Structural Relations of Organic Corrosion Inhibitors and Scale Preventives as Applied to Oil Field Chemistry

Abstract

Abstract Semipolar molecules such as surfactants are extensively employed in the production of petroleum for the solution of problems of petroleum for the solution of problems of corrosion, scaling, emulsion formation, etc. This paper describes some fundamental relations which have been developed between the structure of surfactant molecules and their action as corrosion inhibitors and as scale preventives. Also given are laboratory methods for predicting when scaling, etc., may be expected due to incompatibility of oil-field brines with one another or with additives such as employed in polymer and micellar flooding. polymer and micellar flooding. Correlation of published data on certain polar materials based on sulfur, oxygen and polar materials based on sulfur, oxygen and nitrogen have shown that in a given homologous series, corrosion inhibition effectiveness increases with increasing number of carbon atoms in the alkyl chain(s) attached to the polar group which adsorbs onto the metal. The polar group which adsorbs onto the metal. The Langmuir Adsorption constant increases by a factor of ten for each additional four carbon atoms added to the molecule, whether the chains are straight or branched, for sulfuric acid used in the pickling of steel. There is no significant difference in corrosion inhibitor efficiency in this system among the homologous series of oxygen and nitrogen compounds such as amines, ketones, and aldehydes reported; however, sulfur compounds of a given carbon number appear to be about two orders of magnitude more effective than nitrogen or oxygen compounds of the same carbon number. Studies carried out on polar materials used as corrosion inhibitors and/or as scale preventives in other systems such as simulated preventives in other systems such as simulated oil field brines, cooling waters, boiler feed-waters, have indicated that although the adsorption concepts developed for acid corrosion inhibitors are of importance, other factors are of equal or greater importance. The concept of rate control of a precipitating salt such as calcium carbonate is developed and data presented indicating that the effectiveness presented indicating that the effectiveness of rate control additives such as phosphonates and polymers is determined by the magnitude of the formation constant of the compound formed by the cation and the additive as compared to that of the cation and the precipitating anion.