The hard/soft acid/base (HSAB) principle is a cornerstone in our understanding of chemical reactivity preferences. Motivated by the success of the original (e.g., "global") version of this rule, a "local" counterpart was readily proposed to account for regioselectivity preferences, in particular, in ambident reactions. However, ample experimental evidence indicates that the local HSAB principle often fails to provide meaningful predictions. Here we examine the assumptions behind the standard proof of the local HSAB rule, showing that it is based on a flawed premise. By solving this issue, we show that it is critical to consider not only the charge transferred between the different reacting centers but also the charge reorganization within the non-reacting parts of the molecule. We propose different reorganization models and derive the corresponding regioselectivity rules for each.
Mexican industry generates tons of organic wastes that are not used and cause social, environmental, and health problems. The main organic residue which is generated during wood production is the sawdust (biomass). In order to reduce the problems generated by its waste, a prototype to manufacture biofuel pellets was designed by considering a flat die pelletizing machine according to the standard EN 14961-2. The machine design consists of stainless steel 304 and carbon steel to produce pellets of 6 mm and 30 mm in diameter and length, respectively, at 50–100 rpm. The matrix types proposed were radial, spiral, and hexagonal. In order to be constructed quickly, the design is standardized. Results from finite-element analysis indicate that it is possible to manufacture pellets from 50 to 1000 PSI (344.7 kPa to 6894.7 kPa) with this design complying with the standard.
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