Chlorinated condensate

Figure 8.3 Scheme for global acetylene chlorination/condensation mechanism leading to hexachlorobenzene. (From A. Wehrmeier et al., Environ. Sci. Technol, 1998.)... 

From the mode of the formation of the gas and the condensation that takes place at the time, from the results of the decomposition of its ammoniacal salt, and from the analysis of the gas by metals and metallic oxides, it appears to be a compound of carbonic oxide and chlorine condensed into half the space Miich they occupied separately. 

Starting with enantiomerically pure ( )-(-)-l-NpPhMeSiH 4, successive chlorination, condensation with alkyllithium, bromine cleavage of the silicon naphthyl bond, and reduction with lithium aluminum hydride afforded the new (S)-(+)-alkylphenylmethylsilanes 61-63. Their configurations were established using chemical correlations, cleavage of silicon-aryl bonds having been shown independently to cause inversion at the silicon atom (88). 

Diohloroethane and other products of ethylene chlorination condense in the heatexohanger (5) and than get to the collector (7) for raw storage. Uncondensed part of the products that gets to the reversal condenser (6), where further condensation of ethylene chlorination products takes place. 

It is unlikely that the chlorinated condensation products result from direct condensation of perchlorophenylcarbenium ion with toluene, since, presumably, the steric strain of the primary products, the (heptachlorophenyl-methyl)toluenes, or that of the relevant transition states, would preclude it. 

The condensate in the gas headers will be electrically conductive. Hydrogen condensate will contain dissolved caustic entrained from the cathelyte. Chlorine condensate will contain entrained salt and chlorine dissolved from the gas. 

B. Chlorinated Condensate. An important aspect of chlorine cooling is the composition of the condensate. The water removed from the gas, or in the case of direct cooling of the cooling water as well as that condensed, will be saturated with chlorine. This water is often a process waste, and it must be made innocuous before discharge. Usually, the bulk of the chlorine is stripped from the water after adding acid to reverse its hydrolysis. Hie basics of dechlorination of aqueous streams were covered in the chapter on brine treatment (Section 7.5.9). 

The condensate can be dechlorinated in a dedicated stripper or in a brine dechlor-inator. The form is more characteristic of a diaphragm-cell plant. The latter is a unit required in a mercury- or membrane-cell plant to allow depleted brine to be recycled to the process. It can be designed to treat chlorinated condensate as well as brine, in which case there is no need for separate apparatus. 

L = fraction of incoming chlorine condensed p = ratio of vapor pressure of chlorine to total pressure (= y = mole fraction of chlorine in feed gas... 

C. Formation of Chlorine Hydrate. Because of the presence of traces of water in compressed chlorine, the chlorine hydrate discussed in Section 9.1.3.5 again becomes a problem. As chlorine condenses, some of the water accompanies it. Depending on the temperature, a certain amount of water is soluble in the chlorine. So long as this solubility is not exceeded, the condensate remains homogeneous and solid hydrate does not form. Below we develop an estimate of the solubility of water in liquid chlorine and show that, because of its very low solubility in chlorine and therefore its very high activity coefficient in solution, it behaves as a volatile component. The practical effect of this is that water tends to concentrate in the gas phase in most first-stage liquefiers. 

J. H. Boyette, The BOCOSI Chlorine Condensing System, 39th Chlorine Institute Plant Managers Seminar, Washington, DC (1996). 

We shall treat handling of these condensates in a mercury-cell plant as a special case in Section 16.5.5.3. In the other technologies, with the exception of chlorinated condensate, the condensed streams usually present no severe hazard, and their disposal is relatively simple. Contamination with caustic or salts is usually through entrainment from an evaporating system. Unless there is an accidental massive entrainment, the dissolved solid content of these streams can usually be kept within reasonable bounds. 

Chlorinated condensate arises in the chlorine cooling system and must be stripped before disposal and even before reuse in the process. A secondary dechlorination may be necessary if the water is to be discarded or transferred to another operating unit. 

The principal source of chlorine-containing gas in caustic-chlorine plants is the liquefaction step where noncondensables are vented from chlorine condensers as sniff gas containing 30 to 40% chlorine by weight. Dilute gas may be collected at other points in the operation this gas also requires purification before it can be vented to the atmosphere. A number of processes have been developed to recover the chlorine from the vent-gas streams, including its use for the manufacture of bleach. Where the demand for bleach does not justify this operation, a regenerative recovery system is neces.sary, and one of the simplest of these involves absorption in water. The absorption of chlorine gas in water is also an important step in the manufacture of certain types of wood pulp. In this application, the process is intended primarily to provide a source of concentrated bleaching solution however, design data which have been obtained for the absorption step are equally applicable to gas-purification or chlorine-recovery operations. 

Add 6 g powdered iodine very slowly to S cm liquid chlorine condensed as above. Allow the temperature to rise slowly when excess chlorine is lost and the yellow orange solid remains. Quickly pack into an ampoule and seal off. 

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