In the chemical production process, extraction is a common separation technique used to separate different components of a mixture. Traditional extraction towers, although widely used in industry, have some efficiency and performance limitations. In recent years, a new type of Rotor extraction column (NRDC) has begun to emerge in the chemical industry due to its excellent performance and efficiency.
A Rotor extraction column is a device that uses a rotating disc to enhance the contact area between two immiscible solutions. Inside the column, the dispersed phase (usually smaller droplets) rises in the continuous phase, creating vortices through the rotation of the carousel, thereby increasing the mass transfer efficiency between the two phases.
Although Rotor extraction columns excel in many ways, they face a number of challenges. The most significant problems are axial back-mixing and channelised flow, which reduce the mass transfer efficiency and result in a less efficient extraction process.
The New Rotor Extraction Column (NRDC) solves these problems by adding sieve baffles in the plane of the stationary ring. These baffles effectively suppress axial back-mixing and reduce the portion of the high column that is used to compensate for the reduction in mass transfer driving force due to back-mixing, thus improving the overall mass transfer efficiency.
1) Background
Caprolactam is an important chemical raw material mainly used in the production of nylon 6 (polycaprolactam), a synthetic polymer widely used in textiles, plastics and other materials. The production process of caprolactam requires the removal of impurities through a refining step to ensure the purity and quality of the final product.
2) Challenges of Conventional Extraction Towers
In the refining process of caprolactam, traditionally used Rotor extraction columns (RDCs) face problems with axial back-mixing and channelised flow, which can lead to a reduction in mass transfer efficiency, increase production costs and potentially affect product quality.
3) Design Improvement of New Rotor Extraction Columns
In order to solve these problems, the new Rotor extraction column (NRDC) was innovative in design. It adds a sieve baffle in the plane of the fixed ring, and this improvement effectively inhibits axial back-mixing and reduces the negative impact of back-mixing on mass transfer efficiency.
4) Application in the Refining Process of Caprolactam
In the refining process of caprolactam, the new Rotor extraction tower uses benzene as the extractant, and generates vortex through the rotation of the Rotor, which increases the contact area between the continuous phase and dispersed phase, thus improving the mass transfer efficiency. This process allows for more efficient removal of impurities generated during the formation of caprolactam from the Beckman rearrangement reaction of cyclohexanone oxime.
In a 70 kt/a caprolactam refining unit renovation project of a large domestic enterprise, the application of the new Rotor extraction tower has brought the following effects:
Improvement of mass transfer efficiency: By suppressing axial back-mixing, the new Rotor extraction tower improves mass transfer efficiency and reduces the need for tower height.
Operational stability: the new Rotor extractor shows good operational stability in industrial applications and can adapt to different production conditions.
Improve product quality: the application of the new Rotor extraction tower makes the mass fraction of caprolactam in benzene reach more than 20%, and the conductivity is less than 25 μS/cm, which indicates that the inorganic impurities entrained in the crude caprolactam are significantly reduced, and the extraction and separation effect is better.
Reduced production costs: Due to improved mass transfer efficiency and operational stability, the new Rotor extraction tower helps to reduce production costs and improve production efficiency.
These make the 70 kt/a caprolactam refining unit of the project operate better than the original 50 kt/a unit, and this unit has higher extraction efficiency.
The successful application of the new Rotor extraction column (NRDC) has not only made a breakthrough in caprolactam production, but also provided new solutions for other areas of the chemical industry. With the continuous progress and innovation of technology, we expect this new Rotor extraction column to play a greater role in the future chemical production.
