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How to make absolute ethanol?

【Fermentation Method】

Starch-rich agricultural products such as cereals, potatoes, etc. or wild plant fruits are washed with water and crushed, then subjected to pressure cooking to gelatinize the starch, then add an appropriate amount of water, cool to about 60 ℃, add amylase to make the starch in order Hydrolyzed to maltose and glucose. Then add enzyme mother bacteria to ferment to produce ethanol.

【Water Law】

Using ethylene and water as raw materials, it is prepared by addition reaction. Water laws are divided into indirect water laws and direct water laws. The indirect hydration method is also called the sulfate method, and the reaction is carried out in two steps. First, 95-98% sulfuric acid and 50-60% ethylene are reacted in a 2:1 (weight ratio) in a tower reactor to produce sulfate ester under 60-80℃ and 0.78-1.96MPa conditions. The second step is to hydrolyze the sulfate ester in a hydrolysis tower at 80-100°C under a pressure of 0.2-0.29 MPa to obtain ethanol, and at the same time produce ether as a by-product. Ene reacts directly with water to produce ethanol. Direct hydration is a one-step method. By ethylene and water in the presence of phosphoric acid catalyst under high temperature hydration. This method is simple in process, less corrosive, does not require special steel, and has a small amount of by-product ether, but requires high purity of ethylene and large power consumption. Regardless of the fermentation method or ethylene hydration, the ethanol produced is usually an azeotrope of ethanol and water, that is, industrial ethanol with a concentration of 95%.

Purification method

Commercially available absolute ethanol can generally only achieve 99.5% purity. In many reactions, higher purity absolute ethanol is required, and it is often necessary to prepare it yourself. Generally, 95.5% ethanol used in industry cannot directly produce absolute ethanol by distillation, because 95.5% ethanol and 4.5% water form a constant boiling point mixture. To remove water, the first step is to add calcium oxide (quick lime) to boil and reflux, so that the water in the ethanol interacts with the quick lime to form calcium hydroxide, and then the anhydrous ethanol is distilled off. In this way, absolute ethanol is obtained with a purity of up to about 99.5%. Anhydrous ethanol with higher purity can be treated with metallic magnesium or metallic sodium.

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