Ethanol as Automotive Fuel

Remember in the last column we spoke about ethanol and how it is made. Today I would like to explore the role of ethanol in automotive fuel.

First, let’s take a quick look at gasoline. Gasoline, as with most fuels, is a hydrocarbon. That means that its molecules are made up of carbon atoms and hydrogen atoms, with the carbon atoms forming either a straight chain or a branched chain. Hydrocarbons make good fuels because they burn easily in the presence of air. You are already familiar with natural gas, a one-carbon hydrocarbon, with a simple formula of CH4, and called methane. Propane, the common barbecue fuel, is three carbons long, so its formula is C3H8. Methane is a gas at room temperature, and propane is a gas but becomes liquid when compressed. By the time we get to 6 carbons atoms, the hydrocarbons are liquids, and become solids above about 14 carbons… wax! So, gasoline is typically about 8 carbons. I say typically because gasoline is not a single compound, but a range of very similar chemical compounds that have a specific boiling point, or that boils over a narrow temperature range.

So, when gasoline and air are introduced into an internal combustion engine, compressed and ignited, the mixture burns very rapidly, and the resulting displacement of the piston in the cylinder turns the crankshaft and thus the wheels. However, we do not live in a perfect world. There is never quite enough air mixed with the fuel to burn everything, so as well as the carbon dioxide, we get carbon monoxide and some chemical fragments of the gasoline molecules that form soot and other compounds. If we add something to the gasoline that has oxygen in it, such as ethanol, (remember the formula for ethanol is C2H5OH) we can achieve a better and more complete combustion. Nevertheless we are still stuck with carbon monoxide and dioxide, serious greenhouse gases.

There is a downside, of course. The oxygen in the ethanol molecule means that weight for weight it doesn’t have the bang that gasoline has, so there is a fuel mileage penalty, estimated at up to 10%, but a cleaner exhaust. The trick is to add enough ethanol that the exhaust quality improves, but not too much to upset the fuel injectors and the internals of the engine management system. If you look at most pumps around Brockville, you will see a sticker saying “may contain up to 10% ethanol”. This level can be tolerated by most modern vehicles without modification. If we want to run higher levels of ethanol, we have to make sure our vehicle is equipped to handle the additional ethanol.

There is a current oxygen-containing additive called MTBE (we’ll skip the formula for now) which serves the purpose of providing extra oxygen, but there are issues around its safety and it is made from crude oil, whereas we know where we can get ethanol.

Some of you may be familiar with the situation in Brazil. There is little natural petroleum in Brazil, but a huge quantity of sugarcane and low cost labour. Therefore ethanol derived from sugarcane forms a large part of the Brazilian motor fuel supply, and all vehicles sold in Brazil are designed to use this fuel. As well, there would be operational problems using pure ethanol as a fuel in our winter conditions, something the Brazilians do not have to consider.

So, using ethanol as a fuel additive or substitute will have a beneficial effect upon emissions, and will reduce our reliance on crude oil, but it is not the magic cure that some have promised. The latest estimates, and they are only estimates, indicate that the substitution of a major portion of our gasoline with ethanol may result in a reduction of the transportation component of greenhouse gases of up to 25 – 40%. Another issue is that a major new market for ethanol will benefit farmers but may drive up the cost of chicken, beef, and other foods for which the corn from which ethanol is made is a food source or raw material.

There is also controversy around the overall energy balance of ethanol – that is, how much energy in diesel fuel, fertilisers, etc. does it take to make a kilogram of ethanol from corn, vs. how much energy it gives to the gasoline. I have seen estimates from 50% to 150%. It is easy to see how anyone with a vested interest can make the data look favourable for their cause.

The only fuel that can play a really significant role in reducing greenhouse gases is hydrogen, and we will look at that in a future column.

Science Matters... Ethanol

There are many complicated issues facing the public these days, ranging from waste disposal, recycling, air and water emissions, energy generation and consumption, transportation, and many others. These issues have at their core some elements of science, whether it is chemistry, physics, biology, engineering, statistics, or some combination of these. With your help, I would like to explore some of these issues and examine the science in more detail and together we can understand what is going on, what we are being told, whether it makes scientific sense, and perhaps make a slightly better judgement about the issue. I hope to use my contacts and experience in the scientific community to assist you, the readers, in understanding these issues. I welcome your input.

Our area is about to benefit from the construction and operation of an ethanol plant, and I thought it might be appropriate to look at some of the chemistry of ethanol and try to understand what it is, what it does (as a fuel additive) and what are the pros and cons.

Most of us are familiar with ethanol in the form of alcoholic beverages: wine, beer and distilled spirits. It is suggested that the manufacture of alcoholic beverages counts as the first chemical industry, dating back thousands of years. The ethanol we drink is diluted, with water, fruit extracts and flavourings, to about 5% in beer, about 12% in wine, and about 40% in distilled spirits.

Ethanol, or ethyl alcohol as it is known in chemistry, is a clear colourless flammable liquid, completely miscible (mixes with) water in all proportions. It is the second in a chain of alcohols, because of the two carbon atoms, the first being methanol. The chemical formula is C2H5OH, with the OH group giving the characteristics of an alcohol.

The first and still most important way of making ethanol is via fermentation of sugar or starch. Grapes were among the first fruits to be fermented because grapes are naturally sweet, the enzyme that produces ethanol is found on grape skins, and ethanol production is very simple, and takes place at room temperature, especially if your room is in the Mediterranean basin. Many fruits, vegetables and grains have been fermented in pretty much the same way to arrive at ethanol with many flavours, but the basic chemistry remains the same.

When you are making beer and wine, you allow the fermentation to proceed to a specific point then you stop it chemically, filter or decant your product, and depending on your patience, let it mellow a little before drinking. Because the enzymes that do the work are killed off when the ethanol concentration is above about 15%, no wine or beer is naturally stronger than this.

If you are making spirits (such as rum, rye, vodka etc.) or industrial ethanol, you must distil your mixture. Because ethanol boils at a lower temperature than water, if the fermentation mixture is heated above the boiling point of ethanol (78°C) but below 100°C the ethanol will boil and can be captured by cooling the vapour, giving pure ethanol.

So, our plant in Johnstown will be taking corn, the same corn we feed to cattle and other animals, and fermenting it, then distilling it on a large scale.

Here is what is happening, shown another way:

C6H12O6 --> 2 CO2 + 2 C2H5OH
glucose carbon dioxide ethanol

This is how we show a reaction in chemistry, and it isn’t really complicated. Glucose is the simplest sugar. What is really interesting is that for every kilogram of ethanol produced, we get, free and for nothing, 0.95 kilograms of carbon dioxide. So far, no-one has said anything about the carbon dioxide by-product of fermentation.

Another issue with ethanol is this: Right now all the fermentation technology relies on acting on the fruit or the seed grain portion of the plant material, because that is where the sugar or starch is concentrated. As anyone who has shucked corn knows, there is a pile of the corn plant that is wasted. If we can figure our how to convert that waste material, mostly cellulose, into ethanol, we will have some real progress. Thankfully, an Ottawa company called IOGEN has developed a process to do exactly that, and when it is commercialised (it is currently in the pilot-plant stage) then ethanol may become a significant player in the alternate fuel debate.

As we currently stand, the energy balance, that is, the amount of energy you have to put into making ethanol vs. the amount of energy you get out is subject to considerable controversy. We will take a look at this later.

Now, ethanol may have significant benefits with respect to automotive emissions, and reducing our reliance on fossil fuels, but as you can see it certainly doesn’t get us off the hook with respect to carbon dioxide, one of the main greenhouse gases.

Next week we will take a look at what ethanol does when it is mixed with gasoline and diesel fuel.