Phosphoric acid chemical process activated carbon making machine

Phosphoric acid undergoes the following changes during the whole process:

Low temperature stage (100–200°C): dehydration and esterification Physical changes:
Liquid phosphoric acid (H₃ PO₄) penetrates into the raw material (such as sawdust) and is evenly distributed through capillary action.
Water gradually evaporates, the concentration of phosphoric acid increases, and a viscous liquid film is formed to wrap the cellulose fibers.
Chemical changes:
Dehydration reaction: Phosphoric acid releases H⁺, which reacts with the hydroxyl group (-OH) in cellulose to form phosphate ester (cellulose-OPO₃ H₂)
and removes water:
Cellulose-OH + H₃ PO₄ → Cellulose-OPO₃ H₂ + H₂O Cellulose-OH + H₃ PO₄ → Cellulose-OPO₃ H₂ + H₂O
Ester bond formation: destroys the crystalline structure of cellulose, making it easier to pyrolyze, and fixes the carbon skeleton through cross-linking to prevent excessive shrinkage.

Medium temperature stage (200–400°C): decomposition and cross-linking Physical changes: Phosphoric acid is partially dehydrated to form condensed acids such as pyrophosphoric acid (H₄ P₂O₇) and polyphosphoric acid (H₅ P₃O1₀). The raw materials begin to carbonize, and volatile organic matter (such as tar) is inhibited by phosphoric acid, reducing pore blockage. Chemical changes: Acid-catalyzed cracking: Phosphoric acid accelerates the pyrolysis of cellulose and lignin, generating CO, CO₂ and small molecular organic matter to form initial pores. Cross-linking stability: Phosphoric acid forms P-O-C bonds with the carbon skeleton, enhancing the mechanical strength of the carbon structure and preventing pore collapse at high temperatures. 3. High temperature activation stage (400–600°C): oxidation and pore formation Physical changes: Phosphoric acid is further dehydrated and partially converted into metaphosphoric acid (HPO₃) and phosphorus oxides (such as P₂O₅). The carbon skeleton is etched by phosphoric acid, and a large number of micropores and mesoporous structures are generated.

1.The Principle of Phosphoric Acid in Activated Carbon Preparation:
01.Catalytic Hydrolysis and Dehydration
Phosphoric acid catalyzes the hydrolysis of polysaccharides (such as cellulose and hemicellulose) in biomass precursors (such as wood, plant fiber, and sludge) into oligosaccharides or monosaccharides.
At the same time, phosphoric acid catalyzes the dehydration of oligosaccharides and their degradation products, promoting aromatization and forming a graphite-like microcrystalline structure, which is the basis for the high specific surface area and excellent adsorption properties of activated carbon.
Cross-linking Reaction and Pore Formation
Phosphoric acid forms a stable carbon skeleton by cross-linking with biopolymers. It also creates pores through chemical etching and space-filling during the activation process. After removal of the phosphoric acid, the etched channels and the spaces occupied by the phosphoric acid are converted into pores, thereby increasing the specific surface area and pore volume of the activated carbon.

02.Inhibiting Tar Formation
During the carbonization process, phosphoric acid catalyzes the cleavage of macromolecular bonds, reducing tar formation through cyclization and polycondensation reactions. This helps increase the carbon yield of activated carbon and improve its pore structure.

Effect of Phosphoric Acid on the Pore Size Distribution of Activated Carbon
Pore Size: Phosphoric acid activation tends to form micropores smaller than 2 nanometers, endowing the activated carbon with excellent adsorption properties.
Pore Size Distribution: Higher concentrations of phosphoric acid tend to form more micropores, while lower concentrations or mixed activators may produce a wider pore 03.size distribution.
Porosity: Phosphoric acid activation can significantly increase the porosity of activated carbon and its specific surface area, facilitating its application in adsorption, catalysis, and other fields.

2.Applications of Phosphoric Acid-Activated Activated Carbon:
01.Water Treatment: Activated carbon activated with phosphoric acid can be used to remove organic matter, heavy metal ions, and odors from water, improving water quality.
02.Gas Purification: In the gas purification field, activated carbon activated with phosphoric acid can be used to adsorb harmful gases such as sulfur dioxide and nitrogen oxides, reducing air pollution.
03.Food Decolorization: Activated carbon activated with phosphoric acid can be used in the food industry for decolorization and purification, improving food quality and safety.

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