Nature had a recent article on the poor health of advanced biofuels companies in the US. Entitled ‘Cellulosic ethanol fights for life’, the author took particular aim at the new Abengoa refinery in Kansas that uses enzymes to break up the complex cellulose molecule into sugars that can then be fermented into ethanol.
The Abengoa plant was expensive to build, is one mile square in size and probably produces ethanol from cellulose at a cost that makes it uncompetitive with first generation corn ethanol plants. Nature may have been right to be gloomy about its prospects.
But this doesn’t mean that all the companies intending to make fuels from cellulose – the most abundant organic molecule in the world – suffer from similar problems. Actually, 2014 may see greater advances in the production of low-carbon biofuels than ever before. After nearly a decade of failure, it looks increasingly likely that cellulose will eventually become a useful source of transport fuels around the world. Although Abengoa may have built a refinery that embodies a technological dead-end, others such as the extraordinary Cool Planet, may show that low-value plant matter is capable of being turned into fuel that can compete on price with fossil fuels. And Cool Planet is also turning out large volumes of biochar as a by-product. I think this is one of the most interesting companies in the world.
Five years ago I published a book about the technologies that I thought would help the world wean itself off fossil fuels. Of course I was almost ridiculously optimistic (except about solar PV, where I was too conservative) and many of the low carbon energy sources I wrote – such as power from the flow of the tides - about have made strikingly slow progress.
Another one of the chapters was about using cellulose molecules to create motor fuels. I was at pains to distinguish cellulose-based petrol from the first generation biofuel plants that break down the simple starches in grain to make ethanol. As is now well understood, using foodstuffs to make fuel for cars is a terrible diversion of valuable calories. Moreover, the typical human needs about 2 kWh of food a day but her car might consume ten or twenty times this amount of energy. Turning maize or wheat into motor fuel can never be a real solution to the need for low-carbon travel.
But cellulose could be different, I suggested. It is everywhere. Leaves, grasses and stalks are largely made from it and it provides the soft structure for a plant’s energy capture and conversion systems. (Lignin is the dominant molecule in woody biomass). Cellulose is composed of long chains of strongly linked sugar molecules which cannot be broken down by humans. Some plant eating animals, such as cows, house useful bacteria in their stomachs that exude enzymes that can chop up cellulose into much simpler molecules. But the vast bulk of the world’s cellulose production is wasted, eventually rotting away and giving up carbon dioxide to the atmosphere.
Since I wrote the book in 2008 many companies have tried to find ways of breaking up cellulose from organic sources such as wood chip or maize stalks. Many have mimicked grass eating animals by using enzymes and applying gentle heat to break up these intractable molecules. Once they’ve got a soup of simpler chains of atoms using these enzymes they use fermentation to turn starches into ethanol (a product we usually call alcohol). Most have failed, at considerable cost to their investors including the most important backer, Vinod Khosla. The last few weeks have seen KiOR, one of Khosla’s many investments and one of the few companies actually to build a working refinery, announce it wasn’t certain it could continue. Without more money from Khosla or co-investor Bill Gates, the company would run out of cash because its plant hasn’t been able to produce as much ethanol as it expected or the purity of fuel it needs.
So what’s different about Cool Planet and the other new companies working to get motor fuels out of biomass? The main change is that many of these companies are intending to use pyrolysis, the process of heating biomass in the absence of air, instead of breaking cellulose up using enzymes and then fermentation. When biomass is heated to several hundred degrees during pyrolysis, its molecules break up into simpler hydrocarbons which are then driven off in the form of gas. As they cool, these hydrocarbons become oily liquids, often called bio-oil. What remains at the end of pyrolysis, provided the temperature has been high enough, is a fairly pure carbon charcoal. Or ‘biochar’ to its growing band of enthusiastic followers.
Cool Planet’s patent documents show that the company’s approach is to slice wood or other biomass into very thin strips which then subjected to pyrolysis at higher and higher temperatures in separate chambers. It’s as though a wood chip is moved from a cool oven to increasingly hot ones over a short period. The rising temperatures in each sequential oven drive off a different gas in each case. This has the crucial advantage of ensuring that the Cool Planet biorefinery can capture a pure stream of gas that cools to a distinct oil at each point in the process. In this respect, it is similar to a conventional oil refinery, which distils various oils into different streams, with petrol usually being a key output alongside diesel and aviation fuel. This is presumably why it calls its central process 'fractionation'.
The Cool Planet approach has the crucial advantage of creating separate streams of oils. Older pyrolysis processes produce a mixture of various different oils and other chemicals that have relatively little value as motor fuels. Cool Planet’s trial refinery in California is said to produce oils, such as gasoline, that are chemically indistinguishable from fossil equivalents. One story told by the company is that tests by a sceptical oil company were only able to say it wasn’t a fossil fuel by the use of carbon dating. The cellulose was new, whereas oil is often hundreds of millions of years old.
It’s particularly important to note that Cool Planet and some of its recently formed competitors are seeking to produce a true drop-in replacement for petrol/gasoline. It fuels are chemically identical to what comes out of conventional oil refineries. They are not following the earlier cellulose processors in trying to make ethanol, which is a fuel that can be added to fuel but which modern engines cannot usually accept in high concentrations. (Of course Henry Ford initially believed that plant-derived ethanol was a better fuel for cars but modern engines have been adapted to burn fossil fuels).
After experimenting with its prototype in California for several years, Cool Planet has just broken the ground for a full sized refinery in Louisiana. When I say ‘full-sized’, I mean a plant of perhaps a hundredth or less of the output of a conventional oil refinery. 200 million litres a year is the target production starting late in 2014. What will also come out is a huge amount of residual biochar, dwarfing the current world production of this valuable soil enhancer. Not unexpectedly, the company is trying to get rapid endorsement of the value of biochar in improving agricultural yields. (Earlier articles on this website talk enthusiastically about the potential usefulness of biochar, and another chapter of my 2008 book also lauds its importance, perhaps a little too uncritically).
All companies trying to convert biomass into useful oils bandy figures around about the low cost of cellulosic-based oils. Most have been absurdly optimistic. Nevertheless Cool Planet doesn’t hesitate to join in, offering estimates as low as 20p a litre, or about a third of current petrol prices excluding UK tax. Its biomass sources, initially intended to be trees from Colorado that have been destroyed by beetle infestations, are cheap but the crucial reason for its lower cost than first generation cellulose fuels is probably the relative simplicity of the refinery.
The value of the biochar – trading at up to £4 a kilo in small quantities on UK websites - will help improve the economics of the process, perhaps by a large amount. In some interviews, company executives seem more taken by the value of the char than they are of the oils. They also proudly boast of the carbon negative fuels that their refineries will produce; biochar lasts for hundreds of years in soil, this storing carbon that would otherwise have rotted into CO2 or methane.
Cool Planet envisages hundreds of small refineries around the US, gobbling up local biomass surpluses, whether of dead trees or otherwise useless agricultural wastes. The capital costs of the first Louisana refinery are around 25p per litre of annual output. Executives talk of cutting this in half within a few years. These are really impressive numbers, if true. Other investors in places like Malaysia are licencing the rights to the intellectual property in order to build their own refineries.
Is this all another fantasy, like so much of the renewable fuels experiment has proved to be? Of course I don’t know but something about this company looks profoundly convincing. Investors include Google, BP, the forward looking US electricity company NRG, GE and several other sceptical corporations. The team is strong and the detailed and meticulous research behind its refineries seems robust. The four key patents, although extremely widely drawn, have a simple plausibility about them. I think this will work.