Core Production Process of Hydrogen Peroxide by the Anthraquinone Method (Detailed Explanation)

The anthraquinone process essentially uses 2-alkyl anthraquinone (commonly 2-ethyl anthraquinone, EAQ) as a “hydrogen carrier.” Through a cyclic reaction, it enables the indirect conversion between hydrogen and oxygen to produce hydrogen peroxide (H₂O₂). The overall reaction can be expressed as H₂ + O₂ → H₂O₂, with water as the only by-product. The process mainly consists of the following key steps:

1. Working Solution Preparation

Alkyl anthraquinone (EAQ) is mixed with an organic solvent (such as a mixed solvent of aromatics and trioctyl phosphate, AR + TOP) in a specified ratio to prepare the working solution. This is the “blood” of the entire process and is continuously recycled during operation.

2. Hydrogenation Reaction

The working solution reacts with hydrogen (H₂) in the presence of a palladium (Pd) catalyst in a fixed-bed or fluidized-bed reactor, forming anthrahydroquinone. Typical operating conditions are 40–70°C and 0.1–0.35 MPa. This step is critical to process efficiency, and modern reactor design focuses on optimizing mass transfer and catalyst utilization.

3. Oxidation Reaction

The hydrogenated working solution is contacted with air (or oxygen, O₂), where anthrahydroquinone is oxidized back to anthraquinone while producing hydrogen peroxide. This reaction takes place in an oxidation tower under mild conditions (approximately 40–44°C).

4. Extraction

The oxidized solution enters an extraction tower, where water is used in a counter-current process to extract hydrogen peroxide (H₂O₂), producing a crude aqueous hydrogen peroxide solution. The residual working solution is treated and recycled back to the hydrogenation step.

5. Purification, Concentration, and Post-treatment

The crude H₂O₂ solution is purified to remove impurities and then concentrated via vacuum distillation to produce commercial products at various concentrations (commonly 27.5%, 35%, 50%, and 70%). The solvent is recovered and recycled, ensuring a closed-loop process.

The entire process is highly automated, and the continuous circulation of the working solution is key to long-term operation. Single-pass hydrogenation and oxidation efficiency directly determine production capacity and cost. In recent years, Chinese companies have focused on breakthroughs in hydrogenation reactor optimization and the development of new anthraquinone carrier systems, improving stability and capacity.

From Invention to Industrial Dominance: A Brief History

The anthraquinone process was developed by BASF (formerly IG Farben) in Germany during the 1930s–1940s, replacing energy-intensive electrolysis and isopropanol processes and achieving rapid industrial adoption. China began introducing the technology in 1958 and, through absorption, adaptation, and independent innovation, expanded its production capacity from 28,000 tons per year in 1984 to the world’s largest today.

Currently, fixed-bed reactors remain dominant, while fluidized-bed technologies are being increasingly adopted. New-generation carrier technologies help solve traditional degradation issues and reduce dependence on alkaline treatment, improving both safety and economics. Although emerging methods such as electrochemical and photocatalytic routes are under research, they are still far from large-scale commercialization due to cost and scalability limitations. The anthraquinone process will therefore remain the dominant industrial method in the near term.

Process Advantages and Future Outlook

The process is characterized by high efficiency, closed-loop circulation, low by-product formation, and suitability for large-scale production. Its challenges include strict control of side reactions, safety risks, and solvent management. Looking ahead, continuous technological upgrades will further support the global hydrogen peroxide industry in moving toward greener and more intelligent production.

This classical process is not only a benchmark in chemical engineering but will continue to play a key role in the global transition toward sustainable chemical manufacturing.

The anthraquinone process remains the backbone technology for global hydrogen peroxide production.

It is a highly efficient closed-loop system involving working solution circulation, catalytic hydrogenation, oxidation, extraction, and purification. With continuous innovation in reactor design and carrier systems, the process has significantly improved safety, efficiency, and sustainability.

Despite emerging alternatives such as electrochemical and photocatalytic routes, the anthraquinone process will continue to dominate industrial H₂O₂ production in the near term due to its scalability and mature engineering foundation.

A true benchmark of modern chemical engineering for large-scale green production.