A combination of coal, natural gas and non-food crops used to make synthetic fuel could reduce America's need for crude oil. It's been tried various times, even before World War II, with no success, but it may deserve a rethink.
Less money going to oil-owning dictators is good in lots of ways and there may even be environmental benefits, researchers say. Because plants absorb carbon dioxide to grow, the United States could cut vehicle greenhouse emissions by as much as 50 percent in the next several decades using non-food crops to create liquid fuels.
Synthetic fuels would have an advantage over ethanol (especially the disastrous E15 the US is insisting on implementing, despite any benefit and a great deal of concern) because they could be used directly in automobile engines and are almost identical to fuels refined from crude oil.
The core of the plan is a technique would be using heat and chemistry to create gasoline and other liquid fuels from high-carbon feedstock such as coal or switchgrass from 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.
Christodoulos Floudas, a professor of chemical and biological engineering at Princeton, helped evaluate scenarios in which the United States could power its vehicles with synthetic fuels and also analyzed the impact that synthetic fuel plants were likely to have on local areas. They also identified locations that would not overtax regional electric grids or water supplies.
Accomplishing this would not be easy or quick. A realistic approach would call for a gradual implementation of synthetic fuel technology and Floudas estimated it would take 30 to 40 years for the United States to fully adopt synthetic fuel. It also would not be cheap. He estimates the price tag at roughly $1.1 trillion for the entire system. In 1980, just before being voted out of office, American President Jimmy Carter and a like-minded Congress decided to spend $88 billion developing synthetic fuels. It never came close to working but when his successor, President Ronald Reagan, did not scuttle the program, Arab countries dropped the price of crude oil until the program was finally canceled in his second term. Economically, the same thing may happen again.
"The goal is to produce sufficient fuel and also to cut CO2 emissions, or the equivalent, by 50 percent," said Floudas. "The question was not only can it be done, but also can it be done in an economically attractive way. The answer is affirmative in both cases."
The research is part of a white paper recently produced by the American Institute of Chemical Engineers to advocate greater integration of energy sources and to urge policymakers to rethink chemical conversion as one path to cleaner and cheaper fuels. Energy research is not really done in academia and industry has not embraced synthetic fuels due to cost. The economics are still not good but rising prices for crude oil and competition for fuel from China, coupled with more knowledge than 32 years ago, mean synthetic fuel production could be more viable than before.
What are the factors? Always the price of crude oil, of course, but high prices are not something to wish for. Two-thirds of crude oil consumed by the United States is used for transportation fuel, according to the federal Energy Information Administration (EIA) and the US imports about 45 percent of its annual crude oil consumption. Higher prices primarily impact the people who can least afford it. The type of feedstocks may be a better variable to bring synthetic fuel costs down enough to be viable.
"Even including the capital costs, synthetic fuels can still be profitable," said Richard Baliban, also of Princeton. "As long as crude oil is between $60 and $100 per barrel, these processes are competitive depending on the feedstock."
The chemistry involves taking the carbon and hydrogen from the feedstock and reassembling 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.
They estimate that the United States could meet its entire demand for transportation fuel by building 130 synthetic fuel plants across the country, 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 residue 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, 74 medium and 47 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 11 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."
Synthetic fuels could be an environmental win in other ways. 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 we do about it?"