Ethanol Process with Calculators

Overview

There are five parts to the ethanol process. Conversion, fermentation, distillation, filtration and dehydration. Conversion takes place in the boiler. It uses two enzymes. The first enzyme is alpha amylase. Alpha amylase is used for the liquefaction of the starting grain. The second enzyme used is glucoamylase. Glucoamylase converts the liquefied starch into glucose. Fermentation can take place in the boiler or in a separate fermentation vessel. Fermentation converts the enzyme-produced glucose into ethanol and carbon dioxide. Depending on yeast strain, fermentation can take one to five days. Distillation exploits the difference in the boiling point of two liquids. In this case, the two liquids are ethanol and water. Using a fractional still, we can separate ethanol and water. Filtration utilizes activated carbon to remove dangerous aldehydes and fusel oils from the ethanol. Dehydration is the removal of the residual water left by distillation. A high quality still should produce 90% ethanol with repeatability. Ethanol can be dehydrated chemically or mechanically. In mechanical dehydration, a non-consumed molecular sieve called zeolite adsorbs the water, leaving ethanol in its highest purity. The zeolite is regenerated by heating and pass air through the material. Normally this is achieved industrially by the use of hot captured carbon dioxide.

Conversion

Please note: Conversion can be skipped for fruits, pure sugar, sugar cane and other feedstocks that do not have starch.

Milling

Conversion first begins by milling, crushing, or otherwise grinding our grain. The point here is to increase surface area and to free the starches from inside their protective cell walls. A grain mill or hammer mill are the best choices. Make sure it is crushed and broken up, but grinding to a fine powder is unnecessary.

Liquefaction

After milling, the grain is diluted and alpha amylase is added. This is our mash. Our mash is brought to boiling, where it is held for twenty to thirty minutes to kill all airborn bacteria, wild yeast, fungus and other microbes. Heat is removed, another small dose of alpha amylase is added to continue the liquefaction. Agitation is delivered by bubbling air through the bottom of our vessel.

pH Adjustment

Once liquefaction has finished, pH must be adjusted so that the second enzyme in series will act correctly. Glucoamylase works best in acid environments from pH 4.8 to about 5.2. Outside of these pH ranges, enzyme function is unpredictable. Temperature is also important, as glucoamylase works best around 120F. However, pH is by far the most important. pH is dropped to 5.0 with use of dilute sulfuric acid, muriatic acid or with a pH buffer. Phosphate buffers work extremely well.

Saccharification

The mash is allowed to liquefy until its temperature drops to 140F. When temperature is at 140F, pH is adjusted to 5.0 and glucoamylase is added. Our boiler is then sealed and the mash mixed with a low PSI air agitator. Depending on enzyme loads, saccharification can take from two hours to one day. Insulation is absolutely vital to ensure enzyme temperature requirements are met. After this step, conversion is completed.

Additional Enzymes

Some additional enzymes can convert plant material into usable glucose. Glucanase, xylanase and cellulase degrade a plants cellular wall into simple sugars. Glucanase and cellulase convert plant wall material into glucose. Xylanase converts xylan to xylose. While most yeasts do not metabolize xylose, some do. However, all grains are at least some percentage cellulose and glucan. Depending on feedstock, these enzymes could increase yields significantly. In some feedstocks, no significant increase is to be expected.

Fermentation

Pitching the Yeast

Yeast dosage is dependant on sugar content and percent of alcohol we wish to ferment to. Fermentation severely slows past 14%, since alcohol denatures the zymase enzyme. However, some yeasts can ferment up to 21%. Things like sugar and molasses are not very nutrient rich and may require additional yeast nutrients.

Temperature Control

Temperature of the boiler or fermentation vessel (which ever you are using) is best kept at 70F. One method is to first ice the mash after liquefaction. A cooling coil can also be used. Some yeast strains are very temperature tolerant, some are not. For the most part, past 85F, fermentation will cease.

Air Locking and Fermentation Traps

Yeast has two methods of metabolism. When oxygen is present, sugar is consumed and yeast divides. This is a good way of getting our yeast started, but a very bad way of producing alcohol. The best way is to seal the fermenter and run a hose from the top of the fermener into a vessel of water. This way carbon dioxide bubbles up through the water, but no air is able to enter the vessel. The same bucket can be used for cooling reservoir and air locking.

Distillation

About Distillation

Distillation is the process by which alcohol is separated from the mash and water. It exploits the difference in boiling points of alcohol and water. In a fractionating column, a condensor unit packed with insulating material and strips the water from the vapor. As the water falls, the alcohol vapor continues up the column. When new, hot vapor is introduced from the boiler it is cooled by the falling water. At the same time it revaporizes any of the alcohol that may have condensed in the column. At the top of the column there is another collection unit. This unit is free of insulating material and is kept at 173F. Vacuum distillation is also exploits this difference in phase change by lowering the pressure of the entire vessel. As the vessels pressure is lowered, ethanol begins to vaporize at a lower temperature.

Using a Fractionating Column

To distill, heat the boiler and pipe the exhaust into the inlet of the fractionating column. Once the mash has begun to boil, ethanol should come from fuel outlet attached to the reflux column.

Filtration

About Filtration

Filtration uses activated carbon to adsorb the dangerous organic volatiles yeast also produces. Activated carbons surface area is large enough such that organic compounds are easily trapped. Ethanol and water pass through, unadsorbed.

Filters can be attached directly to the fuel outlet, or you can filter your alcohol after it has been produced using a funnel and a long tube filled with carbon.

Dehydration

About Dehydration

Water and alcohol form an azeotrope at atmospheric pressure. Basically, fractional distillation can only achieve a certain proof quality. Past about 94% ethanol, 6% water, distillation is not a viable option. In order to remove the water, we must use either a chemical that does not react with ethanol or use a dessicant. Calcium hydroxide has been suggested as a chemical method of drying ethanol. Another method is to add gasoline to the ethanol and redistill. Both of these options complicate the process and redistillation wastes energy. Corn grits and glycerin have been used to produce absolute ethanol as well, however, the far simplest method is to use a molecular sieve.

Zeolite

Zeolite is a synthetic aluminum-silica material. The surface of which is covered by pores of a certain size. Three angstrom and four angstrom zeolite are suitable for the dehydration of ethanol. The "pore size" of the zeolite gives the critical diameter of the molecules it can adsorb. Three and four angstrom zeolite are usually used as dessicants to remove carbon dioxide and water. The critical diameter of ethanol is 4.4 angstroms. Because of this, its molecules will not fit in the pigeon-holed surface of the zeolite. Water has a critical diameter of around 2.4 and is readily adsorbed. Zeolite is not consumed in the process. It can be regenerated by heating to boiling point of the substance it has adsorbed.