The production method of chlorine gas has experienced a long development process. 1774, Swedish chemist Scheler used pyrolusite (containing manganese dioxide) and concentrated hydrochloric acid to produce chlorine gas.
4HCl (concentrated) +MnO? = heating = MnCl? +2H？ O+Cl？ ↑
However, because hydrochloric acid could not be produced in large quantities at that time, this method was limited to the preparation of chlorine gas in the laboratory. Later, French chemist Bertholle put the mixture of sodium chloride, pyrolusite and concentrated sulfuric acid into a lead distiller and heated it to produce chlorine gas:
2NaCl+3H？ So what? (concentrated) +MnO? = heating =2NaHSO? +MnSO？ +2H？ O+Cl？ ↑
Since Scheler made chlorine gas in 1774 to 1836, people have been using Berto Lei Faming's method to produce chlorine gas.
1836, Gusag invented a coking tower to absorb sodium carbonate (Na? CO？ Hydrochloric acid is obtained from the hydrogen chloride gas discharged from the process (this gas containing hydrogen chloride used to be considered as waste gas and fully utilized from Gusag), and then hydrochloric acid becomes a relatively cheap acid, which can be widely used. The method of producing chlorine invented by Scheler was improved and became a method of producing chlorine on a large scale at this time.
1868, Dickon and Hont Hungary invented the method of oxidizing hydrogen chloride gas to generate chlorine gas with copper chloride as catalyst when heating;
4HCl+O？ =2H？ O+2Cl？ ↑
This method is called Deakin method (also translated as Deakin method).
Although these methods of chlorine production have played a certain role in history, they are far less than electrolytic chlorine production in terms of economic benefits and production scale. When electrolysis was put into practice, these methods of producing chlorine were gradually eliminated.
The birth of electrolysis can be traced back to 1833. Faraday found that when current acts on sodium chloride aqueous solution, chlorine can be obtained:
2NaCl+2H？ O =2NaOH+H？ ↑+Cl？ ↑
Later, the British scientist Watt also discovered this method, and obtained a British patent for producing chlorine at 185 1. However, because there was no practical DC generator to generate enough current at that time, the electrolysis method could only stay in the laboratory scale and could not be put into industrial production, so it was put on hold. It was not until the 1970s and 1980s that a better DC generator appeared and electrolysis was widely used. Since then, the industrial production of chlorine has entered a new era. But at that time, the electrode used for electrolysis of chlorine gas was mercury, which led to a considerable amount of mercury vapor mixed with chlorine gas and hydrogen gas obtained by electrolysis. This "chlorine production by mercury" is very harmful to the environment, so the new "ion exchange membrane method" is more environmentally friendly and energy-saving. Using mercury to produce chlorine gas is still the mainstream method to produce chlorine gas. For example, in 20 10, China produced 46% chlorine gas, and in 2000, 50. 1% chlorine gas in western Europe was produced by this method. )
Chlorine liquefaction
Chlorine gas can usually be used directly, but in order to make pure chlorine gas, considering the convenience of storage and transportation, a part of chlorine gas is liquefied into liquid chlorine, which is transported to users by steel cylinders or tank trucks. In production, the hot chlorine gas (containing a small amount of impurities such as hydrogen, oxygen and carbon dioxide) coming out of the electrolytic cell is washed with cold water or condensed and dehydrated in a heat exchanger, then dried with sulfuric acid (liquid chlorine can be used to remove moisture and impurities if necessary), and then sent to liquefaction. Because wet chlorine has corrosive effect on iron, the moisture in chlorine before liquefaction should be less than 50ppm.
The temperature and pressure range of chlorine gas liquefaction is very wide, which can be divided into low pressure method, medium pressure method and high pressure method in industrial production. Liquefaction adopts low-pressure method, with chlorine of 0.078 ~ 0. 147 MPa (gauge pressure) and cooling temperature of -35 ~-40℃. Liquefaction adopts medium pressure method, chlorine pressure is 0.245~0.49MPa, and cooling temperature is-15 ~-20℃. Chlorine produced by high-pressure method is 0.98 ~ 1. 17 MPa, which can be liquefied when it is cooled to 15 ~ 25℃ with water. Compared with the low-pressure method, the high-pressure method has lower energy consumption and less circulating water consumption, but the equipment cost is higher, which is suitable for large-scale production. Medium pressure method is mostly used in small and medium-sized chlor-alkali plants. The liquefaction rate is determined by the hydrogen content in chlorine. The hydrogen content in liquefied tail gas shall not exceed 4% (by volume). The tail gas contains 60% ~ 70% chlorine gas, which can be used as raw gas for synthesizing hydrochloric acid, chlorobenzene and hypochlorite, and can also be further purified and refined, so that the liquefaction rate can reach 98% ~ 99%.