Plastic pyrolysis is a process that converts waste plastics into pyrolysis oil through high-temperature pyrolysis. Generally, it is considered as an effective method of waste plastic disposal. However, during the pyrolysis process, wax oil is often generated as a byproduct. The generation of wax oil not only reduces the yield of pyrolysis oil, but also has an adverse effect on subsequent processes and equipment. This article will take you to learn more about wax oil in plastic pyrolysis process.
HowWax Oil is Formed?
In the plastic pyrolysis reactor, the polymer chains in waste plastics break. Thus, it is converted into various hydrocarbon molecules. The products of this process can be light gaseous or liquid hydrocarbons, or long-chain heavy hydrocarbons, that is, wax oil. The formation of wax oil is mainly due to the following reasons:
Incomplete Decomposition:
During the pyrolysis process, high temperatures help to break long-chain molecules in plastic into shorter-chain hydrocarbons. However, if the temperature is not high enough or the reaction is not thorough, some long-chain molecules cannot be completely pyrolyzed. As a result, this causes the pyrolysis products to appear in the form of heavy oil, that is, wax oil.
Lack of Catalytic Reaction:
During the pyrolysis of plastics, if no catalyst is used, the pyrolysis reaction can only rely on high temperature. Without the support of catalytic pyrolysis, the products generated tend to be long-chain heavy hydrocarbons, which have large molecular weights and high boiling points, and appear as viscous waxy substances after cooling.
The Harm of Wax Oil
The generation of wax oil during the pyrolysis of plastics will bring a series of negative effects:
Reduce Pyrolysis Oil Production:
The goal of plastic pyrolysis is to produce light liquid pyrolysis oil. These fuels can be used directly in industry or energy supply. However, the generation of wax oil means that long-chain hydrocarbons have not been completely decomposed. Therefore, the yield of light oil decreases.
Impact on Equipment Operation:
The viscous nature of wax oil makes it easy to clog pipelines of pyrolysis equipment during cooling and storage. It increases the frequency of equipment maintenance and may even cause equipment failure. This not only increases operating costs, but also affects production continuity.
Difficult to Handle:
Wax oil is a difficult intermediate product to handle. It cannot be used directly in most fuel applications. Wax oil needs to undergo additional processing, such as secondary distillation or refining, to be converted into more valuable light products. This increases energy and economic costs.
Wax Oil Removal Solution: Catalytic Pyrolysis
Adding a catalytic tower to the plastic pyrolysis system helps convert heavy wax oil into light pyrolysis oil. Specifically, the working principle of the catalytic tower includes the following two aspects:
Long Chain to Short Chain
Heavy wax oil has a high molecular weight and viscosity. The catalyst in the catalytic tower can reduce the activation energy of these long-chain hydrocarbons through chemical reactions. This allows them to pyrolysis into shorter-chain molecules at relatively low temperatures.
Reaction Condition Optimization:
By adjusting the temperature, pressure and reaction time in the tower, the degree of pyrolysis reaction can be more accurately controlled. The presence of the catalyst can reduce the energy required for the reaction, allowing the reaction to proceed efficiently at a lower temperature.
Below is a video showing the catalytic pyrolysis process of plastic:
Conclusion
The generation of wax oil is a challenge that cannot be ignored in the process of plastic pyrolysis. By introducing a catalytic tower to optimize the reaction conditions, the generation of wax oil can be effectively controlled. With the advancement of technology, the plastic pyrolysis process is moving towards a more efficient and environmentally friendly direction. Reducing the output of wax oil will further improve the economy and sustainability of this technology.
