The viability of cellulosic ethanol

Cat on Parliament Hill

Corn-based ethanol fuels have received a lot of welldeserved criticism lately. This includes criticisms that they take more fossil fuels to produce than they replace, that they have a marginal effect on total greenhouse gas emissions, and that they raise food prices and starve the poor. Ethanol defenders use two approaches to counter-attack. They claim that these problems are not as severe as reported, and they argue that corn ethanol is a necessary step on the road to cellulosic ethanol, which will be made from non-food crops grown in ways that don’t use fossil fuels intensively.

A recent post at R-Squared questions whether that transition will ever occur. Rapier argues:

Cellulosic ethanol, and by that I mean cellulosic ethanol in the traditional mold of what Iogen has been working on for years – will never be commercially viable.

If so, this is bad news for biofuels in general. Rapier points out problems including the large amount of lignin in biomass, the difficulties in transporting such quantities of biomass to refineries, and the energy use involved in drying the stuff out.

Additional criticisms of cellulosic ethanol can be found in a recent study from Iowa State University. According to their economic analysis, cellulosic ethanol will never be produced at the levels envisioned by the American Renewable Fuel Standard, and will only be produced in substantial quantities if it gets three times the subsidy already granted to corn ethanol:

Competition for land ensures that providing an incentive to just one crop will increase equilibrium prices of all. Also, at pre-EISA subsidy levels, neither biodiesel nor switchgrass ethanol is commercially viable in the long run. In order for switchgrass ethanol to be commercially viable, it must receive a differential subsidy over that awarded to corn-based ethanol.

Largely, this is on account of how growing any crop in massively increased quantities will affect factor prices for other crops: from land to labour to farm equipment.

There is no doubt about it, if technology is going to help us transition to a low-carbon society without giving up liquid-fuel driven transport, we are going to need to come up with some awfully clever new ideas.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

21 thoughts on “The viability of cellulosic ethanol”

  1. this,
    “the difficulties in transporting such quantities of biomass to refineries, and the energy use involved in drying the stuff out.”

    Seems to ignore some of the realities of the lumber industry. Right now, huge amounts of biomass are burned to produce nothing – that heat is now beginning to be used to run steam turbines, or to heat cities. That heat can also be used to dry biomass out.

    The whole critique is a bit empty, the point is to come up with new bacterias to break the biomass down. The fact that we haven’t found those bacterias yet is no argument at all. You need to argue why we will never find such a bacteria, and this is like arguing against a breakthrough in science – very impossible to predict.

  2. Tristan,

    Waste products can certainly provide a certain quantity of feedstock, but it seems dubious to suggest that they could provide more than a tiny fraction of the building material required. Even assuming the development of cellulosic technology, the estimates I have seen suggest that matching current liquid fuel output would require converting a significant portion of all land to biomass generation.

    As far as bacteria and enzymes go, you are right to say that development is in progress. That said, even with a 100% efficient process for converting switchgrass or wood to ethanol, the energy use involved in collecting the biomass, transporting it, and running the facility would remain.

    When I have a touch more time, I will read that Iowa study more comprehensively.

  3. Your photo is just begging for a lolcat caption.

    That is one of thew cats that lives on Parliament Hill. Let me tell you, it takes some scrambling around in the snow to take a decent 1 second exposure photo of a cat otherwise unhappy to sit still.

    Twice, this one charged the camera when the delay timer LED was blinking.

  4. I think you fail to recognize the epic size of the cellulose reserve, which consists mostly of pine beetle dead trees, which could be converted into fuel.

    When we’re talking about transport costs, its important to be clear about what we’re talking about “transporting”. When we’re talking about transporting the waste product from lumber production, that will be shipped from forest to plant anyway. And, if it needs to be shipped to a different plant from the sawmill, it can be shipped by train rather than truck, reducing the shipping energy costs by tenfold.

    What is more interesting, however, is the idea of growing plankton-like goup in huge shallow vats and converting that into fuel. Solar-gasoline. That has the advantage of hardly any transport costs at all.

  5. Published online 9 April 2008 | Nature 452, 670-671 (2008) | doi:10.1038/452670b

    Advanced biofuels face an uncertain future

    Aggressive US mandate may do more harm than good.

    Several companies are moving forward with demonstration plants — partially sponsored by the US Energy Department — to produce ethanol from cellulose in corn (maize) stover (the leaves and stalks), wood chips and other plant materials, rather than from the edible part of crops such as corn. But industrial-scale plants remain on the distant horizon, because the technique for efficiently making ‘cellulosic ethanol’ is still in its infancy. That has many wondering whether the investments are being made to meet the federal mandate, which ramps up to nearly 4 billion litres annually by 2013 and some 60 billion litres annually by 2022.

  6. Chemistry: The Future of Cellulose

    By Robert Rapier

    I am not a big believer in a commercial future for the biochemical conversion of cellulose into fuels. There are many big hurdles in place that are going to have to be overcome before cellulose is commercially converted to ethanol. In a nutshell, one is the logistical problem, which I have covered before. Beyond the logistical problem is the issue that biochemistry often starts to malfunction as the conditions in a reactor change, and with cellulosic ethanol that means that if you get a 4% solution of ethanol in water, you are doing well. But from an energy return point of view, a 4% solution is about like the trillions barrels of oil shale reserves we have. If it takes over a trillion barrels of energy to extract and process them, that largely defeats their usability.

    Chemistry is a different matter, which is why I favor gasification processes over fermentation processes. But even beyond gasification, I have wondered about chemically processing cellulose in a refinery. I used to have a guy who e-mailed me all the time and told me he had invented a chemical process for reacting cellulose to hexane, which can then be turned into gasoline. If you look at cellulose (there is a graphic of a segment of cellulose at the previous link), you can envision that it could be done. (Whether he had actually done it is a different story).

  7. Ethanol production could jeopardize soil productivity
    Published: Tuesday, June 2, 2009 – 10:08 in Earth & Climate

    There is growing interest in using crop residues as the feedstock of choice for the production of cellulosic-based ethanol because of the more favorable energy output relative to grain-based ethanol. This would also help provide a solution to the debate of food versus fuel, because less of the grain would be diverted to ethanol production, leaving more available for food and feed consumption. Crop residues are viewed as a low cost and readily available source of material since more than 50% of crop production is residues. However, crop residues should not be considered simply a waste or benign material. They possess a critical role in sustaining soil organic matter. Consequently, extensive removal of crop residues for ethanol production—or for other industrial purposes—may impact the long-term productivity of soils.

    Agriculture and Agri-Food Canada scientists at the Indian Head Research Farm in Indian Head and the Semiarid Prairie Agricultural Research Centre in Swift Current, all located in Saskatchewan (SK), measured the impact of straw removal after 50 years on soil organic carbon (SOC) and soil organic nitrogen (SON) using the Indian Head Long-Term Rotations established in 1958. These rotations included a series of fallow–spring wheat–spring wheat crop sequences where straw was removed through baling on selected plots. In this study, straw removal with baling occurred 2 years out of 3, or 66% of the time. The study was converted to no-till in 1991.

    Guy Lafond, who was the study leader, says, “The results would support the recommendation that some straw could be removed from fields providing that the frequency of removal was less than 66% and that no more than 40% of the aboveground residues other than grain are removed. From a crop management perspective, proper nitrogen fertility combined with no-till would further reduce the possibility of net losses in SOC and SON.”

  8. If Today’s Biofuels Aren’t the Answer, Tomorrow’s Biofuels Will Be.”

    Doubtful. The latest U.S. rules, while continuing lavish support for corn ethanol, include enormous new mandates to jump-start “second-generation” biofuels such as cellulosic ethanol derived from switchgrass. In theory, they would be less destructive than corn ethanol, which relies on tractors, petroleum-based fertilizers, and distilleries that emit way too much carbon. Even first-generation ethanol derived from sugar cane — which already provides half of Brazil’s transportation fuel — is considerably greener than corn ethanol. But recent studies suggest that any biofuels requiring good agricultural land would still be worse than gasoline for global warming. Less of a disaster than corn ethanol is still a disaster.

    Back in the theoretical world, biofuels derived from algae, trash, agricultural waste, or other sources could help because they require no land or at least unspecific “degraded lands,” but they always seem to be “several” years away from large-scale commercial development. And some scientists remain hopeful that fast-growing perennial grasses such as miscanthus can convert sunlight into energy efficiently enough to overcome the land-use dilemmas — someday. But for today, farmland happens to be very good at producing the food we need to feed us and storing the carbon we need to save us, and not so good at generating fuel. In fact, new studies suggest that if we really want to convert biomass into energy, we’re better off turning it into electricity.

    Then what should we use in our cars and trucks? In the short term … gasoline. We just need to use less of it.

  9. The fundamental reason that cellulosic ethanol won’t scale up to displace large amounts of gasoline is that the energy efficiency of the process is so low. You have the sugars that make up cellulose locked up tightly in the biomass – which has a low energy density to start with. So you add energy to unlock the sugar and turn it into ethanol, and then you end up with ethanol in water. More energy inputs are required to get the ethanol out. Even if the energy can be supplied by the by-products of the process like lignin, the net BTUs of liquid fuel that you end up with are going to be low relative to what you started with.

  10. Consider for a moment the amount of energy locked up inside the 1.3 billion tons of dry biomass that the Department of Energy suggests can be sustainably produced each year. Woody biomass and crop residues – the kind of biomass covered in the 1.3 billion ton study – contains an energy content of approximately 7,000 BTUs per pound (bone dry basis). The energy content of a barrel of oil is approximately 5.8 million BTUs. Thus the raw energy contained in 1.3 billion tons of dry biomass is equivalent to the energy content of 3.1 billion barrels of oil, which is equal to 42% of the 7.32 billion barrels the United States consumed in 2008.

    This calculation tells you a couple of things. First, the 42% represents an upper limit on the amount of oil that could be displaced by 1.3 billion tons of biomass. The true number would be much lower because energy is required to get the biomass to the biorefinery and then to process it. So replacing oil with biomass isn’t going to be a trivial task, and a process must be capable of turning a respectable percentage of those biomass BTUs into liquid fuel if it is to be a contender.

    Imagine a process that only captures 25% of the starting BTUs as liquid fuel. The liquid fuel production of 1.3 billion tons would then be 10.5% of our oil usage instead of 42% – and that’s before we consider the energy requirements from the logistical operations (like getting that wood to the biorefinery). This is the realm of the pretenders; they waste a lot of BTUs during the production of their liquid fuel. What we really need is a process that can capture >50% of the BTUs as liquid fuels. That’s what it will take to be a contender, and quite frankly I don’t believe cellulosic ethanol has a chance of pulling this off on a large scale.

  11. Cellulosic Ethanol

    I see two major problems with the scalability of cellulosic ethanol. First, the logistical challenges of getting a lot of biomass into the plant is going to limit the size of the plant. As I pointed out in an essay on Coskata, to run their proposed plants would take the equivalent of over a million trees per year. In terms of rail cars, this is over 1 per hour, 24 hours a day, 365 days a year in and out of the plant to dump the biomass. And bear in mind that this is really a gasification to ethanol plant, with higher forecast yields than a conventional cellullosic process (i.e., a real cellulosic plant of this size would require even more biomass).

    But beyond that, the ethanol that is produced from the cellulosic process is at a far lower concentration than that of corn ethanol. That means big energy inputs in order to make pure ethanol.

    A good niche application for cellulosic ethanol could be a situation in which there is a lot of waste heat available near a point source of biomass. Generally, there isn’t a lot of high quality waste heat that would contribute a lot to the steam needs of a cellulosic ethanol plant. But picture something like a cogeneration unit near a collection point for woody waste. The waste is being collected and is coming in anyway for disposal, and the heat output from the cogen unit may improve the economics.

    Another alternative could be if there is another very cheap source of steam around that can’t be better utilized. If you had a lot of coal in the same location as a lot of biomass, again a cellulosic process might work (but I would argue that depending on the source of biomass, gasification might be a more efficient solution here).

  12. I don’t think I have ever had the privilege of using a literature reference from 1819, but here it is. In 1819, Henri Braconnot, a French chemist, first discovered how to unlock the sugars from cellulose by treating biomass with sulfuric acid (Braconnot 1819). The technique was later used by the Germans to first commercialize cellulosic ethanol from wood in 1898 (EERE 2009).

    But believe it or not, commercialization also took place in the U.S. in 1910. The Standard Alcohol Company built a cellulosic ethanol plant in Georgetown, South Carolina to process waste wood from a lumber mill (PDA 1910). Standard Alcohol later built a second plant in Fullteron, Louisiana. Each plant produced 5,000 to 7,000 gallons of ethanol per day from wood waste, and both were in production for several years (Sherrard 1945).

    To put that in perspective, Iogen claimed in 2004 that they were producing the world’s first cellulose ethanol fuel from their 1,500 gallon per day plant. (While 1,500 gal/day is their announced capacity, if you look at their production statistics they have never sustained more than 500 gallons per day over the course of a year; 2008 production averaged 150 gal/day).

    Many companies are in a mad rush to be the “first” to commercialize cellulosic ethanol. The next time you hear someone say that they will be the first, ask them if they plan to invent the telephone next.

  13. “If a good gauge of Gore’s enthusiasm for something is how voluble and technical he gets, then you can be sure that he loves biofuels. There is some irony in that, since biofuels were the subject of his worst political mistake on the environment. As vice president, he cast the tie-breaking vote in the Senate in 1994 to institute an ambitious federal ethanol program even though, he admits in the book, “there were already ample warnings” that production of corn ethanol is responsible for more greenhouse gases than the gasoline it displaces. But next-generation biofuels are a different story, he says. “The pathway that I think is likely to be the winner is enzymatic hydrolysis, which essentially uses engineered enzymes to break down the cellulose, the lignin, into fermentable compounds that would then yield many more liters per hectare than any of the first-generation ethanol options,” Gore tells me. “I think it’s going to play a significant role … One of the many advantages of third-generation biofuels is that they can yield fuels like biobutanol that don’t have any blending problems. You just burn them directly. Enzymatic hydrolysis, if I can make another point about that: there is no theoretical upper limit to how efficient they can become. So I think there might be some pleasant surprises on enzymatic hydrolysis.””

  14. “As I have pointed out, cellulosic ethanol technology is more than 100 years old. You heard it here, and you can hold me to it: There will be no breakthrough that suddenly makes it cost-competitive to produce. On the other hand, press releases that announce big breakthroughs for small incremental steps? No end to those I am afraid, nor any retraction when they can’t replicate this outside the lab. The impression this leaves is a steady upward march in the commercialization of cellulosic ethanol – and no setbacks that weren’t simply related to lack of funding.

    Cellulosic ethanol will never be produced in large volumes for less money than corn ethanol can be produced for – and keep in mind that we are still subsidizing that after 30 years. What may happen is that it eventually can be mildly successful in certain very specific instances. But to think that a billion tons of U.S. biomass will contribute a major portion of the U.S. fuel supply via cellulosic ethanol? Hogwash from many people who have never scaled up anything. The reasons are not from lack of funding, they are fundamental based on physics, chemistry, and the nature of biomass.”

  15. But Shell acknowledges that second-generation biofuels, contrary to earlier optimistic forecasts, could take as long as a decade to develop. Last year it sold its stake in Choren, an aspiring German producer of second-generation biofuels. Meanwhile, governments around the world are mandating the use of ethanol in an effort to reduce emissions of greenhouse gases. Brazil’s sugarcane ethanol performs much better than ethanol made from maize in that respect: Shell claims it produces 70% less carbon dioxide than petrol, mile for mile. And sugarcane needs less land than maize. That provides some defence against complaints that Shell and Cosan are depriving the poor of food, although sugar prices are at their highest for nearly 30 years.

    If the combination constitutes an admission that Shell’s hopes for second-generation biofuels have stalled, it also marks an acceleration of Cosan’s ambitions. The firm has grown rapidly in recent years thanks to a series of mergers. With few obvious takeover targets left in Brazil, this deal offers the firm expanded horizons.”

  16. The reduced expectations reflect the fact that making fuel out of cellulose turns out to be hard and costly. Today’s cellulosic ethanol is competitive with the petrol it is supposed to displace only when the price of crude oil reaches $120 a barrel. In Dr Shaw’s view, a lot can be done by scaling up (and using the appropriate enzymes, of course, which Codexis will be only too happy to sell you). And big plants will, indeed, bring the price down—probably not to the point where cellulosic ethanol can compete in a fair fight, but quite possibly to a level at which fuel companies will make or buy the stuff rather than pay fines for not doing so.

  17. Robust paths to net greenhouse gas mitigation and negative emissions via advanced biofuels

    PNAS September 8, 2020 117 (36) 21968-21977; first published August 24, 2020

    The climate benefits of cellulosic biofuels have been challenged based on carbon debt, opportunity costs, and indirect land use change, prompting calls for withdrawing support for research and development. Using a quantitative ecosystem modeling approach, which explicitly differentiates primary production, ecosystem carbon balance, and biomass harvest, we show that none of these arguments preclude cellulosic biofuels from realizing greenhouse gas mitigation. Our assessment illustrates how deliberate land use choices support the climate performance of current-day cellulosic ethanol technology and how technological advancements and carbon capture and storage addition could produce several times the climate mitigation potential of competing land-based biological mitigation schemes. These results affirm the climate mitigation logic of biofuels, consistent with their prominent role in many climate stabilization scenarios.

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