Properties and Preparation of Acetylene

     Acetylene(molecular formula C2H2) commonly known as wind coal or calcium carbide gas, is the smallest member of alkyne compounds, mainly used in industry, especially in welding metals. Acetylene is a colorless, extremely flammable gas at normal temperature. Industrial acetylene has a garlic odor due to impurities such as hydrogen sulfide and phosphine.

I. Nature of acetylene

Basic physical parameters:

· Molecular formula: C2H2

· Molecular weight: 26.038

· Molecular volume in standard state: 22.223L

· Density in standard state: 1.17167kg/m3

· Density in standard state: 1.17167kg/m³

Triple point parameters

· Temperature: 192.6 K (-80.55℃)

· Pressure of 128 kPa

Liquid acetylene is explosive, but solid acetylene is relatively stable under normal conditions.

Critical parameter

·  Temperature: 308.33 K (35.18℃)

·  Pressure:6,191 kPa

Liquid acetylene is a dangerous substance that may decompose and explode with very little excitation energy. Liquid acetylene formationshould be avoided during compression and handling.

2. Solubility 

3. Explosive nature

    Acetylene is a particularly dangerous flammable and explosive gas that is even more dangerous when pressurized.

·   The autoignition point of acetylene is relatively low, 305°C in air and 296°C in oxygen. When the phosphine content in acetylene gas is greater than 200ppm, its auto-ignition point in air can be as low as 100℃.

·   The minimum ignition energy is very low. 0.019mJ in air, the same as hydrogen; 0.0003mJ in oxygen.

·   Acetylene has a wide range of explosions. 2.5%~100% in air; 2.8%~100% in oxygen.

·   Acetylene has strong spreading ability. The minimum propagation gap is less than 0.4mm, and the propagation speed at the ignition distance of 10 meters can reach more than 2000m/s.

·   Acetylene can decompose and explode. Pure acetylene begins to decompose and explode when the pressure reaches 580℃when the pressure is 147 kPa. High-pressure acetylene is more prone to decomposition and explosion.

·   Acetylene also produces compound explosiveness. When acetylene and chlorine gas meet, the ash undergoes a violent chemical reaction and explodes under certain conditions. Acetylene and copper, silver and other metals have long-term contact, which can generate acetylene copper, acetylene silver and other explosive substances.

Ⅱ. Production of acetylene

    Calcium carbide is an inorganic substance (its chemical formula is CaC2), which is the main component of calcium carbide. It is a white crystal, and the industrial product is a gray-black block with a purple or gray section. Calcium carbide reacts violently with water immediately to generate acetylene and release heat. Calcium carbide is an important basic chemical raw material, mainly used to generate acetylene gas. Also used in organic synthesis, oxyacetylene welding, etc.

Preparation of acetylene

Reaction principle:CaC2+2H2O=Ca(OH)2+C2H2↑

Factors affecting acetyogenesis：

1. The effect of calcium carbide particle size

·  Too large: slow hydrolysis reaction

·  Too small: fast rate, large heat release, rapid heating and explosion

2. The effect of temperature on the hydrolysis reaction of calcium carbide

· Considering the safety production and other aspects, it is better to use the range of 80 to 90°C.

The effect of reaction temperature on the occurrence of the reaction

What is DMF?

    Conventional acetylene is a soluble gas and dissolves in acetone, but for electronic grade acetylene, it is usually dissolved in DMF.

    What is DMF? It is N,N-dimethylformamide, an organic compound with the chemical formula C3H7NO, which is a colorless and transparent liquid. It is not only a very wide use of chemical raw material, but also a very wide use of good solvent. In addition to halogenated hydrocarbons, it can be freely mixed with water and most organic solvents, and has good solubility for various organic and inorganic compounds.