What Is Acetylene Gas?
Acetylene gas is a 2-carbon hydrocarbon.
It has the simplest structure of all the alkynes, with the molecular formula C2H2 and the IUPAC systematic name “ethyne”. At room temperature, it is a colorless, odorless gas with a gas density of 0.908, slightly lighter than air.
It is not a naturally occurring substance but is obtained through the thermal decomposition of hydrocarbons such as natural gas and naphtha.
Uses of Acetylene Gas
Acetylene gas is used as a flammable gas in metal welding and fusing processes. Its high flame temperature enables efficient work, and its low oxygen consumption reduces the number of oxygen containers used. It is used for pressure welding of reinforcing bars, thermal spraying, brazing, cutting of steel plates, and quenching of steel materials.
When completely combusted, the flame temperature of acetylene reaches 3,300°C, higher than other combustible gases like methane (2,780℃), propane (2,800℃), propylene (2,900℃), and ethylene (3,000℃).
It is also easy to handle due to its low ignition temperature of 305°C. Furthermore, its oxygen consumption is about one-fourth that of propane gas. Acetylene is used in synthesizing organic compounds such as ethylene, acetaldehyde, and benzene.
The following are applications for higher-purity acetylene gas:
- Raw material for semiconductor carbon
- Raw material for the production of hard carbon films
- Raw material for the synthesis of new materials such as carbon nanotubes and carbon nano coils
- Atomic absorption spectrometry
Principle of Acetylene Gas
This section explains the principle of acetylene gas in terms of its properties, synthesis methods, and chemical reactions.
1. Properties of Acetylene Gas
Acetylene gas, represented by the chemical formula C2H2, has one triple bond in the molecule and is linear. At room temperature, it is soluble in water and more soluble in organic solvents like tetrahydrofuran.
While useful as a flammable gas, it is extremely easy to ignite and burns explosively in the absence of oxygen, so care must be taken when handling it.
2. Acetylene Gas Production Methods
The main methods for producing acetylene gas include:
- Carbide method: Adding water to calcium carbide.
- Pyrolysis method: Thermal decomposition of hydrocarbons.
Small-scale applications use the carbide method, while the pyrolysis method is for large-scale industrial manufacturing.
3. Chemical Reaction of Acetylene Gas
Addition Reactions: The triple bond of acetylene is susceptible to addition reactions, producing ethylene and ethane with hydrogen addition. It also reacts with hydrogen halides.
Addition Polymerization: Acetylene can undergo addition polymerization, producing monovinylacetylene, a raw material for butadiene, and chloroprene for synthetic rubber. Benzene is synthesized from three acetylene molecules. Polyacetylene is used as a conductive material.
Types of Acetylene Gas
Acetylene gas is filled into gas cylinders as dissolved acetylene, pressurized, and dissolved in a solvent like acetone or DMF.
Dissolved acetylene generally has a slight odor due to impurities like phosphine and hydrogen sulfide. It is mainly used for metal welding and fusion processing.
Other high-purity products are used as raw materials for semiconductor carbon and for the production of hard carbon films. Compressed acetylene gas should be handled with caution due to its explosive nature.