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Biofuels may not be as green as we’ve been told

Are biofuels better for the environment? Not necessarily.

The combustion engine is, hands down, one of the most important inventions of all time. But, it comes with a very high cost to the environment – hazardous emissions. While many leaps in efficiency and emission control have been made over the decades, we can never fully eliminate the release of emissions like carbon dioxide into the air. But, what if the fuel for these engines could be grown rather than dug up? And that is precisely the promise that biofuels have made over the last few decades. However, not everything is all that it seems when it comes to this “holy grail” of clean energy.

What are biofuels?
Biofuels, as the name might suggest, are types of liquid and gas fuels created “naturally” through the conversion of some kind of biomass. While the term can be used to encompass solid fuels, like wood, these are more commonly termed biomass rather than biofuel per se. For this reason, biomass tends to be used to denote the raw material that biofuels are derived from or those solid fuels that are created by thermally or chemically altering raw materials into things like torrefied pellets or briquettes.

Various forms of biofuels exist but are by far the most commonly used today are ethanol (sometimes called bioethanol) and biodiesel. The former is an alcohol and is usually blended with more conventional fuels, like gasoline, to increase octane and cut down on the toxic carbon monoxide and smog-causing emissions usually associated with combustion engines. The most common form of the blend, called E10, is a mixture of 10 percent ethanol and 90 percent gasoline. Some more modern vehicles, called flexible-fuel vehicles, can actually run on another blend of ethanol and gasoline called E85 that contains between 51 percent and 83 percent ethanol. According to the U.S. Department of Energy, roughly 98% of all gasoline you put in your car will contain some percentage of ethanol.

Most ethanol for fuel use is made from plant starches and sugars but there are an increasing number of biofuels in development that use cellulose and hemicellulose. These are the non-edible fibrous material that constitutes the bulk of plant matter. To date, several commercial-scale cellulose-based ethanol biorefineries are currently operational in the United States. The most common plant “feedstock” used to make ethanol, are corn, grain, and sugar cane.

As with alcohol production, as for your favorite beer or wine, bioethanol is created through the age-old process of fermentation. As with alcoholic beverages, microorganisms like bacteria and yeast use plant sugars as an energy source and produce ethanol as a waste product.

This ethanol can then be fractionated off, distilled, and concentrated ready for use as a liquid fuel. All is well and good, but blending with ethanol does come at a cost. As the U.S. Department of Energy explains, “ethanol contains less energy per gallon than gasoline, to varying degrees, depending on the volume percentage of ethanol in the blend. Denatured ethanol (98% ethanol) contains about 30% less energy than gasoline per gallon. Ethanol’s impact on fuel economy is dependent on the ethanol content in the fuel and whether an engine is optimized to run on gasoline or ethanol.”

Biodiesel, the other most common biofuel, is made from vegetable and animal fats and is generally considered a cleaner-burning direct replacement for petroleum-based diesel fuel. It is non-toxic, biodegradable, and is produced using a combination of alcohol and vegetable oil, animal fat, or recycled cooking grease. It is a mono-alkyl ester produced by the process of transesterification, where the feedstock reacts with an alcohol (such as methanol) in the presence of a catalyst, to produce biodiesel and glycerin.

Like ethanol, biodiesel can be blended with regular diesel to make cleaner fuels. Such fuels range from pure biodiesel, called B100, with the most common blend, B20, consisting of 20 percent biodiesel and 80 percent fossil-fuel diesel. Just like ethanol, biodiesel is not without its own problems when compared to more traditional fuels. For example, it can be problematic in colder climates as it has a tendency to crystallize. Generally speaking, the less biodiesel content, the better the performance of the fuel in cold climates. This issue can also be overcome by adding something called a “flow improver” that can be added to the fuel to prevent it from freezing. Another form of biodiesel that is also quite popular is “green diesel”, or renewable diesel. Formed by the hydrocracking of vegetable oils or animal fats (or through gasification, pyrolysis, or other biochemical and thermochemical technologies) to produce a product that is almost indistinguishable from conventional diesel. Vegetable oil can also be used unmodified as a fuel source in some older diesel engines that don’t have common fuel injection systems.

Other forms of biofuel also exist, including biogas or biomethane that are created through the process of anaerobic digestion (basically rotting) of organic material. “Syngas,” another form of biofuel gas is created by mixing carbon monoxide, hydrogen, and other hydrocarbons through the partial combustion of biomass.

Worldwide biofuel production reached in excess of 43 billion gallons (161 billion liters) in 2021, constituting around 4% of all the world’s fuel used for road transportation. This is hoped by some organizations, like the International Energy Agency, to increase to 25% by 2050.

Why are biofuels considered green?
In order to fully answer this question, we need to take a little trip back in time. Around the turn of the 21st-century, many governments around the world were scratching their heads trying to figure out ways to combat the amount of carbon emissions their countries were emitting. One of the main polluting activities happened to be the cars and trucks used to ferry people and stuff around. In fact, this is one of the largest contributing factors to human global carbon dioxide emissions that, according to some sources, account for almost a quarter of all annual emissions around the world.

The transport sector is also one of the fastest-growing around the world, as a result of the growing use of personal cars in many countries around the world. Of these, the vast majority are still combustion-engine vehicles rather than “cleaner” solutions like the growing electrical vehicle market.
Something, in their view, needed to be done about this and so the concept of biofuels was proposed as a potential “silver bullet”.

Since biofuels are formed, primarily, from the growth and harvesting of living plant material rather than long-sequestered hydrocarbon sources like fossil fuels. The main argument is that biofuels draw down as much carbon dioxide, more or less, as they release when combusted. This is because carbon is stored in the plant tissue and soil as plants grow. They are, in effect, “carbon neutral”, and in some cases have been shown to be carbon negative – in other words, they remove more carbon from the atmosphere than is released when they are harvested, processed, and burned/converted.

https://interestingengineering.com/biofuels-not-as-green-as-told

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