Inhibition of carbon steel corrosion by long alkyl-chain amino acid corrosion inhibitors.

摘要

Carbon steel (CS) is the most commonly used material for equipment and pipes in the oil production processes. However, presence of water/salts and carbon dioxide, among other gases, in the oil is a serious problem due to increased corrosion rate of the material. The most common way of mitigating this problem is by using corrosion inhibitors. However, many common corrosion inhibitors that are in use today are health hazards. Therefore, there is a need to develop more environmentally compatible and biodegradable corrosion inhibitors. Bioorganic and naturally occurring molecules, such as amino acids, are the most obvious candidates.;In this study the inhibiting effect of 12AA on corrosion of CS in CO 2-free and CO2-saturated 0.5 HCl was investigated as a function of various parameters: inhibitor concentration, electrolyte pH, temperature, treatment time, CS surface roughness, electrolyte flow rate and pattern, effect of electrolyte type. In addition, the interaction of 11AA with the CS surface under selected experimental conditions was also investigated.;It was found that 12AA inhibits both partial corrosion reactions, with a slightly stronger inhibition of the anodic corrosion reaction which indicated that 12AA acts as a mixed-type inhibitor. The corrosion protection mechanism is by formation of a surface-adsorbed 12AA monolayer that offers a hydrophobic barrier to transport of solvated corrosive ions to the surface yielding a maximum inhibition efficiency of ∼98%. The adsorption of 12AA onto the CS surface was described by the Langmuir adsorption isotherm. The corresponding Gibbs energy of adsorption was calculated to be --26 and --28 kJ mol--1 in the CO2-free and CO2-saturated 0.5 M HCl, respectively. This indicated that the self assembled monolayers (SAM) formation process is spontaneous and reversible. PM-IRRAS measurements revealed that the SAM is amorphous, which could be attributed to the repulsion between the neighboring positively charged amine groups and also to a high heterogeneity of the CS surface. The study showed also that the 12AA can be used as an effective inhibitor of CS general corrosion in several other electrolytes including; acetic acid, perchloric acid and sodium chloride, but its application in nitric and sulfuric acid should be avoided. The corrosion inhibition of the CS surface by 12AA is also effective at higher pH values, although the corresponding corrosion inhibition efficiency decreased due to a decrease in 12AA solubility. 12AA was also confirmed to be an efficient corrosion inhibitor of a CS surface of different roughness.;The effect of flow and flow pattern of CO2-saturated HCl on the corrosion inhibition of CS by 12AA was also investigated in a square duct, rotating disk electrode (RDE) and jet impingement cell configuration. 3 mM 12AA provided high corrosion inhibition efficiency in the square duct and RDE configuration. However, in 1 mM 12AA solution, the inhibition efficiency decreased with an increase in Reynolds number (Re), due to desorption of 12AA from the CS surface. 12AA was found to poorly protect CS in the impingement-jet configuration at low Re, while at high Re, acceleration of CS corrosion was recorded.;This work was aimed at studying the influence of some amino acids, 11-aminoundecanoic acid (11AA) and 12-aminododecanoic acid (12AA), as corrosion inhibitors for carbon steel (CS) in hydrochloric acid and some other electrolytes that might be used in certain industries.;Similar results were also obtained for inhibition of CS corrosion by 11AA. In fact, this molecule was found to better protect CS from corrosion than 12AA. This was attributed to the higher surface coverage of 11AA on the CS surface, i.e. the formation of a more compact 11AA monolayer.