(Posted Thu. Apr 12th, 2012)
By Pam Keck, Ph.D.
Apr. 12: The word “gas” conjures a wide variety of images depending on the preconceived notion of the thinker. In this article, though, the term specifically refers to the gases in the air -- namely nitrogen, oxygen and carbon dioxide. As it turns out, what many people think about the relationship between gases and respiration misses the scientific mark.
First, nitrogen, not oxygen, is the main component of the air on earth. With oxygen levels of around 21 percent and nitrogen levels of about 78 percent, it plays a much larger part in air’s composition. The remaining one percent of air includes, among other gases, argon and carbon dioxide (CO2). On average, CO2 is present at levels of about 0.038 percent.
When asked what they exhale, many people respond by saying, “carbon dioxide.” While breathing does allow our bodies to get rid of the carbon dioxide it produces, as most learned in elementary school, exhaled breath is not mainly carbon dioxide. In all actuality, it is only about 3.8 percent of the total gases exhaled when we breathe. While the concentration of CO2 increases 100-fold between inhale and exhale, even our exhaled breathe is composed mainly of nitrogen, oxygen and moisture.
Humans and plants share a symbiotic relationship in that plants take in the carbon dioxide humans exhale and convert it into an energy source, sugar (glucose), and oxygen gas, which is transferred to the air. In turn, humans take in and use the oxygen produced by plants, utilizing it in our cells for a host of chemistries that occur in our bodies.
As it turns out corn, since it’s a plant, takes in carbon dioxide, converts it to glucose and then strings long chains of the glucose units called polymers to form starch. When humans eat starch, our bodies break down the linkage units thus releasing the glucose units for other uses in our bodies.
Starch is also used to make beverage alcohol which can be made from plant sources from grapes to dandelions. This same alcohol, ethanol, is used as a fuel. Today, approximately 90 percent of the fuel supply is blended with ethanol.
Alcohol is subdivided into a variety of categories but, from a chemist’s perspective, they all share a similar molecular structure in which an O-H group is attached to a carbon. The O-H indicates oxygen attached to hydrogen; the oxygen portion is attached to a carbon. For example, isopropyl alcohol, the rubbing alcohol used in first aid, has three carbons and one of these is attached to oxygen which is attached to hydrogen. Ethanol has only two carbons and one of these is attached to the O-H group. Alcohols end in the two letters ‘ol’ so a single carbon alcohol is methanol, two carbon is ethanol, three carbon propanol, four carbon butanol, etc. These are common names, not the official chemistry names as determined by IUPAC (International Union of Pure and Applied Chemists).
Why does this matter in daily life if people continue to breathe without this knowledge every day? It is significant because public discourse about global warming frequently references carbon dioxide as a greenhouse gas and, therefore, a contributing factor. While other gases contribute to warming, CO2 is a major contributor.
Many studies have set out to determine our carbon footprint as individuals and societies. Basically, what these studies attempt to create is an estimate of the amount of CO2 generated from various processes. Any process that utilizes transportation sources will produce this gas as a result of fuel combustion, including the combustion of gasoline and ethanol.
In making such determinations, it is necessary to note that the CO2 produced from ethanol combustion is accounted for from the time that the plant takes it into the air until it is burned to fuel a car. Here are the scientific equations:
6 CO2 + 6 H2O → C6H12O6 + 6 O2
(Translation: 6 carbon dioxides and 6 water molecules are converted to one glucose and six oxygen molecules.)
In the ethanol production facility (another type of ‘plant’):
C6H12O6 → 2 C2H5OH + 2 CO2
(Translation: One glucose is converted to 2 ethanol molecules and 2 carbon dioxide molecules.)
During combustion (in the fuel tank):
2 C2H5OH + 3 O2 → 2 CO2 + 3 H2O + heat (energy)
(Translation: 2 ethanol molecules are converted to 2 carbon dioxides and 3 water molecules.)
Simply, the 6 carbon dioxides from the air (first equation above) equals the carbon dioxide used to make ethanol and to burn it. Just accounting for the carbon dioxide taken in from the air, the production of carbon dioxide from corn starch is carbon neutral.
Other resources are needed to grow and transport the corn used to make ethanol. However, in comparison with non-carbon neutral petroleum though, it is clear that ethanol has a smaller environmental impact in this respect.