Topics

The Editors

Email Us

Lucretius

Telling the Good Biofuels from the Bad Biofuels

The Redoubt

Some bio-fuel ideas are just economic snake-oil, but others are viable ideas. This is a guide for telling the difference.

Telling the Good Biofuels from the Bad Biofuels

It seems like we can't turn around these days without reading about another supposed Biofuel Break-Through! Articles claiming biofuel from Food Crops, biofuel from waste Cooking Oil, biofuel from Sugar, biofuel from Cellulose, biofuel from Algae, even biofuel from Pig Manure are becoming increasingly common. Unfortunately, many of these biofuel concepts lack a fundamental grounding in business sense, and industrial compatibility. There are, however, a few gems in this wilderness of Biofuel concepts. The goal of this article is to show you a formula by which you can recognize a good biofuel technology from a bad one.

There are several different issues that a successful biofuel must address. It should work with existing engine designs and it should use existing fuel distribution infrastructure. The existing transportation infrastructure in the form of fueling stations, refineries, pipelines and vehicles represents an investment of many billions of dollars. That investment is a prohibitively large barrier to entry for alternative fuels like hydrogen[1]. However, within the limitations that a biofuel process should produce a fuel compatible with existing infrastructure, the key to recognizing a good biofuel concept from a bad one is to focus on just one question:

What is the Feed Stock that is used to produce the biofuel? You can't get something from nothing. This is especially true about fuel... the physical material that is the fuel, and the energy that will be liberated when the fuel is used has to come from somewhere. The fact that it's a BIO fuel does not change this. Once you know what that feed-stock is, you have to determine if it's a good one. This is determined by the answers to the following questions: how much does the feed stock cost? Does that include any pre-processing costs before it is turned it into fuel? Is the feed stock available in industrial quantities? If so, is getting it collected and transported to a processing plant for conversion into fuel going to be a challenge? Let's take a walk through some of the commonly suggested feed stocks and see how they stack up to these questions.

Sugar: Several groups have engineered microbes such as E. coli to use sugar to make biofuel. Sugar is both a source of carbon and of energy that can be used by just about every organism on the planet. However, while it might work biologically, it does not work economically. The problem is that, as I demonstrate below[2], the cost of sugar in terms of energy per dollar is optimistically at least four times that of gasoline made from fossil fuels. What this means is that for every $1 of fuel that you made from sugar, you would have to spend $4 on the sugar itself. It doesn't take a genius to see why this doesn't work.

Food-Crops: As of 2009, 26% of all corn grown in the USA was used to make fuel ethanol. Obviously, it IS possible to make significant quantities of biofuel from food crops. However, as has been documented elsewhere, corn-based ethanol has the same basic problems as sugar. Namely it can not be produced economically, and indeed the only way one we have managed to convert a quarter of all grown corn into ethanol is via subsidies. (Corn based ethanol has other problems too, but that's the important one). Subsidies have a place in the economics of energy, but a small one. Their proper place is to help a VIABLE industry get past barriers to entry in the market place, not to prop-up an unviable business model or product.

Cellulose: Because food-crops and sugar are too expensive as feed stocks, people naturally decided to reverse their thinking. Instead of starting with a feed stock that is easy to turn into a fuel, they decided that it would be a good idea to start with a feed stock that was cheap. The cheapest feed stock is one with a negative price... that is to say a waste product that one would otherwise have to pay money to have disposed of. The most plentiful such waste product is cellulosic biomass. Cellulose is a polymer of sugars that is used in most plants as part of their cell wall. It's what makes wood stiff, and is in just about every kind of plant matter. At first, this seems like a great idea there are enzymes, called cellulases, that break cellulose into sugar and from there one could build up a biofuel just like from sugar except that cellulose based waste is available in vast quantities for less than nothing (people regularly pay to have it carted off).

Unfortunately, not all cellulosic waste is created equal. Inevitably, when one hears about cellulose-based biofuels, the fuel is produced from something like recycled newspaper. Newspaper is a highly processed form of cellulose. It is wood that has been mashed, washed, bleached, and pressed into thin sheets with lots of surface area per unit mass. What's more, there isn't all that much recycled newspaper out there, certainly not the industrial scales needed to be a serious fuel source. Any large scale cellulosic biofuel process will need to work on the sorts of cellulose wastes that exist in large quantities... Wood chips, Corn-stalks, grass-clippings... relatively unprocessed cellulose-bearing biomass. Processing this sort of raw biomass is MUCH HARDER than processing already purified cellulose like in newspaper. The reason for this is that there's all sorts of cellular debris in unprocessed plant material and a substance called lignin sticking strands of cellulose together. We CAN process plant matter to eliminate these contaminants, but, here's the rub, doing so costs more energy and money than the resulting biofuels are worth. That is to say, plant-waste may be cheap, but processed cellulose from plant waste is not as cheap as gasoline.

Further, biology will not come to our aid in solving this problem. There's an easy way to prove this: trees exist. If nature had a fast efficient way to break down cellulose, then trees would have died out from this resulting wood-eating bacterium. As it is, a dead tree can take YEARS to decompose even under optimal conditions with a whole ecosystem working on it.

Other Municipal, Household, and Farm Wastes: There are a myriad of schemes that one can read about to turn everything from Adult Diapers, to Used Cooking Oil, to Pig Manure into biofuels. These concepts usually have the same sorts of problems that are described above. However they also have the added problems that the waste they use, while often being in large over-all quantities across a nation, it is also distributed very widely so that simply collecting a large amount of it into one place is a huge task that uses more fuel than it creates. As a result, these schemes generally focus on processing the feed stock into fuel onsite and then using the fuel onsite as well. This can provide a niche application for the feed stock, but it also prevents such systems from being any use for a general purpose transportation fossil fuel replacement. Another problem with distributed collection and processing of fuel is that industrial processes almost always work more efficiently in large centralized plants or factories than in a bunch of small plants or factories. This is because a single large effort prevents duplication of effort and gains efficiencies of scale. So, while such one-off biofuel ideas may appeal to the do-it-your-self and live-off-the-grid crowds, they will never be competitive on the open market. This is the same reason why small organic farmers simply can't compete on price with the produce from big factory farms. The small farmer overcomes this by competing on quality, rather than price, but unlike food, fuel is a straight commodity where price is the only major consideration.

Algae: The solution to all of these problems is the right kind of algae-based biofuel. Algae should NOT be grown as a feed stock for some other biofuel process. That would be unlikely to be any more economically viable than any other agricultural product as a feed stock. Rather, algae itself can be the PROCESS by which a feed stock is turned into a biofuel. Further, the feed stocks that algae uses are plentiful, free, and do not require transportation or pre-processing like cellulose. Algae are single celled plants that eat salt-water, CO2, and sunlight and can be engineered to produce biofuels directly. (Note how all of those feed stocks: CO2, salt-water, and sun light are abundant and free). In the past, difficulties in genetically modifying algae, as well as the fact that they grow slowly, have slow metabolic turn-overs, and the fact that the fuel-chemicals are toxic have prevented this avenue towards biofuels from bearing fruit. However, unlike the intractable economic barriers to the biofuel schemes described above, these are merely engineering barriers, and thus solvable.

And they ARE being solved. The problem of slow growth is solved by focusing upon fuel production in a continuous flow system rather than growing a batch of algae and then harvesting it. The problem of difficulty in genetic engineering of algae strains is being solved through massive industrial investment, the use of old-school hybridization techniques, and also by the identification of strains that naturally produce fuel-chemicals. Slow metabolic turn-over has been solved by growing algae in the presence of enriched CO2. This does not make the CO2 into a more expensive feed stock the way pre-processing cellulose does because waste-streams of pure CO2 are available from cement factories and power-plants. These sources of CO2 are being vented to the atmosphere, and can be easily and cheaply redirected into an algae growth system. Lastly, the toxicity of the fuel chemicals can be solved the same way the slow-growth problem was solved: by using a continuous run process rather than a batch process. In a batch process the algae grows until its waste-product (the fuel) is concentrated enough to kill it. In a continuous process, the algae's waste products are extracted on a continuous basis and never reach toxicity levels.

In addition, none of the secondary problems that have plagued agriculture based biofuels are likely to crop up in algae based biofuels. Algae grows in tanks that can be on any kind of land, including land that is poisonous, contaminated, or simply unable to support crops. It can even grow on barges floating out to sea. As such it does not compete with food production. Algae strains that produce fuel exist that grow in salt water, so there is no competition for the fresh water supply.

All of these advances have come together in a Florida based company called Alganol. Their Direct to Ethanol process uses a continuous growth and ethanol extraction system to produce ethanol directly from free feed stocks. They predict that they will be cost competitive with gasoline without subsidies as long as oil remains more expensive than $30 per barrel. Further, they are partnering with the kind of industrial heavy hitters (Dow Chemical, Linde Gas, and Valero) that should make their upcoming pilot plant a success. In a recent press-release, they indicated that their pilot plant in Florida is being complete in November 2011, and that they are anticipating production of 2 million gallons of ethanol a year at $0.90 per gallon before subsidies starting in 2012. The current bulk fuel-grade ethanol prices are around twice that. I expect that the limitation in how much this technology can be scaled up is in how much CO2 can be fed into the system. (The Algenol process requires a concentrated CO2 source such as the output of a electrical power station that operates from burning fossil fuels. The CO2 source however does not need to be high pressure or high purity). Their process produces 150 gallons of ethanol from 1 metric ton of CO2. The average coal plant produces 1.2 million metric tons of CO2 a year. Therefore the feedstock limitation of how much ethanol a single Algenol production plant could produce is on the order of 180 million gallons a year. That's about a 75 fold increase in production over the projected output of the Florida pilot plant that they have already completed. If that prediction holds, the entire US fuel-ethanol market (13.5 billion gallons of ethanol a year, or about one tenth the total liquid fuels used by the US a year) could be serviced by just 75 full-scale Algenol style plants.

It may be obvious that I'm very impressed with Algenol, but the key here is not a particular company, but rather the core requirements for ANY biofuel effort to be viable: The feed stock plus all processing must be less expensive on a unit for unit basis than the market price of the resulting fuel. The feed stock must be easily available and in large quantities. Economic sustainability is at least as important as environmental sustainability! The good news is that bio fuel companies with processes that meet these requirements are coming online. Algenol is just the first.

[1]

While it is outside the scope of this article, which is focusing on biofuels, electric cars do not have to overcome this sort of barrier to entry because an equivalent investment in infrastructure for the production and distribution of electricity already exists.

[2]

This get's into a bit of math and biochemistry, but it's not actually very complicated, and any 4th grader should be able to follow it.

Most microbes use glycolysis. It is a biochemical process that can extract energy from glucose (a simple sugar). It can extract this energy in the form of ATP which is a small molecule that can store energy. One glucose molecule releases energy in the form of 32 ATP molecules in aerobic growth. (Actually 34, but it costs two ATP in the process, so net 32).

The ATP molecules are ADP molecules that are then charged with a third phosphate. The energy in the addition of that 3rd phosphate is 30.5 kilojoules per mole.

The least expensive source of glucose in the economy is to buy sucrose. For our purposes, 1 sucrose = 2 glucose. (When hydrolyzed, sucrose produces a glucose and a fructose. For the purpose of producing energy from glycolysis, fructose is the same thing as glucose... it enters the glycolysis pathway at the point of fructose-6-phosphate instead of glucose-6-phosphate, but the first thing that glucose-6 phosphate does in glycolysis is get changed into frucrose-6-phosphate. This bypasses the ATP costing step of glucose-->glucose-6-phosphate, but requires an equivalent step of fructose-->fructose-6-phosphate, so net, it all comes out in the wash.)

Thus, one mole of sucrose is, energy-wise, equivalent to 2 moles of glucose, which via glycolysis nets 64 moles of ATP. Those 64 moles of ATP have a biological energy in their third phosphate bond of 1952 kilojoules.

One mole of sucrose masses 342.30 grams. The cost of raw unrefined sucrose is (wholesale): 27.49 cents per pound as of 09 Aug 2011. That's 0.06 cents per gram or 20.7 cents per mole. Therefore the price of energy from sucrose or glucose, assuming aerobic glycolysis, is 10.6 cents per megajoule.

The amount of energy in conventional gasoline is 125,000 BTU per US Gallon. That's 131.9 megajoules. A gallon of gasoline is going for $3.558-$3.923 on 8/8/2011. Thus, the price of energy in the form of gasoline is 2.70-2.97 cents per megajoule.

Energy from sugar using glycolysis is four times as monetarily expensive as energy from gasoline. But could a better process of utilizing sugar escape this problem? Nope. More advanced organisms than bacteria supplement glycolysis with electron transport chains. However, even this increase of efficiency of the use of glucose can not get more chemical energy than is actually in the sugar. That amount of energy is 2.80 megajoules per mole of glucose or 5.60 megajoules per mole of sucrose. Even this maximum efficiency use of the energy in sugar amounts to 3.7 cents per megajoule... still well above the cost of gasoline.

Further, even these numbers are ridiculously optimistic. They assume that the conversion of the sugar to a usable fuel is 100% efficient, and costs nothing at all. In reality, some of the energy from the sugar must be siphoned away by the organism doing the fuel-conversion or it will die. Also, no process is 100% efficient, nor 100% free. Conversely, all such inefficiencies and processing costs are already in the gasoline number. As if all of this were not enough, the price of sugar is as low as it is, in large part because gasoline prices are low, so if gasoline prices did go up, sugar prices would also go up, so in fact gas prices would have to truly sky-rocket for sugar to be an economically reasonable feed stock.

Discuss this article on reddit.

Copyright ©2009 The Last Redoubt