S.C Nwigbo, V. Okafor and A.O Okewale
Keywords: Mild steel, H2SO4 solution, palm wine, corrosion inhibitor, weight loss
Abstract:
This work has explored the possibility of using a typical plant extract other than the use of conventional materials as corrosion inhibitor. Elaeis guinensis exudates (Palm wine), which contains carbonyl groups, double bonds and triple bonds as shown by the FTIR, Gas chromatography – mass spectrometry and phytochemical tests is a one of good natural materials as corrosion inhibitor. This paper was focus on the behaviour of palm wine as corrosion inhibitor for mild steel in 0.1M and 0.5m H2SO4 solution at 303K and 333K temperatures and inhibitor concentrations using weight loss measurement. Results showed that rate of corrosion increases with increase in concentration of solution. Temperature decreases with increase in concentration of inhibitor. The kinetics showed that activation energy increases with increase in temperature and concentration of corrosion inhibitors. Palm wine inhibitor adsorbed on the surface of mild steel through physical adsorption.
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ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Elaeis Guiniensis Exudates (Palm Wine) as a Corrosion Inhibitor for Mild Steel in Acidic Solution. *S.C Nwigbo, **V. Okafor and **A.O Okewale. *Mechanical Engineering Department, schuka3@yahoo.com **Chemical Engineering Department, Nnamdi Azkiwe University Awka. Abstract This work has explored the possibility of using a typical plant extract other than the use of conventional materials as corrosion inhibitor. Elaeis guinensis exudates (Palm wine), which contains carbonyl groups, double bonds and triple bonds as shown by the FTIR, Gas chromatography mass spectrometry and phytochemical tests is a one of good natural materials as corrosion inhibitor. This paper was focus on the behaviour of palm wine as corrosion inhibitor for mild steel in 0.1M and 0.5m H2SO4 solution at 303K and 333K temperatures and inhibitor concentrations using weight loss measurement. Results showed that rate of corrosion increases with increase in concentration of solution. Temperature decreases with increase in concentration of inhibitor. The kinetics showed that activation energy increases with increase in temperature and concentration of corrosion inhibitors. Palm wine inhibitor adsorbed on the surface of mild steel through physical adsorption. Keywords: Mild steel, H2SO4 solution, palm wine, corrosion inhibitor, weight loss. Introduction Mild Steel is the most commonly used engineering material [1]. It is cheap, is readily available in a wide range of standard forms and sizes, and can easily be worked upon and welded. It has a good tensile strength and is ductile in nature. However, mild steel © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 is not resistant to corrosion, except in certain specific environments such as concentrated tetraoxosulphate (vi) acid and sodium hydroxide solutions. Acids are widely used in the industries, the most important areas of application being acid pickling, industrial acid cleaning, acid descaling and oil well acidizing [2]. Organic compounds are found to be effective corrosion inhibitors due to the adsorption of molecules and ions on the metal surface [3]. The presence of large molecules with functional groups containing of hetero-atoms (such as oxygen, nitrogen, sulphur, and phosphorus), triple bonds or aromatic rings in the inhibitor's chemical structure enhance the adsorption process [4]. Considerable efforts are made to find suitable compounds to be used as corrosion inhibitors in various corrosive media. Some works were conducted to examine extracts from natural substances [5, 6]. The extracts contain mixtures of compounds having oxygen, sulphur, and nitrogen elements, which help in the corrosion inhibition process [3]. These naturally occurring compounds are environmentally friendly, safe, cheap and an anti oxidants. The inhibitive mechanism of a corrosion inhibitor affects the formation of passivating layer that blocks the access of corrosive agent to the steel, inhibiting either the oxidation or reduction part of the redox reaction or by scavaging and dissolved oxygen. Investigation of the use of palm olein from crude palm oil as corrosion inhibitor for mild steel in acidic solution was done by [6]. The Elaeis guiniensis exudates (Palm wine) contain equal amounts of saturated and unsaturated fatty acids. The unsaturated fatty acid portion consists of oleic, octadecanoic, and hexadecanoic (stearic) acids. The acids contain carbonyl groups and double bonds [7]. Consequently, the large molecular structure, double bonds, reactive centres or © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 groups are among the attributes that give the compound the ability to cover a large area of a metal surface [5]. Hence, palm wine has a good characteristic as a corrosion inhibitor owning to the fact that it contains inhibitive components such as tannins, alkaloids, phenolic compounds, saponins, oligosaccharides, and flavonoids [8]. The inhibitive action of palm wine is as a result of the adsorption of its phytochemical components on the steel surface which protects the metal surface from corrosion process. There are virtually little or no reports on the use of palm wine as corrosion inhibitor on mild steel which necessitated this work. This work will also cover the operating conditions and characteristics of the corrosion environment as the Elaeis guiniensis exudates (palm wine) acts as corrosion inhibitor for mild steel exposed in varying concentration of H2SO4 solution. Materials and Experimental Procedure The material studied was mild steel. The palm wine (Elaeis guiniensis exudates) was obtained from Awka South, Anambra State, Nigeria. Two different concentrations of 5g and 15g/100ml of inhibitor were used. H2SO4 of analytical grade was procured from an accredited chemical dealer at Onitsha, Anambra State, Nigeria. Concentrations of 0.1M and 0.5M of H2SO4 were used for the experiment. For the weight loss test, the mild steel (specimens) were mechanically polished with silicon carbide abrasive paper, degreased with ethanol, washed in distilled water and dried. The plate dimensions and weight were measured accurately. Each metal coupon was of the size 4cm × 3cm × 0.3cm. Before polishing, a hole of about 0.1cm was drilled on each coupon. The coupon was suspended with the aid of nylon thread and glass rod in a 300ml beaker with 100ml of the acid (0.1M and 0.5M H2SO4) © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 without and with different concentrations of the inhibitors. To prevent evaporation of solution and contamination, the corrosion vessel was covered with parafilm. At various time intervals the sample was retrieved dipped in distilled water and immersed in saturated sodium carbonate solution scrubbed with bristle brush, to remove residual acids and then washed with washing liquor (NaOH + Zn dust) thouroughly, rinsed with distilled water, dried in acetone before reweighed. The corrosion test was performed at two different temperatures of 303K and 333K. Table 1.0 Composition of Mild Steel Chemical Constituents Percentage Composition (wt. %) Carbon 0.14 Silicon 0.03 Manganese 0.32 Sulphur 0.05 Phosphorus 0.20 Copper 0.01 Chromium 0.01 Iron Balance Phytochemical Test Analysis Preliminary phytochemical screening 1gm of the Palm wine was dissolved in 100ml of its own mother solvents to obtain a stock of concentration 1% (v/v). The extracts obtained were subjected to preliminary phytochemical screening using the recommended standard screening procedure. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Determination of Alkaloids 5ml of the palm wine was added to 2ml of HCl followed by addition of 1ml of Dragendroff's reagent. An orange or red precipitate produced immediately indicates the presence of alkaloids. Determination of Saponins 5ml of palm wine was diluted with 20ml of distilled water, agitated in a graduated cylinder for 15minutes. The formation of 1cm layer of foam showed the presence of saponins. Determination of Flavonoids 1ml of the palm wine, few drops of dilute NaOH was added. An intense yellow colour was produced in the plant extract, which becomes colourless on addition of a few drops of dilute acid (HCl) indicates the presence of Flavonoids. Determination of Anthraquinones 5ml of the palm wine solution was hydrolysed with diluted conc. H2SO4 extracted with benzene. 1ml of dilute ammonia was added to it. Table 2.0 Chemical Constituent of the Palm wine. Chemical Constituents Percentage Compositions (%) Tannins 6.5 Saponins 3.1 Alkaloids 10.6 Anthraquinones Nil Flavonoids 1.6 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Determination of the functional group in the palm wine. The Fourier transforms infrared spectrophotometer (FTIR 8400S) SHIMADZU was used for the identification of the palm wine functional group. Determination of Compounds in the Palm wine Gas chromatography mass spectrometry (GC MS QP2010) plus SHIMADZU was used to identify the different compounds present in the palm wine. Results and Discussions Fig. 1.0 2.0 shows the weight loss of mild steel in 0.1M and 0.5M H2SO4 solution with and without the presence of inhibitor at 303K. The weight loss of mild steel in the absence of palm wine was very much higher as compared to the weight loss in other solutions in the presence of inhibitor. The corrosion was due to the presence of the OH-, air, H2+, and SO42- which accelerate the corrosion process of the mild steel. Increased in concentration of palm wine inhibitor reduced the weight loss of mild steel which indicated the positive effect of the inhibitor on corrosion of mild steel. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 1.4 ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 1.2 Weight Loss, (g) 1 0.8 0.6 0.4 Blank 5g/mol 15g/mol 0.2 0 0 20 40 60 80 100 120 140 Duration of exposure, (hr) Fig. 1.0 Weight loss (g) against duration of exposure (hr) at 303K, 0.1M H 2SO4 7 6 Weight loss, (g) 5 4 3 2 Blank 5g/mol 15g/mol 1 0 0 20 40 60 80 100 120 140 Duration, (hr) Fig. 2.0 Weight loss (g) against duration of exposure (hr), at 303K, 0.5M H 2SO4 Fig. 3.0 4.0 indicates that as concentration of acid increases with temperature the © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 weight loss of the mild steel decrease. For each concentration at both temperatures, an increase in duration of exposure from 24hours showed decrease in the corrosion of mild steel. 1.6 1.4 Weight loss, (g) 1.2 1 0.8 0.6 0.4 Blank 5g/mol 15g/mol 0.2 0 0 20 40 60 80 100 120 140 Duration of exposure, (hr) Fig.3.0 Weight loss (g) against duration of exposure (hr) at 333K, 0.1M H 2SO4 7 6 Weight loss, (g) 5 4 3 2 Blank 5g/mol 15g/mol 1 0 0 20 40 60 80 100 120 140 Duration exposure, (hr) Fig. 4.0 Weight loss (g) against duration of exposure (hr) at 333K, 0.5M H 2SO4 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Fig. 5.0 gives the GCMS result of the palm wine. The oleic acid, hexadecanoic acid (palmitic acid) and octadecanoic acid (stearic acid) are the main compounds present in the palm wine but oleic acid which is a monosaturated omega- 9 fatty acid has the highest peak value. The carbonyl group and double bonds carbon present in oleic acid compound suggest that the palm wine inhibited the mild steel corrosion. The presence of the stearic acid that results from the hydrogenation of the double bond of oleic acid also suggests the palm wine as a good corrosion inhibitor. Fig. 5.0 GCMS of the Palm wine Fig. 6.0 shows the FTIR result of the palm wine with the peak of the double bond carbon functional also confirms the palm wine as good corrosion inhibitors on the mild steel. The presence of the tannins and alkaloids in the phytochemical test also aided corrosion inhibition of the mild steel. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Fig. 6.0 FTIR spectrometry of the palm wine Fig. 6.0 shows the FTIR result of the palm wine with the peak of the double bond carbon functional also confirms the palm wine as good corrosion inhibitors on the mild steel. The presence of the tannins and alkaloids in the phytochemical test also aided corrosion inhibition of the mild steel. Adsorption Isotherms Adsorption isotherms are very important in understanding the mechanism of corrosion inhibition reaction of mild steel. From the weight loss measurement data, Langmuir adsorption isotherm was performed in the analysis. Langmuir relationship: C = 1 θ K +C (1) where K is the equilibrium constant of adsorption (M-1), C (M) is the concentration of the adsorbate in the bulk of the electrolyte (inhibitor), θ is the degree of surface coverage. Taking logarithm of both sides of equation (1) above log C = log C – log K. (2) θ © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 A plot of log C/ θ against log C gives a slope of K. Langmuir isotherm is an ideal isotherm for physical or chemical adsorption where there is no interaction between the adsorbate and the adsorbent. The applicability of Elaeis guinensis exudates on mild steel confirms the formation of multi-molecular layer of adsorption where there is no interaction between the adsorbate and the adsorbent [9]. Using the K value determined from the Langmuir isotherm relationship, the standard free energy of adsorption ? Goads (kJ/mol) value at different temperature can be determined according to the following equation; ln K = ln 1 55.5 - ? Go ads (3) RT ? Goa ds = -2.303RT log (55.5K) (4) Where (1/55.5) is the standard molar of water in the solution, R is the gas constant (8.314 J/mol K) and T (K) is the temperature [10]. Table 3.0 and 4.0 shows the value of K and ? Goads at 303K and 333K temperatures and 0.1M and 0.5M H2SO4 solution. The negative sign of the free energy of adsorption indicates that the adsorption of the inhibitor at the metal surface is a spontaneous process. The ? Go ads values which were below 40 KJ/mol indicate physical adsorption on the transfer of unit mole of the inhibitor from solution on to the metal surface [10]. Table 3.0. The values of K and ? Goads at 0.1M H2 SO4 solution Inhibitor Conc. Temperature (K) K (M-1 ) ? Go ads (kJ/mol) 5g/100ml 15g/100ml 5g/100ml 15g/mol 303 303 333 333 0.041 0.012 0.013 0.014 -10.58 -20.89 -23.03 -33.67 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Table 4.0 The Volume 14, Preprint 34 values of K and ? Goads at 0.5M H2SO4 solution submitted 10 August 2011 Inhibitor Conc. Temperature (K) K (M-1 ) ? Go ads (kJ/mol) 5g/100ml 15g/100ml 5g/100ml 15g/100ml 303 303 333 333 0.047 0.015 0.036 0.014 -19.39 -24.31 -26.40 -35.87 Kinetics Activation energies (Ea) of the corrosion process were evaluated from the Arrhenius equation; Log CR2 = Ea [ 1 – 1] CR1 2.303R T1 (5) T2 Where CR 1 and CR2 are the corrosion rates at temperatures T1 and T2 , respectively. The activation energy as evaluated from equation (5) above gives; Ea = [2.303R log (CR2 /CR 1)] (6) (1/T1) – (1/T 2) Corrosion rate of the mild steel by the inhibitors is as follows; R = 534 w (7) l AT where T is the operational time, w is the weight loss of mild steel, l is the density of mild steel, and A is the exposed area of corrosion. From Table 5.0, it was shown that an increase in temperature from 303K to 333K had an increase in the value of activation energy value. However, increases in concentrations of the inhibitor increase the activation energy which indicated the resistance of mild steel towards corrosion. The increase in activation energy indicated that physical adsorption of palm wine occurred on the mild steel surface [11]. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 Table 5.0 Activation Energies of Reaction at 303K and 33K respectively. 0.1M H2SO4 solution Blank 5g/100ml 15g/100ml 0.5M H2SO4 solution Blank 5g/100ml 15g/100ml Activation Energy (kJ) 8.679 24.5 34.52 Activation Energy (kJ) 4.461 24.67 91.83 Conclusion Increase in temperature favours a decrease in corrosion of mild steel. The Langmuir adsorption isotherm fitted well for the experimental data for both temperatures studied. Increase in concentration of acid solutions increase rate of mild steel corrosion. Activation energy increase with inhibitors concentrations. FTIR result of the palm wine with the peak of the double bond carbon functional also confirms the palm wine as good corrosion inhibitors on the mild steel. References [1] ‘Chemical engineering design’, 5th ed., R. Sinnott, G. Towler, Butterwort – Heinemann, USA, pp.294, 2009. [2] ‘Protective coatings for metal surfaces from ethyl esters of fatty acids and waste products of oil industry’, D.Yordanov, P. Petkov, Journal of University of Chemical Technology and Metallurgy, 43, 3, pp.315 – 318, 2008b. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 14, Preprint 34 submitted 10 August 2011 [3] ‘Palm olein as an eco –friendly corrosion inhibitor for aluminium in corrosive solution’, J. Jai, W.S.Wan – Ali, Journal of Corrosion Science and Engineering, 12, Preprint 32, 2009. [4] ‘Inhibition of acid corrosion of carbon steel using aqueous extract of olive leaves’, A.Y. El – Etre, Journal of Colloid and Interface Science, 314, pp578 – 583, 2007. [5] ‘Inhibition of aluminium corrosion using opuntia extract’, A.Y. El- Etre, Corrosion Science, 45, pp2485 – 2495, 2003. [6] ‘Development of palm oil based anti – corrosion material for underwater protection’, N. Yaakob, Master dissertation, Universiti Teknologi MARA, pp56, 2007. [7] ‘New school chemistry’, 3rd ed. O. Y. Ababio, African first publishers, Onitsha, Nigeria, pp509, 2001. [8] ‘Production and utilization of palm wine’, C.O Akachukwu, Mann and wend land, 2001. [9] ‘Protection of corrosion of aluminium using exudates gum from pachylobus edulis in the presence of halide ions in HCl’, S.A. Umoren, I.B. Obot, and E.E. Ebenso, E-Journal of Chemistry, 5, 2, pp355 – 364, 2008. [10] ‘Carboxymenthylchitosan as an ecofriendly inhibitor for mild steel in 1M HCl’, S. Cheng, S. Chen, T. Liu, X. Chang, Y. Yin, Materials Letters, 61, 14 – 15, pp3276 – 3280, 2007. [11] ‘Investigation of adsorption and inhibitive effect of 2 – mercaptothiazoline on corrosion of mild steel in hydrochloric acid media’, R. Solmaz, et al., Electrochimical Acta, 53, 20, pp5941 – 5952, 2008. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.