# Utilization of Natural Adsorbents in the Purification of Used Sunflower and Palm Cooking Oils
## 4 Discussion
The IV decreases from 129.02 g l\({}_{2}\)/100 g in the case of fresh sunflower oil to values between 116.14 and 122.14 g l\({}_{2}\)/100 g for the used one. The values for palm oil decrease from 55.5 g l\({}_{2}\)/100 g in the case of the fresh one to 43.20 and 45.72 g l\({}_{2}\)/100 g for the one used for frying and are consistent with the studies undertaken by [PERSON] et al. [78]. The viscosity of oil increases with the length of fatty acids and the formation of polymers [79]. The PV of oils serves as a measure of its freshness by measuring the primary oxidative damage of edible oils, namely, the conversion of hydroxyl groups of unsaturated fats in oils by molecular oxygen to hydroperoxides and peroxides [80]. The results of the research show that the effects of treating sunflower--WCO with zeolite are similar to those of [PERSON] et al. [81], with natural adsorbents showing high efficiency in reducing the PV. Through heat treatment applied to food cooking, oils lose unsaturation from radical reaction (insertion, addition, substitution, bond breaking, and bond formation) with atmospheric oxygen [82]. In the case of the studied sunflower and palm oils, it was found that the spectra of the WCO (S2, S3, S4, S10) and the purified (S5-S8, S11) and fresh oils (S1 and S9) were very similar to each other. This results from the fact that the functional groups of the WCO samples remained intact after the application of heat treatment and different foods. The degree of unsaturation of the oil is analyzed based on some characteristics of the frequency bands--FT-IR. The percentage of transmittance for all the functional group regions show a small increment from fresh cooking oil (S1 and S9) in comparison with WCO (S2-S4 and S9) and the purified ones (S5-S8 and S11). These provide information on the quality of the oils and a unique mechanism for the deterioration of the oil samples. The FT-IR spectra of palm oil are largely similar to those of sunflower oils subjected to frying treatments, and the greatest difference is observed in the range of 500-1500 cm\({}^{-1}\). The bands at 1743 cm\({}^{-1}\) for both sunflower and palm oil lies in the range 1800-1700 cm\({}^{-1}\), which can be attributed to C=O stretching, typical of esters, and, thus, are common in both fatty acid methyl esters and refined oil spectra. These findings are similar to toe of [PERSON] et al. [83] and [PERSON] and [PERSON] [84]. FT-IR bands between 1100 and 1300 cm\({}^{-1}\) can be attributed to the stretching of C-O and are found in the spectra of other organic compounds such as carboxylic acids, ethers, or alcohols. Methyl esters of long-chain fatty acids lead to bands of 1237, 1160, and 1097 cm\({}^{-1}\). This observation is in line with those of [PERSON] et al. [85] and [PERSON] et al. [86]. The band of 1377 cm\({}^{-1}\) can be attributed to the glycerol group O-CH\({}_{2}\) (mono-, di-, and triglycerides) aligning with the findings of [PERSON] et al. [87]. According to the results, the bands of 2922 and 2853 cm\({}^{-1}\) show the stretching vibrations of C-H in CH\({}_{2}\) and CH\({}_{3}\) groups, respectively. [PERSON] et al. [88] evaluated FT-IR spectra of biodiesel produced from WCO. [PERSON] et al. [89] explained that the maximum absorption of the infrared at 3006 cm\({}^{-1}\) band in the case of palm oil is related to the unsaturation degree of the vegetable oils. [PERSON] et al. [90] showed the height of the band increases with the degree of alteration of the oils. In the case of sunflower oil, the band at 3008 cm\({}^{-1}\) which is in the range of 3007-3009 cm\({}^{-1}\) corresponds to C-H symmetric stretching vibration of the cis double bonds, =CH [89; 91]. Applications of purified oils are related to environmental pollution, through the production of biodiesel, animal feed, or in their use in the cosmetic industry (detergents, soaps, etc.) [14; 37; 92]. Studies have shown the efficiency of eggshells as a catalyst in the preparation of biodiesel from waste oil.