Green Chemistry Principles and Metrics

Green Chemistry Overview

• Green chemistry focuses on designing chemical products and processes that minimize or eliminate hazardous substances.
• Examines pollution prevention at the molecular level, emphasizing sustainable practices.

Key Concept: Reducing

• Central to green chemistry principles including:
  • Cost reduction
  • Material utilization
  • Risk and hazard reduction
  • Energy conservation
  • Waste minimization
  • Usage of renewable resources

The 12 Principles of Green Chemistry

• Developed by Anastas and Warner, aiming for safer, more efficient chemical processes:
  • Prevention of Waste: Proactive approach is preferred over remediation after waste has been created.
  • Atom Economy: Emphasizes maximizing the inclusion of all materials in the final product to minimize waste.
  • Less Hazardous Chemical Syntheses: Focuses on designing processes that decrease chemical hazards.
  • Design Safer Chemicals: Ensuring the inherent safety of chemicals used.
  • Real-time Analysis for Pollution Prevention: Encouraging immediate monitoring for pollutants to prevent their creation.
  • Use Safer Solvents: Advocating for safer solvent alternatives.
  • Design for Energy Efficiency: Prioritizing energy-saving methodologies during synthesis.
  • Use Renewable Feedstocks: Utilizing renewable resources whenever possible.
  • Design for Degradation: Ensuring that chemical products can degrade safely after use.
  • Use Safe Catalysts: Promoting the usage of inherently safe catalysts.
  • Reduce Derivatives: Minimizing unnecessary derivatization to avoid additional waste.

Waste Generation Insights

• Major sources of waste in chemical processes include:
  • Stoichiometric Reagents: Common acids, bases, oxidants, and reductants lead to significant waste.
  • Solvent Losses: Solvents contribute to approximately 85% of non-aqueous mass waste.

Pollution Prevention Hierarchy

• Organized as a strategy for increasing "greenness":
  • Prevention & Reduction: Primary focus.
  • Recycling & Reuse: Secondary efforts.
  • Treatment: Tertiary interventions.
  • Disposal: Last resort.

Case Study: Ethylene Oxide

• Conventional Method: Two-step synthesis using chlorohydrin produced 5 kg of waste for every kg of product.
• Alternative Production: Utilization of molecular oxygen reduces waste production significantly, generating over 16 times less waste while eliminating wastewater creation.

Atom Economy

• Definition: Designed processes should maximize the incorporation of all materials into the final product.
• Higher atom economy correlates with lower waste generation, enhancing material efficiency.
• Introduced by Barry Trost in 1991, aiming to increase the usability of all atoms in the synthesis process.