OLIGOMERS OF VINYLPRYRIDINE AS CORROSION INHIBITORS OF MILD STEEL IN 3 % BRINE SOLUTION SATURATED WITH CARBON DIOXIDE

• Main Author: Ilim
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/37691
• Institution: Institut Teknologi Bandung

Mild steels are widely used as fluid supply pipe materials in oil and natural gas industry because they are safe to use, environmentally friendly, and cheaper than stainless steel or other metal alloys. Crude oil and wet natural gas at the time of mining are almost always mixed with water and acidic gases such as carbon dioxide (CO2) and/or hydrogen sulfide (H2S) gases. The presence of water-soluble CO2 gas produces carbonic acid (H2CO3) which can corrode the inner surface of the mild steel pipe, therefore corrosion of mild steel pipe due to CO2 has been a problem for many years in the wet oil and natural gas industry. The corrosion control on the inner surface of the mild steel pipe is generally accomplished by the addition of corrosion inhibitor into the corrosive environments. Corrosion inhibitors can decrease the corrosion rate of metals by forming a thin layer protector on metal surface. Polymer compounds have multi- functional groups with the ability to form better protective layer on metal surface compared to smaller molecules. In addition, the inhibition capabilities of polymers are also supported by structures, particularly cyclic rings and the presence of heteroatoms, in particular oxygen, phosphorus, sulphur and nitrogen. Because of their good performance as corrosion inhibitor, many polymer compounds containing heteroatoms primarily nitrogen have been investigated, including polyvinylpyridine. Poly (4-vinylpyridine) or P(4-VP) has been widely used as a corrosion inhibitor for various metals in various environments, but based on literature tracing, no specific report on the use of P(4-VP) as a mild steel corrosion inhibitor in a medium containing CO2. This study focused on the use of oligomeric compounds (4-vinylpyridine) and 2-vinylpyridine (2-VP) as corrosion inhibitors of mild steel in a 3 % NaCl solution saturated with CO2 gas. The oligomers of 4-vinylpyridine (4-VP) and 2-vinylpyridine (2-VP) were synthesized using varied amounts of hydrogen peroxide initiator to produce four (4) 4-vinylpyridine oligomers symbolized as O(4-VP)A , O(4-VP)B, O(4-VP)C, O(4-VP)D and 4 oligomers 2-vinylpyridine; O(2-VP)A, O(2-VP)B, O(2-VP)C, O(2-VP). Of all the synthesized compounds, the O(4-VP)B was successfully characterized to study its structure and molecular weight with MALDI-TOF MS, and showed that the compound has a mass (m/z) of 200-2400, which in accordance with chain length of 2-22 monomer units. Fractionation of 4- v vinylpyridine oligomer using sephadex LH 20 with methanol as eluent yielded 6 (six) fractions. Each fraction contains a number of compounds with varying molecular weights, F1 composed of compounds with higher molecular weight while F6 consists of mainly dimers. The 4-vinylpiperidine oligomer was also synthesized by hydrogenation of 4-vinylpyridine oligomer. The molecular weight of synthesized oligomers was determined using MALDI- TOF MS, and that of oligomeric fractions using mass spectroscopy (MS. The performance of oligomers as inhibitor was evaluated by weight loss or wheel test method and electrochemical methods include linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS,) and Tafel plots. Surface analysis was performed with Raman spectroscopy and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS. As a comparison, several commercial corrosion inhibitors were tested. This study also studied the characteristics of the adsorption and protection mechanisms of each of the corrosion inhibitors tested. To evaluate the performance of corrosion inhibitors in oily media, the study was also carried out in the corrosive solution containing 20% (v/v) of kerosene. 4-Vinylpyridine and 2-vinylpyridine oligomers can decrease the corrosion rate of mild steels in corrosive solution, their protection abilities are better at higher concentration. The effect of temperature on these two types of oligomeric compounds is different, in which the corrosion protection of O(4-VP) increased with temperatures, suggesting that the oligomers were chemically adsorbed by the mild steel surface while for the oligomer of O(2-VP), the opposite is true which is related to physisorption. This is supported by thermodynamic quantities of each compound, especially ?Gads (about -40 kJ mol-1) and ?Hads (about 77 kJ mol-1) and the value of f and Kads decreases with increasing temperature for O(4-VP, while O(2-VP) has ?Gads (about -20 kJ mol-1) and ?Hads is negative. The more negative the value of ?Hads, the more physisorption and the more positive the value leads to chemisorption. Both 2-vinylpyridine and 4-vinylpyridine monomers give opposite results to their oligomers, in which the monomers exhibit no inhibition activity, instead they promoted the corrosion of the mild steel. O(4-VPP) synthesized protect the mild steel in a corrosive solution through chemisorption. The existence of chemisorption is also supported by the results of wheel test experiments performed at low speed and the results of EIS and LPR conducted at high speed. The results show that O(4-VP ) and O(4-VPP) protect corrosion by chemisorption while O(2-VP) and IKK tested protect through physisorption. The experiments in the presence of kerosene show that in general, the inhibitors adsorbed chemically, O(4-VP) and (4-VPP), are more resistant to kerosene than the inhibitors involving physisorption, although the difference is not significant according t test (significant test. The six oligomer fractions of 4- vinylpyridine may also decrease the corrosion rate, but the relationship between molecular weight and corrosion inhibition activity has not been able to be explained, because each fraction is still a mixture of oligomers. The surface analysis shows the differences in surface composition and morphology in the presence of corrosion inhibitors.