How To Make Calcium Carbide

Acetylene

Background

Acetylene is a colorless, combustible gas with a distinctive scent. When acetylene is liquefied, compressed, heated, or mixed with air, it becomes highly explosive. As a event special precautions are required during its production and handling. The most common apply of acetylene is equally a raw material for the production of various organic chemicals including i,iv-butanediol, which is widely used in the training of polyurethane and polyester plastics. The second nearly common employ is as the fuel component in oxy-acetylene welding and metal cutting. Some commercially useful acetylene compounds include acetylene black, which is used in certain dry out-cell batteries, and acetylenic alcohols, which are used in the synthesis of vitamins.

Acetylene was discovered in 1836, when Edmund Davy was experimenting with potassium carbide. One of his chemical reactions produced a combustible gas, which is now known equally acetylene. In 1859, Marcel Morren successfully generated acetylene when he used carbon electrodes to strike an electric arc in an atmosphere of hydrogen. The electrical arc tore carbon atoms away from the electrodes and bonded them with hydrogen atoms to form acetylene molecules. He called this gas carbonized hydrogen.

Past the belatedly 1800s, a method had been developed for making acetylene by reacting calcium carbide with h2o. This generated a controlled flow of acetylene that could exist combusted in air to produce a brilliant white light. Carbide lanterns were used past miners and carbide lamps were used for street illumination before the general availability of electric lights. In 1897, Georges Claude and A. Hess noted that acetylene gas could be safely stored by dissolving it in acetone. Nils Dalen used this new method in 1905 to develop long-burning, automated marine and railroad point lights. In 1906, Dalen went on to develop an acetylene torch for welding and metal cut.

In the 1920s, the German firm BASF adult a process for manufacturing acetylene from natural gas and petroleum-based hydrocarbons. The start constitute went into operation in Germany in 1940. The engineering came to the United States in the early 1950s and quickly became the primary method of producing acetylene.

Demand for acetylene grew equally new processes were adult for converting it into useful plastics and chemicals. In the United States, demand peaked sometime between 1965 and 1970, and then brutal off sharply as new, lower-cost alternative conversion materials were discovered. Since the early 1980s, the need for acetylene has grown slowly at a charge per unit of about 2-4% per year.

In 1991, in that location were 8 plants in the United States that produced acetylene. Together they produced a full of 352 million lb (160 million kg) of acetylene per year. Of this production, 66% was derived from natural gas and 15% from petroleum processing. Most acetylene from these two sources was used on or near the site where it was produced to make other organic chemicals. The remaining nineteen% came from calcium carbide. Some of the acetylene from this source was used to make organic chemicals, and the rest was used by regional industrial gas producers to fill pressurized cylinders for local welding and metal cutting customers.

In Western Europe, natural gas and petroleum were the chief sources of acetylene in 1991, while calcium carbide was the chief source in Eastern Europe and Nippon.

Raw Materials

Acetylene is a hydrocarbon consisting of two carbon atoms and two hydrogen atoms. Its chemical symbol is C ₂ H ₂ . For commercial purposes, acetylene tin can be made from several different raw materials depending on the process used.

The simplest process reacts calcium carbide with h2o to produce acetylene gas and a calcium carbonate slurry, chosen hydrated lime. The chemic reaction may be written as CaC ₂ + 2 H _ii O → C ₂ H _two + Ca(OH) _two .

Other processes use natural gas, which is mostly marsh gas, or a petroleum-based hydrocarbon such as crude oil, naphtha, or bunker C oil as raw materials. Coal can also be used. These processes utilise high temperature to convert the raw materials into a wide variety of gases, including hydrogen, carbon monoxide, carbon dioxide, acetylene, and others. The chemical reaction for converting methane into acetylene and hydrogen may be written 2 CH _iv → C ₂ H _two + 3 H ₂ . The other gases are the products of combustion with oxygen. In order to separate the acetylene, information technology is dissolved in a solvent such every bit water, anhydrous ammonia, chilled methanol, or acetone, or several other solvents depending on the process.

The Manufacturing
Process

At that place are two basic conversion processes used to make acetylene. One is a chemical reaction process, which occurs at normal temperatures. The other is a thermal not bad process, which occurs at extremely high temperatures.

Here are typical sequences of operations used to catechumen diverse raw materials into acetylene past each of the two basic processes.

Chemical reaction process

Acetylene may exist generated by the chemic reaction between calcium carbide and water. This reaction produces a considerable amount of heat, which must exist removed to prevent the acetylene gas from exploding. There are several variations of this procedure in which either calcium carbide is added to water or h2o is added to calcium carbide. Both of these variations are chosen wet processes because an excess amount of water is used to blot the heat of the reaction. A third variation, called a dry out process, uses only a limited amount of water, which and so evaporates as it absorbs the heat. The first variation is almost usually used in the United States and is described below.

Most high-chapters acetylene generators use a rotating screw conveyor to feed calcium carbide granules into the reaction chamber, which has been filled to a certain level with water. The granules measure out about 0.08 in x 0.25 in (two mm x 6 mm), which provides the correct corporeality of exposed surfaces to allow a complete reaction. The feed rate is determined by the desired charge per unit of gas flow and is controlled by a pressure switch in the sleeping room. If too much gas is existence produced at one fourth dimension, the pressure switch opens and cuts back the feed charge per unit.
To ensure a complete reaction, the solution of calcium carbide granules and water is constantly agitated by a set of rotating paddles inside the reaction bedroom. This also prevents any granules from floating on the surface where they could over-heat and ignite the acetylene
The acetylene gas bubbles to the surface and is drawn off under low pressure. Every bit it leaves the reaction chamber, the gas is cooled by a spray of water. This water spray besides adds water to the reaction chamber to keep the reaction going as new calcium carbide is added. Later the gas is cooled, information technology passes through a flash arrester, which prevents whatever accidental ignition from equipment downstream of the chamber.
Equally the calcium carbide reacts with the h2o, information technology forms a slurry of calcium carbonate, which sinks to the bottom of the chamber. Periodically the reaction must be stopped to remove the built-up slurry. The

Acetylene may exist generated by the chemical reaction between calcium carbide and water. This reaction produces a considerable corporeality of heat, which must be removed to preclude the acetylene gas from exploding.

slurry is tuckered from the sleeping accommodation and pumped into a holding pond, where the calcium carbonate settles out and the water is drawn off. The thickened calcium carbonate is then dried and sold for use as an industrial waste water treatment agent, acrid neutralizer, or soil conditioner for road construction.

Thermal groovy process

Acetylene may also be generated by raising the temperature of various hydrocarbons to the betoken where their atomic bonds break, or crevice, in what is known as a thermal peachy process. Afterwards the hydrocarbon atoms suspension apart, they can be made to rebond to course different materials than the original raw materials. This process is widely used to convert oil or natural gas to a diverseness of chemicals.

In that location are several variations of this process depending on the raw materials used and the method for raising the temperature. Some corking processes apply an electrical arc to heat the raw materials, while others utilize a combustion sleeping accommodation that burns function of the hydrocarbons to provide a flame. Some acetylene is generated every bit a coproduct of the steam slap-up process used to make ethylene. In the The states, the most common process uses a combustion chamber to heat and burn natural gas as described below.

Natural gas, which is mostly methane, is heated to nearly 1,200° F (650° C). Preheating the gas volition cause information technology to self-ignite once information technology reaches the burner and requires less oxygen for combustion.
The heated gas passes through a narrow pipe, called a venturi, where oxygen is injected and mixed with the hot gas.
The mixture of hot gas and oxygen passes through a diffuser, which slows its velocity to the desired speed. This is critical. If the velocity is too high, the incoming gas volition accident out the flame in the burner. If the velocity is besides depression, the flame can wink back and ignite the gas earlier it reaches the burner.
The gas mixture flows into the burner block, which contains more than 100 narrow channels. As the gas flows into each channel, it self-ignites and produces a flame which raises the gas temperature to about two,730° F (1,500° C). A modest amount of oxygen is added in the burner to stabilize the combustion.
The called-for gas flows into the reaction space just beyond the burner where the high temperature cause about 1-3rd of the methane to be converted into acetylene, while most of the rest of the methyl hydride is burned. The entire combustion process takes just a few milliseconds.
The flaming gas is rapidly quenched with h2o sprays at the signal where the conversion to acetylene is the greatest. The cooled gas contains a large corporeality of carbon monoxide and hydrogen, with lesser

Acetylene may as well exist generated by raising the temperature of various hydrocarbons to the point where their atomic bonds break, or crack, in what is known as a thermal cracking process.

amounts of carbon soot, plus carbon dioxide, acetylene, methane, and other gases.
The gas passes through a water scrubber, which removes much of the carbon soot. The gas and so passes through a second scrubber where it is sprayed with a solvent known as N-methylpyrrolidinone which absorbs the acetylene, but not the other gases.
The solvent is pumped into a separation belfry where the acetylene is boiled out of the solvent and is drawn off at the pinnacle of the tower equally a gas, while the solvent is drawn out of the lesser.

Storage and Handling

Because acetylene is highly explosive, it must be stored and handled with great care. When information technology is transported through pipelines, the pressure is kept very low and the length of the pipeline is very short. In nigh chemic product operations, the acetylene is transported simply as far equally an adjacent plant, or "over the argue" as they say in the chemical processing business.

When acetylene must be pressurized and stored for use in oxy-acetylene welding and metal cutting operations, special storage cylinders are used. The cylinders are filled with an absorbent textile, like diatomaceous earth, and a small amount of acetone. The acetylene is pumped into the cylinders at a force per unit area of about 300 psi (two,070 kPa), where it is dissolved in the acetone. In one case dissolved, it loses its explosive capability, making it condom to ship. When the cylinder valve is opened, the pressure level drop causes some of the acetylene to vaporize into gas again and catamenia through the connecting hose to the welding or cut torch.

Quality Control

Grade B acetylene may have a maximum of 2% impurities and is generally used for oxyacetylene welding and metal cut. Acetylene produced by the chemical reaction process meets this standard. Grade A acetylene may accept no more than 0.5% impurities and is more often than not used for chemical production processes. Acetylene produced past the thermal nifty process may meet this standard or may crave further purification, depending on the specific process and raw materials.

The Future

The use of acetylene is expected to keep a gradual increase in the future as new applications are developed. One new application is the conversion of acetylene to ethylene for apply in making a multifariousness of polyethylene plastics. In the past, a minor corporeality of acetylene had been generated and wasted as part of the steam cracking process used to make ethylene. A new catalyst developed by Phillips Petroleum allows near of this acetylene to be converted into ethylene for increased yields at a reduced overall toll.

Where to Learn More

Books

Brady, George S., Henry R. Clauser, and John A. Vaccari. Materials Handbook, 14th edition. McGraw-Colina, 1997.

Kroschwitz, Jacqueline I. and Mary Howe-Grant, ed. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons, Inc., 1993.

Other

Acetylene Pamphlet G-1. Compressed Gas Association, 1990.

Compressed Gas Clan. http://world wide web.cganet.com .

— Chris Cavette