One of the videos that particularly struck me from Chemistry class was “Bioethanol,” from the Periodic Table of Videos. In the video, Professor Poliakoff discusses his travels in Brazil, a country known for its high use of ethanol fuel, as well as his discovery regarding the use of bioethanol versus common gasoline. He found that while Brazilians domestically produced an abundant supply of ethanol fuel for use, most citizens continued to use regular gasoline to fuel their cars because it was more cost-effective (meaning that their cars could run on more kilometers per gallon with gasoline than with ethanol, and the difference in price between the two fuels was minimal). Poliakoff then went on to provide an economic explanation for this – because ethanol is fermented from sugar, and because sugar is also consumed in the diet, there is an increasing demand for sugar in both industries. Thus, the costs of producing bioethanol from sugar increase, and in turn, its price as a fuel increases. He then briefly mentioned that an alternative to using sugar in the production of ethanol could be cellulose, a material that is not specifically used for food (Haran, n.d.).Upon mentioning this, he piqued my interest and I decided to further investigate bioethanol and cellulose. This brought me to my question: How is bioethanol manufactured from cellulose, and to what extent is the use of cellulosic ethanol a cost-effective solution to preserve our environment?
To begin, I conducted background research on bioethanol, otherwise known as ethanol. Ethanol, whose chemical formula is C2H5OH, belongs to the chemical family of alcohols. It is “a colorless liquid and has a strong odor.” (European Biomass Industry Association, n.d.) A number of incentives have fostered the use of ethanol as an alternative fuel source. Among the most pressing of these include the increasing greenhouse gas emissions and harmful pollutants such as carbon monoxide and nitrogen oxide to the environment (Derry et al., 2008), the increasing scarcity of fossil fuel resources, and the growing dependence on foreign imports of oil (CropEnergies AG, 2011). All these concerns for developed countries, such the United States and those in the EU, that result from excessive consumption of fossil fuels contribute to the utilization of ethanol as a cleaner alternative energy source for automobiles. Ethanol releases energy according to the following equation when combusted:
CH3CH2OH (l) + 3O2 (g) –> 2CO2 (g) + 3H2O (g)
(Derry et al., 2008)
There are three main steps in manufacturing ethanol. The first is the formation of “a solution of fermentable sugars,” the second is the “fermentation of these sugars to ethanol,” and the third requires the “separation and purification of the ethanol, usually by distillation.” (Badger, 2002) Traditionally, the fermentable sugars used to produce ethanol come from either sugar crops, such as sugar cane or sugar beet, or cereal crops, such as maize or wheat (European Biomass Industry Association, n.d.). Fermentation of these sugars occurs when microorganisms, such as yeast, ferment the C-6 sugars (commonly glucose) obtained from the crops by using them as food and producing byproducts that include ethanol (Badger, 2002). However, because these sugar crops and cereal crops are also necessary for human consumption, they can be relatively expensive to use for production of ethanol.
So, a third mechanism of developing ethanol for fuel has been developed, using cellulose, the waste residues from forests and the parts of plants that are not needed for food. Also known as Lignocellulosic or Cellulosic bioethanol, this biofuel is considered less expensive and “more energy-efficient than today’s ethanol because it can be made from low-cost feedstocks, including sawdust, forest thinnings, waste paper, grasses, and farm residues (i.e. corn stalks, wheat straw, and rice straw).” (Detchon, 2007) As a person who never likes when things go to waste, I was delighted at the fact that we could create fuel from cellulose, which in turn helps to save so many of our natural resources and eliminate much of our waste. To my dismay, however, I discovered that this advantage is accompanied with many costly limitations.
Cellulose, like starch, is composed of long polymers of glucose, which can be used for fermentation in producing ethanol. However, the structural configuration of cellulose is different from that of starch, and this, combined with its encapsulation by lignin, a material that covers the cellulose molecules, makes hydrolysis of cellulosic materials very difficult because the process requires the aid of enzymes or specific reaction conditions or equipment (Badger, 2002).
The three main methods of cellulosic hydrolysis are acid, thermochemical, and enzymatic hydrolysis (Badger, 2002). For the purposes of this blog post, I will focus on the latter form, involving enzymes, which are “biological catalysts.” Enzymes are introduced into a reaction to provide an alternative pathway with a lower activation energy so that the reaction can take place (Derry et al., 2008). However, enzymes must be able to make contact with the reactants of the reaction, which is quite difficult to achieve with cellulose molecules. Thus, a “pretreatment process” is needed to separate the tightly-bound sugars that comprise cellulose. These processes are often energy-intensive, and are thus associated with high costs (Badger, 2002). In addition, the costs of the enzymes are also currently quite high, although biotechnology research is gradually decreasing their costs (Novozymes, as cited in Detchon, 2007) The National Renewable Energy Laboratory (NREL) uses a process known as simultaneous saccharification and co-fermentation (SSCF) to hydrolyze cellulose. A “dilute acid pretreatment” to “dissolve the crystalline structure” of the cellulose is first employed. A portion of the “slurry” that results is then placed into a vessel that grows a cellulase enzyme, while another portion is placed into another vessel to grow a yeast culture (Badger, 2002). In this process, sugar conversion and fermentation occur simultaneously, rather than consequentially, to yield the product of ethanol as quickly as possible, usually a few days (Lynd, 1999 as cited in Warner & Mosier, 2008). However, SSCF still requires expensive enzymes in order to occur, and because the process lasts a few days, the reactor vessels must run for long periods of time (Badger, 2002).
So, simply from observing the process of SSCF, I realize that the industrial creation of ethanol from cellulose is a tiresome process. The reactions needed to convert a molecule of cellulose into its glucose constituents are both costly and time-consuming, contrary to what I had believed would have been quite simply a breaking down of a polymer of glucose. There are numerous implications to this issue, and this brings me to the second part of my question: to what extent is the use of cellulosic ethanol a cost-effective solution to safeguard the environment? Here I discovered the advantages and disadvantages of cellulosic bioethanol. Firstly, greenhouse gas emissions from ethanol-fueled cars are reduced by 85% to 94% compared to those running on regular gasoline. Cheap feedstock that is non-related to food materials is another added benefit of bioethanol created from cellulose, since the question of food vs. fuel is eliminated. And, much of the infrastructure adapted for ethanol fuel use is already in place – roughly 2,000 stations serving E85 (a fuel containing 85% ethanol and 15% petrol) and most automobiles are already built to run on both gasoline or ethanol-based fuel. What’s even more favorable to the environment from using bioethanol is that because ethanol is an organic compound, it is highly biodegradable, making fuel spills much less hazardous than regular gasoline spills (Green the Future, 2008).
Furthermore, the overall benefits gained from using bioethanol made from any other means also cannot be ignored – for example, lower carbon emissions, less reliance on foreign oil reserves, and conservation of finite fossil fuel resources (CropEnergies AG, 2011).
These pros do no exist without their cons, however. I also found that in addition to the high costs of production of cellulosic ethanol that may make it relatively expensive for consumers, there were other disadvantages as well. Commercialization of this type of ethanol is limited, as most production plants are pilot plants and find it difficult to transition to full-scale commercial plants. In addition, because ethanol absorbs water, it is easily contaminated as a fuel and thus is difficult to transport. The high costs of production also could not be outweighed by ethanol-run automobile performance, since it takes about 1.4 gallons of E85 to run the same distance as it would take 1 gallon of regular gasoline (Green the Future, 2008). This was also the main reason, as stated by Poliakoff, that Brazilians continued to use regular gasoline as opposed to bioethanol – their cars simply ran more efficiently on petrol.
From analyzing both sides of the argument, I have come to the conclusion that even though bioethanol seems to have its many disadvantages, the biofuel has come a long way in improving the welfare of our environment. The implications of a better environment per se are perhaps enough to convince me to purchase ethanol as the source of fuel for my car (when I get one, eventually). But also, because cellulosic materials are often wasted and abundant in nature, I find it simply fascinating that we have come across yet another resource with which to provide energy to sustain our lifestyles. Of course, though, I am careful not to jump to the conclusion that this is a panacea to the global peril of climate change, because I know that exploitation of our environment will lead to destruction of it. But now I have understood that even the smallest of steps taken to achieve ecological sustainability can have drastic rewards for the wellbeing of society.
Badger, P.C. (2002). Ethanol from Cellulose: A General Review. Trends in new crops and new uses, 1, 17-21. Retrieved from http://www.hort.purdue.edu/newcrop/ncnu02/v5-017.html
CropEnergies. (2011). Bioethanol report [Brochure/report]. Retrieved from http://www.cropenergies.com/en/Bioethanol/Produktionsverfahren/Bioethanol-Magazin_CE_2011-en_1_1.pdf
Derry, L., Clark, F., Janette, E., Jeffery, F. Jordan, C., Ellett, B., & O’Shea, P. (2008). Chemistry for use with the IB diploma programme: Standard level. Port Melbourne, Victoria: Pearson Education Australia.
Detchon, R. (2007). The Biofuels FAQs: The Facts about biofuels: ethanol from cellulose. Retrieved from http://www.energyfuturecoalition.org/biofuels/fact_ethanol_cellulose.htm
European Biomass Industry Association. (n.d.). Bioethanol Production and use [Brochure]. Retrieved from http://www.erec.org/fileadmin/erec_docs/Projcet_Documents/RESTMAC/Brochure5_Bioethanol_low_res.pdf
Green the Future. (2008). Cellulosic Ethanol: Pros and cons. Retrieved from http://greenthefuture.com/CELLETHANOL_PROSCONS.html
Haran, B (Producer). (n.d.). Bioethanol [Video episode]. United Kingdom: University of Nottingham. Retrieved from http://periodicvideos.com/videos/feature_brazil_bioethanol.htm
Warner, R.E. & Mosier, N.S. (2008). Ethanol from Cellulose Resources. Retrieved from http://bioweb.sungrant.org/Technical/Biofuels/Technologies/Ethanol+Production/Ethanol+from+Cellulose+Resources/Default.htm
Bioethanol for Sustainable Transport. (n.d.). CO2 cycle for bioethanol [Image]. Retrieved from http://www.best-europe.org/Pages/ContentPage.aspx?id=120
Warner, R.E. & Mosier, N.S. (2008). Fermentation of glucose to carbon dioxide and ethanol [Image]. Retrieved from http://bioweb.sungrant.org/Technical/Biofuels/Technologies/Ethanol+Production/Ethanol+from+Cellulose+Resources/Default.htm
Warner, R.E. & Mosier, N.S. (2008). Structure of cellulose polymer [Image]. Retrieved from http://bioweb.sungrant.org/Technical/Biofuels/Technologies/Ethanol+Production/Ethanol+from+Cellulose+Resources/Default.htm