Thursday, July 14, 2011



Biofuels have been in the news lately.  I feel as though a lot of people have strong opinions on the subject without a strong understanding of the subject matter.  It is my hope that some may stumble upon this post, don monocles and top hats, and be able to have informed opinions.

In this post, I will choose to focus upon the issues surrounding ethanol, as it is the most prevalent technology at the moment.  I realise there exists a plethora of other options, but they are not as well developed.  The reason that ethanol has been selected as a biofuel is that is comparatively non-toxic and as a liquid phase organic molecule, it blends well with gasoline.  It is also fairly easy to make, as we humans are no strangers to ethanol (go to your local liquor or beer store to see all the things we can do with it).  The first generation of biofuels was made primarily from corn.  The conversion takes three steps.  First, the starch from the corn is broken down into simple sugars either by thermal processes or enzymatic breakdown.  Second, the sugars are converted into ethanol by using yeast or some similar bacterium.  The third step, as I understand, is the most energetically demanding step of the three.  The ethanol must be distilled from the mix, which costs large amounts of energy.  Water is comparatively very difficult to boil, which must be done to extract the ethanol.

This would be fine if not for a few looming problems. The first is that corn is comparatively energy-intensive to grow, requiring a large amount of fertilizer.  The second is that corn requires good quality soil, and displaces farmland which could be used to grow food for humans (known commonly as the food vs. fuel economy).  This lowers the available land for growing food crops, and increases food costs.  Another major issue is the distillation step for processing, which requires very large amounts of energy.  In a class on applied chemistry, we were advised that industry will avoid distillation wherever possible because of the energy (and thus monetary) costs involved.  As a result of high fertilisation and energy costs, the energy input required for one unit of ethanol is often equal to the chemical potential energy stored in the ethanol, if not greater.  Put simply, that means that burning the gasoline directly would have been a better idea.  There would be no food vs. fuel economy and the energy would not have been wasted.  I must specify however, that this is the case with most corn ethanol, particularly in Canada and most of the United States.  Brazil can use this sort of method with sugarcane because of the warm climate.  The more temperate climates cannot accomplish these feats with corn or sugarcane, unfortunately.

There is a [not so-]simple tweak that would boost the efficiency of this process.  If the entire corn plant was used rather than just the kernels, the yield of ethanol would be greatly increased.  Cellulose is the woody material that makes up the majority of plant biomass.  Like starch, it is a long chain of sugar molecules. Unlike starch, cellulose is bonded in a way that makes it more difficult to break down without specialised processes.  You have experienced this personally, dietary fiber is mostly cellulosic material, and cannot be digested.

Ethanol derived from cellulose has been dubbed "cellulosic ethanol", and is described by federal governments as "second generation biofuels", with the first being ethanol derived from corn kernels.  A benefit from this technology is that the feedstock needn't be corn.  Rather, any number of agricultural products could be evaluated.  Ideally, it would not require large energy inputs, and would not displace croplands used for food.  I have my own ideas about what this feedstock would be, but that is another post in itself.    Ultimately, cellulosic ethanol could prove to be a sustainable technology for biofuel production.

In my opinion, cellulosic ethanol is not the ideal solution, but it is a good start.  I will freely admit that I am not an expert in the field, but I would like to offer my ideas without any solicitation whatsoever.  I feel that distillation is prohibitively expensive energetically speaking.  I also feel that the time required for fermentation of sugars should be a deterrent.  Rather, I would like to see a thermochemical (heat energy which begets chemical change) solution employed.  You see, cellulose can be thermally broken down into "syngas", short for synthesis gas.  The name of syngas was coined due to its original purpose, which was to make methanol.  Methanol, like ethanol, is a combustible, liquid alcohol.  Unlike ethanol, it is not suitable for human consumption.  Most sources prefer ethanol for this reason, but I would counter that no one wishes to drink gasoline.  Take that as you will.  In any case, syngas may be directly (and catalytically) converted to methanol with little to no energy inputs.  This means that, in theory, feedstocks could be converted to biofuels quickly and more efficiently than with distillation and fermentation.  While I cannot remember the exact source, but I saw a story on a chemical plant in the southern United States which was employing a similar solution.  The plant was thermochemical, but I believe it produced ethanol.  This is slightly more complicated than making methanol and will have lower energy yields, but in my opinion it is a better idea.  The most attractive aspect of this process in my opinion is the time required.  Rather than fermentation which could take weeks, a truckload of fuel can be ready in roughly ten seconds via thermochemical methods.

Now you, my monocled, brandy swirling, non-spambot audience know what I think about the current state of biofuels.  I believe my next post shall regard what I believe is the ideal feedstock.  I knew it would come, my obsession with it has yielded a large body of informal and scholarly sources of information on the subject, and I tend to gab to anyone willing to listen.  I can only assume you wait with bated breath for my next post.

Also, for the record, I think biofuels are a great idea.  Oil won't last forever.


No comments:

Post a Comment