Manufacturing anhydrous hydrogen fluoride products using fluorosilicic acid.
Fluosilicic acid is a byproduct in several industries, such as the production of phosphate fertilizers and hydrogen fluoride, or it can contain hydrofluoric acid, as in the case of photovoltaic and display panel thinning production lines.
Fluosilicic acid with H2SiF6 concentration greater than or equal to 10% has high economic value as a raw material for producing hydrogen fluoride (AHF).
The higher the concentration of fluosilicic acid, the lower the cost of producing hydrogen fluoride.
Fluosilicic acid is a byproduct of various industries, including phosphate fertilizers and hydrogen fluoride production, and can contain hydrofluoric acid, as is the case in photovoltaic and display panel thinning production lines.
Fluosilicic acid with a concentration of H2SiF6 equal to or greater than 10% has significant economic value as a raw material for producing anhydrous hydrogen fluoride (AHF), and the higher the concentration of fluosilicic acid, the lower the cost of producing AHF.
To produce anhydrous hydrogen fluoride, concentrated sulfuric acid and fluosilicic acid are used as raw materials.
The technical principle involves decomposing the concentrated fluosilicic acid with concentrated sulfuric acid to form a mixed gas of HF and SiF4, separating the gas, converting the HF gas into HF liquid, and rectifying it to obtain anhydrous hydrogen fluoride.
The SiF4 gas is absorbed by dilute fluosilicic acid, which is then concentrated along with the SiF4.
Concentrated sulfuric acid can be recycled within the system after dilute sulfuric acid is concentrated at high temperatures.
The chemical reaction for the decomposition of fluosilicic acid is: H2SiF6 (concentrated) → SiF4↑+ 2HF↑+Q.
The concentration of fluosilicic acid can be achieved through desilication, with the formula 3SiF4+2H2O → 2H2SiF6 (concentrated)+SiO2↓+ Q.
Sulfuric acid can also be concentrated with the formula 70% H2SO4 → 92% H2SO4+H2O–Q.
The recycling process for dilute fluorosilicic acid (H2SiF6≥10%) from phosphate fertilizer production involves several steps
After filtration, impurity removal, and arsenic and phosphorus removal, the purified dilute fluosilicic acid is sent to the concentration unit, where it's mixed with SiF4 gas from the subsequent process to produce new fluosilicic acid and silica.
This Increasing process results increased concentration of fluosilicic acid (H2SiF6≥42%) , then silica separated and cleaned , dried to become a silica product.
The concentrated fluosilicic acid is then mixed with concentrated sulfuric acid in the decomposition reaction unit, producing a mixed gas of silicon tetrafluoride (SiF4) and hydrogen fluoride (HF).
The sulfuric acid becomes diluted with HF (H2SO4≤72%). The SiF4 gas is sent back to the concentration unit for further processing.
Next, the HF gas is condensed into HF liquid using a condenser after the mixed gas absorbs water with concentrated sulfuric acid, which is temporarily stored in the crude acid tank.
Dilute sulfuric acid with HF is sent to the HF desorption unit, where HF is released and becomes HF gas.
The condensed HF liquid is temporarily stored in the crude acid tank for later use.
The HF liquid stored in the crude acid tank is refined in a separate unit where heavy and light components are removed through rectification and degassing, resulting in pure hydrogen fluoride liquid.
After undergoing testing, the hydrogen fluoride liquid is transported to a storage tank and becomes the anhydrous hydrogen fluoride (AHF) product.
The desorbed dilute sulfuric acid enters the concentration unit where water is separated at high temperature, yielding concentrated sulfuric acid with H2SO4≥92% and wastewater (with H2SO4≤1% and HF≤0.1% concentration).
The concentrated sulfuric acid is returned to the sulfuric acid mixer, while the wastewater is treated at the wastewater treatment station and can be returned to the phosphate fertilizer production line or discharged up to the standard.