30 IPTEK, The Journal of Engineering, Vol. 9, No. 1, 2023 (eISSN: 2807-5064) T Carbon Dioxide (CO 2 ) Absorption Process Using Sodium Hydroxide (NaOH) M Aldi Nugroho 1* , Yoga Bekti Susanto 1 , Villia Lidzati Kamilah 1 , Regita Prameswari 1 Abstract⎯ An absorption process can be carried out to reduce carbon dioxide gas emissions in the surrounding environment. Absorption is a contact process between a mixture of gas and liquid that aims to remove one of the gas components by dissolving it in a suitable liquid. In this study, the CO 2 absorption process was carried out to determine the effect of CO 2 flow rate on the amount of CO 2 absorbed with NaOH absorbent. The results showed that the correlation between CO 2 flow rate and absorption factor was inverse because an increase in CO 2 flow rate caused the contact between CO 2 gas and NaOH to decrease. As a result, the absorption factor decreased because the ratio of CO 2 was greater than the absorbent. While the relation between L/V and the absorption factor is directly proportional if the flow rate of the liquid increases, the retained liquid tends to saturate and can accelerate the diffusion of CO 2 in the water, so the absorption factor also increases. In addition, after the absorption of CO 2 gas, sodium carbonate is produced, which is the result of the reaction of CO 2 with NaOH. Keywords⎯ Absorption, Carbon Dioxide, Sodium Hydroxide I. INTRODUCTION he rapid development of industries in Indonesia, such as the cement and petrochemical industries, impacts environmental pollution, especially that caused by carbon dioxide (CO 2 ) exhaust gases. The concentration of CO 2 in the atmosphere has increased significantly every year. Based on data from the Ministry of Energy and Mineral Resources in 2015, CO 2 emissions from the industrial sector alone have risen from 83 million metric tons in 2013 to 162 million metric tons of CO 2 in 2035, with an average increase of 5.2% per year. CO 2 gas is one of the greenhouse gases with the smallest global warming index. Still, it has the second- highest concentration after water vapor, making it the dominant contributor to temperature changes [1]. The magnitude of the impact caused by CO 2 gas on global warming prompted the Indonesian Ministry of National Development Planning to commit to reducing CO 2 gas emissions by 26%. Therefore, to achieve this commitment, it is necessary to make efforts to control all activities that have the potential to produce CO 2 exhaust gas, for example, industrial activities that act as the largest source of CO 2 emissions, namely the cement, iron, paper, and petrochemical industries. Mitigation efforts to manage industrial activities in order to reduce CO 2 gas emission products may be beneficial in reducing the risk of CO 2 gas emission growth [2]. Gas-liquid absorption is a separation process that can be used to separate certain gases, such as carbon dioxide, from flue gases using certain solvents. The absorption process aims to reduce or eliminate toxic gases to comply with quality standards and reduce impurities, thereby increasing the efficiency of the production process [3]. The method commonly used for CO 2 gas reduction is absorption with amine-based solvents such as monoethanolamine, followed by a desorption process because this process can reduce CO 2 emissions by up to 85% [4]. One application of the absorption process in industry is CO 2 capture in the 1 Department of Industrial Chemical Engineering, Sepuluh Nopember Institute of Technologym ITS Sukolilo Campus, Surabaya, 60111, Indonesia. E-mail: aldinugroho637@gmail.com petrochemical industry, methane gas separation, and the capture of carbon emissions from the coal combustion process in the energy industry [3]. Absorption of carbon dioxide using NaOH absorbents offers higher stability, lower costs, and is safe for the environment [5]. Because NaOH has faster reaction kinetics with CO 2 than Monoethanolamine (MEA) and its derivatives amines, it outperforms organic adsorbents in CO 2 capture. In addition, alkaline solutions have a higher absorption efficiency (92-99%) than amine solutions (61-90%) or ammonia solutions (78-98%) [6]. Using membrane technology, the CO 2 gas absorption process obtained carbonate by-products by reaction with NaOH, which then returned as Na 2 CO 3 .10H 2 O crystals in a membrane crystallizer [7]. NaOH absorbent is used in a spray dryer system to absorb carbon dioxide. Increasing the absorbent concentration and operating temperature increases reaction speed and CO 2 removal efficiency [8]. Therefore, this study aims to determine the absorption factor of CO 2 gas to NaOH and the ratio of CO2 flow rate and NaOH flow rate to absorption. A. Absorption Absorption is the process of separating substances by contacting a flue gas (gas mixture) with a certain absorbent. The absorption process aims to reduce or eliminate toxic gases to comply with quality standards and reduce impurities, thereby increasing the efficiency of the production process [3]. There are two types of absorption, physical absorption and chemical absorption. Chemical absorption occurs when a chemical reaction does not follow the gas dissolved in the absorbent because the absorption process occurs when there is physical interaction, such as gas diffusion into the liquid. The absorption of H2S gas with carbonate solvents is an example of physical absorption. Then, chemical absorption occurs when the absorption of gas is followed by a chemical reaction, for example, when absorbing CO 2 gas using sodium hydroxide (NaOH) as a solvent. The main principle of the gas absorption process is that there is contact between the gas and the liquid, and the gas will diffuse into the fluid because of its