Introduction of Glycerin

Glycerol, also known as glycerin, is an organic compound with a chemical formula of C3H8O3. It is a colorless, odorless, transparent viscous liquid that can absorb moisture from the air, as well as hydrogen sulfide, hydrogen cyanide and sulfur dioxide. It can be mixed with water and alcohols , amines, and phenols are miscible in any proportion, and insoluble in benzene, chloroform, carbon tetrachloride, carbon disulfide, petroleum ether, and oils. It is mainly used as an organic chemical raw material, and can also be used as an analytical reagent and a lubricating laxative.
Physical and chemical properties of glycerin

Melting point: 17.4°C

Boiling point: 290°C

Flash point: 177°C (OC)

Refractive index: 1.474 (20°C)

Appearance: Colorless, odorless, transparent viscous liquid

Solubility: Can absorb hydrogen sulfide, hydrocyanic acid, sulfur dioxide, miscible with water and ethanol, insoluble in benzene, carbon disulfide, chloroform, carbon tetrachloride, petroleum ether, chloroform, oil

Toxicological data for glycerol

1. Toxicity classification

poisoned

2. Acute toxicity

Rat caliber LD50: 26000mg/kg;

Mouse caliber LC50: 4090mg/kg.

3. Stimulus data

Rabbit transdermal: 500mg/24h, mild irritation;

Rabbit eyes: 126mg, mild irritation.

Production method of glycerin

The industrial production methods of glycerin can be divided into two categories: the method using natural oil as raw material, the obtained glycerin is called natural glycerin, and the synthetic method using propylene as raw material, the obtained glycerin is called synthetic glycerin.

natural glycerin

Before 1984, all glycerin was recovered from the by-products of soap making from animal and vegetable fats. So far, natural oils and fats are still the main raw materials for the production of glycerin, of which about 42% of natural glycerin is obtained from soap by-products, and 58% is obtained from fatty acid production. Saponification of fats and oils in the soap making industry. The saponification reaction product is divided into two layers: the upper layer mainly contains fatty acid sodium (soap) and a small amount of glycerin, and the lower layer is waste lye, which is a dilute glycerin solution containing salts and sodium hydroxide, generally containing 9-16% glycerin and 8 inorganic salts -20%. Grease reaction. Glycerin water (also known as sweet water) obtained from oil hydrolysis has a higher glycerol content than soap-making waste liquid, about 14-20%, and inorganic salt 0-0.2%. In recent years, the continuous high-pressure hydrolysis method has been widely used, and the reaction does not use a catalyst. The obtained sweet water generally does not contain inorganic acids, and the purification method is simpler than that of waste lye. Whether it is soap making waste liquid or glycerin water obtained from oil hydrolysis, the glycerin content is not high, and all contain various impurities. The production process of natural glycerin includes purification, concentration to obtain crude glycerin, and crude glycerin distillation, decolorization, Refining process for deodorization.

synthetic glycerin

The various pathways for the synthesis of glycerol from propylene can be grouped into two broad categories, namely, chlorination and oxidation. Propylene chlorination and propylene irregular acetic acid oxidation are still used in industry.

Propylene Chlorination

This is the most important production method in the synthesis of glycerol, including four steps, namely high-temperature chlorination of propylene, hypochlorination of chloropropene, saponification of dichloropropanol, and hydrolysis of epichlorohydrin. The hydrolysis of epichlorohydrin to glycerin is carried out in an aqueous solution of 10% sodium hydroxide and 1% sodium carbonate at 150°C and 1.37MPa carbon dioxide pressure to generate an aqueous glycerin solution containing sodium chloride with a glycerin content of 5-20% , after concentration, desalting, and distillation, glycerol with a purity of more than 98% is obtained.

Propylene peracetic acid oxidation method

Propylene reacts with peracetic acid to synthesize propylene oxide, which is isomerized into allyl alcohol. The latter reacts with peracetic acid to generate glycidol (ie, glycidol), which is finally hydrolyzed to glycerin. The production of peracetic acid does not require a catalyst. Acetaldehyde is oxidized with oxygen gas phase. Under the conditions of normal pressure, 150-160°C and contact time of 24s, the conversion rate of acetaldehyde is 11%, and the selectivity of peracetic acid is 83%. The above-mentioned latter two-step reactions are carried out continuously in a special-structured reactive distillation column. After the raw material allyl alcohol and the ethyl acetate solution containing peracetic acid are sent into the tower, the bottom of the tower is controlled at 60-70°C and 13-20kPa. Ethyl acetate solvent and water were evaporated from the top of the tower, and an aqueous glycerin solution was obtained from the tower kettle. This method has high selectivity and yield, adopts peracetic acid as the oxidant, does not need a catalyst, has a fast reaction speed, and simplifies the process. The production of 1t of glycerin consumes 1.001t of allyl alcohol, 1.184t of peracetic acid, and 0.947t of by-product acetic acid. At present, the production of natural glycerin and synthetic glycerin accounts for almost 50% each, while the chlorination of propylene accounts for about 80% of the production of synthetic glycerin. my country's natural glycerin accounts for more than 90% of the total output.

Industrial Grade Glycerin

The amount of industrial grade glycerin is diluted with 1/2 amount of distilled water. After stirring well, add activated carbon and heat to 60-70°C for decolorization treatment. Then, vacuum filter to ensure that the filtrate is clear and transparent. Control the dropping speed, add the filtrate to the column mixed with 732 type strong acid cation resin and 717 type strong base anion and cation resin to absorb and remove the electrolyte and aldehydes, pigments, esters and other non-electrolyte impurities in glycerin.

The glycerin solution after removing impurities is distilled under reduced pressure, the vacuum degree is controlled above 93326Pa, the kettle temperature is 106-108°C, after most of the water is evaporated, the kettle temperature is raised to 120°C for rapid dehydration, and the heating is stopped when no water comes out. The material in the kettle is the finished product.

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