Feed enters the reactor and splits into a product stream (amber
particles) and a waste stream (grey particles). Atom economy sets
what fraction of the feed's mass can, in principle, end up in the
product; a catalytic route avoids consuming a stoichiometric
reagent that would otherwise leave as spent salt waste. Turning up
solvent recovery re-routes a fraction of the waste stream back
into the feed through the recycle loop, cutting net waste without
changing the chemistry.
E-factor = mass(waste) / mass(product)
PMI = mass(total input) / mass(product)
Atom economy (%) = MW(product) / Σ MW(reactants) × 100
- Atom economy — theoretical maximum fraction of reactant mass that becomes product, from the reaction's stoichiometry.
- Solvent recovery — fraction of solvent/by-product mass recycled back to the reactor via the loop instead of discarded.
- Feed mass — total mass charged to the reactor per batch.
- Catalytic vs stoichiometric — a catalyst is regenerated and reused, avoiding the extra reagent mass a stoichiometric route sheds as waste.
The E-factor (kg of waste per kg of product) is the metric Sheldon
introduced to compare how "green" different manufacturing routes
really are — pharma processes historically ran E-factors of 25-100,
which green chemistry design tries to drive down.