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Written by Suzanne Heibel   
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Wednesday, 12 November 2008

Cellulose Fuel

The hunt for new energy sources began with the obvious: products of mother earth that are known to be energy-rich. When the consequences of petroleum use became too hot to handle, and sources of gasoline were rumored to be dwindling in supply, people sought a source that was renewable. The genius behind renewable energy sources is that they are abundant because when they run out we can always make more.

Corn, the kernel of corn, was the first swing we took at this energy crisis. At first it made sense, it is the fruit of the plant so it is naturally the most appealing and the most obvious fuel source. But corn, we learned, was environmentally backwards because it needed too much energy and water in order to be produced and processed into fuel, called ethanol. It has also been criticized on a socially level because it raised food prices world wide and thrust societies further into starvation. Furthermore, massive subsidization was provided for US farmers using corn crops for ethanol production rather than food production, thus making it cost more to make than revenue generated.

Luckily the search did not start and stop with the edible portion of the corn plant. People soon thereafter sought out something that possessed ample energy but was perhaps not so obvious: cellulose! Cellulose can also be used to produce ethanol. First, cellulose is waste, it lies within the stalks of plants like corn. We don't really do anything significant with the stalks of corn. We see stalks as an important part of the plant, but only in the sense that they aid the growth of our foods. However, processing this natural waste into a fuel, called cellulosic ethanol, is viable. It is cost effective because it is essentially recycling, and using cellulose to produce energy does not involve a tradeoff and reduction in food production.1 So what exactly is cellulose?

Cellulose: A Quick Definition

Cellulose gives plants structure, and cell walls of plant cells are cellulose. Cellulose is the basis of wood, grass, and stalks of plants, and makes up 44% of all biomass.2 Nutritionally, cellulose is a fibrous carbohydrate, meaning itís a little tough but healthy in a human diet. And if you have ever researched nutrition, you know that in the end, all carbohydrates break down into their most basic form of simple sugars, fiber is just a longer burning energy than straight up sugar.

The Process: Stalk to Fuel


Cellulose is a structural entity, so its purpose is to provide the plant with stability. Wood and corn stalks are both made out of cellulose. In order to make cellulose into a fluid that can be used as a combustible energy source, the first thing you need to do is to break the cellulose down. This can be done with hydrolysis, which is the breaking of cellulose down into its basic sugar form. Next, these sugars are fermented by microbes which create ethanol. Through a distillation and a purification process, quality ethanol is produced.3

Distillation and a purification process


Diagram courtesy of the US Department of Energy of Science:
http://genomicsgtl.energy.gov/biofuels/placemat1.shtml


Transforming wood chips or corn stalks into fuel sounds like a fairly basic process. While creating fuel from stalk is more intricate than doing so with corn, cellulosic ethanol actually produces a greater net energy yield than corn ethanol!4

How Viable is it?


The U.S. National Commission on Energy Policy Forum reported on cellulosic ethanol in 2003 with an overwhelmingly positive assessment.5 Another exciting possibility for making this type of ethanol even cheaper is to harvest bamboo, which grows rapidly and like crazy and needs very little water. Corn stalks are usually the focus of use because they are our waste, but there are easy options out there if we just wanted to dedicate land solely to fuel, which is controversial but still a possibility.

Another source of biofuel stealing center stage is algae. Algae naturally produce oils which can be processed into a particular bio-diesel. And since algae are comprised mainly of carbohydrates, they can be changed into an ethanol.6 There are thousands of species of algae, and different types have varying carbohydrate contents and rates of oil production so finding the right algae to transform into the most efficient ethanol or biodiesel requires extensive research.7 Algae are somewhat tricky to grow but at their full potential they can double in volume overnight. Current technology is still being worked out to get the most out of this renewable resource. In fact, researchers are currently looking to grow algae vertically in plastic bags to maximize land usage and increase efficiency.8

Most importantly, green house gas emissions from producing energy from cellulose and algae are both low. (Since that is the point of renewable fuels, we would have hoped so.) The Commission on Energy Policy Forum stated that net emissions are minimal thanks to the modest levels of inputs needed to produce the biomass.9 Plus, since the cycle of ethanol starts with growing plants, then using them, every time plants are grown, they absorb CO2 via photosynthesis. Then when the plants are converted into ethanol, and combust, the gases are again released, creating a cycle of almost equal give-take of carbon dioxide. Plus, grasses, trees, and roots are the entities that preserve the environment by preventing soil erosion, and increasing soil fertility.

The breakdown of all this information is that cellulose ethanol is easy, cheap, and needs very little to grow. It is slightly more expensive to process than ethanol from corn kernel, but it produces a substantial amount of energy, and is a low green house gas emitter. Cellulose carries with it few social and economic externalities and reinstates the idea that nothing needs to be waste, and everything can have a purpose.

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1http://www.seco.cpa.state.tx.us/re_ethanol_cellulosic.htm.
2http://genomicsgtl.energy.gov/biofuels/placemat1.shtml.
3Id.
4http://www.seco.cpa.state.tx.us/re_ethanol_cellulosic.htm.
5http://www.energycommission.org/files/finalReport/IV.4.c%20-%20Cellulosic%20Ethanol%20Fact%20Sheet.pdf.
6http://edition.cnn.com/2008/TECH/science/04/01/algae.oil/index.html.
7http://www.popularmechanics.com/science/earth/4213775.html.
8http://edition.cnn.com/2008/TECH/science/04/01/algae.oil/index.html.
9http://www.energycommission.org/files/finalReport/IV.4.c%20-%20Cellulosic%20Ethanol%20Fact%20Sheet.pdf.




Comments (2)
RSS comments
1. 21-10-2011 03:31
The biomass-derived energy of selection is hexane, not ethanol. And the ligno cellulose is not used, but become propylbenzene, a substance feedstock forerunner, with the chlorophyll being become diesel-powered energy, where it comes from in the first location.
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2. 17-04-2011 19:33
Cellulosic ethanol production should result in a fairly large net energy surplus, certainly MUCH better than ethanol from corn that is only just barely positive. t would make an excellent source of cellulose needing little water, fertilization, or pest control. 
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