Riel Chemical realized the phosphoric acid thermal process in 2005, with product purity up to 85%. Production process of phosphoric acid. This industry replaces the wet process of phosphoric acid, which solves the problem of producing up to 65% purity. In 2010, Riel Chemical will publicize this new process without reservation, aiming to protect the environment by improving the utilization rate of phosphorus, and thus maintain the reputation of made in China, improve the market environment and improve the quality of Chinese chemical products.
Thermal method: electric furnace phosphorus → yellow phosphorus combustion → absorption and hydrolysis → phosphoric acid
Wet method:
Inorganic acid decomposition of phosphate rock: commonly used nitric acid, hydrochloric acid, sulfuric acid, fluorosilicic acid
Ca5(PO4)3F+10HNO==3H3PO4+HF+5Ca(NO3)2
Ca5(PO4)3F+10HCl ==3H3PO4+HF+5CaCl2
Ca5(PO4)3F+5H2SO4==3H3PO4+HF+5CaSO4.nH2O
Ca5 (PO4) 3 f + 5 h2sif6 h3po4 = = 3 + HF + 5 casif6. 2 h2o
Because the solubility of calcium sulfate is very small, it is easy to separate from phosphoric acid, so wet phosphoric acid actually refers to phosphoric acid obtained by sulfuric acid decomposition of phosphate rock.
First, thermal phosphoric acid production process
1. Complete combustion method: (one-step method), the furnace gas containing element phosphorus from the electric furnace is directly burned, and the CO in the furnace gas is also burned together:
P4+10CO+10O2==2P2O5+10CO2+△
2P2O5+2H2O == 4HPO3
HPO3+H2O == H3PO4
This method has not been used in industry due to poor heat utilization (strong corrosion of phosphate anhydride, a large number of reaction heat can not be used).
2. Liquid phosphorus combustion method (two-step method),
- Common industrial process, the first: yellow phosphorus combustion → phosphorus penoxide → water cooling, absorption → phosphoric acid, also known as water cooling process.
- The second one: yellow phosphorus combustion → phosphorus penoxide → cold phosphoric acid cooling, absorption → phosphoric acid, also known as acid cooling process.
- Thermal phosphoric acid generally contains > 85% phosphoric acid, high concentration, pure quality, is the main raw material of phosphoric acid for food and pharmaceutical industry.
- Thermal phosphoric acid production with elemental phosphorus, 1 ton of elemental phosphorus can produce 1.38 tons of 100% phosphoric acid, requiring electricity consumption of 12,500 ~ 15,000kwh, is a high energy consumption industry.
Dust removal of furnace gas
The dust content of the furnace gas when it leaves the electric furnace is general: 50 ~ 150g/m3. Dust removal can improve the condensation of phosphorus vapor and phosphorus refining, but the condensation of phosphorus vapor must be prevented when dust removal.
According to the chemical reaction equation, the formation of 1 molecule of phosphorus (P4) simultaneously generates 10 molecules of CO and 0.33 molecules of SiF4, and the phosphorus vapor accounts for 1/11.33 of the total volume of gas. If the system is operated under negative pressure (<90KPa), the partial pressure of phosphorus vapor is < 8 KPa, and the corresponding temperature is 175.7 ℃
In the process of dust removal operation, in order to ensure that phosphorus in the furnace gas exists in gaseous state and avoid the loss of phosphorus, the operating temperature should not be lower than the dew point temperature (160℃) (when the phosphorus vapor content is 300 ~ 350g/m3, the dew point is 160 ~ 170℃)
Common dust removal equipment: phase type dust collector, high voltage electrostatic precipitator (operating temperature >200℃)
Condensation of phosphorus vapor in furnace gas
Generally, two or more columns are used to promote the condensation of phosphorus vapor at suitable supersaturation.
The gas velocity in the tower is general: 0.1 ~ 0.2m/s, and it is difficult to separate the liquid through the atmosphere.
Gas residence time in the tower: >100min
Tower outlet exhaust temperature: <35℃, so that the condensation rate of phosphorus > 99%
Refinement of phosphorus
A small amount of dust is scattered in the condensed liquid phosphorus, which must be further refined to meet the quality standards of yellow phosphorus products.
The density of phosphorus liquid is 1.75g/cm3, which is greater than the density of impurities. With enough time, phosphorus and impurities can be separated, and appropriate additives can also be added to improve the refining efficiency. (such as diatomaceous earth)
When refining, the temperature is generally controlled to destroy the colloidal structure of phosphorus and impurities.
Indirect steam heating and hot water agitation (60~70 ℃) are often used for refining
Refining time: 60 ~ 80℃, generally need more than 16 hours.
Author: RIel Chemical. Release date: April 2010. Last edited: September 2010