GC-MS and Adsorption Studies of Corrosion Inhibition ...

Nigerian Journal of Science Vol 54 - No 1 (2020) 157-167Date Received 01/11/2019

Corrected & Acceptance Date 24/07/2020

Abstract

The corrosion inhibition effect of Citrullus spp. (water melon) peel extract on mild steel in 1.5 M H SO 2 4

has been investigated by weight loss and Fourier transform infrared (FTIR) spectroscopy with various concentrations of the extract and at two temperatures, 303 K and 333 K. The gravimetric results obtained indicated that Citrullus spp. peel extract acted as an effective inhibitor in the acid environment with inhibition efficiency of 60.84 % and 47.85 % at 0.5 g/L inhibitor concentration at 303 K and 333 K respectively. The inhibition efficiency of the extract increased with increase in

2concentration but decreased with increase in temperature. The correlation coefficient (R ) found at 0.9860 revealed that the adsorption occurred according to Langmuir adsorption isotherm model. Thermodynamic parameters such as Activation energy, E (24.56 kJ/mol), Heat of adsorption, Q (-a ads

12.41 kJ/mol) and Gibb's free energy, (-11.38 kJ/mol) suggested that the adsorption of Citrullus spp. on mild steel surface was consistent with the mechanism of charge transfer from the inhibitor's molecule to the charged metal surface and it is spontaneous, which supports physical adsorption mechanism. Furthermore, GC-MS and FT-IR analyses confirmed that the Citrullus spp. peel extract contained several antioxidants and there seemed to have been an interaction between the metal and the inhibitor through bond breakage and bond formation.

Introduction

Mild steel is an alloy of iron and other elements containing the composition (wt %): C (0.14), Mn (0.35), Si (0.17), S (0.025), P (0.03), and the rest Fe (Siaka et al., 2012). Mild steel is one of the most important widely used engineering materials particularly for the structural, automobiles, pipes etc. applications (Prabhu et al., 2009) because of their special properties. Mild steel suffers from severe corrosion in aggressive medium of variety of strong acids and, industrial cleaning processes

such as pickling and acid de-scaling (Muhammad et al., 2011 and Ostovari et al., 2009).Hydrochloric acid is widely used for pickling, descaling, and chemical cleaning processes of mild steel, while 90 % of pickling problems can be solved by introducing appropriate pickling inhibitor to the medium (Shyamala and Kasthuri, 2011). Corrosion is a gradual destruction of a material because of its reaction with environment. Both direct and indirect losses due to corrosion are huge. The control of corrosion is thus primarily an economic problem. Corrosion inhibitors reduce the rate of either anodic oxidation or cathodic reduction or both (Murugavel and Gunavathy, 2012). Many synthetic compounds offer good

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Keywords: Adsorption, Corrosion, Mild Steel, Inhibition Potentials and Citrullus spp. Peel

GC-MS and Adsorption Studies of Corrosion Inhibition Potentials of Citrullus Spp. (Water Melon)

Peel Extract on Mild Steel in Sulphuric Acid Solution

1* 2N.S. GULUMBE AND A.A. SIAKA

1Department of Science Education, Waziri Umaru Federal Polytechnic, Birnin Kebbi, Nigeria2Department of Applied Chemistry, Federal University Dutsin-Ma, Katsina State, Nigeria

*Corresponding Author E-mail:[email protected]

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anticorrosive action; but most of them risk being highly toxic to both human beings and environment. In these later years, researchers reorient their studies to the use of naturally occurring substances such as plant extracts and oils (Dahmani et al., 2010). In today's industrial world there is a focus on cost savings and there is a continuous search for new innovative technologies and solutions to extend the working life of existing assets and infrastructure while lowering environmental impact. The world of pipelines is no different in its search for smarter and greener solutions. As large number of liquid transport pipelines increases, maintenance and operating costs continue to rise, there has been an increased focus on finding environmentally friendly, innovative solutions to achieve these goals (Boris et al., 2009). Considerable efforts are being deployed to find suitable compounds to be used as corrosion inhibitors in various corrosive media to stop or delay, to the maximum, the degradation of metal and metallic materials. Many metals and alloys that are used in different human activities are susceptible to different mechanisms of corrosion due to their exposure to different corrosive media. The study of mild steel corrosion phenomena has become important particularly in acidic media because of the increased industrial applications of acid solutions.

This study intended to enrich the existing body of literature on the corrosion inhibition potentials of several green plants (Ebenso et al., 2008; Eddy and Ebenso, 2008; Eddy, 2009; Eddy and Mamza, 2009; Ebenso and Eddy, 2010; Mejeha et al., 2010; Murugavel and Gunavathy, 2012; Fidrusli et al., 2018) using Citrullus spp. peel extract as green and alternative eco-friendly corrosion inhibitor source.

Materials and Methods

Preparation of Mild Steel SpecimenThe mild steel sheet used in the study were mechanically pressed-cut into a dimensions 4.5 × 2 × 0.2 cm with the following composition (wt %): C (0.14), Mn (0.35), Si (0.17), S (0.025), P (0.03), and the rest Fe (Siaka et al., 2012). The

mild steel strips were degreased by washing with ethanol, cleaned with acetone and allowed to dry in the air before preservation in a moisture free desiccator (Eddy and Ebenso, 2008; Mejeha et al., 2010 and Shyamala and Kasthuri, 2011).

Preparation of the Plant ExtractWatermelon fruit peels were collected from watermelon sellers in Aliero town, Kebbi State. The fruit peels were thoroughly washed with clean water and cut into small pieces, sun-dried for prolong period of time and ground well into powder. The sample was soaked into ethanol for 72 hours, a refluxed solution was then filtered carefully. The filtrate was further subjected to evaporation at 352 K in order to leave the sample free of the ethanol. The stock solution of the extract so obtained was used in preparing different concentrations of the extract ranging from 0.1 g/l to 1.5 g/l in 1.5 M H SO solution 2 4

(Eddy and Ebenso, 2008; Mejeha et al., 2010; Shyamala and Kasthuri, 2011).

Gravimetric MethodThe sampled mild steel strips were weighed using a digital weighing balance, labelled and immersed in the test solutions (1.5 M H SO ) with 2 4

and without inhibitor for 24 hours at 303 K and 333 K. After immersion, the pieces of coupon were removed, washed with NaOH and zinc dust, degreased in ethanol, dried with acetone and weighed again, and the process was carried out for 168 hours. The weight loss of the metal in the corrosive solution, the inhibition efficiency (%I) of

the inhibitor, the degree of surface coverage (q) and the corrosion rate of the mild steel (CR) were calculated using equation 1, 2, 3 and 4 respectively (Elewady et al., 2008; Mejeha et al., 2010; Murugavel and Gunavathy, 2012):

..................................................(1)

........................(2)

...............................................(3)

..................................................(4)

N.S. Gulumbe & A.A. Siaka: (water Melon) Peel Extract on Mild Steel in Sulphuric Acid Solution

GC-MS and Adsorption Studies of Corrosion Inhibition Potentials of Citrullus Spp.

Nigerian Journal of Science Vol 54 - No 1 (2020): 157-167

159

where W and W are the weight of metal before 1 2

and after exposure to the corrosive solution respectively, is degree of surface coverage, is weight loss of the mild steel in g after time "t", W is weight loss in g, T is exposure time in hours and

2A is exposed area of coupon in cm .

GC-MS Analysis of the Plant ExtractGas Chromatography (GC) has played a fundamental role in determining how many components and in what proportion they exist in a mixture by separating volatile and semi-volatile compounds with a great resolution but, it has no ability to identify their nature and chemical structures – it requires a spectroscopic detection system for that (Elena and Jairo, 2014). Mass Spectrometry (MS) provides detailed structural information on most of compounds such that they can exactly be quantified but it cannot readily separate them. Thus, GC-MS can be said to be an analytical method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. Both techniques used a vapour phase sample of not more than 1 ng. GC-MS enables mixture of small molecules mainly organic compounds of low molecular weight (<600) to be analysed (Asha et al., 2017).

Gas chromatography-mass spectrophotometer (Agilent Technologies 6890 made) was used for the GC-MS analysis of ethanol extract of Citrullus spp. in accordance with the method described by (Asha et al., 2017). The molecular weight and structure of the compounds present in the Citrullus spp. extract were determined by comparing the mass spectrum obtained (unknown component) with the available patterns/spectra (known component) stored database in National Institute Standard and Technology library (Eddy et al., 2012).

Results and Discussion

Weight Loss, Corrosion Rate and Inhibition EfficiencyThe weight loss study, corrosion rate and inhibition efficiency for mild steel was carried-out in 1.5 M H SO acid in the absence and presence of various 2 4

concentrations of the Citrullus spp. extract ranging from 0.1 g/l to 0.5 g/l. Using the weight loss data, inhibition efficiency, surface coverage of the inhibitor and the corrosion rate have been calculated. The results obtained in the weight loss method are summarised on Table 1.

Table 1: Corrosion parameters for mild steel in 1.5 M H2SO4 in absence and presence of different concentrations of the inhibitor

Concentrations (g/l)

Inhibition Efficiency (%I)

Surface Coverage (q)

Corrosion Rate (g/cm2h)

303 K 333 K 303 K 333 K 303 K 333 K

Blank - - - - 1.63 ×10-4 2.95 ×10-4

0.1 30.23 4.47 0.3023 0.0447 1.14 ×10-4 2.82 ×10-4

0.2 55.55 23.20 0.5555 0.2320 7.26 ×10-5

2.26 ×10-4

0.3

54.47

39.61

0.5447

0.3961 7.44 ×10-5 1.78 ×10-4

0.4

59.95

46.37

0.5995

0.4637 6.54 ×10-5

1.78 ×10-4

0.5 60.84 47.85 0.6084 0.4785 6.40 ×10-5 2.95 ×10-4

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Figure 1: Variation of weight loss with time for the corrosion of mild steel in 1.5 M H2SO4 in the presence for various concentrations of inhibitor

Figure 2: Variation of weight loss with time in the absence of inhibitor

Effect of TemperatureThe effect of temperature on the corrosion of mild steel in 1.5 M H SO , in the absence and 2 4

presence of various concentrations of Citrullus spp. was assessed from the Arrhenius equation which is represented as in equation 5 (Siaka et al., 2012):

..................................(5)

where CR is the corrosion rate of the mild steel, A is the Arrhenius or pre-exponential factor, Ea is the activation energy, R is the universal gas constant and T is the temperature. Taking the logarithm of both sides of equation yields the equation 6:

.......................(6)



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If the corrosion of mild steel at temperatures T1 (303K) and T2 (333K) is CR1 and CR2, then substitutions into equation 6 yields equation 7 (Eddy et al., 2012):

.......................(7)

The activation energies and heat of adsorption calculated from equation (7) and (8) are presented on Table 2. From the result obtained, it can be seen that the activation energies are below the

-1threshold value (80 kJmol ) expected for the mechanism of chemical adsorption. Therefore, the adsorption of Citrullus spp. on mild steel surface is consistent with the mechanism of charge transfer from the inhibitor's molecule to the charged metal surface, which supports physisorption mechanism (Siaka et al., 2012).

Table 2: Activation energy and heat of adsorption for the adsorption of Citrullus spp. on the mild steel surface

Concentration (g/l) Ea (kJ/mol) Qads (kJ/mol)

0.1 2.53 -62.290.2

3.18

-39.71

0.3

24.45

-16.800.4

24.72

-15.33

0.5 24.56 -12.41

Thermodynamic and Adsorption ConsiderationsThe heat of adsorption of Citrullus spp. extract on mild steel surface was calculated using equation 8:

......(8)

As presented on Table 3, there is notable decrease in the value of corrosion rate with increase extract concentration due to higher degree of surface coverage, because of enhanced inhibitor adsorption. The adsorption characteristics of ethanol extract of Citrullus spp was also investigated by fitting data obtained for the degree

of surface coverage using Langmuir adsorption isotherm. The assumption of Langmuir adsorption isotherms is expressed in equation 9 below (Eddy, 2009):

..................................................(9)

where C is the concentration of the inhibitor in the

bulk electrolyte, q is the degree of surface coverage of the inhibitor and K is the adsorption equilibrium constant. Taking logarithm of equation 9 yields equation 10:

...........................(10)

.......(11)

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Figure 3: Langmuir isotherms for the adsorption of Citrullus spp. inhibitor on the mild steel surface at 303 K

Table 3: Values of Langmuir Adsorption Parameters for the adsorption of ethanol extract of Citrullus spp. on mild steel surface at 303 K.

Temperature (K) Log Kads Slope DGads R2

303 0.217 1.097 -11.38 0.986

FT-IR Analysis of the Citrullus spp. ExtractThe Fourier Transformed Infrared (FT-IR) spectrum of pure sample of by Citrullus spp. extract is presented in Figure 4, while the wavelengths and peaks of IR adsorption are presented on the Table 4. Fig. 5 shows the FTIR spectrum of the Citrullus spp. extract after being used as inhibitor. With Citrullus spp. as inhibitor,

-1the C-O stretch at 1084.03 cm shifted to 1047.38

-1 -1 cm , the aromatic C=C stretch at 1431.23 cm

-1shifted to 1448.59 cm , the C=H stretch at

-1 -11652.09 cm shifted to 1689.70 cm , the C-H stretch -1 -1at 2931.90 cm shifted to 2918.40 cm and O-H

-1 -1stretch at 3570.36 cm shifted to 3552.03 cm , which indicated that probably there was an interaction between the metal and the inhibitor (Eddy and Mamza, 2009). On the other hand, the

-1aromatic CºC bonds at 2103.44 cm was absent in the spectrum of the corroded product indicating that the bond might have been involved in the adsorption of the inhibitor onto the metal surface (Ebonso et al., 2008 and Siaka et al., 2012).




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Figure 4: FT-IR spectrum of pure sample of Citrullus spp. extract

Table 4: Peaks, intensity and assignments of IR adsorption by Citrullus spp. extract after being used as an inhibitor

Citrullus spp. Corrosion Rate

Peak (cm-1) Intensity Assignments Peak (cm-1) Intensity Assignments 456.18 11.616 615.31 33.484 -C=C- 1084.03 77.594 C–O stretch 1047.38 35.688 C–O stretch 1431.23 73.513 Aromatic C=C 1448.59 33.973 Aromatic C=C 1652.09 70.311 C=C stretch 1689.70 34.083 C=C stretch 2103.44 93.818 C=C(monosubstituted)

2136.23 35.955 2931.90 69.760 C–H stretch 2918.40 32.867 C–H stretch 3570.36 64.069 O–H stretch 3552.03 29.581 O–H stretch

Figure 5: FT-IR spectrum of Citrullus spp. extract after being used as an inhibitor

GC-MS Analysis of the Citrullus spp. ExtractThe gas chromatography mass spectroscopy analysis of the Citrullus spp. extract was conducted and the spectrum obtained is given in the Figure 6 below.

Figure 6: GC-MS spectrum of ethanol extract of Citrullus spp. inhibitor

Retention time, molecular formula, mass peaks, concentrations and compound name obtained from reliable spectral library are presented on Table 5. From the results obtained, it was revealed

that the separated compounds can be classified into the following classes of hydrocarbons; aliphatic alcohol (butane-2,3- diol), phenol (3,5-Di-tert-butylphenol), aliphatic acid (2-Hydroxy-2-methylmalonic acid), aromatic ketone (3,5-Dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one), aromatic aldehyde (2-Furancarboxaldehyde, 5-(hdroxymethyl), ester (2-hdroxy-1,3-propanediyl ester) and aromatic amine (Cyclohexaneethanamine,

N, a– dimethyl).

Table 5: Characterization of peaks obtained from GC-MS spectrum of ethanol extract of Citrullus spp. inhibitor

Line Concentration (%)

Chemical formula

Retention time (s)

Mol. Weight (g/mol)

Name of Compound

1 8.07 C4H10O2 3.425 90 Butane-2,3-diol 2 12.20 C4H6O5 5.830 134 2-Hydroxy-2-methyl malonic acid

3 3.13 C6H8O4 8.700 144 3,5-Dihydroxy-6-methyl-2,3-dihydro-4Hpyran-4-one

4 3.43 C6H6O3 10.158 126 2-Furancarboxaldehyde,5-(hydroxymethyl)-

5

0.78

C14H22O 13.583

206

3,5-Di-tert-butylphenol

6

13.61

C16H32O2

20.233

256

Pentadecanecarboxylic (Palmitic) acid

7

24.62

C18H34O2

23.058

282

9-Octadecanoic acid

8

17.88

C18H36O2

23.275

284

Octadecanoic acid (Stearic acid)

9

2.03

C10H21N

25.708

155

Cyclohexaneethanamine,N, a-dimethyl-

10

9.06

C39H74O6

27.392

638

1,2,3-propanetriyl ester (Glyceryl trilaurate)

11

5.18

C27H52O5

27.808

456

2-(Dodecanoyloxy)-1-(hydroxymethyl)ethyl laurate



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3,5-Di-tert-butylphenol with molecular weight 206 g/mol constitute the least concentration at 0.78 %, while, 2-hydroxy-1,3-propanediyl ester with molecular weight 624 g/mol and 9-Octadecanoic acid with molecular weight of 282 g/mol constitute the minimum at 17.88 % and maximum at 24.62 % of the chemical constituents of Citrullus spp. inhibitor respectively. However, it has been noted that 9-Octadecanoic acid attained the highest peak in line 7 as indicated in figure 6 above.

In line 1, the major constituent is Butane-2,3-diol (8.07 %), which is a valuable chemical feedstock because of its application as a solvent, a liquid fuel, and a precursor of many synthetic polymers and resins. A wide variety of chemicals can also be easily prepared from Butane-2,3-diol. Currently, the manufacturing of Butane-2,3-diol is still growing by an annual rate of 4–7 % due to the increased demand for polybutylene

terephthalate resin, ã-butyrolactone, spandex, and their precursors (Maesomeh and Reza, 2011).Line 2, 6-8, 10 and 11 comprised several carboxylic acids, which included; malonic acid (line 2), palmitic acid (line 6), 9-Octadecanoic acid (line 7), stearic acid (line 6 and 8), lauric acid (line 10 and 11) and Dodecanoic acid (line 11). The concentration of these acids in the extract was found to range from 5–24 % and forms the dominant constituents of the plant extract. Industrial applications of carboxylic acids cannot be overemphasized. Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents and food additives (Nnabuk et al., 2011).

In line 3 and 4, different aldehydes and ketonic compounds were obtainable which included; 3,5-Dihydroxy-6-methyl-2,3-dihydro-4Hpyran-4-one (line 3) and2-Furancarboxaldehyde,5-(hydroxymethyl) (line 4).

Figure 7: Chemical structures and labelling of some of the molecules found in the Citrullus spp. extract


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In line 5, 3,5-Di-tert-butylphenol was identified. The alcohol and its derivatives are used industrially as UV stabilizer and an antioxidant for hydrocarbon- based products ranging from petrochemicals to plastics. Illustrative of its usefulness, it prevents gumming in aviation fuels. 2,6-Di-tert-butylphenol is a precursor to more complex compounds used as antioxidants and light-protection agents. Representative derivatives include 3,5-di-tert-butylbenzyl chloride, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and methyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)- propionate. Such derivatives are prepared from 2,6-di-tert-butylphenol by chloromethylation and hydroxymethylation using formaldehye and alkylation with acrylic acid.

In line 9, different forms of amine compounds were identified which included; Cyclohexaneethanamide, N,a–dimethyl, N1-isopropyl-2-methyl-1,2-propandiamine etc.

Conclusions

From the study, inhibition of mild steel corrosion by Citrullus spp. extract was found to be thermodynamically feasible. The adsorption mechanism of inhibition of mild steel corrosion by Citrullus spp. is by physical adsorption according to the classical Langmuir isotherm model. Citrullus spp. extract acted as a good green inhibitor for mild steel corrosion.

Acknowledgement

We, the authors highly appreciated the support and assistance received from the academic and non-academic staff of Chemistry Department of Kebbi State University of Science and Technology, Aliero in the course of this study.



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