Overview[1]
Sodium tripolyphosphate is a white powdery crystal with good fluidity and is easily soluble in water. Its aqueous solution is alkaline. It is often used in food as a moisture retaining agent, quality improver, pH regulator, and metal chelating agent.
Purpose[2-3]
As a food additive, sodium tripolyphosphate can be used in meat products, aquatic products, dairy products, fruit drinks, etc. as a water retention agent and quality improver; used in ham and steaks to tenderize the meat and improve the taste; It can increase the weight and retain water of seafood and river fresh food; it can be used as an antioxidant in fruit juice drinks to extend the shelf life; it can be used as a dispersing agent for beans and dairy products. In addition, it can also be used as water softener, thickener, etc. in the industrial field. In the food industry or industrial field, sodium tripolyphosphate is generally used in a solution. Currently, when most sodium tripolyphosphate is put into water, it will instantly hydrate to form sodium tripolyphosphate hexahydrate. Sodium tripolyphosphate hexahydrate has low solubility and is Supersaturated state, causing material to agglomerate.
Preparation[2]
The traditional preparation method of sodium tripolyphosphate is to use soda ash suspension to neutralize thermal phosphoric acid with a mass fraction of H3PO4 of 75% to prepare a neutralized slurry with a Na/P ratio of 5:3. The resulting slurry is then sprayed into a polymerization furnace to be dehydrated at high temperatures and condensed into sodium tripolyphosphate at about ℃. This traditional method not only requires expensive thermal phosphoric acid, but also consumes a large amount of heat energy; in addition, when preparing the slurry during neutralization, it also needs to be heated to drive out CO2, which is a complicated process. Although chemically purified wet phosphoric acid can be used instead of hot phosphoric acid to produce sodium tripolyphosphate, due to the high content of metallic iron and other metals in wet phosphoric acid, it is difficult to meet the quality requirements of current sodium tripolyphosphate products, and it is difficult to meet the national standards. indicators specified by the standard.
At present, people have studied some new processes for the production of sodium tripolyphosphate, such as Chinese patent application No. 94110486.9 “A production method of sodium tripolyphosphate” and No. 200310105368.6 “A new process for the production of sodium tripolyphosphate” , No. 200410040357.9 “Method for producing sodium tripolyphosphate using dry and wet integrated method”, 200 Pigment Carbon Black 510020871.0 “Method for producing sodium tripolyphosphate using Glauber’s salt metathesis method”, 200810197998.3 “A method for producing sodium tripolyphosphate with by-product chlorine” “Methods for ammoniumization”, etc.; although these technical solutions have their own characteristics, most of them involve changing the neutralizing raw materials.
Method for producing sodium tripolyphosphate from crude sodium pyrophosphate
Crude sodium pyrophosphate first enters the salt washing tank to remove most of the sodium chloride through salt washing, and then enters the plate and frame filter press for primary filtration. The filter cake contains a large amount of sodium pyrophosphate, and the sodium chloride mass concentration is less than 2.5%, and then use steam to heat the solution to 85°C in the dissolving tank for stirring and dissolution. When dissolving, add sodium sulfide to remove metal ions. The insoluble matter is copper hydroxide and other impurities. Then perform a second press filtration. The filtrate is sodium pyrophosphate. Solution, add activated carbon to the filtrate to remove pigments, add phosphoric acid to acidify, accelerate dissolution, and finally add liquid caustic soda to adjust the pH value to 7.5 to 8.5 to prepare a refined solution.
Part of the refined liquid goes directly to the sodium tripolyphosphate neutralizing liquid preparation section for use, and the other part of the refined liquid is pumped into the DTB crystallizer. The refined liquid in the DTB crystallizer is sent through a forced circulation pump and a chilled water unit at 5°C. The water exchanges heat and cools in the heat exchanger; when the temperature of the solution drops to 15°C, it crystallizes into floc and is transported to a high-level tank and entered into a centrifuge for centrifugal separation to obtain sodium pyrophosphate crystals. The sodium pyrophosphate crystals are added to tripolyphosphoric acid. The neutralizing liquid preparation section in the sodium production process mixes phosphoric acid and liquid caustic soda to prepare a neutralizing liquid as a raw material for the production of sodium tripolyphosphate. Return the above-mentioned washing brine to wash crude sodium pyrophosphate; when the sodium chloride content in the washing brine reaches saturation, the washing brine will be pumped into the buffer tank, and the washing brine in the buffer tank will enter the sodium tripolyphosphate tail gas duct jacket through the pump It exchanges heat with high-temperature exhaust gas, and the washed brine after heat exchange returns to the buffer tank for spray evaporation.
Method for producing sodium tripolyphosphate by one-step condensation polymerization of yellow phosphorus combustion and caustic soda solution
The measured yellow phosphorus with a mass fraction of more than 99.9% is continuously sprayed into the polymerization furnace with 600kPa compressed air, and at the same time, the pressureThe force pump continuously pumps the measured 20% caustic soda solution into the polymerization furnace. The mass ratio of yellow phosphorus to 20% caustic soda solution is controlled at 5:54. The yellow phosphorus is sprayed from the phosphorus gun in the furnace, atomized and burned immediately. Phosphorus pentoxide is generated, and phosphorus pentoxide reacts with 20% caustic soda solution and is condensed at ℃ for 30 minutes to become sodium tripolyphosphate, which is then made into sodium tripolyphosphate product through conventional cooling and crushing processes.
