Archive » May 31, 2007
On the Road
By William Korchinski
“It just so happens that ethanol and biodiesel will help improve the quality of the environment in our respective countries,” said President George Bush while in Brazil in March.
The President is not alone in his commitment to biofuels. Willie Nelson, Julia Roberts, Jack Johnson, Morgan Freeman, Woody Harrelson and Daryl Hannah are also supporters of the alternate energy source. Singer Sheryl Crow is riding in a biodiesel bus on her Global Warming tour. Willie Nelson's pithy quote sums up the sentiments of many: “I drove the car, loved the way it drove. The tailpipe smells like French Fries.” Biofuels are the new green, environmentally friendly way forward – a sustainable fuel source with a small carbon footprint. It is unfortunate that like so many things that seem too good to be true, biofuels are no exception.
How the Process Works
The popular understanding of how biofuels work is simple. Plants grow, and as they do, they convert carbon dioxide (CO2) from the air into biomass. Plant biomass is harvested and converted to liquid fuel, which is used to power cars and trucks. In the process of combustion, CO2 is released back to the atmosphere to be again converted back to new plant biomass. The “magical biofuels cycle” is depicted in Figure 1.
Biofuels are thought to be good for two reasons. First, the CO2 goes around in a perpetual recycle, never getting a chance to build up in the atmosphere, and it is thus seen as “carbon neutral.” Second, homegrown fuel allows a measure of energy self-sufficiency; we no longer have to rely on geopolitically unstable countries to satisfy our transportation needs. The sun's energy grows plants. Plant are turned into fuel. The fuel powers cars, and the cars' exhaust gets made back into fuel. On the surface, this seems to be a sustainable process with no carbon buildup, and minimal energy requirements.
The “real biofuels cycle” is shown in Figure 2. It takes a great deal of energy and many types of raw materials to drive this cycle. For example, in order to efficiently grow corn, it takes rich, mineral-laden soil, corn seeds, fertilizer, pesticides and water. Harvesting corn takes diesel fuel. Making fertilizer and pesticides requires natural gas, crude oil and electricity. Farming leads to soil erosion. All of these processes produce significant quantities of chemical waste, wastewater, CO2 and other byproducts. So, while the popular perception of biofuels is that they arise naturally (Figure 1), in reality they must be manufactured using energy-intensive and materials-intensive industrial processes (Figure 2) that produce waste and byproducts.
We talk about using biofuels to replace current transportation fuels. But what do we mean when we say this? The United States currently consumes about 400 million gallons of gasoline per day and 200 million gallons of diesel fuel a day. While both of these fuels are derived from crude oil, they can also be made using plant matter, or biomass. Some of the plants that can be turned into biofuels include corn, soybeans, sunflower, sugarcane, algae, hemp and trees. There are many types of industrial processes available for converting these plants into fuels. Each combination of raw plant material and industrial process has its own set of efficiencies, energy requirements and waste production. When discussing the “sustainability” of biofuels, what really matters is how efficiently biofuels can be made.
Let's start by looking at the production of ethanol from corn, since this is one of the most common configurations being considered at present. The U.S. currently produces 44% of the world's corn on 70 million acres of land. If we were to replace all 400 million gallons per day of gasoline with ethanol from corn, we would need to plant 570 million acres of corn, 25% of the total land mass of the United States and evidently far more than the total arable farmland currently available.
Farming corn on this massive scale would lead to substantial soil erosion and mineral depletion. This is important because contrary to popular belief, soil is not a renewable resource. It needs to be replenished – and replenishing soil takes raw materials and significant amounts of energy. Processing corn requires other resources as well, including water for farming – between 18 and 24 inches of water per season – as well as 30-37 gallons of industrial water per gallon of ethanol manufactured.
In addition to land, soil and water, ethanol production from corn requires energy for planting, harvesting, transporting, processing and so on. Much of this energy is supplied by gasoline and diesel. For every gallon of ethanol produced, it takes more than a gallon of gasoline and diesel fuels to power the harvesting machinery, trucks and other parts of the manufacturing process. When all of the thermodynamic efficiencies in the process of converting corn into ethanol are taken together, it takes between 3.6 and 6.2 gallons of ethanol to displace a single gallon of gasoline. There are other large costs as well, including the need to dispose of process waste. A single ethanol production facility produces as much wastewater as a medium-sized city.
Sustainable, or Not?
What about biodiesel? It's a commonly held belief that used French fry oil can and should be made into biodiesel. However, converting all of our French fry oil supplies would only supply 2.5% of our current conventional diesel demand. Like ethanol, biodiesel must be produced in large industrial processes in order to be made efficiently. And as with ethanol production, there are large energy requirements and large amounts of waste generated. It would take 10% of the entire landmass of the United States to replace our current conventional diesel fuel demands with biodiesel made from soybeans. In terms of energy efficiency, biodiesel production loses between 8% and 32% compared to conventional diesel.
How sustainable are biofuels? “Sustainable” is a common word these days, but one that is rarely defined. One way to measure sustainability is to compare how much fuel energy one gets out of a process, compared to the amount of energy that must be spent to make fuel. Processes that produce more fuel energy than is used to make fuel are sustainable.
About 97 energy units usable coal can be manufactured by investing 3 units of coal energy, a “sustainability ratio” of 97/3, or 32.3. The high ratio indicates a highly sustainable process. Both ethanol and biodiesel are unsustainable from an energy efficiency point of view – it takes more energy to manufacture the fuel than the fuel itself is worth.
Why are biofuels unsustainable compared to conventional fuels such as gasoline and diesel? The main reason is that it takes many extra steps to manufacture biofuels, steps such as planting, fertilizing, harvesting, watering, transporting grains, producing unrefined product, etc. Each of these extra steps takes energy and requires raw materials. Diesel and gasoline, on the other hand, are derived from crude oil, which was prepared “automatically” 500 million years ago, thanks to the sun and Earth.
On the surface, biofuels apparently hold much promise. Because they are based on plant life, they are variously described as “green,” “environmentally friendly,” “sustainable” and so on. Digging deeper, however, reveals that the common myths regarding these fuels are not accurate, and that indeed the costs far outweigh the benefits.
In a pursuit of a sustainable carbon-neutral life, does it make sense to dedicate valuable farmland to the manufacture of transportation fuels – or would we be better off growing crops for food? For now, it would be simpler, faster and less expensive to alter our transportation habits by driving smaller cars, carpooling and investing in public transportation.
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