Pyrimidine derivatives as novel acidizing corrosion inhibitors for N80 steel useful for petroleum industry: A combined experimental and theoretical approach

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Abstract

The corrosion inhibition performance of two pyrimidine derivatives namely 5-styryl-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d] pyrimidin-4(1H) one (PP-1) and 5-(2-hydroxyphenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d]-pyrimidin-4(1H) one (PP-2) on N80 steel corrosion in 15% HCl has been studied using gravimetric method, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy (AFM), scanning electron microscopy (SEM), DFT, molecular electrostatic potential and Monte Carlo simulation. The corrosion inhibition efficiencies at optimum concentration (250 mg/L) are 89.1% (PP-1) and 73.1% (PP-2) respectively at 308 K. The corrosion inhibition efficiency increases with increase in concentration and decreases with temperature. PPs obeyed Langmuir adsorption isotherm. AFM and SEM analyses supported formation of protective film on N80 steel in presence of inhibitors. DFT and Monte Carlo simulation calculations supported experimental results.

Introduction

Corrosion of metals is considered as a challenging research area due to its impact on economic and safety issues [1]. Acidization of oil wells is one of the effective techniques for enhancing oil production. It is conducted by forcing a solution of 15% HCl into oil well through N80 steel tubes [2], [3]. HCl causes severe corrosion of N80 steel and to reduce the corrosive effect of acid inhibitors are incorporated [1]. Organic compounds containing heteroatoms are considered as effective corrosion inhibitors for acid medium [4], [5], [6]. They are adsorbed on the metal surface and reduce corrosion [7], [8].

Commercially available acidizing inhibitors are acetylenic alcohol, aromatic aldehyde, alkenylphenones, quaternary salts and some carbonyls and amines condensation products [9]. Most of these compounds are toxic, non-degradable and cause the adverse effect on living beings and environment [10], [11], [12]. Therefore, the current research is focused on the development of non-toxic eco friendly inhibitors. The literature survey shows that few pyrimidine derivatives have been previously reported as corrosion inhibitors at lower acid concentration [13], [14], [15], [16]. The pyrimidine derivatives in the present study were synthesized from relatively inexpensive chemicals. The calculated cost of 100 L of acid solution containing 25 g of inhibitors is approximately Rs 40–45.

In the present study, two pyrimidine derivatives namely, 5-styryl-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d] pyrimidin-4(1H)one (PP-1) and 5-(2-hydroxyphenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d] pyrimidin-4(1H)one (PP-2) have been selected for corrosion inhibition study of N80 steel in 15% HCl. The selection is based on the facts that they are non-toxic and also show diverse biological activities such as antibacterial and fungicidal activities [17]. The corrosion inhibition study of investigated compounds has been performed using gravimetry, electrochemical impedance spectroscopy (EIS), Tafel polarization, quantum chemical methods and molecular dynamic simulation. The surface morphology was studied by AFM and SEM, which supported the adsorption of inhibitor molecules on the metal surface.

Section snippets

Synthesis of inhibitors

Pyrimidine derivatives were synthesized by the previously reported method [17]. A mixture of 2-thiobarbituric acid (0.01 mol), aromatic aldehyde (0.01 mol), thiourea (0.01 mol), absolute ethanol (10 ml) and 36% HCl (3 ml) are taken in a round bottom flash and heated under reflux for 4 h and the reaction mixture was allowed to cool. The formed precipitate was filtered off and washed with ethanol. The molecular structures of inhibitors were confirmed by IR and 1H NMR and are shown in supplementary file

Effect of inhibitor concentration

The effect of concentration on the corrosion of N80 steel in 15% HCl at 308 K was investigated by gravimetric measurements and shown in Fig. 2(a) As observed from the Figure, the inhibition efficiency of PPs increased with the increase of concentration from 50 to 250 mg/L. At the same concentrations, the inhibition efficiency of PP-1 is higher than PP-2, which means that PP-1 is better inhibitor than PP-2. The maximum η% for PP-1 and PP-2 are 89.1% and 73.5% respectively, reached at 250 mg/L, and

Conclusions

The results obtained from gravimetric, EIS and Tafel polarization support the protection ability of PPs for N80 steel in 15% HCl. Tafel polarization reveals that PPs are mixed type inhibitors but suppressing more cathodic reactions. Both the inhibitors obeyed Langmuir adsorption isotherm. ΔG°ads results reveals adsorption of the PPs on metal surface is spontaneous. SEM and AFM micrographs show that N80 steel surface is protected in presence of PPs. Quantum chemical study revealed that both

Acknowledgement

Jiyaul Haque and K. R. Ansari gratefully acknowledge Ministry of Human Resource Development (MHRD), New Delhi, India for the financial assistance and facilitation of study.

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