Investigation of DiospyrosKaki L.f husk extracts as corrosion inhibitors and bactericide in oil field
© Zhang et al.; licensee Chemistry Central Ltd. 2013
Received: 23 May 2013
Accepted: 27 June 2013
Published: 1 July 2013
Hydrochloric acid is used in oil-well acidizing commonly for improving the crude oil production of the low-permeable reservoirs, while it is a great challenge for the metal instruments involved in the acidification. Developing natural products as oilfield chemicals is a straight way to find less expensive, green and eco-friendly materials. The great plant resources in Qin-ling and Ba-shan Mountain Area of Shannxi Province enable the investigating of new green oil field chemicals. Diospyros Kaki L.f (persimmon), a famous fruit tree is widely planted in Qin-ling and Ba-shan Mountain Area of Shaanxi Province. It has been found that the crude persimmon extracts are complex mixtures containing vitamins, p-coumaric acid, gallic acid, catechin, flavonoids, carotenoids and condensed tannin and so on, which indicates the extracts of persimmon husk suitable to be used as green and eco-friendly corrosion inhibitors.
Extracts of persimmon husk were investigated, by using weight loss and potentiodynamic polarisation techniques, as green and eco-friendly corrosion inhibitors of Q235A steel in 1M HCl. The inhibition efficiency of the extracts varied with extract concentration from 10 to 1,000 mg/L. There are some synergistic effects between the extracts and KI, KSCN and HMTA. Potentiodynamic polarization studies indicate that extracts are mixed-type inhibitors. Besides, the extracts were screened for antibacterial activity against oil field microorganisms, and they showed good to moderate activity against SRB, IB and TGB.
The inhibition efficiency of the extracts varied with extract concentration from 10 to 1,000 mg/L, and the highest reaches to 65.1% with the con concentration of 1,000 mg/L WE. KI, KSCN and HMTA they can enhance the IE of WE effectively to 97.3% at most, but not effective for KI and KSCN to AE. Tafel polarisation measurements indicate the extracts behave as mixed type inhibitor. Investigation of the antibacterial activity against oil field microorganism showed the extracts can inhibit SRB, IB and TGB with moderate to highly efficiency under 1,000 mg/L, which makes extracts potential to be used as bifunctional oil field chemicals.
The present work focuses on the assessment of persimmon extracts as corrosion inhibitors for Q235A steel in HCl solution. The corrosion protection effect and the mechanism of corrosion inhibition were investigated by means of linear DC polarization. The bioactivity against oil field microorganisms was also screened for the inhibition of MIC.
Materials and methods
Persimmon husk, gathered in October 2011 in Qinling Mount, were washed by clean water and dried at 60°C. Then it was shattered into powders, and the powders were heated under reflux with water or alcohol for 4 h. The mixture was cool to the room temperature, and yellow solution was filtered, and solvent was removed to yield dry extract. The persimmon husk extracts obtained by use of water and alcohol were named as WE and AE respectively.
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 1 M HCl, prepared from analytical grade 38% HCl and distilled water. The concentrations of persimmon leaves extracts were employed as 10, 50, 100, 200, 500, and 1,000 mg/L. All tests have been performed in water solutions and at 60 ± 0.5°C for 5 h. The gravimetric tests were carried out according to the Standard of Petroleum and Natural Gas Industry of People’s Republic of China (Method of SY/T5273-2000, Evaluation method for behavior of corrosion inhibitor for produced water of oilfield) with a few modifications. Each test was done with three specimens simultaneously to give reproducible results.
The electrodes were mechanically abraded with a series of emery papers (800 and 1,200 grades), then rinsed in acetone and double-distilled water before their immersion in the experimental solution. Electrochemical measurements were conducted in a conventional three-electrode thermostated cell. The electrode was inserted into a Teflon tube and isolated with polyester so that only its section (0.5 cm2) was allowed to contact the aggressive solutions. A platinum disk as counter electrode and standard calomel electrode (SCE) as the reference electrode have been used in the electrochemical studies.
The potentiodynamic curves were recorded using a CS350 system connected to a personal computer. The working electrode was first immersed in the test solution for 60 min to establish a steady state open circuit potential. After measuring the open circuit, potential dynamic polarization curves were obtained with a scan rate of 0.5 mV/s. Corrosion rates (corrosion current densities) were obtained from the polarization curves by linear extrapolation of the anodic and cathodic branches of the Tafel plots at points 100 mV more positive and more negative than the Ecorr.
CS350 electrochemical workstation hardware parameters:
Potentiostat potential control: ± 10 V; Current Control Range: ± 2.0A; Potential control precision: 0.1% × full scale reading ± 1 mV; Current control accuracy: 0.1% × full scale reading; Potential resolution: 10 μV (>100 Hz), 2 μV (< 10 Hz); Current resolution: < 10 pA; Potential rise time: < 1 μS (< 10 mA), < 10 μS (< 2A); Auxiliary 24-bit data acquisition-10 KHz, 20bit-1 KHz; Reference electrode input impedance: 1012 ohms || 20 pF; Current range 2A-00 nA, a total of 8 files; Tank pressure: 21 V; CV and LSV scan rate: 0.01-20000 mV/s; CA and CC pulse width: 0.0001-1000 s; Potential scan potential incremental: 0.1 mV-1 V/mS; SWV frequency: 0.001-100 KHz; DPV and NPV pulse width: 0.0001-1000 s; AD data acquisition: 16 bits-1 MHz, 24bit-100Hz; Minimum potential increment CV: 0.075 mV.
Viable counts of SRB, TGB and FB were determined according to the Standard of Petroleum and Natural Gas Industry of People’s Republic of China (Method of SY/T 5890–1993, The national method of the bactericidal agent’s performance). The produced water containing the three kinds of bacteria was gathered from Zichang Oilfield Factory, Yanchang Oilfield.
Inhibitor properties and mechanism
The inhibition efficiency of WE and AE measured by weight loss
(g/m2 · h)
In addition, the phenol compounds are high reductive, and researches have demonstrated that persimmon extract affords protection against lipid peroxidation in ex vivo liver homogenates when the tannin of persimmon is added before incubation with Fe2+/ascorbic acid or H2O2, which indicate that the phenols can be oxidized to benzoquinone by the O2 dissolved in the solution, which can inhibit the oxygen-adsorption corrosion.
The corrosion rate inhibition efficiency of extracts companioning with KI, KSCN and HMTA
(g/m2 · h)
WE + KI
WE + KSCN
WE + HMTA
AE + KI
AE + KSCN
AE + HMTA
Potentiodynamic polarization parameters for the corrosion of the Q230A steel in the HCl solution containing WE
Tafel polarisation measurements
Antibacterial activity against oil field microorganism
Produced water is a consequence of oil field exploitation by waterflood or steam injection or having an aquifer linked to the reservoir. The most usual disposal way for the high-volumed produced water is to re-inject it to the well after treatment, which will meet some requirements imposed by environmental and exploitation regulations, among which microbiologically influenced corrosion (MIC) is an example. MIC, mainly caused by the growth of such oil field microorganism as sulfate reducing bacteria (SRB), iron bacteria (IB) and total general bacteria (TGB) in oil pipelines, is considered as a major problem for water treatment in the oil field . Based on this case, different treatment system to inhibit corrosion should be considered, among which using bactericide has received the greatest acceptance. Currently, oxidizer, aldehyde, quatemary ammonium salt and heterocycle compounds, such as Cl2, ClO2, formaldehyde, pentane-1,5-dial, trichloroisocyanuric acid (TCCA) and ect., have been used as bactericides , but the toxicity and oxidation tests have been conducted on a limited selection.
The antifungal activity of persimmon extracts against oil field MIC
The water and alcohol extracts of persimmon husk showed moderate to high effective inhibition in the range 10 to 1,000 mg/L in 1 M HCl at 60°C, and the highest inhibition of 65.1% was obtained by using WE solution of 1,000 mg/L. KI, KSCN and HMTA can enhance the IE of WE effectively to 97.3% at most, but not effective for KI and KSCN to AE. Tafel polarisation measurements indicate the extracts behave as mixed type inhibitor. Investigation of the antibacterial activity against oil field microorganism showed the extracts can inhibit SRB, IB and TGB with moderate to highly efficiency under 1,000 mg/L, which makes extracts potential to be used as bifunctional oil field chemicals.
Financial support from Scientific and Technological Plan Projects of Shaanxi Province (2012KJXX-40), Scientific Research Program Funded by Shaanxi Provincial Education Department (2013JK0647).
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