Sodium tripolyphosphate

Sodium tripolyphosphate can be divided into high-temperature type (type I) and low-temperature type (type ii) due to different formation temperatures. the difference lies in the different bond lengths and bond angles of the two types of sodium tripolyphosphate. both type I and type ii products generate hexahydrate Na5P3O10·6H2O after hydration. under the same conditions, type I hydration produces high heat quickly, and when dissolved in water, it is easy to generate caking phenomenon. this is due to the presence of sodium ions in type I structure with four ligands, which have strong affinity for water, whereas type ii generates hexahydrate at a very slow speed in water.
Sodium tripolyphosphate
is quite stable at room temperature, and will slowly undergo hydrolysis reaction in humid air to finally generate sodium orthophosphate, and the reaction is as follows: Na5P3O10+2H2O→2Na2HPO4+NaH2PO4.
Chelating Ability to Metal Ions
Sodium tripolyphosphate has complexation with metal ions such as Ca2+, Mg2+, Fe3+ dissolved in water to form soluble complexes, such as: na5p3o10+Ca2+→ na3 (cap3o10)+2na+.
The complexing ability of sodium tripolyphosphate is generally expressed in terms of calcium value, i.e. the gram number of calcium ions that can be complexed by 100g of phosphate, and the theoretical value is 13.4.
buffer action
The aqueous solution of sodium tripolyphosphate is weakly alkaline (the PH value of 1% aqueous solution is about 9.7), and it forms a suspension (similar to emulsion) in water with a PH of 4.3-14, i.e. dispersion. Sodium tripolyphosphate can also enable liquid and solid particles to be better dissolved in liquid (such as water) medium, making the solution completely transparent in appearance, like a real solution, which is solubilization. As sodium tripolyphosphate has the above unique properties, it becomes an important ideal raw material in washing powder. [3]
Production process

Sodium tripolyphosphate is prepared by neutralizing phosphoric acid with soda ash to form sodium orthophosphate, and then condensing. There are two methods to produce phosphoric acid: wet method and thermal method. Wet process is to react phosphate rock with inorganic acid (usually sulfuric acid or hydrochloric acid), then extract and refine to obtain phosphoric acid. The thermal method is to roast phosphate rock together with coke and silica in an electric furnace, reduce phosphate rock to phosphorus, and then oxidize and hydrate to obtain phosphoric acid.
The process of preparing sodium tripolyphosphate
from orthophosphate is relatively simple, with short process and convenient control operation. There are mainly two methods.
(1) spray drying-converter polycondensation two-stage method: the spray dryer is a cylinder, the upper part of which is connected with a horizontal burner with a gas nozzle. The gas with the temperature of 400-500℃ is introduced into the upper part of the spray drying tower through the burner, and at the same time, the solution of orthophosphate is injected by a high pressure (4.2MPa) pump. Dried products containing less than 5% water are continuously taken out from the lower part of the dryer. Orthophosphate mixture is dehydrated and polycondensed into sodium tripolyphosphate in revolver. The method is characterized in that the product does not need to be crushed, the spray dryer has high drying efficiency, the dried materials are uniform, and delamination phenomenon does not occur. The disadvantage is that drying and polycondensation are carried out in two stages, and dust loss is large when directly heating and dehydrating.
(2) Drying-dehydration one-stage method: the slurry is sprayed into the revolver, and hot gas or burning oil is sent into the furnace through a nozzle to heat. The annular baffle divides the furnace into a flame section and a heating section. In the heating section, the material is finally dehydrated and polycondensed to be converted into sodium tripolyphosphate. The cooling cylinder is connected with the revolver as a whole. Granular products from the cooling cylinder are ground in a grinding machine, and a small amount of powder from the furnace is recovered in a cyclone separator. This method combines drying, dehydration and cooling in one unit equipment, which greatly simplifies the process, has high heat utilization rate, and can reduce infrastructure investment and improve working conditions.
Technical requirements
1. Appearance: white particles or powder
2. industrial Sodium Tripolyphosphate shall meet the requirements of the following table (GB9983-2004)
Project indicators
Excellent products, first-class products, qualified products
Whiteness,% ≥ 90.085.080
Phosphorus pentoxide (P2O5),% ≥ 57.0 56.5 55.0
Sodium tripolyphosphate (Na5P3O10) content,% ≥ 96.0 90.0 85.0
Insoluble sludge content,% ≤ 0.10 0.10 0.15
Iron content (Fe),% ≤ 0.007 0.015 0.030
PH value (1% solution) 9.2-10.0
The sieving rate of the particle size passing the 1.00mm test sieve is not less than 95%
Content analysis
(FCC law)
I preparation of reagents

1。 Potassium Acetate Buffer (pH5.0) Take 78.5g of Potassium Acetate, dissolve in 1000mL of water, and adjust the solution to pH5.0 with acetic acid. Add a few milligrams of Mercury(II) iodide to inhibit mold growth.
2。 Take 22.35g of potassium chloride from 0.3 mol/L potassium chloride solution, dissolve in water, add 5mL of the above-mentioned Potassium Acetate buffer solution, dilute with water to 1000mL, and mix well. Add Mercury(II) iodide, mg.
3。 Take 4.7g of potassium chloride from 0.6 mol/L potassium chloride solution, dissolve in water, add 5mL of the above-mentioned Potassium Acetate buffer solution, dilute with water to 1000mL, and mix well. Add Mercury(II) iodide, mg.
4。 Take 74.5g of potassium chloride from 1mol/L potassium chloride solution, dissolve it with water, add 5mL of the above-mentioned Potassium Acetate buffer, dilute it with water to 1000mL, and mix. Add Mercury(II) iodide, mg.
II. Chromatographic Columns
Using a standard chromatographic column with a length of 20-40 cm and an inner diameter of 20-28 mm, seal a coarse-hole sintered plate. If there are no stoppers respectively, connect a short polyethylene hose at the outlet of the column, and then connect a stopcock with an aperture of 3-4 mm.
III. Operation
Close the stopcock, fill the space between the sintered plate and the stopcock with water, and connect a vacuum line to the stopcock. Using 100-200 mesh or 200-400 mesh strong alkali anion exchange resin (Dowex 18) or styrene/divinylbenzene ion exchange resin of similar grade, and water according to the ratio of 1:1 to make each slurry. Decant the extremely fine particles and foam, and repeat this for 2-3 times, or until there is no fine suspended matter or foam. Fill the chromatographic column with slurry, open the stopcock, and vacuum the tree bed until the water level is slightly higher than the top of the Resin bed, then immediately close the stopcock. Under no circumstances should the water level be lower than the resin level. This is repeated until the resin is 15cm higher than the sintered plate. Take a piece of filter paper closely attached to glass fiber and place it on the top of Resin bed, then take a perforated polyethylene dish and place it on the filter paper. You can also install a layer of loose glass wool on top of the Resin bed. Plug the top of the column with a rubber stopper, insert a 7.6cm long capillary tube (inner diameter 1.5mm, outer diameter 7tnm) in the center of the rubber stopper, and extend about 12mrn below the stopper. Connect the capillary tube with a 500mL separatory funnel lower tube using a length of polyethylene hose. And put separatory funnel in the iron ring above the column. Close all stoppers and add 100mL of water to the separatory funnel to wash the chromatographic column. Loosen the separatory funnel stopcock first, then release the chromatographic column stopcock at a flow rate of about 5mL/min. When the separatory funnel is released, first close the column stopcock, then close the separatory funnel stopcock.
Accurately weigh about 500mg of test sample that has been dried at 105℃ for 4 hours, put it into a 250mL volumetric flask, dissolve it with water and mix it after constant volume. Take 10.0mL of this solution and transfer it to separatory funnel. Open the two stoppers to allow the solution to flow into the chromatographic column. Rinse separatory funnel with water and discard the eluate.
370mL of 0.3mol/L potassium chloride solution was added to the separatory funnel, and the solution was passed through a chromatographic column to discard the eluate. Add 250mL of 0.6mol/L potassium chloride solution to separatory funnel, let the solution pass through the chromatographic column, and collect the eluate in a 400mL beaker. (In order to ensure a clean chromatographic column during the next round of operation, 100mL of 1mol/L potassium chloride solution can be passed through the chromatographic column, with several drops of solution (TS-148), and the solution is neutralized with concentrated ammonia test solution (TS-14). Add 1g ammonium nitrate to crystallize, stir to dissolve, and cool. Add 15mL ammonium molybdate test solution (TS-22) under stirring, and stir strongly for 3min, or place for 10 ~ 15 min under intermittent stirring. The contents of the beaker were filtered by suction filtration, and a 25 mm high porcelain funnel was used, in which a 6 ~ 7mrn thick pulp cushion was placed, and the cushion was covered with a layer of diatomite suspension. After the contents of the beaker are transferred to the filter, the beaker is washed with 1% sodium nitrate or potassium nitrate solution for 5 times and 10mL each time, and the washing liquid is passed through the filter. Then use this lotion to wash the filter 5mL each time 5 times. Return the filter pad and sediment to the beaker, flow them into the beaker with a Photographic processing funnel, and dilute to about 150mL with water. 0.1mol/L sodium hydroxide is added dropwise through a burette until the yellow precipitate is dissolved, and then 5 to 6 RNL is added. Add a few drops of phenolphthalein solution (TS-167) and titrate the excess alkali with 0.1mol/L nitric acid. Finally, it was titrated with 0.1mol/L sodium hydroxide until pink appeared for the first time. The difference between the total amount of 0.1mol/L sodium hydroxide added minus the amount consumed by titration of nitric acid is the amount of 0.1mol/L sodium hydroxide consumed by phosphomolybdate (V; In mL). Finally, the amount of sodium tripolyphosphate (Na5P3O10) in the sample is calculated according to the formula of 0.533×25V, in mg.
Classification
According to its structure and shape, it can be divided into white powder anhydrous substance (Na5P3O10) and hexagonal hydrate (Na5P3O10·6H2O) crystallized from right-angle parallelepiped. anhydrous substance is divided into Type I and Type II. Sodium tripolyphosphate for industrial use is actually a mixture of Type I and Type II. Type I has a fast dissolution rate and a large thermal effect when hydrated to form hexahydrate, which is easy to absorb moisture and agglomerate in the atmosphere. Type II absorbs moisture slowly and is not easy to agglomerate. Therefore, the content of type I in sodium tripolyphosphate for detergent should not be too high, and is generally controlled at 10-30%. [4]
Safety
LD50: 6500 RNG/kg (BW) orally in rats; ADI:MTDI70mg/kg (based on total phosphorus from various sources, FAO/WHO,1994); GRAS:FDA-21CFR173.370; 182.6760 [1] 。
use
Industry
It can be used as detergent additive, and can also be used in petroleum, metallurgy, mining, papermaking, water treatment, etc. It is mainly used as an auxiliary agent for synthetic detergents, as a soap synergist and to prevent soap grease precipitation and silvery. It has strong emulsifying effect on lubricating oil and fat, and can be used to adjust the PH value of buffer soap solution. Water softener for Industrial Water Use. Tanning-agent. Dyeing auxiliaries. In the industries of paint, kaolin, magnesium oxide, calcium carbonate and so on, it is used as dispersant when preparing suspension. Dispersant for drilling mud. The paper industry is used as an anti-oil stain agent. Quality improvers and water retention agents for canned food, fruit juice drinks, dairy products, soybean milk, etc. in the food industry. It is mainly used for tenderizing canned ham and softening bean skin in canned broad bean. It can also be used as softener and thickener.
STPP also has its inevitable environmental hazards. Because it contains phosphorus, it is easy to cause eutrophication of water body.
Due to the introduction of the national phosphorus limitation policy, the application of sodium tripolyphosphate in detergent additives is gradually reduced and gradually replaced by layered sodium silicate, molecular sieve and other products.
Food industry
Water retention agent, quality improver, pH regulator, metal chelating agent. China’s Hygienic Standard for the Use of Food Additives (GB2760-2011) stipulates that the maximum amount of canned food, fruit juice (fruity) drinks and vegetable protein drink is 1.0g/kg;. Dairy products, Poultry products, meat products, ice cream, instant noodles, the maximum amount of ambassador is 5.0g/kg. When compound phosphate is used, the canned meat products shall not exceed 1.0g/kg; based on phosphate. Condensed milk shall not exceed 0.50 g/kg; When this product is used in combination with sodium pyrophosphate and sodium phosphate, it shall not exceed 5g/kg based on phosphate. Western-style cooking and smoked ham shall comply with GB13101-1991 “Hygienic Standard for Western-style Cooking and Smoked Ham”, and the compound usage shall not exceed 5g/kg (western-style ham may be appropriately added, and 8g/kg calculated as phosphate). Other usage reference: For canned ham, it is beneficial to improve the product quality under appropriate conditions, such as the finished product is complete in shape, good in color, tender in meat quality, easy to slice and glossy in section. Sodium tripolyphosphate is used for curing ham raw meat. No.3 mixed salt (refined salt 91.65%, granulated sugar 8%, sodium nitrite 0.35%)2.2kg and sodium tripolyphosphate 85g are added to every l00kg of meat, and the mixture is fully stirred evenly and cured in a cold storage at 0-4℃ for 48-72 hours, with good effect. It can be used in the production of canned broad bean, and can soften bean skin. Many fruits and vegetables have tough skins. As fruits and vegetables mature, the skins become tougher. In fruit and vegetable processing blanching or soaking water, polyphosphate is added to complexe calcium, thus reducing the toughness of the outer skin [1].
Precautions for use
Risk terms: r36/37/38: irrating to eyes, respiratory system and skin. Stimulate eyes, respiratory system and skin.
Security terminology: s24/25: avoidcontact with skin and eyes. Avoid contact with skin and eyes.
Note: s24/25 avoidcontact with skin and eyes. Avoid contact with skin and eyes.
S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice。
After contact with eyes carelessly, please use plenty of clear water to Photographic processing immediately and consult a doctor.
S36 Wear suitable protective clothing。
Wear appropriate protective clothing.
Storage and transportation: Store in a sealed container. Store in a cool, dry and well ventilated place away from incompatible substances. Storage is conducive to protected humidity