The new process of aluminum based molten salt converts polyethylene waste plastics into gasoline and diesel, and adds new options to the polymer recycling path

Process Core: Aluminum based Molten Salt Fractured Polyethylene Long Chain

According to ScienceDaily, researchers at Oak Ridge National Laboratory in the United States have developed a relatively simple method to convert polyethylene – a common material in daily plastic products such as shopping bags and cutting boards – into gasoline and diesel fuels. This process uses inexpensive aluminum based molten salt as the reaction medium to break the long-chain molecules of polyethylene into smaller hydrocarbon molecules, and can obtain about 60% of gasoline fractions under relatively mild conditions. Polyethylene is one of the most widely produced general-purpose plastics, with strong chemical inertness and stable C-C backbone. Traditional pyrolysis usually requires higher temperatures and longer residence times. The value of the aluminum based molten salt route reported this time lies in achieving chain breakage with a lower cost medium, and the high proportion of gasoline fractions in the product distribution, indicating that the cracking depth and selectivity have certain controllability.

Significance for the polymer additive industry

From the perspective of material recycling, the promotion of such chemical recycling routes will directly change the problems that the polymer additive industry needs to face.

. Polyethylene products are usually added with antioxidants, light stabilizers and other additives during the molding and use stages to suppress thermal and photo oxidative aging during processing and use. When these products enter the depolymerization reactor, the additives and their degradation products do not disappear out of thin air. They may enter the molten salt system together with the materials, affecting the reaction rate, product distribution, and even the lifespan of the catalyst or medium. Therefore, the amplification of chemical recycling processes has actually put forward new requirements for additives: on the one hand, it is necessary to have a clearer understanding of the conversion pathways of commonly used antioxidants and light stabilizers under high-temperature molten salt or pyrolysis conditions; On the other hand, it is also necessary to evaluate whether there are new polymer additives that can be designed to maintain sufficient weather resistance during the service life of the product, while not becoming interfering components during the recycling stage. For UV absorbers, their migration and residual behavior in polyolefins are also worthy of re examination in the context of recycling.

Extended requirements for weather resistance testing and formula validation

The process mentioned in the report is still in the laboratory research stage and still far from industrialization.

. But it can be foreseen that if this type of depolymerization route is applied, the composition fluctuation of the recycled material flow will be greater than that of the original resin, and the residual additives, aging degree, and impurity types will all affect the final product. This means that formula design and weather resistance testing methods need to cover a longer material life cycle: not only to verify the weather resistance performance of the product in outdoor use, but also to pay attention to its behavior in the recycling and conversion process. For polymer additive companies, this is both a challenge and an opportunity. Designing additive systems around recyclability and establishing evaluation methods that match chemical recycling may become a direction for research and innovation. Meanwhile, the composition analysis of polyolefin depolymerization products may also provide new technical means for the rapid determination of additive content and aging status.

Issues that still need to be observed

It should be pointed out that the source information only discloses the process principle, medium type, raw material type, and about 60% gasoline yield, without involving key engineering parameters such as reaction temperature, pressure, residence time, catalyst life, feasibility of scaling up, and economy. It also does not specify the specific proportion and quality of diesel fractions in the product.

. The adaptability of this process to actual waste plastics containing additives is also not supported by data. Therefore, its impact on the polymer additive industry is currently more of a directional indication rather than a directly applicable conclusion.

Information source:A new process turns plastic waste into gasoline and diesel fuel， Organized by Herun Chemical.