Making Ethanol From Sawdust
Adapted from a paper in Acres, USA June 1983 by Mike Brown.
Use the laboratory rubric to grade.
Georgia Performance Standards for chemistry: SCSh 1-8, SC2 a & b, SC6 c, SC7 a & b,
Background:
With the rise in gas prices, we are often searching for new fuels to use. Automobile
manufacturers are now making “flex fuel” vehicles that are able to run on a mixture of
85% ethanol and 15% gasoline (called E85). Normal gasoline engines can run on a
mixture of E10 (10% ethanol, 90% gasoline) aka gasohol with no modifications.
Most of the ethanol made today comes from the fermentation and distillation of
Midwestern corn. Scientists are looking for new sources for ethanol production since
corn can sometimes be more expensive, less readily available, or require greater energy
to produce. Many cellulosic (woody-material) feedstocks are being investigated such as
corn stalks, forest waste, grasses and other paper wastes.
Materials Needed:
 Sawdust
 18 M H2SO4 in bottles
 Packages of yeast
 Water
 pH paper
 6.0 M NaOH solution in dropper bottles
 Anhydrous Ethanol
 600 mL beakers
 Electronic balance
Procedure:
Safety notes: concentrated (18M) sulfuric acid is very dangerous. Wear safety goggles at
all times and use gloves to handle. A fume hood should also be used if available – use in
a well-ventilated space. Should you get concentrated sulfuric acid on your hands, wash
IMMEDIATELY with lots of soap and water. Sulfuric acid spills on a lab bench should
be cleaned up using a baking soda and water mixture to neutralize before using paper
towels. Aprons should be used to avoid contact with clothes.
ALWAYS add acid to water and NOT water to acid.
Make sure there are no flames present when doing this lab. Ethanol is very flammable.
Note to teacher: You may want to pre-measure out the sulfuric acid into bottles so all the
students have to do is open and pour. That will minimize student contact with the acid
and avoid spills.
Day 1:
1. Put on gloves, and apron, and goggles. Make sure chemicals do not get on your
hands.
2. Obtain enough sawdust to reach the 50 mL mark on a 600 mL beaker.
3. Add about 50 mL 18M sulfuric acid on top of the sawdust. Make sure the sawdust
has been thoroughly (but not excessively) covered by the acid – you may need a
little more or less than 50 mL. Write down your observations in your lab
notebook.
4. Taking a second beaker, fill it to about 200 mL with distilled water.
5. Add the sawdust and acid mixture to the distilled water – NOT THE OTHER
WAY AROUND. Be careful that the beaker will get HOT.
6. Test the pH of the sawdust, acid and water mixture with the pH paper. Continue
to add water until the pH reaches a value between 5.0 and 6.0. Do NOT exceed
the 400 mL mark with water. If you have added water up to 400 mL and the pH is
still not high enough at that point, add 6.0 M NaOH solution drop by drop until
the pH is in the right range.
7. Once the pH is in the correct range, add ¼ a package of yeast to your beaker.
8. You may notice bubbles of carbon dioxide start to form. Label your beaker with
your names and set it aside for two-three days.
Day 2:
1. Put on goggles, and an apron.
2. Obtain 200 mL of anhydrous ethanol.
3. Using the 200 mL of ethanol, you need to make several dilutions of ethanol with
water. Dilutions need to be in percent by VOLUME. You will need to make 0%,
25%, 50%, 75%, and 100% ethanol in water. You must check your calculations
with your teacher before you actually make the dilutions.
4. You will then measure the densities of these mixtures using the electronic
balances and a graduated cylinder.
5. You need to make a graph of percentage ethanol vs. density to use during day 3.
Day 3:
1. Put on gloves, and apron and goggles.
2. Set up a suction filtration apparatus using a Büchner
funnel and filter paper as shown to the side.
3. You will need to filter your sawdust (which is now
lignin) mixture, separating the black “chunks” from the
liquid. Lignin is the substance that bonds the sugar
molecules together to make cellulose.
4. The leftover fluid should be yellowish in color and contains the alcohol (with
water) you produced.
5. You need to find the density of this yellowish liquid and compare the density to
the graph you made on Day 2. Using the graph, calculate the approximate
percentage of alcohol you were able to ferment.
Questions:
1. What did you notice about the density of the ethanol/water mixtures as you
increased the percentage of ethanol?
2. Did you create as much ethanol as you thought you would?
3. Was the reaction of sawdust with sulfuric acid exothermic or endothermic? How
do you know?
4. Write up a thorough lab report covering all three days worth of labs activities.