Hydrocarbonaceous liquids are known to induce corrosion in metals with which they have contact during the various phases of production, transport, and use. For example, during transportation via a pipeline, air and water contaminants present in the hydrocarbonaceous liquid can cause corrosion where they contact the interior surface of the pipe. In this situation, the. corrosion appears to be primarily due to the action of water and air on the steel and is not due to the action of the hydrocarbon. While the hydrocarbonaceous liquid itself is not believed to take part in the corrosion, certain hydrocarbonaceous products may actually inhibit corrosion as a result of traces of polar compounds present in the hydrocarbonaceous product. Thus, hydrocarbonaceous liquids free of polar compounds can lead to corrosion problems in pipelines. Consequently, certain pipeline operators have established a minimum corrosion standard for hydrocarbonaceous liquids transported by their pipelines. A widely used test method is NACE Standard TM0172-2001 which in this disclosure may be conveniently described as “NACE”. The NACE test involves exposing a rotating steel test specimen to the hydrocarbon, distilled water, and air. Following the contact period, the steel strip is examined for corrosion, and a rating from A to E is assigned based upon the percent of the surface corroded. Generally, a NACE value of B+ or better is required for transportation via pipeline.
Hydrocarbonaceous liquids having a NACE value of B or less usually will require the addition of a corrosion inhibitor to raise the NACE value to an acceptable level. Various corrosion inhibitors are commercially available and well known to those skilled in the art. Although the compositions of these additives are proprietary, typically, they will contain long chain carboxylic acids, alkyenylsuccinic acids, or their amine salts. It is speculated that the acid function attaches to the metal surface and the long pendent portion of the molecule acts as a protective surface against corrosion. These additives are expensive, and it would be desirable to reduce or eliminate their use.
The present invention uses an acidic Fischer-Tropsch product as a corrosion inhibitor for use with hydrocarbonaceous liquids. It has been found that the NACE value may be improved for hydrocarbonaceous liquids by blending in as little as 0.1 weight percent of an acidic liquid Fischer-Tropsch product. For example, it has been found that by blending in an acidic Fischer-Tropsch product as described in this disclosure hydrocarbonaceous liquids having a NACE value of C may achieve a NACE value of B+ or better without the addition of conventional corrosion inhibitors. At the same time, in order to control corrosion in the absence of air and water during the distillation, storage, and other processing operations, it is preferred that the acid number of the hydrocarbonaceous liquid as measured by ASTM D664 not exceed 1.5 mg KOH/gm. Even more preferably, the acid number should not exceed 0.5 mg KOH/gm as measured by ASTM D664.
The “hydrocarbonaceous liquid” referred to in this disclosure may be either petroleum derived or derived from a synthetic process, such as a Fischer-Tropsch synthesis. Liquid hydrocarbons within the scope of this invention include, but are not necessarily limited to, crude oil; base oil; liquid hydrocarbonaceous fuels, such as, for example, motor gasoline, kerosene, naphtha, diesel, fuel oil, aviation kerosene, military DFM; various hydrocarbon feedstock or product blending components, such as, for example, FCC gasoline, iso-octane, reformate, hydrotreated straight run naphtha, hydrotreated mid-distillates; and the like.
As used in this disclosure, the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” is intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.