Fuel From Sawdust

by Mike Brown

(from Acres, USA, 19 June 1983)

NOTE: There is no set measure for how much sulfuric acid is needed per how much sawdust -- there are too many different kinds of sawdust, and its condition and water content vary widely. To determine the right amount for the sawdust you're using, make small, bracketed test-batches first, varying the amount of acid used until you get the best result.

This is the old way of making ethanol from cellulose. It works, but it's not efficient, and not economical.
The new ways of doing it get a lot of publicity, but they aren't quite there yet -- see Ethanol from cellulose.

Ordinary distillation works well, using starch or sugar crops -- or wastes. There's a LOT of good waste going to waste!

There are do-it-yourself ethanol manuals online at the Biofuels library, and more how-to's here:
Ethanol resources on the Web

-- Journey to Forever


This procedure uses hazardous materials and anyone who attempts it does so entirely at his or her own risk. Sulfuric acid is an EXTREMELY DANGEROUS CHEMICAL. Take full safety precautions, wear safety goggles, gloves and apron. Take the advice of your chemicals supplier on industrial-standard protective equipment that meets the required safety specifications. Have running water nearby. Don't inhale fumes! The workspace must be thoroughly ventilated. No children or pets allowed. Try small test-batches first to familiarize yourself with the process.

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 time.

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, safer scale.

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 ferment completely.

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 newspaper.

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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