The world’s thirst for transport fuels shows no sign of slackening anytime soon. Indeed, with affluence rising across much of Asia and Eastern Europe, vehicle numbers are steadily increasing. Almost all the demand for fuel is met from petrol and diesel refined from crude oil, a fossil fuel. Burning fossil fuels releases carbon into the atmosphere, where carbon dioxide levels are steadily rising and, in the opinion of many, contributing to global warming. At the same time, oil reserves are becoming depleted and political instabilities in several major oil-producing countries are exacerbating supply worries, leading to escalating prices.
Many countries around the world, including New Zealand, are looking to reduce their dependence on foreign oil supplies both to increase energy security and to reduce the burgeoning economic strain of paying for all that expensive imported oil.
Further oil discoveries in New Zealand would offset the cost of importing oil, but would not reduce the price motorists pay at the pump nor ameliorate the carbon dioxide problem. (An average vehicle is estimated to emit 53,000 kg of carbon dioxide over its lifetime).
In 1994, Jim Watson, a biology professor from Auckland University, founded New Zealand’s first biotechnology company, Genesis Research and Development Ltd. The company’s latest interest is in developing economic biofuels that could be produced locally to replace imported petroleum. After considerable investigation, it has determined that ethanol is an acceptable replacement fuel for petrol and willows belonging to the genus Salix have clear advantages as a raw material for producing biofuels. In conjunction with The Lake Taupo Development Company, Genesis is setting up BioJoule Technologies Limited to manufacture ethanol and other products from plantations of special willow cultivars they are establishing in the Taupo district.
What makes ethanol—an alcohol identical to that present in wine and beer—a potentially good fuel for vehicles? Unlike hydrogen or natural gas, ethanol is a liquid at normal temperatures, however it is less volatile than petrol so would require a cold starting system at temperatures below 13º C. Compared with petrol, it is higher in octane rating, but has only 66 percent of the overall energy content. This means many engines need modification to run on ethanol, including larger carburettor jets, higher compression, and altered spark timing. Ethanol also damages a range of plastics and rubbers commonly used in petrol-fuelled vehicles, but none of these difficulties are major. It is miscible with water, so washing away spilt fuel is easy, but it also forms a very stable mixture with 4 percent water, meaning it cannot be distilled to give 100 percent pure ethanol. Again, this is a nuisance but not an insuperable problem as molecular sieve technology can dehydrate the ethanol for blending with petrol. Ethanol is cleaner-burning than petrol in terms of some pollutants produced, although it releases a similar amount of carbon dioxide.
However—and this is the big thing—if the ethanol has been made from plant matter, the carbon dioxide is not adding to the atmosphere’s pool, merely turning over carbon a plant earlier captured from the air as it carried out photosynthesis.
Although much ethanol at present is made from oil, it can be readily produced from plants. Enzymes present in yeast easily convert plant sugars to ethanol, although simultaneously releasing carbon dioxide. But plants—including trees—always contain much cellulose, a very stable polymer of glucose. Although it cannot be converted directly to ethanol, microbes (but not animals) possess cellulose enzymes which break it down into glucose, and glucose can be readily fermented into ethanol.
It is the economic conversion of cellulose to ethanol that is the holy grail with ethanol, and rising petrol prices are making it feasible. Not many plants have a lot of free sugar waiting to be turned into ethanol, and those that do (eg sugarcane) have competing demands for that sugar. But every plant is rich in cellulose and it is not currently used when crops are harvested. Cellulose is also available elsewhere. Waste paper is mostly cellulose and sewage contains a goodly amount of the stuff as well.
Another advantage of ethanol as a fuel is that it can be introduced to the market gradually. As long as ethanol is free of water, it can be mixed with petrol in any proportion. Engines burning low percentages of ethanol (eg 10 percent ethanol, 90 percent petrol, E10) require no modifications at all. In Brazil, sugarcane waste is used to make ethanol and cars run on petrol containing 22 percent ethanol. Some vehicles are now being manufactured that can run on either petrol or pure ethanol or any mixture of the two.
BioJoule began a 2 ha trial of Salix cultivars in September 2004 on land provided by a Tuwharetoa farm trust and a second, much larger series of trials was initiated in September 2005 on 6.6 ha. On three separate sites, the performance of up to seven different Salix cultivars planted at a density of 12,000 stakes per ha has been compared together with such things as fertilizer trials, land preparation methods and weed management regimes. A third series of trials are planned for setting out in July, 2006 on a further 2.3 ha of land with 24,000 more plants.
High biomass yield is the most important trait for a bio-energy crop. Salix has been chosen because of its rapid growth rate in a wide range of climatic and soil conditions. It can produce up to 16 tonnes of dry matter per hectare per year without the addition of nitrogen fertiliser. Conventional plant breeding has been used to enhance biomass productivity and significant yield gains have been achieved by crossing Asian Salix clones with European clones. Further gains through breeding programmes are assured.
But why use Salix at all? Why not Pinus radiata or maize? Hardwood trees offer certain advantages over other plants. Some of them, including Salix, coppice— sprout again from the roots after felling. The existence of a large established root system means that trunks regrow much faster than those of newly-planted trees. However, grasses also regrow once mown, and some biofuel feedstock options involving use of switchgrass are being promoted in the US. Grass contains much less lignin than trees.
It is worth noting that wood and plant cell walls are composed of three main materials—a core of cellulose (50 per cent of the dry matter) wrapped in protective layers of hemicellulose and lignin (each about 20 to 30 per cent). While cellulose can be broken down into glucose and fermented to ethanol, the sugars that make up hemicellulose (mainly xylose) are not so easily turned into ethanol. Lignin is not sugar at all but a complex of polyphenols. In hardwoods, the lignin is mostly in the S form which is more amenable to processing than the G form found in softwoods. Lignin and hemicellulose must be removed before the cellulose can be processed. Most companies interested in obtaining ethanol from cellulose regard lignin and hemicellulose as obstacles. At best, they burn lignin to provide energy for processing.
BioJoule sees things differently. It intends to salvage the xylose from hemicellulose and the lignin. Xylose, processed to xylitol, is a sweetener like sucrose, but does not promote either diabetes or tooth decay. Lignin can be used in place of oil products, as a source of raw materials for making paints, resins, plastic films, adhesives and more. Low temperature pyrolysis of lignin yields such basic organic chemical feedstocks as toluene, ethylene and propylene. Hence Biojoule plans multiple income streams from its wood processing— willow stake sales, ethanol, xylose and lignin—and hopefully more. It is for this reason, total biomass refining to multiple products, that makes Salix such an attractive material.
So far the company has made Salix selections and determined how it will process the wood, using its scientific and engineering resources and laboratory-scale experiments. The next step is to construct a pilot plant that can process up to 1000 kg of dry matter a day.
The processing of woody biomass from corn and forest trees to produce bioethanol has been investigated for more than 30 years worldwide. Current technologies use a variety of high pressure chemical processing systems to disrupt the structure of the wood to remove lignin. These processes expose the cellulose for enzymatic degradation to sugars. BioJoule have evaluated, at laboratory-scale, the operation of the out-of-patent Organosolv process and have shown that this process efficiently separates lignin from Salix cellulose. Incidentally, using pine, a softwood, the process does not work nearly as well. It involves treating willow chips with 50–70 per cent ethanol at high temperature and pressure in a digestor designed by BioJoule. In contrast to lignin produced from the pulp and paper industry, the BioJoule lignins released are sulphur-free natural lignins that are insoluble in water and suitable for use as raw materials in paint, resin and plastic fi lm manufacture. A subsequent treatment of the chips with high pressure hot water solubilises the xylose.
The remaining insoluble solids are mainly cellulose. Cellulose enzyme (initially purchased commercially but later perhaps produced by BioJoule generated yeast strains that secrete celluloses) are added to break the cellulose down to glucose, and then yeast ferments the glucose to ethanol.
Biojoule believes it can improve the processing pathway in several ways. Firstly, by using an advanced biological pretreatment step to enhance the release of lignin from cellulose, secondly by streamlining the processing to make more use of local sources of cellulose enzymes to degrade the cellulose into fermentable sugars, and finally, by finding microbes that convert several types of sugars to ethanol more efficiently.
In addition, the company would like to modify the whole process to run as a continuous flow system rather than batchwise, which is how other experimental cellulose-to-ethanol plants overseas currently operate. New Zealand was the first country to implement continuous flow beer brewing, and we also have great experience in milk processing and papermaking, both industries with engineering parallels to ethanol production.
BioJoule actually aims to develop licensable technologies for efficient bio-refineries. These technologies will encompass know-how and intellectual property spanning the development of biomass, including micropropagation, nursery and plantation development through to engineering issues associated with processing and refining of the biomass to generate products including ethanol, natural lignin and xylose. The company hopes to license the technology overseas and generate revenue internationally—once it has proved the system locally.
The Salix cultivars it is testing can be harvested at any time of the year and will grow in any temperate country. No other cellulose-to-ethanol operation is also producing xylose and natural lignin, products for which there are substantial markets and which will also greatly improve the economics of ethanol production.
Modelling suggests that a biorefinery should, ideally, be located within a 20 km radius of Salix plantations. In Sweden there are 15,000 ha of Salix plantations. The trees are burned to generate electricity and a similar scheme is being tried in Britain. A plantation of 2600 hectares would provide 100 dry tonnes per day for processing with an output of 30,000 litres of ethanol per day, plus lignin and xylose. A refinery of this size is estimated to cost $50 million.
In New Zealand, 42 per cent of energy use is for transport fuels. We import 3,200,000,000 litres of petrol annually. The government has introduced legislation allowing the sale of E10 blends, and E3 blends have also been discussed. It has also committed to zero transport tax on ethanol fuel sales. So far, it has not set a timetable for introducing ethanol blended fuels. Moving to E10 fuel means that we would require 320,000,000 litres of ethanol a year. One $50 million plant could produce about 11,000,000 litres of ethanol annually, so we would need 25 such plants of this size, although larger plants may prove more economic. The willows needed to fuel these plants would cover 76,000 ha. For comparison, forestry covers 1.9 million ha, dairying 2 million ha, sheep and beef 10 million ha, horticulture 110,000 ha. In the Taupo area, 76,000 ha of land is suitable for growing Salix. The small trees would be very densely planted, and mechanically harvested, so slopes up to 15 degrees would be suitable.
A number of plastics and similar industries are setting goals of adopting P10 (10 per cent of raw material from renewable sources) to reduce dependence on petrochemicals from fossil sources.
Biojoule estimates that farmers could make $300—350 per ha per annum from Salix growing—more than most make from sheep and beef farming at present. The Taupo area offers a couple of advantages to BioJoule. Geothermal steam energy could be available for processing, reducing energy costs. There is much concern about eutrophication of the lake water through agricultural runoff. Converting farmland to trees would reduce this problem substantially.
The matter of reducing processing energy is worth a comment. Some people hold that the whole business of converting plant matter to ethanol is a nonsense, because the process consumes more energy than is finally present in the ethanol produced! In contrast to maize where for each Joule of energy used in the process only 1.6 joules of energy are produced, Salix produces an amazing 11 –16 joules. Indeed, the International Energy Agency (www.iea.org) projects that woody crops such as Salix will be major contributors to fuel production from biomass in the future.
The world market for ethanol is potentially vast. The gap between the current level of fuel ethanol production and amounts countries around the world aspire to use as a petrol replacement by 2010–2012 exceeds 50 billion litres. Higher targets for 2020 will increase this amount substantially. Globally, energy security is increasingly seen as an intrinsic part of national economic prosperity. Until an alternative new fuel emerges, ethanol will likely contribute to economic growth in virtually every economy.
In New Zealand we are witnessing a confluence of the need for energy supply at reasonable cost, the need to remediate waterways and lakes threatened by eutrophication due to fertiliser use and animal effluent, and concern about likely global warming due to the burning of fossil fuels. BioJoule’s proposal offers real progress on all these issues.