Oxygen content in chlorine

KU is working on both of these points to improve the chlorine quality. Point (1) is continually being optimised jointly with the coating manufacturers, with whom KU maintains close liaison. Figure 16.10 plots the acidification results in an operational plant and represents the optimisation of point (2). The quantity of hydrochloric acid used is as low as 18-20 kg per tonne of NaOH leading to an anolyte pH of 2.4-2.8 and an oxygen content in chlorine gas of 0.5-0.8 vol.%. 

Fig. 16.10 Achievable oxygen content in chlorine gas from an electrolyser (158 elements) versus the anolyte pH and the HCI quantity used (100%) per tonne of NaOH.

Low oxygen content in chlorine gas with hydrochloric acid addition... 

Fig. 19.8 Oxygen content in chlorine with hydrochloric acid addition to the AZEC Improved B-1 facility at Kashima.

In the Improved B-1 at the Kashima factory, low-oxygen content chlorine gas can be obtained by adding hydrochloric acid to the feed brine. Figure 19.8 shows the dependence of the oxygen content in the chlorine gas upon the content of the hydrochloric acid in the feed brine at 6 kA m 2 current density operation. 

It is possible to neutralize the invading OH ions in the membrane process by addition of hydrochloric acid into the anode compartment and to decrease the pH value down to 2. Then, hypochlorite and chlorate formation is stopped, and the oxygen content in the anode gas is reduced to 0.5 vol.%. No OH ions are formed within the electrolysis cell of the amalgam process so that the oxygen content of chlorine gas is less than 1 vol.%. 

Cartridge-type respirators with or without facepiece (or full facepiece respirators with chemical cartridge) offer adequate temporary protection provided the oxygen content in the air is greater than 19.5 percent and the chlorine concentration does not exceed the rated capability of the respirator. The NIOSH rating for maximum chlorine concentration for each type of respirator should be noted and followed. The need to protect the eyes from chlorine should be part of the evaluation of appropriate respiratory equipment. A supplied-air SCBA with full face-piece is required for performing tasks when chlorine may be present unless air sampling verifies the chlorine concentration is such that a lower level of respiratory protection provides protection. 

Most chlorine releases are at low concentrations where the oxygen content in the air is greater than 19.5 percent and chemical cartridge respirators (up to 10 ppm) or canister masks (25 ppm, maximum) would offer adequate protection. However, without chlorine-monitoring equipment for sampling air in the vicinity of the leak, the use of positive pressure self-contained breathing apparatus (SCBA), with full face piece, is required. 

Electrochemically active film-forming materials such as Mn02, which may lead to an increased oxygen content in the chlorine. 

The apparatus is sometimes referred to as an oxygen electrode , but it is actually a cell. Although the Teflon membrane is impermeable to water and, therefore, to most substances dissolved in water, dissolved gases can pass through, and gases, such as chlorine, sulphur dioxide and hydrogen sulphide, can affect the electrode. The apparatus can be made readily portable and it is, therefore, of value for use in the field and can be used to monitor the oxygen content of rivers and lakes (see Ref. 53). 

In its reactions SsO shows properties typical for both sulfur homocycles and sulfoxides. With elemental chlorine SOCI2 and S2CI2 are formed, with bromine SOBr2 and S2Br2 are obtained. Water decomposes SsO to H2S and SO2 besides elemental sulfur while cyanide ions expectedly produce thiocyanate. The reaction with iodide in the presence of formic acid is used for the iodometric determination of the oxygen content [70] ... 

Elsewhere in this book, White and Sandel [7] discuss the integration of chlorine and ethylene dichloride (EDC) processes. The oxygen content of the chlorine fed to an EDC unit must be kept within the process specification. This can be achieved by liquefying at least part of the chlorine in order to reject non-condensables or by acidifying the brine fed to the cells. Oxygen results from the anodic oxidation of hydroxide ions free acid in the feed brine will neutralise those ions and so reduce the amount of oxygen formed. 

Plotting the oxygen content measured at a current density of 4 kA m-2 versus the measured anolyte pH, the relationship as shown in Fig. 16.11 is obtained as expected. This proves again the high internal anolyte circulation of the KU Single Element that makes possible an oxygen content of 0.6% in chlorine at an anolyte pH of only 2.5. 

After conducting trials on various prototypes and testing a large number of components over many years, ICIETB installed a BiChlor demonstration electrolyser at Id s Lostock Plant in the UK. The BiChlor electrolyser achieved an oxygen content of approximately 1.5% in chlorine with alkaline feed brine. 

Interestingly enough, the oxygen contained in the chlorine feed actually has a real benefit. Around one-half mol% oxygen content is useful in the direct chlorination process where it limits the formation of by-products. In fact, when liquid chlorine is used as the feed, oxygen is often added for just this reason. 

---