Analysis of the application of precious metal catalysts in hydrogenation towers for h₂o₂ production
In the anthraquinone process for h₂o₂ production, the hydrogenation tower is a core unit, where precious metal catalysts are dominated bypalladium (pd)-based catalysts. Common types include:
- Supported pd catalysts: Such as pd/al₂o₃ and pd/c (activated carbon support), with pd loading typically ranging from 0.3% to 0.5%. By highly dispersing pd nanoparticles on the support surface, the utilization efficiency of active sites is maximized.
- Alloy catalysts: Some processes use pd-ag or pd-pt alloy systems. By adjusting electronic effects and geometric structures, these alloys enhance selectivity and poisoning resistance. For example, pd-ag alloys reduce excessive hydrogenation of anthraquinones to by-products.
Ii. Mechanism of action
In the hydrogenation tower, precious metal catalysts generate hydroanthraquinones (key intermediates) through the"Anthraquinone hydrogenation reduction"Reaction. The core mechanism is as follows:
1.Hydrogen activation: H₂ molecules are adsorbed and dissociated on the pd surface to form active hydrogen atoms (h*).
2.Anthraquinone adsorption and hydrogenation: 2-ethylanthraquinone (eaq) in the working solution binds to pd active sites via c=o bonds, and h* is gradually added to the carbonyl group to form 2-ethylhydroanthraquinone (heaq).
3.Product desorption: Heaq desorbs from the catalyst surface and enters the subsequent oxidation unit to generate h₂o₂.
Key feature: The d-electron orbitals of pd can stably adsorb π-electrons of anthraquinone molecules while avoiding excessive hydrogenation of c=c bonds, ensuring high-selectivity heaq production (selectivity > 95%).
Iii. Application advantages
Compared with traditional ni-based catalysts, precious metal pd-based catalysts offer significant advantages in h₂o₂ hydrogenation towers:
1.High activity and selectivity: They achieve >98% anthraquinone conversion and >95% heaq selectivity under mild conditions, with by-products (e.g., tetrahydroanthraquinone) accounting for <2%, thus improving h₂o₂ yield.
2.Excellent stability: Pd exhibits strong chemical inertness, resisting corrosion from trace water and organic acids in the working solution. Its service life can reach 6–12 months (vs. 3–6 months for ni-based catalysts), reducing replacement frequency.
3.Low energy consumption and environmental friendliness: Operation under low temperature and pressure reduces energy consumption (15–20% more efficient than ni-based catalysts). Additionally, spent catalysts enable >99% pd recovery via precious metal recycling technologies (e.g., roasting-dissolution), aligning with circular economy principles.
4.Strong process compatibility: Suitable for various hydrogenation tower configurations (fixed bed, fluidized bed, etc.), it operates stably in large-scale h₂o₂ plants (capacity >100,000 tons/year), meeting large-scale production needs.
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