E- Factor

The E-factor, a metric proposed by Sheldon [26], has become one of the most cited and commonly used metrics in the batch chemical processing industry. It is defined as follows  

Despite the simplicity of the metric, it may be subject to ambiguity depending on how waste is defined and where one draws system boundaries for any given 

These types of questions will undoubtedly complicate our use of the metric and the interpretation of the results as we attempt to put it into routine use. In addition, this metric does not consider the degree of hazard of the waste that is being created for instance, is it better to generate 100 kg of non-hazardous waste that is difficult to treat, or 50 kg of highly hazardous waste  

As you have been reminded of these definitions, you have also seen several important concepts related to chemical selectivity that will inform any discussion and debate around what is green. We can readily see, for example, that when working with chiral molecules we not only have to worry about reacting with a particular type of bond or functional group, but we also have to do it in such a way that only the bond of interest forms that preserves or creates the desired isomer. As any synthetic organic chemist knows, there remains a considerable amount of chiral chemistry that suffers from a lack of selectivity (stereo-, regio-, and enantioselectivity) and in many cases more than 50% of the starting material ends up as waste. 

Atom economy is deliberately kept simple by making certain key assumptions it ignores the reaction yield, molar excesses of reactants, solvents, and reagents. Before discussing the pros and cons of atom economy, it is worth clarifying what atom economy means. 

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E-factor for bubble tray gas load moles of component j gas flow rate flow rate of iaert gas... 

The term in equation 42 is called a Souders-Brown capacity parameter and is based on the tendency of the upflowing vapor to entrain Hquid with it to the plate above. The term E in equation 43 is called an E-factor. and E to be meaningful the cross-sectional area to which they apply must be specified. The capacity parameter is usually based on the total column cross section minus the area blocked for vapor flow by the downcomer(s). Eor the E-factor, typical operating ranges for sieve plate columns are... 

E, Factor, ratio of temperature difference across sheU-side film to overaU mean temperature difference Dimensionless Dimensionless... 

On a rank-by-rank (i.e. factor-by-factor) basis, we rotate, or perturb, each pair of factors, (1 spectral factor and its corresponding concentration factor) towards each other to maximize the fit of the linear regression between the projections of the spectra onto the spectral factor with the projections of the concentrations onto the concentration factor. 

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 ... 

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%. 

From this further analysis, the actual amount of waste (and its nature) per kilogram of product will become evident. At this stage it is also important to look forward and assess options for recycling or reusing the waste on site for example if a solvent can be efficiently recovered then this should be taken into account in calculating the E-factor. Although the choice of which route to fully optimize may not be obvious even from this further analysis, it will facilitate a reasoned discussion of the issues. 

Review a recent synthetic reaction you have carried out in the laboratory. Write a balanced equation for the reaction(s) and calculate the atom economy. From your experimental results calculate the Yield, E-factor and Effective Mass Yield (ignoring any water used). Identify ways in which this reaction could be made greener. 

Industry segment Product tonnage E factor kg waste/kg product... 

To express that it is not just the amount of waste but rather its environmental impact, Sheldon introduced the environmental quotient EQ as the E factor multiplied by an unfriendliness quotient, Q, which can be assigned a value to indicate how undesirable a byproduct is. For example, Q = 0 for clean water, 1 for a benign salt, NaCl, and 100-1000 for toxic compounds. Evidently, catalytic routes that avoid waste formation are highly desirable, and the more economic value that is placed on, for example, the unfriendliness quotient, the higher the motivation to work on catalytic alternatives. Waste prevention is much to be preferred over waste remediation. 

Explain the concepts of atom efficiency and environmental friendliness. What is an E-factor Which processes usually have the highest E-factors Explain what catalysis means on the different length scales indicated in Eig. 1.8. 

Table 3.1 Typical E-factors for chemical industry sectors. ...

Sheldon, R.A. (2000) Atom Utilisation, E Factors and the Catalytic Solution. Comptes Rendus de VAcademic des Sciences Paris, Serie lie, Chimie, 3, 541-551. 

The picture does look different when environmental factors are considered a slightly higher E-factor has been obtained for the biocatalytic as compared to the chemical catalytic procedure (Figure 5.7). Both approaches show a high contribution of solvent use, sewage. 

The urgency of the need for waste reduction is readily appreciated by considering the amount of waste generated per kg product, designated as the E factor solvents (Sheldon, 1992, 1992a, 1993, 1994, 1996, 1997, 1997a) in various segments of the chemical industry (Table 2.7). 

Put in another way, the E factor represents the ratio of kilos in to kilos out i.e. it is the mass balance or the weight ratio of all the raw materials, including solvent losses, to the amount of desired product. It can be readily calculated for a particular product line, production site, or even a whole company. It is quite amazing, therefore, that so few... 

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