H-Acid is a key intermediate used in the synthesis of more than 90 types of dyes, including Acid Fuchsin and Reactive Brilliant Red, and plays an important role in the global dye supply chain. However, the acid precipitation and filtration stages in the H-Acid production process inevitably generate large quantities of high-concentration crystalline mother liquor wastewater. Typical characteristics of this type of wastewater include extremely high color, strong acidity, COD concentrations as high as 20–50 g/L, and large amounts of naphthalene derivatives and supersaturated sodium sulfate/ammonium sulfate. It also exhibits significant biological toxicity, making it difficult for conventional oxidation or biological treatment processes to simultaneously achieve detoxification and resource recovery. If not properly treated, it may cause long-term impacts on the ecological environment of receiving water bodies.

Faced with increasingly stringent environmental regulations and wastewater discharge standards worldwide, H-Acid manufacturers urgently need a pretreatment technology that can effectively reduce toxicity while recovering valuable by-products, thereby reducing the load on downstream biological treatment and achieving circular economy objectives.

Why Solvent Extraction Has Become a Preferred Solution

Among the existing treatment methods, macroporous resin adsorption has limited adsorption capacity for high-COD wastewater, requires frequent resin regeneration, and presents difficulties in treating the regeneration solution. Chemical oxidation consumes large quantities of oxidants and offers limited oxidation selectivity for organic compounds with fused naphthalene-ring structures. Catalytic wet air oxidation requires high temperature and high pressure, resulting in high equipment investment and operating energy consumption. Direct biological treatment is also difficult to apply because the sodium sulfate content in the wastewater can often exceed 20%, and the high-salt environment can directly cause activated sludge inactivation.

Solvent extraction, with its mild operating conditions, recyclable extraction solvent, high recovery rate of naphthalene-based organic compounds, and potential for reuse in the production of water-reducing agents, is widely recognized as an ideal technical route for the pretreatment of H-Acid wastewater.

Core Process: Two-Stage Cross-Current Extraction + Stripping and Solvent Regeneration

Based on the characteristics of H-Acid wastewater, Zhengzhou Tiei Extraction Technology Co., Ltd. has developed a mature process consisting of two-stage cross-current extraction combined with one- or two-stage stripping. The core process is as follows:

1.Cross-current extraction section
The wastewater and dedicated extractant are fed into two stages of centrifugal extractors at an optimized phase ratio. Rapid mixing and mass transfer take place under a high-speed centrifugal field, allowing naphthalene-based organic compounds to be efficiently transferred into the organic phase. After treatment, the COD of the raffinate is significantly reduced, while its biodegradability is substantially improved, allowing it to be smoothly introduced into the downstream biological treatment system.

2.Stripping section
The loaded organic phase enters a one- or two-stage cross-current stripping unit, where an alkaline stripping agent is used to strip the target naphthalene-based compounds from the organic phase. A high-concentration stripping solution is obtained, which can be directly used in the production of naphthalene-based water-reducing agents, enabling value-added resource recovery.

3.Solvent regeneration
After stripping, the extractant is regenerated and recycled. The system has low solvent consumption, helping keep operating costs under control.

Core Equipment: CWL-M Centrifugal Extractor

The implementation of this process relies on the high-efficiency separation capability of the CWL-M Series top-suspended centrifugal extractor. Compared with traditional gravity settling equipment, its key advantages include:

1.Rapid separation and efficient mass transfer: With a centrifugal field several hundred times greater than gravity, the two phases can be rapidly separated after contact. The separation performance is stable and less susceptible to the emulsification tendency of the process fluids.

2.Fully enclosed operation: The equipment is fully sealed, effectively reducing extraction solvent volatilization, improving the operating environment, and reducing solvent loss as well as health and safety risks.

3.Top-suspended rotor design: The design eliminates the need for a mechanical seal at the bottom, avoiding potential leakage risks, simplifying maintenance, and significantly extending continuous operating periods.

4.Industrial-scale validation: This model has been operating stably over the long term in multiple H-Acid wastewater treatment projects, demonstrating a mature and reliable process.

Process Validation Support: Reliable Transition from Laboratory to Industrial Scale

For customers facing fluctuations in wastewater quality or uncertainties in process conditions, Zhengzhou Tiei Extraction can provide the CWL50-M laboratory-scale centrifugal extractor for pilot testing. The equipment can accurately simulate industrial operating conditions and help customers verify extraction and stripping efficiency while obtaining key design parameters, such as phase ratio, rotational speed, and residence time. These results provide a reliable basis for industrial equipment selection and scale-up design.

To meet the practical needs of H-Acid manufacturers worldwide, Zhengzhou Tiei Extraction provides more than just a piece of equipment. We offer a systematic engineering solution covering extraction, stripping, solvent regeneration, and integration with downstream wastewater treatment processes. This solution has been proven in actual projects to effectively reduce COD loading, recover high-value by-products, and significantly reduce the pressure on downstream biological treatment, delivering both environmental and economic benefits.
Welcome to contact our technical team for customized consultation and process solutions.
Email: sales@tieiextraction.com
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