SYNTHESIS AND CHARACTERIZATION OF HYDROXYL AMMONIUM IONIC LIQUIDS AS CORROSION INHIBITOR FOR CARBON STEEL UNDER ACIDIC MEDIA

The inhibition of carbon steel corrosion becomes of such interest because it is widely used as constructional materials in many industries, such as erecting boilers, drums, heat exchangers, pipe line, and many more. The acidization of oil and gas wells is probably the most widely used work over and stimulation practice in oil industry. HCl is widely used for stimulating carbonate-based reservoirs. Since HCl is strong aggressive medium for oil and gas well equipment, the effective way to protect these materials is to inject a suitable corrosion inhibitor. Accordingly, corrosion inhibitors must be injected with the HCl solution to avoid the destructive effect of acid on the surface of the pipe lines. Hence it is very important to measure the physical properties of the new corrosion inhibitor.

A variety of organic additives as corrosion inhibitors have been tested in these processes. However, there are some disadvantageous with the current inhibitor such as toxic, difficult preparation method and the high material cost. Also it has been reported that the lack of their physical properties data, has limited the design and application of these corrosion inhibitors. Even though ionic liquids have been proven as a potential inhibitor on carbon steel corrosion in acidic media, their price is relatively higher compared to the commercially available corrosion inhibitor. An alternative way is to find cheaper ionic liquids that can be applied as corrosion inhibitor on carbon steel corrosion in acidic media. Hydroxyl ammonium ionic liquids are relatively cheap and easy to produce in purity greater than 99%. In order to develop low cost inhibitors, the recent investigations on application of the hydroxyl ammonium ionic liquids as inhibitor on corrosion of carbon steel in 1 M HCl, seem really worthwhile.
The objectives of this research are to synthesis and characterize the range of ionic liquids, and to study their potential application as inhibitor on carbon steel corrosion in acidic media. For this study, sixteen hydroxyl ammonium ionic liquids were synthesized and characterized. The structures of synthesized ionic liquids were confirmed by infrared, 1H-NMR, and 13C-NMR spectra. Composition of synthesized ionic liquids was also confirmed from elemental analysis. Water content of these ionic liquids was found to be lower than 200 ppm. Physical properties of the ionic liquids such density, viscosity, and refractive index were measured at atmospheric pressure and temperature from 293.15 to 353.15 K, while refractive index was measured at temperature from (293.15 to 323.15) K. The coefficients of thermal expansions were calculated from experimental density data. In practical condition, corrosion inhibitors are mixture of active components, solvents, and surfactant. In this work, the effects of alcohol such as methanol, ethanol, and 1-propanol, as co-solvent on physical properties namely density, viscosity, and refractive index of the ionic liquids were also studied. The ionic liquids Bis(2-hydroxyethyl)ammonium formate, [BHEAF] was chosen as model due to the highest inhibition performance.
The inhibition performance of the synthesized ionic liquids on carbon steel corrosion in 1 M HCl was measured within concentration range of ionic liquids from 0.02 to 0.08 M while temperature range from 298.15 – 343.15 K using two methods, weight loss and electrochemical. The obtained results showed that the inhibition performance increased with increasing concentration of ionic liquids and decreasing temperature of system. Tafel Plot analysis showed that these ionic liquids were mixed type inhibitor, which reduced the corrosion rate by blocking both cathodic and anodic site. Electrochemical Impedance Spectroscopy analysis showed that the addition of ionic liquids did not change the mechanism of corrosion of carbon steel. The synthesized ionic liquids reduced the corrosion rate of carbon steel by adsorbing themselves on the carbon steel surface. The adsorptions of the ionic liquids on the surface of carbon steel obey the Langmuir’s isotherm adsorption. The high values of equilibrium constant and standard free energy of adsorption indicated that the adsorption of ionic liquids on the surface of carbon steel was spontaneous and occurred only by physisorption. The apparent activation energy of corrosion of carbon steel in the presence of ionic liquids was higher compared to without ionic liquids. This result indicated that the addition of ionic liquids give energy barrier for corrosion. These results were also supported by their enthalpy and entropy of adsorption. Addition of alcohol on ionic liquids did not alter the inhibition efficiency. Thus, it can be concluded that these alcohols can be used as co-solvent with ionic liquids, without reducing the ionic liquids performance. The organic solvent is particularly helpful for reducing the viscosity of ionic liquids which is known to be highly viscous
From these experimental results, it shows that hydroxyl ammonium ionic liquids have potential as inhibitor on corrosion of carbon steel in 1 M HCl. It suggests that all the synthesized hydroxyl ammonium ionic liquid in this work has the potential to be used as inhibitor on carbon steel corrosion in 1 M HCl.