Acetylene, commonly known as air coal or calcium carbide gas, is the simplest alkyne and a very important industrial fuel gas and chemical raw material.

Physical Properties

State and Appearance: At room temperature and pressure, acetylene is a colorless, odorless gas (when pure).

Odor: Industrial-grade acetylene has a pungent, garlic-like odor due to impurities such as phosphine (PH₃) and hydrogen sulfide (H₂S).

Density: Slightly lighter than air (vapor density approximately 0.9, air = 1).

Solubility: This is a critical property. Acetylene is highly soluble in acetone. Under standard conditions, 1 volume of acetone dissolves approximately 25 volumes of acetone. This solubility increases significantly under high pressure. This property is widely used for the safe storage of acetylene (dissolving acetylene in a cylinder filled with porous material and acetone to stabilize it against explosion).

Boiling and Melting Points: Boiling point -84°C, melting point -81°C (under pressure). Sublimation point -84℃.

Acetylene (C₂H₂), an important basic industrial gas, is used primarily for its two core properties: 1. It generates extremely high temperatures when burned; 2. Its highly unsaturated molecular structure makes it an excellent chemical raw material.

1. Metalworking and Welding (the most traditional and primary application)

This is the largest consumer of acetylene, utilizing the high temperatures released during combustion.

Oxyacetylene Flame Welding and Cutting:

Principle: Acetylene burns in oxygen, producing flame temperatures reaching approximately 3100°C, the highest of all commonly used combustible gases.

Welding: The flame melts the metal at the interface between the welding rod and the workpiece, fusing them together. This is commonly used for welding cast iron and some steels.

Cutting (more common): A high-temperature flame is used to heat the metal to its ignition point. A high-velocity stream of oxygen is then applied to the metal, causing it to oxidize (burn) violently and blowing away the slag, ultimately cutting the metal. This is one of the most common methods for cutting steel plates, steel structures, and other materials.

2. Chemical Synthesis (Most Important Raw Material Use)

Acetylene is a building block for many important organic chemicals.

Polyvinyl chloride (PVC) production: This is acetylene's largest chemical use.

Process: Acetylene reacts with hydrogen chloride (HCl) gas over a catalyst to produce vinyl chloride (VCM), which is then polymerized to form polyvinyl chloride (PVC).

Uses: PVC is one of the world's most produced general-purpose plastics, used in the manufacture of pipes, doors and windows, wire coverings, flooring, films, and more.

Acrylonitrile Production:

Process: Acetylene reacts with hydrocyanic acid (HCN) to produce acrylonitrile.

Uses: Acrylonitrile is an important monomer in the synthesis of acrylonitrile-butadiene-styrene copolymer (ABS resin) and synthetic rubbers such as nitrile-butadiene rubber. ABS resin is widely used in automotive, electronic, and consumer product casings.