Ensuring Safety and Quality in PET Production: How Does Wankai Enhance Control of Acetaldehyde and Antimony?

The Formation of Acetaldehyde in PET and Its Potential Hazards

During the high-temperature, high-pressure polymerization of PET, acetaldehyde(AA) is generated as a by-product. This process typically involves the polycondensation of terephthalic acid (PTA) and ethylene glycol (EG). Under these reaction conditions, ethylene glycol may not fully react or could degrade, resulting in the formation of acetaldehyde.

Since PET is widely used in food packaging for items like bottled water, juices, edible oils, and carbonated beverages, the presence of acetaldehyde poses concerns. Acetaldehyde can affect the quality of PET packaging and is also a potential health risk. Classified as a probable carcinogen, long-term exposure or ingestion of acetaldehyde could lead to health issues such as damage to the central nervous system, liver, and respiratory system. Furthermore, acetaldehyde may alter the taste and aroma of food products, reducing their appeal to consumers. Therefore, controlling acetaldehyde levels in PET during production is essential for ensuring food safety and protecting consumer health.

Existing technologies typically use nitrogen as an inert gas to remove small molecular by-products. In conventional production, nitrogen gas is recirculated through filters into the preheater. However, the recycled nitrogen often contains impurities like ethylene glycol, acetaldehyde, and moisture. These impurities hinder the growth of PET molecular chains and can cause PET hydrolysis, ultimately affecting product quality. Additionally, the presence of acetaldehyde in the nitrogen makes it difficult to further reduce acetaldehyde levels in the PET pellets. 

Wankai's AA Control: Achieving ≤1 µg/g for Superior PET Quality

To mitigate the health risks associated with acetaldehyde, Wankai New Materials Co., Ltd. has developed advanced low-acetaldehyde control technologies during the polycondensation process. These technologies effectively suppress or remove acetaldehyde generated during PET production, reducing its presence in the polymer while also lowering reaction temperatures and energy consumption. This approach establishes a high-quality, environmentally friendly production system.

Wankai has successfully optimized its PET de-acetaldehyde production equipment, addressing the issue of residual acetaldehyde in PET chips even after nitrogen treatment. The company has managed to control acetaldehyde levels to below 1 µg/g, fully complying with both EU and FDA standards.

The working principle and advantages of this solution are as follows: In practice, a spray tower and demister are connected to a nitrogen purification system. During PET production, the PET chips formed in the crystallizer are fed into the preheater. High-purity nitrogen, purified via the spray tower and extracted through the demister, is either mixed with nitrogen supplied by a backflush filter or fed directly into the preheater via a fan. This high-purity nitrogen aids in driving the PET reaction forward, promoting molecular chain growth and improving PET’s viscosity. At the same time, this process significantly reduces acetaldehyde levels in the preheater, thereby lowering acetaldehyde content in the final product.

With this solution, the concentration of nitrogen circulating into the preheater is increased, and the levels of impurities (such as ethylene glycol, acetaldehyde, and moisture) are reduced, facilitating the forward progress of the PET polymerization reaction. Compared to conventional methods, this improvement further lowers acetaldehyde content in PET, enhancing both product safety and quality.

Risks of Excessive Antimony Content in PET Bottles

Antimony content in PET chips bottle-grade is a critical parameter that must be carefully controlled. Antimony compounds are primarily used as catalysts in the production of PET, facilitating the polymerization of PTA and EG to improve reaction efficiency and yield. Additionally, antimony-based catalysts enhance the thermal stability of PET, reducing the risk of thermal degradation during processing and use. These catalysts also help increase the molecular weight of the polyester, thereby improving its mechanical strength, toughness, and performance in bottle applications.

However, during the manufacturing process, some antimony compounds may be reduced to elemental antimony, which can negatively affect the production process. More importantly, as a heavy metal, antimony poses potential environmental and health risks. Prolonged exposure to antimony can lead to antimony poisoning, with symptoms such as coughing, respiratory issues, and liver or kidney damage. Furthermore, antimony has been linked to certain types of cancer, particularly with high levels of exposure. 

Therefore, controlling the antimony content in PET chips bottle-grade  is crucial to ensure both product safety and environmental sustainability.

Wankai Antimony Control: Application of New Catalysts in PET Production

Wankai has developed a new catalyst to replace antimony-based compounds, effectively mitigating the associated risks. This innovative catalyst uses nano-silica as a support, loaded with titanium glycolate, which is applied through an alcohol-exchange method. This approach eliminates the adverse effects of acidic by-products on the purity and yield of titanium glycolate in traditional processes, while also preventing the formation of harmful substances. As a result, it simplifies the reaction process and reduces reaction time.

Titanium glycolate exhibits excellent hydrolytic stability in organic solvents and even in water, significantly minimizing the risk of producing unstable by-products during manufacturing. This not only reduces risks to operators and the environment but also enhances the polyester's color quality, effectively addressing the yellowing issue common in titanium-based polyester catalysts. The catalyst allows the production of high-performance polyester at lower catalyst concentrations and polycondensation temperatures, meeting both environmental and safety standards while also lowering production costs.

The use of nano-silica improves the dispersion and catalytic activity of the composite catalyst while also enhancing its thermal stability. This gives the alcohol-exchange product superior thermal stability and catalytic polycondensation performance, offering broad applications in polyester manufacturing. Furthermore, the overall preparation method is simple, making industrial-scale production easier. The addition of anhydrous ethanol during the reaction prevents the hydrolysis of titanate, eliminating the need for nitrogen protection systems (such as glove boxes). This simplifies process control, increases synthesis yield, and improves product purity.

Wankai's Enhanced Quality Control Testing for PET Safety

Wankai New Materials Co., Ltd. is committed to rigorous quality management across all aspects of research, production, and service, strictly adhering to the ISO 9001 quality management system. The company has implemented advanced quality management practices such as Quality Control Circles (QCC), 6S management, and Total Productive Maintenance (TPM), fostering a strong culture of quality excellence. Wankai’s Testing Center, accredited by CNAS in 2014, follows ISO/IEC 17025:2017 standards to ensure accuracy and reliability in all testing procedures.

The testing center is equipped with 128 advanced instruments, including Agilent GC, GCMS, and LC analyzers from the U.S., PerkinElmer DSC and ICP devices, and precision analysis tools from Mettler Toledo and Metrohm of Switzerland. These instruments provide comprehensive support for raw material quality assessments, water quality monitoring, production control, and final product inspections.

Wankai emphasizes both precision and efficiency in its testing processes. The testing center aims to maintain an error rate below 0.2%, ensures a 100% resolution rate for customer complaints, and achieves a customer satisfaction rate above 95%. All testing equipment is regularly calibrated, and certified technicians are employed to conduct testing with a report delay rate of less than 0.5%. These measures ensure the safety of Wankai’s PET bottle products and enhance their competitive edge in the market.

Conclusion

Wankai's commitment to maintaining the highest safety and quality standards in PET production reflects its dedication to consumer health and environmental sustainability. By implementing innovative low-acetaldehyde control technologies and introducing new catalysts to replace antimony compounds, Wankai enhances the safety and performance of its PET resin. With a robust quality control system and cutting-edge testing facilities, Wankai continues to lead the way in delivering superior PET resin, reinforcing its position as a trusted partner in the market.