Unfriendliness quotient

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. 

Figure 9.1 compares the synthesis of acetophenone by classic oxidation of 1-phenylethanol with stoichiometric amounts of chromium oxide and sulphuric acid, with an atom efficiency of 42%, with the heterogeneous catalytic oxidation with O2, with an atom efficiency of 87%, and with water as the only by-product. This is especially important if we consider the environmental unfriendliness of chromium salts the potential environmental impact of reactions can be expressed by the environmental quotient (EQ), where E is the E-factor (kg waste/kg product) and Q is the environmental unfriendliness quotient of the waste. If Q is... 

All the above metrics are only based on masses of waste they do not take into account the nature of the waste. The necessity of metrics that consider not just the amount of the waste but also its environmental impact was first recognized by Sheldon [9]. To put it in his words Comparing alternative routes solely on the basis of the amount of waste is to grossly oversimplify. So, he defined the environmental quotient (EQ) as the product of the E-factor (E) and an unfriendliness quotient, Q. 

Several green metrics have already been proposed and published over the years with perhaps the most well known being the E-Factor described by Roger Sheldon4 as the Amount of waste produced per kg of product. Table 1 shows some typical figures for E from the Sheldon publication. A further refinement suggested in this paper is to use the Environmental Quotient which is the product of the E-Factor and Q, where Q is defined as the unfriendliness quotient (e.g. NaCl, Q=l heavy metal salts, Q=100). 

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 ... 

Environmental quotient, EQ This represents the characterization of the environmental unfriendliness of the produced waste. This indicator is computed as shown in the following equation by multiplying the E factor (an Efficiency indicator) by the quotient Q. This quotient is an assigned coefficient that can be 1 if the waste is identified as innocuous, while for toxic materials such as heavy metals, Q could be a scalar between 100 and 1000. 

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