CO₂ recovery and purification is a critical pre-process in the carbon capture, utilization, and storage (CCUS) technology system. "Recovery" refers to capturing and separating CO₂ from various industrial waste gases (such as those emitted by chemical plants and steel mills), while "purification" involves using physical or chemical methods to remove impurities from the recovered CO₂, transforming waste into valuable resources. Specifically:
I. Recovery (Capture and Separation)
This primarily focuses on extracting CO₂ from flue gas mixtures generated after combustion. Common methods include:
● Chemical Absorption: Selectively capturing CO₂ using specialized chemical solvents.
● Physical Adsorption: Separating CO₂ based on the varying adsorption capacities of materials like activated carbon or zeolite molecular sieves under different pressure or temperature conditions. This is achieved through pressure swing adsorption (PSA) or temperature swing adsorption (TSA).
● Membrane Separation: Utilizing hollow fiber membranes with selective permeability to separate CO₂ from other gases (e.g., N₂, O₂) based on differences in diffusion rates.
II. Purification (Refinement)
The initially recovered CO₂ typically has a purity of 70%-90% and contains impurities such as water vapor, nitrogen oxides, sulfides, and hydrocarbons. Since food-grade or industrial-grade CO₂ requires purity exceeding 99.9%, further purification is necessary. Key methods include:
● Dehydration and Drying: Removing residual moisture to prevent ice blockage or corrosion during liquefaction/compression.
● Cryogenic Distillation: Liquefying and separating CO₂ from other gases at ultra-low temperatures, leveraging differences in boiling points.
● Catalytic Oxidation: Eliminating trace contaminants like oxygen, carbon monoxide, and hydrocarbons.
Significance of CO₂ Recovery and Purification
This process delivers dual benefits: reducing greenhouse gas emissions and enabling resource recycling.
With global emphasis on carbon reduction, many countries and regions are implementing carbon taxes and emission trading systems (ETS), imposing additional costs on CO₂-emitting industries. By recovering CO₂, companies can directly lower carbon tax liabilities and even generate revenue by selling surplus carbon credits.
Additionally, governments often provide financial incentives, tax breaks, and subsidies for CCUS projects, strengthening corporate confidence and resources for low-carbon transitions.
Moreover, purified CO₂ can be repurposed as valuable industrial raw material for sectors like food processing, chemicals, and enhanced oil recovery, creating direct economic opportunities.
In summary, CO₂ recovery and purification bridges "carbon emissions" and "carbon utilization," accelerating the shift toward a circular low-carbon economy and advancing global "dual carbon" goals.
