Core principle: The essence of countercurrent mass transfer and heat transfer distillation is the coupling of mass transfer and heat transfer.

1. Volatility difference: The more volatile components (lighter components) in the mixture have lower boiling points, while the less volatile components (heavier components) have higher boiling points.

2. Partial vaporization and condensation: Heating a liquid produces vapor with a higher concentration of light components than the original liquid; cooling and condensing this vapor results in a liquid with a higher concentration of heavy components than the original vapor.

3. In-column process: Inside the distillation column, rising vapor is supplied through the reboiler at the bottom of the column, and reflux liquid is supplied through the condenser at the top. The rising vapor and the falling liquid come into countercurrent contact on each tray (or each section of packing) within the column, exchanging heat and mass.

4. Separation results: Light components continuously accumulate at the top of the column and are eventually extracted as high-purity steam and condensed; heavy components continuously accumulate at the bottom of the column and are eventually extracted as high-purity liquid.