Ethanol from trees – a fuelish concept
by Stan Hirst
I have meticulously calculated, on the back of an envelope, that there are least a gazillion trees in British Columbia. And, using another envelope, I figured that if one excludes trees growing in national parks, old-growth forests, recreation areas, parks and other areas where you don’t want guys in plaid shirts and yellow hardhats hanging out with chain saws, then there would still be a humongous number of trees available for harvesting (on a sustainable basis, of course).
I dug out my chemistry notes from a half century ago and found a neat diagram which showed that if you started with a box marked “cellulose” on one side of the page, and then drew lots of squiggly lines and arrows in all directions, you could wind up with another box named “ethanol” on the other side of the page. Now, for those of you who didn’t take chemistry fifty years ago, I can tell you that trees contain lots of cellulose, in fact cellulose makes up about half the mass of the average tree. And, for those of you who maybe don’t get out much, I can divulge that ethanol makes passable motor fuel.
So therefore, using my last envelope, I deduced that if British Columbia set to work making ethanol from wood cellulose, we would end up with enough home-grown fuel to run all our trucks, SUVs, cars and scooters, and still have enough left over to send over to Alberta.
Now, you might ask, why on earth would we want to do that? Well, for a number of reasons, some sound and some less so. One major reason is to replace or reduce the amount of fossil fuels used by motor vehicles and thereby cut back on carbon dioxide emissions, which in turn will lead to a reduction in the overall carbon loading in the atmosphere.
Carbon dioxide (CO2) is one of the exhaust products produced when gasoline is burned as a fuel to power a motor. Burning just 1 litre of regular gasoline produces 2.4 kilograms of CO2 (most of the weight of CO2 comes from the oxygen it contains, not the carbon). CO2 is also produced in large quantities from the combustion of coal, oil and natural gas by power stations, industry and homes. We’ve been spewing the stuff into the atmosphere since the industrial revolution, with the result that the global atmosphere now contains in excess of 390 parts per million CO2, an increase of 40% since the 1800’s. CO2 is a potent greenhouse gas and absorbs a significant part of the long wave radiation beamed upward from the earth’s surface. It then radiates part of that energy back downwards to add to the surface warming effect. More CO2 in the atmosphere thus means more return of heat. As a result, the mean global temperature has risen by 0.8°C over the past century, giving rise to a multitude of climatic changes, many of which may well be irreversible.
There are many ways to reduce CO2 outputs from vehicles. The best way, and you don’t need an envelope to figure this one out, is simply not to use the vehicle at all. That’s not a favoured choice for most of us in the 21st century. The next best way is to use vehicles less or use fewer vehicles by switching to mass transit or pedal power. Other ways are to use really, really fuel efficient vehicles or even vehicles which don’t need petroleum-based fuels, e.g. electric cars. And yet another approach is to switch from petroleum-based fuels to biofuels such as ethanol made from starch, dextrose, cellulose and other green plant-derived feedstocks.
This confuses a lot of folks. Ethanol, like any carbon-based inflammatory substance, also produces CO2 when burned. In fact, a litre of ethanol, when burned, will produce about 2 kg of CO2, only slightly less than the output from the combustion of the same volume of petroleum. But ethanol’s energy content is 40% lower than that of regular fossil-fuel gasoline, so one needs to use more of it to get the same power from a motor, which means more CO2. By one estimate, using ethanol as a motor fuel (blended in with regular gasoline) produces 54% more CO2 per kilometre driven than conventional gasoline alone.
So then, why even think of using ethanol as motor fuel at all? One good reason (which is often overlooked in the ethanol versus gasoline debate) is that the carbon released as CO2 when ethanol fuel is burned is recent carbon which was in the atmosphere (as CO2) just a few growing seasons before the ethanol was distilled from corn, sugar cane or whatever plant feedstock was used. And that released CO2 will be drawn back out of the atmosphere again when the newly replanted crops of corn, sugar cane and the like are actively growing and fixing energy through photosynthesis. Contrast this with the carbon released from fossil fuels which is old. Actually very old – fossil fuels were formed by compaction and anaerobic decomposition of buried dead organisms millions of years ago. This means that CO2 derived from the combustion of petroleum and other fossil fuels is added to the existing carbon loading of the atmosphere, hence the steady rise in global atmospheric CO2 over the last two centuries.
Ethanol production in the U.S.A. has increased exponentially during the past decade, from 6.2 billion litres in 2000 to 13.2 billion litres in 2010. By comparison, Canada’s ethanol production now exceeds 2 billion litres annually, virtually all of it from prairie-based corn and cereal crops. Enerkem operates a small ethanol plant at Westbury, Quebec, using wood waste (used telephone poles) as feedstock.
The proportion of ethanol in commercially available gasoline continues to hover around 10% which is the safe maximum proportion for engines built for regular petroleum-based fuels. Flex-fuel vehicles can use up to 85% ethanol in their fuel and are slowly increasing in availability across North America. Ethanol production from corn has worked so well because it is chemically easy to change the starch in mashed corn into dextrose and from there to ethanol by fermentation.
Many factors drive the recent increase in ethanol production in the U.S., including corn crop subsidization schemes, powerful farming lobbies in Washington, and strategic concerns over oil imports. An increasingly difficult issue for the fuel ethanol industry is the rise in food prices, brought about by land competition between fuel and food production. The Food & Agriculture Organization of the United Nations estimates that about 40% of recent global food price increases are due to land competition between food farming and the ethanol industry in the U.S. and elsewhere. The rest of the increase has been brought about by economic factors, droughts and increasing human populations.
Which, cunningly, brings me back to the subject of trees in British Columbia, which are a vast potential source of ethanol fuel. Not necessarily the whole tree. Waste produced during normal tree harvesting (tree tops, branches, bark) makes up 25-35% of the overall tree volume, and the proportion of waste is increasing as the number of trees damaged or killed by the Pine Beetle epidemic increases. The annual wood waste production in Canada now exceeds 35 million tonnes, of which over 26 million tonnes are produced in British Columbia.
The main constituent of wood, lignocellulose, is composed of three organic components – cellulose, hemicellulose and lignin. The cellulose part is a polysaccharide, i.e. a very long molecular chain of dextrose molecules, which can be converted into ethanol. But the cellulose has first to be separated from the other two components. Industrial plants typically use a variety of chemical treatments involving acids, ammonia, sulphites and/or solvents, as well as physical treatments involving steam or ozone to separate cellulose from lignin in wood-derived feedstocks.
Thanks to a few million years of biological evolution, cellulose it is a very durable substance. Cellulose in discarded cotton in landfills (mainly from “disposable” diapers) has been found to remain intact for more than 20 years. Present-day industrial processes use two basic approaches to break cellulose down into its dextrose components. One approach is to uses chemical hydrolysis, i.e. to attacking the cellulose with diluted acid under condition of high heat and high pressure. The second is to use enzymatic hydrolysis. Enzymes are proteins produced by living organisms and which catalyze (i.e. assist) chemical reactions. The prospect of being able to derive huge quantities of chemical energy in the form of ethanol fuel from cellulose has spurred technological innovation on an impressive scale within the past decades, and there are diverse approaches being developed. Many technology companies are combing chemical and enzymatic treatments to make the cellulose breakdown process faster and more efficient. There are now upwards of 25 companies developing cellulosic ethanol plants in the U.S. In Canada Iogen Corporation has built a demonstration facility near Ottawa to produce ethanol from the cellulose in wheat, barley and oat straw, and Lignol has established a Cellulosic Ethanol Development Centre in Vancouver, consisting of a pilot plant and an enzyme development laboratory.
Would the widespread and increased use of ethanol (and other similar biofuels such as biodiesel made from plant oils) as motor fuel make a significant environmental difference? The only valid way of comparing ethanol and fossil-derived fuels is in terms of their life-cycles which measure energy and carbon balances. This means calculating and comparing the energy and carbon contents of commercially-produced ethanol and oil-derived gasoline from the very start of the manufacturing process all the way through to the final stage when they are burned as fuels and release their energy and carbon. For fossil fuels this is a well-to-wheel analysis, i.e. starting at the oil well where the crude oil is tapped and ending at the gas pump which supplies the motor vehicle with fuel. For ethanol, the process starts with the harvesting and processing of the green plants which are used as feedstock and ends at the gas pump. In both cases, all the energy used by the production processes are included in the analysis, including the energy costs of the refineries, transportation, farming the crops and crop fertilization. They also include the energy values of useful by-products from fuel synthesis such as co-generated electricity and feed for livestock.
The results of these types of analyses show that ethanol production and use as a fuel can indeed reduce overall carbon emissions, but it depends on the way it is produced and used. Overall vehicle CO2 emissions may be hardly impacted at all if the fuel refineries use fossil fuels such as coal or oil as a power source and ethanol added to gasoline does not exceed 10% (the present standard for gasoline in B.C.). On the other hand, total emissions can be cut by more than 50% if refineries are powered by natural gas or, better yet, a waste product such as wood chips, and if ethanol contribution to motor fuel is hiked to 85%.
What life-cycle analysis does not do, at present, is include the costs of dealing with responses and adaptations to climate changes, and deciding how much of those costs are chargeable to the accounts of fossil fuel versus ethanol use
The playing field in the market is not yet level for biofuels. Research and development funding for ethanol development in Canada from 2006 through 2008 was $300 million annually. By comparison, the Alberta Oil Sands currently receive tax subsidies in excess of $1 billion annually. The refinery cost of ethanol is close to 55¢ per litre, but if the price is adjusted for energy content, then ethanol energy costs roughly the same as fossil fuel gasoline energy to produce, i.e. about 90¢ per litre. But there is lots of wood feedstock available, and ethanol fermentation technology is moving ahead by leaps and bounds, so future ethanol production costs are likely to be trimmed. Fossil fuel production, on the other hand, may face significant future cost increases as supplies of easy oil become ever more difficult to retrieve and refine.
What is the future of ethanol production from wood and its acceptance into the marketplace? I think I need another envelope.