Phosphoric Acid Production via Calcium Sulfate Hemihydrate Conversion
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Solution Overview
Problem
Conventional methods for producing phosphoric acid by attacking phosphate rock with sulfuric acid result in low P2O5 extraction yield and unsuitable gypsum for certain applications, requiring costly and bulky installations for filtration and desulfatation processes.
Innovation Solution
A method involving an initial reaction of phosphate rock with sulfuric acid at 70-90°C to form a dihydrate slurry, followed by heating to solubilize and recrystallize calcium sulfate into hemihydrate, allowing for high P2O5 extraction and filtration of pure phosphoric acid without the need for additional filtration steps or costly installation modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If phosphate rock is attacked by sulfuric acid under conventional conditions to form gypsum slurry, then phosphoric acid is obtained with 25-35% free P2O5 content, but the P2O5 extraction yield is limited and gypsum contains co-crystallized P2O5 making it unsuitable for certain applications
Solution Approach 1:
The patent applies parameter changes by controlling the attack temperature between 70-90°C and adjusting the P2O5 concentration to 38-50% and SO3 content to 0.05-0.5% in the acid aqueous phase. These specific parameter ranges optimize the reaction conditions to achieve high P2O5 extraction yield while preventing co-crystallization of P2O5 in gypsum, thereby improving both extraction efficiency and gypsum purity.
2Ease of operation
If gypsum slurry is subjected to ripening to enlarge sulfate grains for improved filterability, then filtration is enhanced, but the installation size increases enormously requiring two filters
Solution Approach 1:
The patent changes the crystallization parameters by controlling the attack temperature (70-90°C) and acid composition (P2O5: 38-50%, SO3: 0.05-0.5%) to directly form filterable calcium sulfate hemihydrate crystals during the attack process itself, eliminating the need for separate ripening and additional filtration steps, thus maintaining good filterability without increasing installation size.
3Quantity of substance
If the acid aqueous phase has high P2O5 content (38-50%) and low SO3 content (0.05-0.5%), then P2O5 extraction yield is improved, but the free SO3 content must be precisely controlled to avoid contamination
Solution Approach 1:
The patent establishes precise parameter ranges for the acid aqueous phase: P2O5 content of 38-50% and SO3 content of 0.05-0.5%. This controlled parameter range allows high P2O5 extraction while maintaining SO3 content low enough to prevent contamination of the phosphoric acid product, achieving both high yield and product purity through optimized reaction conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances P2O5 extraction yield to over 35% and produces high-quality, pure phosphoric acid with low free SO3 content, utilizing existing infrastructure and simplifying the process while improving filtration coefficients and product suitability.
Implementation Method 1
an attack in an aqueous medium of phosphate rock by means of sulfuric acid at a first temperature comprised between 70 and 90° C., with formation of a first slurry of calcium sulfate dihydrate crystals
Implementation Method 2
formation of a first slurry of calcium sulfate dihydrate crystals in an acid aqueous phase
Implementation Method 3
a conversion of this first slurry by heating to a temperature above 90° C., with solubilization of the calcium sulfate dihydrate crystals
Implementation Method 4
recrystallization of the solubilized calcium sulfate giving rise to a second slurry formed of calcium sulfate hemihydrate crystals
Implementation Method 5
conversion of this first slurry by heating to a temperature above 90° C.
Data Source
AI summary
The invention relates to a method for producing phosphoric acid, including: attacking phosphate rock by means of sulfuric acid between 70° and 90° C. with formation of a first calcium sulfate dihydrate crystal slurry, the aqueous acid phase of said slurry having free P2O5 content between 38 and 50 wt % and free SO3 content that is less than 0.5 wt % and greater than 0.05 wt %; converting said first slurry by means of heating at a temperature greater than 90° C., thus giving rise to a second slurry formed of calcium sulfate hemihydrate crystals; and, within the second slurry, separating a produced phosphoric acid, having a free SO3 content that is less than 2%, and a calcium sulfate hemihydrate filter cake.