{"id":132503,"date":"2023-10-04T07:29:00","date_gmt":"2023-10-04T05:29:00","guid":{"rendered":"https:\/\/renewable-carbon.eu\/news\/?p=132503"},"modified":"2023-09-27T13:10:12","modified_gmt":"2023-09-27T11:10:12","slug":"making-aviation-fuel-from-biomass","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/making-aviation-fuel-from-biomass\/","title":{"rendered":"Making aviation fuel from biomass"},"content":{"rendered":"\n\n
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\"Yuriy
Professor Yuriy Rom\u00e1n-Leshkov and collaborators have demonstrated a new way to produce a critical component of aviation fuel from lignin, a plant material that\u2019s generally discarded as waste during biomass processing.\u00a0Photo: Gretchen Ertl\u00a0<\/figcaption><\/figure><\/div>\n\n\n

In 2021, nearly a quarter of the\u00a0world\u2019s carbon dioxide emissions came from the transportation sector, with aviation being a significant contributor. While the growing use of electric vehicles is helping to clean up ground transportation, today\u2019s batteries can\u2019t compete with fossil fuel-derived liquid hydrocarbons in terms of energy delivered per pound of weight \u2014 a major concern when it comes to flying. Meanwhile, based on projected growth in travel demand, consumption of jet fuel is projected to double between now and 2050 \u2014 the year by which the international aviation industry has pledged to be carbon neutral.<\/strong><\/p>\n\n\n\n

Many groups have targeted a 100 percent sustainable hydrocarbon fuel for aircraft, but without much success. Part of the challenge is that aviation fuels are so tightly regulated. <\/p>\n\n\n

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\"Jamison
Postdoc Jamison Watson joined the Rom\u00e1n Lab in January 2021 to focus on the catalytic upgrading and conversion of lignin into the aromatic fraction needed to make aviation fuel fully sustainable. Here, he adjusts the trickle-bed reactor to optimize its performance.\u00a0 Photo: Gretchen Ertl\u00a0<\/figcaption><\/figure><\/div>\n\n\n
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\u201cThis is a subclass of fuels that has very specific requirements in terms of the chemistry and the physical properties of the fuel, because you can\u2019t risk something going wrong in an airplane engine,\u201d says Yuriy Rom\u00e1n-Leshkov, the Robert T. Haslam Professor of Chemical Engineering<\/strong>. \u201cIf you\u2019re flying at 30,000 feet, it\u2019s very cold outside, and you don\u2019t want the fuel to thicken or freeze. That\u2019s why the formulation is very specific.\u201d<\/p>\n<\/blockquote>\n\n\n\n

Aviation fuel is a combination of two large classes of chemical compounds. Some 75 to 90 percent of it is made up of \u201caliphatic\u201d molecules, which consist of long chains of carbon atoms linked together. \u201cThis is similar to what we would find in diesel fuels, so it\u2019s a classic hydrocarbon that is out there,\u201d explains Rom\u00e1n-Leshkov. The remaining 10 to 25 percent consists of \u201caromatic\u201d molecules, each of which includes at least one ring made up of six connected carbon atoms.<\/p>\n\n\n\n

In most transportation fuels, aromatic hydrocarbons are viewed as a source of pollution, so they\u2019re removed as much as possible. However, in aviation fuels, some aromatic molecules must remain because they set the necessary physical and combustion properties of the overall mixture. They also perform one more critical task: They ensure that seals between various components in the aircraft\u2019s fuel system are tight. <\/p>\n\n\n\n

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\u201cThe aromatics get absorbed by the plastic seals and make them swell,\u201d explains Rom\u00e1n-Leshkov<\/strong>. \u201cIf for some reason the fuel changes, so can the seals, and that\u2019s very dangerous.\u201d<\/p>\n<\/blockquote>\n\n\n\n

As a result, aromatics are a necessary component \u2014 but they\u2019re also a stumbling block in the move to create sustainable aviation fuels, or SAFs. Companies know how to make the aliphatic fraction from inedible parts of plants and other renewables, but they haven\u2019t yet developed an approved method of generating the aromatic fraction from sustainable sources. <\/p>\n\n\n\n

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As a result, there\u2019s a \u201cblending wall,\u201d explains Rom\u00e1n-Leshkov<\/strong>. \u201cSince we need that aromatic content \u2014 regardless of its source \u2014 there will always be a limit on how much of the sustainable aliphatic hydrocarbons we can use without changing the properties of the mixture.\u201d He notes a similar blending wall with gasoline. \u201cWe have a lot of ethanol, but we can\u2019t add more than 10 percent without changing the properties of the gasoline. In fact, current engines can\u2019t handle even 15 percent ethanol without modification.\u201d<\/p>\n<\/blockquote>\n\n\n\n

No shortage of renewable source material \u2014 or attempts to convert it<\/strong><\/h3>\n\n\n\n

For the past five years, understanding and solving the SAF problem has been the goal of research by Rom\u00e1n-Leshkov and his MIT team \u2014 Michael L. Stone PhD \u201921, Matthew S. Webber, and others \u2014 as well as their collaborators at Washington State University, the National Renewable Energy Laboratory (NREL), and the Pacific Northwest National Laboratory. Their work has focused on lignin, a tough material that gives plants structural support and protection against microbes and fungi. About 30 percent of the carbon in biomass is in lignin, yet when ethanol is generated from biomass, the lignin is left behind as a waste product.<\/p>\n\n\n\n

Despite valiant efforts, no one has found an economically viable, scalable way to turn lignin into useful products, including the aromatic molecules needed to make jet fuel 100 percent sustainable. Why not? As Rom\u00e1n-Leshkov says, \u201cIt\u2019s because of its chemical recalcitrance.\u201d It\u2019s difficult to make it chemically react in useful ways. As a result, every year millions of tons of waste lignin are burned as a low-grade fuel, used as fertilizer, or simply thrown away.<\/p>\n\n\n\n

Understanding the problem requires understanding what\u2019s happening at the atomic level. A single lignin molecule \u2014 the starting point of the challenge \u2014 is a big \u201cmacromolecule\u201d made up of a network of many aromatic rings connected by oxygen and hydrogen atoms. Put simply, the key to converting lignin into the aromatic fraction of SAF is to break that macromolecule into smaller pieces while in the process getting rid of all of the oxygen atoms.<\/p>\n\n\n

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\"Left-hand
The two vials shown contain products from key steps in the procedure. The brown lignin oil in the left-hand vial formed when the biomass was exposed to the first catalyst. The clear liquid in the right-hand vial formed when the lignin oil passed though the trickle-bed reactor for the second time. Now free of oxygen molecules, it is the aromatic fraction needed to make today\u2019s aviation fuel 100 percent sustainable.\u00a0Photo: Gretchen Ertl\u00a0<\/figcaption><\/figure><\/div>\n\n\n

In general, most industrial processes begin with a chemical reaction that prevents the subsequent upgrading of lignin: As the lignin is extracted from the biomass, the aromatic molecules in it react with one another, linking together to form strong networks that won\u2019t react further. As a result, the lignin is no longer useful for making aviation fuels.<\/p>\n\n\n\n

To avoid that outcome, Rom\u00e1n-Leshkov and his team utilize another approach: They use a catalyst to induce a chemical reaction that wouldn\u2019t normally occur during extraction. By reacting the biomass in the presence of a ruthenium-based catalyst, they are able to remove the lignin from the biomass and produce a black liquid called lignin oil. That product is chemically stable, meaning that the aromatic molecules in it will no longer react with one another.<\/p>\n\n\n\n

So the researchers have now successfully broken the original lignin macromolecule into fragments that contain just one or two aromatic rings each. However, while the isolated fragments don\u2019t chemically react, they still contain oxygen atoms. Therefore, one task remains: finding a way to remove the oxygen atoms.<\/p>\n\n\n\n

In fact, says Rom\u00e1n-Leshkov, getting from the molecules in the lignin oil to the targeted aromatic molecules required them to accomplish three things in a single step: They needed to selectively break the carbon-oxygen bonds to free the oxygen atoms; they needed to avoid incorporating noncarbon atoms into the aromatic rings (for example, atoms from the hydrogen gas that must be present for all of the chemical transformations to occur); and they needed to preserve the carbon backbone of the molecule \u2014 that is, the series of linked carbon atoms that connect the aromatic rings that remain.<\/p>\n\n\n\n

Ultimately, Rom\u00e1n-Leshkov and his team found a special ingredient that would do the trick: a molybdenum carbide catalyst. <\/p>\n\n\n\n

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\u201cIt\u2019s actually a really amazing catalyst because it can perform those three actions very well,\u201d says Rom\u00e1n-Leshkov.<\/strong> \u201cIn addition to that, it\u2019s extremely resistant to poisons. Plants can contain a lot of components like proteins, salts, and sulfur, which often poison catalysts so they don\u2019t work anymore. But molybdenum carbide is very robust and isn\u2019t strongly influenced by such impurities.\u201d<\/p>\n<\/blockquote>\n\n\n\n

Trying it out on lignin from poplar trees<\/strong><\/h3>\n\n\n\n

To test their approach in the lab, the researchers first designed and built a specialized \u201ctrickle-bed\u201d reactor, a type of chemical reactor in which both liquids and gases flow downward through a packed bed of catalyst particles. They then obtained biomass from a poplar, a type of tree known as an \u201cenergy crop\u201d because it grows quickly and doesn\u2019t require a lot of fertilizer.<\/p>\n\n\n\n

To begin, they reacted the poplar biomass in the presence of their ruthenium-based catalyst to extract the lignin and produce the lignin oil. They then flowed the oil through their trickle-bed reactor containing the molybdenum carbide catalyst. The mixture that formed contained some of the targeted product but also a lot of others that still contained oxygen atoms.<\/p>\n\n\n\n

Rom\u00e1n-Leshkov notes that in a trickle-bed reactor, the time during which the lignin oil is exposed to the catalyst depends entirely on how quickly it drips down through the packed bed. To increase the exposure time, they tried passing the oil through the same catalyst twice. However, the distribution of products that formed in the second pass wasn\u2019t as they had predicted based on the outcome of the first pass.<\/p>\n\n\n\n

With further investigation, they figured out why. The first time the lignin oil drips through the reactor, it deposits oxygen onto the catalyst. The deposition of the oxygen changes the behavior of the catalyst such that certain products appear or disappear \u2014 with the temperature being critical. <\/p>\n\n\n\n

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\u201cThe temperature and oxygen content set the condition of the catalyst in the first pass,\u201d says Rom\u00e1n-Leshkov<\/strong>. \u201cThen, on the second pass, the oxygen content in the flow is lower, and the catalyst can fully break the remaining carbon-oxygen bonds.\u201d <\/p>\n<\/blockquote>\n\n\n\n

The process can thus operate continuously: Two separate reactors containing independent catalyst beds would be connected in series, with the first pretreating the lignin oil and the second removing any oxygen that remains.<\/p>\n\n\n\n

Based on a series of experiments involving lignin oil from poplar biomass, the researchers determined the operating conditions yielding the best outcome: 350 degrees Celsius in the first step and 375 C in the second step. Under those optimized conditions, the mixture that forms is dominated by the targeted aromatic products, with the remainder consisting of small amounts of other jet-fuel aliphatic molecules and some remaining oxygen-containing molecules. The catalyst remains stable while generating more than 87 percent (by weight) of aromatic molecules.<\/p>\n\n\n\n

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\u201cWhen we do our chemistry with the molybdenum carbide catalyst, our total carbon yields are nearly 85 percent of the theoretical carbon yield,\u201d says Rom\u00e1n-Leshkov<\/strong>. \u201cIn most lignin-conversion processes, the carbon yields are very low, on the order of 10 percent. That\u2019s why the catalysis community got very excited about our results \u2014 because people had not seen carbon yields as high as the ones we generated with this catalyst.\u201d<\/p>\n<\/blockquote>\n\n\n\n

There remains one key question: Does the mixture of components that forms have the properties required for aviation fuel? \u201cWhen we work with these new substrates to make new fuels, the blend that we create is different from standard jet fuel,\u201d says Rom\u00e1n-Leshkov. \u201cUnless it has the exact properties required, it will not qualify for certification as jet fuel.\u201d<\/p>\n\n\n\n

To check their products, Rom\u00e1n-Leshkov and his team send samples to Washington State University, where a team operates a combustion lab devoted to testing fuels. Results from initial testing of the composition and properties of the samples have been encouraging. Based on the composition and published prescreening tools and procedures, the researchers have made initial property predictions for their samples, and they looked good. For example, the freezing point, viscosity, and threshold sooting index are predicted to be lower than the values for conventional aviation aromatics. (In other words, their material should flow more easily and be less likely to freeze than conventional aromatics while also generating less soot in the atmosphere when they burn.) Overall, the predicted properties are near to or more favorable than those of conventional fuel aromatics.<\/p>\n\n\n\n

Next steps<\/strong><\/h3>\n\n\n\n

The researchers are continuing to study how their sample blends behave at different temperatures and, in particular, how well they perform that key task: soaking into and swelling the seals inside jet engines. <\/p>\n\n\n\n

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\u201cThese molecules are not the typical aromatic molecules that you use in jet fuel,\u201d says Rom\u00e1n-Leshkov<\/strong>. \u201cPreliminary tests with sample seals show that there\u2019s no difference in how our lignin-derived aromatics swell the seals, but we need to confirm that. There\u2019s no room for error.\u201d<\/p>\n<\/blockquote>\n\n\n\n

In addition, he and his team are working with their NREL collaborators to scale up their methods. NREL has much larger reactors and other infrastructure needed to produce large quantities of the new sustainable blend. Based on the promising results thus far, the team wants to be prepared for the further testing required for the certification of jet fuels. In addition to testing samples of the fuel, the full certification procedure calls for demonstrating its behavior in an operating engine \u2014 \u201cnot while flying, but in a lab,\u201d clarifies Rom\u00e1n-Leshkov. In addition to requiring large samples, that demonstration is both time-consuming and expensive \u2014 which is why it\u2019s the very last step in the strict testing required for a new sustainable aviation fuel to be approved.<\/p>\n\n\n\n

Rom\u00e1n-Leshkov and his colleagues are now exploring the use of their approach with other types of biomass, including pine, switchgrass, and corn stover (the leaves, stalks, and cobs left after corn is harvested). But their results with poplar biomass are promising. <\/p>\n\n\n\n

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If further testing confirms that their aromatic products can replace the aromatics now in jet fuel, \u201cthe blending wall could disappear,\u201d says Rom\u00e1n-Leshkov<\/strong>. \u201cWe\u2019ll have a means of producing all the components in aviation fuel from renewable material, potentially leading to aircraft fuel that\u2019s 100 percent sustainable.\u201d<\/p>\n<\/blockquote>\n\n\n\n

This research was initially funded by the Center for Bioenergy Innovation, a U.S. Department of Energy (DOE) Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. More recent funding came from the DOE Bioenergy Technologies Office and from Eni S.p.A. through the MIT Energy Initiative. <\/em><\/p>\n\n\n\n

Michael L. Stone PhD \u201921 is now a postdoc in chemical engineering at Stanford University. Matthew S. Webber is a graduate student in the Rom\u00e1n-Leshkov group, now on leave for an internship at the National Renewable Energy Laboratory.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

In 2021, nearly a quarter of the\u00a0world\u2019s carbon dioxide emissions came from the transportation sector, with aviation being a significant contributor. While the growing use of electric vehicles is helping to clean up ground transportation, today\u2019s batteries can\u2019t compete with fossil fuel-derived liquid hydrocarbons in terms of energy delivered per pound of weight \u2014 a […]<\/p>\n","protected":false},"author":59,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"none","nova_meta_subtitle":"MIT researchers are converting the plant material lignin into hydrocarbon molecules that could help make jet fuel 100 percent sustainable","footnotes":""},"categories":[5572],"tags":[10794,5838,5842,11828,16792],"supplier":[1936,371,3791,4116,2878],"class_list":["post-132503","post","type-post","status-publish","format-standard","hentry","category-bio-based","tag-aviationfuel","tag-bioeconomy","tag-biomass","tag-lignin","tag-saf","supplier-massachusetts-institute-of-technology","supplier-national-renewable-energy-laboratory-nrel","supplier-pacific-northwest-national-laboratory","supplier-us-doe-office-of-science-sc","supplier-washington-state-university"],"_links":{"self":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/132503","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/users\/59"}],"replies":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/comments?post=132503"}],"version-history":[{"count":0,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/132503\/revisions"}],"wp:attachment":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/media?parent=132503"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/categories?post=132503"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/tags?post=132503"},{"taxonomy":"supplier","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/supplier?post=132503"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}