8.1 Principles of adsorption and ion exchange

Adsorption and ion exchange are crucial separation processes in chemical engineering. These techniques rely on molecules adhering to surfaces or ions swapping between solutions and materials. Understanding the principles and mechanisms behind these processes is key to their effective application.

Physical factors like temperature, pressure, and pH greatly influence adsorption and ion exchange. Equilibrium in these processes is described by isotherms and selectivity coefficients, which help engineers predict and optimize separations in various industrial applications.

Fundamentals of Adsorption and Ion Exchange

Principles of adsorption and ion exchange

Top images from around the web for Principles of adsorption and ion exchange

• 

  Tailoring and visualizing the pore architecture of hierarchical zeolites - Chemical Society ... View original

  Is this image relevant?

• 

  Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures - RSC ... View original

  Is this image relevant?

• 

  Zeolites and related sorbents with narrow pores for CO 2 separation from flue gas - RSC Advances ... View original

  Is this image relevant?

• 

  Tailoring and visualizing the pore architecture of hierarchical zeolites - Chemical Society ... View original

  Is this image relevant?

• 

  Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures - RSC ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Principles of adsorption and ion exchange

• 

  Tailoring and visualizing the pore architecture of hierarchical zeolites - Chemical Society ... View original

  Is this image relevant?

• 

  Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures - RSC ... View original

  Is this image relevant?

• 

  Zeolites and related sorbents with narrow pores for CO 2 separation from flue gas - RSC Advances ... View original

  Is this image relevant?

• 

  Tailoring and visualizing the pore architecture of hierarchical zeolites - Chemical Society ... View original

  Is this image relevant?

• 

  Adsorption–desorption of CO2 on zeolite-Y-templated carbon at various temperatures - RSC ... View original

  Is this image relevant?

1 of 3

• Adsorption process molecules adhere to surface driven by concentration gradient between bulk fluid and adsorbent surface (activated carbon)
• Adsorbate substance being adsorbed attaches to adsorbent material (methylene blue dye onto activated charcoal)
• Ion exchange process exchanges ions between solution and ion exchanger through electrostatic attraction between ions and charged functional groups (water softening)
• Reversible process allows regeneration of ion exchange materials (zeolites)
• Equilibrium in both processes described by adsorption isotherms (Langmuir, Freundlich) and ion exchange selectivity coefficients

Physical adsorption vs chemisorption

• Physical adsorption involves weak van der Waals forces forming reversible process with low heat of adsorption 20-40 kJ/mol
• Physical adsorption allows multiple layers without electron transfer (nitrogen gas on silica gel)
• Chemisorption forms strong chemical bonds often irreversible with high heat of adsorption 80-400 kJ/mol
• Chemisorption creates monolayer formation with electron transfer occurring (hydrogen on palladium)

Mechanisms of ion exchange

• Counter-ion exchange replaces ions of same charge in solution with those on exchanger
• Co-ion exclusion prevents ions of same charge as fixed groups from entering exchanger
• Donnan equilibrium maintains electroneutrality between solution and exchanger phases
• Ion exchangers contain fixed ionic groups and mobile counter-ions in porous structure
• Applications include water softening removing calcium and magnesium ions
• Wastewater treatment removes heavy metals and other contaminants
• Metal recovery extracts valuable metals from solutions
• Chromatography separates complex mixtures based on ionic interactions
• Catalysis uses ion exchange resins as heterogeneous catalysts

Factors and Equilibria in Adsorption and Ion Exchange

Factors in adsorption equilibria

• Temperature affects adsorption exothermically decreases with increasing temperature
• Ion exchange can be endo- or exothermic temperature impact varies
• Increased pressure generally increases gas adsorption (methane on activated carbon)
• pH influences surface charge of adsorbents and ionization state of adsorbates
• Smaller particles and larger surface area increase adsorption capacity (nanoparticles)
• Pore size distribution affects accessibility of adsorption sites (mesoporous materials)
• Higher concentrations of adsorbate or ions generally increase adsorption or exchange
• Competing species can reduce adsorption or ion exchange efficiency (mixed metal solutions)
• Nature of adsorbent or ion exchanger chemical composition and surface functionality impact performance
• Solvent polarity and dielectric constant affect adsorption and ion exchange processes