Acetylene (C2H2) is a simple molecule that finds applications across a wide range of fields. Its unique properties – high flame temperature, rapid heat transfer, and diverse chemical reactivity – make it a valuable material for industries such as metalworking and chemical production.
1. Use of Acetylene in Metal Processing
Acetylene finds extensive applications in metal and material processing because it has exceptionally high flame temperature and propagation velocity. This gives a concentrated energy densities and rapid heat transfer to target workpieces.
Studies conducted at Linde reveal a remarkable 50% efficiency increase when utilizing acetylene for extreme oblique sections compared to propane.
An oxyacetylene flame exhibits a characteristic two-part structure: a hotter primary flame and a surrounding secondary flame. The peak temperature resides at the primary flame tip, making it crucial for material processing. Its heating efficiency stems from the combined effect of its volumetric heat release and propagation velocity.
Heat transfer during welding occurs through three primary mechanisms: radiation, convection, and thermal conduction. A steep temperature gradient between the flame and the workpiece further enhances heat transfer.
By adjusting the oxygen-to-acetylene ratio, different flame types are achievable: oxidizing, neutral, or reducing (carburizing). Neutral or slightly reducing flames are preferred for steel, alumina, and copper welding, while oxidizing flames are suitable for brass welding, cutting, pickling, and surface hardening.
Oxyacetylene flames are employed in a wide range of industrial processes, including:
- Welding
- Cutting
- Brazing
- Soldering
- Surfacing
- Flame spraying
- Heating
- Hardening
- Straightening
- Cleaning
- Pickling
- Rust removal
- Decarbonizing
While oxyacetylene flames offer superior performance, acetylene-air flames find occasional use in niche applications like tin brazing, hot air welding of thermoplastics, glassworking, and paint removal. However, the convenience and safety of alternative fuels like propane or butane have largely replaced acetylene in these areas.
Notably, softer acetylene-air flames are used in soft and hard soldering, flame hardening, and flame tempering. For such applications, Bunsen-type and acetylene-compressed air burners are typically employed.
2. Use of Acetylene in the Chemical Industry
Acetylene’s diverse chemical properties have made it a valuable precursor for numerous industrially significant products. Figure 1 summarizes these products and their applications. Between 1960 and 1970, most of these products were derived from it.
However, since the 1970s, acetylene have been substituted by olefins like ethylene and propene particularly in acetaldehyde and acrylonitrile production. Currently, acetylene’s primary applications lie in vinyl chloride, vinyl acetate, and other vinyl esters; acrylic acid; acetylene black; and specialized chemicals like 1,4-butynediol and acetylenic alcohols.
For these specialty chemicals, the acetylene route remains the sole or dominant commercial production method.
While vinyl chloride, vinyl acetate, and acrylic acid were historically major acetylene derivatives, they are now predominantly produced from ethylene and propene in most countries. Interestingly, China presents a unique case.
Since 1997, China’s acetylene demand for vinyl chloride monomer has skyrocketed by 15.9% per year, prompting the construction of new calcium carbide-based production facilities between 2008 and 2013.
China currently is the world’s leading acetylene producer and consumer, accounting for over 80% of global production.
Reference
- Acetylene; Ullmann’s Encyclopedia of Industrial Chemistry. – https://onlinelibrary.wiley.com/doi/10.1002/14356007.a01_097.pub4
