Hydrogen diffusion process

Models for following the hydrogen diffusion process may be based on Monte Carlo simulation or network simulation incorporating both a regular lattice structure and irregular grain regions (Herrmann et ah, 2001). 

The result of a fit with this model to the observed linewidths and weights is represented by the solid lines in Fig. 3. It is obvious from the fit that the model allows a semlquantitative description of the hydrogen diffusion process the resulting microscopic parameters are listed in Table I. ... 

Compounds such as hydrogen sulfide and cyanides are the most common metal surface poisoners occurring in process units subject to aqueous-phase hydrogen attack. In many process units, these compounds can be effectively eliminated and hydrogen diffusion stopped by adding ammonium polysulfides and oxygen to the process streams which converts the compounds to polysulfides and thiocyanates, provided the pH is kept on the alkaline side. 

The differences in rate for the two positions of naphthalene show clearly that an additional-elimination mechanism may be ruled out. On the other hand, the magnitude of the above isotope effect is smaller than would be expected for a reaction involving rate-determining abstraction of hydrogen, so a mechanism involving significant internal return had been proposed, equilibria (239) and (240), p. 266. In this base-catalysed (B-SE2) reaction both k and k 2 must be fast in view of the reaction path symmetry. If diffusion away of the labelled solvent molecule BH is not rapid compared with the return reaction kLt a considerable fraction of ArLi reacts with BH rather than BH, the former possibility leading to no nett isotope effect. Since the diffusion process is unlikely to have an isotope effect then the overall observed effect will be less than that for the step k. ... 

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