What Are the Methods of Chemical Recycling for Waste Plastics, and What Are Their Respective Applications?

Chemical recycling of plastics is a process that breaks down the polymer chains of plastics into smaller chemical molecules or fuels through heat, chemical solvents, or catalysts. It is a key technology for achieving high-value utilization of low-value and mixed plastic waste. Unlike mechanical recycling, which primarily handles high-value, single-category plastics, chemical recycling can process materials that are difficult to treat through mechanical methods. It serves as a crucial pathway for achieving closed-loop plastic recycling and transforming "white pollution" into "white oil fields."

Based on the type of polymerization reaction, chemical recycling is mainly divided into two categories: pyrolysis methods for addition polymers and depolymerization methods for condensation polymers.

I. Pyrolysis Method: Primarily for Processing Addition-Polymerized Plastics like Polyolefins

Pyrolysis is a method that breaks the carbon chains of plastic polymers through heating (thermal pyrolysis) or the addition of a catalyst (catalytic pyrolysis) under anaerobic or low-oxygen conditions. This method is primarily applicable to plastics produced via addition polymerization reactions, such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), which are also the most common types of plastics in everyday life.

The main end products of pyrolysis include fuels (i.e., "plastic-to-oil") and chemical raw materials such as olefin monomers. Depending on the technical approach, pyrolysis can be categorized into thermal pyrolysis and catalytic pyrolysis, among others.

Among these, thermal pyrolysis is currently one of the more mature technologies for processing mixed waste plastics. Represented by companies like Niutech, pyrolysis enterprises utilizing continuous pyrolysis technology have demonstrated significant advantages in the field of waste plastic recycling. Their plastic pyrolysis systems have achieved industrial-scale application and implementation in numerous countries and regions worldwide.

II. Depolymerization Methods: Primarily for Condensation Polymers Such as PET and Nylon  

Depolymerization employs chemical reactions (e.g., hydrolysis, alcoholysis) to selectively break specific chemical bonds (such as ester or amide bonds) in plastic molecules, reverting them to their original monomers or intermediates. This method is primarily suitable for plastics formed via condensation polymerization.

- Hydrolysis: Typically used for polyethylene terephthalate (PET, commonly found in beverage bottles). In acidic, alkaline, or neutral aqueous media, PET is depolymerized into terephthalic acid (TPA) and ethylene glycol (EG).  

- Alcoholysis: Also mainly applied to PET recycling. It involves reacting PET with methanol to produce dimethyl terephthalate (DMT) and EG, or with ethylene glycol to produce bis(2-hydroxyethyl) terephthalate (BHET).  

- Other depolymerization technologies target specific plastics such as polyamides (nylon, PA) and polyurethanes (PU).

In summary, cracking is the mainstream technology for processing mixed polyolefin waste, while depolymerization is more adept at handling single-category condensation polymers like PET.

Chemical recycling is emerging as a new direction in global plastic pollution management, and scientifically sound plastic waste-to-energy solutions continue to be explored. Companies specializing in pyrolysis technology, such as Niutech, are poised to play a significant role in waste plastic pollution control—particularly in treating low-value plastic waste—contributing to global sustainable plastic utilization and the circular economy.