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Distilling Ethanol - The conversion of cellulose, such as sawdust, cornstalks, newspaper and other substances
Fermenting sugars produces ethanol. The sugars can be derived from a variety of sources. In Brazil, sugar from sugar cane is the primary feedstock for the huge Brazilian industry. In North America, the sugar is usually derived from the enzymatic hydrolysis (the conversion of starch to sugar) of starch containing crops such as corn or wheat. The enzymatic hydrolysis of starch is a cheap, simple, and effective process. This well developed process sets the baseline that other hydrolysis processes are compared against. The drawback to producing ethanol from sugar or starch is that the feedstock tends to be expensive and widely used for other applications. These costs are offset by the sale of co-products such as Distillers Dried Grains. The North American ethanol industry is spending considerable effort on finding new co-products that are higher in value and thus capable of making the ethanol from grain industry more cost competitive.
Lignocellulosic materials such as agricultural, hardwood and softwood residues are potential sources of sugars for ethanol production. The cellulose and hemi-cellulose components of these materials are essentially long, molecular chains of sugars. They are protected by lignin, which is the glue that holds all of this material together. The technological hurdles that are presented by the materials are:
- The separation of lignin from the cellulose and hemi-cellulose to make the material susceptible to hydrolysis.
- The hydrolysis of cellulose and hemi-cellulose takes place at different rates and over reaction can degrade the sugars into materials that are not suitable for ethanol production.
- The hydrolysis of these materials produces a variety of sugars. Not all of these sugars are fermentable with the standard yeast that is used in the grain ethanol industry. The pentose sugars are particularly difficult to ferment.
Agricultural residues and hardwoods are similar in that they have a lower lignin content and the hemi-cellulose produces significant amounts of pentose sugars. Softwoods have a higher lignin content, which makes the hydrolysis step more difficult, but they generally produce less pentose sugars.
The five processes reviewed in this report each take a different approach to the problems that lignocellulosic material present. As a result some are better suited to one type of material or another. The suitability of the process for the feedstock is addressed in each section. In some cases there is more than one company marketing the basic technological approach. In those cases the companies reviewed here were chosen because they have been active in the BC either promoting projects or participating in the development of the knowledge base here.
Four of the five processes involve hydrolysis, fermentation, and product recovery routes. Some of these also involve a pretreatment step. The fifth process is a chemical process rather than biological one. The processes are at different stages of development that makes comparisons between them difficult. A summary is provided in the conclusion section. http://www.pyr.ec.gc.ca/ep/wet/section16.html
Fuel From Sawdust
by Mike Brown (submitted by Keith Addison <email@example.com>
(From Acres, USA, 19 June 1983)
The conversion of cellulose, such as sawdust, cornstalks, newspaper
and other substances, to alcohol is a fairly uncomplicated and
straightforward process. At the moment, it is a bit expensive; but
that is hardly a problem that needs to be addressed here. Just a few
years ago the idea of running a car engine on alcohol was
preposterous -- it was too expensive. Of course, back then gasoline
was less than 50 cents a gallon. What might be uneconomical at this
writing might be a bargain by the time you read this.
Let's say you want to make alcohol from sawdust. There are two types
of alcohol you can obtain from wood -- methanol and ethanol. Methanol
can be obtained from wood by high temperature destructive
distillation. Methanol is also known as wood alcohol. The other
method used to obtain ethanol involves converting the sawdust to
simple sugars, the usual fermenting by yeast, and the usual
distillation of the fermented solution. There are a couple of other
steps involved prior to distillation that are distinct from the
standard processes almost everyone is familiar with. To save you the
trouble of trying to remember whose book you read last week or where
in this one you need to rummage around in for the supporting
information, I will provide the usual cookbook instructions.
The first step involves obtaining our standard piece of chemical
engineering equipment -- the discarded 55 gallon drum. You will need
more than one.
The substances you will need to conduct the chemical phase of this
operation are sawdust (for example), sulfuric acid, water, and
possibly some sodium hydroxide, NaOH.
For the mechanical segment, you will need standard window screens you
can buy at the hardware store, plumbing pipes, elbows, couplings,
nipples, flanges, and a welding outfit.
I will describe this just the way my partner and I did it in the lab
with the exception of some of the plumbing connections. This is
necessary because you can't pick up a 55 gallon drum between your
thumb and forefinger the way we do a test tube or beaker in the lab.
Be sure that you read all the way to the end before you put your
hands on the chemicals. You might be unpleasantly surprised.
Pour the sawdust you intend to convert to alcohol into the drum.
Don't fill the drum more than one-third full or you will be taking a
chance on part of the process slopping over the sides of the drum.
Next, pour what chemists refer to as 18 Molar H2SO4, sulfuric acid,
over the sawdust. The commercial designation, if you order it from a
chemical supply house, would be 100% sulfuric acid. However, as low
as 91% will work. We tried 9.2 Molar, or 51%, in the lab and it
simply didn't work. It just sat there and looked at us.
Make sure that you put the sawdust in first. If you don't, the
sawdust will float on top of the acid -- unless you pour in more
sawdust than the acid can absorb. In that case, you will simply have
to, pour in more acid anyway. It's easier to do it right the first
When you pour the sulfuric acid on the sawdust, the reaction is
almost immediate. The sawdust and acid react in such a fashion as to
turn black almost immediately. It resembles an ugly collection of
coal tar or oitch. Bubbles rise up through the solution. The bubbling
is primarily due to air pockets inside the sawdust. Even though the
reaction appears to be instantaneous, you should let the mixture sit
for a day or two to allow whatever reaction doesn't take place at
once to proceed at its own leisure.
Once the reaction is complete, you can simply dump in yeast and
expect the mixture to ferment. The pH of the mixture is so low, that
is the substance is so acidic, that any microorganism such as yeast
that you dump in is simply going to explode. Of course, they will be
very tiny explosions.
The proper procedure here is to supply enough water to raise the pH
to the proper level for fermenting or yeast propagation -- 5.0 to
6.0. In Kentucky, where the water is lightly acidic, diluting the
solution 50% by adding an equal volume of water will raise the pH to
about 3.0. In areas where the water tends toward alkalinity (or is
basic, in chemical terms) the pH will go higher. If you don't want to
keep adding water, add some sodium hydroxide, NaOH, to raise the pH
up to optimum conditions.
The trick here is that this mixture must be poured into the water
used to dilute it with. If you pour the water onto the acid, a
natural inclination, what you will get is a loud hissing sound
followed by acid vapors rising up out of the solution to attack you.
If you add the acid to the water, the dilution factor is much
greater. The same reaction will take place but on a much smaller,
What takes place is an exothermic reaction. That is, large quantities
of heat are liberated. You can get a good idea of how much heat is
liberated by simply placing your hand on the container during various
stages of the proceedings. Briefly put your hands on the drum when
the sulfuric acid is poured on the sawdust and you will experience
the same discomfort that you would if you placed your hand in the
middle of a hot frying pan. You will get burned.
Once the solution has been adjusted to the proper pH, it is time to
pitch in your yeast. A small packet of Fleischman's, available at the
local supermarket, will do just fine. Watch for bubbles of carbon
dioxide to appear. They might be hard to recognize coming up through
the black gunk; 72 hours, or 3 days should be enough to allow it to
A word of caution. You might think that simply diluting the acid with
half water before you pour it on the sawdust would save a lot of
trouble. In a way it does. You don't have to worry about distillation
if you do it like that because 50% sulfuric acid won't convert
cellulose to sugar and the yeast won't ferment anything else. We
tried it in the lab and it simply doesn't work.
Before you run your solution into your still, you need to get as much
of the black gunk, big gobs of it, out of the solution. Remove as
much as possible. The material is lignin or the substance that bonds
sugar molecules together to make cellulose out of them. In a
chemistry lab you use a buchner funnel and filter paper. A buchner
funnel has tiny holes in the base. The filter paper is placed on the
bottom, covering the holes, allowing the liquid to pass and trapping
practically all the lignin. For a barnyard operation, you can punch
nail holes in the bottom of a 55 gallon drum and cover them with
Given the fact that the chunks of lignin in an outdoor operation will
be much larger than those in a lab, you will probably want to install
a series of wire mesh screens between your fermentor and the
eventual, modified buchner funnel. The screens toward the fermentor
should increase in mesh size and those toward the funnel should
decrease in mesh size.
The fluid that gets past the newspaper should be yellow in color. The
filter won't catch everything. In the lab, we observed a ring of
small, brown flakes that settled to the bottom of our distilling
flask. This fluid contains ethanol and it is ready to be distilled.
At this point go back and scrape the lignin off the screens and
remove the lignin-saturated paper from your funnel. This is the fuel
to fire your still with. There won't be enough to get the whole job
done, but it will help and it does eliminate the problem of what to
do with all that black gunk. Just be sure you give everything a
chance to dry out before you try to light it.
The alcohol you get from distilling the yellow fluid is identical to
that obtained from sugar or starch. We obtained 190 proof ethanol the
first time through a fractionating column. The yield-per-pound
appeared to be quite good. According to most of the chemical
literature we read prior to conducting this experiment, the
commercial yield of cellulose is far inferior to that of corn or
other common feedstocks. However, a ton of cellulose (saw dust) is
free for the asking
In place of the sodium hydroxide, NaOH, that we used in the lab, you
can substitute common garden variety lye to adjust your pH. If you
spill sulfuric acid on yourself -- it is a strong acid and it will
burn -- dilute it with water and scrub with soap. However, the soap
should be one that lathers very well because the acid is a very
strong acid and the soap is a very weak base, or neutralizer. Lather
the soap up well and use a lot of it.
Once you have distilled the alcohol, you can raise the temperature
under your column and boil off the water. Because the sulfuric acid
has a much higher boiling point than water, you are simply repeating
the distillation process to recover whatever unused sulfuric acid is
available from the bottom of your still. You can't recover much of it
because H2SO4 loses the two hydrogen atoms, or protons, in the
initial reaction and is no longer sulfuric acid.
In a commercial plant, the elements involved in the reaction could be
recovered in the following fashion. It is a process too long and
involved to go into in detail here:
S02 + H20 ---- H2S04
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