Efactor

Efactor, also written E-factor, is a metric in green chemistry that quantifies the environmental burden of a chemical process by measuring waste generated per unit mass of product. It is defined as E-factor equals the mass of waste divided by the mass of product. In many conventions, water is excluded from the waste term, though definitions vary.

Introduced by Roger A. Sheldon in the early 1990s, the E-factor is used to compare alternative routes and to guide waste minimization during process development. It captures only material waste, not energy use, toxicity, or broader life-cycle impacts, and it does not reflect the hazardous nature or handling risks of the waste.

Typical E-factor values vary widely by industry and process. Bulk chemical production often has relatively low E-factors, while pharmaceutical and fine chemical manufacturing can exhibit high values due to multi-step syntheses and extensive purification; nevertheless, trends toward greener solvents and catalytic processes have driven reductions in many sectors.

The E-factor has inspired related concepts such as process mass intensity (PMI), which considers all input materials, including solvents, regardless of whether they become waste. It remains a focal point in green chemistry education and industrial benchmarking, though its limitations require complementary environmental metrics for a complete assessment.