It is understood that: Glycerin (also known as glycerin) is a colorless, odorless, sweet-tasting organic substance with a clear and viscous liquid appearance. It is miscible with water, alcohols, amines and phenols in any proportion, and the aqueous solution is neutral. Glycerin is a polyol moisturizer. The hydroxyl groups in the molecular structure can form hydrogen bonds with water molecules, which plays a good role in absorbing and locking water. Glycerin has a wide range of uses. Currently, it has more than 1,700 uses. It is used in both food and industry. The industrial production methods of glycerol can be divided into two categories: methods using natural oils as raw materials, and the resulting glycerin is commonly known as natural glycerin; and synthetic methods using propylene as raw materials, and the resulting glycerol is commonly known as synthetic glycerol.
Production of synthetic glycerol: The various pathways for synthesizing glycerol from propylene can be summarized into two major categories, namely chlorination and oxidation. Propylene chlorination method and propylene irregular acetic acid oxidation method are still used in industry.
1. Propylene chlorination method:
This is the most important production method in the synthesis of glycerol, which includes four steps, namely High temperature chlorination of propylene, hypochlorous acidification of propylene chloride, saponification of dichloropropanol and hydrolysis of epichlorohydrin. The hydrolysis of epichlorohydrin to glycerol is carried out at 150°C and 1.37MPa carbon dioxide pressure in an aqueous solution of 10% hydrogen oxide and 1% sodium carbonate to generate a glycerol aqueous solution containing sodium chloride with a glycerol content of 5-20%. After concentration, desalination and distillation, glycerin with a purity of more than 98% is obtained.
2. Propylene peracetic acid oxidation method:
Propylene and peracetic acid react to synthesize propylene oxide, and propylene oxide isomerizes into ene and propanol. . The latter reacts with peracetic acid to form glycidol (glycidol), which is finally hydrolyzed to glycerol. The production of peracetic acid does not require a catalyst. Acetaldehyde is oxidized with oxygen in the gas phase. Under normal pressure, 150-160°C, and a contact time of 24 seconds, the acetaldehyde conversion rate is 11% and the peracetic acid selectivity is 83%. The above-mentioned last two steps of reaction are carried out continuously in a reactive distillation tower with a special structure. After the raw materials allyl alcohol and ethyl acetate solution containing peracetic acid are sent into the tower, the tower still is controlled at 60-70°C and 13-20kPa. The ethyl acetate solvent and water are evaporated from the top of the tower, and a glycerin aqueous solution is obtained from the tower still. This method has high selectivity and yield, uses peracetic acid as the oxidant, does not require a catalyst, has a fast reaction speed, and simplifies the process. The production of 1 ton of glycerol consumes 1.001t of allyl alcohol, 1.184t of peracetic acid, and 0.947t of acetic acid as a by-product. At present, the output of natural glycerol and synthetic glycerol account for almost 50% each, while the propylene chlorination method accounts for about 80% of Hezhi glycerol output.
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