The Pathways to Biofuels: A Survey of Why We Should Stop Fretting

May 24, 2023

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byMichael Barnard (CleanTechnica) We have enough waste biomass feedstock to fulfill all of our transportation needs, and the market and a bunch of bright people will figure out which ones are cheapest and lowest impact.

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And in this future world of biofuels for longer haul aviation and marine shipping, the heavy lifting will be done, I think, by stalk cellulosic (#1) technologies to make ethanol, which will be upgraded to biokerosene and biodiesel. That technology takes the stalks of wheat, grain, and rice, and instead of burning them or letting them rot in middens, puts them into fermenters and distillers as a valuable feedstock while the ears of the grains are used to feed animals or humans. Dual cropping for food and fuel has both sufficient biomass by itself for all the biofuels we need globally as long as we sensibly electrify everything we can and restrict biofuel use to actually difficult to decarbonize segments of transportation.

What are the basics of this? Well, our ecosystem has plants that grow. They take CO2 from the air and water and nutrients and the ground and make them into hard and soft things that are made up of carbon, oxygen, and hydrogen.

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Making beer has been something we’ve done with fermentation using yeast for something like 8,000 years. Making alcohol using beer equivalents and heat is something we’ve done with distillation for something like 6,000 years. Those processes do the heavy lifting of turning plants into useful precursors for biofuels that we need, then we need to do a bit more to get them to a truly useful place.

So what are the other pathways to biofuels?

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A variant of stalk cellulosic is switchgrass (#2) as a feedstock instead of the stalks of food grains. Switchgrass is just a prairie grass that’s native to North America, but every grassland in the world has something virtually identical to it in function, shape, and biological niche. It grows just fine on semi-arable land that’s not worth doing intensive agriculture on.

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Then we harvest the switchgrass every once in a while, push it all into stalk cellulosic systems, and turn it into biofuels. It’s a bit more work than using the stems of grain crops in some ways, because it’s spread wide and far and the ground is more uneven, so while I think we’ll be doing it, I don’t think it will dominate.

Corn ethanol (#3) is an obvious one.

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Take the ear of corn, process it to maximize sugars, ferment it, and distill it, and there’s ethanol. That can be upgraded to useful biokerosene and biodiesel, something it has in common with all alcohols, with various processes.

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As I’ve often noted, here at length in print, seeing climate solutions clearly through biases and missing data is challenging. I encourage everyone who is against biofuels to spend a bunch of time updating their knowledge and confronting their biases.

I’m bullish on agriculture decarbonizing fertilizer and using a lot less of the other products over the coming decades. Green ammonia cuts the massive carbon debt of ammonia-based fertilizers, and precision agriculture, increasingly with electrically powered drones like those from Hylio, massively reduces the amounts required for good yields and the diesel used to spread it. Agrigenetics is working to displace lots of ammonia-based fertilizers as well, with Pivot Bio’s nitrogen fixing microbe hack being a prime example. The figures shared with and found by me indicate that drone-spraying can reduce product requirements by 30% to 50%, avoid soil compaction giving 9% to 55% yield improvements, and Pivot Bio’s microbes are already reducing fertilizer requirements by 25%. They had a million acres of corn under their product and were seeing exactly that when I spoke to them a couple of years ago.

Add in low-tillage agriculture, removal of subsistence and most small-hold, undercapitalized, farmers from the world’s food production, and high-tech agriculture is going to stop being a climate problem.

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Next up is sugarcane ethanol (#4). When I lived in São Paulo, Brasil, the urban air was unexpectedly clear and reasonably sweet. The reason is that all light vehicles in the city of 23 million people were required to be able to run on either ethanol or gasoline. You couldn’t drive as far without filling up again on ethanol — sound familiar, everyone who has ever talked to anyone about electric cars? — but it was cheaper. As a result, most people, most of the time, filled up with ethanol.

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After sugarcane, there’s palm oil (#5). It gets a bad rap due to the low environmental standards, including clear burning plantations in southeast Asia. But that’s cleaning up under a lot of regional pressure too.

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Neste’s expanded palm oil distillery in Singapore just added about a million tons of sustainable aviation fuel (SAF) biokerosene to its output, and it’s handling a lot more of the palm plant as part of improved processes that have a lot less waste. As prime Changi Airport tenant Singapore Airlines used about 6.3 million tons of kerosene a year for operations pre-COVID, a million tons is not a rounding error.

Next up is turning animal dung (#6) into fuel.

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That animal dung is a climate problem right now, as a lot of it rots anaerobically in the middle of piles or in pig manure ponds and emits a lot of methane, with its global warming potential of up to 86 times that of CO2.

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There is no reason that it can’t be viable to turn this waste biomass into fuel, and the EU is working on the problem. They are spending some money to work the kinks out of using hydrothermal liquefaction to turn manure into a biocrude which can be refined into SAF biokerosene.

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Next is pyrolysis (#7) of literally any biomass, including wood scraps from lumber mills. Recently a research engineer with Bosch in Germany, Roland Gauch, pointed me at Carbonauten GMBH‘s pyrolysis process and asked if it could work.

The generic pyrolysis process puts biomass into a sealed rotary kiln without any oxygen and heats it up to temperatures between 400° and 700° Celsius. The lack of oxygen means it doesn’t catch fire and burn, turning into ash and CO2. Instead, at the lower end of the range all of the liquids turn into a biocrude and get siphoned off, then the temperature gets turned up and the solids bake down to carbon black.

Carbonauten’s approach is slightly different. It uses static kilns instead of rotary kilns and runs the process more slowly as a result. Then it pairs the kilns, using the waste heat from the high temperature process of one to bake the other in the lower temperature process. And it runs the high temperature process on the biocrude it gets out, with biocrude left over. As a result, the biomass bakes itself, which is obviously pretty energy efficient. That’s not perpetual motion, by the way, although it seems like it.

That said, I haven’t seen independent verification of the energy-mass balances, so am withholding judgment.

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Next up is food waste (#8). A lot of agricultural crops end up rotting in the field due to some market or logistics glitch, also notably producing more biomethane. A bunch more gets bruised in transit and gets thrown out by grocery stores because consumers won’t buy it. Again, biomethane. A bunch more goes home and gets scraped off of plates into the garbage. Again, biomethane.

One study found that a full third of produced food, 2.5 billion tons annually, was simply wasted.

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Maximizing and optimizing biowaste diversion, and shoving it into one or more of the technologies above is completely viable and climate sensible.

Finally, there’s that biomethane (#9) I keep talking about. It bakes off of landfills, hydro dam reservoirs, livestock dung, and piles of rotting vegetation.

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Putting pipes into landfills to vent methane and either capturing it for use, burning it for electricity on site (yes, that’s a thing), or flaring it is a lot better than letting it vent to the atmosphere.

That all said, we have so much biomethane above background creation from natural processes, so much of it is concentrated, and our ability to eliminate it completely is non-existent, so how can we take advantage of it for biofuels?

Well, as I said in a discussion thread with Michael Liebreich and others recently related to his podcast chat with Sir Chris Llewellyn-Smith about building massive salt caverns under the UK and electrolyzing green hydrogen to shove into them for the every ten years when the wind and sun just disappear in northern Europe for a couple of weeks, I’d prefer to just divert as much biomethane as possible into those caverns instead. It’s a waste product that’s a lot less expensive than green hydrogen and is much less likely to leak away.

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But then there’s the next question: can we turn methane into a useful biofuel that doesn’t cause global warming when it leaks? Well, yes. I don’t think methanol is it, personally, but I’m not adverse to a biomethanol marine shipping industry if that ends up penciling out and the biomethane is captured from our anthropogenic emissions instead of being manufactured en masse in anaerobic digesters. But methane can be turned into biodiesel and biokerosene through some fun with methanotrophic microbes, bugs that love to eat methane for food and which leave a biocrude behind.

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Finally, there are variants of some of these processes that add hydrogen to optimize output (I’ll call that #10). Naturally, none of them use green hydrogen today, but obviously they are all claiming that of course they’ll do that. READ MORE

Tags

waste-to-fuel biomass Marine/Maritime Bio and Renewable/Sustainable Fuel (SMF) Jetfuel (Sustainable Aviation Fuel (SAF)) Aviation Fuel/Sustainable Aviation Fuel (SAF) wheat straw rice straw/paddy straw corn stover corn stalks anaerobic digester/digestion aerobic digestion photosynthesis hydrothermal liquefaction (HTL) fermentation Switchgrass Grasses corn ethanol ammonia Methanol/Biomethanol/Renewable Methanol methane/biomethane fertilizer microorganisms/microbes genetically enhanced microbes precision farming/agriculture sugarcane Brazil palm oil Singapore BioRefineries/Renewable Fuel Production manure European Union (EU) pyrolysis Biocrude/Green Crude/SynCrude biochar black carbon conversion technology food waste Agricultural waste/residue landfill methane Landfills UK (United Kingdom) Hydrogen/Renewable Hydrogen markets/sales market forces Sustainability

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