|Ethanol in "Beer"|
Alcohol can be made from various agricultural products in a sequence of three basic steps
1. Chemically decompose raw materials (raw materials) through processes that may involve cooking and adding enzymes.
2. Fermentation, the effect of microorganisms (usually yeast) producing "beer" (the term "beer" describes the liquid traction of a fermented mixture of water and ground or crushed grains, usually not more than 10 -12% alcohol, so The process and final alcohol content are similar to domestic beer.) Contains a small amount of alcohol, as well as raw material residues, yeast cells and various other substances dissolved in water.
3. Separate alcohol from the water and other components in beer, usually by distillation, to obtain alcohol with sufficient purity as fuel.
Fermented grains (cooked in water and treated with enzymes to break down starch and convert it into sugar) will produce an alcohol concentration of about 5-10%. The final concentration or "beer" depends on the water consumption, grain and fermentation quality. This beer has a very low alcohol content and cannot be used as a fuel. It must be further concentrated to obtain an ignitable and combustible mixture. For this reason, distillation towers are used to produce higher concentrations of alcohol.
|Distillation - how it works|
We are usually familiar with how distilled water is produced. The water is heated and the steam or water vapor is taken away in the tube. If the tube loops down and cools under the hump, the steam will condense and distilled water will be obtained. This is "simple" distillation-the removal of volatile substances (water) from non-volatile substances (lime, impurities, etc.).
"Fractional distillation" is used to separate a mixture of two liquids with different boiling points, such as alcohol and water. Ethanol with 4% water boils at approximately 173°F, while water boils at 212°F. The mixture of these two liquids will boil at all temperatures between 173° and 212°, depending on the ratio of alcohol to water.
Consider a beaker or glass jug partially filled with a mixture of alcohol and water at a certain temperature. The top of the container is closed, with only a small hole, and a balloon is attached to it to prevent air from entering. Therefore, the container is at atmospheric pressure, but the shell above the liquid level is basically not disturbed by the airflow circulating around the tank.
After a period of time, the amount of water vapor and alcohol vapor contained in the gas mixture above the liquid in the container will reach a constant value, which depends on the temperature and pressure. The liquid and vapor mixture reaches "equilibrium", in which case there is no net change in the liquid/vapor ratio or alcohol/water ratio in the liquid or vapor mixture. However, the ratio of alcohol to water in the vapor phase is generally greater than that in the liquid phase because alcohol is generally more volatile than water. It is the liquid and vapor state properties of this substance that enable us to distill increasing concentrations of alcohol from alcohol/water mixtures.
By performing a series of controlled continuous sequences of re-evaporation, condensation, re-evaporation and re-condensation), each re-condensation from the previous vapor state achieves a higher alcohol concentration. This is because the alcohol concentration in the vapor is higher than the concentration in the liquid mixture in which it is evaporated.
The previous relationship of alcohol-water mixtures applies when the alcohol concentration is as high as about 95.6%. At this concentration, the two substances stop boiling separately (that is, the alcohol in the gas phase is no longer higher than the concentration in the liquid phase), and fractional distillation no longer works. A mixture of this composition is called an "azeotropic mixture."
Generally, a third substance must be introduced into the mixture to allow separation by distillation, or some other separation scheme must be used.
|The most suitable type of distillation process|
There are two general types of distillation processes that seem to be suitable for large-scale production of fuel alcohol using existing technology. One is a continuous feed distillation tower system, in which beer with a constant alcohol content is continuously pumped into the tower. The other is a tank distillation system, in which a batch of beer does not remove heavy solids (waste grains), but is boiled in place to evaporate the alcohol. The alcohol-steam is then forced to flow through the distillation tower for concentration.
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