Industrial application of the two major uses of acetylene and ethylene are metal working, chemical manufacturing and creation of new materials where both are utilized to a wide extent depending upon their typical chemical properties such as high heat of combustion and reactivity. For instance, acetylene ignites at 3,100°C in an oxygen-acetylene flame (ethylene only 2,900°C), can cut up to 300 mm thick steel plates (cutting speed 0.5 m/min), and almost 65% of metal processing businesses worldwide utilize acetylene in the repair of heavy machinery. Ethylene, with its regulated combustion (flame temperature of 2,700°C), is used for accurate welding, i.e., body sheets of automobiles, and the width of its HAZ is 40% less than that of acetylene (0.8 mm vs. 1.3 mm), due to which the risk of deformation (scrap rate from 5% to 2%) is reduced.
In the chemical synthesis industry, ethylene is the main raw material of polyethylene (PE) and polyvinyl chloride (PVC), global annual production over 150 million tons of polyethylene (amounting to 34% of all plastics produced), one ethylene cracker plant (for example, BASF 1.2 million tons/year capacity) has to burn 500 tons of ethylene raw material/day. Acetylene is used to produce vinyl acetate (VAM, global annual production of 6.5 million tons), and the route process (acetylene process) accounts for 55% in China, with a calcium carbide resource-rich area (VAM per ton price is $200 lower than ethylene method). However, acetylene ethylene gas mixtures are found to produce synergistic effects in certain reactions, such as the manufacture of vinyl chloride monomer (VCM), in which copolymerization process of acetylene and ethylene (ratio 1:3) has the ability to increase the rate of conversion from 85% to 92% (savings in raw material cost by $1.2 million for 100,000 tons per year plant).
With regard to novel material production, acetylene derived carbon nanotubes (CNT) have 99.8% purity (98.5% ethylene derived CNT), 63GPa tensile strength (50 times that of steel), and application in aerospace composite materials (e.g., Boeing 787 fuselage weight reduction by 15%). Polymerization of ethylene at high pressure (200-300MPa) results in low-density polyethylene (LDPE), which is 92% transparent (better than acetylene-based materials) and is largely used as films for food packing (worldwide demand of 8 million tons per year). Acetylene is utilized in the semiconductor industry to film diamond films (growth rate of 10μm/h), while ethylene cracked carbon nanofibers (diameter 50-100nm) are utilized in lithium-ion battery anodes that increase the energy density to 400Wh/kg (traditional graphite anodes 372Wh/kg).
In the energy and fuel sector, acetylene is used as rocket fuel (i.e., SpaceX Falcon 9 gas generator fuel) due to its excellent combustion value (54MJ/kg), but its storage risk (pressure >0.2MPa easy decomposition) limits its large-scale application. Ethylene is produced by high-octane gasoline alkylation (research octane number RON 95-100), and the ethylene base and fuel account for 28% of the world’s refineries (Sinopec’s 2023 production of 12 million tons). The mixture of acetylene ethylene (1:4) provides low-emission combustion (NOx<25ppm) in a gas turbine, which results in 12% higher combustion efficiency compared to pure acetylene (thermal efficiency increased from 35% to 39%).
Safety and cost considerations influence application choice. Acetylene cylinders (40L volume, 1.5MPa pressure) are three times more expensive to lease than ethylene tanks (liquid, -104°C) ($150 vs. $50/month). Acetylene cutting is 20% faster than plasma cutting (3 minutes vs. 3.6 minutes to cut a 20mm thick steel plate). According to the American Chemical Society (ACS), over 12 million tons of acetylene were used across the world annually (48 percent in China) and more than 170 million tons of ethylene consumed (45 percent in Asia Pacific), the market for both in acetylene ethylene mixed applications is forecast to grow at 4.5 percent per annum (2023-2030).
Case studies include:
Germany ThyssenKrupp uses acetylene cutting to refurbish ship propellers (250mm thickness), saving 24,000 euros per repair price (compared to laser cutting).
The Saudi Basic Industries Corporation’s (SABIC) ethylene cracking unit generates 13 million tons of ethylene per year, supporting $32 billion of Middle Eastern petrochemical exports.
China’s Ningde Times uses vinyl carbon nanotubes to increase battery cycle life to 6,000 cycles (50% more than traditional materials).
Through minimization of cost and technology development, synergy application of ethylene acetylene will continue to be a pace-setting development driver in industry through innovation and material innovation.