Jurnal Rekayasa Kimia dan Lingkungan Volume 16, Number 2, Page 68-74, 2021 ISSN 1412-5064, e-ISSN 2356-1661 https://doi.org/10.23955/rkl.v16i2.18156 68 Utilization of Natural Extracts as Corrosion Inhibitors in the Seawater Environment Pocut Nurul Alam 1,4* , Cut Meurah Rosnelly 1 , Justaman Arifin Karo Karo 2 , Akhar Ilhamdi 1 , Raiyan Soekarno 1 , Izzan Nur Aslam 3,4 1 Departement of Chemical Engineering, Faculty of Engineering, Universitas Syiah Kuala, Jalan Tgk. Syech Abdurrauf As Singkili, No. 7, Darussalam, Banda Aceh, 23111, Indonesia 2 Balai Riset dan Standardisasi Industri (Research Center and Industrial Standardization), Jalan Sisingamangaraja, No. 24, Pasar Merah Baru, Medan Kota, Medan, 20214, Indonesia 3 Western Australia School of Mines: Minerals Energy and Chemical Engineering, Curtin University, 95 Egan Street, Kalgoorlie, Western Australia, 6430, Australia 4 Department of Mining Engineering, Faculty of Engineering, Universitas Syiah Kuala, Jalan Tgk. Syech Abdurrauf As Singkili, No. 7, Darussalam, Banda Aceh, 23111, Indonesia * E-mail: pocutnurulalamm@unsyiah.ac.id Article History Received: 29 September 2020; Received in Revision: 27 August 2021; Accepted: 28 September 2021 Abstract Infrastructures in coastal area are mostly made of metal which is susceptible to corrosion due to direct contact with the seawater. The Seawater greatly affects the corrosion rate of metals because it contains chloride ions which can penetrate metal surface. The process of corrosion can be inhibited or slowed by decreasing the corrosion rate in one way, namely the addition of corrosion inhibitors derived from natural materials containing tannin compounds. This study proposed organic corrosion inhibitors which were derived from natural material extracts (coffee leaves and catappa leaves), the effect of time variations on the efficiency of organic inhibitors was investigated, and the efficiency of each inhibitor organic was compared. The corrosion rate with and without inhibitors was analysed by using the method of weight loss. The results showed that the corrosion rate can be reduced by adding the natural ingredients extract. The addition of 2% concentration coffee leaves extract resulted in the lowest corrosion rate with the addition of 0.00226 mmpy. The addition of catappa leaves extract concentration as much as 2% yield the lowest corrosion rate with the addition of 0.0012 mmpy. The highest efficiency of inhibition system was obtained by using 2% catappa leaves extract at 14 days soaking time at 69.23%, and the lowest by using 1% coffee leaves extract. Keywords: inhibitor, natural extract, tannin, corrosion, sea water 1. Introduction Corrosion is one of the causes of weathering in metals. Corrosion is a process that occurs naturally leading to a decrease in material quality through chemical or electrochemical reactions with the surrounding environment (Xhanari and Finsgar, 2016). In the mechanism, the metal will oxidize in a positive electrode which loses electrons and turns into positive ions (Chen et al., 2017). While on a negative electrode, there will be a reduction reaction and get electrons while forming negative ions. Positive and negative ions will join the electrolyte solution and produce hydroxides that are not soluble in water. The hydroxide formed is then oxidized with oxygen and water. Fe → Fe 2+ + 2e - O2 + 2H2O + 4e - → 4OH - Fe 2+ + 2OH - → Fe(OH)2 4Fe(OH)2 + O2 + 2H2O →Fe(OH)3 Some environmental factors that can affect the corrosion process include (Haryono et al., 2010): a. Temperature The increase in temperature will cause an increase in the speed of the corrosion reaction. This effect occurs because of the higher temperature of the particles in action will increase so that it exceeds the magnitude of the activation energy price which results in the corrosion rate of metal also getting faster, and vice versa. b. Fluid flow speed Corrosion rate of metals tends to increase if the rate of fluid flow increases, this is because of the contact between the reactant and the metal will be greater. As a result,