Carbohydrate Polymers 124 (2015) 280–291
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Performance evaluation of pectin as ecofriendly corrosion inhibitor for X60 pipeline steel in acid medium: Experimental and theoretical approaches Saviour A. Umoren ∗ , Ime B. Obot, A. Madhankumar, Zuhair M. Gasem Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 17 July 2014 Received in revised form 10 February 2015 Accepted 14 February 2015 Available online 26 February 2015 Keywords: Pectin Carbon steel Acid corrosion Corrosion inhibition Electrochemical techniques Surface analysis
a b s t r a c t The corrosion inhibition effect of pectin (a biopolymer) for X60 pipeline steel in HCl medium was investigated using weight loss, electrochemical, water contact angle measurements, and scanning electron microscopy techniques. The results obtained show that pectin acts as a good corrosion inhibitor for X60 steel. Inhibition efficiency increased with increase in pectin concentration and temperature. Potentiodynamic polarization results reveal that pectin could be classified as a mixed-type corrosion inhibitor with predominant control of the cathodic reaction. The effective corrosion inhibition potential of pectin could be related to the adsorption of pectin molecules at the metal/solution interface which is found to accord with the Langmuir adsorption isotherm model and a protective film formation. Quantum chemical calculations provided insights into the active sites and reactivity parameters governing pectin activity as a good corrosion inhibitor for X60 steel. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction There are serious concerns on the suitability of inorganic and organic compounds as metal corrosion inhibitors. This is because they have been found to exhibit high toxicity and consequently prohibited to use for industrial applications as well as exorbitant cost. The search for perfect replacement of inorganic and organic metal corrosion inhibitors has long begun and attention seems to be geared toward the development of environmentally friendly and biodegradable corrosion inhibitors. In this regard, plant extracts, drugs, amino acids, medicinal products, natural polymers etc. have been advocated by various researchers (Abd El-Hafeza & Badawy, 2013; Fu, Li, Wang, Liu & Lu, 2011; Fu, Zang, Wang, Li, Chen & Liu, 2012; Gece, 2011; Zadeh, Danaee & Maddahy, 2013; Roy, Pal & Sukul, 2014; Solomon, Umoren, Udosoro & Udoh, 2010; Umoren, Banera, Alonso-Garcia, Gervasi & Mirífico, 2013; Umoren, Gasem & Obot, 2013). Interest in natural polymers is principally due to its biodegradability and eco-friendliness in addition to the inherent stability and multiple adsorption centers (Umoren, Banera, AlonsoGarcia, Gervasi & Mirífico, 2013). A number of naturally occurring polymers have been investigated and have been reported to show
∗ Corresponding author. Tel.: +966 3 860 7902; fax: +966 3 860 3996. E-mail address: [email protected] (S.A. Umoren). http://dx.doi.org/10.1016/j.carbpol.2015.02.036 0144-8617/© 2015 Elsevier Ltd. All rights reserved.
promising results as metal corrosion inhibitors in different corrosive environments. For instance the corrosion-inhibiting effect of chitosan has been reported for mild steel and copper in acid medium (El-Haddad, 2013; Hussein, El-Hady, Shehata, Hegazy & Hefni, 2013; Umoren, Banera, Alonso-Garcia, Gervasi & Mirífico, 2013). Glucose, gellan gum, and hydroxylpropyl cellulose have been assessed as green inhibitors for cast iron in acidic environment by means of chemical and electrochemical techniques (Rajeswari, Kesavan, Gopiraman & Viswanathamurthi, 2013). Solomon et al. and Bayol et al. (Bayol, Gürten, Dursun & Kayakirilmaz, 2008; Solomon, Umoren, Udosoro & Udoh, 2010) have also reported on the corrosion inhibition effect of carboxyl methyl cellulose (CMC) for mild steel in acid media. Gum Arabic has also been reported to be a promising corrosion inhibitor for aluminum and steel in different corrosive environments (Bentrah, Rahali & Chala, 2014; Umoren, 2008; Umoren, Obot, Ebenso, Okafor, Ogbobe & Oguzie, 2006). Modified cassava starch has also been evaluated as corrosion inhibitors of carbon steel under alkaline conditions in 200 mg L−1 NaCl solutions (Bello et al., 2010). Hydroxyethylcellulose and hydroxypropyl methylcellulose have been investigated and reported as corrosion inhibitors for mild steel and aluminum in acid and 3.5% NaCl media (Arukalam, 2014; Arukalam, Madufor, Ogbobe & Oguzie, 2014a; Arukalam, Madufor, Ogbobe & Oguzie, 2014b; El-Haddad, 2014). Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It is produced commercially as a white to light brown powder, mainly extracted from citrus
S.A. Umoren et al. / Carbohydrate Polymers 124 (2015) 280–291
fruits. A number of other fruits are very good sources of pectin and these include apples, all berries (notably for their pectin content include strawberries, blackberries, raspberries, and dewberries), peaches, apricots, cherries, grapes, and banana. It is used in food as a gelling agent, particularly in jams and jellies. It is also used in fillings, medicines, and sweets as a stabilizer in fruit juices and milk drinks, and as a source of dietary fiber. Pectins are rich in galacturonic acid. Several distinct polysaccharides have been identified and characterized within the pectic group. These include homogalacturonans which are linear chains of ␣-(1–4)-linked d-galacturonic acid, substituted galacturonans characterized by the presence of saccharide appendant residues and rhamnogalacturonan I pectins (RG-I) which contain a backbone of the repeating disaccharide: 4␣-d-galacturonic acid-(1,2)-␣-l-rhamnose. The main use of pectin is as a gelling agent, a thickening agent, and a stabilizer in food. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include its use in edible films, paper substitute, foams and plasticizers, etc. (Thakur, Singh & Handa, 1997). The unique properties of pectin include polyfunctionality, biodegradable nature, flexible structural network, nontoxicity, and low production costs. Inspection of the molecular structure of pectin repeat unit shown in Fig. 1 reveals the presence of carboxyl, ester, and hydroxyl groups which offer the possibility of ionic interactions with a metal surface, hence fulfilling an important criterion to function as a corrosion inhibitor. It has been reported as efficient green corrosion inhibitor for aluminum in HCl solution using the weight loss technique (Fares, Maayta & Al-Qudah, 2012). Pectingrafted polyacrylamide (Pec-g-PAAm) and pectin-grafted polyacrylic acid (Pec-g-PAA) were synthesized and their corrosion inhibition potentials for mild steel in 3.5% NaCl were evaluated using electrochemical techniques (Geethanjali, Sabirneeza & Subhashini, 2014). The results obtained showed that the grafted polymers inhibited the corrosion of steel in the neutral medium. Corrosion inhibition efficiency of the polyacrylamide-grafted pectin polymer was found to be slightly higher than that of polyacrylic acid-grafted pectin polymer. Generally, the inhibition efficiency was found to be around 85%. The effect of pectin on the corrosion of cadmium in 0.5 M HCl studied using electrochemical techniques has been reported by Khairou and El-Sayed (Khairou & El-Sayed, 2003). The findings from the investigation revealed that pectin acted predominantly as an anodic inhibitor and slightly as a cathodic inhibitor only at higher pectin concentrations. This behavior was attributed to weak adsorbability of pectin at the cathodic sites. The corrosion inhibition performance of pectin with propyl phosphonic acid (PPA) and Zn2+ for corrosion control of carbon steel in neutral aqueous solution has been reported (Prabakaran, Ramesh, Periasamy & Sreedhar, 2014). The results obtained show excellent synergistic effects of pectin with other additives in the corrosion control of carbon steel. Typically, a formulation consisting of 250 ppm pectin, 50 ppm PPA, and 20 ppm Zn2+ gave the optimum inhibition efficiency of 94%. However, there is no published report on the corrosion inhibition effect of pectin for low carbon steel in HCl
Fig. 1. Chemical structure of the pectin repeat unit.
281
solution and electrochemical investigations highlighting the influence of pectin on kinetics of anodic and cathodic partial reactions of the corrosion process. Therefore, the present study was undertaken to assess the corrosion inhibition effect of pectin for X60 steel in HCl solution using chemical and electrochemical techniques. Scanning electron microscopy (SEM) and water contact angle measurements were used for surface morphological characterization. Quantum chemical calculation was also carried out in order to get more information on the active sites and reactivity parameters governing its activity as a good corrosion inhibitor for X60 steel. 2. Experimental 2.1. Materials and materials preparation A low carbon X60, which is a typical pipeline steel and in conformity with API X60 material specifications, was used. The major composition (wt%) of the steel specimen are as follows: C (0.125). Si (0.52), Mn (1.83), Cr (0.121), Cu (0.296), W (0.134), Ni (0.091), Mo (0.079), Al (0.043), Sn (0.081), Nb (0.053), V (0.078), Pb (0.030), Zn (0.032), and Fe (
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Performance evaluation of pectin as ecofriendly corrosion inhibitor for X60 pipeline steel in acid medium: Experimental and theoretical approaches Saviour A. Umoren ∗ , Ime B. Obot, A. Madhankumar, Zuhair M. Gasem Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 17 July 2014 Received in revised form 10 February 2015 Accepted 14 February 2015 Available online 26 February 2015 Keywords: Pectin Carbon steel Acid corrosion Corrosion inhibition Electrochemical techniques Surface analysis
a b s t r a c t The corrosion inhibition effect of pectin (a biopolymer) for X60 pipeline steel in HCl medium was investigated using weight loss, electrochemical, water contact angle measurements, and scanning electron microscopy techniques. The results obtained show that pectin acts as a good corrosion inhibitor for X60 steel. Inhibition efficiency increased with increase in pectin concentration and temperature. Potentiodynamic polarization results reveal that pectin could be classified as a mixed-type corrosion inhibitor with predominant control of the cathodic reaction. The effective corrosion inhibition potential of pectin could be related to the adsorption of pectin molecules at the metal/solution interface which is found to accord with the Langmuir adsorption isotherm model and a protective film formation. Quantum chemical calculations provided insights into the active sites and reactivity parameters governing pectin activity as a good corrosion inhibitor for X60 steel. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction There are serious concerns on the suitability of inorganic and organic compounds as metal corrosion inhibitors. This is because they have been found to exhibit high toxicity and consequently prohibited to use for industrial applications as well as exorbitant cost. The search for perfect replacement of inorganic and organic metal corrosion inhibitors has long begun and attention seems to be geared toward the development of environmentally friendly and biodegradable corrosion inhibitors. In this regard, plant extracts, drugs, amino acids, medicinal products, natural polymers etc. have been advocated by various researchers (Abd El-Hafeza & Badawy, 2013; Fu, Li, Wang, Liu & Lu, 2011; Fu, Zang, Wang, Li, Chen & Liu, 2012; Gece, 2011; Zadeh, Danaee & Maddahy, 2013; Roy, Pal & Sukul, 2014; Solomon, Umoren, Udosoro & Udoh, 2010; Umoren, Banera, Alonso-Garcia, Gervasi & Mirífico, 2013; Umoren, Gasem & Obot, 2013). Interest in natural polymers is principally due to its biodegradability and eco-friendliness in addition to the inherent stability and multiple adsorption centers (Umoren, Banera, AlonsoGarcia, Gervasi & Mirífico, 2013). A number of naturally occurring polymers have been investigated and have been reported to show
∗ Corresponding author. Tel.: +966 3 860 7902; fax: +966 3 860 3996. E-mail address: [email protected] (S.A. Umoren). http://dx.doi.org/10.1016/j.carbpol.2015.02.036 0144-8617/© 2015 Elsevier Ltd. All rights reserved.
promising results as metal corrosion inhibitors in different corrosive environments. For instance the corrosion-inhibiting effect of chitosan has been reported for mild steel and copper in acid medium (El-Haddad, 2013; Hussein, El-Hady, Shehata, Hegazy & Hefni, 2013; Umoren, Banera, Alonso-Garcia, Gervasi & Mirífico, 2013). Glucose, gellan gum, and hydroxylpropyl cellulose have been assessed as green inhibitors for cast iron in acidic environment by means of chemical and electrochemical techniques (Rajeswari, Kesavan, Gopiraman & Viswanathamurthi, 2013). Solomon et al. and Bayol et al. (Bayol, Gürten, Dursun & Kayakirilmaz, 2008; Solomon, Umoren, Udosoro & Udoh, 2010) have also reported on the corrosion inhibition effect of carboxyl methyl cellulose (CMC) for mild steel in acid media. Gum Arabic has also been reported to be a promising corrosion inhibitor for aluminum and steel in different corrosive environments (Bentrah, Rahali & Chala, 2014; Umoren, 2008; Umoren, Obot, Ebenso, Okafor, Ogbobe & Oguzie, 2006). Modified cassava starch has also been evaluated as corrosion inhibitors of carbon steel under alkaline conditions in 200 mg L−1 NaCl solutions (Bello et al., 2010). Hydroxyethylcellulose and hydroxypropyl methylcellulose have been investigated and reported as corrosion inhibitors for mild steel and aluminum in acid and 3.5% NaCl media (Arukalam, 2014; Arukalam, Madufor, Ogbobe & Oguzie, 2014a; Arukalam, Madufor, Ogbobe & Oguzie, 2014b; El-Haddad, 2014). Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It is produced commercially as a white to light brown powder, mainly extracted from citrus
S.A. Umoren et al. / Carbohydrate Polymers 124 (2015) 280–291
fruits. A number of other fruits are very good sources of pectin and these include apples, all berries (notably for their pectin content include strawberries, blackberries, raspberries, and dewberries), peaches, apricots, cherries, grapes, and banana. It is used in food as a gelling agent, particularly in jams and jellies. It is also used in fillings, medicines, and sweets as a stabilizer in fruit juices and milk drinks, and as a source of dietary fiber. Pectins are rich in galacturonic acid. Several distinct polysaccharides have been identified and characterized within the pectic group. These include homogalacturonans which are linear chains of ␣-(1–4)-linked d-galacturonic acid, substituted galacturonans characterized by the presence of saccharide appendant residues and rhamnogalacturonan I pectins (RG-I) which contain a backbone of the repeating disaccharide: 4␣-d-galacturonic acid-(1,2)-␣-l-rhamnose. The main use of pectin is as a gelling agent, a thickening agent, and a stabilizer in food. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include its use in edible films, paper substitute, foams and plasticizers, etc. (Thakur, Singh & Handa, 1997). The unique properties of pectin include polyfunctionality, biodegradable nature, flexible structural network, nontoxicity, and low production costs. Inspection of the molecular structure of pectin repeat unit shown in Fig. 1 reveals the presence of carboxyl, ester, and hydroxyl groups which offer the possibility of ionic interactions with a metal surface, hence fulfilling an important criterion to function as a corrosion inhibitor. It has been reported as efficient green corrosion inhibitor for aluminum in HCl solution using the weight loss technique (Fares, Maayta & Al-Qudah, 2012). Pectingrafted polyacrylamide (Pec-g-PAAm) and pectin-grafted polyacrylic acid (Pec-g-PAA) were synthesized and their corrosion inhibition potentials for mild steel in 3.5% NaCl were evaluated using electrochemical techniques (Geethanjali, Sabirneeza & Subhashini, 2014). The results obtained showed that the grafted polymers inhibited the corrosion of steel in the neutral medium. Corrosion inhibition efficiency of the polyacrylamide-grafted pectin polymer was found to be slightly higher than that of polyacrylic acid-grafted pectin polymer. Generally, the inhibition efficiency was found to be around 85%. The effect of pectin on the corrosion of cadmium in 0.5 M HCl studied using electrochemical techniques has been reported by Khairou and El-Sayed (Khairou & El-Sayed, 2003). The findings from the investigation revealed that pectin acted predominantly as an anodic inhibitor and slightly as a cathodic inhibitor only at higher pectin concentrations. This behavior was attributed to weak adsorbability of pectin at the cathodic sites. The corrosion inhibition performance of pectin with propyl phosphonic acid (PPA) and Zn2+ for corrosion control of carbon steel in neutral aqueous solution has been reported (Prabakaran, Ramesh, Periasamy & Sreedhar, 2014). The results obtained show excellent synergistic effects of pectin with other additives in the corrosion control of carbon steel. Typically, a formulation consisting of 250 ppm pectin, 50 ppm PPA, and 20 ppm Zn2+ gave the optimum inhibition efficiency of 94%. However, there is no published report on the corrosion inhibition effect of pectin for low carbon steel in HCl
Fig. 1. Chemical structure of the pectin repeat unit.
281
solution and electrochemical investigations highlighting the influence of pectin on kinetics of anodic and cathodic partial reactions of the corrosion process. Therefore, the present study was undertaken to assess the corrosion inhibition effect of pectin for X60 steel in HCl solution using chemical and electrochemical techniques. Scanning electron microscopy (SEM) and water contact angle measurements were used for surface morphological characterization. Quantum chemical calculation was also carried out in order to get more information on the active sites and reactivity parameters governing its activity as a good corrosion inhibitor for X60 steel. 2. Experimental 2.1. Materials and materials preparation A low carbon X60, which is a typical pipeline steel and in conformity with API X60 material specifications, was used. The major composition (wt%) of the steel specimen are as follows: C (0.125). Si (0.52), Mn (1.83), Cr (0.121), Cu (0.296), W (0.134), Ni (0.091), Mo (0.079), Al (0.043), Sn (0.081), Nb (0.053), V (0.078), Pb (0.030), Zn (0.032), and Fe (
