Green Process Metrics

In Chapter 1 the concept of atom economy was discussed as a design tool. Similarly in Chapter 2 the term E-factor was introduced as a measure of the amount of by-products formed per unit weight of product. Unlike atom economy the E-factor is determined from an actual process or can be extrapolated from laboratory work. As a valuable extension to the E-factor concept Sheldon has proposed an Environmental Quotient which is the product of the E-factor and a by-product unfriendliness  

By way of illustration, taking the simple esterification of butanol with acetic acid, the balanced equation for the reaction is  

The atom economy for this process is 86.5% (100 X 116/134), which is reasonable. To calculate the E-factor and EMY further information is needed. From published literature (Vogel s Practical Organic Chemistry ), a standard procedure is to mix butanol (37 g) with glacial acetic acid (60 g), and a small amount of sulfuric acid catalyst (ignored in all calculations). Following completion of the reaction the mixture is added to water (250 g). The crude ester is washed further with water (100 g), then saturated sodium bicarbonate solution (25 g) and finally water (25 g). After drying over 5 g of anhydrous sodium sulfate the crude ester is distilled to give product (40 g) in a yield of 69%. 

Whilst some of these measures attempt to take account of the hazardous nature of by-products and effluent, they do not take account of the hazardous nature of any starting materials. The other major omission from these measures is any measurement of the energy involved. 

Following an assessment of the criteria in Table 3.2 it may become evident that there is only one viable route, but more probably two or three options will be difficult to choose between. In this case the alternatives should be screened experimentally to refine the data in Table 3.2 and to complete a pro-forma similar to that shown in Table 3.3. 

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Lectures 9 + 10 real-time analysis for pollution prevention the importance of measurement, lifecycle assessments, green process metrics, environmental management systems, eco-labels, legislation... 

Green Chemistry Metrics Measuring and Monitoring Sustainable Processes. Edited by Alexei L kin David J. C. Constable 2009 Blackwell F iblishing Ltd. ISBN 978-1-405-15968-5... 

Green Chemistry Metrics Measuring and Monitoring Sustainabie Processes... 

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