Investigation of Ligustrum lucidum Ait. Seeds Extract as Green Corrosion Inhibitors and Bacteriostatic Agent

The extract of Ligustrum lucidum Ait. seeds, as green and eco-friendly corrosion inhibitors, have been investigated on the corrosion inhibition of Q235A steel in 1M hydrochloric acid solution at 60°C by weight loss and potentiodynamic polarisation techniques. The inhibition efficiency of the extracts varies with extract concentration from 10 mg/L to 1000 mg/L and the highest one reaches to 95.0%. The extracts inhibit corrosion mainly by adsorption mechanism. Besides the hydroxyl and ether groups of polyphenols can capture the H to reduce the corrosion, and the polyphenols can eliminate the dissolved O2 to inhibit the oxygen-adsorption corrosion. Potentiodynamic polarisation studies show that extracts are mixed type inhibitors. Introduction During the acidification operation in oilfield, hydrochloric acidic fluid is pumped into wells, which etches the fracture walls irregularly to create highly conductive channels[1]. So it is a challenge for the metal instruments involved. Great attentions have been drown to heat treatment and changing chemical composition to improve its corrosion resistance. But, for the aggressiveness of acidic media, the use of corrosion inhibitors is considered as the most effective method for the protection of many metals against such acid attack [2,3]. Compounds, containing functional electronegative groups and p and/or π-electron in triple or conjugated double bonds, are found to be efficient as inhibitors against metal corrosion [3-6]. It has been commonly recognized that an organic inhibitor usually promotes formation of a chelate on a metal surface, by transferring p and/or π-electrons from the organic compounds to the metal and forming a coordinate covalent bond during the chemical adsorption[7-10]. Organic compounds, containing heteroatoms, such as sulfur, phosphorus, nitrogen and oxygen, together with aromatic rings in their structure are the major adsorption centers, and the Schiff bases, a condensation product of an amine and a ketone/aldehyde, are such typical molecules [3-10]. Some polydentate Schiff base compounds (PSCs) have been reported as effective corrosion inhibitors for various metals in acid media [11-15]. Ligustrum lucidum (broad-leaf privet, Chinese privet, glossy privet, tree privet or wax-leaf privet) is a species of privet (Ligustrum genus), a flowering plant in the olive family, Oleaceae, native to the southern half of China and naturalized in many places: Spain, Italy, Algeria, Canary Islands, New Zealand, Lesotho, South Africa, Japan, Korea, Australia, Norfolk Island, Chiapas, Central America, Argentina, and the southern United States. The name "Chinese privet" is more frequently used for Ligustrum sinense[16-18]. 5th International Conference on Advanced Materials and Computer Science (ICAMCS 2016) © 2016. The authors Published by Atlantis Press 978 Figure 1 The tree, flower and seeds of Ligustrum lucidum The seeds are known as Nu-zhen-zi (female chastity seed) in traditional Chinese medicine and are believed to nourish liver and kidney Yin and Jing in the treatment of tinnitus (ringing in the ears), vertigo (dizziness), premature graying of the hair, and soreness/weakness of the lower back and knees. Ligustrum lucidum Ait. has been used in traditional Chinese medicine for over 1000 years because of its anti-tumor, antimutagenic, antidiabetic, and hepatoprotective properties. Due to the belief in the seeds' ability to nourish the liver, they are also used in the treatment of disorders of the eye involving red or dry eyes, blurred vision, and pain. Chemical constituents of the seeds include oleanolic acid(a), nuzhenide(b), and ligustroside(c), as shown in Figure 2 [16-20]. The aim of this work is to investigate the inhibition of Ligustrum sinense seeds extraction as corrosion inhibitors and bacteriostatic agent in oil field. Figure 2 Chemical constituents of the Ligustrum sinense seeds Experiment Gravimetric measurements. The corrosion tests were performed on Q235A with a composition (in wt.%) C: 0.22, P: 0.045, Si: 0.35, S: 0.05, Mn: 1.40, and Fe balance. The electrolyte solution was 1M HCl, prepared from analytical grade 38% HCl and distilled water. The concentration range of Ligustrum lucidum Ait. seeds extract (LSE) was employed as 50 mg/L to 1000 mg/L. All tests have been performed in deaerated solutions. The gravimetric tests were carried out according to the People's Republic of China Standard of Petroleum and Natural Gas Industry (Evaluation method for behavior of corrosion inhibitor for produced water of oilfield, SY/T5273-2000) with a few modifications. Each test was done with three specimens at the same time to give reproducible results. Microbiological monitoring. Viable counts of SRB, TGB and FB were determined with the “most probable number” method, People’s Republic of China Standard of Petroleum and Natural Gas Industry, the national method of the bactericidal agent’s performance, SY/T 5890-1993). The produced water containing the three kinds of bacteria was gathered from Zichang Oilfield Factory, Yanchang Oilfield.