"Even including the capital costs, synthetic fuels can still be profitable," said Richard Baliban, a chemical and biological engineering graduate student who graduated in 2012 and was the lead author on several of the team's papers. "As long as crude oil is between $60 and $100 per barrel, these processes are competitive depending on the feedstock," he said.
The core of the plan is a technique that uses heat and chemistry to create gasoline and other liquid fuels from high-carbon feedstock ranging from coal to switchgrass, a native North American grass common to the Great Plains. The method, called the Fischer-Tropsch process, was developed in Germany in the 1920s as a way to convert coal to liquid fuels.
The chemistry is complicated, but it basically takes the carbon and hydrogen from the feedstock and reassembles them into the complex chains that make up fuels like gasoline and diesel. Essentially, the feedstock material is heated to 1,000 to 1,300 degrees Celsius and converted to gas, and using the Fischer-Tropsch process, the gas is converted to chains of hydrocarbon molecules. These hydrocarbon chains are then processed over catalysts such as nickel or iron. The end products include fuels, waxes and lubricants normally made from crude oil.
The Princeton team's method adds a step to recycle CO2 through the process to reduce the amount of the gas vented by the plants. Baliban said there is a limit to how much CO2 can be economically recycled, although plants could also trap unused CO2 emissions for later storage.
Over the years, engineers have refined the original Fischer-Tropsch method to increase efficiency. But the high cost of building new synthetic fuel plants, coupled with the low price of crude oil, has made synthetic fuels too expensive for widespread acceptance.
As the price of oil has increased, however, synthetic fuels have become more pract
|Contact: John Sullivan|
Princeton University, Engineering School