Investigation of Diospyros Kaki L.f husk extracts as corrosion inhibitors and bactericide in oil field

Jie Zhang
Yingpan Song
Huijun Su
Li Zhang
Gang Chen
Jingrui Zhao
Investigation of Diospyros Kaki L.f husk extracts as corrosion inhibitors and bactericide in oil field
S H O R T R E P O R T Open Access
Background: 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.Findings: 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. Conclusions: 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.

Introduction

Hydrochloric acid is used in oil-well acidizing commonly for improving the crude oil production of the lowpermeable reservoirs [1], while it is a great challenge for the metal instruments involved in the acidification, as shown in Figure 1. Due to the aggressive nature of HCl and other corrosive factors, the practice of inhibiters is commonly used to reduce such corrosive attack [2]. Compounds, containing functional electronegative groups and abundant p-electron in conjugated double or triple bonds, are found to be very efficient as corrosion inhibitors [3]. It has been commonly recognized that an organic inhibitor usually promotes the formation of a chelate film on a metal surface by transferring electrons from the organic compounds to the metal and forming a coordinate covalent bond during the chemical adsorption, thereby resisting the corrosion in acidic solutions [4]. In present, the heteroatomic organic compounds as well as aromatic compounds are the widely used efficient corrosion inhibitors.

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 [5], which indicates the extracts of persimmon husk suitable to be used as green and ecofriendly corrosion inhibitors. Moreover, microbiologically influenced corrosion (MIC) caused by oil field microorganisms, such as sulfate reducing bacteria (SRB), iron bacteria (IB), and total general bacteria (TGB), is also a considerable problem. As it has been reported that the compounds combine with proteins and show some antibacterial activities [6], the persimmon extracts are anticipated to be corrosion inhibitors and bactericides for oil field microorganisms in oil field water treatment, as shown in Figure 2.

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.

Experimental

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.

Gravimetric measurements

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.

Electrochemical measurements

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 threeelectrode thermostated cell. The electrode was inserted into a Teflon tube and isolated with polyester so that only its section (0.5 cm 2 ) 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 E corr .

Microbiological monitoring

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.

Findings

Inhibitor properties and mechanism

Developing natural products as oilfield chemicals is a straight way to find less expensive, green and ecofriendly materials. Based on the fruitful and large quantity of local plant resources of Shannxi Province, several plants have been investigated in our work for the application in oilfield chemistry. The inhibition efficiency (IE) of extracts of persimmon husk were investigated in the concentration range 10 to 1,000 mg/L in 1 M HCl, and the changes of IE (%) with the inhibitor concentration are summarized in Table 1. From the table, it is apparent that the extracts inhibit the corrosion with different efficiency under different concentrations, the IE increases with increasing extract concentration, and the highest reaches to 65.1%.

Increasing in IE with increasing additive concentration can be explained on the basis of additive adsorption. The presence of N, O, S atoms and conjugated double bonds in the organic compounds makes the formation of p-d bonds from overlap of p electrons with the vacant 3d orbital of iron atoms, which enhances the adsorption of the compounds on the metal surface [7]. The steady conformations of two phenol compounds in persimmon, epicatechin gallate and hydrolysable tannin, were shown in Figure 3. It is apparent that there are abundant oxygen atoms with couples of p electrons and several conjugated double bonds and aryl groups, which may afford different manner to coordinate with steel surface.

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 Fe 2+ /ascorbic acid or H 2 O 2 [8], which indicate that the phenols can be oxidized to benzoquinone by the O 2 dissolved in the solution, which can inhibit the oxygen-adsorption corrosion.

Synergistic effect

KI, KSCN and hexamethylenetetramine (HMTA) are used as synergistic additives in some corrosion inhibitor formulations effectively. In the following work, the effect of KI, KSCN and HMTA on the inhibitive performance of the extracts was studied using weight loss determinations. The IE values under the concentration of 100 mg/L of KI, KSCN and HMTA companied with 500 mg/L of extracts are presented in Table 2. Inspection of Table 3 reveals that KI, KSCN and HMTA they can enhance the IE of WE effectively to as high as 97.3%. But the synergistic effect is not effective for KI, KSCN to AE, only HMTA is effective to give the IE of 90.5%. The reason might lie on the fruitful p-electrons of N, O and triple bond, which can form covalent bonds between the molecules and the ion surface, capture H + to release the acidity and even join the molecules as "bridges" to conform the protective film on the ion surface.

Tafel polarisation measurements

The anodic and cathodic polarization curves for a mild steel electrode in 1 M HCl in absence and presence of different concentrations of AE at 298 K are shown in Figure 4. Table 3 shows the electrochemical corrosion kinetic parameters, i.e., corrosion potential (E corr ), cathodic and anodic Tafel slopes (βa, βc) and corrosion current density I corr obtained by extrapolation of the Tafel lines. The IE (%) is also calculated from the following equation:
E % ð Þ ¼ I corr −I corr I corr  100ð1Þ
where I corr and I corr(i) are corrosion current densities obtained in the absence and presence of inhibitors, respectively. As it was expected both anodic and cathodic reactions of mild steel electrode corrosion were inhibited by the increase of the AE. This result suggests that the addition of the WE reduces anodic dissolution and also retards the hydrogen evolution reaction [9]. It can be seen that the corrosion rate is decreased and inhibition efficiency IE is increased by increasing inhibitor concentration. With a concentration of 1,000 mg/L, WE exhibits maximum IE of 79.6%. The extract causes changes in the anodic, cathodic Tafel slopes and the Ecorr values  in the presence of different concentrations. E corr , βa and βc values do not change appreciably with the addition of the inhibitor, which indicates that the inhibitor is not only interfering with the anodic dissolution or cathodic hydrogen evolution reactions independently but also acts as a mixed-type (anodic/cathodic) of inhibitor [10]. Increasing IE with increasing concentration of the AE shows that the inhibition actions are due to its adsorption on the steel surface [11]. The IEs obtained from potentiodynamic polarization were quite different from those calculated from weight-loss measurements, which is attributable to the fact that the weight-loss method gives average corrosion rate, whereas electrochemical method gives instantaneous corrosion rates. These differences may arise frequently because of the difference in the time required to form an adsorbed layer of inhibitors on metal surface [12].

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 [13]. 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 Cl 2 , ClO 2 , formaldehyde, pentane-1 ,5-dial, trichloroisocyanuric acid (TCCA) and ect., have been used as bactericides [14], but the toxicity and oxidation tests have been conducted on a limited selection.

Since tannins have been found to incline to combine with proteins and shown some antibacterial activities [6], the persimmon extracts are anticipated to be bactericides for oil field microorganism. In the following work, the antifungal activity of these extracts against oil field microorganism was tested under the concentrations of 1,000 mg/L and 500 mg/L, and the results are summarized in Table 4. The table showed that extracts are highly antifungal active against the three microorganisms under the concentration of 1000 mg/L. As the concentration of the extracts is reduced to 500 mg/L, the inhibitions are still potent for AE, but the inhibitions of WE are depressed obviously.

Conclusions

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.

Figure 1
1The corrosion in the re-injection pipes of the oil field.

Figure 2
2Development of persimmon extract as oil field chemical.

Figure 3
3The steady conformation of epicatechin gallate and hydrolysable tannin.

Figure 4
4Typical polarization curves for corrosion of Q235A steel in 1 M HCl in the absence and presence of different concentrations of WE.

Table 1
1The inhibition efficiency of WE and AE measured by weight lossExtract
Concentration
Corrosion rate
Inhibition efficiency

(mg/L)
(g/m 2 · h)
(%)

__
__
90.6
0

WE
10
60.2
33.6

WE
50
41.9
53.7

WE
100
39.6
56.3

WE
200
38.7
57.2

WE
500
35.3
61.1

WE
1,000
31.6
65.1

AE
10
59.0
34.5

AE
50
52.3
42.0

AE
100
48.1
46.7

AE
200
44.6
50.5

AE
500
39.7
55.9

AE
1,000
38.1
57.7

Table 2
2The corrosion rate inhibition efficiency of extracts companioning with KI, KSCN and HMTAFormulation
Corrosion rate
Inhibition efficiency

(g/m 2 · h)
(%)

-
90.6
/

KI
36.1
60.3

KSCN
40.7
55.3

HMTA
24.7
72.8

WE + KI
2.5
97.3

WE + KSCN
8.6
90.6

WE + HMTA
4.9
94.6

AE + KI
21.4
76.5

AE + KSCN
45.1
50.4

AE + HMTA
8.6
90.5

Table 3
3Potentiodynamic polarization parameters for the corrosion of the Q230A steel in the HCl solution containing WEConcentration
−Ecorr
Icorr
βa
βc
Corrosion rate
IE
(%)
(mg/L)
(mV)
(μA/cm 2 )
(mV/dec)
(mV/dec)
(mm/a)

-
0.46083
151.440
90.431
155.08
1.7753
-

10
0.46344
89.193
77.592
142.57
1.0491
40.9

50
0.46471
141.990
107.110
166.89
1.5727
11.4

100
0.45503
90.507
77.031
146.09
1.0646
40.0

200
0.45521
31.412
63.159
119.64
0.3695
79.2

500
0.46082
51.929
62.717
81.32
0.6974
60.7

1,000
0.45254
30.770
58.282
135.34
0.36192
79.6

Table 4
4The antifungal activity of persimmon extracts against oil field MICExtract
Concentration
Microbiotic Concentration/mL

mg/L
iSRB
IB
TGB

-
-
110.0
110.0
110.0

WE
500
110.0
110.0
70.0

1,000
2.0
2.0
1.3

AE
500
2.0
0.6
25.0

1,000
0.9
0.0
6.0

http://journal.chemistrycentral.com/content/7/1/109
Competing interestsThe authors declare that they have no competing interests.Authors' contributions GC has conceived the study, formulated the research idea and prepared the manuscript draft version, JZ and YS carried out the corrosion inhibition experiments, HS and LZ out the Microbiological monitoring, and JZ participated in its design and coordination. All authors have read and approved the final manuscript.
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From Neighbourhood to Bioregion: The City as a Living System

Intermezzo By
John Thackara
From Neighbourhood to Bioregion: The City as a Living System
13
The Greek physician Hippocrates described the effects of "airs, waters, and places" on the health of individuals and communities. For a short period, the industrial age distracted us from this whole-systems understanding of the world -but we are now learning again to think of cities as habitats, and as ecosystems, that co-exist on a single living planet. Humanising the city in this context-making it healthy for people -therefore means making it habitable for all of life, not just human life. It means thinking of the city as a local living economy, not as a machine. And it means the embrace of biodiversity, and local economic activity, as better measures of a city's health than the amount of money that flows through it. The notion of the city as a living system generates cultural energy, too: A narrative based on caring -for each other, and for our places -creates the meaning and shared purpose we've been so badly lacking.Civic EcologyOne design consequence of this cultural awakening is the growth of ecological urbanism, or civic ecology. These practices study how to help living organisms and their environment thrive together. They enrich city design with the insights of ecology, botany, climatology, hydrology, geology, and geography 1 . The movement is growing rapidly: The Urban Nature Atlas, for example, contains more than one thousand examples of nature-based solutions from across 100 European cities 2 ; And another fast-growing platform, The Nature of Cities, hosts 650 professional contributors from around the world 3 .

From Neighbourhood to Bioregion: The City as a Living System

Intermezzo By John Thackara The Greek physician Hippocrates described the effects of "airs, waters, and places" on the health of individuals and communities. For a short period, the industrial age distracted us from this whole-systems understanding of the world -but we are now learning again to think of cities as habitats, and as ecosystems, that co-exist on a single living planet. Humanising the city in this context-making it healthy for people -therefore means making it habitable for all of life, not just human life. It means thinking of the city as a local living economy, not as a machine. And it means the embrace of biodiversity, and local economic activity, as better measures of a city's health than the amount of money that flows through it. The notion of the city as a living system generates cultural energy, too: A narrative based on caring -for each other, and for our places -creates the meaning and shared purpose we've been so badly lacking.

Civic Ecology

One design consequence of this cultural awakening is the growth of ecological urbanism, or civic ecology. These practices study how to help living organisms and their environment thrive together. They enrich city design with the insights of ecology, botany, climatology, hydrology, geology, and geography 1 . The movement is growing rapidly: The Urban Nature Atlas, for example, contains more than one thousand examples of nature-based solutions from across 100 European cities 2 ; And another fast-growing platform, The Nature of Cities, hosts 650 professional contributors from around the world 3 .

Ecological urbanism is not much about planting seeds on barren ground. On the contrary, it builds on some surprisingly good news. Scientists are finding that there can be more biodiversity in cities than in many rural areas that we think about as 'nature' 4 . Urban biologist Claudia Biemans, an edible plants researcher in The Hague, identified about 300 different species in one square km of her city compared to 50 different species found in the same area of industrially-farmed countryside nearby. In fact, an ecological approach is not preoccupied by the concepts of 'urban' and 'rural'. On the contrary, this approach to city design involves care for living systems that already exist at a bioregional scale, but have been neglected or ignored: watersheds, foodsheds, fibersheds and food systems.

Urban food projects are a good indication of the extent to which social innovation, and civic ecology, are converging. Twenty years ago, urban farming projects were small and disconnected. They are now becoming pervasive. This is thanks to supporting infrastructures. Educational and leadership programs, job training for underserved young people, internships, and hands-on workshops have empowered a new generation of community leaders to transform lives and neighbourhoods. By 2017 the city of Milwaukee boasted more than 100 urban farms. As pioneer Will Allen puts it, "we're not just growing food, we're growing community" 5 .

Locality

A growing body of research confirms that small-scale, locally owned food businesses create communities that are more prosperous, entrepreneurial -and, yes, connected -across a wide range of metrics 6 . The beauty of local-ness as a measure of value is that it generates a practical to-do list in the form of new enterprises, new economies, and new livelihoods that need to be created. A variety of local economy blueprint tools are now available to help citizens and city managers begin this work: Tools to measure the percentage of food grown locally; the amount of local currency in circulation as a percentage of total money in circulation; the number of businesses locally owned; the percentage of energy produced locally; the quantity of renewable building materials available; the proportion of essential goods being manufactured within the community 7 .

The convergence of civic ecology and local economic development is not just a task for scientists and policy makers. A variety of different stakeholders -formal and informal, big and small -need to work together. The question -and it is also a design question -is how?

One precondition for working together is to curate meaningful conversations among all the people who need to be involved. An especially effective approach has been developed in England by Encounters Arts. Their Art of Invitation practice uses techniques from theatre, as well as the insights of psychology, to bring people together who are diverse in age, experience and background. The group's facilitators -many of them artists -have developed groundbreaking approaches to the co-creation of a shared response to systemic challenges facing their communities 8 .

Co-operation

Once local-scale conversations are under way, the next challenge is to organise real-world activities in an equitable way. A good candidate for this task are so-called Platform Co-ops. These platforms enable multiple actors -including businesses, government institutions & NGOs -to meet basic needs collaboratively: shelter, transportation, food, mobility, water, and elder care. Value, in a Platform Coop, is shared fairly among the people who make it valuable. Its activities depend more on social energy, and trust, than on fixed assets and real estate. There's an emphasis on collaboration and sharing; on person-to-person interactions; on the adaptation and re-use of discarded materials and abandoned buildings and land. Thriving neighbourhoods also need shared community spaces. In London, the Participatory City Foundation is breathing life into communities by helping citizens develop shared gardens, canteens, kitchens, workshops, and maker spaces.

m If humanising the city is mainly about life-friendly and resource-light ways to meet daily life needs, then the poor people of the world are further down the learning curve than the rest of us. The diverse ways in which poor people meet daily life needs are usually described as poverty, or a lack of development -but in 35 years as a guest in what used to be called the 'developing' world, this writer has come to a startling conclusion: Living sustainably is second nature for people who cannot depend on the high entropy support systems of the industrial world. Humanising the city must surely include connecting with the shadow economy of poor people and their diverse cultures. This is not to trivialise the extreme challenges faced by poor people on a daily basis -but the fortunate among us have much to learn from the ways people with low cash incomes meet these needs in an ad hoc way. Other cultures than our own have developed sophisticated ways to mutualise risk among traditional networks of reciprocity and gifts; many social systems based on kinship and myriad ways to share resources already flourish outside the formal economy.

Commoning

Millions of local living economies already exist wherever people are meeting practical needs using local resources. But a lot of this work feels fragmented. We need an umbrella concept, a coordinating idea, to make sense of the work we do as individuals in the swarm.

The Commons is that umbrella concept. As an idea, and a practice, it generates meaning and hope. Commoning gives shared meaning to the emerging 'leave things better' politics that otherwise lacks a name. It's the opposite of the drive to turn everything into money. Seen through that lens, the commons provides a motive for all a city's inhabitants to care collectively for the living systems of a city: land, watersheds, and biodiversity, for sure; public buildings and spaces, of course; but also social systems such as common knowledge, software, sharing platforms, or skills. The important thing is that the commons are a form of wealth that a community looks after, through the generations. The idea embodies a commitment to 'leave things better' rather than extract value from them as quickly as possible. And because the commons, as an idea, affirms our codependency with living systems and the biosphere, it also represents the new politics we've all been looking for to replace the industrial growth economy we have now. The commons is a system by which a community agrees to manage resources, equitably and sustainably -as we have done for most of human history.
 http://annewhistonspirn.com/pdf/ spirn_ecological_urbanism-2011.pdf 2 https://naturvation.eu/atlas. 3 https://www.thenatureofcities.com/
https://ilsr.org/key-studies-why-localmatters/. 7 http://www.reconomy.org/wp-content/ uploads/2017/06/How-to-do-a-Local-Economic-Blueprint2.doc.pdf
http://www.encounters-arts.org. uk/index.php/the-art-of-invitation-creative-engagement-for-ourselves-and-our-communities/