Production process and application of phosphoric acid
Introduction
Phosphoric acid (HPO) is one of the most important industrial chemicals, with global production exceeding 50 million tons annually. As a key intermediate in phosphate chemistry, it serves as the foundation for numerous products ranging from fertilizers to food additives. This article examines the two primary production methods – wet process and thermal process – and explores their respective advantages, limitations, and applications across industries.
1. Production Processes
1.1 Wet Process Phosphoric Acid
The wet process accounts for approximately 90% of global phosphoric acid production due to its cost-effectiveness for fertilizer-grade acid.
Chemical Principle
The core reaction involves treating phosphate rock with sulfuric acid:
Ca(PO)F + 5HSO + 10HO 3HPO + 5CaSO2HO + HF
Production Steps
- Raw Material Preparation: Phosphate rock (typically 30-40% PO content) is ground to 100-150 m particle size.
- Acidulation: Reacted with 93-98% sulfuric acid in a series of stirred reactors at 70-80C.
- Filtration: Gypsum (CaSO2HO) byproduct is separated using vacuum belt filters.
- Concentration: Evaporated from 28-32% PO to 40-54% PO in forced-circulation evaporators.
Technical Parameters
- Typical PO recovery: 92-96%
- Energy consumption: 0.9-1.2 GJ/ton PO
- Impurities: 2-4% fluorosilicates, 1-2% iron/aluminum compounds
1.2 Thermal Process Phosphoric Acid
The thermal process produces high-purity acid (75-85% HPO) for food and technical applications.
Production Mechanism
- Phosphorus Production:
2Ca(PO) + 6SiO + 10C P + 6CaSiO + 10CO (at 1400-1500C) - Combustion & Hydration:
P + 5O PO PO + 6HO 4HPO
Key Process Stages
- Electric furnace: Reduces phosphate rock with coke and silica
- Condensation: Phosphorus vapor is condensed under water
- Combustion tower: P burns in excess air at 1800-3000C
- Hydration tower: PO gas is absorbed in recycled phosphoric acid
Quality Specifications
- Purity: 85% HPO
- Heavy metals: <1 ppm As, <10 ppm Pb
- Color: APHA 20
2. Comparative Analysis
| Parameter | Wet Process | Thermal Process |
|---|---|---|
| PO concentration | 28-54% | 75-85% |
| Energy consumption | Low | Very high |
| Capital cost | $200-400M/plant | $500-800M/plant |
| Product purity | Technical grade | Food/pharma grade |
| Byproducts | Gypsum (5-6t/t) | None |
3. Industrial Applications
3.1 Fertilizer Production (Wet Process)
- MAP/DAP: 60% of global output becomes (NH)HPO/NHHPO
- NPK fertilizers: Provides water-soluble phosphorus
- Superphosphates: Reacts with phosphate rock to create Ca(HPO)
3.2 Food Industry (Thermal Process)
- Acidulant: E338 in colas (0.05-0.1%) and processed cheeses
- pH control: Adjusts acidity in jams (pH 3.0-3.5)
- Chelating agent: Binds metal ions in meat products
3.3 Other Applications
- Metal treatment: Phosphating for steel (2-5% solutions)
- Detergents: Builder in TSP formulations (NaPO)
- Electronics: Etchant for silicon wafers (85% solutions)
- Pharmaceuticals: Excipient in dental cements
4. Environmental Considerations
- Wet process: Gypsum stacks may contain 0.2-0.5% residual PO
- Thermal process: Energy intensity (~12 MWh/ton P)
- Emerging technologies: Hemihydrate process reduces waste by 30%
Conclusion
While the wet process dominates bulk production for fertilizers, the thermal method remains essential for high-purity applications. Ongoing developments in purification techniques (solvent extraction, membrane filtration) are blurring the traditional quality divide between the two processes. Future advancements may focus on reducing the environmental footprint through improved byproduct utilization and energy recovery systems.
PolyblueChem is the supplier of Phosphoric acid, CAS:7664-38-2
Further technical detail on phosphoric
The following sections expand on the technical and practical aspects covered above.
Production Methods of Phosphoric Acid
Phosphoric acid is produced primarily by two methods: the wet process and the thermal process. Each method produces phosphoric acid of different purity levels, and the choice of process depends on the intended application.
1. Wet Process (Most Common)
The wet process is the most widely used method for producing phosphoric acid, particularly for use in fertilizers. This process involves reacting phosphate rock (typically calcium phosphate, Ca3(PO4)2) with sulfuric acid (H2SO4) to form phosphoric acid and calcium sulfate (gypsum).
In the production of fertilizers, phosphoric acid is obtained through the wet process, which is then used to create monoammonium phosphate (MAP) or diammonium phosphate (DAP) fertilizers. These fertilizers are key in promoting plant growth due to their high phosphorus content, which is vital for root development and flowering. For example, in agricultural regions of the U.S. Midwest, where corn and wheat are grown, DAP is a critical fertilizer in maintaining soil fertility and boosting crop yields.
2. Thermal Process
The thermal process involves burning elemental phosphorus in oxygen to form phosphorus pentoxide (P4O10), which is then hydrated to produce phosphoric acid. This method is used when high purity is required, such as in the food and pharmaceutical industries.
Food-grade (thermal) phosphoric acid is the standard acidulant in cola-type soft drinks, where it provides a sharp, tangy flavor and acts as an acidity regulator to balance sweetness. It is also used in jams and processed foods where a controlled pH is needed.
Energy Production
Phosphoric acid plays a crucial role in the production of fuel cells, particularly in Phosphoric Acid Fuel Cells (PAFCs). Phosphoric acid acts as an electrolyte, facilitating electrochemical reactions to generate electrical energy. These fuel cells hold great potential in energy production and storage.
Phosphoric acid fuel cells (PAFCs) are used for stationary power where a stable, continuous supply is needed, for example as backup power for data centres and industrial facilities.
Phosphate-based lithium iron phosphate (LiFePO4) batteries also play an important role in some high-end electric vehicles and buses as an alternative. These batteries are a significant choice in the electric vehicle sector due to their higher stability and safety, with increasing demand in markets like China and Europe.
Phosphoric acid, as an acidulant and pH regulator, is widely used in the pharmaceutical and cosmetic industries. In drug manufacturing, phosphoric acid is often used as an excipient to adjust pH levels and improve stability. Phosphoric acid can also be a source of calcium-phosphate compounds, which are widely used in treating osteoporosis.
In pharmaceutical products, phosphoric acid and its salts are commonly used as excipients to stabilise drugs or regulate pH. Phosphate salts are also used in calcium supplements to support calcium absorption.
In the cosmetics industry, phosphoric acid is used in acid-based exfoliating products that help remove dead skin cells and promote skin renewal.
Phosphoric acid is widely applied in industrial cleaning and descaling, particularly in chemical plants and the power industry. Phosphoric acid can effectively remove scale and oxides from metal surfaces, preventing equipment damage and enhancing efficiency.
In thermal power plants and nuclear plants, phosphoric acid is used to clean scale and mineral deposits from boilers and heat exchangers. Phosphoric acid treatment can remove hard water mineral deposits from the equipment’s surfaces, maintaining optimal performance of the heat exchangers and preventing efficiency losses. In many industrial facilities, phosphoric acid is also used to remove oxide layers and rust from metal surfaces, ensuring the longevity of the equipment. For example, in the petrochemical industry, phosphoric acid is often used to clean pipelines and reactors to prevent corrosion and efficiency degradation.
Phosphoric acid is also widely used in the electronics industry, particularly in the manufacturing of printed circuit boards (PCBs) and semiconductors. Phosphoric acid is used to clean and etch metal surfaces, ensuring proper connectivity and stability of the components.
In semiconductor manufacturing, phosphoric acid is used to clean silicon wafers and remove surface oxides and impurities. Combined with fluorides, it can selectively remove metal layers while preserving the conductivity of the semiconductor material.
In PCB manufacturing, phosphoric acid is used to clean and etch copper circuits, removing excess copper to leave precise circuit patterns and helping to protect the performance and stability of the board.
Phosphoric Acid: Grades
Phosphoric acid (H3PO4, CAS 7664-38-2) is supplied in several grades, and the grade – not just the concentration – determines what an application can use.
| Grade | Concentration supplied | Typical use |
|---|---|---|
| Technical / industrial grade | 75% and 85% | Metal treatment (phosphating), water treatment, general industry |
| Food grade (E338) | 85% only | Acidulant in foods and beverages; requires tight heavy-metal limits |
| Fertiliser grade | Various | Phosphate fertilisers and feed phosphates |
| Electronic / high-purity grade | Various | Semiconductor and high-purity process use |
Food-grade phosphoric acid is defined by strict limits on arsenic, fluoride and heavy metals, which is why it commands a premium over technical grade despite being the same molecule.
How Phosphoric Acid Is Made: Wet vs Thermal Process
Two industrial routes dominate, and they produce very different qualities of acid.
| Route | Feedstock | Product quality | Main use |
|---|---|---|---|
| Wet process | Phosphate rock + sulfuric acid | Contains impurities; lower purity | Fertilisers and industrial phosphates |
| Thermal process | Elemental phosphorus burned to P2O5, then absorbed in water | High purity | Food-grade, technical and high-purity acid |
In the wet process, phosphate rock is digested with sulfuric acid and the phosphoric acid is separated from the calcium sulfate (gypsum) by-product. In the thermal process, elemental phosphorus is burned and the resulting phosphorus pentoxide is absorbed in water to give very pure acid. The thermal route is more energy-intensive, which is why food-grade acid carries a higher cost.
Applications of Phosphoric Acid
| Sector | Use |
|---|---|
| Fertilisers | The largest use – phosphate fertilisers and animal-feed phosphates |
| Food and beverage | Acidulant (E338) in soft drinks, jams and processed foods |
| Metal treatment | Phosphating of steel surfaces before painting or forming |
| Water treatment | pH adjustment and scale/corrosion control in water systems |
| Cleaners and detergents | Acid cleaning and descaling formulations |
| Other | Catalysts, dental products, and as a chemical intermediate |
Handling and Storage
Phosphoric acid is a corrosive mineral acid. Concentrated solutions should be handled with appropriate personal protective equipment, and spills neutralised carefully. It is normally stored in acid-resistant vessels (for example stainless steel or plastic) and kept away from strong bases and reactive metals. The safety data sheet should be consulted for full handling, first-aid and transport information.
Industrial Grade vs Food Grade Phosphoric Acid
| Property | Industrial / technical grade | Food grade (E338) |
|---|---|---|
| Concentration offered | 75% and 85% | 85% only |
| Typical standard | Industrial specification | Food-grade monograph (E338) with tight limits |
| Arsenic and heavy metals | Per industrial specification | Strictly controlled, low ppm / ppb limits |
| Fluoride | Per industrial specification | Tightly limited |
| Typical use | Phosphating, water treatment, cleaning, catalysts | Soft drinks, jams, processed foods and food processing |
| Documentation | COA and SDS per batch | COA and SDS per batch, food-grade specification |
Both grades are the same molecule (H3PO4, CAS 7664-38-2); the difference is the impurity profile and the paperwork. Food-grade acid is made from high-purity acid so that arsenic, fluoride and heavy metals stay inside the food limits, while industrial acid is supplied against an industrial specification for lower-cost process use.
Concentrations We Supply
| Concentration | Grades available | Notes |
|---|---|---|
| 75% H3PO4 | Industrial / technical | Common strength for phosphating, cleaning and acidulation where 85% is not required |
| 85% H3PO4 | Industrial / technical and food grade (E338) | The standard commercial strength, and the only concentration offered as food grade |
If your process needs a different strength, 75% and 85% can be diluted to the target concentration on request. Tell us the grade and concentration when you request a quotation.
REACH Registration and Supplying the European Market
Phosphoric acid (CAS 7664-38-2) is a widely used substance in the EU, and we supply it as a REACH-registered substance so that European customers do not have to register it themselves in order to buy. We support EU deliveries with the documentation European buyers normally ask for:
- REACH status – supplied as a REACH-registered substance; the exact status is confirmed per order.
- Food additives – food-grade acid corresponds to E338.
- Documentation – specification, certificate of analysis (COA) and safety data sheet (SDS) issued per batch.
- Packaging and delivery – drums, IBCs and bulk for EU destinations, with transport documents.
- Paperwork – documents issued in English; confirm any additional EU requirements before shipment.
If you are buying phosphoric acid for a European plant, tell us the grade, concentration, annual volume and delivery port, and we will quote against your specification.
Frequently Asked Questions about Phosphoric Acid
What concentrations of phosphoric acid do you supply?
We supply 75% and 85% phosphoric acid as aqueous solutions. The 85% grade is available in both industrial and food grades, while the 75% grade is available as industrial acid.
Is food-grade phosphoric acid available in 75%?
Food-grade phosphoric acid (E338) is supplied at 85%, the standard commercial strength for food and beverage use. If your application needs a lower strength, 85% food-grade acid can be diluted to the target concentration.
Do you have REACH registration for phosphoric acid?
Yes – phosphoric acid (CAS 7664-38-2) is supplied as a REACH-registered substance for the European market. Confirm the exact status and documentation you need when you request a quotation.
Can you ship phosphoric acid to Europe?
Yes. We support EU deliveries with specification, COA and SDS per batch and appropriate packaging and transport documentation. Tell us the delivery port and volume for a quotation.
What is phosphoric acid used for?
Its largest use is in phosphate fertilisers, alongside food and beverage acidulation, metal phosphating, water treatment and industrial cleaning and catalysis.
What is the difference between food-grade and technical-grade phosphoric acid?
Both are H3PO4, but food grade (E338) must meet strict limits on arsenic, fluoride and heavy metals. Technical grade is used where those limits are not required.
How is phosphoric acid produced?
By the wet process (phosphate rock digested with sulfuric acid) or the thermal process (elemental phosphorus burned and absorbed in water). The thermal process gives higher-purity acid for food and technical use.
What concentration is supplied?
Most commonly about 85% as an aqueous solution, with 75% and other concentrations available depending on grade and application.
Is phosphoric acid the same as phosphate?
No. Phosphoric acid is H3PO4, an acid; phosphates are its salts and esters. Phosphoric acid is a precursor to phosphate products.
How should phosphoric acid be stored?
In acid-resistant, closed containers, away from strong bases and reactive metals. Consult the SDS for handling and first-aid information.
How do I buy phosphoric acid?
PolyBlueChem supplies phosphoric acid (CAS 7664-38-2) in food and technical grades. Contact our team for specifications, COA and a quotation.
Related reading
- Phosphoric acid price and supply: what drives the cost
- Phosphoric acid supply to Africa
- Phosphoric acid in water treatment and industrial cleaning
- How to buy phosphoric acid: a buyer’s guide
- Phosphoric acid in metal phosphating and surface treatment
- Food-grade phosphoric acid (E338): uses and selection
- Phosphoric Acid (CAS 7664-38-2) – product page