Percentage atom utilization

R. A. Sheldon has developed a similar concept called percentage atom utilization. For instance, the percentage atom economy and percentage atom utilization calculation for the oxidation reaction of benzene to maleic anhydride is given below ... 

Percentage atom utilization = mfW (maleic. nhydriJe + 2 carbon dioxide + 2 w.ter) ><... 

A central issue in making chemistry greener is the efficiency of incorporating the reactant atoms into the product compound. Any atoms that are used in the reaction but are not part of the product are wasted, and this waste must subsequently be disposed of. If chemists can design reactions that do not have wasted atoms, there are no disposal issues and no potential for environmental impact. This type of efficiency can be measured in terms of percentage atom utilization ... 

It is instructive to compare the atom economies of the two pathways. Atom economy is a measure of the efficiency of a chemical process, defined in percentage terms as x (formula wt. of atoms utilized)/(formula wt. of all reactants). For the old six-step ibuprofen synthesis the atom economy was only 40% (with MeC02H, EtOH, NaCl, Et0C02H, 2H2O and NH3 as waste). This is dramatically improved to 77% for the new three-step route with only MeC02H as a by-product from the first step. Recovery and use of this increases the atom economy to 99%. Additionally, the catalytic amounts of HF and Pd complex used in the BHC process are recovered and reused, whereas stoichiometric quantities of AICI3 hydrate were produced as waste by the old route. 

A logical extension of B. M. Trost s concept of atom economy is to calculate the percentage atom economy. This can be done by taking the ratio of the mass of the utilized atoms to the total mass of the atoms of all the reactants and multiplying by 100. 

A wax can be defined as a linear, branched, or cyclic hydrocarbon typically containing from 17 to 60 carbon atoms. Low-carbon-number waxes are found in middle distillate fuels and typically constitute a low percentage of the paraffins found in distillate fuel. Higher-carbon-number waxes can be found in residual fuels and lubricating oil. The percentage of wax in residual fuel oils can vary widely depending upon the refining processes utilized. 

The fuel utilization is referred to as bumup. The bumup may be expressed as the percentage of fuel used before it must be replaced. For example, 1 % bumup means that for each ton of fuel 10 kg of the fissile plus fertile atoms have been consumed (in fission and capture). However, usually the fuel bumup is given in amount of energy obtained per ton of initially present fuel atoms (in case of mixed U - Pu fuels per ton of initial heavy metal. 

In recent decades, there has been a strong tendency to characterize coals by structural analysis. Thus, coal can be characterized in terms of aromaticity (percentage of total carbon atoms existing in aromatic structures), number of aromatic atoms (or rings per cluster), number and types of functional groups, locations of oxygen atoms, location and types of heteroatoms. This has led to the postulation of speculative structure for coal which may (questionably) lead to a better understanding of utilization processes such as combustion. 

The thermal utilization factor will be highest if there is no water in the core, The thermal utilization factor is basically considering the percentage of neutrons in the core that are absorbed in the fuel. If there were no water and no the hydrogen and oxygen atoms, then a higher neutrons would be absorbed by the fuel atoms, simplified reactor of only fuel and moderator,... 

The size control is essential because by decreasing the particle diameter, a higher percentage of surface atoms are exposed, and thus Pt utilization increases. In this sense, there is huge debate about particle size and catal 4ic activity (Maillard et al, 2009), in which maximum catal3hic activities are found for diameters in the range of 2-5 nm (Sun et al., 2007). A decrease in the particle size leads to an increment of low-coordinated atoms as well as that of the oxophilic character of... 

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