TL&DR Summary: we’ll need biofuels for shipping and aviation, which need rather than merely want liquid fuels. We’ll also potentially need biofuels to serve as our reservoir of stored fuels to serve periods of renewable electricity drought and to respond to other emergencies. While these fuels are absolutely possible to produce in the quantities required, they will at scale represent quite a high cost per tonne of net CO2e emissions averted. They are with certainty going to be cheaper at scale than any fuel made from its combustion products using electricity. While some hydrogen will be needed to deoxygenate biofuels, so-called e-fuels are thermodynamic and hence economic nonsense, so we’d better hope we don’t need them.
I spent more than a decade working on chemical and biochemical biofuels schemes, so I know a lot about what has been tried, what worked, what didn’t, and why. And while some of that knowledge is subject to durable client NDAs, some of it is just public knowledge within the biofuels industry that needs to be spread more broadly.
Where Biofuels are Needed
All land transport is going electric, with certainty. The very edge cases- remote and rural transport for instance, running trucks over ice roads into northern Canada for instance, won’t go electric- but amount to ¾ of f*ck all in terms of GHG emissions anyway. And they’re sure as hell not going to be served by hydrogen, either.
What’s left, then? What actually needs, rather than merely wants, a liquid chemical fuel?
Only really a few things:
1) Transoceanic aviation. Batteries won’t be high enough in energy density for decades, barring a major unforeseen breakthrough. And hydrogen isn’t a feasible alternative for many reasons.
2) Transoceanic shipping. Ships don’t need higher energy density batteries, but for a ship to be feasibly recharged only once every month after a crossing of the Pacific, batteries will need to be greatly cheaper than they’re likely to get in the next decade or two, again barring major unforeseen breakthroughs. Hydrogen isn’t an alternative, and the easiest so-called e-fuel, ammonia, is a toxic corrosive nightmare that will have a body count.
3) Dunkeflaute and emergency storage. 100% decarbonization using electricity is economically infeasible unless we use stored fuels to satisfy 5-10% of demand. Season to season storage of electricity, either in batteries or in chemical fuels like hydrogen made from electricity, is an economic myth. So our choices for seasonal fuel energy storage are either fossils, or biofuels. While my bet is on the former, the latter, in the form of biogas methane, could become an economic contender if we were worried about the last few percent of decarbonization
4) A few applications where fire, rather than just heat, is needed in industrial processes. While electric heating can do nearly everything, there are still a few applications where a carbonaceous reducing agent and/or a hot flue gas are required, rather than just heat. And those applications may be best served by burning biomass or fuels derived from biomass.
The Myth of Insufficient Biomass
The myth of insufficient biomass arose when hyperbolists and interested parties were seriously talking about replacing land transport fuels with biofuels. That was a nonsense concept that could easily be disproven by a Google search and a simple mass balance.
The myth is also exacerbated by the assumption that biofuels must be made from food biomass, or must not be made from food biomass. Both assumptions are wrong.
Currently, food-derived biomass in the form of corn, sugarcane, wheat, food oils etc. is converted into molecules like ethanol and biodiesel (fatty acid methyl esters) for use in land based engines. Those fuels can be redeployed for the applications that actually need rather than merely want them.
There is also a myth related to the economic impossibility of cellulosic biofuels. In past, people were trying to make biofuels from non-food cellulose- woody materials, agricultural leftovers like corn stover or sugarcane bagasse, or purpose grown cellulose crops like switchgrass (miscanthus), in the hope that these fuels could compete, bare knuckles, with gasoline and diesel made from $150 barrels of petroleum. Of course this turned out to be economically impossible. But in a decarbonized future, we’ll need fuels for shipping and aviation that are not derived from fossils. And since the alternative will be to not ship long distances or to not fly, the costs per joule or litre of delivered fuel energy can be considerably higher than those of fossils and still make economic sense- to some users.
Whether or not they make sense in terms of dollars spent per tonne of CO2e emissions averted, is entirely another matter.
There certainly is no shortage of cellulosic biomass.
But to be clear, agriculture today is optimized around generating concentrated food calories, not biomass. Accordingly, biofuels will use food biomass because this will produce cheaper fuels of the required quality. Food will be used as a fuel, unless we regulate or tax food derived biofuels out of the fuel system. However, in my view, we need to be much less precious about food, and more honest about what causes high food prices at the grocery store. When we do that, we’ll be less concerned about farmers having alternative markets for their crops, and more interested in rooting out the parasites who eat 9 out of every 10 dollars that we spend on commodity foodstuffs like corn meal at the grocery store.
https://www.linkedin.com/pulse/corn-farming-food-prices-amateur-study-cost-value-paul-martin-dmzbc/
Let’s look in turn at each application and consider the various approaches. We’ll do this in only the most perfunctory way however, as I leave the real meat and potatoes of this analysis for my paying clients- feel free to contact Spitfire Research to inquire.
Aviation
Jet aircraft are durable assets with a huge associated infrastructure and regulatory cost component. Accordingly, the only economically and practically feasible option for aircraft is to replace fossil jet fuel with the same molecules, except made from biomass.
The cheapest way to do that is via the hydrotreating of vegetable and animal fats (trigylcerides). These molecules are already nearly the same length as those required for jet fuel, but they do need their oxygen-containing acid groups and their carbon-carbon double bonds to be reacted with hydrogen to remove them. The necessary hydrogen can be produced by reforming byproducts from the hydrotreating process, or by the electrolysis of water if you can afford that. These fuels are referred to as hydrotreated vegetable oils (HVO) or hydrotreated esters and fatty acids (HEFA). The end result is a blendstock that, combined with aromatics produced from biomass by other processes, would make a perfectly acceptable jet fuel of pure biological origin. The only fossil GHG emissions associated with such fuels would, in the ideal case, be those associated with upstream agricultural production.
Sadly, the maximum amount of food fats that we can realistically produce, is too low to satisfy even aviation demand. And if we further restrict supply by requiring that only “used” or “waste” non-comestible oil products be used for fuel production, we’ll come up very short.
While some have proposed using the Fischer Tropsch process to make jet fuel, either from syngas produced by gasifying biomass or biogas methane or, stupidest of all, by reacting CO2 and electrolytic hydrogen, I have too much experience with F-T to give that any credence. F-T stands for “fundamentally terrible”, and another even more accurate word starting with f. You can’t fix this process- it is fundamentally unsuited to making just jet fuel, or even to making “synthetic petroleum” even if you could find a use for the entire suite of other products produced. Fischer Tropsch’s problems are many, but non-selectivity and inefficiency plus high capital intensity are the major ones, and they’re all deal killers here. It can’t make money even when given a free feedstock and a free atmosphere to dump its effluent into, unless it is also built at a scale of tens of billions of dollars worth of capital. The notion that F-T will ever make money when fed CO2 and expensive green hydrogen and constrained to sell just jet fuel, is just nonsense.
So: once we’ve tapped out the food oils, how will we satisfy the rest of jet fuel demand?
Sadly, pyrolysis won’t do it. The molecules you get from either biomass pyrolysis plus hydrotreating, or better still, integrated hydropyrolysis and hydrotreating (Shell/GTI’s IH^2 process), are just too short to be useful as a jet fuel.
There are but two remaining options.
One is making ethylene by removing water from ethanol. We’ll have plenty of ethanol left over when we stop wasting it as a gasoline additive.
CH3CH2OH ==> H2O + H2C=CH2
This conversion is 1960s technology or even older, and is not difficult in terms of operating conditions, catalyst durability etc. The yield is reportedly excellent, and few byproducts are produced.
Ethylene is a workhorse industrial chemical, used for all sorts of purposes. However, whereas we could continue to use fossil ethane and naphtha to make ethylene to make polyethylene- as long as we don’t burn it at end of life- for fuels use, ethanol is really our only source.
Ethylene can then be made into short oligomers with precisely the range of lengths required for jet fuel, with again very few byproducts and excellent yield. This again is at least 1980s technology, used to make linear alpha olefins for the production of surfactants and synthetic lubricants. There’s nothing magical here, just routine chemical engineering.
The end result will, of course, be much more expensive than fossil jet fuel- but it is very far from impossible. LanzaJet is doing this already in a facility built for them by my former employer.
Sadly, once you add cellulosic ethanol production’s extra cost to this, the resulting jet fuel is likely unaffordable. So if we look at the ethanol to jet pathway, we’re still definitely talking about a food-to-fuel pathway, just like with HEFA/HVO.
The other “alcohol to jet” conversion pathway can start with non-food cellulosic biomass- but it’s not without its problems. This pathway is to make methanol, which will be discussed in relation to shipping, and convert it to olefins, which themselves can be short oligomerized to jet fuel range molecules. About 30% of world methanol production is already converted to olefins, so that technology is already commercially deployed at scale. But that’s a lot of steps: biomass to syngas, syngas to methanol, methanol to olefins and olefins to jet fuel…the economic viability of this pathway is very much in dispute.
Because the cost of a typical airline ticket is currently only about 20% fuel cost, aviation has a lot of potential to absorb higher fuel costs should we, as a worldwide society, decide to force it to decarbonize. But the notion that it will voluntarily transition to fuels which cost a significant integer multiple of the cost of the fuels they’re using today, just to avoid GHG emissions, is idiotic. Aviation will decarbonize only to the extent that we force it to with durable carbon pricing and emission bans.
Transoceanic Shipping
Ships are energetic garbage dumps. While they do need liquid fuels for fuel logistics reasons, and can’t use hydrogen due to its ineffectiveness (its low energy density per unit volume, making it impractical for bunkering), the operating cost per tonne-mile of freight is today around 40% fuel cost, even using the cheapest fossils they can buy.
There are really only two economic contenders for shipping that merit consideration: methanol, and liquefied biogas methane (bioLNG).
While ships could burn ethanol, my bet is that ethanol stocks will go into either ethylene production for plastics or into ethylene to jet fuel as noted above. Aviation can out-bid shipping for fuel in a fuel supply-constrained future.
While I see biogas methane production as very important, biogas is already useful as a fuel without further processing. Separating out the CO2, liquefying the methane (wasting about 8% of the energy in the methane in the process) and then feeding it to ships, offers the advantage of being able to re-fuel the small fraction of ships already converted to run on fossil LNG. Sadly, methane is a poor engine fuel, particularly in low pressure ships engines. The problem is methane slip through the engine, leading to significant GHG emissions. While engines can be modified to reduce methane slip, it’s not an easily solved problem- and can easily negate any GHG emission benefit from using biomethane versus burning fossil residuum-derived fuels.
Methanol is the cheapest liquid biofuel that can be made from cellulosic biomass. Aviation will outcompete shipping for any HEFA/HVO fat derived fuels, which, like ethanol, will be supply constrained as already discussed.
Those pushing ammonia as a shipping fuel, are doing so in violation of the first principle of safety in design. While ammonia would be the cheapest even marginally effective fuel per joule that you could make from electricity, it is a toxic and corrosive gas utterly unsuitable for use as a marine fuel. Those pushing this concept will have a body count to contend with. And I say that as an experienced chemical engineer, who has designed systems for handling chemicals vastly more hazardous than ammonia.
https://www.linkedin.com/pulse/ammonia-ship-fuels-more-like-fuel-fools-paul-martin-jb7nc/
It is also unclear if ammonia’s lower theoretical cost per joule of fuel energy, would actually end up being cheaper once its significant hazards are even approximately accounted for.
Methanol is made from synthesis gas, i.e. mixtures of carbon monoxide (CO) and hydrogen. Syngas can be made by gasifying biomass or by reforming biogas methane. While it can also be made by running the water-gas shift reaction in the unconventional direction by reacting CO2 with H2 to produce water and CO, this is unnecessary in methanol synthesis because all methanol catalysts are also water-gas shift catalysts. However, green hydrogen will not be cheap enough to make this feasible in the foreseeable future, for reasons discussed at length in my other articles:
https://www.linkedin.com/pulse/scaling-lesson-2-water-electrolysis-paul-martin/
The major problems for e-methanol are as follows:
– the need for purely biogenic CO2 where green hydrogen is also available cheaply enough to make methanol synthesis make sense. This is a geographically rare condition
– expensive green hydrogen is wasted making CO and water
– the water is co-produced with the product, requiring energy-intensive distillation to separate them
It is clear to me, based on my analysis, that methanol should be possible to produce from gasified biomass or biogas methane at lower costs than we will ever see for e-methanol. Conditions which would shift the underlying economics without relying on subsidy unsustainable at scale seem extremely unlikely.
Methanol can also be used to make olefins as noted in the section under Aviation- but importantly, 1980s methanol to gasoline technology can also be used to make the aromatics fraction required in commercial jet fuels. Byproduct naphtha from other biofuels processes can also be cyclized and dehydrogenated to make aromatics, just as we “plat-form” petroleum naphtha today to make them. They won’t be cheap, but if you start with biomass, they will be biogenic.
While biogas methane is itself already a useful, transportable fuel without further modification, cellulosic biomass must be collected and transported to plants for conversion. And its distribution in space, water content, low energy density per unit mass and volume, and intermittent production in time (harvests in many places are only once per year) make it a potentially very troublesome feedstock. While the maximum feasible transport distance for cellulosic biomass will increase as the rest of transport becomes cleaner and electrified, those who are betting on e-methanol are in fact betting that it will be cheaper to move biologically generated CO2 and electrolytic hydrogen to large, centralized methanol plants than it will be to make methanol in more numerous but smaller and hence less economic plants from cellulosic biomass. In my view, green hydrogen’s cost both as a feedstock and in terms of distribution infrastructure that doesn’t exist and is unlikely to ever be built, make the troubles of moving around cellulosic biomass seem worth the considerable bother.
Note that syngas can be made from pyrolysis products, too. I prefer this option when possible, because it would allow us to make transport carbon-negative by returning biochar to the fields and forests from whence it came- and along with it, all the inorganics that came from those soils in the biomass that was harvested there. To be clear, this will drop the yield of biofuel and will cost more money. Carbon credits for the biochar will need to be quite high to justify doing this.
Dunkelflaute Storage
Emergency energy storage systems need to meet the following requirements:
1) They must be reliable, above all else
2) They must have a stable fuel that can be stored without difficulty
3) They must have low capital cost, because they must distribute their capex over comparatively few kWh
Energy efficiency and fuel cost, therefore, matter less than they do in bulk energy generation or fuels uses like transport.
The ideal solution therefore is something which can re-use infrastructure which already exists and hence only needs to be maintained.
Accordingly, to me, the obvious solution for providing the small amounts of electricity to keep essentials running during “kalt dunkelflaute” conditions (when the wind isn’t blowing, and the solar panels are covered in snow for instance) is to re-use the existing fossil gas storage and transport/distribution infrastructure.
In Canada, depleted gas reservoirs are used as gas storage. Gas produced throughout the year is stored in these reservoirs to satisfy peak heating and power demand in the winter months. Unlike with hydrogen, new bespoke salt caverns are not required.
In my view, the likely optimal solution to dunkelflaute energy storage is to simply store and burn fossil gas. We can gradually transition from fossil gas to storing a year’s worth of biogas methane, made by the anaerobic digestion of food waste, manure, and other wet organic waste streams. If we really become concerned about the last few percent of our fossil GHG emissions to bear that cost, that is. Anaerobic digestion will be required to dispose properly of wet biomass such as food and yard waste, human and animal manure etc., simply to reduce methane emissions to the atmosphere. It seems obvious that we’ll want to maximize biogas generation therefore as a source of chemical heat energy and energy storage.
It also makes sense to me that these emergency storage and production systems, be publicly rather than privately owned. Public institutions and governments have the lowest possible borrowing cost, which gives them a tremendous advantage relative to private entities in providing capital for essential but rarely used assets.
Storing excess hydrogen made in summer for use as a fuel in winter is simply uneconomic. It is technically feasible, but the intermittent use of capital kills the idea by burdening every kg of hydrogen, and hence every kWh of electricity, with the double whammy of costs due to poor efficiency and poor, intermittent capital utilization. There’s no way to make this idea look pretty in economic terms.
Agricultural Emissions
Critics of biofuels, other than those whose concerns are misplaced worry about the impact of food prices on the poor etc., generally are concerned about the emissions of intensive agriculture. And those concerns are very well founded. Agriculture uses fossil fuels, including fossil derived hydrogen to make ammonia from which all nitrogen derived fertilizers are produced. Nitrogen fertilizer use results in nitrous oxide (N2O) being generated by soil organisms and released as a powerful GHG to the atmosphere. Methane from agricultural practices makes global warming worse. And then on top of the GHG emissions, we have the very real worries that people in developing countries will want to hew down their forests and plant crops, just as Europeans did all over Europe and later in North America.
However, there are a few truths about agriculture that make it clear to me that we’re going to use biofuels, despite these concerns- and that doing so won’t be an environmental disaster:
– Agricultural emissions need to be mitigated anyway, because we still need to eat
– We all would do well to eat less meat and animal products, for health and also to reduce agricultural emissions. If we do so, we’ll leave more agricultural production potential that can, without increasing the amount of tilled land, make increased biofuels production more feasible. And even today, biofuels production can be and is paired with animal agriculture: distiller’s grains plus solubles from ethanol production is already used as a high protein feed supplement for cattle
– Much of the attributed emissions associated with today’s biofuels production arise from the use of blend mandates rather than carbon taxes or emission bans as the implementation and funding mechanism. Ethanol producers burn natural gas therefore, rather than corn stover, to raise steam to run their stills and dehydrators. Good GHG emission reduction policy will also result in reduced biofuels-associated emissions
Biomass For Materials
I think there are many biomass materials- wood and engineered wood materials, biomass fibre composites, and a handful of bio-derived polymers- that make sense already. However it’s crystal clear to me that we won’t be making -CH2- from C6 H10 O5 (the generic atomic ratio formula for biomass) when there’s -CH2- in the form of petroleum lying around in the subsurface that we know about. And if we use that petroleum only for chemicals and materials that we don’t burn at their end of life, we can reserve biomass for those applications where CO2 will ultimately end up back in the atmosphere- for plants to recycle to useful carbohydrates for us.
https://www.linkedin.com/pulse/refinery-future-thought-experiment-paul-martin-4pfoc/
Summary and Conclusions
I’m not worried about biofuels availability or environmental impact. That said, I think it’s crazy for us to even worry about aviation and shipping right now. There are far cheaper, quicker gains to be had by cleaning up electrical production, and by electrifying land transport and low temperature heating.
Biofuels options are all expensive per tonne of CO2e emissions averted, even in the best case. And because we haven’t decarbonized agriculture yet for its most important purpose- feeding ourselves- stoking emissive current agricultural production with yet more demand to decarbonize aviation and shipping would be foolishly premature.
Like replacing black, fossil hydrogen with green hydrogen, biofuels for shipping, aviation and dunkelflaute storage, are something we should be thinking about for the future. Research and development? Certainly. Planning? Strategy? Sure. But public subsidy and market building? To me, that’s premature. Because carbon dioxide in the atmosphere has a time value, and because public resources are always limited, we should focus on the easy, fast GHG tonnage savings first, and focus on the hard stuff later when those major gains have already been made.
Disclaimer: this article has been written by a human, and humans are known to make mistakes from time to time. Show me where I’ve gone wrong, with good references, and I’ll be happy to correct my work.
If I’ve taken a dump on your pet idea however, or you wish to use this topic to push your pet technology, your ideological concerns, your veganism, fallacious notions about “regenerative agriculture”, or enviro-religionism, then please reach out to my employer, Spitfire Research, who will be very happy to tell you to piss off and write your own article.