Performance Evaluation of Bryophyllum Leaves Extract as Corrosion Inhibitor for Mild Steel in 1M Phosphoric Acid

doi:10.21203/rs.3.rs-3996094/v1

The severe consequences of corrosion process cause global issues most especially in petroleum refineries. This research investigates performance evaluation and optimization of bryophyllum pinnatum leaves extract for mild steel corrosion inhibition. The extract was subjected to phytochemical analysis to determine the inclusion of any bioactive component. Box Behnken design was used to optimize process variables which include Temperature (30°C-60°C), Immersion time (3–12 days), and amount of extract (0.2–0.8 g/l). Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) were used for characterization. Phytochemical analysis revealed the presence of flavonoids, tannins, saponins, alkaloids, terpenoids, and steroids. It was established from experimental results that Temperature of 30°C, Immersion time of 3 days, Inhibition concentration of 0.8g/l gave the best process, while the optimal process variables gave: Immersion time: 6.3 days, Inhibition concentration: 0.63g/l days; Temperature: 58.6°C respectively. The results of SEM, EDS and FTIR revealed that mild steel via validated optimal process level had more protective film and was formed through adsorption. Hence, Bryophyllum pinnatum extract has been established as an effective corrosion inhibitor.

Box-Behnken Design

Bryophyllum Pinnatum Leaves

Corrosion

Inhibition Efficiency

Materials

Mild steel has become a material with increasing demand for structural applications. It is a choice metal employed in industries for engineering purpose. However, corrosion is one of the major challenges affecting its functionality and optimum performance [1]. The term "corrosion" refers to the degradation of metal caused by an environmental chemical or electrochemical reaction. It has been asserted that corrosion cannot be completely eradicated [2]. As a result, prevention would be more effective than elimination. Therefore, using corrosion inhibitors to prevent corrosion of metals is highly recommended. Corrosion inhibitors are substances that reduce, obstruct, or stop metal corrosion. [3]. Charge sharing or charge transfer from the inhibitor molecules to the metal surface via a coordinate-type bond occurs during the chemisorption process and only occurs when heteroatoms (P, N, and S O) with lone pair electrons and/or aromatic rings are present in the molecular structure. [4]. Corrosion is unavoidable in manufacturing industries especially in Oil and gas. Green technology/ corrosion inhibitors are highly acceptable due to their environmental friendliness, low cost, lack of toxicity, and accessibility. Plant extracts are becoming a more viable, affordable, and environmentally friendly alternative to the toxic chemical corrosion inhibitors now used. Plant extracts primarily reduce corrosion by physisorption, chemisorption, and retro donation. Flavonoids, terpenoids, tannins, phenolic acids, alkaloids, lipids and other nitrogen-containing metabolites all interact physically and chemically with steel surface to prevent corrosion. Some extracts that had been used as inhibitors are include: bryophyllum pinnatum leaves [5]; Falcaria vulgaris leaves [6];Papaya leaves [7], Sweet Potato Leaf Extract [8], Ceratonia siliqua L. seeds extract [9], Chrysanthemum coronarium leaves extract [10], Artemisia Capillaris Leaf Extract [11], Multileaf (Pterocarpusmsantalinoides) [12], Nettle (Urtica dioica L.) plant extract [13], Artemisia annua L. Extract [14], maple leaves extract [15] Tulsi and green tea extracts [16]; leaves of Calamintha plant [17]. Furthermore, the presence of phytochemicals constituents in plant extracts affects mechanism of inhibition and formed absorption on the surface of metals in the corrosive environment e.g. in bryophyllum pinnatum extract (BPE) with 0.5 M HCl [5]. This novelty in this study identified the optimal variables that maximized the effectiveness of BPE in H₃PO₄ acidic medium. Furthermore, no work had been reported using the Box Behnken design despite extensive research on the application of BPE.

2.1 Materials

Bryophyllum pinnatum leaves extract and Mild steel were used in this study. The reagents were Ethanol, Phosphoric acid and Acetone. Reagents used in this research were of analytical grade.

2.2 Preparation of Bryophyllum pinnatum Extract

Bryophyllum pinnatum leaves were taken from Landmark Research Farms. Thirty (30) grams of bryophyllum pinnatum extract were inserted in the body of a Soxhlet extractor which was filled with 350 ml of ethanol (solvent). The procedure lasted 5 hours. Finally, the extract was collected and refrigerated for further use. This methodology was adapted from previous studies [18, 19].

2.3 Preparation of Metal specimen

Mild steel was obtained from Landmark University's Mechanical Workshop. Furthermore, to enable complete immersion of the mild steel during the experiments, it was divided into coupons measuring 2 cm ×2 cm × 0.5 cm with a 0.1 cm hole drilled in the center. The mild steel was cleaned with emery paper, washed, degreased with acetone and weighed.

2.4 Preparation of Corrosive Medium (1M of Phosphoric acid)

In order to prepare 1M of phosphoric acid solution, 67.8 ml of phosphoric acid was dissolved in 1L of distilled water.

Phytochemical analysis was done to examine quantitative and qualitative of the phytochemical constituents.

3.1 Experimental Design

The Box-Behnken Design in Design Expert (v12.0.0) was used to investigate process variable interactions, resulting in a model that correlates the independent variables with the corrosion rate. (Response). Box-Behnken design generated 17 experimental runs from the 3 variables considered for this study.

The process variables that were considered for this research include;

Time (3 days-12 days)
Temperature (30 ^oC-60 ^oC)
Inhibition concentration (0.2 g/l-0.8g /l).

Variables with low and high levels is illustrated in Table 1 while Table 2 is for the variables interactions as generated by the software.

Table 1

Variables with levels
Variables	Unit	Levels
Variables	Unit	Low	High
Time of immersion	Days	3	12
Temperature	⁰C	30	60
Inhibition concentration	g/l	0.2	0.8

Table 2

Variables Interaction
Std	Run	Variable 1 A:Time of immersion (Days)	Variable 2 B:Temperature (^oC)	Variable 3 C:Inhibition concentration (g/l)
2	1	12.00	30.00	0.50
13	2	7.50	45.00	0.50
3	3	3.00	60.00	0.50
6	4	12.00	45.00	0.20
12	5	7.50	60.00	0.80
10	6	7.50	60.00	0.20
16	7	7.50	45.00	0.50
9	8	7.50	30.00	0.20
15	9	7.50	45.00	0.50
8	10	12.00	45.00	0.80
14	11	7.50	45.00	0.50
5	12	3.00	45.00	0.20
11	13	7.50	30.00	0.80
1	14	3.00	30.00	0.50
4	15	12.00	60.00	0.50
7	16	3.00	45.00	0.80
17	17	7.50	45.00	0.50

3.3 Weight Loss Analysis

Weight Loss Analysis was calculated using Eq. 1

$$\varDelta \text{W}=\text{W}\text{b}-\text{W}\text{a}$$

1

where Wb is weight before immersion; Wa is weight after immersion

While the corrosion rate (g/cm²days) in the absence and presence of inhibitors was calculated using;

$$\text{C}\text{R}= \frac{\varDelta \text{W}}{\text{A}\text{t}}$$

2

where ΔW is weight loss (g) exposure time t (days), A is area of the specimen (mm²) and t is time of exposure in days, and CR is corrosion rate at each exposure time.

3.4 Fourier Transform Infrared spectroscopy (FTIR) Analysis

FTIR Analysis was used to identify active functional groups of corrosive mediums of: blank mild steel, mild steel of lowest corrosion rate (from result of box Behnken design) and mild steel of optimal process variables (validated).

3.5 Scanning Electron Microscopy (SEM) Analysis.

Surface chracterization for following materials: blank mild steel, mild steel of lowest corrosion rate and mild steel of validated experiment were done using SEM

3.6 Energy Dispersive Spectroscopy (EDS) Analysis

The elemental compostions of following materials: blank mild steel, mild steel of lowest corrosion rate (from result of box Behnken design), and mild steel of validated experiment were analysed using EDS.

4.1 Result of Phytochemical Analysis

Qualitative and quantitative analyses findings are as shown in Tables 4 and 5. Futhermore, the result observed in Table 4 confrimed what was reported by [20]

Table 3

Table of Results of Qualitative Analysis
Constituents	Result
Saponins	+
Flavonoid	+
Tannin	+
Phenolic Content	+
Steroid	+
Terpenoid	+
Alkaloid	+
+ indicates phytochemical present

Table 4

Table of Results of Quantitative Analysis
Constituents	Bp (mg/g)
Saponins	0.0247
Flavonoid	0.0921
Tannin	0.0057
Phenolic Content	0.0096
Steroid	0.0058
Terpenoid	0.0102
Alkaloid	0.0091

4.2 Results of the Weight Measurement Analysis

The lowest corrosion rate was observed in experimental run: 16 is shown in Table 5.This result has lower corroison rate than what was observed by [5] with the same amount of extract but in HCl corrosive environment both at 30 and 45 ^oC respectively

Table 5

Table of Results from Weight Loss analysis
Std	Run	A: Time of immersion (days)	B: Temperature (⁰C)	C: Inhibition concentration (g/l)	Weight loss	Corrosion rate(g/cm² days)
2	1	12.00	30.00	0.50	0.133	0.002471
13	2	7.50	45.00	0.50	0.087	0.002587
3	3	3.00	60.00	0.50	0.138	0.010260
6	4	12.00	45.00	0.20	0.279	0.005184
12	5	7.50	60.00	0.80	0.065	0.001933
10	6	7.50	60.00	0.20	0.324	0.009633
16	7	7.50	45.00	0.50	0.087	0.002587
9	8	7.50	30.00	0.20	0.164	0.004876
15	9	7.50	45.00	0.50	0.087	0.002587
8	10	12.00	45.00	0.80	0.096	0.001784
14	11	7.50	45.00	0.50	0.087	0.002587
5	12	3.00	45.00	0.20	0.075	0.005575
11	13	7.50	30.00	0.80	0.109	0.003241
1	14	3.00	30.00	0.50	0.079	0.005872
4	15	12.00	60.00	0.50	0.224	0.004162
7	16	3.00	45.00	0.80	0.015	0.000115
17	17	7.50	45.00	0.50	0.087	0.002587

4.3 Results of Analysis of Variance (ANOVA)

The ANOVA is shown as in Table 6a, P-value represented the probability of the occurrence of the interraction. The implied model's Model F-value is 5.73. The significant terms in the model are A, B, C, and B². The regression coefficient R² and adjusted R² are 0.8804, and 0.7267. The statistical analysis was done for Normality Test using SPSS Version 14. Table 6b showed that; corrosion rate is normally distributed by skewness (standard vale / std. error) = 1.93 ( which within the range of ± 1.96).Table 6c showed the test for Normality.

Table 6

a. **Result of ANOVA**
Source	Sum of Squares	df	Mean Square	F-value	p-value
Model	0.0001	9	0.0000	5.73	0.0157	significant
A-Time	0.0000	1	0.0000	5.69	0.0486
B-Temp	0.0000	1	0.0000	6.07	0.0432
C-Inhibition Conc	0.0000	1	0.0000	19.77	0.0030
AB	1.818	1	1.818	0.9728	0.3568
AC	2.809	1	2.809	0.1503	0.7098
BC	9.196	1	9.196	4.92	0.0621
A²	2.688	1	2.688	1.44	0.2695
B²	0.0000	1	0.0000	11.97	0.0106
C²	3.420	1	3.420	0.0018	0.9671
Residual	0.0000	7	1.869
Lack of Fit	0.0000	3	4.362
Pure Error	0.0000	4	0.0000
Cor Total	0.0001	16

Table 6b: Stastistical Descriptives
			Statistic	Std. Error
Corrosion rate	Mean		.00379346	.000698012
	95% Confidence Interval for Mean	Lower Bound	.00231374
		Upper Bound	.00527318
	5% Trimmed Mean		.00363123
	Median		.00258700
	Variance		.000
	Std. Deviation		.002877975
	Minimum		.000247
	Maximum		.010260
	Range		.010013
	Interquartile Range		.003521
	Skewness		1.065	.550
	Kurtosis		.787	1.063

Table 6

c:Tests of Normality
	Kolmogorov-Smirnov^a			Shapiro-Wilk
	Statistic	df	Sig.	Statistic	df	Sig.
corrosionrate	.192	17	.097	.895	17	.057
a. Lilliefors Significance Correction

According to the Kolmogoro-Smirnov analysis Table 6c, the P value is 0.097, which is greater than 0.05, and is considered significant. Accepting the null hypothesis, we came to the conclusion that there is no appreciable deviation from the normal distribution in the sample data.

According to the Shapiro-Wilk analysis table, the P value is 0.057 (greater than 0.05, level of significance). The null hypothesis is still accepted, and we determine that normally distributed data.

Figure 1 is the Plot of Normal Plot of Residuals and Fig. 2a showed the Plot of Predicted Vs. Actual. Figure 2b showed that there is an outliner. Figures 3–5 depicted the 3D plots. According to Fig. 3, corrosion rate increased as temperature increased. However, in Fig. 4, corrosion rate decreased as inhibition concentration increased. Figure 5 demonstrated that corrosion rate increased with increasing temperature. The regression equation in terms of actual variables is in Eq. 4.

Regression equation in Terms of Actual Variables

Corrosion rate = 0.0173468–0.000496639(Time) − 0.000599311(Temp) + 0.00620903 (Inhibition Conc) − 9.98889 (Time * Temp) + 0.000196296 (Time * Inhibition Conc) -0.000336944 (Temp * Inhibition C Raphinus onc) + 3.94568(Time²) + 1.02456 (Temp²) + 0.000316667 (Inhibition Conc²). (4)

4.4 Experimental Validation

The optimal variables predicted by the software were: Temp: 58.6^oC, Time: 6.3 days and Conc: 0.63g/l. This was validated.

4.5 Results of the FTIR Analysis

Figure 6 showed the spectra of lowest corrosion rate mild steel with protective film; with C = O (carboxylic acids), N–H (amines), C–H bonds (Alkanes); C-Cl (Alkyl halides), OH⁻ (carboxyl group) and = C–H(Alkenes). while Fig. 6 (Mild steel with OPL) revealed N–H; C = O; C = N; C-Cl; C = N; C-H bonds, was responsible for adsorption process that acted as barrier more to corrosion.

This confirmed results of [20, 21].

4.6 Results of Scanning Electron Microscope (SEM) Analysis

Figure 7a showed the surface of balnk mildsteel; which was heavily damaged due to itsd corrosive environment. The mildsteel of the best proceee as oberved from the experimental design as shown in Fig. 7b; reealved that there was less damage with reduced surface roughness and formation of passive film which indicated minimal corrosion due to the presence of inhibitor. Moreover; the midlsteel of the optiaml process level (validated experiment) as shown in Fig. 7c; showed that more passive film was formed that was absorbed on the metal surface.This acted more asa barrier to bolck access of the corrosive species and laso mititgated corrosion. This reuslt confirmed adsorption of BLE on metal surface and also justifed results of [18, 23–24].

4.7 Results of EDS Analysis

The EDS result of blank mildsteel was shown in Fig. 8a. Figure 8c showed that more heteroatoms containing organic molecules exhibit remarkable corrosion inhibition than Fig. 8b. The inhibition was attributed to presence of lone pair and pi electrons in the molecule, which allow them to easily deposit on metal surface. This demonstrated that phytochemicals acted as inhibition which formed more adsopriton to the metal surface in Fig. 8c which confirmed the results of [22–23].

The result of phytochemical analysis indicated the presence of Saponins, Flavoniod, Tannin, Phenolic, Steroids, Terpenoids,and Alkaloids which confirmed and established that Bryophyllum Pinnatum extract is an effective corrosion inhibitor in 1M Phosphoric Acid. The established optimal process variables are 6.3 days, 58.6°C, and 0.63 g/l of inhibitor concentration. Moreover, the results of SEM images and EDS showd that more adsorption was formed on the Mild steel of the validated experiment which blocked the active site against corrosion. Hence, it can be concluded that Bryophyllum pinnatum extract inhibited the Mild steel corrosion in 1M phosphoric acid. Therefore, it can potentially serve as an effective, economical, biodegradable, and eco-friendly inhibitor in petroleum refineries.

Conflict of interest

The authors declare that there is no conflict of interest.

Author Contribution

O.O. and B.T wrote the main manuscript textA.A. and T.O edited the manuscriptJ.A and P.O prepared figures 1-4A.T and T.O prepared figures 5-8All authors reviewed the manuscript

Acknowledgements

The authors appreciate the entire Landmark University Management for the relentless contributions towards this work.

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No competing interests reported.

Performance Evaluation of Bryophyllum Leaves Extract as Corrosion Inhibitor for Mild Steel in 1M Phosphoric Acid

Status:

Journal Publication

Version 1

Abstract

Figures

1.0 INTRODUCTION

2.0 EXPERIMENTAL