Q Overview The world is in the midst of a global energy crisis right now. Oil prices are higher than ever. What fuel options do we have? Read the following article on "Green fuels for shipping" and respond to the following prompts. • Share a golden line from the article: • Green fuels for shippingTransporting goods by sea contributes significantly to global carbon emissions. Switching from traditional marine fuels to low-carbon alternatives could drastically shrink shipping’s climate impact Cover story • Massive ships transport billions of metric tons of goods around the globe every year, emitting greenhouse gases as they sail. FEBRUARY 28, 2022 | CEN.ACS.ORG | C&EN 23 Look at all the stuff around you. Unless you’re in the middle of the desert or somewhere else far from civilization, nearly everything you see traveled to you by sea.“Ships bring 80–90% of most every-thing you want or need, or the raw mate-rials used for making those things,” says Natasha Brown, a senior spokesperson for the London-based International Maritime Organization (IMO), a United Nations agency with 175 member states. The organization oversees shipping safety and security and is responsible for preventing water and air pollution from ships. “Mo- bile phones, iPads, grains for breakfast cereal, iron ore, crude oil, bananas, and avocados. All of it crosses the oceans by ship.” Raw materials and manufactured prod- ucts cross the oceans every day in enor- mous vessels, including bulk cargo carri- ers, tankers, and container ships. The vari- ety of goods shipped across the oceans in 2019 weighed a whopping 11 billion metric tons (t), an increase of roughly 3 billion t from just a decade earlier, according to the United Nations Conference on Trade and Development. This volume of shipping traffic burns massive amounts of fuel and produc- es large amounts of air pollution. “The C R E D I T : M A R T I N L U E K E / S H U T T E R S T O C K . C O M • 24 C&EN | CEN.ACS.ORG | FEBRUARY 28, 2022 shipping industry uses more than 300 million tons of fossil fuels every year, roughly 5% of global oil production,” says Camille Bourgeon, a specialist in air pollution and energy efficiency in the marine environment at the IMO. In 2018, global shipping activity emitted roughly 1.05 billion t of carbon dioxide into the atmosphere, accounting for about 2.9% of the total global anthropogenic CO2 emis- sions for that year, according to the IMO’s 2020 greenhouse gas study. As global commerce continues to grow, transoceanic shipping will grow too. So the shipping industry and regulators see a need for change. “We are faced with a real crisis, a real urgency here, and we need to respond,” says Morten Bo Christiansen. Christiansen is head of decarbonization at Copenhagen, Denmark–based A.P. Moller-Maersk, one of the world’s largest shipping companies. Maersk and other shippers are working to cut emissions from shipping by at least 40% by 2030 relative to 2008 levels, in keeping with international agreements reached in 2018 by the IMO’s member states. The plan calls for cutting all green- house gas emissions in half by 2050 and entirely phasing out ship emissions as soon as possible in this century. The industry hopes that by switching from standard marine fuels to green- er alternatives and by boosting energy efficiency, it can cut emissions of cli- mate-changing gases and air pollutants known to harm human health. The indus- try is evaluating numerous sources of en- ergy for propelling ships, including lique- fied natural gas, methanol, hydrogen, and ammonia, and it is testing demonstration vessels. But a front-runner has yet to emerge. The current state Heavy fuel oil (HFO) has been the fuel of choice for large ships for more than a century because it is inexpensive and energy dense—a relatively small amount can propel a ship for great distances. Also known as residual fuel oil, HFO is the gooey, tar-like residue that remains after petroleum crude has been catalyt- ically treated (cracked) and distilled to separate lighter, more valuable fuels such as gasoline and automotive diesel. The viscous leftover, which must be heated to flow through ship engines, contains a mix of paraffins, olefins, aromatics, and as- phaltenes, as well as compounds contain- ing sulfur, nitrogen, and metals. “Ships use so much fuel, and historical- ly, they got away with using the worst bits, the stuff no one else wants,” says Stephen R. Turnock, a maritime engineer at the University of Southampton. “What’s more, they burned it out of sight and out of mind,” he adds, meaning they burned it in the middle of the ocean, where for many years, few people cared about noxious emissions. “It’s only when lots of ships congregate in port that people start to re- alize how bad these emissions are.” The shipping industry has already faced initiatives and regulations to clean their emissions. The IMO previously adopted mandatory caps on emissions of nitrogen oxides (NOx) and sulfur oxides (SOx), both of which can produce acid rain and lung-penetrating particulate matter. In 2020, for example, a new policy came into force that lowered the maximum sulfur content of ship fuel from 3.5% by weight to 0.5%. Stricter limits, 0.1% sulfur, apply in coastal regions and other desig- nated areas. The IMO’s NOx limits, which vary by the ship’s engine size, operating speed, and construction date, have grown increasingly stringent in the past decade and can now be as low as 2 g of emissions per KW h of energy output. Many shippers have met the more strin- gent regulations by switching from stan- dard supplies of marine fuels to cleaner, costlier ones with less sulfur or by blend- ing very-low-sulfur fuels with others to achieve the needed purity. In some cases, ship operators comply with the regula- tions by switching to less-polluting fuels just in certain coastal regions. But other shippers continue using standard fuels and treat engine exhaust chemically to remove the oxides of ni- trogen and sulfur. NOx forms at the high temperatures typical of marine engines as air, which is mostly dinitrogen, reacts with fuel to drive combustion. More than 95% of nitrogen oxides in the exhaust can be removed readily via a process known as se- lective catalytic reduction, which is widely used to control NOx emissions from diesel trucks and cars. In the process, a reducing agent such as an aqueous urea solution is added to the stream of exhaust gas. The exhaust species and reducing agent then react on the surface of a catalyst to pro- duce dinitrogen and water. Many ships strip sulfur and other con- taminants from engine emissions using exhaust-gas scrubbers. These devices work by reacting acidic exhaust gases with an al- kaline scrubbing material. The technology can reduce ship emissions of SOx to man- dated levels. But scrubbers are a source of controversy because some ships discharge the spent scrubbing medium into the oceans, polluting those waters. Key players in the shipping industry agree that the most promising path to Hydra (left), a Norwegian ferry that carries automobiles and passengers, can run on a hydrogen-powered fuel cell and batteries. And E5 (artist’s conception, right) is a lithium-ion-battery powered tanker scheduled to begin fueling ships in Tokyo Bay in 2023. C R E D I T : N O R L E D ( HYDRA) ; A S A H I TA N K E R ( E5 TA N K E R ) • FEBRUARY 28, 2022 | CEN.ACS.ORG | C&EN 25 further clean up emissions is by moving away entirely from traditional HFO and toward alternative fuels. The alternative fuels that the industry is considering all have advantages and disadvantages, which experts are weighing. Liquefied natural gasLiquefied natural gas (LNG) tops the list of nontraditional fuels currently used in commercial ships, including some large container vessels. The number of LNG-fueled ships has climbed in the past decade from tens to hundreds, and more have been ordered. LNG typically consists of roughly 90% methane, several percent ethane, and a mixture of other light alkanes. Suppliers cool the gas mixture to cryogenic tempera- tures (–162 °C) to liquefy the fuel so it can be stored in nonpressurized containers, occupying about one six-hundredth of the volume of the gas. In several ways, LNG would be an improvement over HFO. For example, switching from HFO to LNG could reduce SOx emissions by 99%, NOx emissions by 80%, and CO2 emissions by as much as 20%. LNG also produces relatively little particulate matter. A key disadvantage of LNG is that it consists primarily of methane, which has a far higher global warming potential than CO2—86 times as high, by some esti- mates. So even small gas leaks during production, refueling, or use could result in a relative increase in greenhouse gas emissions. Other drawbacks include the large capi- tal investment required for LNG-compati- ble engines, fuel tanks, and new infrastruc- ture for refueling ships in port, a process known as bunkering. In addition, some in- dustry watchers question the suitability of investing further in LNG because it would extend the use of carbon-based fuels for at least another 20 years, which is a common life span for large ships. MethanolMaritime engineers, naval architects, and other shipping experts are busy eval- uating other alternative fuels and ways to achieve low-emission or zero-emission shipping. These analyses consider the raw materials, production methods, perfor- mance, and overall life cycles of fuels, in addition to other factors, such as the eco- nomics of shipping. In one study, Joanne Ellis and Martin Svanberg of SSPA Sweden, a ship research and testing center, together with col- leagues at Luleå University of Technology, evaluated renewable methanol as a ship- ping fuel (Renewable Sustainable Energy Rev. 2018, DOI: 10.1016/j.rser.2018.06.058). Methanol is currently produced mainly via the catalytic conversion of synthesis gas, a mixture of carbon monoxide and hy- drogen obtained from reforming natural gas or from coal gasification. But meth- anol has also been produced from many types of solid and liquid biomass feed- stocks, including agricultural and forest residues and farming and poultry waste. Switching to methanol made from these biomass sources could lower emissions from shipping and reduce the industry’s overall environmental impact, Ellis says. She also notes that although many of the technologies needed to produce methanol from these biosources have not been com- mercialized at the large scale needed for the shipping industry, they have proved feasible at the pilot or demonstration scale. Methanol offers advantages over some alternative fuels. Because methanol is a liquid that is stored, transported, and used at ambient temperature, implementing it as a shipping fuel would be more straight- forward than switching to cryogenic LNG or gaseous fuels such as hydrogen. “Renewable methanol is a technically viable option to reduce emissions from shipping,” and there are no major chal- lenges with potential supply chains, Ellis says. She adds that there are economic barriers, including capital investments and the fact that biomethanol currently costs more than conventional fuels, “but they do not seem to be insurmountable.” HydrogenHydrogen is often touted as a clean fuel because water is its only combustion product. The way the fuel is made, howev- er, greatly affects its ecofriendliness. Sel- ma Atilhan and Mahmoud M. El-Halwagi of Texas A&M University and coworkers analyzed hydrogen as a shipping fuel, as- sessing the environmental impact of the ~11 billion t The mass of goods transported internationally by ship. 80–90% Percentage of internationally traded goods transported by sea. ~100,000 Number of large (>100 gross tons) cargo vessels in global commercial fleet. 300 million t Mass of fossil fuels used annually by shipping. ~1 billion t Amount of CO2 emitted annually from shipping. Shipping produced 3% of global human-made CO2 emissions in 2018. Sources: International Maritime Organization and United Nations Conference on Trade and Development C R E D I T : W I K I M E D I A C O M M O N S / G L A S B R U C H 2 0 0 7 Shipping by the numbers Heavy fuel oil is a viscous, tar-like petroleum product widely used to power large ships. • 26 C&EN | CEN.ACS.ORG | FEBRUARY 28, 2022 fuel based on its production method. The group classified hydrogen in three ways. They labeled it as gray when it was made by reforming natural gas or other fossil fuels, which is the case for about 95% of global hydrogen production. Blue refers to standard hydrogen production when carbon emissions are captured, stored, or used. Green corresponds to hydrogen made from renewable feed- stocks using a renewable source of energy throughout production. Global hydrogen production from fossil sources currently generates 830 million t of CO2 equivalents (CO2 eq) per year, a unit that accounts for other greenhouse gases. Hydrogen can be made renewably, however, by splitting water using energy from solar power, wind, nuclear power, hy- dropower, and other sources. Plants that will generate hundreds of metric tons of hydrogen per day via some of these routes are under construction. The analysis led the Texas A&M re- searchers to conclude that liquid hydrogen is a top choice for substantially cutting carbon emissions, but the fuel needs to be green. The team found that gray liquid hydro- gen is reasonably cost effective (close to one-fourth the cost of green hydrogen), and it produces almost no carbon emis- sions when combusted to propel the ship. But during hydrogen production, gray hydrogen’s carbon footprint, 120–155 g CO2 eq per megajoule of energy contained in the fuel, exceeds that of heavy fuel oil, about 90 g CO2 eq/MJ. The production of blue liquid H2 can have a lower carbon footprint (40–90 g CO2 eq/MJ) depend- ing on carbon-capture technology and other factors. The carbon footprint of green liquid H2 can be as low as 4.6 and 11.7 g CO2 eq/MJ for hydrogen made with wind and solar energy, respectively, making it a promising shipping fuel (Curr. Opin. Chem. Eng. 2021, DOI: 10.1016/j. coche.2020.100668). Fuel cellsBack at Southampton, Turnock and maritime engineering colleagues Charles J. McKinlay and Dominic A. Hudson con- ducted a detailed analysis of hydrogen, ammonia, methanol, and other fuels. The team finds that although these compounds can be burned in internal combustion engines, using the compounds in fuel cells instead would extract the greatest amount of energy from the fuels and provide the potential for generating emission-free electricity. Are fuel cells up to the challenge? Could they be used to power a large container ship? Thomas T. Petersen, a manager with Ballard Power Systems Europe, a major fuel-cell manufacturer, thinks so. “The problem is not the technology but the fuel supply infrastructure. It is simply not there yet, and it will take a while before quantities are readily available to bunker a large container vessel.” And using fuel cells requires vessels with electrically powered propulsion sys- tems. Electrified ships are less common than internal combustion engine ships, but many are sailing across the globe. Most of those electric ships derive their power from lithium-ion batteries, which may be unsuitable for long-distance ship- ping because of their size, weight, and charging needs. In terms of fuels to pair with the fuel cells, ammonia has a few advantages: it’s a carbon-free material, it can be conve- niently stored and used as a liquid under mild conditions, and it isn’t flammable. But as McKinlay points out, ammonia isn’t harmless—it can form NOx and atmo- spheric particulate matter. And it is highly toxic and corrosive. The Southampton research- ers note that hydrogen is often thought to be too low in volu- metric energy density for ship- ping, meaning that storing suf- ficient fuel quantities on board would take up too much space, leaving little room for cargo. But according to their analysis, cryogenic liquid storage of hydrogen is a viable option. The team concludes that hy- drogen is the leading candidate to support zero-emission large-scale shipping in the future (Int. J. Hydrogen Energy 2021, DOI: 10.1016/j.ijhydene.2021.06.066). Low-emission ships today and tomorrowNumerous demonstration ships pow- ered by nontraditional energy sources sail the seas today, generating real-world data and experience for industry and regula- tors to learn from. Most of these ships are relatively small, but larger ones are on the way. Yara Birkeland is a Norwegian ship powered by lithium-ion batteries. It runs between three ports in Norway and can transport up to 120 standard containers. A Japanese tanker named E5 also runs on Li-ion batteries and delivers fuel to cargo ships in Tokyo Bay. Hydra is a Norwegian ferry that can carry 80 automobiles and nearly 300 passengers. It can run on batteries, fuel cells powered by liquid hydrogen, or both. Other demonstration ships operating on alternative fuels include a biomethanol-fueled pilot boat that’s part of a Swedish project called Fastwater, and Hydroville, a small, private, hydrogen-pow- ered shuttle operating in Antwerp, Belgium. Maersk plans to take alternative ship- ping fuels to a whole other level. The shipping giant recently announced that in the first quarter of 2024, it will begin op- erating eight methanol-fueled oceangoing container vessels capable of transporting 16,000 standard containers each. Most of today’s largest ships have a capacity of roughly 10,000 to 20,000 containers. The new ships will replace older, less efficient ones, reducing annual CO2 emissions by 1 million t, according to Ole Graa Jakobsen, head of Maersk’s fleet technology. He’s quick to put that number in perspective. In 2020, Maersk’s global fleet emitted 33 million t. “That’s 1 down and 32 million to go,” he says. Maersk plans to add four more of these ships to its fleet in 2025, bringing the total CO2 emission reduction to 1.5 million t, or 4.5% of Maersk’s 2020 fleet emissions. “We are at the start of a long voyage to decarbonize shipping,” the IMO’s Bourgeon says as he surveys the flurry of activity that’s beginning to move the ship- ping industry from conventional fuels to environmentally friendlier ones. “These ships are huge and they use a vast amount of fuel. This won’t be an easy task, but we don’t have a choice.” ? • and why you selected that quote. • Of the alternative fuels presented, list them in order from the worst to best alternatives to oil. • What alternative fuel do you think is the best alternative to oil? Why? Use evidence from the paper. • Engage in a meaningful discussion with at least two classmates. Next week, we will look into other alternative energy sources and their environmental costs.