Abstract
Since 1920, certain crude oils have been found to be corrosive in refineries. At temperatures between 428 and 752°F (220 and 400°C), sulfur-containing and organic acid species in crude oils are known to promote corrosion. Elemental sulfur, mercaptan, sulfide and polysulfide species convert to hydrogen sulfide which attacks carbon and low-alloy steels. Organic acids, such as naphthenic acids consisting of cycloalkane ring(s) with an attached aliphatic chain having a terminal carboxylic acid group, have been implicated. However, neither total sulfur content measured by elemental analyses, nor total acid content, measured by total acid number (TAN), have been found to correlate well with corrosivity of engineering alloys.
A fundamental study of the relationships between the molecular structure of organic acid compounds to elevated temperature corrosion of refinery alloys has been performed. In particular, the corrosion rates of steel exposed to a series of homologous organic acids with respect to temperature has been assessed in a test unit that simulates corrosion found in refinery vacuum distillation towers. As well, organic acids from Athabasca bitumen have been isolated and characterized. The corrosivity of the model compounds and how they compare to the corrosivity of Athabasca bitumen will be discussed in terms of the molecular structure of the different organic acids. This work is partially supported by the Alberta Energy Research Institute and the Canadian Association of Petroleum Producers.
