Green Metrics Flashcards
What is the purpose of green metrics?
LCA often hard to do, green metrics give a suggestion of impact of a chemical process and potentially allow comparison between methods
What is atom economy?
(FW of desired product)/(combined FW of starting materials) x 100%
Benefits of atom economy?
Easy to use, expresses how efficiently a reaction “makes use” of atoms, based upon suggestion that synthetic methods should be designed to maximise incorporation of all materials used in final product
Limitations of atom economy?
Does not take into account yield
What is experimental atom economy?
(mass of products)/(mass of reagents) x 100%
Benefits of experimental atom economy?
Takes in account excess reagents and product yield, still relatively easy to measure, improvement on atom economy
Limitations of experimental atom economy?
No consideration of solvents
What is the Sheldon E-Factor?
[mass (kg) of waste]/[mass (kg) of product)], where waste is everything that is not product or process water
Benefits of E-factor?
Considers the total amount of waste - takes into account yield, excess reagents, solvent losses, process aids, and potentially energy
Limitations of E-factor?
Process water generally excluded from value as get very high E-factors, scale of production also needs to be taken into account when comparing
What is the effective mass yield?
(mass of products)/(mass of reagents + non-benign solvents) x 100%
Benefits of effective mass yield?
Takes in account excess reagents and product yield, still relatively easy to measure, considers relative toxicity of solvents
Limitations of effective mass yield?
Big problem - how do you judge what reagents are benign? Subjectivity makes comparison hard. Also obviously still have benign solvents - additional energy in their clean up or disposal?
What is process mass intensity?
(mass of input materials inc. process water)/(mass of product)
Benefits of process mass intensity?
Takes into account everything that is put into a reaction and the yield, target is to decrease quantity of materials used to create the product
