Tanning agent for tanning
Tannin is mainly used for tanning heavy leather, such as sole leather, industrial leather and accessory leather, accounting for about 80% of the total amount of tannin extract. The whole tanning process is a process in which tannin particles in tannin extract diffuse, permeate, adsorb and aggregate to collagen fibers. Multi-functional groups (phenolic hydroxyl groups) of tannin combine with peptide groups between adjacent molecular chains of collagen, which is an important mechanism of tanning leather. Tanning methods of heavy leather include pool tanning, pool drum tanning and quick tanning with few baths. Tank tanning has been replaced by the other two methods because of its high labor intensity, long tanning period (about 2 months) and low efficiency. Tank-drum tanning method uses the mechanical action of drum to shorten the tanning cycle (about 10 day) and improve the production efficiency. Fast tanning with less bath is a new technology developed in modern times. The tanning period was shortened to about 3 days, and the quality of finished leather met the requirements. Leather tanned with tannin extract has the advantages of high leather yield, firm and plump leather, small extensibility, difficult deformation and strong water resistance.
Woodworking tannin glue
In condensed tannins (such as 155 125 wood tannin extract and black wattle tannin extract), the 6-and 8-position carbon atoms of the tannin molecules cross-link with formaldehyde under the catalysis of alkali or acid to form an adhesive. Tannin glue can replace phenolic glue in wood-based panel production, and the substitution amount of phenol is as high as 80%. Condensed or hydrolyzed tannin extract can also be used as curing accelerator of phenolic adhesive to shorten curing time.
Tannin gum was used in plywood production at 1960. Countries that use tannin glue include South Africa, Australia, India, Finland, the United States, the Soviet Union and Malaysia. There are several methods to prepare tannin gel: ① direct condensation of tannin extract with formaldehyde; (2) Simultaneous condensation of tannin extract, phenol and formaldehyde; ③ After phenol and formaldehyde are condensed, tannin extract is added. Tannin gum can be divided into black wattle tannin gum, 155 125 wood tannin gum and pine tannin gum. According to the curing methods, there are thermosetting tannin glue and cold-setting tannin glue. This glue is used in the production of wood-based panels. In addition, it can also be made into tannin starch adhesive, which can be used as the adhesive of corrugated board. (See Tannic Acid Adhesive)
Mud thinner for drilling
Tannin extract is made by adding a certain amount of caustic soda (1∶ 1), also known as alkaline tannin extract, and its main component is the sodium salt of phenolic carboxylic acid. Sodium phenolcarboxylate can weaken the network structure between clay particles in mud and has a good dilution effect on mud. In the 1940s, it was widely used as a diluent for mud in shallow wells (within 65,438+0,000m). When drilling, the amount of tannin extract accounts for about 1 ~ 3% of the mud volume, and 155 125 wood tannin extract, black wattle tannin extract, chestnut tannin extract and rubber bowl tannin extract are mainly used. Alkaline tannin extract is only used in shallow wells with well temperature below 100℃. After modification, such as adding sulfite, formaldehyde and metal ions (such as zinc, iron and chromium), the temperature resistance and pollution resistance of tannin extract can be improved, and it can be used for higher well temperature (120 ~ 65438+).
Ore flotation inhibitor
The hydroxyl and carboxyl groups of tannin in tannin extract can be adsorbed on the surface of minerals, which can reduce the floatability of minerals and inhibit flotation after forming hydrophilic films. For example, in the flotation of fluorite, scheelite, manganese ore and zinc oxide ore, as an inhibitor of gangue; When flotation is used to enrich iron ore, it is used as an inhibitor of iron oxide.
Under alkaline conditions, tannin in tannin extract and its decomposition products penetrate into the scale, which makes the hard scale crystal structure loose. Under the action of heat in the boiler, the scale cracks and gradually falls off. At the same time, it permeates between the oxide scale and the furnace steel plate to dissolve the iron oxide on the surface of the steel plate and separate the oxide scale. Exfoliated scale is discharged from the furnace body with the dirt to achieve the purpose of scale removal.
When descaling, tannin extract and soda ash are put into the furnace at one time or several times, and the amount of tannin extract is 5- 10 kg per ton of water, and the amount of soda ash is determined according to the scale properties. The dosage of carbonate scale is 1/3- 1/2 of tannin extract, and the pH is controlled at 65438. The dosage of sulfate scale is 1/2 ~ 2/3 of tannin extract, and the pH is controlled at 1 1. When the boiler runs for more than 72 hours, it should be stopped, cooled, drained and descaled. Tannin extract is suitable for descaling of small and medium-sized boilers, and it has a good effect on removing carbonate scale, but it has a poor effect on removing sulfate and silicate scale.
Under alkaline conditions, the following points are used to achieve the purpose of scale prevention: ① Tannin in boiler water forms precipitation with calcium and magnesium plasma; (2) Tannin reacts with iron ions on the furnace wall to form a new protective film, which inhibits the deposition of calcium and magnesium salts on the steel plate surface and prevents the formation of oxide scale. In addition, tannin absorbs oxygen in boiler water, which can prevent oxygen corrosion.
During scale prevention, tannin extract and soda ash are added into the furnace, and the amount of tannin extract is 5-10g per ton of influent per decimeter; Soda consumption, the total alkalinity is greater than the total hardness of high alkaline water, you can not add soda; For water with carbonate hardness with total alkalinity greater than total hardness, the amount of soda ash is1/3 ~1/2 of the amount of tannin extract; For permanent hardness water with total alkalinity less than total hardness, the dosage of soda ash is 1/2 ~ 1 of tannin extract. In the process of scale prevention, sewage discharge should be strengthened, and the sewage discharge should be 5 ~ 10% of boiler water. Pay attention to regular inspection to prevent pipe blockage and accidents. Tannin extract is only suitable for scale prevention of small and medium-sized boilers. Water with high permanent hardness is not suitable for tannin extract scale prevention.
Metal antirust coating
Tannin can react with iron ions to form insoluble and stable iron tannin complex. Taking advantage of this characteristic, tannin extract can be used as conversion agent, film forming agent, pigment, catalyst, netting agent and stabilizer to make conversion rust coating and used as primer to protect metal. Directly coated on the surface of steel with residual rust to passivate the rust and transform the harmful rust into a stable protective substance. Using rusty paint can reduce the workload of rust removal, improve working conditions and improve labor productivity. Treating copper, zinc, aluminum, lead and other metals with tannin extract can also inhibit corrosion.
In addition, tannin in tannin extract condenses with ethanolamine and formaldehyde under acidic conditions to generate secondary amine salt (flocculant) of tannin, which is used to purify drinking water, industrial water and wastewater.