Biofuel

• 1. Fuel From Living Things

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  Biofuel is a fuel produced over a short time span from biomass, not by the slow natural processes that form fossil fuels like oil. That single difference in timescale sits at the heart of why some people call it the answer to transport emissions and why others call it a problem dressed up as a solution. The carbon a biofuel releases when burned was first pulled from the air by the very crops grown to make it. So in theory the loop closes and nothing new is added to the atmosphere. The reality is far messier. Estimates of the climate impact of biofuels vary widely depending on the methodology and the exact situation examined. In some scenarios biofuel emissions look much like those of fossil fuels. In others, the use of biofuel produces negative emissions. How can one fuel be both? What does it take to grow energy instead of drilling for it? And why does a renewable fuel keep getting tangled up in a fight over food?

• 2. The Food Versus Fuel Fight

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  Up to 40% of the corn produced in the United States is used to make ethanol, and worldwide 10% of all grain is turned into biofuel. Those numbers explain why the "food vs fuel" debate follows biofuels everywhere. A 50% reduction in the grain used for biofuels in the US and Europe would replace all of Ukraine's grain exports. The competition is not abstract. First-generation biofuels, also called conventional biofuels, are made from food crops grown on arable land. Their sugar, starch, or oil content is converted into ethanol or biodiesel. When fuel demand pulls on the same fields that feed people, the tension is built into the system. To sidestep the dilemma, researchers turned to feedstocks that do not directly compete with food. Second- and third-generation biofuels, also called advanced, sustainable, or drop-in biofuels, draw on waste products and energy crops instead. Rice straw, rice husk, wood chips, and sawdust can all be converted through biochemical and thermochemical processes. Some of these feedstocks are byproducts of a main crop. Others grow on marginal land unsuited to food. The list runs to straw, bagasse, perennial grasses, jatropha, waste vegetable oil, and municipal solid waste, a quiet shift away from the dinner plate.

• 3. Ethanol And Brazil

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  Ethanol fuel is the most common biofuel worldwide, and nowhere more so than in Brazil. It is an alcohol made by fermentation, mostly from carbohydrates in sugar or starch crops such as maize, sugarcane, or sweet sorghum. The production chain runs through enzyme digestion to release sugars from stored starches, then fermentation, distillation, and drying. The IEA estimates that ethanol production used 20% of sugar supplies and 13% of corn supplies in 2021. Distillation demands significant energy to generate heat, and where that heat comes from shapes the fuel's real footprint. Sometimes it comes from unsustainable natural gas. In Brazil the most common fuel for the job is bagasse, the fibrous residue left after sugarcane is crushed. In Europe, pellets, wood chips, and waste heat are more common. Ethanol can run in a vehicle in its pure form, labelled E100. More often it is blended into gasoline to raise octane ratings and improve emissions. Brazil produces and uses large amounts of bioethanol in vehicles, including some flex-fuel cars sold only there. The United States is the largest producer of bioethanol of all. The push away from corn and other food stocks toward non-food sources gave rise to cellulosic ethanol, drawn from trees and grasses.

• 4. The Diesel Substitutes

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  Biodiesel is the most common biofuel in Europe, produced from oils or fats through a reaction called transesterification. Chemically it is mostly fatty acid methyl or ethyl esters, and it can run in its pure form, labelled B100, or blended into mineral diesel. The feedstock list is long: animal fats, vegetable oils, soy, rapeseed, jatropha, mahua, mustard, flax, sunflower, palm oil, hemp, field pennycress, Pongamia pinnata, and algae. Pure B100 can reduce emissions by up to 60% compared to diesel. It is non-toxic and biodegradable, with a high flash point of about 300 degrees Fahrenheit, against 125 degrees Fahrenheit for petroleum diesel. Because biodiesel is an effective solvent, it cleans residues left by mineral diesel, which means engine filters may need replacing more often as old deposits dissolve. The EU is the largest producer of biodiesel. In France, biodiesel is incorporated at a rate of 8% in the fuel used by all French diesel vehicles. The Avril Group, the leading European producer, makes a fifth of the 11 million tons of biodiesel the European Union consumes each year, under the brand Diester. A different path produces green diesel, also called renewable diesel or hydrotreated vegetable oil. Made by hydroprocessing biological oils with hydrogen, it has exactly the same chemical properties as petroleum diesel and needs no new engines or pipelines. It is being developed in Louisiana and in Gothenburg, Sweden, where Preem makes what is known as Evolution Diesel.

• 5. Gases, Ethers, And Outliers

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  Biogas is a mixture composed mainly of methane and carbon dioxide, made when micro-organisms break down organic material without oxygen in a process called anaerobic digestion. Its trace components include water vapor, hydrogen sulfide, siloxanes, ammonia, and more. When the impurities are stripped away, it becomes biomethane. In Sweden, waste-to-energy power plants capture methane biogas from garbage and use it to power transport systems, while farmers can produce biogas from cattle manure in anaerobic digesters. Landfill gas, a less clean form, forms naturally in landfills and acts as a greenhouse gas if it escapes. Syngas takes a different route, made by partial combustion of biomass with too little oxygen to burn it fully. It can be burned directly in engines, turbines, or fuel cells, or converted through the Fischer-Tropsch process into a diesel substitute. Gasification normally relies on temperatures above 700 degrees Celsius. Then there are the smaller players. Butanol is formed by ABE fermentation, named for the acetone, butanol, and ethanol it yields, and Escherichia coli strains have been engineered to produce it. Bioethers act as octane enhancers, made by reacting iso-olefins such as iso-butylene with bioethanol. Ethers were introduced in Europe in the 1970s to replace the highly toxic lead in fuel.

• 6. The Algae Promise

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  By 2017, due to economic considerations, most efforts to produce fuel from algae had been abandoned or shifted to other uses. That outcome is striking, because on paper algae looked ideal. Algal fuels offer high yields and a high ignition point. They can be grown with minimal impact on fresh water resources, can use saline water and wastewater, and are biodegradable and relatively harmless if spilled. Crucially, cultivating algae and cyanobacteria does not require arable land, sidestepping the food competition that haunts earlier generations. These third- and fourth-generation biofuels can be produced by bioengineered organisms that use water, carbon dioxide, and solar energy. The fuels they secrete are expected to have higher photon-to-fuel conversion efficiency than older generations. The catch lies in the costs that do not show up in the chemistry. Production requires large amounts of energy and fertilizer, and the fuel degrades faster than other biofuels and does not flow well in the cold. When the full picture is measured, the environmental cost of building the infrastructure and energy for third-generation production has been shown to exceed the benefits the fuel provides. The method that needs no farmland remains, for now, stuck at the research level.

• 7. The Land Beneath It All

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  Biofuels can have greenhouse gas emissions as low as -127.1 grams of CO2 equivalent per megajoule when carbon capture is built into production, or above 95 grams when land-use change is significant. That enormous spread is the real story of biofuel sustainability. Feedstock and its origin, the production technique, system boundaries, and energy sources all push the number around. Many government policies respond by setting a floor: the European Union and the UK require biofuels to deliver at least 65% greenhouse gas emissions savings against fossil fuels, or 70% for renewable fuels of non-biological origin. Land-use change is the variable that does the most damage. Life-cycle assessments of first-generation biofuels show large emissions tied to converting land to grow more feedstock. Without that change, first-generation biofuels can on average emit less than fossil fuels. The trade-offs reach beyond carbon, into acidification, eutrophication, water footprint, and biodiversity loss. Palm oil drew the sharpest response. The European Commission has officially approved a measure to phase out palm oil-based biofuels by 2030, after unsustainable palm oil agriculture drove deforestation and pollution. One assessment from 2017 put the ceiling plainly: biofuels will never be a major transport fuel because there is not enough land in the world to grow plants to fuel all vehicles. They can, it added, be part of an energy mix that carries us into a future of renewable energy. The IEA points to where that part fits best, in applications that are difficult to electrify, such as shipping and aviation, where demand for aviation biofuel is forecast to rise toward 1% of aviation fuel by 2027.