dcsimg

published on 5 March 2009 in energy

Biofuels

Biofuels
Biofuels are one of our biggest hopes in the struggle against climate change. Growing crops to be transformed into alcohol or biodiesel, replacing gasoline and diesel fuel, seems to be the perfect way to stop emitting carbon  dioxide (CO2) into the atmosphere, since plants use this gas for their growth. However we mustn’t underestimate the impact of their complete production cycle: incorrect use of the available land can even increase the amount of greenhouse gas emissions and heavy use of nitrogenous fertilizers can release nitrous oxide. Besides it is important to consider the environmental and economic impact of biomass transportation logistics to the conversion plants as well as end product distribution. Large scale crop growth means also taking away land and resources from food production. This would lead to an increase in the cost of some basic foods as well as animal feed and the consequences could be catastrophic.
When we talk about biofuels nowadays we mean alcohol that comes from sugar or vegetable starch (sugar cane, corn, beetroot), to replace gasoline, biodiesel obtained from vegetable oil (soy, colza, palm oil) and biogas from the fermentation of organic substances to replace natural gas.
Unfortunately however, the more in depth we study  the whole procedure for their production and  more down sides arise on their ability to make us save on fossil fuels thus finding a solution to global warming.

Biofuel pros and cons
Many large countries such as Brazil are focusing on ethanol which is already replacing one third of their gasoline consumption and the United States intend to increase many times this alcohol production by the year 2020, mixing it with gasoline to decrease oil dependency and CO2 emissions.
One of the problems with ethanol is that it is a different kind of fuel from the one that traditional engines use. This problem can be solved but replacing all gasoline fueled vehicles wouldn’t be simple.A worse problem, is that crops used for ethanol production require too much work and energy in terms of farming and fertilizers.
We already know for instance that growing corn requires more energy than the one it yields. Biodiesel fuels are a little bit better: crops grown at the tropics, such as oil palm  or soy, have higher yields.
A study led by Joseph Fargione from the Minneapolis Nature Conservancy claims that deforestation and land tilling will be necessary to grow these crops resulting in a dramatic increase in greenhouse gas emissions. According to Fargione 700 tons of CO2 will be released by wood and root burning or decomposition for each hectare of Brazilian forest that will be converted to soy fields. To offset these CO2 emissions it would be necessary to continue to grow soy for biodiesel fuel on that same hectare for 300 years. In the case of oil palm, another useful plant for biodiesel fuel production which grows on peaty soil which is very rich in carbon it would take as much as 400 years to make up for the CO2 emissions during deforestation. If we really want to replace 15% of fossil fuels with biofuels within the next twenty years, we must be aware of the massive tropical deforestation that this will entail.
The third and greatest problem of them all is the immediate effect that crop growth for biofuels would have in terms of the drastic decrease in crops grown for food. In our increasingly crowded and hungry planet, the cost of basic foods would skyrocket thus bringing on a serious crisis particularly in poor underdeveloped countries.

Fuel from cellulose
Huber’s method
At the university of Massachusetts, the chemist Gorge Huber developed a chemical process that obtained in just one production stage from cellulose gasoline instead of ethanol, without complex reactions purifications.
With the Huber Method, the cellulose in a reaction is mildly heated with a specific catalyst becoming in two minutes a mix of hydrocarbons similar to gasoline. This mix is full of aromatic valuable hydrocarbons, which increase the octane number .
According to Huber, its system does not require much energy. Most of it can be recuperated an re-utilized making the cellulose – hydrocarbons conversion totally neutral from the energy and CO2 emitted standpoint. In the article published in the “chemist and sustainability, energy and materials” magazine, the American chemist didn’t speed many detailed information on his method, to convey less information to numerous competitions trying to achieve the same results.

Energy from cellulose
The quest for more efficient solutions has already begun and the United States are starting to have some feedback. Apparently the best idea would be to obtain sugar for fermentation into ethanol from nonfood sources. A low cost and abundant source is cellulose, a polymer made of a closely knit chain of sucrose molecules (ordinary table sugar). All plants contain cellulose, meaning paper, which is to say a good part of the waste that we produce. If we could convert this into sugar and then into alcohol it would mean that all vegetable waste, from tree branches to paper to grass cuttings could be turned into fuel. Also fast growing trees, such as poplar, that would have a high yield compared to the necessary space to grow them on.
However this isn’t problem free either: it is very difficult to separate the single sucrose molecules in cellulose to then get them to ferment into alcohol. Nature did a great job at creating a simple substance which is yet very resistant to chemical tampering. At present, companies that try to obtain alcohol from paper or vegetable waste cellulose (there are some experimental plants in the USA and Canada) must first grind the biomass and then submit cellulose to rough high temperature alcohol treatments, then expose it to bacteria enzymes from microorganisms that are able to digest it and then use other biological enzymes to make the sucrose ferment into alcohol.
Obtaining alcohol from cellulose with this method is more expensive, polluting and energy consuming than getting it from sugar producing plants. Cellulose hydrolysis, essential for its subsequent decomposition, is what makes the process economically and energetically inefficient as well as polluting.
However, nature has more efficient ways of digesting cellulose. For instance fungi and bacteria, such as those in termite stomachs, are able to do this easily because the enzymes they produce can break down cellulose into more digestible sucrose at room temperature and without pollutants. The drawback is that it takes a long time for these enzymes to do their job.
Cellulose – hungry microorganisms
However, the University of Maryland has just announced the discovery of a bacterial enzyme from the microorganisms S. degradans, which destroys the cellulose fast. Researchers found the bacterium nearby since in the marshes of the Maryland coast. However it has been tough to isolate its active principle. Once they got it, the research team of the biology professors Steve Hutcheson and Ron Weiner, could recreate a synthetic version they call Ethazine, which the foresee should revolutionize the ethanol sector. With this enzyme, in fact, we could convert to alcohol the majority of the U.S. Agricultural waste, getting from them about 250 billion liters of ethanol instead of 13 we actually produce mostly from corn.

Energy from the american prairies
Finally Ken Vogel, of the University of Nebraska, just finished for the U.S. Department of agriculture, a study on the switchgrass the most widespread grass in the American glass – lands, this graminaceous wildly grows till men’s height, and has been used just for pasture till now.
For this study, the switchgrass has bee n sown in 2001 – 2003 in several Midwest fields to evaluate the output under controlled conditions, during the four flowing years Vogel thus, discovered that the cellulose output of man – grown switchgrass is double than the wild planet.
Therefore to transform switchgrass in alcohol with existing technologies would give you a 5 time increase in the energy employed in the growing harvest and transformation and the 93% CO2 rebate on the same energy obtained from oil.
Furthermore, switchgrass does not require rich agricultural soils, it grows very well also in the limited ones, useless for the edible species, and the study is based just on wild species. In fact, particular variations produce already 50% more cellulose than the wild ones, while the transformation technologies from cellulose to alcohol still can improve a lot. Also, swithgrass is perennial plant which can harvest for several years without being sowed.
This leads to energy savings in agricultural manufacture. Therefore we can hope some “weeds” might propel the motorcars of the future.

Written by Videoscienza

With the sponsorship of the Italian Ministry of Education, Universities and Research
 
Eni S.p.A. - P.IVA 00905811006