The Paper's reporter Sen Ning
Airplanes are climate killers – a painful but indisputable fact, and flying in the air is one of the most carbon-emitting activities for humans. To reduce carbon emissions from the aviation industry, governments and the aviation industry around the world are once again trying to convert farm waste and food waste into aviation fuel.
According to global information firm Markets and Markets, the global market for renewable aviation fuels (SAFs) could reach nearly $15.7 billion by 2030.
Nearly 1,000 kilograms of carbon dioxide per passenger on a round-trip flight from New York to London is more than the average annual carbon dioxide emissions per person in 47 other countries, including Burundi and Nicaragua. Every year, the world's aircraft emit about 920 million tons of carbon dioxide, accounting for about 3.5% of global greenhouse gas emissions.
Derek Vardon, chief technology officer at Alder Fuels, a renewable aviation fuel company based in the United States, hopes a magical liquid can change that. This pale yellow, foul-smelling liquid comes from decaying food waste such as chicken and Greek salads and is a short-chain molecular collection of volatile fatty acids (VFAs) in it. Vardon and his colleagues vaporized volatile short-chain fatty acids, using zirconia particles to weave them into longer chains of fatty acids, known as ketones. Ketones are then joined together by platinum particles and stripped of oxygen atoms, eventually becoming kerosene, or jet fuel.
Vardon believes that this process of converting food and other different forms of biomass waste into fuel represents the future of the aviation industry and offers the greatest hope for the industry to reduce greenhouse gas emissions. According to Vardon, the cost of aviation fuel produced in this way is almost comparable to that of fuel produced from oil. And because the carbon it contains comes from plants, plants are able to fix carbon from the atmosphere, so the net emissions of renewable aviation fuel carbon are only a fraction of fossil fuel emissions.
In the fall of 2021, United Airlines pledged to buy 5.7 billion liters of renewable aviation fuel from Alder, the largest deal of its kind in the aviation industry at the time.
Alder isn't the only company in the world that produces renewable aviation fuel. In recent years, more than a dozen similar companies have been established in countries such as the United States, China, Japan, Singapore, India, Finland, Sweden, Austria and Canada.
More than a decade ago, several companies around the world tried to convert agricultural waste into vehicle fuel, but failed miserably. Time has changed, and these renewable aviation fuel companies are more likely to succeed today, partly because they are experimenting with multiple paths, and partly because airlines are eager to find ways to reduce their carbon footprint, and there are few other options. Cars can be loaded with batteries, but airplanes need liquid fuel because liquid fuel is able to store more energy at a given volume.
"Flying a battery-powered plane from the U.S. to Australia may not be able to do it for a short period of time." Eric McAfee, CEO of Aemetis, a company that converts wood waste and kitchen grease into renewable aviation fuel.
The shift has begun. In addition to United, more than a dozen airlines around the world have pledged to jointly purchase about 21 billion litres of renewable aviation fuel over the next few years. In 2008, renewable aviation fuel was first mixed with fossil fuel-derived kerosene for airline flights. In December 2021, United's flight from Chicago to Washington, D.C., became the first passenger flight to run 100 percent on renewable aviation fuel.
A lesson in cellulosic ethanol
Nearly every U.S. car driver has injected some renewable fuel into their tanks. In the United States, this is ethanol made from corn pellets. The U.S. currently produces about 59 billion liters of corn ethanol a year, but growing and harvesting corn requires large amounts of fertilizer and other energy-intensive inputs, which makes its climate benefits negligible.
Cellulosic ethanol, made from corn stalks, forest humus and other waste carbon, should have changed that. Farm and forest waste is abundant and inexpensive, and businesses use microbial enzymes to convert it into sugar, which is fermented by yeast, which can then be fueled. Their climate effects are equally convincing. Corn ethanol can reduce CO2 emissions by 20% to 40% compared to the equivalent amount of fossil fuels; Ethanol made from waste biomass reduces CARBON dioxide emissions by 90%.
Since the U.S. Congress set renewable fuel standards in 2005 to develop a market for ethanol and other vehicle renewable fuels, billions of dollars have been invested in the space. But according to the U.S. Environmental Protection Agency (EPA), less than 1 million liters of cellulosic ethanol will be produced nationwide in 2021.
In 2014, a plant called Project Liberty was created in Emmetsburg, Iowa, USA, for a $275 million business that converts farm waste, including decaying corn stalks and corn cobs, into ethanol for use in blended gasoline. The factory's technology development was successful, but the factory closed in 2020, and in 2021, the owners of Project Liberty switched to the production of hand sanitizer.
Industry cases show that there is currently a lack of feasible methods for the large-scale manufacture of cellulosic ethanol. Most biomass waste contains large amounts of water, and it is costly to transport them to processing plants by truck; The harvest period for maize lasts only about 1 month per year, and straw and other wastes must be stored for the remainder of the year to be supplied to bio-factories, which will further drive up costs; The price of microbial enzymes is not cheap; Corn stalks and other woody biomass often clog grinding machines. "The chemical industry is built on the processing of liquids and gases," says Bruce Dale, a biofuels engineer at Michigan State University, "and solid materials are more difficult than solid materials." ”
A multi-pronged approach hopes to avoid repeating the mistakes of the past
In October 2021, the Biden administration ambitiously outlined a new blueprint for producing 11.4 billion liters of renewable aviation fuel annually in the United States by 2030, and 100 percent of renewable aviation fuel to meet the fuel needs of the aviation industry by 2050, when production is expected to reach about 160 billion liters.
To achieve this goal, the U.S. Department of Energy's Office of Bioenergy Technology (BETO) announced a grant of nearly $65 million for 22 projects, and unlike the "one-legged walk" of cellulosic ethanol, the new program hopes to multi-pronged the development of diverse new renewable fuel technologies.
Aemetis is building a large chemical facility in an almond orchard in Northern California. Almond growers typically rotate trees every 15 to 25 years, which makes orchards produce more than 2 million tons of agricultural waste each year. Farmers previously burned these wastes directly, but given the air quality in the area, such practices are being phased out. Aemetis has now contracted orchards to buy the waste for $20 per tonne and will extract hydrogen from it using a "gasification" high-temperature process. CEO Eric McAfe said the carbon dioxide produced by the process would be captured and sealed underground.
The company will use these hydrogens for chemical treatment of vegetable oils and animal fats. This "hydrotreating" breaks down oil molecules (usually hydrocarbons with three or more branches) into chains with only one branch. These chains are then rearranged into the hydrocarbons that make up the standard jet fuel (Jet A) through the next step of "hydroisomerization."
Other processes for renewable aviation fuel are also being spewed out. A company called LanzaJet is converting municipal waste, wood waste and waste industrial gases into ethanol and then upgrading it to jet fuel. The company first stripped the water molecules from ethanol, converting them into ethylene. Multiple ethylene molecules are then linked together to make olefins, short hydrocarbons. Olefins are converted into a series of hydrocarbons, including kerosene, by further reaction with hydrogen, and finally refined into aviation fuel.
Colorado-based Gevo is converting corn stover and other agricultural waste into isobutyl alcohol and then upgrading it to aviation fuel. Canada's Enerkem is working with Shell to use heat and steam to convert municipal waste and other feedstocks into syngas — a mixture of hydrogen and carbon dioxide — which can then be purified and converted into renewable aviation fuel.
Currently, all of these technical routes have been tested and approved for use in manufacturing by the American Institute for Testing and Materials, the standards body responsible for aviation fuel blends, where they are blended into standard jet fuels. Engineers say one of the benefits of raw material diversity is the ability for companies to utilize locally available waste materials at the lowest cost.
The diversity of feedstocks also helps to increase the overall fuel production to meet the needs of airlines. Derek Vardon expects wet waste, including food scraps, to be converted into 15 billion litres of renewable aviation fuel per year; Treating fats, oils and fats with hydrogen can produce another 19 billion litres; Converting municipal and farm waste could also add billions of litres. The market for renewable aviation fuels looks so big that "producing chemicals and fuels from waste carbon needs to be economically and technically viable," said Laurel Harmon, a chemist and vice president of government relations at LanzaTech.
Still, price is an issue. According to the United Nations' Intergovernmental Panel on Climate Change, renewable aviation fuel currently costs three times as much as oil-derived kerosene, and technology and large-scale production can only bring prices down to that point. Zia Abdullah, project manager for NREL's biomass laboratory, notes that converting solids into fuel requires more processing and processing procedures than using liquid petroleum, "which makes renewable aviation fuels less cost-competitive than fossil aviation fuels." Zia Abdullah said.
Airlines, on the other hand, while they have made climate commitments, they may be reluctant to accept the additional costs of clean fuels, which currently account for around 30 percent of aviation costs. However, the International Air Transport Association, which includes 290 airlines around the world, has committed to renewable aviation fuels to meet its commitment to achieve net-zero carbon emissions for the aviation industry by 2050. But to avoid the withering of renewable aviation fuel like cellulosic ethanol before it, industry may need government involvement, said Lauren Riley, United's chief sustainability officer.
Incentives and subsidies are on the way
In July 2021, the European Commission put forward a proposal to require fuel suppliers to blend renewable aviation fuel into jet fuel, a share that will rise from 2% in 2025 to 63% in 2050. In 2022, the EU is likely to have a final vote on the proposal. But an aviation coalition of more than a dozen aircraft manufacturers, airports and fuel suppliers argues that directives alone are not enough and that the renewable aviation fuel market also needs government incentives to thrive.
The United States is already exploring incentives. California's 13-year-old Low Carbon Fuel Standards (LCFS) system is using a credit-trading mechanism to subsidize fuel suppliers: fuel suppliers can be paid $150 for every ton of carbon dioxide emissions reduced compared to the baseline emissions of fossil fuels. (Emissions from the baseline fuel are reduced annually, making carbon reduction standards stricter over time.) Industry insiders say LCFS has already had a significant boost to renewable fuel producers.
More changes are likely to happen across the United States. In 2021, members of the U.S. House of Representatives introduced two bills to support renewable aviation fuel. One is that fuel suppliers who mix every gallon of renewable aviation fuel in aviation fuel are entitled to a $1.50 tax credit as long as they reduce greenhouse gas emissions compared to fossil fuels by 50 percent. Another bill would allocate $1 billion to support the construction of renewable aviation fuel plants and require the U.S. Environmental Protection Agency (EPA) to create a national program for the aviation fuel market similar to California's Low Carbon Fuel Standards (LCFS). Two bills have been pushed forward in the Senate but have stalled in Congress.
Industry insiders said that the success of the renewable aviation fuel industry in the future will depend on the combination and cooperation of chemical processes, logistics and government policies, which are not only related to investors' funds, but also to the prospects of the aviation industry, and its importance to the planet that needs to further prevent catastrophic climate change is self-evident.
Editor-in-Charge: Kang Yimei
Proofreader: Liu Wei