Mass intensity indicators

Scheme 5.1 shows the reaction taken as an example by Constable et al. [39] and the main elements needed to calculate the above indicators. The various mass intensity indicators are calculated considering a yield of 90%. 

Scheme 5.1 Reaction used as an example to estimate the value of different mass intensity indicators. Source adapted from Constable [39].

Co-production is still used in many relevant industrial processes. A typical example is the synthesis of phenol via the cumene process, which involves the formation of acetone as by-product. This example is discussed in a more detail later in Chapter 13. Direct oxidation of benzene to phenol using H2O2 is an attractive industrial alternative, but a main motivation is to avoid the formation of acetone, as there is actually excess acetone on the market. The process requires a single step versus three steps in the cumene process, one of which is related to the synthesis of a cumene hydroperoxide intermediate that shows significant problems of safety. There are thus various aspects that make more sustainable the direct synthesis of phenol over the cumene process, but atom economy (or related mass intensity indicators) is not the correct indicator to assess sustainability. 

As discussed for mass intensity indicators, energy intensity indicators are simple to calculate but give only a partial overview of sustainability, as processes outside the chemical reaction or the chemical plant are not included. In addition, no discrimination is made between renewable and non-renewable sources, which have very different implications with regard to sustainability. Finally, the energy intensity related to material production (reactants, solvents, etc.) is also not included. As a consequence, energy intensity indicators must always be accompanied by material intensity indicators, which are measured in different units and cannot be directly aggregated. 

In order to compare different systems, energy and mass intensity " were calculated as reported below, taking into account the power required by the system (eqn (19.1)), the H2 produced and its fraction recovered in the permeate (eqn (19.2)) as valuable product with respect to the total mass fed and the steam and cooling water necessary (eqn (19.3)). Moreover, another index was defined as productivity to footprint ratio (eqn (19.4)). Lower values of these indicators are related to an intensified process. In the ideal situation the mass intensity indicators would approach 1, whereas the energy intensity and the productivity to footprint ratio should be as low as possible ... 

Mass Intensity may also be expressed as a percentage by taking the inverse and multiplying by 100. This metric is also known as mass productivity or mass efficiency and provides an indication of how much of the input mass, expressed as a percentage, is integrated into a final, saleable product (how much of what we buy ultimately produces a profit). This is perhaps valuable for its shock value and ease of interpretation, especially for non-technical business people. 

In Fig. 2.13 the mass intensities for carbon dioxide (m/e = 44) and methyl formate (m/e = 60) during a potential scan are given. While the signal for C02 follows the current pattern in the whole potential range that for HCOOCH3 does not. This indicates the existence of parallel pathways. Methyl formate was also detected as an electrolysis product in long duration experiments [66],... 

Figure 5. Mass intensities v.v. time using Fes(MoOt)3/Mo03 at 270°. Curve numbers indicate mass. Key 40, Ar/20 30, CHsO 31, CH3OH and 18, HtO.

The data clearly indicated that the use of route 4 for the synthesis of radafaxine had several advantages, for example, lower Mass Intensity and greater Mass Efficiency, in comparison to the DKR procedure, route 3. 

If Ti or Cr were present in the steel, there would be a peak of nominal mass 51 due to Cr while the intensity indicating a mass of 50 would be disturbed by the presence of the Ti. 

These pentapyrrolic macrocycles contain a 22-jr-electron ring system, and are expected to be the largest members of the [An + 2] n aromatics. In fact, their spectroscopic characteristics, i.e. the intense absorption band in visible region, the large diamagnetic shift of peripheral H and inner NH NMR signals, and relatively strong parent (M+) and dicationic (M2+) mass peaks, indicate the existence of a delocalized cyclic aromatic n system (Table 11). 

Intense EE and PIE have been observed during fracture as well. In recent work, we have succeeded in determining the predominate ionic species created during the fracture of UV grade fused silica. (Langford, S. C. Dickinson, J. T. Jensen, L. C. J. Vac. Sci. Technol. A. in press.). Both time-of-flight and quadrupole mass spectroscopy indicate the presence of ions of mass 16,28,44, and 76, which we... 

Figure 3 presents the reconstructed mass spectrum of the first discriminant function which separated the river and marine stations in the DiD2-map of Figure 1. The positive D-function describes the covariant mass peaks with higher intensities with respect to the zero point spectrum. All sample spectra with such characteristics will have positive score values. This spectrum is a representation of the characteristics of riverine material. The negative D-function spectrum in Figure 3 is indicative of the marine characteristics. The D spectrum shows a number of mass peaks indicative for carbohydrates, lignin and proteinaceous material (12). The mass peak m/z=86 and 100 are uncommon and a special characteristic of these fluvial samples. It can be speculated to be the molecular ion of (alkyl)thiadiazole (a metal binding pollutant), however a cyclic ketone, short chain alcohol or unsaturated acid are also possibilities. These mass peaks were chosen for further study because of their rare occurrence and their high discriminating power in the factor-discriminant analysis.

There are more indicators (e.g., mass intensity, MI, and mass productivity) that belong to this general class of resource intensity indicators, for example, which quantify greermess of chemical processes and products in terms of effectiveness of mass and energy intensity. 

All the indicators discussed above are based on mass intensity. These indicators have been developed specifically for their use in synthetic chemistry, either at the laboratory or industry level. They have in common the objective of showing to what extent a chemical reaction is wasteful in material terms simplicity is their main merit, as most of them can be easily calculated as soon as the chemical reaction is defined and quantified. 

Figure 3.3 Separation and molecular weight determination of peptides by mass spectrometry. Intensity indicates the number of molecules of a peptide, whereas the time of flight indicates the molecular weight of a peptide.

Tabulated positive ion frit-FAB mass spectra of lAA, lAA amino acid and sugar conjugates and related compounds [lOO], Ions without relative intensity indicated have... 

The mass spectrum of henningsoline did not show the peaks at m/e 144 and 130, characteristic of unsubstituted dihydroindole alkaloids. However, intense peaks at m/e 190 and 176 (144 and 130 plus 46 replacement of H by OH and H by OMe = 46 mass units) indicated a substituted dihydroindole structure. 

Fig. 2.3 Mass intensity signals of Ni species for the thermal decomposition of a nickel nitrate sample containing 0.5 fig Ni (a) NiO+, (b) Ni(N03)J, and (c) Ni+. The experimental conditions are indicated in Table 2.1. (Reprinted from [12], with permission.)...

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