Preparation method for polyphosphoric acid

Abstract

The invention relates to the field of phosphorus chemical industry, in particular to a preparation method for polyphosphoric acid. The method for preparing polyphosphoric acid includes: letting dilute phosphoric acid enter a heater through a heat exchange tube acid inlet to be heated to 185DEG C-230DEG C, then discharging the dilute phosphoric acid out of the heater from a heat exchange tube acid outlet, and making the dilute phosphoric acid enter a separator to undergo flash concentration, keeping the vacuum degree in the separator ranging from -500 to -700mmHg, discharging the concentrated acid liquor out of the separator through an acid outlet tube at the lower end of the separator, and leading the concentrated acid liquor into a concentrated acid tank through a concentrated acid tank acid inlet to undergo cooling and storage. The heat exchange tube is coiled in an S shape in the heater, from the heat exchange tube acid inlet to the heat exchange tube acid outlet, the heat exchange tube tilts downward at an angle of 1-3 degrees. The preparation method for polyphosphoric acid provided by the invention has a simple process, can prepare high concentration polyphosphoric acid from dilute phosphoric acid by one-step polymerization. By taking dilute phosphoric acid as the raw material, the acid liquor cannot adhere to the heat exchange tube wall, thus avoiding blocking of the heat exchange tube. Further, the prepared polyphosphoric acid product has uniformly distributed components.

Description

technical field [0001] The invention relates to the field of phosphorus chemical industry, in particular to a method for preparing polyphosphoric acid. Background technique [0002] In the 1930s, the Tennessee Valley Authority Research Institute of the United States found that in orthophosphoric acid (H 3 PO 4 ) and pyrophosphate (H 4 P 2 o 7 ) between liquid phosphoric acid with a eutectic composition. its ωP 2 o 5 is 76% [equivalent to ω (H 3 PO 4 ) is 105%], of which about 49%P 2 o 5 It exists in the form of orthophosphoric acid, 42% is pyrophosphoric acid, and 8% is tripolyphosphoric acid (H 5 P 3 o 10 ), 1% is tetrapolyphosphoric acid (H 6 P 4 o 13 )exist. This mixture of orthophosphoric acid and polyphosphoric acid is called polyphosphoric acid (poly phosphoric acid). [0003] Polyphosphoric acid, also known as tetrapolyphosphoric acid, polyphosphoric acid or polyphosphoric acid, is a colorless, transparent, viscous liquid, easy to deliquescence, non-...

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Problems solved by technology

The above-mentioned method for preparing polyphosphoric acid has the following disadvantages: 1, the mixed acid solution of phosphoric acid and phosphorus pentoxide has a high viscosity, which easily causes blockage in the graphite tube, further causing production accidents; 2, the acid solution is heated in the heat exchange tube , the heat is transferred from the wall of the heat exchange tube to the center of the heat exchange tube. Due to the high viscosity of the hot acid liquid, the mass transfer and heat transfer inside the acid liquid are particularly small, so that part of the acid liquid close to the heat exchange tube wall is prone to polymerization, and the obtained Polyphosphoric acid, and part of the acid liquid close to the center of the heat exchange tube has a low temperature and is difficult to polymerize, which leads to uneven distribution of components in the prepared polyphosphoric acid product; 3. Using high-temperature steam (above 200°C Steam) heats the graphite tube, the pressure of the steam is high and the pressure is easy to fluctuate, the graphite heat exchange tube is prone to rupture, and the strength of the heat exchanger material is high; at the same time, the use of steam to heat the graphite tube results in high energy consumption and high production cost ; 4, utilizing phosphorus pentoxide to produce polyphosphoric acid, the production cost is high and the production process is complicated

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