Cooling chlorinated

Any equipment used for gas-liquid contact can in principle be used to cool chlorine gas. In practice, spray colunms and packed beds are most common. Beds are more expensive Init, because they offer improved staging, more efficient. Ceramic ring or saddle packing is the type most often found in large units. Vessels are of rubber-lined steel or FRP construction. 

Example. Here we consider the size of a packed column to cool chlorine cell gas from 87 to 40 C. This is the same duty as in the example of Section 9.1.3.1, which covered the duty curve and calculation of the mean temperature differential. The same data allow us to calculate the number of transfer units required. We shall assume the use of 50-mm rings (packing factor = 187 m m ). 

A. Minimum Gas Temperature. While the goed in cooling chlorine is to remove as much water as possible, there are fundamental limitations that must be observed. 

After cooling, chlorine gas is dried by contact with concentrated sulfuric acid, a powerful desiccant over which the vapor pressure of contained water is very low. Other drying processes have been suggested from time to time, but none has had wide commercial success. The absorption of water by sulfuric acid is highly exothermic (more than 3 MJ kg ), and many combinations of feed and spent acid strengths can result in boiling if the heat is not removed. This section covers the amounts of acid required, equilibrium considerations in the process, the types of apparatus used, and the handling of the acid. 

The purpose of cooling chlorine at this point in the conventional process is largely to remove most of the accompanying water. One of the speculations on chlorine drying, discussed below, would make it possible to eliminate this step and replace it with a liquid-phase cooler. 

FIGURE 24.4 Evaporatively cooled chlorinator used for chlorinating slurries. (Redrawn from Nicolaisen, B.H., U.S. Patent 3,241,912,1966.)... 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

Phosphorus pentachloride is prepared by the action of chlorine on phosphorus trichloride. To push the equilibrium over to the right, the temperature must be kept low and excess chlorine must be present. Hence the liquid phosphorus trichloride is run dropwise into a flask cooled in ice through which a steady stream of dry chlorine is passed the solid pentachloride deposits at the bottom of the flask. 

Chlorine has a boiling point of 238 K and is a greenish-yellow diatomic gas at room temperature. It can be liquefied by cooling or by a pressure of a few atmospheres at room temperature. 

Sodium Hypochi ite. zM- This may be prepared with sufficient accuracy by dissolving 100 g. of NaOH in 200 ml. of water in a large beaker, cooling the solution, and then adding about 500 g. of crushed ice. Now counterpoise the beaker on a rough set of scales, and pass in chlorine from a cylinder until an increase in weight of 72 g. is obtained. Make up the solution to i litre and stir well. The solution must be kept in a cool dark place, but even then slowly decomposes. 

Apply the test to compounds which contain chlorine or bromine. If the compound is a solid, dissolve 0 1 g. in the minimum volume of pure, dry acetone. To 1 ml. of the sodium iodide acetone reagent add 2 drops of the compound (if a hquid) or the acetone solution (if a sohd). Shake and allow to stand at room temperature for 3 minutes. Note whether a precipitate is formed and also whether the solution acquires a reddish-brown colour (liberation of iodine). If no change takes place at rocrm temperature, place the test-tube in a beaker of water at 50°. After 5 minutes, cool to room temperature, and observe whether a reaction has occurred. 

A mixture of 0.10 mol of the acetylenic alcohol, 0.12 mol of triethylamine and 200 ml of dichloromethane (note 1) was cooled to -50°C. Methanesulfinyl chloride (0.12 mol) (for its preparation from CH3SSCH3, (08300)30 and chlorine, see Ref. 73) was added in 10 min at -40 to -50°0. A white precipitate was formed immediately. After the addition the cooling bath was removed and the temperature was allowed to rise to -20°0, then the mixture was vigorously shaken or stirred with 100 ml of water. The lower layer was separated off and the aqueous layer was extracted twice with 10-ml portions of CH2CI2. The combined solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum (note 2). The yields of the products, which are pure enough (usually 96%) for further conversions, are normally almost quantitative. 

The cooled, dried chlorine gas contains - 2% HCl and up to 10% O2, both of which are removed by Hquefaction. A full scale 600-t/day plant was built by Du Pont ia 1975. This iastaHatioa at Corpus Christi, Texas operates at 1.4 MPa (13.8 atm) and 120—180°C and uses tantalum-plated equipment and pipes. Oxidation of HCl Chloride by JSHtricHcid. The nitrosyl chloride [2696-92-6] route to chlorine is based on the strongly oxidi2iag properties of nitric acid... 

Because this reaction is highly exothermic, the equiUbrium flame temperature for the adiabatic reaction with stoichiometric proportions of hydrogen and chlorine can reach temperatures up to 2490°C where the equiUbrium mixture contains 4.2% free chlorine by volume. This free hydrogen and chlorine is completely converted by rapidly cooling the reaction mixture to 200°C. Thus, by properly controlling the feed gas mixture, a burner gas containing over 99% HCl can be produced. The gas formed in the combustion chamber then flows through an absorber/cooler to produce 30—32% acid. The HCl produced by this process is known as burner acid. 

Cooled dust-laden gas is dedusted in an electrostatic precipitator and sent to the cleaning unit to remove impurities such as arsenic, fluorine, and chlorine before being sent on to the sulfuric acid production plant. 

Gas-phase chemiluminescence is illustrated by the classic sodium—chlorine cool flame (174) ... 

A number of chemiluminescent reactions have been studied by producing key reactants through pulsed electric discharge, by microwave dissociation, or by observing the reactions of atoms and free radicals produced in the inner cone of a laminar flame as they diffuse into the flame s cool outer cone (182,183). These are either combination reactions or atom-transfer reactions involving transfer of chlorine (184) or oxygen atoms (181,185—187), the latter giving excited oxides. 

---