Introduction

Whether we like it or not, all materials utilized in a synthesis - except the final product - will end up as waste, to be recycled or disposed. Given the fact that material disposal costs (including recycling) often equal or even exceed their acquisition costs, their assessment is essential for a comprehensive synthesis analysis.


     

While it is straightforward to assess material acquisition costs, the situation is more complex when it comes to the disposal overhead. There are many different disposal options, including recycling, burning and waste water treatment. Take recycling as an example: Recycling a single solvent by distillation is quite different from recycling a solvent mixture forming azeotropes. Usually the actual costs of such operations only can be accurately assessed on a case-by-case basis by specialists.

 

Therefore ChemProject does not attempt to calculate absolute disposal/recycling costs. Instead, the user can assign a disposal category to a waste volume (default, elevated cost, medium cost, high cost and very high cost). This assignment is subjective and it is advisable to define common criteria for category assignments to allow meaningful synthesis comparisons. Thus, e.g. the "very high cost" category most likely will be reserved for waste volumes containing highly toxic, bioactive compounds,  "medium costs" for halogenated solvents, etc. However, there is no need to assign a disposal category to each and every material used in a synthesis - just assign a category to items with assumed higher than baseline disposal costs.

Waste Groups

In practice, assigning a disposal category to one single compound usually is not sufficient. Take the example of 25 g potassium cyanide dissolved in 1.5 liters of water. Here the disposal volume will not be 25 g, but 1.5 liters. The same is true when mixing a halogenated solvent with non-halogenated solvents - at the end, the complete mixture will have to be treated as a halogenated solvent for disposal. In both examples the effect was that unproblematic solvents became part of a higher disposal category. 


ChemProject maps this situation by introducing waste groups. The screen shot below illustrates a waste group consisting of potassium cyanide (primary waste component) mixed with methanol and water (collateral volumes).

 


 

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