Online analysis of permanganate absorption number (PAN)

Caprolactam, a vital precursor to Nylon 6, is widely used in the production of various industrial fibers, textiles, and plastics. Maintaining consistent caprolactam purity is essential for ensuring the quality of these finished products. The permanganate absorption number (PAN) analysis serves as a key indicator of caprolactam purity within the production process, adhering to ISO 8660 standards.

This Process Application Note describes the straightforward 24/7 monitoring of the permanganate absorption number (PAN) as a measure of the caprolactam purity in the corresponding process.

In 2023, global caprolactam production capacity was approximately 9 million tons [1], the majority of which went on to produce Nylon 6. Nylon 6 is mainly used to manufacture fibers for clothing, carpets, and industrial purposes. About 30% of produced Nylon 6 is used for resin production [1].

Caprolactam is primarily manufactured from cyclohexanone, cyclohexane, or toluene. The dominant industrial process involves converting cyclohexanone to cyclohexanone oxime, followed by Beckmann rearrangement to yield caprolactam with nearly 98% efficiency [2].

The industry standard Beckmann rearrangement process employs sulfuric acid (or oleum) as a catalyst to transform cyclohexanone oxime into caprolactam (Reaction 1). However, this method generates ammonium sulfate as a byproduct. While valuable for fertilizer production, its environmental impact has led to restrictions in certain regions.

Maintaining caprolactam quality is crucial for its downstream applications like Nylon 6 production. This can be achieved by employing a specific test – permanganate absorption number (PAN) analysis.

This standardized procedure, detailed in international references like ISO 8660, measures the presence of oxidizable impurities within the caprolactam sample.

Essentially, PAN analysis measures the stability of caprolactam by evaluating its reaction with potassium permanganate. Lower PAN values indicate a purer caprolactam sample, leading to the production of better-quality Nylon 6.

Traditional laboratory analysis employing manual sampling is a viable option, but it presents certain drawbacks. The time-consuming nature of this approach misses real-time process variations. Analyzing multiple process streams concurrently becomes labor-intensive, and the use of sulfuric acid introduces safety concerns within the laboratory environment.

In light of these limitations, online process analyzers such as the 2060 TI Process Analyzer (Figure 2) have emerged as the preferred solution. This process analyzer exhibits cutting-edge technology and offers continuous, high-precision analysis of caprolactam impurities, ensuring the consistent production of top-quality Nylon 6.

• Fully automated diagnostics – automatic alarms for when samples are out of specification parameters.
• Guarantee compliance with global standards.
• Avoid unnecessary costs by measuring multiple parameters simultaneously in the process stream.
• Enhanced control over the caprolactam production process, enabling fine-tuning for optimal purity and efficiency.
• Safer working environment for employees (no handling of H₂SO₄).