Biological Carbon Fixation
Carbon fixation is a process that takes inorganic carbon (in the form of things like CO2) and converts it into organic compounds. In other words, any process that converts carbon dioxide into a molecule that would be found in a living organism is carbon fixation. If this process occurs in a living organism, it is referred to as 'biological carbon fixation'.Fuel
The next part of the definition of a biofuel involves fuel. A fuel is nothing more than something from which we humans can get energy. Carbon fixation can lead to a number of different compounds, like proteins, fats, and alcohols (just to name a few). If any of those molecules can be used to provide energy in a mechanical setting, we call it a fuel.The Real Definition of a Biofuel and the Practical Definition
A biofuel is a hydrocarbon that is made BY or FROM a living organism that we humans can use to power something. This definition of a biofuel is rather formal. In practical consideration, any hydrocarbon fuel that is produced from organic matter (living or once living material) in a short period of time (days, weeks, or even months) is considered a biofuel. This contrasts with fossil fuels, which take millions of years to form and with other types of fuel which are not based on hydrocarbons (nuclear fission, for instance).What makes biofuels tricky to understand is that they need not be made by a living organism, though they can be. Biofuels can also be made through chemical reactions, carried out in a laboratory or industrial setting, that use organic matter (called biomass) to make fuel. The only real requirements for a biofuel are that the starting material must be CO2 that was fixed (turned into another molecule) by a living organism and the final fuel product must be produced quickly and not over millions of years.
Biomass
Biomass is simply organic matter. In others words, it is dead material that was once living. Kernels of corn, mats of algae, and stalks of sugar cane are all biomass. Before global warming related to burning fossil fuels became a major factor in determining where energy came from, the major concern was that fossil fuels, which are considered limited in supply, would run out over the next century. It was thought that if we could produce hydrocarbons another way, and quickly, then we could meet our energy demands without much problem. This leads to one of the major separating factors between a biofuel and a fossil fuel - renewability.A fossil fuel is not considered renewable because it takes millions of years to form and humans really can’t wait that long. Biofuel, on the other hand, comes from biomass, which can be produced year after year through sustainable farming practices. This means biomass and biofuel are renewable (we can replace used biofuel over a very short period of time).
It is important to note that 'renewable' energy is not the same thing as 'green' energy. Renewable energy simply won’t run out any time soon, like biofuels, hydroelectric, wind, and solar. A “green” energy is one that is also good for the planet because it does not harm ecosystems, contribute to acid rain, or worsen global warming. Solar energy is a 'green' energy. All 'green' energy is considered renewable, but not all renewable energy is green. Biofuels are examples of renewable energy sources that aren’t always green because they produce greenhouse gases.
Types of Biofuels
The chemical structure of biofuels can differ in the same way that the chemical structure of fossil fuels can differ. For the most part, our interest is in liquid biofuels as they are easy to transport. The table below compares various biofuels with their fossil fuel counterparts.| Biofuel | Fossil Fuel | Differences |
| Ethanol | Gasoline/Ethane | Ethanol has about half the energy per mass of gasoline, which means it takes twice as much ethanol to get the same energy. Ethanol burns cleaner than gasoline, however, producing less carbon monoxide. However, ethanol produces more ozone than gasoline and contributes substantially to smog. Engines must be modified to run on ethanol. |
| Biodiesel | Diesel | Has only slightly less energy than regular diesel. It is more corrosive to engine parts than standard diesel, which means engines have to be designed to take biodiesel. It burns cleaner than diesel, producing less particulate and fewer sulfur compounds. |
| Methanol | Methane | Methanol has about one third to one half as much energy as methane. Methanol is a liquid and easy to transport whereas methane is a gas that must be compressed for transportation. |
| Biobutanol | Gasoline/Butane | Biobutanol has slightly less energy than gasoline, but can run in any car that uses gasoline without the need for modification to engine components. |
The chart above is only a limited list of the biofuels available, covering only the most popular and widely used. It is worth nothing that ethanol is found in almost all gasoline mixtures. In Brazil, gasoline contains at least 95% ethanol. In other countries, ethanol usually makes up between 10 and 15% of gasoline.
Biofuel versus Fossil Fuel
Biofuels are not new. In fact, Henry Ford had originally designed his Model T to run on ethanol. There are several factors that decide the balance between biofuel and fossil fuel use around the world. Those factors are cost, availability, and food supply.All three factors listed above are actually interrelated. To begin, the availability of fossil fuels has been of concern almost from day one of their discovery. Pumping fuel from the ground is a difficult and expensive process, which adds greatly to the cost of these fuels. Additionally, fossil fuels are not renewable, which means they will run out at some point. As our ability to pump fossil fuels from the ground diminishes, the available supply will decrease, which will inevitably lead to an increase in price.
It was originally thought that biofuels could be produced in almost limitless quantity because they are renewable. Unfortunately, our energy needs far out-pace our ability to grown biomass to make biofuels for one simple reason, land area. There is only so much land fit for farming in the world and growing biofuels necessarily detracts from the process of growing food. As the population grows, our demands for both energy and food grow. At this point, we do not have enough land to grow both enough biofuel and enough food to meet both needs. The result of this limit has an impact on both the cost of biofuel and the cost of food. For wealthier countries, the cost of food is less of an issue. However, for poorer nations, the use of land for biofuels, which drives up the cost of food, can have a tremendous impact.
The balance between food and biofuel is what keeps the relatively simple process of growing and making biofuels from being substantially cheaper than fossil fuel. When this factor is combined with an increased ability (thanks to advances in technology) to extract oil from the ground, the price of fossil fuel is actually lower than that of biofuel for the most part.
The Carbon Equation: Would Biofuels Contribute to Global Warming?
Assuming we can overcome the problem of biofuels interrupting the food supply (such as growing algae in the ocean), can we overcome the problem of biofuels contributing to global warming? The answer, surprisingly, may be yes.It is true that biofuels produce carbon dioxide, which is a potent greenhouse gas and the one most often blamed for global warming. However, it is also true that growing plants consumes carbon dioxide. Thus, the equation becomes a simple balancing act. If the plants we grow utilize the same amount of carbon dioxide that we produce, then we will have a net increase of zero and no global warming. How realistic is this view?
It may seem like a simple matter to only produce as much carbon dioxide as plants use. After all, couldn’t we only burn biofuels and thus keep the equation balanced? Well, the math actually doesn’t quite add up. Research has shown that energy must be invested into producing crops and converting them into biofuels before any energy is obtained. A 2005 study from Cornell University found that producing ethanol from corn used almost 30% more energy than it produced. In other words, you can’t produce a perpetual motion machine using biofuels because you lose the energy you invest in creating them in the first place. In fact, you can’t even break even.
The other problem that we run into with biofuels is that carbon dioxide is not the only greenhouse gas we have to worry about. Other chemicals, like nitrous oxide, are also greenhouse gases and growing plants using fertilizer produces a lot of nitrous oxide. Basically, fertilizer contains nitrogen, which plants need to grow. However, most plants cannot convert molecular nitrogen into the elemental nitrogen they need. For this process, plants rely on bacteria. As it turns out, bacteria not only produce nitrogen that plants can use, they also produce nitrogen products like nitrous oxide, and probably more than was previously thought. The net result is that we may be balancing the CO2 equation by using biofuels, but we are unbalancing the N2O part of the equation and still causing global warming.
The Future of Biofuel
A decade ago, subsidies for biofuel growth and development in many countries (especially the U.S.) were high. However, better understanding of global warming, increased awareness of the fragility of the food supply, and a general trend toward “greener” alternatives have all led to a decline in the popularity of biofuels. In 2011, The U.S. Senate voted 73 to 27 to end tax credits and trade protections for corn-based ethanol production. As the second largest producer of ethanol, this is a substantial move that reflects the changing pressures on our energy needs and shifted focus to environmentally friendly energy sources.Biodiversity and Biofuels
There is one last problem presented by biofuels that needs to be addressed: biodiversity. Biodiversity refers to the variety of different living things in an environment. For instance, if you grow only sweet corn in a field, you have low biodiversity. If, however, you grow sweet corn, dent corn, flint corn, flour corn, and popcorn, then you have high biodiversity. Why should we care?Growing a single type of corn is easier for producing biofuels because we can select that type that yields the best raw product, is easiest to grow, and which requires the least amount of water and other resources. This sounds great, but then down side to this is that pests that eat this type of corn will begin to proliferate. What is worse, if we spray with pesticide to kill these pests, some will inevitably be resistant to the pesticide. Over time, these pests will grow in number and we will be left with pests that are resistant to our chemical defences. In the end, we have a bigger problem that what we started with and probably no corn because the new “super pest” ate it all.
Biodiversity is important to ensuring that pests do not grow out of control. The type of farming needed to produce large quantities of biofuels is generally not amendable to high levels of biodiversity. This presents a fundamental problem in producing biofuels that is enhanced by the fact that “super pests” produced in the effort to grow biofuels can also threaten food crops.
