Chlorination reactor conditions

Basie of design Extrapolation of subpilot reactor conditions and results Keactor charge consisting of 2,038 g of organic phase and 285 g of the aqueous phase permitted the absorption of 20 liters/hr (59 g/hr) of chlorine at a reaction temperature of 70 C with 99 per Cent conversion of the chlorine... 

Reactions with very large chemical equilibrium constants (e.g., > 10,000) at reactor conditions of temperature and pressure provide an opportunity for approaching 100% conversion during a single pass through the reactor. In addition, when the feed contains stoichiometric proportions of the reactants with no impurities and the reaction leads to only one product, then in principle no separation section is needed. One such situation exists. It is the manufacture of anhydrous hydrogen chloride gas from pure, evaporated chlorine and a stoichiometric amount of pure, electrolytic hydrogen by the reaction ... 

Thus, even in an adiabatic mode of tubular turbulent chlorination reactor operation (without heat removal), the temperature growth in the reaction zone in the case of BR chlorination (12-15% solution) with molecular chlorine in a tubular reactor, operating in the optimum plug-flow mode in turbulent flows, does not exceed 2 1 °C. The process can be thought to proceed under quasi-isothermal conditions and does not require external or internal heat removal, or special stirring devices for heat and mass exchange intensification. 

Ethylene, chlorine and oxygen feeds are supplied from headers and/or supply tanks. Therefore, no design constraint is required to be set for the production rate control. In terms of the relationships between the reactor conditions and the production rate, the pyrolysis has the most influence on the production rate through the reaction conversion by manipulating the reaction temperature. However, this manipulation needs great attention due to the trade-off between the reaction conversion and coke formation and by-product production. 

Figure 18 shows the responses for a 5% step change in the feed flowrates to the direct chlorination reactor. According to this process disturbance, the temperature and pressure controllers of the direct chlorination reactor bring the reactor condition to set point values. This increase in the feed flow results in an increase in the EDC formation and consequently increases the feed flow to the purification columns. Fig. 18 shows that the response of the light column is faster compared to that of the heavy column as the disturbance moves sequentially through the units. 

Selenium and precious metals can be removed selectively from the chlorination Hquor by reduction with sulfur dioxide. However, conditions of acidity, temperature, and a rate of reduction must be carefliUy controlled to avoid the formation of selenium monochloride, which reacts with elemental selenium already generated to form a tar-like substance. This tar gradually hardens to form an intractable mass which must be chipped from the reactor. Under proper conditions of precipitation, a selenium/precious metals product substantially free of other impurities can be obtained. Selenium can be recovered in a pure state by vacuum distillation, leaving behind a precious metals residue. 

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) ... 

Addition Chlorination. Chlorination of olefins such as ethylene, by the addition of chlorine, is a commercially important process and can be carried out either as a catalytic vapor- or Hquid-phase process (16). The reaction is influenced by light, the walls of the reactor vessel, and inhibitors such as oxygen, and proceeds by a radical-chain mechanism. Ionic addition mechanisms can be maximized and accelerated by the use of a Lewis acid such as ferric chloride, aluminum chloride, antimony pentachloride, or cupric chloride. A typical commercial process for the preparation of 1,2-dichloroethane is the chlorination of ethylene at 40—50°C in the presence of ferric chloride (17). The introduction of 5% air to the chlorine feed prevents unwanted substitution chlorination of the 1,2-dichloroethane to generate by-product l,l,2-trichloroethane. The addition of chlorine to tetrachloroethylene using photochemical conditions has been investigated (18). This chlorination, which is strongly inhibited by oxygen, probably proceeds by a radical-chain mechanism as shown in equations 9—13. 

Chlorination of Hydrocarbons or Chlorinated Hydrocarbons. Chlorination at pyrolytic temperatures is often referred to as chlorinolysis because it involves a simultaneous breakdown of the organics and chlorination of the molecular fragments. A number of processes have been described for the production of carbon tetrachloride by the chlorinolysis of various hydrocarbon or chlorinated hydrocarbon waste streams (22—24), but most hterature reports the use of methane as the primary feed. The quantity of carbon tetrachloride produced depends somewhat on the nature of the hydrocarbon starting material but more on the conditions of chlorination. The principal by-product is perchloroethylene with small amounts of hexachloroethane, hexachlorobutadiene, and hexachloroben2ene. In the Hbls process, a 5 1 mixture by volume of chlorine and methane reacts at 650°C the temperature is maintained by control of the gas flow rate. A heat exchanger cools the exit gas to 450°C, and more methane is added to the gas stream in a second reactor. The use of a fluidi2ed-bed-type reactor is known (25,26). Carbon can be chlorinated to carbon tetrachloride in a fluidi2ed bed (27). 

Reaction Conditions. Typical iadustrial practice of this reaction involves mixing vapor-phase propylene and vapor-phase chlorine in a static mixer, foEowed immediately by passing the admixed reactants into a reactor vessel that operates at 69—240 kPa (10—35 psig) and permits virtual complete chlorine conversion, which requires 1—4 s residence time. The overaE reactions are aE highly exothermic and as the reaction proceeds, usuaEy adiabaticaEy, the temperature rises. OptimaEy, the reaction temperature should not exceed 510°C since, above this temperature, pyrolysis of the chlorinated hydrocarbons results in decreased yield and excessive coke formation (27). 

Many techniques have been developed to accomplish this, for example, the use of a cooled recirculating system in which the chlorine is dissolved in one part and the allyl chloride is dissolved and suspended in another (61). The streams are brought together in the main reaction zone and thence to a separator to remove water-insoluble products. Another method involves maintaining any organic phase present in the reaction zone in a highly dispersed condition (62). A continuous reactor consists of a recycle system in which make-up water and allyl chloride in a volume ratio of 10—50 1 are added... 

Halogenated Butyl Rubber. The halogenation is carried out in hydrocarbon solution using elemental chlorine or bromine in a 1 1 molar ratio with enchained isoprene. The reactions ate fast chlorination is faster. Both chlorinated and brominated butyl mbbers can be produced in the same plant in blocked operation. However, there are some differences in equipment and reaction conditions. A longer reaction time is requited for hromination. Separate faciUties are needed to store and meter individual halogens to the reactor. Additional faciUties are requited because of the complexity of stabilising brominated butyl mbber. 

Although the flowsheet shown in Figure 13.7a is very attractive, it is not practical. This would require careful control of the stoichiometric ratio of decane to chlorine, taking into account both the requirements of the primary and byproduct reactions. Even if it were possible to balance out the reactants exactly, a small upset in process conditions would create an excess of either decane or chlorine and these would then appear as components in the reactor effluent. If these components appear in the reactor effluent of the flowsheet in Figure 13.7a, there are no separators to deal with their presence and no means of recycling unconverted raw materials. 

In the chloride process, developed in about 1960, the titanium in the ore is converted to titanium(IV) chloride by heating it to 800 °C with chlorine in the presence of carbon, which combines with the released oxygen. The purified chloride is then oxidised to titanium dioxide at 1000 °C and the chlorine formed is recycled. Technical problems arise because the oxidation of titanium(IV) chloride is not sufficiently exothermic to make the reaction self-sustaining but these can be overcome by pre-heating the reactants and by burning carbon monoxide in the reactor to raise the temperature. By careful control of the conditions, it is possible to produce pure rutile particles of a mean size of 200 nm. 

When the capacity is increased under the same process conditions the caustic concentration is increased on higher dosing. As the quantity of free caustic in the end-product and in the liquid flow of the jet-loop reactor is the same, the percentage of caustic reacting with chlorine increases by roughly 25-60% when the production capacity is increased. Depletion of caustic at the liquid-gas interface can then occur more easily. 

The resist has been used as a mask in wet etching and in lift-off processes, and more recently in etching chromium films in a chlorine-oxygen-helium plasma. In the latter, the etch rates have ranged from 4 to 5.5nm/min at lOOW power in a barrel type reactor. Chromium etches at about 6.5nm/min under these conditions. The etch rate of the resist appears to be independent of the degree to which it has been cured before exposure, so the sensitive form described here is just as effective a mask as the highly cross-linked resists described earlier, at least in the chromium etching 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. 

In the production of carbon tetrachloride, chlorination is carried out in excess chlorine. The lower-boiling, partially chlorinated products then enter into a series of reactors where they react with added chlorine to achieve almost full chlorination of methane. In another process called chlorinolysis, higher aliphatic hydrocarbons undergo exhaustive chlorination at pyrolytic temperature (>600°C).177 182 183 Under such conditions carbon-carbon bond fission and simultaneous chlorination occur. Aliphatic hydrocarbon wastes are the preferred feedstock, as they react with about 20% excess chlorine. 

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