Turning waste into treasure! Chinese scientists have discovered a new way to make gasoline from plastic waste, with a yield of up to 80%

Polyethylene plastics are everywhere in our daily lives, from lightweight shopping bags to durable food packaging bags, from fashion clothing to building materials. Its wide application has greatly facilitated people's life needs. Along with it, there is a problem that cannot be ignored - the pollution of waste plastics to the environment.

People's dependence on the use of disposable plastic products has led to a large amount of discarded polyethylene plastics being discarded in the natural environment. These plastic wastes are difficult to degrade. While polluting the environment, they also threaten the survival of wild animals and plants, and even indirectly affect human health through the food chain. In the long run, it will have a negative impact on the soil, water sources and ecosystems that cannot be ignored.

So, how can we achieve environmentally friendly recycling and reuse of waste polyethylene plastics?

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On April 9, 2024, Chinese scientists published an article in the journal Nature Chemistry on the recycling of polyethylene to produce high-quality gasoline, which is expected to achieve efficient utilization of waste polyethylene plastics.

The research results were published in the journal Nature Chemistry. Image source: Nature Chemistry

Transforming polyethylene plastic into high-quality gasoline

The resource utilization of waste plastics can not only solve the problem of environmental pollution, but also achieve sustainable development of resources. Among the waste plastics, polyethylene is very difficult to convert, and its non-polar "carbon-carbon bond" is difficult to activate and break under low temperature conditions.

At present, the main strategy for converting polyethylene is to achieve it under high reaction temperature (above 400°C), precious metal catalysts and external hydrogen sources. The strict reaction conditions limit the application of industrial recycling of polyethylene.

Based on the problems faced in the catalytic conversion of polyethylene, the researchers used tetrabutylammonium hydroxide (C16H37NO) as a structure-directing agent and adopted a "one-step hydrothermal reaction" to synthesize a molecular sieve with a layered self-supporting structure (LSP) for the catalytic conversion of polyethylene.

Among them, structure-directing agents, by adding specific ligands or additives in chemical reactions during crystal synthesis or growth, guide the molecular assembly to form a highly crystallized ordered structure with ideal physical and chemical properties. Layered self-supporting structures (LSPs) are formed by cations and anions bonded together through ionic bonds, and have sufficient strength and stability to exist independently without additional support.

Mesoporous channels are between micropores and macropores, with a pore size between 2-50Nm, and have a highly ordered structure and rich surface activity, which plays an important role in catalyst performance. Layered self-supporting molecular sieves have a larger specific surface area and rich mesoporous channels, which can make the reactants fully contact the catalyst in the catalytic reaction and increase the reaction rate.

Compared with traditional molecular sieve materials, it has a unique self-supporting structure and more strong Lewis acid sites. Lewis acid sites are a chemical substance that can accept electrons at specific locations (or regions) and achieve catalysis by adsorbing and activating reactants. The strong Lewis acid sites in the molecular sieve and its shape selectivity can play a key role in catalyzing the conversion of polyethylene. Therefore, the layered self-supporting molecular sieve can better catalyze the conversion of polyethylene.

Characterization of the catalyst (a. High-resolution transmission electron microscopy; b. X-ray diffraction; c. Nitrogen adsorption-desorption isotherm; d, e. NMR characterization results; f, g. IR characterization results). Image source: Reference [1]

Gasoline is mainly composed of hydrocarbons in the C4-C12 range, which is a mixture of alkanes, alkenes and cycloalkanes. The octane number is a numerical indicator to measure the anti-knock ability of gasoline in the cylinder, and is usually used to evaluate the performance of automotive gasoline, that is, the quality of gasoline.

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The experimental results show that the layered self-supporting molecular sieve (LSP-Z100) prepared in this study can achieve the conversion from high-density polyethylene to gasoline in 4 hours at a temperature of 240°C and without an external hydrogen source, with a yield of up to 80%. By detecting its liquid phase product, the C4-C12 component accounts for up to 99%, and the branched alkane accounts for 72%, with a high octane number (88.0), comparable to the octane number of commercial gasoline (86.6).

The above results show that the layered self-supporting molecular sieve (LSP-Z100) has the feasibility of catalytically converting polyethylene into high-quality gasoline. This study provides a new thinking path for solving the environmental pollution problem of waste polyethylene plastics and how to effectively realize resource utilization.

Conversion rate and product yield of high-density polyethylene under different catalyst conditions. Image source: Reference [1]

When we think about the pollution caused by discarded plastics to the environment, starting with the little things we do ourselves is the beginning of our contribution to environmental protection.

Reduce the use of unnecessary plastic products in daily life (such as disposable straws, plastic bags and tableware) to promote the improvement of social environmental awareness. Garbage classification is also a key link. Separate recyclable plastics from other garbage to reduce the chance of polyethylene entering the natural environment and promote the recycling of various resources. Ecological civilization is everyone's responsibility.

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References

[1] Cen, Z., Han, X., Lin, L. et al. Upcycling of polyethylene to gasoline through a self-supplied hydrogen strategy in a layered self-pillared zeolite[J]. Nature Chemistry, 2024.

[2] Xie Yufei, Wang Qi, Zeng Junmin, et al. Research progress in recycling and application of waste polyethylene plastics[J]. Plastics Science and Technology, 2022.

[3] Zhang Jinqing, Guo Ming, Zhang Yuanwen, et al. Research progress in the production of fuel from cracking of waste polyethylene plastics[J]. Petrochemical Technology, 2022.

[4] Gautam KR .A Novel Process of Converting Polyethylene to Gasoline, Middle Distillate and Heavy Oil through Hydropyrolysis Route[J].International Journal of Energy Engineering, 2013.

Planning and production

Produced by Science Popularization China

Author: Shi Chang, PhD in Physical Chemistry

Producer丨China Science Expo

Editor: Dong Nana

Proofread by Xu Lailinlin