Conventional chemical reactors use high-temperature furnaces to "crack," or break down natural gas feedstock such as ethane and propane into molecular fragments. After passing through the cracking furnaces, the fragments re-form into new compounds, including olefins. One of the single largest costs in producing olefins is the energy required to heat the furnaces to 900-1,100 degrees Celsius to crack the feedstock. Even at those temperatures only about 60% of the feedstock is converted into new compounds, and just over 50% of the converted materials re-form into the desired end product such as ethylene.

For years, the fact that yields of ethylene can increase by raising furnace temperatures and reducing reaction times has been known. This has been successfully carried out with liquid feedstock but isn't possible with gases due to the higher temperatures required. A new technique for processing natural gas, saving the petrochemical industry billions of dollars in energy and maintenance costs, has been developed by researchers from University of Washington.
Experiments using supersonic steam and shock waves, instead of a conventional furnace to break down natural gas compounds recently produced yields of ethylene that are 20-25% higher than the industry norm. A shock wave is a disturbance in a flow of gas that forms when the flow suddenly changes from supersonic to subsonic speeds, as in supersonic flow about an airplane wing. Shock waves, which can instantaneously heat feedstock to optimum temperatures, may break through the wall and yield several other benefits for petrochemical processing.

Using the UW's Kirsten Wind Tunnel, the researchers conducted studies to design and test supersonic flow control devices, measurement and diagnostic instruments and optimum flow channel dimensions for the shock wave reactor. The facility has a large boiler that heats steam to about 1,250 degrees Celsius. The steam is fed into the reactor channel through specialized nozzles that force it to supersonic speeds. In a separate reservoir, ethane is also heated and injected into the channel at supersonic speeds. The supersonic flow lowers the temperature of the steam and ethane to prevent it from reacting prematurely. A shock wave is formed in the channel as the mixture slows to subsonic speeds. The shock wave heats the flow in microseconds to roughly 1,150 degrees Celsius, the optimum temperature for cracking ethane. After passing through the shock wave and reacting for a brief period, the mixture goes into a quencher that cools the gas and preserves the chemical products.
The researchers have successfully converted about 80% of the ethane feedstock, and 80-90% of the converted material turned into ethylene, representing a 20% improvement in yield over the industry average using the conventional process.

The benefit of the new process is that the quick reaction time and the use of steam greatly reduce coking and fouling of the channel tubes. Another advantage is the potential of the new process to crack methane, a far more abundant component of natural gas than ethane. Methane requires a temperature of 1,800 degrees Celsius to crack and produce usable amounts of ethylene. The high temperature makes it impossible to process methane using conventional methods. The most important reason the petrochemical industry is so interested in the UW process, is that it can be utilized with only minimal retrofitting of existing plants.