Coupled Adsorption-Distillation Purification Process in Pyrolysis Oil Refining Equipment

Pyrolysis oil—whether derived from biomass, waste tires, or waste plastics—possesses a highly complex composition. In addition to the target hydrocarbon components, it typically contains oxygenated, nitrogenous, and sulfur-bearing compounds, as well as certain unsaturated hydrocarbons and polar impurities. These impurities are the primary causes of the oil's dark color, pungent odor, and poor stability. Consequently, a core task in the design of pyrolysis oil refining equipment is to establish an effective separation and purification sequence that removes these undesirable components, thereby enhancing the oil's commercial value.

Overall Design Logic of the Coupled Process

Among the various purification techniques available, a coupled process combining adsorbent treatment with distillation separation has proven to be both economical and reliable. The logic of this process centers on leveraging the selective adsorption capabilities of polar adsorbents. Specifically, the pyrolysis oil undergoes pretreatment to adjust its polarity through the addition of non-polar solvents. This step is crucial, as it directly influences the efficiency of the subsequent adsorption stage. Research indicates that diluting the pyrolysis oil with C5–C7 alkanes (such as hexane or heptane) effectively modulates the overall polarity of the medium, making polar, non-hydrocarbon impurities more readily capturable by the adsorbent.

Selection and Mechanism of Polar Adsorbents

The key material in the adsorption stage is activated attapulgite clay (also known as palygorskite). This material features a unique chain-layer crystal structure and abundant micropores, providing a vast number of active adsorption sites. Experiments demonstrate that activated attapulgite exhibits excellent selective adsorption capabilities for polar compounds found in pyrolysis oil, including benzoic acid, quinolones, stearic acid oxidation products, and sulfur- or nitrogen-containing species. In the process design, the polarity-adjusted pyrolysis oil is passed through a fixed-bed adsorption tower packed with activated attapulgite, effectively trapping the polar impurities on the adsorbent's surface and within its pore channels. This treatment effectively removes the black color of the pyrolysis oil and significantly diminishes the initially unpleasant sulfur-amine odor; simultaneously, the polycyclic aromatic hydrocarbon (PAH) content is controlled to a certain extent, resulting in a transparent, light-yellow oil product.

Distillation Recovery and Solvent Recycling Unit

Following adsorption purification, the mixture of oil and diluent solvent enters a separation unit for recovery. This stage typically employs a distillation column or a wiped-film evaporator. Given that the boiling points of solvents such as hexane are significantly lower than that of the pyrolysis oil, separation via distillation is operationally feasible. The equipment utilizes a jacket or internal heater to raise the mixture's temperature to a range above the solvent's boiling point but below that of the oil, thereby facilitating solvent vaporization and recovery. Notably, the use of a distillation column or wiped-film evaporator not only enables solvent recycling but also allows for a design where operational flexibility is constrained by the packing capacity of the upstream adsorption tower; this facilitates a continuous process flow in which the throughput of the entire production line is determined by the adsorption unit rather than the distillation unit.

Adsorbent Regeneration and Recycling

Clays saturated with impurities can be regenerated using polar solvents—such as acetone or methanol—to restore their adsorption capacity and enable material recycling. The regeneration process generally involves placing the saturated adsorbent in a regeneration vessel and repeatedly washing it with an appropriate amount of polar solvent to desorb the polar impurities from the active sites. After drying and activation, the regenerated attapulgite recovers more than 80% of its initial adsorption performance, allowing it to be reintroduced into the adsorption process. This regeneration step significantly lowers consumable costs during refining and reduces solid waste generation, aligning with the dual demands for economic efficiency and environmental sustainability in continuous industrial production.

Conclusion

In summary, the coupled process of solvent dilution, attapulgite adsorption, and distillation-based regeneration constitutes a viable technical pathway for pyrolysis oil refining. Through precise physicochemical interactions, it selectively removes key impurities that compromise oil quality, providing a reliable technical solution for upgrading and utilizing low-quality pyrolysis oil.