process, on the other hand, operates at an elevated temperature where the heat of the direct chlorination reaction actually vaporises a portion of the EDC. This reactor is also a natural circulation reactor, with the liquid EDC circulation driven by the vaporising material. 

Catalyst Poisons. Synthesis gas prepared by the partial combustion of sweet natural gas can be charged to the reactors directly without purification. However, synthesis gas containing more than 0.1 grain of sulfur per 100 cubic feet must be purified before use over fluidized iron catalysts. Other catalyst poisons are known, such as chlorine (14), but they are not likely to be encountered in the natural gas to gasoline process. 

Carbon tetrachloride represents an example of the change to petroleum raw materials in this field. The traditional source of this widely used product has been the chlorination of carbon disulfide, either directly or through the use of sulfur dichloride. Military requirements in World War II caused an increase in demand, and in addition to expansion of the older operations, a new process (28) was introduced in 1943 it involved direct chlorination of methane at 400° to 500° C. and essentially atmospheric pressure. This apparently straight-forward substitution of halogen for hydrogen in the simplest paraffin hydrocarbon was still a difficult technical accomplishment, requiring special reactor construction to avoid explosive conditions. There is also the fact that disposal of by-product hydrochloric acid is necessary here, though this does not enter the carbon disulfide picture. That these problems have been settled successfully is indicated by the report (82) that the chlorination of methane is the predominant process in use in the United States today, and it is estimated that more than 100,000,000 pounds of carbon tetrachloride were so produced last year. 

Orejas, j.A Model evaluation for an industrial process of direct chlorination of ethylene in a bubble-column reactor, Chem. Eng. Sci., 56, 513-522, 2001... 

RHENIUM PENTACHLORIDE AND VOLATILE METAL CHLORIDES BY DIRECT CHLORINATION USING A VERTICAL-TUBE REACTOR... 

Application Vinnolit s new high-temperature direct chlorination (DC) reactor provides an energy efficient technology for the production of furnace feed and sales ethylene dichloride (EDC) without distillation from chlorine and ethylene. 

Ethylene dichloride (EDC) is used to manufacture vinyl chloride monomer (VCM), which is one of the largest commodity chemicals produced in the world. EDC may be produced by the direct chlorination of ethylene or oxychlorination of ethylene in the presence of oxygen and hydrogen chloride. Pyrolysis of EDC produces VCM and an equal amount of hydrogen chloride as a co-product. This hydrogen chloride produced in the pyrolysis reactor is utilized by the oxychlorination process as one of the reactants. Therefore, the component processes of direct chlorination, EDC pyrolysis and oxychlorination are combined to develop a balanced process for the production of VCM with no net consumption or production of hydrogen chloride ... 

Chlorine and ethylene are fed to a direct chlorination reactor where the reaction... 

Simulate the vinyl chloride process (Problem 5.4) using Aspen Plus. Take the feed at room temperature and 20 psia. Operate the direct chlorination reactor at 65°C and 560 kPa. A distillation column removes the trichloroethane and the rest of the stream is sent to the furnace. Heat the stream to 1500 F so pyrolysis takes place. Cool the effluent from the furnace, and recycle the vapor (mostly HCl). Send the hquid (vinyl chloride and ethylenedichloride) to a distillation column for separation. 

Combine two reaction steps, as direct chlorination and cracking, in a single plant (VCM), and treat separately the recovery of HCl. Thus, DCE coming from the oxy-chlorination, becomes an external feed for the VCM plant, which has two distinct reactors, but a common part for the separation system. 

Monsanto and MW Kellogg have entered into an agreement to offer technology for VCM plants. The process combines Monsanto s direct chlorination, EDC pyrolysis and purification technology with Kellogg s Kel-Chlor technology for making chlorine from hydrochloric acid. The Kel-Chlor step replaces the oxychlorination section of a conventional balanced process and the chlorine product is sent to the direct chlorination reactor for conversion to EDC. 

Chlorination reactor and condenser. The direct chlorination operation in Figure 3.7 is replaced by a cylindrical reaction vessel, containing a rectifying section, and a condenser. A pool of liquid dichloroethane, with ferric chloride catalyst dissolved, fills the bottom of the vessel at 90°C and 1.5 atm. Ethylene is obtained commonly from large cylindrical vessels, where it is stored as a gas at an elevated pressure and room temperature, typically 1,000 psia and 70°F. Chlorine, which is stored commonly in the liquid phase, typically at 150 psia and 70°F, is evaporated carefully to remove the viscous liquid (taffy) that contaminates most... 

Stream Information. Directed arcs that represent the streams, with flow direction from left to right wherever possible, are numbered for reference. By convention, when streamlines cross, the horizontal line is shown as a continuous arc, with the vertical line broken. Each stream is labeled on the PFD by a numbered diamond. Furthermore, the feed and product streams are identified by name. Thus, streams 1 and 2 in Rgure 3.19 are labeled as the ethylene and chlorine feed streams, while streams 11 and 14 are labeled as the hydrogen chloride and vinyl-chloride product streams. Mass flow rates, pressures, and tempera-mres may appear on the PFD directly, but more often are placed in the stream table instead, for clarity. The latter has a column for each stream and can appear at the bottom of the PFD or as a separate table. Here, because of formatting limitations in this text, the stream table for the vinyl-chloride process is presented separately in Table 3.6. At least the following entries are presented for each stream label, temperature, pressure, vapor fraction, total and component molar flow rates, and total mass flow rate. In addition, stream properties such as the enthalpy, density, heat capacity, viscosity, and entropy, may be displayed. Stream tables are often completed using a process simulator. In Table 3.6, the conversion in the direct chlorination reactor is assumed to be 100%, while that in the pyrolysis reactor is only 60%. Furthermore, both towers are assumed to carry out perfect separations, with the overhead and bottoms temperatures computed based on dew- and bubble-point temperatures, respectively. 

Lead chloride can be prepared by direct chlorination of lead concentrates either as dry chlorination in a suitable reactor such as a fluidised bed, or by wet chlorination in a suspension in water as part of a leaching operation. Alternatively lead concentrates can be leached with a ferric chloride solution according to Equation 9.7 ... 

The direct chlorination reaction of the ethylene to EDC is carried out in a liquid phase reactor by mixing ethylene and chlorine in liquid EDC. Cooling water is used to remove the heat produced by this exothermic reaction. Direct chlorination reactions may be run rich in either reactant, ethylene or chlorine, and usually the conversion of the lean component is 100% with the selectivity for EDC is greater than 99%. 

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