Residual gases from chlorination

Figures. Explosive limits of chlorine-hydrogen-other gas mixture Horizontally hatched area = Explosive region with residue gas from chlorine liquefaction (O2, Nj, CO2)...

Any hydrogen contained within the chlorine from the electroly2er is concentrated in the residual gas from the Hquefaction process and must not be allowed to exceed the explosive concentration limit of 5%. Although hydrogen concentration can be controUed by adding dry air to the process. 

The explosion pressure is vented by means of a bursting disk to a residual gas absorber. Simultaneously the residual gas from the first stage is passed directly into this absorber. The chlorine gas to the second stage is shut off, and an inert gas purge is introduced. Finally, the liquid chlorine exit valve... 

Sulphonic acids and their salts are analysed by GC after esterification with diazomethane or after chlorination with thionyl chloride or phosgene [119]. Reaction with thionyl chloride proceeds according to Scheme 5.14. A 0.5-g sample of sulphonic acid or its salt is placed into a round-bottomed flask fitted with a magnetic stirrer and a reflux condenser, 0.5 ml of dimethylformamide and 20 ml of thionyl chloride are added and the mixture is refluxed for several minutes up to 2 h (according to the character of the sample) until the evolution of gas from the reaction mixture ceases (detection with the aid of a bubbler filled with chlorobenzene). If a salt is chlorinated, solid chloride produced in the reaction mixture must be removed by dilution with dichloromethane and by careful filtration through a fine glass filter. Excess of thionyl chloride and solvent is evaporated carefully under decreased pressure. The residue is dissolved in a suitable solvent (CCU) and analysed by GC (silicone stationary phase, temperature 160°C). 

Gas Feeders, Chlorine gas is usually fed from a chlorine cjdindet equipped with a pressure gauge, reducing valve, regulating valve, feed-rate indicator, and aspirator-type injector for dissolving the chlorine gas in water. The feeder can be manually, or mote desirably automatically, controlled utilizing continuous amperometric or potentiometric measurement of the free chlorine residual. The chlorine solution is normally introduced into the return line to the filter. 

Finally, a process has been developed for disintegrating chlorinated hydrocarbon residues with recovery of hydrochloric acid [97]. The chlorine content in the flue gas from the combustion process is kept as low as possible by minimizing the oxygen content and feeding steam or water into the combustion chamber. However, the hydrochloric acid produced is apparently not completely free of elementary chlorine, because chlorine is sometimes still found in the waste gas after HCl absorption. 

The objective in incinerating residues containing chlorine is to convert as much as possible of the chlorine content to hydrogen chloride. HCl can be absorbed in water from the reaction gas mixture. Chlorine requires a reagent (caustic) for proper scrubbing and neutralization. 

In addition to the natural components crude oils have been shown to contain very small amounts, in the parts per billion range, of chlorinated pesticide residues. Gas-chromatographic determinations have been carried out on samples of oil seeds, crude and processed oils and by-products from soybeans (Chaudry et al, 1976, 1978 Hashemy-Tonkabony and Soleimani-Amiri, 1976) and on sunflower seed and cottonseed oils (Hashemy-Tonkabony and Soleimani-Amiri, 1976). 

The Shell Chlorine Process. The catalyst developed by Shell consists of a mixture of copper(II) chloride and other metallic chlorides on a silicate carrier [202]. The reaction of the stoichiometric mixture of hydrogen chloride and air takes place in a fluidized-bed reactor at ca. 365 °C and 0.1-0.2 MPa. The yield is 75%. The water condenses out from the gas stream, and the hydrogen chloride is removed by washing with dilute hydrochloric acid. After the residual gas has been dried with concentrated sulfuric acid, the chlorine is selectively absorbed, e.g., by disulfur dichloride. After desorption and liquefaction, the chlorine has a purity > 99.95 %. 

Industrial Hquid chlorine is routinely analy2ed for moisture, chlorine, other gaseous components, NCl, and mercury foUowing estabHshed procedures (10,79). Moisture and residue content in Hquid chlorine is determined by evaporation at 20°C foUowed by gravimetric measurement of the residue. Eree chlorine levels are estimated quantitatively by thiosulfate titration of iodine Hberated from addition of excess acidified potassium iodide to the gas mixture. 

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

Entry into a tank that has contained any chlorinated or any easily evaporated solvent requires special procedures to ensure worker safety. The heavier vapors tend to concentrate in unventilated spaces. The proper tank entry procedure requires positive ventilation, testing for residue solvent vapor and oxygen levels, and the use of respiratory equipment and rescue harness. Monitoring the tank from outside is also important. The use of an appropriate gas mask is permissible in vapor concentrations of less than 2% and when there is no deficiency of atmospheric oxygen, but not for exposures exceeding one-half hour. Skin exposure to 1,1,1-trichloroethane can cause irritation, pain, bHsters, and even burning. Eye exposure may produce irritation, but should... 

Acetic acid and 10, 15, or 20% acetyl chloride were fed as a mixture into a modified falling film micro reactor (also termed micro capillary reactor in [57]) at a massflow rate of 45 g min and a temperature of 180 or 190 °C [57]. Chlorine gas was fed at 5 or 6 bar in co-flow mode so that a residual content of only 0.1% resulted after reaction. The liquid product was separated from gaseous contents in a settler and collected. By exposure to water, acetyl chloride and acetic anhydride were converted to the acid. The hydrogen chloride released was removed. 

Residue analytical chemistry has extended its scope in recent decades from the simple analysis of chlorinated, lipophilic, nonpolar, persistent insecticides - analyzed in the first Si02 fraction after the all-destroying sulfuric acid cleanup by a gas chro-matography/electron capture detection (GC/ECD) method that was sometimes too sensitive to provide linearity beyond the required final concentration - to the monitoring of polar, even ionic, hydrophilic pesticides with structures giving the chemist no useful feature other than the molecule itself, hopefully to be ionized and fragmented for MS or MS" detection. 

---