Plastic pollution and recycling degradation have always been pain points in the industry. How can we truly achieve the upgrading and recycling of waste plastics? Currently, the mainstream global technologies fall into three major recycling routes: physical, chemical, and biological.
First: Physical Recycling
Its core characteristic is that it does not break down the large molecular chains of plastics, relying solely on melting, blending, and modification to complete recycling. It is divided into two main parts: melt recycling and modified recycling. This is the most common recycling method.
Second: Chemical Recycling
Unlike physical recycling, it breaks the chemical bonds of plastics through chemical reactions, decomposing waste plastics into smaller molecules, chemical raw materials, and even original monomers. There are four process routes in total.
The first is peroxidation. This is what we commonly refer to as incineration energy recovery. The plastic is completely burned and oxidized, and the recovered heat energy is used for power generation and heating. However, this method cannot recover plastic raw materials; the final products are only carbon dioxide and water.
The second is partial oxidation. This involves controlling the amount of oxygen to prevent complete oxidation of the plastic, generating syngas composed of carbon monoxide and hydrogen, which can be used as a basic raw material for chemical synthesis.
The third is anaerobic pyrolysis. The first method involves high-temperature decomposition in complete oxygen isolation, encompassing three types: thermal cracking, catalytic cracking, and hydrocracking. Conventional thermal cracking produces fuel oil; catalytic cracking can selectively produce plastic monomers such as ethylene and propylene, which are of higher value; hydrocracking removes chlorine and sulfur impurities through high-pressure hydrogenation, yielding clean naphtha feedstock.
The fourth method is depolymerization. This includes alcoholysis, hydrolysis, and solvation, specifically targeting polyester plastics such as PET and polyurethane. It directly breaks down the plastics into their original monomers, with purity close to that of virgin raw materials, allowing for unlimited closed-loop recycling.
The third method is biorecycling.
This relies on enzymes and microorganisms to complete the resource recovery of plastics, and involves two technical pathways.
The first is bio-enzymatic depolymerization and monomer recovery. Using specialized hydrolytic enzymes, PET polyester plastics are decomposed under mild conditions at room temperature, efficiently extracting high-purity monomers. This method has low energy consumption and low carbon emissions, making it a popular green process.
The second is microbial synthesis technology. The organic carbon source produced after plastic degradation is used as nutrients for microorganisms to synthesize new biodegradable plastics such as PHA through fermentation, forming a complete biological closed loop.
Finally, let's briefly summarize the three types of recycling: Physical recycling does not damage molecules and is simple to operate, but the performance of plastics will decline after multiple recyclings; Chemical recycling completely breaks down plastic molecules, is suitable for mixed waste plastics, and can be infinitely recycled; Biological recycling relies on biological media, has mild reaction conditions, is low-carbon and environmentally friendly, and is currently mainly used in the field of polyester plastic recycling.
