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What is the development history of tannins?

The complex organic compounds contained in Chinese gallnuts. Also known as Chinese tannins. After gallnuts are extracted and concentrated, tannins for industrial use can be made. After further refining, it can be made into medicinal or reagent tannic acid.

A brief history

In 734 AD (the 22nd year of Kaiyuan of the Tang Dynasty), Chen Zangqi listed gallnut in the pharmacopoeia in "Supplementary Materials of Materia Medica". In the "Compendium of Materia Medica" written by Li Shizhen of the Ming Dynasty, there is a record of gallnuts being "made into a decoction of hundreds of medicines to dye soap color, which is of great use". In 1862, gallnuts came as far as Europe. In 1887, S. Mierzinski used Chinese gallnuts to extract tannins as tannins. In 1936, Li Fuhua and others wrote an article introducing Chinese gallnuts and their utilization. Around 1940, Wu Bingyan, Wei Wende, Fang Xinfang and others from the China Huanghai Chemical Industry Society studied methods of extracting tannins from gallnuts and fermenting them to produce gallic acid. During the same period, factories were set up in Shanghai and Chongqing to produce tannic acid and gallic acid. In 1957, Shanghai Renji Chemical Factory moved to Guizhou, where gallnuts are produced, and built a second chemical factory in Zunyi City to continue production. In 1988, Hubei applied new technology and new equipment to build a modern tannic acid (series products) factory in Zhushan County. There are also several small-scale tannin workshops in Henan, Shaanxi, Hunan, Yunnan and other provinces. The annual production capacity of tannic acid factories (workshops) nationwide is about 3,000 tons.

Since the 1830s, Turkey, Peru, and Venezuela have successively used Turkish oranges (also known as dyed oak berries) and cloud pods to produce tannic acid or gallic acid. It is still processed and utilized today.

Physical and Chemical Properties

Tannic acid is a light yellow to light brown powdery amorphous product. It has no special smell, has a bitter taste and has astringent properties. Soluble in cold water, infinitely soluble in hot water; soluble in methanol, ethanol, acetone and ethyl acetate, insoluble in benzene, ether, chloroform, petroleum ether and carbon disulfide. Tannic acid aqueous solution is weakly acidic and easily oxidized. It oxidizes faster in alkaline solutions and makes the solution darker. When encountering ferric ions, the solution turns blue-black and reacts with gelatin and alkaloids to produce precipitation. It reacts with lead, aluminum, zinc, germanium and other metal ions to form multinuclear complexes. Tannic acid decomposes into pyrogallic acid and CO2 when heated to 210-215°C.

Tannic acid (powder) has a bulk density of 400 to 600 kg/cubic meter. The viscosity when containing 10 to 250 grams of tannic acid per liter is 0.001 to 0.005 Pas.

Industrial tannic acid made from gallnuts (gallnuts or gallnuts) contains about 80% of tannins, and also contains a small amount of gallic acid, metagallic acid, trimallic acid and quintuple acylglucose, etc. . Tannic acid is based on 1,3,4,6-tetra-O-galloyl-2-poly-O-galloyl-β-D glucose as the core, and is composed of 1 molecule of glucose and 8 to 9 gallic acids. made of ester. Tannic acid is easily hydrolyzed by acids or enzymes, and the hydrolysis products are gallic acid and glucose. (See Plant Tannins)

In 1985, the U.S. Food and Drug Administration classified tannins as generally recognized as safe (GRAS), indicating that they are harmless or not hazardous. It can be used in the preparation of drugs and cosmetics; as an ingredient in foods such as frozen dairy products, meat products or beverages such as soda, tea, and wine.

Quality

Table 1

Table 2 Processing method

Including the steps of purification, extraction, concentration and drying of grapes. The colloids should be iron-removed and sieved to remove iron and insect corpses, and then sent to the leaching tank. Traditional leaching methods are carried out in wooden barrels or metal tanks. Use a group of 8 to 10 tanks to perform countercurrent circulation leaching to obtain the leaching liquid. In 1986, China adopted a flat-type continuous extractor (see picture) to achieve the same effect as tank group extraction under the conditions of 12 to 16 hours, 60 to 85°C, and adding 500% water. The extract liquid is about 6 Baume, and the tannin extraction rate is over 95%.

The continuous extractor is made of stainless steel and has two layers: an outer ring and an inner ring. The upper layer of the inner ring is a rotatable raw material grid. One circle is divided into 16 grids and is driven by a transmission device. The rotation time can be adjusted as needed, such as one revolution every 8, 16 or 24 hours. The lower part consists of 8 to 10 solution grids in a circle. During leaching, the raw materials are added to the bucket through the screw feeder, and the solution in the solution grid is continuously sprayed through the solution circulation pipe and the spray pipe. As the raw material grid rotates, the bucket in the same grid continuously passes through the lower compartments of solutions with different concentrations. Rinse on the ground and complete the extraction. The waste residue in the grid is discharged from the slag discharge hopper.

The colloidal extract released from the continuous extractor is first clarified in the liquid storage tank, and then sent to the vacuum evaporator (external heating type or falling film type) to concentrate to above 25 Baume, and then After the concentrated liquid is dried by a centrifugal sprayer (see tannin processing technology), a powdery product - industrial tannic acid is obtained.

When preparing medicinal tannic acid (or reagent tannic acid), the extract or concentrated solution is frozen and clarified to remove gums, dextrin, etc., and the clarified solution undergoes ion exchange to remove harmful substances in the solution. Metal ions (Pb, As) removal. Then dry it in a special centrifugal spray dryer. Approximately 1.5 tons of glutinous rice seeds produce 1 ton of industrial tannins, or 0.55 tons of medicinal tannins.

Uses

Industrial tannic acid: ① Used as raw material for gallic acid and pyrogallic acid. ②Mordant. Used for fiber fixation or dyeing, as salt-based dye. ③Ore flotation agent. Extract germanium from lead-zinc ore or smoke, extract rare metals such as thorium and polonium from solution, and extract lead and copper from chalcopyrite. ④Conversion coating. Aluminum and its alloy plates, steel, copper, zinc surface corrosion protection, etc. ⑤Food additives. Such as food antioxidants, beverage clarifiers, premium inks and printing inks. ⑥Drilling mud diluent. ⑦ Synergist. Synthesis of 2,4-diamino-5-(3,4,5-trimethoprim) (trimethoprimam), referred to as TMP or sulfonamide synergist. ⑧Deodorant. Used to remove ammonia and other odors in refrigerators, warehouses, and toilets. In addition, it can also synthesize medicines for heart diseases such as crotondiamine and crotonzolin; synthesize biphenyl diester to treat hepatitis B; synthesize antimony-273 to treat schistosomiasis.

Medicinal tannic acid: directly used in beverages, frozen products, candies, ice cream, and meat products; used as burn and scald wound astringent, gastrointestinal hemostatic agent to prevent infection; can be made into tannin glycerin , tannic acid protein, tannic acid ointment, anti-cold agent (N-diamidinomorpholine tannate), health promoter, insect repellent, insecticide, radiation protection agent, contraceptive agent and special toothpaste, etc.

Trends

The demand for tannins used in the synthesis of drugs has increased year by year since the 1970s, but the production of gallnuts has been reduced due to natural conditions and artificial destruction (tangerine harvesting) . In the future, orange production should be increased for use in pharmaceutical and chemical industries. At the same time, we explore alternative raw materials and develop new products.