Conversion of spent solid phosphoric Acid catalyst to environmentally friendly fertilizer.

Area of Science:

• Catalysis and Environmental Science
• Agricultural Chemistry

Background:

• Solid phosphoric acid (SPA) catalysts are extensively used in petroleum refining.
• Spent SPA catalysts are typically landfilled due to disposal challenges, despite high phosphorus content.
• Carbonaceous deposits on spent SPA catalysts pose potential environmental concerns for reuse.

Purpose of the Study:

• To investigate the feasibility of converting spent SPA catalysts into a viable fertilizer.
• To characterize the carbonaceous deposits on spent SPA catalysts.
• To evaluate the environmental safety and agronomic effectiveness of the derived fertilizer.

Main Methods:

• Characterization of carbonaceous deposits using chemical and physical analyses.
• Milling, neutralization with lime and ammonium hydroxide, and calcination of spent catalyst.
• Toxicity characteristic leaching tests (TCLT) for environmental safety assessment.
• Plant growth studies comparing SPA fertilizer with commercial superphosphate.

Main Results:

• Carbonaceous deposits are primarily polyaromatic (amorphous carbon), with minor oxygenates and aliphatics.
• Neither catalyst composition nor coke presence prevented fertilizer conversion.
• TCLT revealed low levels of metals and organics, indicating minimal environmental risk.
• Plant growth studies showed SPA fertilizer effectiveness comparable to superphosphate in alkaline soils.

Conclusions:

• Spent SPA catalysts can be safely and effectively converted into phosphate-rich fertilizer.
• The derived fertilizer is environmentally benign and economically efficient.
• Repurposing spent SPA catalysts offers a sustainable alternative to landfill disposal.