Hydrogen sulfide inhibition, first

Kinetic Study—Dibenzothiophene Desulfurization. Earlier work at Amoco by Frye and Mosby (8) studied the rate of reaction of single sulfur compounds in light catalytic cycle oil. Conclusions from that study were (1) the reaction kinetics are first order in hydrogen and reactant sulfur (2) hydrogen sulfide inhibits the reaction (3) overall energy of activation is around 28-30 kcal. 

Hoar Ci J found that in the corrosion inhibition of iron in hydrochloric acid by g-naphthoquinoline, the corrosion potential increases monotonically with increasing inhibitor concentration, while in the case of o-tolylthiourea one observes first a decrease of the corrosion potential followed by an increase at higher inhibitor concentrations. A similar predominant inhibition of the cathodic partial reaction at small inhibitor concentrations is exhibited also by phenylthiourea according to Kaesche. Furthermore, in the series of the thiourea derivatives one often finds corrosion acceleration at small concentrations, as for instance in the case of phenylthiourea at concentrations of 10- moles per liter. This appears to be due to a small cathodic decomposition of thiourea and its derivatives in the course of which hydrogen sulfide is formed. As is well known, hydrogen sulfide tends to accelerate corrosion, in particular the anodic partial reaction of dissolution of iron, which has been demonstrated independently by other authors (17). 

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