Liquefaction of chlorine

Liquefaction of chlorine is always incomplete, because the non-condensable impurities carry chlorine at its vapour pressure as they leave the liquefaction process. This exit gas, or tail gas, is handled in any of several different ways. It is of course an intolerable plant emission, and the contained chlorine must at least be destroyed before the gas is released to the atmosphere. There is also a powerful economic incentive for recovering much of the chlorine in some usable form - Silver s estimate of the value of the chlorine in the tail gas produced in the United States alone in 1981 was 50 million [3]. 

As noted already, the electrical energy needed to run the refrigeration unit for liquefaction of chlorine is about 335 kj kg-1, equivalent to 93 kWh per tonne of chlorine. The annual power consumption will be 19.5 million kWh. At a power cost of 5c per kWh, the annual cost is close to US 1.0 million. There will also be an operating cost associated with the incremental cooling water usage that has not been included. 

Raw materials are diluted hydroxide solution containing some 18—20 per cent of NaOH, and electrochemically produced chlorine (it is also possible to use tail gas, escaping from condensers in the liquefaction of chlorine). Chlorination proceeds in two immediately subsequent stages. At first, chloride and hypo-chlorous acid are formed ... 

Thus, it was only with the beginning of World War I when another aspect of the industrial revolution in chemistry had this effect.10 As Robinson points out, the technology initially responsible for bringing toxic weapons out from their prehistory was the large-scale liquefaction of chlorine gas and its packaging into pressure cylinders. 11... 

Faraday, Michael (1791-1867) British chemist and physicist, who received little formal education. He started to experiment on electricity and in 1812 attended lectures by Sir Humphry Davy at the Royal Institution a year later he became Dav/s assistant He remained at the Institution until 1861. Faraday s chemical discoveries include the liquefaction of chlorine (1823) and benzene (1825) as well as the laws of electrolysis [see Faraday s laws). He is probably best remembered for his work in physics in 1821 he demonstrated electromagnetic rotation (the principle of the electric motor) and discovered electromagnetic induction (the principle of the dynamo). In 1845 he discovered the Faraday effect. 

In 1824 Faraday gave an account of earlier work on the liquefaction of gases of which he was not aware when he described the liquefaction of chlorine in 1823 (neither, we must assume, was Davy, who corrected the paper). 

The liquefaction of chlorine and sulphur dioxide by compression by North-more, published in an easily accessible English journal, should have been known to Davy (Northmore says he was in touch with the chemical operator at the Royal Institution). Faraday says there was no doubt that Northmore obtained liquid chlorine and sulphur dioxide, but not liquid hydrogen chloride, as he claimed. The supposed liquefaction of air by compression, claimed by Perkins, an American who settled in London, was, said Faraday, very doubtful a specimen of liquid air sent to him, as far as I could by inquiry make out its nature , was water. 

Faraday later gave a full account of the circumstances attending his first liquefaction of chlorine and Davy s share in the proceedings. ... 

A. Achievable Degree of Liquefaction. The major complication in the liquefaction of chlorine is the presence of noncondensable gases. These arise in several different... 

The discussion of liquefaction of chlorine (Section 9.1.7.2B) also pointed out that new systems operate on refrigerants other than the CFCs that were the industry standard for many years. Many existing systems have also been converted to the newer materials. HCFCs, such as R-22, have much lower ozone depletion potentials than the CFCs but... 

Faraday made an analysis of chlorine hydrate (recognised as a compoimd by Davy, see p. 56), finding the composition ClgjioHjO. He showed the results to Davy, who suggested that he should heat this compound in a sealed tube. The result was the liquefaction of chlorine, reported in a note at the end of the paper, which also says when perfectly dry chlorine is condensed into a tube by means of a syringe, a portion of it assumes the liquid forni imder a pressure equal to that of 4 or 5 atmospheres this is also mentioned in the paper on fluid chlorine there the pressure is said to have been developed by throwing in air . In an account (which Faraday later said was accurate) Dr. Paris says that on 5 March 1823, on his way to dine with Davy, he called at the Royal Institution and fotmd Faraday carrying out the experiment si ested by Davy. He drew Faraday s attention to what seemed to be oil in the sealed tube. Faraday was surprised and filed off the end of the tube, which exploded. 

There are many options in the liquefaction of chlorine, depending upon the storage requirements for the liquid and the system used to handle the tail gas. Low-pressure storage is recommended because of the reduced hazard in the event of a spill. However, this requires lower storage temperatures. Low temperatures also reduce the amount of chlorine in the tail gas from liquefaction. Yet lower temperature may not be necessary if a plant also deliberately produces bleach or HCl from the tail gas. 

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