Sustainability Language

Circular Economy & Materials

E-factor

Roger Sheldon's green-chemistry metric: the mass of waste produced per mass of desired product — the lower, the cleaner the process.

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Definition

The E-factor, introduced by Roger Sheldon, is a green-chemistry metric defined as the mass ratio of total waste generated to the desired product in a chemical process. It counts waste by-products, unreacted reagents, solvent losses and spent catalysts (water is usually excluded unless contaminated). The ideal value is zero; typical acceptable values range from 1–5 for bulk chemicals to several hundred for fine chemicals and into the thousands for pharmaceuticals, reflecting product value and volume.

References

Overview

What it means

A brutally simple number exposing how wasteful a synthesis route is — complementing atom economy, which ignores solvents and actual yields.

How it is used

Chemists and process engineers use the E-factor to benchmark synthetic routes, compare industries and target waste-reduction in pharmaceutical and fine-chemical manufacturing.

Why it matters

The E-factor made process waste visible and comparable, and remains a headline metric of green chemistry and sustainable manufacturing.

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