Biofuels derived from some of the aforementioned food crops are now widely referred to as “first-generation” biofuels. Those that use non-food sources like switchgrass, or waste materials like sawdust or fruit pulp, are known as second-generation biofuels. The latter crops are often cultivated on marginal land, or land of little agricultural value, and typically require few inputs to grow well.
While deriving fuel from agricultural waste and grasses sounds like the obvious choice, it is unfortunately harder (and therefore more expensive) to do than deriving fuel from first-generation sources. This is because second-generation fuels are made from lignocellulosic feedstock—as the name suggests, the plant cells in such feedstock contain both lignin and cellulose. In order to be converted into fuel, the lignocellulose needs to be broken down into each of these components, and the sugar-containing cellulose carbohydrates extracted.
Converting lignocellulosic feedstocks into fuel generally happens through the use of one of two methods. The first is biochemical—meaning that enzymes are used to convert the cellulose into sugars, which are then fermented into ethanol. The second is thermo-chemical, in which biomass undergoes gasification or pyrolysis (thermochemical decomposition at high temperatures), forming a synthesis gas that can be reformed into intermediate gases or bio-oil. Each method has benefits, challenges, and proponents. For biochemical processes, a central challenge is the price tag—in 2013, it cost three to seven cents per gallon for the enzymes used in the production of corn ethanol, compared to 30 to 40 cents for lignocellulosic ethanol. While that gap will narrow as technology advances, it still presents a significant challenge to expansion and scalability. Similarly, thermochemical processes grapple with high costs and inefficiencies in production systems. Both methods also struggle to build a system that can accommodate several different types of feedstock, as processes would have to vary based on the specific characteristics and chemical composition of any given feedstock.
One important distinction between the two methods is the end-product. Biochemical methods create ethanol, and it must be blended with gasoline in order to be used in an internal combustion engine. Most engines can easily accommodate a blend containing 10 percent ethanol, but above that, it starts to get slightly more complicated. A blend containing 85 percent gasoline and 15 percent ethanol, for example, burns much cleaner but cars have to be specifically equipped to burn it. In countries like the United States (US), there are relatively few such “flex” cars; while in Brazil, almost all cars are built to run on a fuel mixture containing more than 20 percent ethanol.
The end result of thermochemical processing are long carbon chain fuels, like biodiesel or aviation biofuels. Biodiesel can be used in most diesel vehicles without having to make any specific alterations to the engine. This is certainly a draw for consumer markets where diesel vehicles are popular, like the European Union (EU), but in markets like the US where most cars are gasoline-powered, the fuel’s main applications are in the aviation, marine, and trucking sectors.
Still, the use cases for both ethanol and biodiesel come from the realm of first-generation biofuels—for ethanol, the most common feedstocks are sugar and corn; while for biodiesel, the inputs tend to be soybean and rapeseed (canola) oils.
While second-generation biofuels remain a relatively small component of total biofuel production and consumption, they are expanding quickly. Between 2008 and 2013, global production capacity of such fuels increased nearly ten-fold. The number of biofuel production units in operation and under construction grew even more quickly over the same period thanks to the increasing number, and efforts, of companies focused on producing advanced biofuels.
One such company is Wisconsin-based Virent. Virent first made major headlines in January 2011, when the company’s partnership with HCL Cleantech won the duo widespread praise and grant money. HCL Cleantech, which after the announcement changed its name to Virdia before being bought out by Finnish papermaker Stora Enso in 2014, had developed a proprietary technology capable of efficiently converting lignocellulose to non-food sugars. According to the firm, the technology was capable of obtaining 97 to 98 percent of the sugar from lignocellulosic material. After the sugar was extracted, Virent’s own proprietary technological methods came into play. Its revolutionary BioForming® technology is capable of converting plant sugars from a variety of sources, ranging from sugarcane to corn leaves and stalks, into hydrocarbon molecules. According to Virent, the technology is capable of replacing 90 percent of the products that come from crude oil.
Virent’s strides toward creating a plant-derived “drop-in” fuel are radical. A “drop-in” fuel essentially refers to a fuel that is almost entirely interchangeable with a petroleum-based one, and can therefore be blended at a higher rate, or displace a petroleum product entirely—without requiring any change to machinery. In 2014, Virent received approval from the Environmental Protection Agency (EPA) for its BioForm gasoline, which can be used in blends of up to 45 percent.
Virent has attracted only more attention since making headlines in early 2011. Later that year, Virent announced its collaboration with a much more famous partner—Coca Cola. The two announced that they would begin working on producing renewable and recyclable packaging for beverages. Excitingly, in June of this year, Virent debuted a renewable “plastic” bottle made entirely from plant materials.
In recent years, several companies producing biofuels have struggled with the limitations of the market. Ethanol demand, for example, seems finite if cars can only handle 10 percent blending; and in the US at least, the diesel market is somewhat limited. But Virent has shown the ability to navigate these challenges. The company’s pursuit of higher technology means that it is breaking down the 10 percent blend maximum through new products, and the diversification into bioplastics helps widen Virent’s potential market.
At the turn of the century, any cutting-edge biofuel discussion included extensive speculation about second-generation biofuels. But in the past several years, as second-generation fuels have become well-understood, discussions now contemplate third- and even fourth-generation biofuels.
Third-generation biofuels are derived from algae—chlorophyll-containing, typically aquatic organisms. Although algae can come in many shapes and sizes, from several-foot-long seaweed to lifeforms invisible to the naked eye, the varieties used for fuel production are typically species of microalgae. Algae used for such production contain significant quantities of oils, carbohydrates, sugars, and proteins—all of which are useful components in the production of biofuels. Interestingly, algae, like any other plant, consume carbon dioxide (CO₂), and when produced in a large scale consume large amounts of the gas. Algae-derived fuels, therefore, have been widely touted as “carbon-negative,” with a unique capacity to consume carbon dioxide while providing consumers with energy.
Algae used for fuel production require little inputs to survive—just some essential nutrients, water, and light. And with few inputs, even in environments that would struggle to support other plant forms, microalgae can grow. In fact, they can thrive, as species can easily double in biomass every few hours. Algal biomass can contain huge amounts of energy-rich oil and per-acre yields can be hundreds of times those of traditional oil crops like soybeans or rapeseed.
The process for algae-based fuel production is relatively straightforward. Most algae is cultivated in either open pond systems, or a closed photobioreactor system. Although they require a considerable amount of space, pond systems are cheap to set up. But being out in the open, they can also be susceptible to contamination, which can become a major cost and liability down the line. Photobioreactor systems require expensive, advanced equipment, with steep up-front capital costs, but their overall efficiency can make the systems worth it.
Algae grown using either of the two cultivation systems is then harvested, and typically dehydrated. Oil is then extracted from this dehydrated algae through one of several means. It can be pressed out of the biomass, or extracted with the aid of solvents or soundwaves. The extracted oil is mixed with alcohol and catalysts in a process known as transesterification, which results in a mixture of biodiesel and glycerol. That biodiesel is then isolated to make a usable fuel.
While that describes the typical algae-to-fuel process, scientists at US-based Genifuel have more recently made progress in developing an alternative, potentially even more promising processing method: hydrothermal liquefaction. In that process, an algae-water mixture is heated in a continuous-flow, pressurized environment, breaking down the algae into oil. Not only is the oil usable in that form—it does not require any further chemicals or processing—it actually has characteristics very similar to those of light, crude oil. That process, which can take less than an hour, mirrors how standard crude oil is made but at a faster speed: start with organic material, add heat, pressure, and get crude oil. This algal oil, amazingly, can be used in the same way as standard crude oil.
While third-generation biofuels have staggering potential, they also face significant barriers, especially when it comes to cost. Both the open pond and photobioreactor systems are currently very expensive–it costs $10 to produce a kilogram of algae in an open pond system and $30 to $70 in photobioreactors. The associated cost of production per liter of oil from the algae ranges from $1.40 to $1.81; significantly higher than the cost of a liter of petrodiesel. The holy grail for algae fuel producers lies in finding a way to cheaply produce and harvest a fast-growing, oil-rich algae strain.
Founded in 2006, US-based Algenol uses carbon dioxide and seawater to process blue-green algae in proprietary photobioreactors directly into ethanol. The company announced in 2015 that it would soon be opening its first commercial facility, due to be completed in 2017, which will commercially distribute algae-derived ethanol. Under optimal conditions, the technology can produce up to 8,000 gallons of ethanol from an acre of land in one year—about 20 times the amount of fuel that can be produced from an acre of corn. The company also claims that it has brought the cost of production down to $1.30 per gallon. To put that into perspective, the lowest cost of gasoline in the US the week of October 19th, 2015 was $2.12 per gallon.
Those involved in the algae-to-fuel sub-sector are optimistic about the ability to compete with traditional fuel sources in the very near future. According to a survey of sector participants conducted by the Algae Biomass Organization in January and February of 2015, 75 percent of respondents believed that algae-derived fuels would be price-competitive with fossil fuels by 2020. More than 91 percent of those surveyed believed that the price for algae-based fuels would dip below $5.00 per gallon by 2020; while 46 percent of them believed that the price would actually be below $3.00 per gallon by that year.
In July 2015, in a move that highlighted the increased importance of algae-based fuels to the US government, the country’s Department of Energy released $18 million to six projects that would help “reduce the modeled price of algae-based biofuels to less than $5 per gasoline gallon equivalent by 2019.”
The constantly-evolving world of biofuels now also includes a fourth-generation. This “newest” form is establishing precision, genetically modified biofuel production. Scientists within the field are engineering plants and algae in order to ensure optimal suitability for conversion into energy. Engineered plants typically boast higher energy yields, and/or are easier for scientists to break down and isolate the energy-containing components. Scientists have been working on identifying and developing more efficient feedstocks from within the second-generation of non-food crops, as well as third-generation algal varieties.
Present-day scientists are making huge steps forward in the field of alternative fuel sources. Now that the technology to convert plant dry matter and carbon dioxide-eating algae into fuel are in place, it’s just a matter of working to make them affordable and accessible. Indeed, this significant progress makes it apparent that the biofuels of the future will be above the “food vs. fuel” debate that has limited the biofuels of the past.