Nomenclature
Soda lime is mainly used as a desiccant (in which calcium oxide acts as a drying agent) to dry neutral gases such as oxygen. It can also be used to absorb acidic gases such as carbon dioxide and sulfur dioxide. If only sodium hydroxide is present, this desiccant can not be used at higher temperatures, because sodium hydroxide can react with the most commonly used glass instruments in the laboratory (the main component is silicon dioxide) to corrode the instruments. Small amounts of methane can be made in the laboratory by heating soda lime and sodium acetate (sodium acetate) **** to produce sodium carbonate and methane.
Folding Editorial Chemical Composition
The main components of soda lime:Calcium oxide CaO, about 75%), sodium hydroxide (NaOH, about 3%), and potassium hydroxide (KOH, about 1%), water (H2O, about 20%). (Calcium oxide with sodium hydroxide and water are substitutes for soda lime in high school textbooks)
Industrial soda lime is calcined lye (i.e., Na2CO3-NaHCO3-2H2O, potassium-sodium-rich limestone) to obtain a Na2O.CaO or K2O.CaO product, and the clarified aqueous solution is concentrated to make caustic soda.
In different chemical reactions play different roles:
Carbonate decomposition can produce CO2 by heating, only (NH4)2CO3 or NH4HCO3, the decomposition of the mixed gas produced by the soda lime, CO2 and H2O is absorbed, you can get the pure NH3.(drying)
Use of drying to realize the gas decontamination, such as NH? Such as NH?(H?O)
Soda lime can also remove SO?, H?S, HCl, CO? and other acidic gases
Middle school commonly used desiccant acidic \basic \neutral points
Desiccant, as the name implies, is used to dry the use of (middle school is common is to dry the gas of course, but also dry the liquid, the middle school is uncommon), of course, according to the nature of desiccant Different types of dry substances are also different.
Common desiccant (brackets for the state of the desiccant):
Acidic desiccant: concentrated sulfuric acid (H?SO?), phosphorus pentoxide (P?O5), etc.; the main drying of acidic or neutral gases
such as SO?,CO?,CO,NO?,O?,NO,H?,N?
Basic desiccant: soda lime (CaO), NaOH, etc.; the main drying of acid or neutral gases
Basic desiccant: soda-lime (CaO), NaOH, etc.; the main drying of alkali. NaOH and so on; mainly drying alkaline or neutral gas
such as NH?,CO,O?,N?,H?,PH?
Neutral desiccant: CaCl?(s),MgSO?(s) and so on; this kind of desiccant is not commonly used because of the complexity, for example, CaCl?(s), it looks as if it doesn't react with acidic gas and seems to be able to dry the acidic gas but it can't dry the hydrogen halide (HCl). Hydrogen halide (HCl HBr), because there will be a complex chemical reaction in secondary school did not learn; furthermore, it can not dry NH?, because it can form complex complexes with NH? In short, this kind of desiccant is mainly used to dry neutral gas.
Another: ①, the choice of desiccant depends not only on the nature of the desiccant but also on the nature of the substance to be dried, such as concentrated sulfuric acid is an acid, so it can not dry alkaline gases; in addition, concentrated sulfuric acid also has a strong oxidizing properties, so it can not be used to dry the reducing substances such as H?S, HI, HBr and so on
② for liquid desiccant is generally installed in the gas-washing cylinders (the gas is from the long tube into the short tube out). . And solid desiccant in the drying tube or U-shaped tube.
Folding editorial misconceptions
that slaked lime is a mixture of sodium hydroxide and calcium oxide is a misunderstanding, may be derived from the "slaked lime experiment", that is, in the sodium hydroxide solution, add calcium oxide, heating, made of slaked lime. Soda lime can be made from both sodium hydroxide and calcium oxide, but it is a substitute, not both. Still, try to write a mixture of sodium hydroxide and calcium oxide on the test. When preparing methane, the quicklime in the soda lime does not participate in the reaction, but the quicklime can dilute the concentration of the mixture, make the mixture loose, so that the methane produced is easy to escape, but also reduces the solid NaOH at high temperatures with the action of the glass, to prevent the test tube from bursting. The absorbency of quicklime prevents the deliquescence of NaOH. The role of soda lime in the preparation of methane is to provide the reactant NaOH and desiccant (CaO).
Folding Editorial Uses
Caustic soda has a wide range of applications in the national economy and is needed in many industrial sectors. The sector that uses caustic soda most is the manufacture of chemicals, followed by paper making, aluminum refining, tungsten refining, rayon, rayon and soap manufacturing. In addition, in the production of dyestuffs, plastics, pharmaceuticals and organic intermediates, the regeneration of old rubber, the system of sodium metal, water electrolysis and the production of inorganic salts, the production of borax, chromium salts, manganates, phosphates, etc., but also to use a lot of caustic soda. Sodium hydroxide for industrial use should be in accordance with national standard GB 209-93; sodium hydroxide for industrial use ion exchange membrane method should be in accordance with national standard GB/T 11199-89; sodium hydroxide for chemical fiber should be in accordance with national standard GB 11212-89; edible sodium hydroxide should be in accordance with national standard GB 5175-85.
Folding Edit section on the harm to the human body
It has a solubilizing effect on proteins and is strongly irritating and corrosive. Drops of 0.02% solution into rabbit eyes can cause corneal epithelial damage. Intraperitoneal LD50: 40 mg/kg in mice, oral LDLo:500 mg/kg in rabbits.Dust irritates the eyes and respiratory tract and corrodes the nasal septum; splashed on the skin, especially on the mucous membranes, it can produce soft scabs and penetrate into the deeper tissues, leaving scarring after burns; splashed into the eyes, it not only damages the cornea but also the deep tissues of the eyes, and in serious cases, it can lead to blindness; accidental ingestion can cause digestive tract Burns, colic, mucous membrane erosion, vomiting bloody stomach contents, bloody diarrhea, sometimes mute, dysphagia, shock, gastrointestinal perforation, gastrointestinal stenosis can occur in the late stage.
Folding editorial protection methods
Large amounts of contact with soda-lime should wear protective gear, coveralls or work caps should be made of cotton or appropriate synthetic materials. Operators must wear work clothes, masks, protective glasses, rubber gloves, rubber aprons, long rubber boots and other labor protection items when working. Neutral and hydrophobic ointment should be applied to the skin. When exposed to slaked lime in flake or granular form, the workplace should be ventilated, and the maximum permissible concentration in indoor air should be China MAC 0.5 mg/m3 (as NaOH), and ACGIH TLVC 2 mg/m3 in the U.S.A. When possible exposure to its dust is possible, a hood-type electrically powered air-fed filtered dust respirator must be worn. If necessary, wear an air respirator. The operator must be specially trained and strictly follow the operating procedures. It is recommended that the operator wear a hood-type electrically powered air supply filtering dust respirator, rubberized acid and alkali resistant clothing, and rubberized acid and alkali resistant gloves. Keep away from flammable and combustible materials. Avoid generating dust. Avoid contact with acids. Load and unload lightly to prevent damage to packaging and containers. Equipped with emergency response equipment for leakage. Empty containers may retain hazardous materials. When diluting or preparing solutions, add alkali to water to avoid boiling and splashing.
Folding Editorial Packaging, Storage and Transportation
Packaging, Storage and Transportation of Soda Lime:
Soda Lime is generally packed in 25kg three-layer plastic woven bags, with the inner and outer layers being plastic woven bags, and the middle layer being a plastic inner film bag. Caustic soda flake is classified as class 8.2 alkaline corrosive by "Classification and Labeling of Commonly Used Hazardous Chemicals (GB 13690-92)", which is class 8 hazardous material, Hazardous Code: 1823. It should be stored in ventilated and dry warehouse or shed. Packing containers should be intact and sealed. It should not be stored and transported together with flammable materials and acids***. Pay attention to moisture-proof and rain-proof during transportation. In case of fire, water, sand and all kinds of fire extinguishers can be used to put out the fire, but firefighters should pay attention to the corrosiveness of caustic soda dissolved in water.
Physical and Chemical Properties Pure product is colorless transparent crystals, relative density 2.130. melting point 318.4℃. Melting point 318.4°C. Boiling point 1390°C. There are two kinds of commercially available caustic soda: pure solid caustic soda is white, with block, flake, rod, granular, brittle; pure liquid caustic soda is colorless transparent liquid. Solid caustic soda has strong hygroscopicity. Easily soluble in water, exothermic when dissolved, aqueous solution is alkaline, slippery; soluble in ethanol and glycerol; insoluble in acetone, ether. Extremely corrosive, corrosive to fibers, skin, glass, ceramics and so on. Reacts with metal aluminum and zinc, non-metal boron and silicon to release hydrogen; disproportionates with chlorine, bromine, iodine and other halogens; neutralizes with acids to produce salt and water.
Preservation of solid sodium hydroxide should pay attention to the seal tightly, to prevent exposure to the air to absorb moisture deliquescence or with carbon dioxide. In the use of glass bottles containing sodium hydroxide or other forms of sodium hydroxide, can not use the glass stopper, should be replaced with rubber stopper, because sodium hydroxide will react with the silica in the glass to generate sodium silicate resulting in the stopper and the body of the bottle is not easy to open the adhesive.
Folding editorial production method
Natural alkali causticizing method first natural alkali crushed, dissolved, clarified, and then the milk of lime added to the clear liquid causticizing reaction; causticizing liquid clarified clear liquid by a evaporation, filtration to remove impurities salt; filtrate by the second evaporation, then filtered in addition to the salt; and finally filtrate boiled into caustic soda.
NaHCO?+Ca(OH)? →NaOH+H?O+CaCO?↓2 soda ash causticizing method first soda ash dissolved in water, mixed with milk of lime causticizing reaction. After the causticizing solution is clarified, the clear liquid is evaporated and concentrated to a certain concentration of liquid products, and the concentrate is further boiled and thickened to obtain solid products.
Na?CO?+Ca(OH)? →2NaOH+CaCO?↓3. Diaphragm electrolysis method will be the original salt (table salt) dissolved in water (chemical salt), respectively, add the appropriate amount of soda ash, caustic soda and barium chloride to remove calcium, magnesium and sulfate ions. In order to accelerate precipitation, causticized bran type precipitant can be added. The salt sludge is filtered and washed, and the wash water is used to chemicalize the salt. The clarified liquid is sand filtered, neutralized with hydrochloric acid, preheated and fed into the electrolysis tank for electrolysis. The electrolyte is pre-evaporated and filtered to remove sodium chloride and other salts, and finally boiled to make solid caustic soda. 2NaCl + 2H?O [electrolysis] → 2NaOH + Cl?↑ + H?↑;
The industrial production of caustic soda has causticization and electrolysis methods.
Causticizing method is divided into soda ash causticizing method and natural alkali causticizing method according to different raw materials; electrolysis method can be divided into diaphragm electrolysis method and ion exchange membrane method. Soda ash causticizing method will be soda ash, lime, respectively, made of soda ash solution, made of lime milk, at 99 ~ 101 ℃ causticizing reaction, causticizing solution by clarification, evaporation and concentration to more than 40%, to produce liquid caustic soda. The concentrated liquid is further boiled and solidified to produce solid caustic soda.
The causticizing mud is washed with water, and the washed water is used for alkali. Its Na?CO?+Ca(OH)? → 2NaOH + CaCO? natural alkali causticizing method natural alkali by crushing, dissolving (or alkali brine), clarification, plus people in the milk of lime at 95 ~ 100 ℃ causticizing, causticizing solution by clarification, evaporation and concentration of NaOH concentration of 46% or so, the clear liquid cooling, precipitation of salt and then further boiled thick. Solid caustic soda is produced. The causticizing mud is washed with water, and the washing water is used to dissolve natural alkali.
The Na?CO?+Ca(OH)? →2NaOH+CaCO?↓ NaHCO?+Ca(OH)? →NaOH + CaCO?↓ + H?O diaphragm electric boat method will be the original salting salt after adding soda ash, caustic soda, barium chloride refined preparation to remove calcium, magnesium, sulfate ions and other impurities, and then in the clarification tank to add sodium polyacrylate or caustic soda bran to accelerate the precipitation, sand filtration and add hydrochloric acid neutralization, brine after preheating sent to the electrolytic solution after preheating, evaporation, salt, cooling, to get a liquid caustic soda, and further boiled thick that is! The liquid caustic soda is produced by preheating, evaporation, salt separation and cooling of the electrolytic solution.
Salt sludge wash water is used for salt. Its 2NaCl + 2H?O [electrolysis] → 2NaOH + Cl?↑ + H?↑ ion exchange membrane method will be the original salt after salting according to the traditional method of brine refining, the primary refined brine filtered by microporous sintered carbon tubular filters, and then by the Sting Ion Exchange Resin Tower for the second refining, so that the brine in the calcium, magnesium content down to 0.002% or less, will be the second refining of brine electrolysis in the anode room to generate chlorine gas, the anode room to generate chlorine gas, the anode room to the solid caustic soda finished products. The electrolysis of the secondary refined brine generates chlorine gas in the anode chamber, and Na+ in the brine in the anode chamber enters into the cathode chamber through the ionic membrane to generate sodium hydroxide with 0H in the cathode chamber, and H+ discharges directly on the cathode to generate hydrogen gas.
An appropriate amount of high-purity hydrochloric acid is added to the anode chamber during electrolysis to neutralize the returning OH-, and the required pure water should be added to the cathode chamber. The concentration of high purity caustic soda generated in the cathode chamber is 30%~32% (by mass), which can be directly used as a liquid caustic soda product or further boiled and thickened to produce a solid caustic soda finished product. Its 2NaCl+2H?O→2NaOH+H?↑+Cl?↑.