Synthetic fuels could entirely eliminate U.S. need for crude oil, create new economy

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.

The high cost of building new synthetic fuel plants, however, 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 practical. The U.S. government has undertaken a number of projects to look into the process; in particular, the Defense Department has studied synthetic fuels as a way to supply transportation fuel without depending on overseas suppliers.

In its work, the Princeton team looked at a broader picture. In a July article in the AIChE Journal, the team found that the United States could meet its entire demand for transportation fuel by building 130 synthetic fuel plants across the country. The article, with Josephine Elia, a graduate student in chemical and biological engineering as the lead author, made its assessment using three feedstocks: coal, natural gas, and biomass. To avoid switching farmland from food production to crops used for fuel production — which would hurt the food supply — the researchers only included non-edible crops such as perennial grasses, agricultural reside and forest residue.

The plants modeled in their scenario were placed in proximity to both feedstock supplies and markets for fuels. The analysis factored in external costs such as water supplies and electricity to power the plants’ machinery.

Ultimately, the team recommended construction of nine small, seventy-four medium, and forty-seven large plants producing 1 percent, 28 percent, and 71 percent of the fuel, respectively. Most of the plants would be clustered in the central part of the country and in the Southeast. The state with the highest level of fuel production would be Kansas, which would have eleven large synthetic fuel plants. Texas would have the largest number of plants, but because of the scattered nature of feedstock in that state, most of those plants would be medium-sized.

The researchers found that the largest contributor to the price of synthetic fuel would be the cost of building the plants, followed by the purchase of biomass and then electricity. They estimated that the nationwide average cost of producing the synthetic equivalent of a barrel of crude oil would be $95.11, although the cost varies regionally. The cost in Kansas, where most production would occur, would average $83.58 for the equivalent of a barrel of crude oil.

The cost could be much lower if plants eliminated biomass and used only coal and natural gas to run the process, Floudas said, but that would eliminate most of the environmental benefit.

“If you want to have a 50 percent reduction in emissions, you need to have the biomass,” he said.

In many ways, synthetic fuels are cleaner than petroleum fuels. The heavy metal and sulfur contaminants of petroleum fuels can be captured in the synthetic plants before the fuel is shipped out. Synthetic fuels also can be used in gasoline and diesel engines with no need for modifications, unlike many biofuels. The biofuel ethanol, for example, is commonly mixed with gasoline, but high levels of ethanol require modifications to car engines and pose special challenges for starting at low temperatures.

Floudas said that synthetic fuels also would allow carbon reduction with the fleet of cars currently on the road. Even if the country immediately converted to zero-emitting electric or fuel cell vehicles, millions of internal combustion vehicles would still be driving. By switching to synthetic fuels, he said, the country would have the opportunity to reduce those emissions, even if it they would not be completely eliminated.

“This is an opportunity to create a new economy,” Floudas said. “The amount of petroleum the U.S. imports is very high. What is the price of that? What other resources to do we have? And what can

 — Read more in Josephine A. Elia et al., “Nationwide energy supply chain analysis for hybrid feedstock processes with significant CO2 emissions reduction,” AIChE Journal 58, no. 7 (July 2012): 2142–54 (DOI: 10.1002/aic.13842)

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