Acetylene, the vogue cutting gas of the 1960s, is seeing something of a revival. It has predominantly been used as an intermediate synthesiser of chemical compounds, and to a lesser extent for welding and cutting, the production of carbon black, and heat treating.
Worldwide production peaked between the 1960s and 70s, but quickly ebbed with concerns about safety and advances in olefins technology. However, as we enter a new decade riddled with volatile and costly oil prices, materials such as acetylene are set to come to the fore.
Additionally, burgeoning industries are expected to increase demand. Robert Esper of Praxair noted, “While there will always be a demand for acetylene in the welding and cutting industry, Praxair sees more growth for acetylene in areas such as low pressure carburization and as a carbon source for nanotechnology.”
Market and production
Esper told gasworld, “Most of all acetylene is used by the chemicals industry, the largest single application is the production of butanediol, a precursor used to manufacture nylon fabrics.”
“Praxair supplies acetylene to the welding and cutting market as well as to the heat treating market. We see a modest growth rate for acetylene of 1-1.5% per year, linked to manufacturing activity. The welding and cutting industry segment using acetylene for steel plate work is pulled through by construction, heavy vehicles and large transformers. The metal heat treating industry is linked to activity level in automotive and aerospace markets.”
In addition, due to its high and controllable reactivity, the gas is particularly suited to speciality and fine chemical industries. Similarly, the characteristic C-C triple-bond means that vinylations and ethynylations are achievable with minor synthetic effort. It is a vital component used to build-up complex molecular structures, which is vital in the production of perfume, vitamins, polymer-additives, solvents for construction industries and surface-active compounds. Nevertheless, during the 1960s, acetylene was replaced with ethylene from low-cost petroleum. It is only in recent years, with increasing oil costs, that this is starting to reverse.
Acetylene is usually produced in one of two ways from calcium carbide, based on either a wet or dry generator. Esper said, “The type of acetylene normally supplied by Praxair is generated from calcium carbide.” When asked about the effects of the financial crisis on the production of acetylene, Esper noted a link between production and finance, “We see calcium carbide prices rising with the cost of electric power and coke however the supply of calcium carbide is stable.” He also noted that, “These trends did not change during the financial crisis.”
Similarly, “Chemical acetylene, another form of acetylene marketed by Praxair, is a by-product of the ethylene process. In this case, acetylene supply is tied to demand for ethylene. As ethylene demand changes the availability of acetylene can change.”
A major reason for acetylene going out of favour in the 1970s surrounded safety concerns. Esper commented on the practicalities, “Due to the carbon-to-carbon triple bond, acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent.”
“Safety is an issue which must be taken very seriously, because acetylene is an unstable gas. However, acetylene is used in many applications and many manufacturing settings in a safe and effective manner. Praxair has procedures in place and has spearheaded efforts to ensure the proper equipment is employed throughout the industry.”
“Acetylene can explode with extreme violence if the pressure of the gas exceeds 15 psi, so it is shipped and stored in acetone or DMF, contained in a cylinder with a porous filling, which renders it safe to transport use.”
Furthermore, Esper stressed that only approved acetylene regulators that are preset to a discharge pressure of no more than 15 psi should be used. The auto-ignition temperature is 763-824˚F, while it is incompatible with bromine, chlorine, copper, mercury and silver.