Method and equipment for preparing polyphosphoric acid by phosphoric acid microwave flash evaporation

Abstract

The invention discloses a method and equipment for preparing polyphosphoric acid by phosphoric acid microwave flash evaporation. The method comprises the following steps of heating by microwaves undera vacuum condition; performing flash evaporation on raw liquid of phosphoric acid, concentrating and polymerizing, so as to obtain the polyphosphoric acid; condensing tail gas of flash evaporation, and recycling. The equipment comprises a microwave generator, a microwave waveguide, a pressure transmitter, an overhead tank, a liquid intake valve, an infrared temperature sensor, a flash evaporationtank, a reaction tank, a liquid outlet valve, a concentrated liquid collecting tank, a valve, a condensing tower, a condensate collecting tank, a collecting tank valve, a vacuum pump, and a tail gasabsorbing device. The equipment has the advantages that the equipment is simple, the heat efficiency is high, the energy consumption is low, the technological process is short, and the treatment speedis quick; compared with the traditional method, the chroma, purity and the like of the produced polyphosphoric acid are better; a continuous, semi-continuous or discontinuous independent manner can be adopted for production, and the production manners are diversified; the problems of easiness in corrosion of a heat exchange surface and a forced circulating pump, high electric consumption, low product purity and the like in the traditional evaporation process are solved, and the purpose of high-efficiency preparation of the polyphosphoric acid with high polymerizing degree can be realized.

Description

technical field [0001] The invention relates to a new technology for microwave enhanced evaporation to treat highly viscous, low thermal conductivity or highly corrosive solutions, in particular to a method and equipment for preparing polyphosphoric acid by microwave flash evaporation of phosphoric acid, which belongs to the technical field of chemical production. Background technique [0002] Polyphosphoric acid is a colorless transparent viscous liquid, which is easy to deliquescence, does not crystallize, is corrosive, and can be hydrolyzed and dissolved in water to become orthophosphoric acid. The melting point under normal pressure is 48~50°C, the boiling point is 856°C, and the density is 2100kg / m 3 , the relative molecular mass is 337.93. In industry, generally P 2 o 5 Phosphoric acid with a content higher than 68% is called polyphosphoric acid. [0003] Polyphosphoric acid is widely used in pigments, spices, pharmaceuticals, leather, flame retardant manufacturing...

AI Technical Summary

Problems solved by technology

However, these production methods need to consume a huge amount of heat, and the extraction process of the extraction agent in the wet purification extraction process still has problems such as long process flow and difficult control.

[0004] Since wet-process phosphoric acid needs to be heated by high-temperature steam through the evaporator, the concentration and viscosity of phosphoric acid will increase after concentration, which will increase the workload of the circulation pump. Aggregation and fouling affect the heat transfer process of the equipment at the same time, and the equipment needs to be cleaned regularly to maintain the smoothness of the flow and the stability of the equipment.

[0005] When dealing with highly viscous, low thermal conductivity or strong corrosive solutions in the traditional evaporation process, there are many equipment, long process, large area occupation, high energy consumption, scaling, corrosion, high impurity content in products, and environmental pollution caused by coal-fired steam heating, etc. question

In the traditional wet-process phosphoric acid heating dehydration polymerization process, phosphoric acid is heated and evaporated by combining tube-and-tube heating evaporators and forced circulation vacuum evaporators. This type of traditional equipment has complex structures, lengthy processes, and general heat pipe materials. It is graphite or alloy. Among them, graphite heat pipes have stable heat transfer, but they are prone to surface fouling, and graphite materials are relatively brittle. After a period of use, cracks occur and need to be replaced.

Alloy tubes are susceptible to phosphoric acid corrosion during heating, resulting in damage

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