Ge Hong (283-363), an alchemist and pharmacologist in Jin Dynasty in China, wrote a medical book "Elbow Backup Emergency Prescription", Volume 5 "Meat-eating Prescription", which recorded: "Take white charcoal ash, glutinous rice ash, etc. Fried like ointment. This should not be rehearsed, and it will be closed on 10. And you can go to the sunspot, which is very poisonous. " "Carnivorous prescription" refers to the prescription that corrodes the skin. Why do you want to corrode the skin? It is probably the "going to the sunspot" mentioned in the article. "Black spots" refer to moles on human skin. According to folk superstition in China, it is unlucky to have moles on some parts of the face, and they should be removed. "White charcoal ash" is lime, namely calcium oxide (Cao); "Tile ash" is plant ash, which contains potassium carbonate (K2CO3) and sodium carbonate (Na2CO3). After adding water, calcium oxide quickly reacts with water, releasing a lot of heat to generate calcium hydroxide (Ca(OH)2), which makes the aqueous solution boil, which is called "decocting" in this paper. Calcium hydroxide generated by adding water to calcium oxide reacts with sodium carbonate and potassium carbonate contained in plant ash to generate sodium hydroxide (NaOH) and potassium hydroxide (KOH), both of which are called caustic alkali and will corrode the skin.
The generated potassium hydroxide and sodium hydroxide will absorb the carbon dioxide gas in the air and convert it into potassium carbonate (K2CO3) and sodium carbonate (Na2CO3), so "this is not suitable for pre-production, and 10 should have a rest."
2 NaOH+CO2 ═ Na2CO3+H2O2 KOH+CO2 ═ K2CO3+H2O, which shows that caustic soda was prepared in China a long time ago, and some of its properties were recognized.
In Europe, until the end of 19, caustic soda was made from plant ash, soda ash and calcium hydroxide.
1773, Swedish chemist Scheler once reacted salt solution with lead oxide to obtain sodium hydroxide solution and yellow lead oxychloride pigment, which converted sodium hydroxide into sodium carbonate.
The ferrous salt method appeared in Germany at 1882. Mixing dried sodium carbonate and crushed iron oxide according to the ratio of 1∶3, and calcining in a furnace to generate sodium ferrite melt;
When Na2CO3+Fe2O3 ═ 2NafeO2+CO2 ↑ hot water acts on sodium ferrite, it decomposes to generate sodium hydroxide and iron oxide;
2 nafeo3+H2O ══ 2 NaOH+Fe2O31800 After the battery invented by Italian physicist Volta was introduced into Britain, the chemist W. Cruickshank,-1810) was electrolyzed by the battery, and sodium hydroxide was detected at the cathode.
It was not until the motor of 19 appeared in the late 1960s that sodium hydroxide was obtained by electrolysis of cheap salt solution.
Electrolytic brine produces hydrogen at the cathode, chlorine at the anode and sodium hydroxide in the solution. However, the generated chlorine will react with sodium hydroxide to generate sodium chloride and sodium hypochlorite (NaClO):
Cl2+2 NaOH/NaClO+NaCl+H2O In order to solve this problem, scientists and technicians have sought solutions. They set an isolation layer between the two poles to divide the electrolyzer into two parts, one is the cathode room and the other is the anode room, so as to prevent the interaction of electrolytic products. The isolation layer should also allow ions to pass freely, so that electrolysis can proceed normally.
1890 Griesheim Chemical Plant, Matthes and Weber jointly developed the cement diaphragm electrolyzer. 1903, Hook Electrochemical Company developed the asbestos diaphragm electrolyzer. Various diaphragms are put into production (Figure 5- 1).
In this way, at the end of 19 and the beginning of the 20th century, a large amount of sodium hydroxide was prepared in the diaphragm tank of electrolytic brine.
Because the salt can not be completely decomposed in the diaphragm tank, the prepared sodium hydroxide solution contains a certain amount of salt, which must be evaporated and concentrated to crystallize out, so as to obtain pure sodium hydroxide.
1892, kastner (1858- 1898), an American chemical technician living in Britain, proposed to prepare sodium hydroxide by electrolysis of brine with mercury as cathode and graphite as anode, and obtained a patent.
On the mercury electrode, sodium ion (Na+) is easier to discharge than hydrogen ion (H+), and electrons are obtained on the electrode to generate metallic sodium. Sodium and mercury form sodium amalgam (sodium amalgam);
Na++Hg+e-══Na(Hg)
Putting the alloy into a mercury dissolving tank, reacting the sodium electrode with water to generate sodium hydroxide, releasing hydrogen and leaving mercury;
Mercury left by 2na (Hg)+2h2o ═ NaOH+H2 ↑+Hg is returned to the electrolytic cell for recycling (Figure 5-2).
In this way, a membrane layer is not needed in the electrolytic cell, and the obtained sodium hydroxide solution has a high concentration.
Kastner is a student of American Mining Institute without a degree. Later, he engaged in chemical production and went to England to work in a metal smelter. Initially, metallic sodium was prepared to reduce aluminum chloride to obtain metallic aluminum. It has been proposed that mercury is used as cathode to electrolyze and hydrolyze water to obtain sodium metal, but sodium hydroxide is obtained.
However, Austrian engineer Cerna (K. Kellner, 185 1- 1905) took the lead in adopting this method to prepare metallic sodium. He applied for a patent for this method before kastner. Without litigation, they jointly established kastner-Cerna Alkali Industry Company in 1895, and set up factories in Niagara Falls, USA and Longkorn, Cheshire, England in 1896 and 1897 respectively. Niagara Falls has a large amount of electricity supply. Long Cohen, near the Irish Sea, is rich in salt supply. By 1898, Longgang factory will produce 20 tons of sodium hydroxide and 40 tons of bleaching powder every day. Bleaching powder is made by using hydrated lime to absorb chlorine gas produced by electrolysis.
The sodium hydroxide prepared by mercury electrode has high concentration, low salt content and no need for evaporation and concentration, and can be directly used in chemical industry with high requirements for sodium hydroxide. However, in the process of electrolytic production of mercury electrode, mercury vapor escapes, which is very harmful to the health of operators, and the discharge of mercury slag pollutes the environment and the operation cost is high. In 1960s, DuPont Company of the United States developed perfluorosulfonic acid ionic membrane. This kind of electrolytic membrane is selective, only a small amount of water molecules containing Na+ are allowed to pass through, and Cl- is blocked, which makes the content of sodium chloride in the cathode product sodium hydroxide solution low and becomes the third method of electrolytic brine.
Chlorine obtained by electrolysis was originally used to make bleaching powder. It was not until 19 12 that kastner-Cerna Alkali Industry Company developed and used chlorine gas to burn in hydrogen to generate hydrogen chloride gas, which was dissolved in water to generate hydrochloric acid.
In this way, three products are obtained by electrolysis of brine: sodium hydroxide, metallic sodium and hydrochloric acid.
Hydrochloric acid was produced as early as the 7th century by Arab alchemist Gerber when he was making aqua regia (1 volume mixture of nitric acid and 3 volumes hydrochloric acid). At that time, it was made by distilling copperas (hydrated crystals of ferrous sulfate) to obtain sulfuric acid, and adding saltpeter (potassium nitrate) and natural ammonium chloride (NH4Cl). When German chemist John Glauber's salt (1604- 1670) discovered mirabilite (Na2SO4) in 1658, salt reacted with sulfuric acid to produce sodium sulfate and hydrochloric acid at the same time.
2NaCl+H2SO4══Na2SO4+2HCl On the issue of direct synthesis of hydrogen chloride gas from hydrogen and chlorine, 1897 French chemistry professors Armand Emile Justin Grautier (1837-1880) and H. Helier once published a report that the two gases are mixed in black. They combine slowly in general light, react quickly in strong light and explode in the sun. 1902, British chemists Mailer (1869- 1938) and Russell (E.J.Russell) found that the two gases were pre-dried and mixed in the sun without explosion, so the direct synthesis of hydrogen chloride gas from hydrogen and chlorine must be pre-dried.
Chlorine gas is burned in hydrogen to synthesize hydrogen chloride. The burner consists of two concentric steel tubes, with dry hydrogen entering from the outer tube and dry chlorine entering from the inner tube. If the outer tube is filled with chlorine gas and the inner tube is filled with hydrogen gas, chlorine gas will remain after combustion, which will affect the health of workers and be harmful to residents and crops near the factory. When hydrogen and chlorine are synthesized, a lot of heat is released, and the generated hydrogen chloride gas is absorbed into hydrochloric acid by water after cooling.