# Utilization of Natural Adsorbents in the Purification of Used Sunflower and Palm Cooking Oils
## 4 Discussion  
During the process of repeated frying (180 \({}^{\circ}\)C) of fats and oils, a large number of volatile and non-volatile substances are formed due to the reactions that occur and which cause changes in the structure of fats and oils [48]. The PV is important for monitoring the peroxides in the first stages of oxidation. The results vary depending on the process used and the temperature [49]. Values of PV around 40.50 mEq Q\({}_{2}\)/kg obtained from the simulation during heating at 180 \({}^{\circ}\)C of the sunflower oils are in accordance with other studies [4; 50]. The degradation of cooking oil is characterized by changes in color, smell, taste, increase in water content, PV, FFA, and metal contamination. These changes are caused by the process of hydrolysis, oxidation, and polymerization of unsaturated fatty acids and results in the formation of ketones, aldehydes, and polymers [43]. These will generate a disagreeable flavor and also impair certain vitamins and essential fatty acids present in the oil. Oil containing water triggers a hydrolysis reaction that causes the oil to go rancid [51]. The water content of the oil greatly affects the quality of the oil, although the low oil's FFA content and PV and a high-water content can lead to a high rate of hydrolysis. This process breaks down fats into glycerol and FFA, potentially posing health risks [52]. WCO can be reused safely if it goes through a purification and bleaching process. Purification of WCO using adsorbents is a simple and effective process [53]. Utilizing adsorbents for oil purification can diminish the presence of metal contaminants, water content, and organic and inorganic compounds. Activated carbon can adsorb  
Figure 4: FT-IR spectra of fresh palm oil (S9), WCO (S10), and purified oil (S11). anions, cations, and molecules in the form of organic and inorganic compounds in solution or gas. The adsorption power is influenced by the porosity of the activated carbon and can be increased by its chemical or physical activation (by heating, which causes the pores of the carbon to open). The use of activated carbon in the purification process is able to adsorb up to 95-97% of the total dyes contained in the oil. [PERSON]'s research [54] shows that the use of activated carbon from coconut shells can reduce oil turbidity and that from sawdust can remove color, resulting in a 2.04% increase in the brightness of the color of WCO [55]. The effectiveness of the adsorption process depends on the dose to be used, but also on the contact time [56]. The stirring time is one of the factors that leads to the decrease of the peroxide level, which agrees with findings by [PERSON] and [PERSON] [57]. They clarified that peroxide, which contains oxygen, is a polar compound that readily binds to polar adsorbents. Eggshells contain minerals, especially calcium carbonate. This material has a porous structure that gives it the ability to adsorb certain impurities and polar compounds from oils [58]. Activated chicken eggshell powder primarily consists of polar calcium carbonate [59]. Stirring enhances the interaction strength between the adsorbate and adsorbent, influenced by their respective polarities. Furthermore, the adsorption process involves van der Waals forces, fostering attraction between molecules. Increasing the amount of eggshell powder as an adsorbent greatly contributes to increasing the adsorption efficiency. These results coincide with those reported by [PERSON] et al. [60] and [PERSON] et al. [45]. The adsorption speed depends on the type and characteristics of the adsorbate, in our case, zeolite or eggshell, and depends on the activation mode. At the same time, the adsorption kinetics are influenced by the expected operating conditions, the temperature, and the dose of the adsorbent. Zeolites are known for their ability to adsorb various substances from liquid and gaseous media, due to their porous structure and the large surface area they provide. This makes them effective in purifying and treating WCO [61].