Research on extracting cardanol from cashew nut shell by supercritical method applied as corrosive agent for carbon steel

Inhibitor is a substance that is added to the corrosive media to inhibit corrosion rate. Organic inhibitors are preferred to inorganic ones since they are environmentally friendly. One of the organic compounds which is rarely reported as a corrosion inhibitor is Cardanol from cashew nut shell extraction.

RESEARCH ON EXTRACTING CARDANOL FROM

CASHEW NUT SHELL BY SUPERCRITICAL METHOD

APPLIED AS CORROSIVE AGENT FOR CARBON STEEL

Pham Quoc Nghiep1*, Le Thi Kim Phung2, Le Anh Kien1

Abstract: Inhibitor is a substance that is added to the corrosive media to inhibit

corrosion rate Organic inhibitors are preferred to inorganic ones since they are

environmentally friendly One of the organic compounds which is rarely reported as

a corrosion inhibitor is Cardanol from cashew nut shell extraction In this study, the

CT3 carbon steel was used with 3.5% NaCl solution as the corrosion medium The

extraction of cardanol oil from cashew nut shell (Anacardium occidentale)

cultivated in Vietnam using supercritical carbon dioxide method was conducted

The purity and extracted oil content were determined by The High-Performance

Liquid Chromatography (HPLC) analysis Potentiondyamic were used to measure

the corrosion rate and behaviour From the electrochemical measurements, it was

found that the addition of 78.8 mg/L inhibitor gave the highest inhibition efficiency

Cardanol's protective effect for inhibiting corrosion of steel reaches 84% So,

cardanol extracted from cashew nut shell by supercritical CO2 method have

potential application as green corrosion inhibitor

Keywords: Cardanol; Cardol; Acid anacardic; Cashew nut shell; Supercritical fluid extraction

1 INTRODUCTION

Corrosion is a prohibitive issue for a diversity of industries Detection and discounting

the expenditure of metals corrosion has been of great interest to the corrosion engineers

and scientists for multitude decades and it is still snowballing Corrosion-resistant

materials, corrosion inhibitors, anodic/cathodic protection, protecting coatings, corrosion

inspection and monitoring tools have been fiercely used in abundant applications to protect

the metallic structures from corrosion and reduce its cost [1-3] The popular and

conventional corrosion protection strategy for safekeeping of metals is application of

corrosion inhibitors Corrosion inhibitors are defined as the ability of substances to

effectively reduce the metal corrosion rate when added at low concentrations to harsh

environment [4, 5] They can be categorized into two domains of organic and inorganic

inhibitors [6, 7] according to chemical structure Recently, many investigations have dealt

with development of the synergistic action between the inorganic-organic corrosion

inhibitors in various media [8-11] In this work, the inhibitor capacity of cardanol from

CNSL on corrosion of carbon steel in 3.5% NaCl solutions at ambient temperature is

determined The effects of operating parameters on the yield and quality of cardanol from

CNS using supercritical fluid extraction (SCFE) method were evaluated

2 MATERIALS 2.1 Extraction of Cardanol from Cashew Nut Shell by supercritical technology

Cashew Nut Shells were collected from Binh Phuoc province, Vietnam It was dried at

60°C for 12 hours Then crushed a range size of 1-2 mm Pure carbon dioxide (99.99%)

maintained at 60oC and 300 bar was used for the extraction; the flow rate of carbon

dioxide was 20 g/min Fresh crushed cashew nut shells (20 g) were charged into the

extractor; the extract was collected every 3 hours

The extract collected in each interval was analyzed by HPLC The mobile-phase

systems were acetonitrile-water-acetic acid (80:20:1), at 1.50 mL/min A XDB – C18

column (4.6 mm X 15cm, packed with 5 µm of octadecylsilica) was used for the analysis

2.2 Corrosion inhibitor of cardanol for carbon steel in 3.5% NaCl solutions

The rate of metal corrosion caused by the environment is determined by the weight method, that is, the amount of metal (in grams) lost for a unit of time and unit area of the sample Sample preparation and corrosion rate assessment of metal samples were carried out according to ASTM G1-03 Potentiondyamic method was used to determine the polarization curve of electrodes on the Autolab PGSTAT30 device with a voltage bias range of ± 250 mV, a scanning speed of 10 mV/s The corrosion rate of electrodes is calculated according to ASTM G102-99 The test solution was 3.5% aqueous NaCl solution, prepared from analytical grade NaCl in distilled water The CNSL was emulsified by dispersing it in ethanol The performances of CNSL as a corrosion inhibitor were monitored at a concentration range from 0 to 92.6 g/L The working electrode is made of steel leaf CT3 with a surface area of 2x2 cm2

3 RESULTS AND DISCUSSION 3.1 Properties of oil extracted by SC-CO 2

The characteristic properties of the CNSL were given in Table 1

Table 1 Characteristic properties of CNSL extracted at 320°C and 1 atm

The properties of CNSL was elucidated in Table 1 The pH result (6.05) indicated that was acidic The density of CNSL was 1.07 g/cm3 in previous study [12], whereas the density of the present work was 0.96 g/cm3 The slight variation in the specific gravity attributed to the extraction technique cum operating conditions employed during the experiment In general, the properties of CNSL in this study reached the standard specifications of CNSL The composition of the CNSL was 67 % cardanol, 20.5 % cardol and 12.5 % anacardic acid and polymer, at 60 oC, 300 bar and 20 g/min was used for the extraction Cardanol recovery performance reached 23 %

Figure 1 HPLC of CNSL using XDB – C18 column (80:20:1)

3.2 Corrosion inhibiting performance of cardanol for CT3 steel in 3.5% NaCl solution

3.2.1 Effect of inhibitor concentration

CT3 steel immersion environment in 3.5% NaCl solution quickly corroded (Figure 2) Corrosion rate of steel CT3 after 168 h showed that corrosion rate reached 0.415 mm/year calculated by mass method and 0.647 mm/year by electrochemical method The corrosion rate increases from 0.185 mm/year to 0.212 mm/year determined by mass method; and

corrosion rate increased from 0.102 mm/year to 0.138 mm/year determined by

electrochemical method when Cardanol concentration increased from 78.8 g/L to 92.6 g/L

CT3 steel protection tends to increase when cardanol concentration increases to 78.8 g/L

(Figure 3a)

Figure 2 Corrosion rate (a) and Protection efficiency (b) of CT3 steel at different

Cardanol concentrations after 168 h

With the method of determining the corrosion rate by electrochemical method (Figure

3b), the corrosion rate of CT3 steel with cardanol inhibitor tends to decrease rapidly when

the concentration of cardanol reaches 78.8 g/L The efficiency of cardanol corrosion

protection is determined at a high level, the protection efficiency reaches more than 70%

with a test time of 672 h at a cardanol concentration of 78.8 g/L

Figure 3 Corrosion rate and Protection efficiency at different Cardanol concentration:

Mass method (a) and Electrochemical method (b)

Polarized resistor of CT3 steel increases when cardanol concentration increases; When

there is no presence of cardanol on the surface of CT3 steel, the polarization resistance value

is 10.18 Ω, after treating CT3 steel surface with cardanol solution at cardanol concentrations

[41,6; 56.6; 78.8] g/L before the corrosion test in the environment of 3.5% NaCl polarization

resistor of steel reaches the corresponding values [13,39; 16.49; 57.68] Ω

Figure 4 Tafel diagram (left), corrosion current intensity and polarization resistors

(right) of CT3 steel at cardanol concentrations after 168 h testing

The presence of cardanol inhibitors not only affects the polarization resistance of CT3 steel but also affects the anodic and cathode polarization curve of steel When there is no cardanol inhibitor, the excess of the steel electrode is low (-0.903 V), the corrosive current

is 0.534 mA

3.2.2 Effect of immersion time

With the mass method, the corrosion rate tends to increase rapidly in the first period, before 672 h After the test period of 1680 h, the corrosion rate at 3 cardanol concentrations [56,6; 78.8; 92.6] g/L is [0.364; 0.352; 0.360] mm/year, the corrosion rate values vary slightly

Figure 5 The corrosion rate of CT3 steel at different time intervals:

mass method (left) and electrochemical method (right)

With the electrochemical method, the corrosion rate tends to increase steadily during the test period, the corrosion rate change path tends to be linear over time

Figure 6 Tafel diagram of CT3 steel at different test times,

Cardanol concentration of 78.8 g/L

The corrosion rate of CT3 steel increases about 4 times from 0.102 mm/year to 0.416

mm/year when the test time increases by 10 times from 168 h to 1680 h The test time also

affects the polarization resistance of the steel surface, when the test time to increase the

polarization resistance tends to decrease, the polarization resistance decreases by about 6

times from 57.68 Ω to 9.56 Ω when the time increases from 168 to 1680 h

4 CONCLUSION

In this work, Cardanol is extracted from cashew shell by supercritical CO2 method The

chemical analysis of obtained in present study showed that it mainly contained cardanol

(67%) The results suggested that cardanol inhibits the electrochemical process taking

place on carbon steel CT3 surface undergoing corrosion in 3.5% aqueous NaCl solutions

Corrosion rate ranged from 0.1018 to 0.6465 mm/year in 1 week, protection efficiency of

various CNSL concentrations during 8 weeks as 30 – 85%

Acknowledgments: We acknowledge the support of time and facilities from Institute of

Tropicalization and Environment and Ho Chi Minh City University of Technology (HCMUT),

VNU-HCM for this study

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TÓM TẮT

NGHIÊN CỨU TRÍCH LY CARDANOL TỪ VỎ HẠT ĐIỀU BẰNG PHƯƠNG PHÁP

SIÊU TỚI HẠN ỨNG DỤNG LÀM CHẤT ĂN MÒN CHO THÉP CARBON

Chất ức chế là một chất được thêm vào môi trường ăn mòn để ức chế tốc độ ăn mòn Chất ức chế hữu cơ được ưa chuộng hơn chất vô cơ vì chúng thân thiện với môi trường Một trong những hợp chất hữu cơ hiếm khi được báo cáo là chất ức chế

ăn mòn là Cardanol từ chiết xuất vỏ hạt điều Trong nghiên cứu này, thép cacbon CT3 được sử dụng với dung dịch NaCl 3,5% làm môi trường ăn mòn Việc chiết xuất dầu cardanol từ vỏ hạt điều (Anacardium Occidentale) được trồng ở Việt Nam bằng phương pháp CO2 siêu tới hạn đã được tiến hành Độ tinh khiết và hàm lượng dầu chiết xuất được xác định bằng phân tích Sắc ký lỏng hiệu suất cao (HPLC) Potentiondyamic được sử dụng để đo tốc độ và hành vi ăn mòn Từ các phép đo điện hóa, người ta thấy rằng, việc bổ sung chất ức chế 78,8 mg/L cho hiệu quả ức chế cao nhất đạt 84% Vì vậy, Cardanol chiết xuất từ vỏ hạt điều bằng phương pháp CO2 siêu tới hạn có tiềm năng ứng dụng làm chất ức chế ăn mòn xanh

Từ khóa: Cardanol; Cardol; Axit anacardic; Vỏ hạt điều; Chiết dịch siêu tới hạn

Received date, 10th August, 2020 Revised manuscript, 12 th August, 2020

Published, 24 h August, 2020

Địa chỉ: 1 Viện Nhiệt đới môi trường, 57A Trương Quốc Dung, P10, Phú Nhuận, TP Hồ Chí Minh;

2 Đại học Bách khoa/ Đại học Quốc gia TP Hồ Chí Minh

*Email: pqnghiep1354@gmail.com