ACGIH: TWA 2 mg/m3 OSHA: TWA 5 mg/m3 NIOSH: IDLH 25 mg/m3; TWA 2 mg/m3
Stability:
Stability Reacts violently with water liberating highly flammable gas (acetylene). Do not use water if this material is involved in a fire. Incompatible with moisture, water, strong oxidizing agents, alcohols, hydrogen chloride, magnesium.
Calcium carbide (molecule formula: CaC2), is a kind of important chemical raw materials produced from the chemical processing of limestone. In 1892, H. Maysan (French) and H. Wilson (United state) simultaneously developed a calcium carbide production approach based on furnace Reduction. The United State had successfully achieved industrial production in 1895. The property of calcium carbide is related to its purity. Its industrial product is mostly the mixture of calcium carbide and calcium oxide, and also contains trace amounts of sulfur, phosphorus, nitrogen and other impurities. With the increasing content of impurities, it color exhibits gray, brown to black. The melting point and electrical conductivity both decrease with the decrease of the purity. The purity of its industrial product is usually 80% with m.p. being 1800~2000 °C. At room temperature, it does not react with air, but it can have oxidation reaction at above 350 ℃, and have reaction with nitrogen at 600~700 ℃ to generate calcium cyanamide. Calcium carbide, when coming across with water or steam, generates acetylene and release a large amount of heating. CaC2 + 2H2O─ → C2H2 + Ca (OH) 2 + 125185.32J, 1kg of pure calcium carbide can produce 366 L of acetylene 366l (15 ℃, 0.1MPa). Thereby, for its storage: calcium carbide should be strictly kept away from water. It is usually packed in a sealed iron container, and sometimes stored in a dry warehouse being filled with nitrogen if necessary.
Calcium carbide will immediately have reaction upon coming across with water, generating acetylene and calcium hydroxide, which is the approach of industrial preparation of acetylene (carbide method), the reaction equation is:
CaC2 + 2H2O = C2H2 + Ca (OH) 2.
Since the impurity of calcium carbide, the generated acetylene gas is usually mixed with a small amount of hydrogen sulfide, phosphine gas and other contaminants, so there is a bad smell. Calcium carbide is produced from the lime and coke in an electric furnace at a high temperature of 3000 ℃:
3C + CaO = CaC2 + CO.
Upon the laboratory preparation of acetylene, owing to the reaction between calcium carbide and water is very fierce, we can apply saturated brine to substitute water so that a pure and smooth airflow of acetylene can be obtained. Calcium carbide won’t have reaction with sodium chloride.
Electric furnace reduction method is the only method for industrial production of calcium carbide at present. Put calcium oxide and coke for reduction reaction at 2000~2200 ℃: CaO + 3C─ → CaC2 + CO-480644.64J, the resulting molten calcium carbide flow into the receiver tank from the bottom of the reactor, and we obtain the final product after cooling. Calcium carbide production belongs to high temperature operation with relative large amount dust being produced and consuming a large amount of electrical energy. In 1980s, the production of per ton of calcium carbide consumes industrial power of about 10~11GJ. In order to reduce the power consumption, people mostly apply large-scale and closed calcium carbide furnace to reduce heat loss and also do good to the recycling of carbon monoxide.
Description
Calcium carbide,is a binary salt. It is a grayish-black hard solid that reacts with water to produce acetylene gas, a solid corrosive that is calcium hydroxide, and release heat. Acetylene gas is manufactured by reacting calcium carbide with water. Because acetylene is so unstable, it is not shipped in bulk quantities.
Calcium carbide is shipped to acetylene-generating plants where it is reacted with water in a controlled reaction. After the reaction process, the acetylene gas is placed into specially designed containers with a honeycombed mesh inside for shipment and use. It is dissolved in acetone for stability. Calcium carbide has a specific gravity of 2.22, which is heavier than water. The four-digit UN identification number for calcium carbide is 1402. The NFPA 704 designation is health 3, flammability 3, and reactivity 2. The white section at the bottom of the diamond contains a W with a slash through it, indicating water reactivity. It is shipped in metal cans, drums, and specially designed covered bins on railcars and trucks. When shipped and stored, it should be kept in a cool, dry place. Primary uses are in the generation of acetylene gas for welding, vinyl acetate monomer, and as a reducing agent.
Chemical Properties
grey or black solid with a garlic-like odour
Physical properties
Grayish-black orthorhombic crystal; density 2.22 g/cm3; melts at 2,200°C; reacts with water.
Uses
Calcium carbide (CaC2) has a garlic-like odor and reacts with water to form acetylene gas
plus calcium hydroxide and heat. In the past, it was used in miners’ lamps to continuously
produce a small acetylene flame to provide some illumination in coal mines.
Uses
Calcium carbide is used as a desulfurizer, dehydrant of steel, fuel in steel making, powerful deoxidizer and as a source of acetylene gas. It is used as a starting material for the preparation of calcium cyanamide, ethylene, chloroprene rubber, acetic acid, dicyandiamide and cyanide acetate. It is used in carbide lamps, toy cannons such as the big-bang cannon and bamboo cannon. It is associated with calcium phosphide and used in floating, self-igniting naval signal flares. Further, it is involved in the reduction of copper sulfide to metallic copper.
Uses
Calcium carbide is the most relevant carbide industrially because of its important role as the basis of acetylene industry. In locations where there is shortage of petroleum, Calcium Carbide is used as the starting material for the production of acetylene (1 kg of carbide yields ~300 liters acetylene), which, in turn, can be used as a building block for a range of organic chemicals (e.g. vinyl acetate, acetaldehyde and acetic acid). In some locations, acetylene is also used to produce vinyl chloride, the raw material for the production of PVC.
A less important use of Calcium Carbide is related to the ferilizers industry. It reacts with nitrogen to form calcium cyanamide, which is the starting material for the production of cyanamide (CH2N2). Cyanamide is a common agricultural product used to stimulate early foliation.
Calcium Carbide can also be employed as desulfurizing agent for producing low-sulfur carbon steel. Also, it is used as a reducing agent to produce metals from their salts, e.g., for direct reduction of copper sulfide to metallic copper.
Preparation
Calcium carbide (CaC2) is manufactured by heating a lime and carbon mixture to 2000 to 2100°C (3632 to 3812°F) in an electric arc furnace. At those temperatures, the lime is reduced by carbon to calcium carbide and carbon monoxide (CO), according to the following reaction: CaO + 3C → CaC2 + CO
Lime for the reaction is usually made by calcining limestone in a kiln at the plant site. The sources of carbon for the reaction are petroleum coke, metallurgical coke, and anthracite coal. Because impurities in the furnace charge remain in the calcium carbide product, the lime should contain no more than 0.5 percent each of magnesium oxide, aluminum oxide, and iron oxide, and 0.004 percent phosphorus. Also, the coke charge should be low in ash and sulfur. Analyses indicate that 0.2 to 1.0 percent ash and 5 to 6 percent sulfur are typical in petroleum coke. About 991 kilograms (kg) (2,185 pounds [lb]) of lime, 683 kg (1,506 lb) of coke, and 17 to 20 kg (37 to 44 lb) of electrode paste are required to produce 1 megagram (Mg) (2,205 lb) of calcium carbide.
Reactions
Calcium carbide is grayish-black solid, reacts with water yielding acetylene gas and calcium hydroxide, formed at electric furnace temperature from calcium oxide and carbon.
General Description
Grayish-black irregular lump solid. Used to make acetylene and in steel manufacture.
Air & Water Reactions
Reacts rapidly with water to generate the flammable gas acetylene and the base calcium hydroxide. Enough heat may be generated to ignite the gas [Jones, G.W. BM Report Invest. 3755 1944].
Reactivity Profile
Calcium carbide is a reducing agent. May react vigorously with oxidizing materials. The powdered mixture of the acetylide and iron oxide and iron chloride burns violently upon ignition, producing molten iron. Calcium carbide incandesces with chlorine, bromine, or iodine at 245, 350, or 305°C., respectively, [Mellor, 1946, Vol. 5, 862]. The carbide burns incandescently when mixed and heated with lead difluoride, magnesium, hydrogen chloride, and tin (II) chloride, [Mellor, 1946, 1940, 1946, and 1941], respectively. Interaction of Calcium carbide with methanol to give calcium methoxide is vigorous , but subject to an induction period of variable length. Once reaction starts, evolution of acetylene gas is very rapid, unpublished observations [Bretherick 1995]. Mixing Calcium carbide with silver nitrate solutions forms silver acetylide, a highly sensitive explosive. Copper salt solutions would behave similarly, [Photogr. Sci. Eng., 1966, 10, 334]. The mixture of Calcium carbide and sodium peroxide is explosive, as is Calcium carbide and perchloryl fluoride as gases at 100-300°C.
Hazard
Forms flammable and explosive gas and
corrosive solid with moisture.
Health Hazard
It is a corrosive solid. Because it is highlywater-reactive, skin contact can cause burn.
Fire Hazard
Behavior in Fire: If wet by water, highly flammable acetylene gas is formed.
Safety Profile
Reaction on contact
with moisture forms explosive acetylene gas.
Flammable on contact with moisture, acid
or acid fumes; evolves heat or flammable
vapors. Moderate explosion hazard.
Incandescent reaction with Cl2 (245℃), Brz
(350℃), IS (305℃), HCl gas + heat, PbF2,
Mg + heat. Incompatible with Se, (KOH +
Ch), AgNO3, Na2O2, SnCl2, S, water.
Mixtures with iron(IⅡ) chloride, iron(IⅡ)
oxide, tin(Ⅱ) chloride are easily ignited and
burn fiercely. Vigorous reaction with
methanol after an induction period.
Addttion to silver nitrate solutions
precipitates the dangerously explosive silver
acetylide. Copper salt solutions behave
similarly. See also CALCIUM
HYDROXIDE and ACETYLENE.
Calcium carbide Preparation Products And Raw materials
