Gel fuel has been used for years as a way to keep food warm in a chafing tray, as a heating oil, and as an emergency survival fuel. It is often referred to as canned heat or Sterno, which is a brand name for methanol gel. Recently I was picking up gel fuel for a fondue party we were having at our house and was astounded at the price - it has gotten quite expensive. After the party I looked at the label on the back and it read "calcium acetate with methanol". Soon after I found myself researching ways to isolate calcium acetate and I began to experiment with egg shells and chalk and I found that it is quite easy to make your own fuel gel for a fraction of the cost.
How to make Gel Fuel from Eggs Shells or Chalk and Vinegar
Supplies: (all links redirect to Amazon.com)
Start with 25 grams (about 2 tablespoons) of calcium carbonate. There are two easy sources for calcium carbonate: eggs shells and high quality chalk (although some chalk is made from plaster which is why I now only use Crayola Anti-Dust White Chalk. Measure and crush 25 grams of egg shells or chalk into a powder.
Mix 100 ml (a little less than 1/2 cup) vinegar (which is 5% acetic acid) with the 25 grams egg shells or chalk. Mix thoroughly. It should begin to bubble as it produces calcium acetate and carbon dioxide. Stop mixing when bubbling stops.
Filter the mixture through a coffee filter by placing the filter into a funnel. The solution that drains out is calcium acetate which is needed to make the gel fuel. Discard the coffee filter in the trash.
Set the calcium acetate solution on a burner or hot plate and gently boil until the volume is reduced by half to reduce the amount of water in the solution. For example, if you start with 30 ml of calcium acetate solution, boil until 15 ml remain. Be sure the glass container is heat resistant.
Allow to cool.
While gently stirring, pour 100 ml (less than 1/2 cup) of ethyl alcohol (also called ethanol) into the calcium acetate solution. As they mix a gel should form. Do not over-mix.
Pour off excess ethyl alcohol into a sink.
Remove the gel and place in small jars or in small paint cans for storage.
To use the gel fuel, simply remove the lid and light the gel on fire with a match. It should burn for a few hours. Replace the lid to put the flame out.
What is the science behind making Gel Fuel?
Reacting Calcium Carbonate and Acetic Acid:
The calcium carbonate (CaCO3) in egg shells and in chalk will react with vinegar, which is 5% acetic acid (CH3COOH) and 95% water to produce calcium acetate Ca(CH3COO)2.
Calcium Carbonate + Acetic Acid --> Calcium Acetate + Water + Carbon Dioxide
CaCO3 + 2CH3COOH --> Ca(CH3COO)2 + H2O + CO2
Reaction between Polar and Non-polar molecules produces the Gel Fuel
Calcium acetate molecules and water molecules are both polar. Polar means that one end of the molecule is positively charged and the other is negatively charged (think of a AA battery which has a positive and negative end). The alcohol in this reaction, ethanol, is non-polar, it does not have a positive and and a negative end. In chemistry, polar and non-polar molecules do not mix. But, polar molecules will mix with other polar molecules and non-polar molecules will mix with other non-polar molecules.
When the polar calcium acetate is mixed with the non-polar ethanol, the acetate molecules turn to a solid (or in this case it is a gel-like substance) structure of calcium hydroxide. As the new calcium hydroxide solid structure forms, some of the ethanol is trapped inside the holes of the structure (think of honey stuck inside a honeycomb).
Calcium Acetate + Ethanol --> Ethyl Ethanoate + Calcium Hydroxide
Ca(CH3COO)2 + 2CH3CH2OH --> 2CH3COOCH2CH3 + Ca(OH)2
Combustion Reaction of Ethanol produces the Flame
The ethanol trapped up in the gel reacts with oxygen in the air to produce a flame and give off heat.
Ethanol + Oxygen --> Carbon Dioxide + Water
2CH3CH2OH + 6O2 --> 4CO2 + 6H2O
Is it safe to make S'Mores with Canned Heat?
Many of the commercially available canned heat gel fuels are not safe to use in cooking foods because they contain methanol. Methanol is toxic but is often used in canned heat because it produces more heat energy than ethanol.
The gel fuel outlined in this experiment is safe to use in cooking food and making S'Mores because we use ethanol which is a non-toxic alcohol. However, do not eat or drink the solution as most ethanol has been denatured (this means that methanol has been added so that the government does not tax the ethanol as 'drinkable alcohol').
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